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2021 Spring Meeting

Nanomaterials and advanced characterization


Defect-induced effects in nanomaterials

Following the success of the four previous similar symposia this symposium addresses the progress in tailoring basic properties of low-dimensional and nano-materials by introducing dopants (e.g., implantation) or applying external loads- and radiation-induced defects.


This symposium focuses on understanding the formation and evolution of defects at the nanoscale through experiments and theory/simulations. Solids without defects are impossible to achieve based on thermodynamics. The defects are a Janus Bifrons: they can deteriorate the properties of materials and structures, but they can also enhance them with unique and useful properties which are absent in the perfect solids. The formation and evolution of defects becomes more critical at the nanoscale as their interaction with grain boundaries and interfaces plays a key role in determining material behavior due to the high surface to volume ratio. This symposium will cover how such defects could be introduced controllably, categorized and controlled in nanostructures. Understanding and controlling defect properties and capturing the grain boundary effects in a wide class of advanced nanostructures (novel 2D materials, multiferroics, quantum dots and wires, etc.) could well be a key to breakthroughs in several crucial areas of science and technology.  Recent work has demonstrated spectacular optical and magnetic effects due to deliberately created defects or radiation-induced transformation of nanomaterials as well as radiation-induced displacements in low-dimensional insulators and semiconductors, with numerous potential applications. The high sensitivity of modern technologies on the submicron scale has promoted the exciting opportunity of developing new advanced materials with reduced dimensionality. This opens new prospects for ion and electron beam applications. Ion tracks and other radiation-induced effects provide a means for controlled synthesis and modification of low-dimensional materials, such as nanoclusters and nanowires, allowing for efficient nano- optoelectronic and energy storage devices.

Hot topics to be covered by the symposium:

  • Defects in nanomaterials, including graphene and other 2D materials
  • Swift heavy ion irradiation as the means to tailor nanomaterials
  • Defect interaction with grain boundaries and interfaces
  • Electronic structure of defects in nanostructures.
  • Defects in nanomaterials for energy storage
  • Defects in semiconductors
  • Creation, evolution and properties of radiation defects in nanosize materials and heterostructures; the role of interfaces, nonstoichiometry.
  • Multiscale modeling capturing defect creation and transformation in nanomaterials.

List of confirmed invited speakers:

  • Andrei Kanaev, Institute of Physics, University of Tartu, Estonia
    Defects induced by He+ irradiation in g-Si3N4
  • Igor Lubomirsky, Dept. Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel
    Ferroelastic relaxor nano-domains in Gd and Sm-doped ceria
  • Eugene Kotomin, Max Planck Institute for Solid State Research, Stuttgart, Germany, & Institute of Solid State Physics, University of Latvia, Riga, Latvia
    First-principles calculations of defects in CsPbX3 (X = Br, I) crystals
  • Alexei Bouravleuv, St. Petersburg Academic University, RAS, Russia
    Spin-LED based on InAs quantum dots selectively doped with Mn
  • Jörg Lindner, Paderborn University, Germany
    Suppression of misfit defects in semiconductors by nanopatterning of surfaces
  • Vladimir Pankratov, University of Latvia, Riga, Latvia
    Luminescence and VUV excitation spectroscopy of nanophosphors under synchrotron radiation
  • Maxim V. Ananyev, Ural Federal University, Russia
    Nano-scale Ordering in Proton-Conducting Oxides Based on Lanthanum Scandate
  • Hanna Bandarenka, Belarusian State University of Informatics and Radioelectronics, Belarus
    Plasmonic Properties of Metallic Nanostructures on Porous Silicon: Contribution of Defects in Parent Silicon
  • Gunnar Suchaneck, TU Dresden, Solid State Electronics, Germany
    Antiphase grain boundaries and magnetoresistance in strontium ferromolybdate thin films
  • Sigitas Tamulevicius, Kaunas University of Technology, Lithuania
    2D nanostructures produced by capillary particle assembly
  • Janis Timoshenko, Fritz-Haber Institute of the Max-Planck Society, Berlin, Germany
    Probing disorder in nanoparticles using in-situ X-ray absorption spectroscopy and machine learning
  • Halyna Klym, Lviv Polytechnic National University, Lviv, Ukraine
    Defect-related free volumes in functional nanomaterials characterized within positron annihilation approach
  • Denis Gryaznov, University of Latvia, Riga, Latvia
    First principles calculations of defect formation energies and oxide crystals
  • Rita Maji, Università di Modena e Reggio Emilia, Italy
    Ab initio study of impurities segregation in silicon grain boundaries: the role of strain and vacancies
  • Hanna Bishara, Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany
    Relationship between structure and local electrical resistivity in copper grain boundaries
  • Sebastian Kruss, Ruhr-Universität Bochum, Germany
    Quantum Defects as a Toolbox for covalent Functionalization of Carbon Nanotubes and Manipulation of Photo Physics
  • Karine Abgaryan, Federal Research Center "Computer Science and Control", RAS, Russia
    Multiscale modeling of metal oxide memristive structures with embedded defects

List of scientific committee members:

  • Elias Aifantis, Aristotle University, Greece
  • Eduardo Alves, Lisbon Univerity, Portugal
  • Regina Dittmann, Juelich Research Center, Germany
  • Anatoly V. Dvurechenski, Acad. Sci., Novosibirsk, Russia
  • Eugene Kotomin, Max Planck Institute, Germany
  • Eugen Rabkin, Technion, Israel
  • Ion Tiginyanu, Acad. Sci., Moldova
  • Andrei I. Titov, St. Petersburg State Polytechnical University, Russia
  • Elke Wendler, Friedrich Schiller University of Jena, Germany


Selected papers will be published in "Physica Status Solidi" (Wiley).

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DEFECTS 1 : Nikolai Sobolev
Authors : E. A. Kotomin (1,2), R. A. Evarestov (3), and J. Maier (1)
Affiliations : (1) Max Planck Institute for Solid State Research, Stuttgart, Germany, (2) Institute of Solid State Physics, University of Latvia, Riga, Latvia, (3) Institute of Chemistry, St.Petersburg University, Russia

Resume : Halide perovskites continue to attract great interest as light absorbers for photovoltaic applications. In particular, hybrid organic–inorganic systems based on methylammonium (MA) and/or formamidinium (FA) lead iodide show excellent performances in solar cell devices. Such hybrid compositions, however, suffer from high instability under operation. An alternative is to move to fully inorganic materials fulfilling both performance and stability criteria, for which CsPbX3 (with X = I, Br) might serve as model compounds. First principles Density Functional Theory (DFT) hybrid functional calculations of the atomic and electronic structure of perfect CsPbI3, CsPbBr3 and CsPbCl3 crystals, as well as defective CsPbI3 and CsPbBr3 crystals were performed here. For the perfect structure, decomposition energy into binary compounds (CsX and PbX2) is calculated, and a stability trend CsPbBr3>CsPbI3 >CsPbCl3 is found. In addition, calculations of the temperature-dependent heat capacity are performed and show to be in a good agreement with experimental data. For phenomena such as recombination, light enhanced ion conduction and kinetic stability hole-trap centers are paramount. It is shown that interstitial halide atoms in CsPbBr3 do not tend to form di-halide dumbbells Br_2 (-1) despite the fact that such dimers are energetically favoured in CsPbI3, analogous to the well-known H-centers in alkali halides. Instead, in the case of CsPbBr3, a loose trimer configuration (Br_3 (2-) is predicted to be energetically preferred [1]. The effects of crystalline symmetry and covalency are tackled, alongside the role of defects in recombination processes. Confirmation of these results by Raman experiments is discussed.. [1]. R. A. Evarestov,,E.A. Kotomin, A. Senocrate, R. K. Kremer, and J. Maier, Phys. Chem. Chem. Phys., 2020, 22, 3914.

Authors : Stefano Ippolito(1), Adam G. Kelly(2), Rafael Furlan de Oliveira(1), Marc-Antoine Stoeckel(1), Daniel Iglesias (1), Ahin Roy (3), Clive Downing (3), Zan Bian(4), Lucia Lombardi (4), Yarjan Abdul Samad (4), Valeria Nicolosi (3), Andrea C. Ferrari(4), Jonathan N. Coleman(2), Paolo Samorì(1)
Affiliations : (1) Stefano Ippolito; Rafael Furlan de Oliveira; Marc-Antoine Stoeckel; Daniel Iglesias; Paolo Samorì Université de Strasbourg, CNRS, ISIS UMR 7006, 8 allée Gaspard Monge, F-67000 Strasbourg, France (2) Adam G. Kelly; Jonathan N. Coleman School of Physics, Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) and Advanced Materials and Bioengineering Research (AMBER), Trinity College Dublin, Dublin 2, Ireland (3) Ahin Roy; Clive Downing; Valeria Nicolosi School of Chemistry, Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) and Advanced Materials and Bioengineering Research (AMBER), Trinity College Dublin, Dublin 2, Ireland (4) Zan Bian; Lucia Lombardi; Yarjan Abdul Samad; Andrea C. Ferrari Cambridge Graphene Centre, Cambridge University, 9 JJ Thomson Avenue, Cambridge CB3 OFA, United Kingdom

Resume : Solution-processed semiconducting transition metal dichalcogenides (TMDs) are at the centre of an ever-increasing research effort in printed (opto)electronics. However, device performance is limited by structural defects resulting from the exfoliation process and poor inter-flake electronic connectivity. Here, we report a new molecular strategy to boost the electrical performance of TMD-based devices via the use of dithiolated conjugated molecules, to simultaneously heal sulfur vacancies in solution-processed transition metal disulfides (MS2) and covalently bridge adjacent flakes, thereby promoting percolation pathways for the charge transport. We achieve a reproducible increase by one order-of-magnitude in field-effect mobility (µFE), current ratios (ION / IOFF), and switching times (?S) of liquid-gated transistors, reaching 10-2 cm2 V-1 s-1, 10^4, and 18 ms, respectively. Our functionalization strategy is an universal route to simultaneously enhance the electronic connectivity in MS2 networks and tailor on demand their physicochemical properties according to the envisioned applications.

Authors : Qi Zhu, Jiangwei Wang*
Affiliations : Center of Electron Microscopy and State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China

Resume : Defects endow nanomaterials with fascinating chemical reactivities while the underlying dynamics remain largely elusive. Here we provide an atomistic visualization of metal oxidation dynamics driven by planar defects inside TEM, supported by density function theory-based calculations. Frequent site-selective oxidation processes are revealed at the junctions between the surface and the coherent twin boundary (TB) or stacking fault (SF) in Ag and Pd, which is attributed to the cooperative preferential oxygen adsorption at surface-fault junctions and fast oxygen diffusion along these planar faults. In specific, the lower coordination number for atoms at the surface-fault junctions yields a higher oxygen binding energy, leading to site-selective oxide nucleation. TB or SF further assists the transport of oxygen into the metal matrix, which is accompanied by the lateral diffusion along the oxide/metal interfaces, giving rise to a layer-by-layer inward growth of the oxide. These findings provide an atomistic understanding of the complex reaction dynamics controlled by planar defects in metallic materials, which could enable the modification of physiochemical performances in nanomaterials through defect engineering. This talk is based on our recent work: Nature Communications 12: 558 (2021).

Authors : David Beke*(1,2), Jan Valenta(3), Bence G. Márkus(2) Katalin Kamarás(1), Ferenc Simon(2), & Adam Gali(1,2)
Affiliations : (1) Wigner Research Centre for Physics, Hungary (2) Budapest University of Technology, Hungary (3) Charles University, Czechia

Resume : There is an urgent quest for room temperature qubits in nanometer-sized, ultrasmall nanocrystals for quantum sensing, hyperpolarization of biomolecules, and quantum information processing. Although the preparation of ultrasmall nanoparticles hosting stable qubits is appealing, the creation of such systems is remaining a challenge. The lack of a suitable synthesis technique may be related, besides surface and crystal reconstruction, to the mechanism of qubit formation in nanoparticles below 10 nm. Qubits in small nanoparticles are often created by irradiation techniques and subsequent annealing, and then they are milled or laser-ablated into smaller crystals. The yield of the vacancies in these nanocrystals below 10 nm falls on the ppm level in most of the time. We developed a chemical synthesis method that avoids any invasive materials fabrication processes and interaction of the solid with high-energy particle by using self-propagated high-temperature synthesis with subsequent electrochemical method, the no-photon exciton generation chemistry to produce room-temperature qubits in ultrasmall nanocrystals of sizes down to 3 nanometers with high yield. We demonstrate room-temperature optically detected magnetic resonance signal of divacancy qubits with emission wavelengths falling in the second biological window (1000-1380 nm).

Authors : Agata Fularz, Sawsan Almohammed, James H. Rice
Affiliations : Agata Fularz - School of Physics, University College Dublin, Belfield, Dublin 4, Ireland; Sawsan Almohammed - School of Physics, University College Dublin, Belfield, Dublin 4, Ireland, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland; James H. Rice - School of Physics, University College Dublin, Belfield, Dublin 4, Ireland

Resume : Using surface plasmons as a catalyst for surface reactions has been of great interest in recent years. Local surface plasmon resonance excitation has been shown to accelerate the rate of chemical reactions due to the excitation of hot carriers and local temperature increase. Nanocomposites containing both metal and semiconductor have also been used in the field in order to control the charge states in the metal and to allow catalytic activity and selectivity tuning. However, the specificmechanisms responsible for plasmon-driven photocatalysis are still not entirely understood, and the precise control of the catalytic reactions using external stimuli remains challenging. Here we report that the use of thermally annealed tungsten oxide WO3+x yields an effective substrate for driving catalytic redox reactions when decorated with silver nanoparticles. We show that the rate of the oxidation reaction of p-aminothiophenol (PATP) can be controlled by introducing defects into the semiconductor structure via heat treatment. We suggest that defect introduction allows for more efficient charge generation and transfer and may be used for catalysis of redox reaction for industrial processes.

10:45 Coffee Break    
DEFECTS 2 : Katerina E. Aifantis
Authors : Thomas Riedl, Jörg K. N. Lindner
Affiliations : Paderborn University, Department of Physics, Warburger Straße 100, 33098 Paderborn, Germany, Center for Optoelectronics and Photonics Paderborn (CeOPP), Paderborn University, 33098 Paderborn, Germany, Institute for Lightweight Design with Hybrid Systems (ILH), Paderborn University, 33098 Paderborn, Germany

Resume : Group III-V and II-VI semiconductor materials are frequently used for opto- and nanoelectronic devices. However, often their performance is limited by the presence of extended defects originating from the lattice misfit between the active device layer and the substrate material used. A viable way to reduce misfit induced strain is by nanopatterning of the surface such that strain can be accommodated by both the substrate and the deposited semiconductor material, leading to larger critical thicknesses for misfit induced defect formation compared to planar films. This so called nanoheteroepitaxy approach is considered in this presentation theoretically (by both molecular static simulations and continuum theory) and experimentally. For the latter, nanopatterning is achieved by employing bottom-up techniques for nanomask formation and reactive ion etching for the transfer of patterns in the third dimension. This combination of techniques will be shown to allow for the simple fabrication of scalable nanostructures on large substrate areas. In particular, hexagonal arrays of vertical nanopillars of SiC and GaAs will be considered, on which III-V semiconductors (GaN and InAs, respectively) are grown by MBE. State-of-the-art HAADF-STEM techniques including differential phase contrast imaging are applied to characterize the growth morphology as well as the defect and strain distribution in overgrown nanopillars.

Authors : Chiara Ricca, Iurii Timrov, Matteo Cococcioni, Nicola Marzari, Ulrich Aschauer
Affiliations : Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland Theory and Simulation of Materials (THEOS) and National Centre for Computational Design and Discovery of Novel Materials (MARVEL), Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland

Resume : DFT calculations of defects in transition metal oxides often require advanced methods such as hybrid functionals to yield a reasonable description of the electronic structure. When properties of defects at dilute concentrations are desired, the - often incompatible - need for large supercells is added to the above functional requirement. We have recently established self-consistent, site-dependent DFT+U and DFT+U+V as promising approaches to address the challenge of simultaneously meeting these requirements. The minimal added cost of DFT+U(+V) compared to a semi-local functional enables the treatment of large supercells, yet the structural and electronic properties relevant for point-defect calculations agree well with hybrid-functionals. We ascribe this to both the self-consistent determination of the Hubbard parameters that leads to an internal consistency of results, as well as the site dependence, which for localized defect states captures chemical changes on multivalent ions around the defect. We will highlight the performance of the method for oxygen vacancies in the perovskite oxides SrTiO3 and SrMnO3. In the former self-consistent DFT+U+V leads to an electronic structure of oxygen vacancies that agrees well with that of hybrid functionals, which also translates to similar formation energies that agree well with experiment. In SrMnO3 the site dependence of Hubbard U significantly lowers defect formation energies and the critical epitaxial strain for magnetic phase transitions.

Authors : Bruno S. de Lima*1, Paulina R. Martínez-Alanis2, Frank Güell2, Weverton A. S. Silva1, Maria I. B. Bernardi1, Naiara L. Marana3, Elson Longo4, Júlio R. Sambrano3, Valmor R. Mastelaro1
Affiliations : 1 Sao Carlos Institute of Physics, University of Sao Paulo, 565-905 São Carlos, SP, Brazil 2 ENFOCAT-IN2UB, Universitat de Barcelona, C/Martí i Franquès 1, 08028 Barcelona, Catalunya, Spain 3 Modeling and Molecular Simulation Group, São Paulo State University, Bauru, SP, Brazil 4 Federal University of Sao Carlos (UFSCar), Department of Chemistry, São Carlos, SP, Brazil

Resume : Recently, it was demonstrated that ZnO thin films sputtered under oxygen-rich atmospheres exhibit localized structural disorder with a significant impact on their physical properties due to the presence of high energetic ions in the plasma. Here, highly disordered ZnO thin films have been realized simply by using a metallic Zn target under deposition atmosphere of pure oxygen (O2). The results of XRD and Raman spectroscopy show that the defects induced during the deposition crystallize a highly disordered wurtzite-type structure. Besides, theoretical DFT calculations were applied to a better comprehension of the nature of these structural defects, in which it is shown that the presence of Zn and O in interstitial positions may be responsible for a symmetry break in the wurtzite structure. It is shown that high disorder of the structure has a significant impact on its fundamental properties. For instance, the UV-vis absorption curve shows a significant increase in the bandgap of ZnO, while photoluminescence (PL) measurements show the emergence of bands in the visible range, confirming the presence of Zn and O in interstitial positions. This manuscript also explores the gas sensing properties of films deposited under a pure oxygen atmosphere. Our results demonstrate that its sensitivity can be significantly enhanced towards oxidizing gas detection, such as ozone. On the other hand, it is shown that the gas sensing properties regarding reducing gas detection, such as H2, are not significantly altered when compared to non-disordered ZnO.

Authors : G. Mineo (1,2), K. Moulaee (3), G. Neri (3), S. Mirabella (1,2), E. Bruno (1,2)
Affiliations : (1) Dipartimento di Fisica e Astronomia “Ettore Majorana”, Università di Catania, via S. Sofia 64, 95123 Catania, Italy. (2) CNR-IMM, Università di Catania, via S. Sofia 64, 95123 Catania, Italy. (3) Dipartimento di Ingegneria, Università degli studi di Messina, Contrada Di Dio, 98158, Sant'Agata, Messina, Italy.

Resume : Nanostructured WO3 represents an fascinating material for hydrogen storage and gas sensing, even if the mechanism regulating the interaction between WO3 and H2 is not completely understood, in particular for what concerns defects in WO3 nanostructures. A simple and low-cost technique to get well controlled WO3 nanorods would represent a key element for H-related applications. Here, we report a high-yield, low-cost method to produce WO3 nanorods in aqueous solution. SEM analysis showed nanorods ~30 nm wide and ~250nm long, and XRD analysis confirms hexagonal crystal structure. We prepared gas sensing devices by drop casting WO3 nanorods onto interdigitated electrodes and investigated the chemo-resistive behaviour in the 250-400°C temperature range and for 2000-50000 ppm of H2 concentrations. The measured response transients have been successfully modelled within the Langmuir theory by hypothesizing two independent active mechanisms, involving atmospheric O2 adsorption onto surface of WO3 nanorods and O vacancy production. Energy barriers to O vacancy production and recombination have been extracted to be 0.46 and 0.82 eV, respectively. These data are presented and discussed in comparison to literature data on WO3 nanorods defects.

Authors : Fiacre E Rougieux
Affiliations : The University of New South Wales, Sydney, NSW, 2052

Resume : Shockley-Read-Hall statistics is but one statistic to model the recombination at a defect with two charge states, a single configuration, no excited states and no bound excitons. In reality, most defects contain more than two charge states and/or multiple configurations and/or multiple excited states. Thus, Shockley-Read-Hall is a very particular case of a more general recombination theory that describes the recombination function in all its richness (charge states, excited states, configurations and bound excitons). The problem with Shockley-Read-Hall statistics is that even if one can fit experimental value of the recombination at a certain temperature and dopant density, the result is not generalizable and will lead to an inaccurate prediction at another temperature or dopant density. The question then arises: How does one know what statistics to select in order to describe the recombination function of a defect in a 2D or bulk semiconductor? More precisely: what are the measurements required to ascertain how many charge states, excited states and configurations a defect contains? In this paper we will outline a new methodology for recombination model selection. This methodology is part of a recent paper here and its rational is documented in our previous papers here and here It allows for accurate and generalizable prediction of recombination at defects.

12:45 Lunch    
Authors : Rita Maji (a), Eleonora Luppi (b), Nathalie Capron (c), Elena Degoli (d , e , f)
Affiliations : (a) Dipartimento di Scienze e Metodi dell?Ingegneria, Università di Modena e Reggio Emilia, Via Amendola 2 Padiglione Tamburini, I-42122 Reggio Emilia, Italy (b) Laboratoire de Chimie Théorique, Sorbonne Université and CNRS, F-75005 Paris, France (c) Sorbonne Université, CNRS, Laboratoire de Chimie Physique Matière et Rayonnement, UMR 7614, F-75005 Paris, France (d) Dipartimento di Scienze e Metodi dell?Ingegneria, Università di Modena e Reggio Emilia, Via Amendola 2 Padiglione Morselli, I-42122 Reggio Emilia, Italy (e) Centro Interdipartimentale En&Tech, Via Amendola 2 Padiglione Morselli, I-42122 Reggio Emilia, Italy (f) Centro S3, Istituto Nanoscienze-Consiglio Nazionale delle Ricerche (CNR-NANO), Via Campi 213/A, 41125 Modena, Italy

Resume : Multi-crystalline silicon (MC-Si) is widely used for producing low-cost and high-efficiency solar cells. During crystal growth and device fabrication, silicon contains grain boundaries (GBs). In MC-Si, grain size, orientation, and grain boundary distribution are interlinked and impact the ultimate quality of the material [1]. GBs can create deep-energy states which induce charge carriers recombination resulting in a significant reduction of carrier lifetimes. [2] GBs are also preferential segregation sites for atomic impurities [1,3] such as transition metals (e.g. Fe, Cu, Cr, Ni, etc.), non-metals (e.g B, P, As, etc.), and common light elements (e.g. C, O, N, etc.). [4,5,6]. Thus reduction of recombination density and controllable segregation activity is extremely important to minimise the detrimental impact and optimize the efficiency of MC-Si based devices. [7] In this presentation, we will show how the electronic properties of most stable ?3{111} Si-GB, in the presence of strain and vacancies, are modified by multiple oxygen segregation. The study, from first-principles, of the structural and energetic properties of GBs in the presence of strain and vacancies, gives an accurate description of the complex mechanisms that control the segregation of oxygen atoms. We analysed tensile and compressive strain both and we obtained that local tensile strain around O impurities strongly favours the process of segregation. [8] We also studied the role of multiple O impurities in the presence of Si vacancies finding that the segregation is favored for those structures which have restored tetrahedral coordination. For each structure, we analysed the density of states and their projection on atoms, the band gaps, the segregation energy, and their correlation to characterise the nature of new energy levels.[8]. In conclusion, the inhomogeneous distribution of strain field around segregating sites, due to both local geometrical distortion or the presence of a Si-vacancy, is the main factor that influences the oxygen segregation at GBs. [8] A similar analysis will be shown for C and N, too. Actually knowing the origin of defined electronic states would allow the optimization of materials and therefore improving corresponding device efficiency. References: 1. P. Käshammer and T. Sinno, Journal of Applied Physics,118, 9 (2015) 2. S. Wang et al. The Journal of Physical Chemistry Letters 10 (2019) 3. D. Zhao and Y. Li, Acta Materialia 168, 52 (2019) 4. A. Stoffers, et al. Prog. Photovolt: Res. Appl., 23, (2015) 5.Y. Ohno et al. Applied Physics Letters 106, 251603 (2015) 6. Y. Ohno et al. Applied Physics Letters 110, 062105 (2017) 7. V. Y. Lazebnykh et al. Journal of Applied Physics 118, 135704 (2015) 8. R. Maji et. al Acta Materialia, 204, 116477 (2021).

Authors : Fei Shuang ( and Katerina E. Aifantis (
Affiliations : Mechanical and Aerospace Engineering, University of Florida, USA

Resume : Graphene nanosheets (GNS) can enhance the strength and ductility of metal-based composites as they can obstruct the propagation of dislocations. The present article employs Molecular Dynamics (MD) simulations to investigate dislocation-GNS interaction mechanisms and possible influencing factors, including the number of GNS layers, the thickness of the metallic amorphous layer and the Csingle bondC bond strength. The results indicated that the shear strength of the metal/GNS interface and the bending stiffness of GNS determined the ability of GNS to block dislocation transmission. A physically based phenomenological parameter that can capture such dislocation-GNS interactions is the mechanical interface energy that has been put forth within gradient plasticity. By fitting the theoretical expressions to the simulation data, it was possible to obtain estimates for the mechanical interface energy for the GNS. It was found that increasing the GNS layers and adding an amorphous layer resulted in a strengthening in the stress–strain response and increased the value of this interfacial parameter. This indicates that the mechanical interfacial energy can be a unified measure for capturing and tuning the strength of various interfaces such as grain boundaries, GNS, amorphous-crystalline interface and bimetal interfaces.

Authors : Tian Tian, Franzisca Naef, Gianluca Vagli, Kemal Celebi , Yen-Ting Li, Shu-Wei Chang, Frank Krumeich, Elton J. G. Santos, Yu-Cheng Chiu, Chih-Jen Shih
Affiliations : Institute for Chemical and Bioengineering, ETH Zürich, CH-8093 Zürich, Switzerland; Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan; National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan; Laboratory of School of Inorganic Chemistry, ETH Zürich, 8093, Zürich, Switzerland; Mathematics and Physics, Queen’s University Belfast, BT7 1NN, Belfast, UK

Resume : The van der Waals (vdW) force is pervasive short-range interaction between atoms and molecules that underlies many fundamental phenomena. Early pairwise additive theories pioneered by Keesom, Debye, and London suggested the force to be monotonically attractive for separations larger than the vdW contact distance. However, as predicted by Lifshitz et al, quantum fluctuations can change the sign of vdW force from attractive to repulsive. Although recent experiments carried out in high-refractive-index fluids have corroborated the long-range counterpart – the Casimir repulsion, it remains controversial whether the vdW repulsion exists, or is sufficiently strong to alter solid-state properties. Here we show that the atomic thickness and birefringent nature of two-dimensional (2D) materials, arising from their anisotropic dielectric responses, make them a versatile medium to tailor the many-body Lifshitz-vdW interactions. Based on our theoretical prediction, we experimentally examine two heterointerface systems in which the vdW repulsion becomes comparable to the two-body attraction. We demonstrate that the in-plane movement of gold atoms on a sheet of freestanding graphene becomes nearly frictionless at room temperature. Repulsion between molecular solid and gold across graphene results in a new polymorph with enlarged out-of-plane lattice spacings. The possibility of creating repulsive energy barriers in nanoscale proximity to an uncharged solid surface offers technological opportunities such as single-molecule actuation and molecular assembly.

Authors : Alexina Ollier[1,2], Marcin Kisiel[1], Remy Pawlak[1], Urs Gysin[1], Erio Tosatti[3] and Ernst Meyer[1]
Affiliations : [1]: Department of Physics, University of Basel,Klingelbergstr. 82, 4056 Basel, Switzerland [2]: Swiss NanoScience Institut (SNI), Klingelbergstrasse 82, 4056 Basel, Switzerland [3]: SISSA,Trieste, Via Bonomea 265, Italy

Resume : Understanding nanoscale energy dissipation is nowadays among few priorities particularly in solid state systems. Breakdown of topological protection, loss of quantum information and disorder-assisted hot electrons scattering in graphene are just few examples of systems, where the presence of energy dissipation has a great impact on the studied object [1]. It is therefore critical to know, how and where energy leaks. Pendulum geometry Atomic Force Microscope (pAFM), oscillating like a pendulum over the surface, is perfectly suited to measure such tiny amount of dissipation [2,3], since a minimum detectable power loss is of the order of aW. We report on a low temperature (T=5K) measurement of striking singlets or multiplets of dissipation peaks above graphene nanodrums surface. The stress present in the structure leads to formation of few nanometre sized graphene wrinkles and the observed dissipation peaks are attributed to tip-induced charge state transitions in quantum-dot-like entities. The dissipation peaks strongly depend on the external magnetic field (B=0T-2T). The magnetic field induce Peierls phase that shit the peaks to lower energy. At large magnetic field this shift induces the vanishing of the peaks. [1] – D. Halbertal,, Nanoscale thermal imaging of dissipation in quantum systems, Nature539, (2016), 407–410. [2] - B.C. Stipe,, Noncontact Friction and Force Fluctuations between Closely Spaced Bodies, Phys. Rev. Lett.87, (2001), 096801. [3] - M. Kisiel,, Suppression of electronic friction on Nb films in the superconducting state, Nature Materials10, (2011), 119-122.

Authors : G. Suchaneck, E. Artiukh, N. Kalanda
Affiliations : TU Dresden Solid State Electronics Laboratory 01062 Dresden Germany; SSPA "Scientific-Practical Materials Research Centre of NAS of Belarus" Cryogenic research division 220072 Minsk Belarus

Resume : Strontium ferromolybdate (SFMO) possesses a tetragonal structure with the I4/m space symmetry group. The perfect SFMO lattice structure can be considered as corner-connected FeO6 and MoO6 octahedra alternating along the three axes. The Sr cations are in the voids formed by the FeO6 and MoO6 octahedra. The Fe and Mo ions form a NaCl-type cation order at the perovskite B-site. Antiphase boundaries (APBs) are natural growth defects that has been revealed in SFMO by transmission electron microscopy and by Mössbauer spectroscopy. At APBs, the ideal pattern of Fe and Mo ion occupancy is mirror-inverted. This leads to planes of strongly antiferromagnetic (AF) Fe-O-Fe bonds. By this way, the APB locally interrupts the ferrimagnetic (FM) coupling between Fe and Mo ions and the indirect Fe-O-Mo-O-Fe exchange interaction occurring in defect-free structures. Strong AF interactions of the Fe-O-Fe bonds across the APB orient magnetic moments of neighboring domains in antiparallel directions. The application of a magnetic field aligns the ferromagnetic domains far away from the APB. At the APB, the spins remain nearly antiparallel and will be oriented nearly perpendicular to the applied field. Consequently, an increasing with distance rotation of spins in field direction occurs in the APB neighborhood. Upon removal of the field, the forces across the antiphase boundary realign the ferromagnetic domains antiparallel to one another yielding a small magnetic remanence due to a different domain size. Other features of APB presence are a low coercive field, a lower compared to bulk samples saturation magnetization, a lack of saturation up to high fields, and a higher resistivity. APBs, antisite disorder, as well as a nonuniform composition of SFMO cause several different mechanisms of magnetoresistance. These mechanisms are strongly dependent on synthesis conditions. They include spin-dependent tunneling, spin scattering, fluctuation induced tunneling and the conventional magnetoresistance. For antiparallel spins in adjacent domains, the transfer of fully spin-polarized electrons is blocked supposing that spin-dependent scattering does not occur at the interface. Here, the theoretical conductivity is zero. Upon application of a magnetic field, the antiparallel spins are tilted and the conductivity becomes finite. Thus, the magnetoresistance can be evaluated in this case by means of the Eerenstein model of two half-FM linear chains AF-coupled at the APB. We have modeled for the first time the contribution of APBs to the magnetoresistance in nanograined SFMO ceramics and nanosized SFMO thin films. The model parameters: Saturation magnetization, anisotropy constant, AF interchange modulus, FM and AF exchange stiffness, distance between two neighboring AF-coupled spin chains were derived from literature data. The dependence on mechanical strain was taken into account. This work was supported by the EU project H2020-MSCA-RISE-2017-778308-SPINMULTIFILM.

15:45 Coffee Break    
POSTER SESSION 1 : Conference Organizers
Authors : Oksengendler B.L.1,7, Doroshkevich A.S.2,3, Lyubchyk A.I.4,5, Nikiforova N.N.1,.Suleymanov S.X.7, Zakharova A.S.2,6, Tikhonova N.S.2,6, Gridina E.A.2,6
Affiliations : 1Ion-plasma and laser technologies Institute after U.Arifov, Uzbekistan, Tashkent, е-mail:; 2Joint Institute for Nuclear Research, Dubna, Russia, е-mail:; 3Donetsk Institute for Physics and Engineering named after O.O. Galkin, Kiev, Ukraine, e-mail:; 4Nanotechcenter LLC, Krzhizhanovsky str., 3, Kyiv 03680, Ukraine e-mail:; 5Lusófona University, IDEGI, Campo Grande, 376 1749-024 Lisboa, Portugal, е-mail:; 6Dubna State University, Dubna, Russia, 19 Universitetskaya street, Dubna, Moscow region,141982 e-mail:; 7Materials Science Institute of SPA “Physics-Sun” Uzbekistan, Tashkent, е-mail: *E-mail:

Resume : The electronic structure of the near-surface regions of nanoparticles of a special type of oxide materials and the possibility, on this basis, to obtain specifically rectifying properties of the contacts were studied theoretically and experimentally. Models of surface states of the Tamm type are constructed, but taking into account the Coulomb long-range action. The discovered variance and its dependence on the curvature of the surface of nanoparticles made it possible to modelly study the conditions for the formation of a contact potential difference in cases of nanoparticles of the same radius (synergistic effect), different radii (doped and undoped variants), as well as to discover the possibility of describing a group of powder particles from a given material within the Anderson model. The contact of chemically homogeneous different sizes hydrated nanoparticles of yttrium-stabilized zirconium oxide (ZrO2 – 3%mol Y2O3, YSZ) with particle sizes of 7.5 and 10 nm in the form of compacts obtained using high hydrostatic pressure (HP-compacts of 300MPa) was studied at direct and alternating current. A unique dimensional effect of the nonlinear (semiconductor type) dependence of the electrical properties (in region U < 2.5 V, I ≤ 25mkA) of the contact of different-sized YSZ nanoparticles of the same chemical composition was established, which confirms the validity of the given graded-gap model and indicates the possibility of creating a new type of semiconductor structures based on chemically homogeneous nanostructured systems. The study was performed in the scope of the Project H2020/MSCA/RISE/SSHARE number 871284 project and RO-JINR Projects № 268/2020 item 57, 59.

Authors : L. Nie1#, A.C. Nusantara1#, M. Chipaux2*, R. Schirhagl1*
Affiliations : 1University of Groningen, University Medical Center Groningen, Department of Biomedical Engineering, A. Deusinglaan 1, 9713 AV, Groningen, The Netherlands 2Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland

Resume : Free radicals play a key role in multiple processes in healthy cells including ageing, signaling or immune responses. Additionally, they are involved in many diseases including cancer, cardiovascular diseases or infections. As free radicals are highly reactive and have a short life-time they are difficult to measure using current methods. Fluorescent Nano diamond (FND) based magnetometry is promising to solve this problem. FNDs contain defects, which change their optical properties based on their magnetic surroundings. These allow magnetic resonance measurements in the nanoscale, which can produce specific, sensitive signals without background noises. Mitochondria are the major source of free radicals in cells. Those radicals are important in redox signaling, aging and disease. The main mitochondrial free radicals are superoxide and *OH. These free radicals generate at various sites in the electron transport chain, and could lead to mitochondrial dysfunction in a variety of disease states. The project aimed to follow mitochondrial radical generation in real time. Here we measured mitochondrial free radicals’ production using diamond magnetometry with nanodiamonds inside cells/isolated mitochondria for the first time. We were able to target nanodiamonds to the mitochondrial surface. To achieve targeting we attached antibodies to the diamond surface. With these targeted diamonds we are able to follow triggering and inhibiting free radical metabolism in mitochondria.

Authors : V.L.Karbivskii, A.A.Romansky, L.I.Karbivska, A.P.Soroka
Affiliations : G. V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine

Resume : The physical properties of 2D structures of metals, as is known, are largely determined by their electronic structure, as a result of which the establishment of regularities in the formation of the electronic structure of the firstly synthesized compounds is the most important stage in the development of methods for obtaining new materials with given characteristics. Previously, we have obtained and experimentally investigated monolayer flake-like structures of gold with a high vacancy defectiveness; however, the mechanisms of their formation and the conditions that make their stable existence possible remain not fully understood. Within the framework of the density functional theory, the features of the electronic structure of gold slabs are investigated depending on the number of monolayers and the concentration of defects. It has been established that the shape of the curve of the total density of electronic states (DOS) of gold slabs with a thickness of 1-3 monolayers is mainly determined by the components of the d-states associated with the z axis. In the case of three monolayers, the shape of the DOS curve is specified by the d-states of the atoms of the outer layers. The shape of the d-state curve for the inner and outer layers differs significantly. The characteristic differences in the curve of the d-states of the atoms of the inner layer are mainly determined by the dxz and dyz components, which indicates a significant influence of the neighbors in the diagonal directions on the pecularities of the electronic states. The curve shape of gold monolayer structures acquires features similar to the DOS of a bulk sample starting from a slab containing 3 atomic layers. Depending on the concentration and ordering of atomic vacancies, significant changes are observed in the DOS curves: splitting of the initial features or / and a shift of the d-states main maximum of the metal towards lower binding energies. In some cases, the shape of the DOS curve of a defective monolayer approached that for thicker slabs. Point defects, which are smaller than the atomic size and are observed in STM images of gold monolayers, are determined by the peculiarities of atomic ordering.

Authors : O.S. Karpenko(1), І.B. Bichko(2)
Affiliations : (1) Chuiko Institute of Surface Chemistry, NAS of Ukraine, 17 General Naumov Str., Kyiv 03164, Ukraine; (2) L.V. Pisarzhevsky Institute of Physical Chemistry, NAS of Ukraine, 31 Nauki Ave., Kyiv 03028, Ukraine

Resume : The equilibrium spatial and electronic structure of hexagon-shaped carbon nanocluster (CNC) C96 limited to six zigzag edges and analogical polyaromatic molecule (PAM) C96H24 have been calculated within the density functional theory method (DFT) with the exchange-correlation potential B3LYP and the basis set 6-31G+(d,p). PAMs were built from related CNC by attaching hydrogen atoms to the peripheral doubly coordinated carbon atoms (C(2)). The structures with vacansies have been obtained from C96 and C96H24 by removing one carbon atom (C96-1(1) and C96-1(1)H24), two non-adjacent carbon atoms (C96-2(1) and C96-2(1)H24) or two adjacent carbon atoms (C96-1(2) and C96-1(2)H24). It have been established that the ground electronic state (GES) of CNCs C96, C96 1(1), C96-2(1) and C96-1(2), PAMs C96H24, C96-1(1)H24, C96-2(1)H24 and C96-1(2)H24, despite they have even amount of electrons, is not singlet. The equilibrium spatial structure of CNC C96 is such that the 2pz atomic orbitals of the outer edge cyclic chain form a conjugate system loosely-coupled with π-system of the central part of the CNC. This suggests that this outer edge chain is relatively isolated and does not participate in the formation of a common conjugate π-system, delocalized throughout the CNC. The degree of separation of the outer edge chain increases from CNC C96 to defect-containing CNCs C96-1(1) and C96-2(1). For systems C96-1(1)H24 and C96-2(1)H24, obtained from PAM C96H24, the formation of one or two monovacancies does not violate a single conjugate system. The spectrum of single-electron energy levels of CNC C96, C96-1(1) and C96-2(1) exhibits that some МОs distributed over outer cyclic chain remain vacant but theirs energies fall into the energy intervals of the highest occupied МОs. The calculated energies of formation of one and two monovacancies in CNC C96 indicate "loosening" of the structure during the transition from C96 to C96-1(1), while for PAM C96H24 the introduction of vacancies "seals" the structure. The formation of bivacances in the CNC C96 (removing the C2 molecule from it) is more favourible energetically in comparison with the sequential removal of two adjacent carbon atoms. Modeling CNCs as PAMs (when carbon atoms (C(2)) saturated with hydrogen atoms) not reproduced correct structure and properties of CNCs. It is correct for defect-free and defect-conteining hexagon-shaped CNCs. The spectra of one-electron density states of CNC in the binding-energy scale of carbon 1s (C1s) core-level allow to identification the different types of carbon atoms depending on the degree of hybridization of their atomic orbitals, the availability of vacancies and their position in the CNC. This work was supported by the National Research Foundation of Ukraine (grant 2020.02/0050).

Authors : Preetam Singh, Santanu Ghosh, Vikash Mishra, Sajal Barman, Sudipta Roy Barman, Arvind Singh, Sunil Kumar, Pankaj Srivastava
Affiliations : Preetam Singh; Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi-110016, India Santanu Ghosh; Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi-110016, India Vikash Mishra; Department of Physics, Indian Institute of Technology Bombay, Powai Mumbai-400076, India Sajal Barman; UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore 452001, Madhya Pradesh, India Sudipta Roy Barman; UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore 452001, Madhya Pradesh, India Arvind Singh; Department of Physics, Indian Institute of Technology Delhi, New Delhi-110016, India Sunil Kumar; Department of Physics, Indian Institute of Technology Delhi, New Delhi-110016, India Pankaj Srivastava; Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi-110016, India

Resume : Magnetic properties of H-ambience annealed pure ZnO films have been reported. ZnO films deposited by DC magnetron sputtering show room temperature ferromagnetism (RT-FM) after annealing in hydrogen atmosphere at different temperatures (350 C and 400 C). Enhancement in O-H concentration has been observed by XPS core level spectra and is supported by XPS valence band results which suggest the enhancement in carrier concentration after annealing in H-ambience. Electrical transport results also indicate rapid decrease in activation energies corresponding to thermally activated band and NNH conduction, i.e. increase in carrier concentration after annealing. Enhancement in the vacancy type defects have been observed by positron annihilation spectroscopy and tailoring of defects have been observed by photoluminescence spectra. Increase in saturation magnetization and Zn vacancy (evident from M-H and PL data) along with the O-H concentration, after annealing in hydrogen ambience, suggest that Zn vacancies along with O-H concentration play a crucial role behind the ferromagnetic nature of the films. The experimental results are further verified theoretically by performing the density functional theory calculations. Based on both experimental results and theoretical model it has been explained that the enhancement of magnetic moment of H-ambience annealed ZnO is due to the increased carrier mediated exchange interaction among the localized magnetic moment at zinc vacancy sites.

Authors : H.Mosbahi*, M.Gassoumi, M.A.Zaidi
Affiliations : 1Département Technologie et Ingénierie du Transport, Institut Supérieur du Transport et de la Logistique, université de Sousse, Tunisia. 2Research Unit Advanced Materials and Nanotechnologies, University of Kairouan, BP 471, Kasserine, 1200 Tunisia. 3Département de Physique, Faculté des Sciences de Monastir, université de Monastir, Tunisia.

Resume : Aluminum gallium nitride/Gallium nitrides based high electron mobility transistors are excellent candidates for high power and high frequency applications. AlGaN/GaN HEMTs in general attract attention due to the possibility for wide band gap, high electron saturation velocity, high breakdown voltage, high conduction band offset, and high thermal as well as chemical stability. AlGaN/GaN heterostructures offer high spontaneous and piezoelectric polarization. The two-dimensional electron gas resulting at the AlGaN/GaN interface provides high sheet carrier concentrations and is suitable for HEMTs devices as well as other high temperature electronics, high power operating at high frequencies.

Authors : Anumol Sugathan, Nihit Saigal, Guru Pratheep Rajasekar, Anshu Pandey
Affiliations : Indian Institute of Science, Bangalore; Indian Institute of Science, Bangalore; Indian Institute of Science, Bangalore; Indian Institute of Science, Bangalore

Resume : Copper iron chalcogenides, viz., CuFeS2 and CuFeSe2, constitute a promising class of semiconductors with interesting opto-electronic properties. They belong to the I-III-VI2 semiconductor family and are narrow bandgap semiconductors. These materials are known to exhibit a relatively low defect formation energy. Thus, nanocrystals of these materials tend to exhibit a large number of defects and consequently exhibit free electrons. This leads to the emergence of several interesting opto-electronic properties. For instance, CuFeS2 is reported to be a semiconductor in the bulk with a bandgap of 0.5 eV. However, nanocrystals of the material bear a striking resemblance to metallic gold nanoparticles, physically as well as optically. This resemblance arises due to the presence of a localized surface plasmon resonance or LSPR around 500 nm region. However, despite possessing a large amount of free charge carriers required to support a plasmon resonance, CuFeS2 nanocrystals still exhibit a photoresponse. While the intrinsic response of the material, as exhibited by their photoconductive devices, is inherently slow, forming heterojunctions of the material with another semiconductor could greatly speed up their response times. Here, I will briefly describe the fabrication and properties of CuFeS2 nanocrystal-bulk Silicon heterojunction photodetectors. These photodetectors possess a broadband photoresponse from 460 nm to 2200 nm with microsecond response times. Furthermore, the photodetectors can also exhibit a slower bolometric response which allows them to sense hot objects at room temperature.

Authors : Zhenyun Lan, Tejs Vegge, Ivano E. Castelli
Affiliations : Department of Energy Conversion and Storage;Technical University of Denmark

Resume : Oxynitride perovskites like BaTaO2N are among the most promising materials to achieve efficient direct solar-to-chemical conversion. Albeit photoelectrochemical water splitting has been demonstrated, the required overpotentials remain prohibitively large compared with the theoretically accessible values, particularly for the oxygen evolution reactions (OER). Here, we apply Density Functional Theory (DFT) calculations to investigate the use of surface strain and cationic doping with Ca and Sr to optimize the OER overpotential. For the TaON-terminated BaTaO2N (001) surfaces, 4% compressive uniaxial strain can lower the overpotential to  = 0.59 V (vs. the Standard Hydrogen Electrode, SHE). For the most stable TaO2N-(100) termination, 1% uniaxial tensile strain, which is perfectly accessible by experiments, is enough to reduces the overpotential from  = 0.43 V to  = 0.37 V under (photo)electrochemical conditions. This value is close to the minimum predicted theoretical overpotential and points out how strain engineering could be efficiently used to improve electrocatalytic reactions.

Authors : Irinela Chilibon
Affiliations : National Institute of Research and Development for Optoelectronics, INOE-2000, 409, Atomistilor Street, P.O. Box MG-5, 077125 code, Bucharest-Magurele, Romania

Resume : Ultrasound effects on the intensification of various physical-chemical processes in solutions and liquids are presented. Ultrasound can provide an excess energy for the new interface formation, and it is possible to obtain emulsions even in the absence of surfactants. The advantages of ultrasound include lower energy consumption and production of more homogeneous emulsion than by a mechanical process. Recent breakthroughs in sonochemistry have made the ultrasound irradiation procedure more feasible for a broader range of applications. The efficacy of ultrasonic emulsification is function of irradiation time, irradiation power, oil/water ratio and physical-chemical properties of the oil. Ultrasound about 25 kHz and 40 kHz are examined in order to find the suitable work frequency to increase the cavitation efficiency. Cavitation results in the generation of hot spots, turbulence associated with liquid circulation currents contribute in the intensification of various physical-chemical operations. Major applications of cavitation effects could be the synthesis of biodiesel, emulsification and extraction of bio-components, in aim to increase the overall efficiency of the emulsification process. Other investigations are made at higher frequencies, for the use of ultrasound in waste water purification or improve the quality of water. The ultrasonic effects to the chemical reactions in sonochemistry involve various processes, such as: hydrolysis, oxidation, and depolymerization. Acknowledgements: The author is grateful for the financial support of Ministry of Research and Innovation (MCI), 2021 Core Program, and Romanian Executive Agency for Higher Education, Research, Development and Innovation Funding (UEFISCDI).

Authors : Wei Liu
Affiliations : School of Materials Science and Engineering, Nanchang Hangkong University, P.R.China

Resume : Nanostructured copper sulfides (CuxS, 1≤x≤2) are an interesting class of polymorph materials that see an expanding development in a systematic physicochemical engineering by varying element composition, valence states, nanocrystal morphologies and shapes. To this interest, we focus on the composition manipulation of CuxS nanomaterials by synthesizing off-stoichiometric CuxS (1

Authors : R.M. Balabai, M.V. Naumenko
Affiliations : Kryvyi Rih State Pedagogical University, Physics departmen; Kryvyi Rih State Pedagogical University, Physics department

Resume : The sensitivity of the β-Ga2O3 semiconductor to a variety of gases arises as a result of surface reactions with molecules of gases, which lead to a chemoresistive change in its conductivity. Recent studies have shown that morphology of nanomaterials has a significant effect on the gas sensitivity of nanostructures [GaN/Ga2O3 Core/Shell Nanowires Growth: Towards High Response Gas Sensors / Quang Chieu Bui, Ludovic Largeau, Martina Morassi et al. // Appl. Sci. 2019, 9, 3528]. So, sensors that are based on flat films have numerous disadvantages, including a limited surface, where there is an interaction between gas molecules and the material, which leads to limited characteristics of the sensors. 1D semiconductor materials have a high surface-to-volume ratio, which could provide significant sensor feedback. Regarding the synthesis of 1D Ga2O3 nanostructures, they can be obtained by various methods, including, physical evaporation, arc discharge, laser ablation, chemical vapor deposition, grinding, thermal decomposition of GaN powders. This work is devoted to the theoretical study, using the methods of electron density functional, ab initio pseudopotential and the author's software [Flexible 2D layered material junctions / Balabai R., Solomenko A. // Applied Nanoscience, 2019, 9, 1011], the sensitivity of β-Ga2O3 nanoparticles of spherical and prism-like forms to the adsorption of CO, NH3, O3 molecules. It is established that the electronic characteristics of actually pure particles of different shapes, but with the same number of atoms (contains 30 atoms) and electrons differ. So, the width of the valence band of a prism-like particle is 20% greater than that of a spherical particle.

Authors : Zalevskyi D.V., Balabai R.M.
Affiliations : PhD student of the Department of Physics (Kryvyi Rih State Pedagogical University, Ukraine); Professor of the Department of Physics (Kryvyi Rih State Pedagogical University, Ukraine)

Resume : Recently, resistive switching memory or resistive random access memory (RRAM) has become one of the most competitive candidates for the role of next-generation non-volatile memory [1]. The structure of resistive RAM should consist of two opposite electrodes and storage material. Metal oxides are interesting to use as storage materials due to a simple change in conductivity. Among the numerous metal oxides, ZnO has such advantageous properties as low cost, wide and direct band gap of ~ 3.3 eV, low synthesis temperature, controlled electrical behavior, chemical stability, electrochemical activity, biocompatibility and environmental friendliness. ZnO can be grown with a wide variety of morphologies that can open the possibility of manufacturing one-dimensional RRAM structures [2]. Switching (SET / RESET process) in ZnO RRAM is associated with the formation / rupture of conductive filaments (CF) consisting of oxygen vacancies. However, convincing quantitative indicators are not enough to demonstrate the role of oxygen vacancies in switching, which leads to difficulties in the development and application of RRAM [3]. In the filamentous model, the RRAM read current flows through the CF. The size of the filament is much smaller than the area of the electrode, which leads to a localized conductivity effect. In addition to the filamentary model, the switching mechanism offers a homogeneous model of the interface type, in which the conductivity of the RRAM material is determined integrally over the entire plane of the electrode. The filamentous switching can be transformed into a homogeneous switching by the formation of oxygen defects in the area near the electrode. Therefore, such RRAM material has more than two conductive states, which can be an effective way to increase the density of information storage. The paper proposes the calculation by methods of the theory of electron density functional and pseudopotential from the first principles of characteristics of the electronic subsystem of the working layer RRAM, built on the basis of ultrafine ZnO film with oxygen vacancies forming threads of a certain morphology in the oxygen atomic planes. The spatial density distributions of valence electrons and their cross sections within the film, the distributions of electric potentials along the film perpendicular to the planes of the proposed electrodes, the distribution of the density of electronic states and switching energy between different conductive states of the working layer RRAM [1]. At the atomistic level, the features of the physical switching mechanisms in the filament and interface model RRAM with the working layer ZnO are established. [1] R. M. Balabai & D. V. Zalevskyi (2020) Properties of materials for resistive RAM based on HfO2 (first principles calculations), Molecular Crystals and Liquid Crystals, 700:1, 95-106. [2] Huang Y, Shen Z, Wu Y, Wang X, Zhang S, Shi X, Zeng H (2016) Amorphous ZnO based resistive random access memory. RSC Adv 6:17867–17872. [3] Simanjuntak FM, Prasad OK, Panda D, Lin C-A, Tsai T-L, Wei K-H, Tseng T-Y (2016) Impacts of Co doping on ZnO transparent switching memory device characteristics. Appl Phys Lett 108:183506.

Authors : L.L. Rusevich (1), G. Zvejnieks (1), E.А. Kotomin (1), M. Maček Kržmanc (2)
Affiliations : (1) Institute of Solid State Physics, University of Latvia, Riga, Latvia; (2) Jožef Stefan Institute, Ljubljana, Slovenia

Resume : Currently, the efficient solar-driven energy production continues to attract great interest. Hydrogen production directly from water is the efficient way to hydrogen energy engineering. Sunlight-driven water splitting is one of the most promising pollution-free strategies for production of hydrogen. Photocatalytic water splitting consists of water decomposition into hydrogen and oxygen by a reaction with photo-generated charge carriers. However, many challenges must be overcome before photocatalytic water splitting can be practically implemented at a large scale. Band engineering is one of the ways for development of the optimal photocatalytic material with both strong visible light absorption and high charge mobility. Band gap of efficient photocatalyst must be above 1.23 eV, to achieve water splitting, but less than 2.7 eV, to use efficiently a visible light. At the same time, the special conditions exist also for valence and conduction bands edges position. In this study, we used ab initio (first-principles) calculations, to investigate the structural and electronic properties of SrTiO3 (STO) perovskite photocatalyst (band gap 3.25 eV) and to modify its electronic band structure by means of defects and impurities. Unrestricted DFT (open-shell) calculations were performed with the CRYSTAL17 computer code within the linear combination of atomic orbitals (LCAO) approximation with using B1WC advanced hybrid exchange-correlation functional. We considered the bulk STO crystal and its (001) slabs, and then employed a supercell model to simulate point defects (neutral and charged oxygen vacancies, nitrogen and aluminum substitutional atoms). The electronic structure of defective systems was studied in details. Our computations demonstrate that introduction of such defects indeed makes STO photocatalyst more efficient for sunlight-driven water splitting. The calculated bandgap of stoichiometric STO and reduced SrTiO(3-x) were compared with the optical bandgaps, determined experimentally by means of diffuse reflectance spectroscopy and Kubelka-Munk method.

Authors : N.A. Kalanda(1), M.V. Yarmolich(1), A.V. Petrov(1), E.A. Artsiukh(1), N.A. Sobolev(2)
Affiliations : (1) Scientific-Practical Materials Research Centre of the NAS of Belarus, 220072 Minsk, Belarus (2) Departamento de Física and I3N, Universidade de Aveiro, 3810-193 Aveiro, Portugal

Resume : The citrate-gel technique was used for the synthesis of Sr2FeMoO6 (SFMO) nanopowders. The final synthesis was carried out in a reducing gas mixture of 5%H2/Ar at 1170°K for 4 h in several stages. The initial solution contained 1.0 g of polyvinylpyrrolidone (PVP) with 15 ml ethanol and 2.0 g of PVP, after which 1.5 g of SFMO nanopowder were added. Further, solution was mixed in a magnetic stirrer, then an ultrasound treatment was implemented during 20 min. SFMO films were obtained on a polycore substrate from the solution by using the spin-coating technique. The film was dried for 2 h at 340 K. To improve the microstructure, the films were subjected to a heat treatment at 570 K for 1 h. The phase composition of the synthesis products has been determined using the X-ray diffraction on a DRON-3 setup using CuKα radiation by means of the ICSD-PDF2 database (Release 2000) and PowderCell software. The microstructure was observed using a JEOL JSM 6360 scanning electron microscope. The magnetic properties were studied in the temperature range from 4.2…600 K in the universal Cryogenic Limited Liquid Helium Free High Field Measurement System (Cryogenic Ltd.) It has been found that the Sr2FeMoO6-δ films obtained by spin-coating at a substrate rotation rate of 4500 rpm had improved structural characteristics and superstructural ordering of Fe3+ and Mo5+ cations. According to the data of the field dependences of the magnetization measured at T = 6 K in magnetic fields up to 10 T applied along the film surface, the saturation magnetization Msat ~ 2 µB/f.u. has been found, which is significantly lower than the theoretical value Mtheor = 4 µB/f.u. Temperature dependences of the magnetization measured in the ZFC and FC modes at B = 0.02 T indicated the presence of magnetic regions with a low coercivity Hc -> 0, which is most likely due to the existence of a magnetically inhomogeneous state with the manifestation of superparamagnetism. For the first time, based on the study of the dynamics of changes in the intensity of paramagnetic lines (Im) in the Mössbauer spectra, the temperatures of the onset (Tcstart) and completion (Tccomp) of the transition from the paramagnetic to the ferrimagnetic state and, thus, the width of the magnetic phase transition have been estimated. The temperature dependence of the electrical resistance in the SFMO granulated films reveals the semiconductor type of conductivity in the temperature range from 4.2…300 K. The charge transfer occurs through the energy barriers created by the interlayers. A negative magnetoresistive effect is manifested in magnetic fields, and the charge transfer is spin-dependent with the highest value of the magnetoresistive effect of -43.6% achieved in a field of 10 T. This work was supported by the European project H2020-MSCA-RISE-2017-778308-SPINMULTIFILM. N.A.S. acknowledges the support through the project i3N, UIDB/50025/2020 & UIDP/50025/2020, financed by national funds through the FCT/MEC of Portugal.

Authors : L.L. Rusevich (1), G. Zvejnieks (1), E.A. Kotomin (1), A.I. Popov (1), T. Scherer (2)
Affiliations : (1) Institute of Solid State Physics, University of Latvia, Riga, Latvia; (2) Karlsruhe Institute of Technology, Germany

Resume : Diamond is unique material for a broad range of technological applications due to its physical and chemical properties. Diamond hosts a wide variety of luminescent defect centers that can act as stable single photon emitters at room temperature or as optically addressable solid-state spin-qubits. It is used in diagnostics and as high power microwave transmission window for plasma heating and stabilization in fusion reactors. In this study, we presented the results of ab initio (first-principles) simulations of vacancies and nitrogen substitutional defects in diamond crystals. Calculations of the atomic, electronic and vibrational properties were performed with the CRYSTAL17 computer code within the linear combination of atomic orbitals (LCAO) approximation. For consideration of defects, we used supercells containing 64 carbon atoms, a few basis sets for C atoms, and performed unrestricted DFT (open-shell) calculations with B1WC and B3LYP advanced hybrid functionals of the density-functional-theory. At the beginning, full geometry optimization and local structural analysis for pristine diamond and systems with defects were performed. Further, for fully-optimized systems and all spin configurations, calculations of harmonic phonon frequencies at the Γ point, infrared (IR) and Raman intensities, IR absorbance spectra, Raman spectra, dielectric functions and loss tangent were performed. It is predicted that in defective diamond additional features in both IR absorbance and Raman spectra as well as in dielectric functions arise in range of 400–1400 cm-1. The calculation results are compared with available experimental data.

Authors : L.S. Khoroshko, A.V. Baglov
Affiliations : Energy Physics Department, Faculty of Physics, Belarusian State University, Minsk, Belarus

Resume : Yttrium Iron perovskites (YIPs) are ferrimagnetic dielectrics promising for electronics, electrical engineering, etc. YIPs' doping with lanthanides, in particular Neodymium, is used to change their dielectric and luminescent properties. However, the effect of Fe and lanthanide ions on the electronic properties of pure and doped YIP has not been established yet. In this work we studied spin-polarized electronic structure and electron-electron interaction of YxNd1-xFeO3 perovskites, where 0 ≤ x ≤ 1, by the ab-initio methods. The simulation of the spin-polarized electronic properties of perovskites was carried out in the OpenMX package. To correctly take into account the 3d electrons of Iron and 4f electrons of Neodymium, we used a version of the density functional theory with the introduced Hubbard correction – DFT+U, where U was 6 eV for Fe and 5 eV for Nd. The electron density was estimated by the Mulliken populations analysis, and then the average value of the difference between spin-up and spin-down charges was found. The valence band maximum (VBM) is formed by spin-down oxygen electrons according to the simulation results between extreme cases x = 0 (YFeO3) and x = 1 (NdFeO3). At a depth of more than 900 meV, spin-up electron states appear. The contribution and spin polarization of metal electrons are insignificant in all cases. The conduction band Minimum (CBM) is formed by spin-up electrons of Fe predominantly, with slightly admixing of oxygen and yttrium (neodymium) electrons. The spin polarization in this case is close to 100% up to ≈5 eV, where spin-polarized states of the Y and Nd electrons begin to appear. Mulliken populations analysis shows increasing of metals electrons polarization with a slight decrease of oxygen electrons polarization when Y ions are replaced by Nd. An increase in the energy gap without a significant effect on the electronic states density and polarization degree may be due to the partial hybridization of Fe d-electrons and Nd f-electrons. The substitution of Y by Nd leads to the unit cell volume increasing (by 2.5% with full substitution). For the spin-down electron states, the gap has indirect dielectric character, Eg is 4.68 eV and 5.47 eV for YFeO3 and NdFeO3, respectively. The spin-up states are characterized by a direct transition at the point Γ of 2.09 eV (YFeO3) and 2.67 eV (NdFeO3). In the general case, the size of the energy gap between VB and CB without taking of spin orientation is 1.23 eV and 1.93 eV for YFeO3 and NdFeO3, respectively. Thus, in YIP doped with Nd up to complete substitution, the band dispersion is preserved with a simultaneous increase in the gap between the maximum of the CB formed by spin-up electrons and the minimum of the VB formed by spin-down electrons by 57% and no more than 20% between areas with the same spin direction.

Authors : Y. Hoshi1, S. Hayashida1, S. Nogamida1, K. Sawano1, K. Watanabe2, and T. Taniguchi2
Affiliations : 1 Tokyo City University, 2 National Institute for Materials Science

Resume : A semiconducting molybdenum ditelluride (MoTe2) monolayer, which is atomically-thin layered materials, has been attracting considerable attentions for development of various opto-electronic devices since it has a direct bandgap around 1.1 eV applicable to optical communications and exhibits an extraordinarily large exciton binding energy of several hundred meV owing to strong electron-hole confinement. However, the MoTe2 crystal has a critical disadvantage of formation of the surface decomposition-induced cluster defects and Te vacancies during thermal treatment even at low temperature of 200 ̊C. On the other hands, atomically-thin layered materials encapsulated by hexagonal boron nitride (hBN) are considered promising structures for enhancement of electrical and optical device performances. In this study, we investigated effects of thermal treatment on the crystal quality in the mechanically-exfoliated MoTe2 monolayer encapsulated by hBN using steady-state photoluminescence measurements, demonstrating suppression of desorption of Mo and Te atoms owing to existence of hBN capping layer. It was furthermore found that residues remained at the interfaces between hBN and MoTe2 for the as-fabricated samples, and the thermal treatment was effective for removal of the residues at the interfaces. These results indicate that combination of hBN encapsulation and thermal treatment is promising for realization of high-performance MoTe2-based opto-electronic devices.

Authors : Takahiro Inoue, Youya Wagatsuma, Kodai Yamada, Kentarou Sawano
Affiliations : Adv. Res. Lab., Tokyo City Univ.

Resume : 1. Introduction Ge has been attracting attentions for the realization of intra-chip optical integrated circuits. In particular, introduction of tensile strain by epitaxial growth of a Ge on a Si substrate enhances the direct transition probability by lowering the Γ-valley, resulting in an increase in a light emission efficiency. Furthermore, by fabricating a microbridge structure based on the Ge-on-Si, the uniaxial tensile strain can be considerably enhanced within the floated microbridge, which is expected to further improve the light emission efficiency [1]. The band shift of the Γ-valley is expected to be the largest along <111> directional tensile strain among various directions [2]. In this study, we fabricate strained Ge microbridge structures based on Ge-on-Si(100) and -Si(110) so as to induce uniaxial tensile strain in the <001> and <111> directions, respectively, where controlling defects and anisotropic etching are key issues of importance, and we evaluate strain states and luminescence properties. 2. Experimental A Ge layer was directly grown on a Si(100) or Si(110) wafer by solid-source molecular beam epitaxy (MBE) by a two-step growth method. The Ge-on-Si consists of a Ge buffer (40 nm) and a Ge (500 nm) layers grown at 350 and 600 °C, respectively, followed by thermal annealing at 800 °C for 10 min to reduce the threading dislocation density in the Ge layer. After the MBE growth, patterning of microbridge structures was performed by photolithography and dry etching. A Si beneath the microbridges was then removed to form free-standing structures by KOH selective wet etching. 3. Results and Discussion Fabrication of the microbridge structure resulted in stronger room temperature (RT) photoluminescence (PL) intensity compared to unprocessed Ge-on-Si. In addition, the PL intensity of the microbridge with the strain along <111> direction was stronger than that along <001>. It is thought that the addition of the uniaxial tensile strain in the <111> direction brings the larger valley shift and leads to the higher emission intensity. On the other hand, Raman measurements showed that the tensile strain in the microbridge was 0.32%, which was smaller than expected. The anisotropy of the etching rate of KOH, which is strongly dependent on the substrate orientations, may have caused insufficient etching of the underneath Si in pad areas (sides of the bridges), resulting in the insufficient increase in the strain. Further increase in luminescence efficiency can be expected via optimizations of the fabrication process that can bring stronger strain. This work was supported in part by Grant-in-Aid for Scientific Research (19H02175, 19H05616, 20K21009) from MEXT, Japan. [1] M. J. Suess et al, Nat. Photonics 7, 466, 2013 [2] H. Tahini et al., J. Phys.: Condens. Matter 24, 195802, 2012.

Authors : Satoshi Nogamida1, Shunya Hayashida1, Kosuke O Hara2, Kentarou Sawano1, and Yusuke Hoshi1
Affiliations : 1.Tokyo City Univ.; 2.Univ. Yamanashi

Resume : Transition metal dichalcogenides (TMDC), which are atomically thin layered materials, have attracting considerable attentions for realization of next-generation optoelectronic devices owing to their unique properties such as valley degree of freedom and extraordinarily large exciton binding energy based on strong carrier confinement. Among the TMDC materials, semiconducting molybdenum ditelluride (2H-MoTe2) has narrow bandgaps of 0.9-1.1 eV depending on the layer number, which is suitable for a light source for optical communications. To enhance the optoelectronic device performance, it is crucial to form Ohmic contact between a metal and 2H-MoTe2. So far, it is reported that a metallic phase can be formed by laser irradiation to a 2H-MoTe2 single crystal and the junction between the laser-induced-metal (LIM) and 2H-MoTe2 has lower Schottky barrier height compared to conventional metal/2H-MoTe2 junctions. The LIM is thought to be formed by the photo-thermal effect, which is the decomposition based on the vacancy formation and the local heating by laser irradiation. In this study, we propose a novel technique to fabricate a defect-assisted-metal (DAM) phase by thermally annealing 2H-MoTe2 multilayers with Ar ion implantation. Multilayer 2H-MoTe2 flakes were directly deposited on 100-nm-thick SiO2/Si substrates by micromechanical exfoliation. To generate vacancies in the multilayer MoTe2 crystal, Ar ions were implanted at ion energies of 30-90 keV and a dose of 5×1011 cm-2. Subsequently, the samples were thermally annealed at 400 ℃ for 1 hour in an atmosphere. As a reference, we prepared the LIM by irradiation of a continuous wave laser (λ=980 nm) to 2H-MoTe2 multilayer on the SiO2/Si substrate. Raman spectra are measured to investigate crystal structures of the samples. For a sample without the defect-assist based on ion implantation, Raman spectral shape is found to be almost the same as that of 2H-MoTe2 single crystal except for the peak intensity. In contrast, a Raman spectrum similar with the LIM is obtained for the DAM sample, demonstrating that the crystal defects of MoTe2 induced by ion implantation assists the metallic phase formation during the thermal anneal. From Auger electron spectroscopy, it is shown that the atomic composition ratio of Mo and Te in the DAM is 1:1, which means the thermal decomposition of Mo and Te in 2H-MoTe2 rather than the structural phase transition to semi-metallic 1T’. To demonstrate the low resistivity of the DAM, we measure two terminal current-voltage properties for the DAM with Ti/Au electrodes. The resistivity is found to be less than 10-4 Ohm·cm, which is comparable to that of the LIM. These results indicates that the DAM has a high potential for realization of large-area optoelectronic devices with low contact resistance.

Authors : Kirill A. Svit(1), Konstantin S. Zhuravlev (1,2)
Affiliations : 1) Rzhanov Institute of Semiconductor Physics, Novosibirsk 630090, Russian Federation;. 2) Novosibirsk State University, Novosibirsk, 630090, Russian Federation

Resume : Due to manifestation of quantum confinement semiconductor quantum dots (QDs) are promising materials for creating different optoelectronic devices such as lasers, solar cells and displays. QD energy spectra can be controlled by varying QDs shape, size, crystal structure and surface condition. Understanding of the QDs optical properties and creation of the QD with high quantum yield value is impossible without detailed considering of the lattice structure and dominating native defects type. A lot of work in this direction was done for colloidal QD, however the QDs obtained using Langmuir-Blodgett technique are poorly investigated. This method is a also based on chemical approach of the QDs synthesis and has such features as simplicity and low cost. The other advantage of this method is possibility of creation of dense packed QDs solid on the large area substrates. At this method QD surface can be passivated by ammonia molecules that length is lower than that for organic ligands in colloidal synthesis, so the distance between the neighboring QDs is less than 1 nm that is interesting in terms of research of different collective phenomena in the QDs solid. In present work structural and optical properties of CdS QDs synthesized within the fatty acid LB matrix were investigated before and after the matrix annealing and QDs surface passivation. Stuctural properties were investigated using X-ray photoelectron spectroscopy, extended X-ray absorption fine structure and high resolution transmission electron microscopy methods. Optical properties were investigated by stationary photoluminescence (PL) and absorption spectroscopy techniques. It was established that initially after the synthesis QDs within the matrix have oblate spheroid shape with semi-diameters equal to 2.4 and 3.4 nm and cubic crystal structure. PL spectra of these QDs fully dominated by defect-assisted PL with peak energy at about 2.3 eV. According to theoretical predictions and our experimental findings defect-assisted PL is due to sulfur vacancies. After the matrix annealing in ammonia atmosphere QDs became spherical with mean diameter equal to 5 nm, the crystal structure changer to hexagonal and PL properties drastically change. Defect-assisted PL becomes weak and band-edge exciton emission dominates. Observed fluorescence properties of the QDs were analyzed in terms of the model based on simultaneous recombination through the band-edge states and sulfur vacancies level. It was established that QDs within the matrix are characterized by high number of sulfur vacancies that leads to fast excited electron capture from the first election level to the trap state resulting in domination of defect-assisted PL and band-edge emission suppression. After the annealing and passivation in ammonia QDs demonstrate low sulfur vacancies density due to effective ammonia passivation of the Cd dangling bond by lone electron pair that leads to the occurrence of high intensity narrow band-edge exciton peak on the PL spectra and suppression of the defect-assisted PL.

Authors : K. Kumarbekov1, A. Dauletbekova1, Zh. Karipbayev1, M/. Zdorovets1,2,3, I. Manika4, J. Maniks4, D. Sugak4,5, S. Ubizskii6, N. Mironova-Ulmane4, A. I. Popov4
Affiliations : 1L. N. Gumilyov Eurasian National University, Nur-Sultan, Kazakhstan, 2Institute of Nuclear Physics, Nur-Sultan, Kazakhstan, 4Institute of Solid State Physics, University of Latvia, Riga, Latvia, 5Lviv Polytechnic National University, Lviv, Ukraine, 6Scientific Research Company “Electron-Carat”, Lviv, Ukraine,

Resume : The single crystal Gd3Ga5O12 (GGG) are widely used and extensively studied as solid-state laser materials, magneto-optical storage materials, and scintillators. In this work, we report on the optical and structural properties of GGG irradiated with 150 MeV Kr+15 ions, up to fluences 1х1013 - 1х1014 ion/сm2 at cyclotron DC-60 (Nur-Sultan, Kazakhstan). Our samples were grown by the Czochralski method in slightly oxidizing atmosphere. Samples were prepared in the form of polished plates with (111) orientation and a thickness of 0.48 mm . In irradiated monocrystals, a shift of the fundamental absorption edge by ~30 nm to the long-wave part of the spectrum is observed. The cause of the observed changes is a disturbance of the structure (depletion of the near-surface layer, creation of oxygen vacancies). This is accompanied by an increase in the crystal lattice parameters. Increasing the irradiation fluence leads to a deterioration of the structural characteristics, as well as an increase in the values of distortions and deformations. Ion-induced deformations and distortions, affecting the hardness of the material. Comparison of the depth behavior of hardness and the corresponding calculated energy losses leads to the conclusion that ion-induced structural and hardness modifications are due to electronic energy losses.

Authors : D. V. Dmitriev (1), D..A. Kolosovsky (1,2), T.A. Gavrilova (1), A.S. Kozhuhov (1), A.I. Toropov (1), K.S. Zhuravlev (1,2)
Affiliations : 1) Rzhanov Institute of Semiconductor Physics, Novosibirsk 630090, Russian Federation;. 2) Novosibirsk State University, Novosibirsk, 630090, Russian Federation

Resume : At the present time InAlAs/InP lattice-matched nanostructures are being aroused interest of researchers [1, 2]. In such structures, specific mechanisms of defect formation are observed: the defects formation at the substrate - layer heterointerface (type I), and the defects formation inside the epitaxial layer (type II). We report a few methods to control the defects formation in InAlAs/InP heterostructures. We varied the substrate annealing temperature, layer growth conditions (temperature, arsenic flux) and investigated the effect of a short-period InGaAs/InAlAs superlattice. InAlAs/InP samples were grown using a Riber Compact 21T MBE system. Annealing of InP substrates was carried out in an arsenic flux to prevent the incorporation of phosphorus into InAlAs layers due to the “memory effect” [3]. We has established that type I and type II defects are stacking faults are formed in the InAlAs layers, propagating along the {111} planes by SEM. At the exit of such defects «pits» are formed on the surface. The formation of type I defects is associated with the substitution of arsenic for phosphorus in the near-surface layer of the substrate and the formation of InAs islands during high-temperature annealing of the substrate. The lattice-mismatch at the initial stages of growth leads to tensile deformation of the InAlAs layers and the formation of a dislocation. The annealing temperature has a significant effect on the density of InAs islands, which can reach 1×1010 cm-2 upon annealing above 540 ℃. The minimum density (1×104 cm-2) and size of InAs islands is observed in annealing temperatures of ~510 ℃ and an arsenic flux FAs<1.5×10-5 Torr. In lower annealing temperatures leaves a significant portion of the oxides on the surface, which also leads to an increase in defects in the grown layers. The growth of InAlAs/InGaAs short-period superlattices after annealing leads to reduce the density of such defects by another 2–3 orders of magnitude. Type II defects are associated with the decomposition of the ternary solid solution InAlAs into binary compounds during growth under nonequilibrium conditions. The density of such defects can be varied by growth conditions in the range 104-108 cm-2. The minimum density of defects in InAlAs layers grown at a growth temperature 505 ℃ and an arsenic flux 1.5×10-5 Torr was experimentally established. The optimal growth conditions for decreasing the density of type I defects by 108 times and of the type II by 104 times were determined. References [1] Jesus A. delAlamo, Nature 479 (2011) 317-323 [2] M.Z.M. Khan, et al, Nanoscale Semiconductor Lasers, (2019) 109–138 [3] A. Antolini,et al, J. Electron.Mater., 21 (1992) 233–8

Authors : I. V. Osinnykh (1,2), I. A. Aleksandrov (1), and K. S. Zhuravlev (1,2)
Affiliations : 1) Rzhanov Institute of Semiconductor Physics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 630090, Russia; 2) Novosibirsk State University, Novosibirsk, 630090, Russia

Resume : AlGaN alloys have emerged as important materials for high- power electronics and deep UV light sources (light emitting and laser diodes). The creation of effective light-emitting devices is impossible without doping the epitaxial layers. The formation of epitaxial n-GaN and Ga-rich AlGaN layers using silicon (Si) as a donor does not cause significant difficulties. However, doping of AlGaN becomes less efficient with an increase in Al content (x) higher than x>0.6. The electron concentration becomes significantly lower than the concentration of silicon atoms due to the self-compensation of Si donors. It is assumed that vacancies or their complexes also lead to the appearance of intense broadband photoluminescence (PL) in the visible spectral range, which was observed in AlxGa1-xN epitaxial layers with a mass fraction of x>0.6 with strong doping with silicon [1]. The aim of this work was to establish the elemental composition of the centers of this luminescence in AlN. The Si, C, and O impurity concentrations in Si doped AlN about 1.5*1020, 8*1019, and 4*1019, cm-3, respectively, were estimated by secondary-ion mass spectrometry (SIMS), using a IMS7f (CAMECA) setup with primary Cs ions. The defect concentrations were calculated in the thermodynamic equilibrium model. The defect formation energies were calculated using the density functional theory (DFT) with hybrid functional HSE with modified fraction of Hartree-Fock exchange a=0.33 in Quantum ESPRESSO software package. Details of the DFT calculation of the formation energies are described in Ref [2]. The defect types included in the calculation of the defect concentrations are intrinsic defects in AlN, C-, O- and Si- containing defects and complexes, which were considered in Ref [2]. The Al chemical potential was related to partial pressures. Chemical potentials of C, O, Si were obtained in such a way that the total concentrations of these elements corresponded to measured values. The concentration of VAl-3SiAl is 4*1019 cm-3 that an order of magnitude higher than concentration of donors SiAl. According to calculations the luminescence maximum position for band to eA transitions for VAl-3SiAl should be about 3.56 eV that higher than the obsereved PL maximum position 3.0 eV. Another complexes VAl-1SiAl and VAl-2SiAl should have luminescence maximum positions close to 3.0 eV, but the concentration of VAl-1SiAl 2*1017 cm-3 is much lower than the concentration of VAl-2SiAl 9*1017 cm-3. Therefore VAl-2SiAl is most likely candidate for the acceptor. [1] P. A. Bokhan, P. P. Gugin, Dm. E. Zakrevsky, K. S. Zhuravlev, T. V. Malin, I. V. Osinnykh, V. I. Solomonov, and A. V. Spirina , J. Appl. Phys., 116, 113103 (2014). [2] I.A. Aleksandrov, and K. S. Zhuravlev, J. Phys.: Condens. Matter, 32, 435501 (2020).

Authors : L.A. Lisitsyna (1), A.I. Popov (2), Zh.T. Karipbayev (3), A.V. Strelkova (3)
Affiliations : (1) Tomsk State University of Architecture and Building, 2 Solyanaya sq., 634003, Tomsk (2) Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV1063, Latvia (3) L.N. Gumilyov Eurasian National University 2 Satbaeva 010000, Nur-Sultan, Kazakhstan

Resume : In terms of their properties, MgF2 crystals are in many respects similar to widely used LiF crystals, which, in particular, have unique luminescent characteristics due to various impurities. It is obvious that MgF2-based ceramics doped with polyvalent ions have many distinct advantages over crystals. However, it is rather difficult to introduce them into the MgF2 lattice. In this study, we presented the results of luminescence characterization of optical ceramics based on MgF2 doped WO3, synthesized by high-energy electron beam assisted methods, namely in an air under the action of a 1.4 MeV electron beam with a very high specific power of 14–20 kW/ cm2. Analysis of the phase structural composition of the synthesized ceramic samples indicates the predominance of the rutile phase. The same conclusion follows from a comparative analysis of the optical properties of color centers in the synthesized samples of MgF2 ceramics and MgF2 single crystals. To study the structural inhomogeneity and imperfections of the synthesized samples, we measured in the wide temperature range (5-300 K) their spectral (1.0 - 6.0 eV) and time-resolved characteristics of photo- and cathodoluminesce as well as their thermoluminescence. In particular, we have found that in ceramic MgF2 samples, the position of the dopant-related photoluminescence band at 2.7 eV, its luminescence decay, and the appropriated excitation spectrum are qualitatively similar to those measured in LiF crystals doped with WO3. This clearly indicates that the dopant is incorporated into the rutile lattice in the form of tungsten trioxide. In addition, we estimated the quantitative characteristic of the efficiency of conversion of the excitation energy into luminescence at 2.7 eV in sintered WO3-doped MgF2 ceramic samples in comparison with YAG: Ce (0.5 at.%), taken as a standard, is about 20%.

Authors : V.D.Bundyukova, S.E.Demyanov, V.V.Prigodich, A.V.Petrov, D.V.Yakimchuk
Affiliations : Scientific-Practical Materials Research Centre of the NAS of Belarus, 220072 Minsk, Belarus

Resume : Silicon is universal platform for immobilization of sensing layers for various applications. The possibility of modifying silicon with various metals allows it to be used as the basis for sensor devices. Numerous works describe the method of electrodeposition of noble metals on the silicon surface to form a microrod array [1, 2]. However, these ones have various limitations, including the size of the formed nanoparticles and morphology, the unevenness of the coating thickness, etc [3]. In this work, a galvanic deposition method was used to obtained gold nanotracks on a silicon surface of n- and p-types from a salt of AuCl3•(H2O) in aqueous solution. The concentration of gold ions in the initial solution ranged from 0.00125 to 0.01 M with the subsequent addition of 5 M HF acid in a 1:1 ratio. The morphological properties of the resulting structures depending on the gold solution temperature, concentration and time of deposition were studied as well as their structural properties. The obtained gold nanotracks demonstrated the potential use for Raman signal amplification on a test analyte Methylene blue (C16H18ClN3S) with a concentration of 10-6 M. Thus, there is a possibility of using gold nanotracks as SERS-active surfaces for sensors. The authors acknowledge the support of the work in frames of H2020 - MSCA - RISE2017 - 778308 - SPINMULTIFILM Project and the Scientific-Technical Programme “Technology-SG” [Project No.]. [1] Fukami, K., Kobayashi, K., Matsumoto, T., Kawamura, Y. L., Sakka, T., & Ogata, Y. H. (2008). Electrodeposition of Noble Metals into Ordered Macropores in p-Type Silicon. Journal of The Electrochemical Society, 155(6), D443. [2] Ogata, Y., Kobayashi, K., & Motoyama, M. (2006). Electrochemical metal deposition on silicon. Current Opinion in Solid State and Materials Science, 10(3-4), 163–172. [3] Tonelli, D., Scavetta, E., & Gualandi, I. (2019). Electrochemical Deposition of Nanomaterials for Electrochemical Sensing. Sensors, 19(5), 1186.

Authors : V.V. Prigodich, V.D. Bundyukova, A.V. Petrov, D.V. Yakimchuk
Affiliations : Scientific-Practical Materials Research Centre of the NAS of Belarus, 220072 Minsk, Belarus

Resume : Recently, ion-track porous templates based on silicon and silicon oxide have been used to obtain new functional materials SiO2/Si. For example, noble metal nanostructures were grown in SiO2 pores on a silicon substrate, which were used to enhance the Raman signal to register low concentrations of molecular substances [1]. In the present work, a similar technology was used to obtain nickel structures in the pores of this template. Such studies have already been carried out, but they were not focused on studying the surface morphology of magnetic structures and identifying the prospects for their use [2]. By changing the parameters of electrochemical deposition, nickel structures with dendritic morphology were obtained in the pores of the SiO2/Si template. Peculiarities of the preparation of SiO2(Ni)/Si heterostructures are revealed, and the dependences of the structural and magnetic parameters of such systems on the electrochemical deposition of metal into the pores of the SiO2/Si template are determined. Such nickel structures with developed fractal morphology can serve as a solution to the problem of wastewater treatment from magnetic impurities. In addition, solid-state heterostructures SiO2(Ni)/Si where nickel is strongly fixed in the pores of a dielectric SiO2 can potentially act as reusable catalysts for chemical reactions [3]. The authors acknowledge the support of the work in frames of H2020 - MSCA - RISE2017 - 778308 - SPINMULTIFILM Project and the Scientific-Technical Program “Technology-SG” [Project No.]. [1] Yakimchuk D.V. [] (2019) Self-organized spatially separated silver 3D dendrites as efficient plasmonic nanostructures for surface-enhanced Raman spectroscopy applications. Journal of Applied Physics, 126 (23), 233105. [2] Kaniukov E.Yu., Demyanov S.E. (2010) Characteristic features of electric charge transfer processes in Si/SiO2/Ni nanostructures in strong magnetic fields. Mater. Sci. (in Russian), 6, 53-58. [3] Sang H.A. [et al.] (2012) Electrodeposited Ni dendrites with high activity and durability for hydrogen evolution reaction in alkaline water electrolysis. Journal of materials Chemistry. 22, 15153.

Authors : V.M.Studzinskii 1 2, K.V.Karabeshkin 2 3, M.V.Mishin 1 2, A.L.Shakhmin 1, A.I.Titov 1 2, P.A.Karaseov1
Affiliations : 1 Peter the Great St.-Petersburg Polytechnic Univesity, St.-Petersburg, Russia; 2 Alferov University, St.-Petersburg, Russia; 3 JSC ELAR, St.-Petersburg, Russia

Resume : Today, great attention is paid to the production and use of nanocomposite materials in various fields of human activity. Nanoparticles of noble metals are used as catalysts, sensors, and transport agents for other substances. Gold nanoparticles are worthy of separate consideration among noble metals, since they are biocompatible with human tissues. Currently, effective route to produce nanoparticles is a chemical reduction from salts. This method is fraught with difficulties associated with the extraction of nanoparticles from solution. There are also anhydrous techniques to make nanoparticles. For example, one can use irradiation of thin metal films on the surface of substrates with accelerated ions. This approach allows controlling the distribution of the obtained gold nanoparticles by varying the parameters of the incident beam: kind of ion, energy, and dose. In addition, it was shown in that bombardment with molecular ions changes the efficiency of ion-stimulated gold film modification processes. An important role in this is played by the material of the substrate, on which the nanoparticles are formed. As polymethylmetacrylate (PMMA) is biocompatible polymer, it is promising to make gold nanoparticles on its surface. A 250-nm-thick PMMA film was deposited on monocrystalline silicon substrate. ~ 6 nm thick gold layer was deposited on top of the polymer by resistive thermal evaporation. The samples obtained were bombardment with 1.3 keV / amuP and PF4 ions in the range of equivalent doses 0.27 × 10-4–0.54 × 10-2 DPA using a 500 keV HVEE implanter. Dose values in DPA were calculated as the number of gold atom displacements in a film calculated according to the binary collision approximation using the TRIM code. Reaching a dose of 1 DPA means that each atom in the film has experienced one displacement from its initial position. Overlapping of collision sub-cascades formed by atomic constituents of a molecular ion gives rise to an increase in the density of the cumulative cascade formed by molecular ion. This can affect process of nanoparticle formation. It is shown that the gold film breaks into nanoparticles under irradiation. Both the gold layer and the polymer film are modified by ions, but the way it happens depends on the type of ion and the radiation dose. Irradiation with molecular ions, at the initial stage, smoothes the gold layer, and then, with dose increase breaks it into nanoparticles. Monatomic ion bombardment does not cause any smoothing of the gold layer. Irradiation with molecular PF4 ions leads to the healing of small pores in PMMA, while irradiation with atomic P ions, on the contrary, enlarges them. Work at Alferov University was supported by the state assignment of Russian Ministry of Science and Higher Education (project № FSRM-2020-009).

Authors : D. Untila1,2, V. Sprincean1, I. Evtodiev1,3, N. Spalatu4, L. Dmitroglo1, Iu. Caraman1
Affiliations : 1 Moldova State University, Alexei Mateevici str., 60, MD-2009 Chisinau, Republic of Moldova. 2 Technical University of Moldova, Stefan cel Mare si Sfint blvd., 168, MD-2004 Chisinau, Republic of Moldova. 3 University of European Political and Economic Studies “Constantin Stere”, Stefan cel Mare si Sfint blvd., 200, MD-2004 Chisinau, Republic of Moldova. 4 Tallinn University of Technology, Ehitajate tee, 5, EE-19086 Tallinn, Estonia.

Resume : β-Ga2O3:Eu3 nanocomposites (NCs) were obtained by thermal annealing (900-1100K), in air atmosphere, on top of GaSe:Eu (0.5-3 at%) blades – cleft from single crystals grown by Bridgman-Stockbarger method. The structure, elemental composition and morphology of the β-Ga2O3:Eu3 NCs were studied by XRD, EDX, SEM and Raman. The mechanism of β-Ga2O3:Eu3 NCs formation was established from the analysis of XRD pattern and Raman spectra. Thus, XRD patterns and Raman spectra revealed peaks at 2θ = 38.05° and 59.05°, and bands at 201 cm-1, 346 cm-1 and 660 cm-1 wavenumbers, respectively, which are characteristic to β-Ga2O3 compound. By analysis of the diffuse light reflection spectra, using the Kubelka-Munk function, the direct bandgap of ~4.6 eV, was determined for the β-Ga2O3:Eu3 NCs formed on the surface of GaSe:Eu 0.5at% blades. An increase of Eu concentration up to 3.0 at%., in GaSe crystals, leads to the decrease of the bandgap of β-Ga2O3:Eu3 NCs, down to 4.48 eV. The PL spectra of β-Ga2O3:Eu NCs consisted of two different types of bands: the first one is a continuous band, with a maximum in the blue range; the second one – located in the 560-720 nm range, contains several narrow bands, among which the dominant one was peaked at 614 nm. The PL band with a maximum in the blue region was identified as donor-acceptor emission in β-Ga2O3, while the band at 614 nm, was attributed to 5D0-7F2 radiative transition in Eu3 ions. From the analysis of PL spectra, a mechanism of PL combined excitation of the Eu3 ions from β-Ga2O3 NCs is proposed.

Authors : L. Borkovska1, T.Stara1, K. Kozoriz1, A. Rachkov2, J.-L. Doualan3
Affiliations : 1V. Lashkaryov Institute of Semiconductor Physics of NASU, 45 Pr. Nauky, Kyiv, Ukraine; 2Institute of Molecular Biology and Genetics of NASU, 150 Zabolotnogo Str., Kyiv, Ukraine; 3CIMAP, CEA-CNRS-ENSICAEN, Normandie Université, 6 Blvd Maréchal Juin,Caen,France

Resume : The interest to luminescent colloidal semiconductor nanocrystals, quantum dots (QDs), is highly motivated by their potential application in opto- and photoelectronics, biology, medicine, etc. The AgInS2 QDs show high photoluminescence (PL) quantum yield and comprise of low-toxic elements that is especially important for the in vivo bio-imaging. In this work, the results of investigations of optical properties of water-soluble AgInS2/ZnS core-shell QDs in buffer solutions of different pH (3.0-9.0) are presented. The QDs were synthesized in aqueous media in the presence of glutathione. In the PL spectra of the QDs, a wide PL band peaked at ~587 nm was observed and ascribed to carrier recombination via the levels of intrinsic defects. The PL relaxation times were found to be dependent on the detection wavelength apparently due to variation of QDs in size. In neutral and acidic buffers, the PL intensity increased with increasing pH from 4.0 to 9.0. Simultaneously, the PL band shifted to shorter wavelengths. These transformations of the PL spectra were accompanied by the changes of the PL relaxation times, which became longer with PL increase. In the acidic buffer with pH 3.0, the PL intensity decreased by several times, the PL band shifted to longer wavelengths by 35 nm, and the PL relaxation times shortened. These changes were ascribed to dissociation of ligands from the ZnS outer shell, resulting in aggregation of QDs and loss of their solubility. It is proposed that glutathione-capped AgInS2/ZnS QDs may be used as a new type of fluorescence pH-sensor or indicator.

Authors : Claudia Barone, Jeetendra Gupta, R.M. Martin, I. Sydoryk, V. Craciun, J. Nomoto, H. Makino, T. Yamamoto, C. Martin
Affiliations : Montclair State University, Montclair, NJ 07043, USA; Ramapo College of New Jersey, Mahwah, New Jersey 07430, USA; Montclair State University, Montclair, NJ 07043, USA; Ramapo College of New Jersey, Mahwah, New Jersey 07430, USA; National Institute for Laser, Plasma, and Radiation Physics, Magurele, Romania; Advanced Coating Technology Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Ibaraki 305-8565, Japan; Research Institute, Kochi University of Technology, Kochi 782-8502, Japan; Research Institute, Kochi University of Technology, Kochi 782-8502, Japan; Ramapo College of New Jersey, Mahwah, New Jersey 07430, USA

Resume : Ga-doped ZnO (GZO) provides a low-cost alternative to the extensively used indium oxide-based transparent conductors (ITO) for various technological applications, such as photovoltaic devices, touch screen technology, or transparent and flexible electronics. More recently, transparent conductors were also proposed for use in space technology and for plasmonic devices. Irradiation with gold ions provides a mechanism for assessing the performance of GZO in space environment and potentially, for enhancing the plasmonic performances by electron doping. Through combined measurements of broadband optical reflectance (10 meV to 6 eV), resistivity and Hall effect, we investigated the effect of gold ions irradiation on optical and electrical properties of GZO thin films, obtained by ion plating direct-current arc discharge. We studied a significant number of films, deposited at various discharge currents (ID = 100 - 200 A) and oxygen (O2)-gas flow rates (OFR = 0 - 25 sccm), exposed to ion fluences in the range of 1014 -1015 cm-2. Our data shows remarkable resilience of optical and electrical properties of films to irradiation. No major changes in electron concentration, dc-conductivity or mobility were observed, even at the highest irradiation fluence. Transmittance and reflectance in the visible range show slight variations with irradiation, mostly due to surface effects. On one hand, our findings suggest that the GZO materials are suitable for space applications. On the other hand, gold irradiation does not add conduction carriers, hence does not improve the plasmonic parameters of GZO, unlike we previously observed on nitride ceramics. Comparison with ZrN films will be discussed in this context.

Authors : A.K. Mutali1,2,3, A.T. Zhumazhanova1,2, A.D. Ibrayeva2,3, V.A. Skuratov3, A.T. Akilbekov1, M.V. Zdorovet2
Affiliations : 1 L.N. Gumilyov Eurasian National University, Nur-Sultan, Kazakhstan 2 The Institute of Nuclear Physics’ Astana branch, Nur-Sultan, Kazakhstan 3 Flerov Laboratory of Nuclear Reactions of Joint Institute for Nuclear Research, Dubna, Russia

Resume : The depth-resolved Raman spectroscopy technique has been used to study the structural disorder and associated residual stresses in polycrystalline silicon nitride across of 167 MeV Xe and 710 MeV Bi ion irradiated layer at fluences ranged from 1E11 to 4.8E13 ions/cm2. To evaluate stress level the peak shifts of the 862 cm-1 band have been converted to stress via piezospectroscopic coefficients knowing from the literature [1]. As was found from Raman spectra and SEM images the amorphization of Si3N4 is induced in surface region and expands toward the depth with ion fluence. Ion track sizes deduced from the threshold ion fluences needed to transform material into amorphous phase are in good agreement with those found from TEM examination [2]. 1. N.Muraki et al., Journal of Materials Science 32 (1997) 5419. 2. Arno Janse van Vuuren et al., Nucl. Instr. Meth. B 473 (2020) 16.

Authors : V.M. Lisitsyn (1); A.T. Tulegenova (2); Zh.T. Karipbayev (3); A.I. Popov (4); A.V. Ermolaev (1); M.B. Aitzhanov(2); G.K. Alpyssova(3); Zh. Zhilgildinov (3);
Affiliations : (1) National Research Tomsk Polytechnic University, 30 Lenin Ave., 634050 Tomsk, Russia; (2) Al-Farabi Kazakh National University, 71 al-Farabi Ave., 050040, Almaty Kazakhstan; (3) Eurasian National University, 2, Satpayev Str., 010008 Astana, Kazakhstan; (4) Institute of Solid State Physics, University of Latvia, 8 Kengaraga st., Riga, Latvia;

Resume : Recently, we have demonstrated the new possibility of the synthesis of YAG: Ce polycrystalline ceramics from powders of Y, Al, Gd, Ce oxides mixed in a stoichiometric ratio by direct action of an electron beam with an energy of 1.4 MeV and a power rate of 20 kW/cm2. This synthesis was carried out without the use of any other additional external influences, as well as the use of additives that facilitate the process. However, the reasons for the high efficiency of such a synthesis are not clear. In particular, it was found that there appears to be a clear dependence of the quality of the resulting ceramic on the loading of the material and the particle size of the starting materials. Here we report our recent research results on the detailed dependence of the synthesis on the bulk density in the range from 1.05 to 2.6 g / cm3 and the time of exposure to an electron beam from 0.4 s. up to 1.0 s.Note that Bulk density was varied by compaction, while irradiation time was varied by scanning speed. It was found that in all cases of electron beam synthesis, ceramics with a characteristic YAG structure are always formed. However, the proportion of the YAG phase depends on the degree of compaction. In the used technology of radiation synthesis, in one cycle of irradiation with a scanning beam in a crucible with a size of 50 x 120 mm, from one to 10-15 samples were formed in the form of plates or a spherical shape, depending on the degree of compaction. On the other hand, in the case of ceramics obtained by repeated radiation synthesis from crushed ceramics obtained by the same method, the proportion of the YAG phase is 100%. Moreover, with an increase in the degree of compaction of the charge before synthesis, the volume of gas inclusions in the resulting samples decreases. And finally, it was found that the radiation synthesis efficiency does not depend on the scanning speed in the range of 1 - 2.5 cm / s at the same absorbed fluence. Subsequent performed measurements showed that the obtained ceramics have luminescence characteristics similar to those of known commercial YAG phosphors, as well as ceramics obtained by solid-phase methods. The luminescent properties of the samples obtained during one cycle synthesis do not depend on their position in the crucible.

Authors : Korostil A.M., Krupa M.M.
Affiliations : Korostil A.M., Krupa M.M., Institute of Magnetism of NANU and MESU, Kyiv, Ukraine

Resume : The spintronics effect consisting in the electrical control and detection of the magnetic order parameter through current-driven spin torque and the magnetoresistance effect in multilayer magnetic nanostructures has enabled the development of promising spin-based devices for magnetic memory and logic applications. In the ferromagnetic case, one manifests, in particular, via the well-known [1] giant magnetoresistance effect, that is applied for new kinds of field-sensing and magnetic memory devices. The spatial and time scales of the spintronics effect are determined by the conditions of the spin coherence, the robustness of magnetic states with respect to magnetic field perturbations and the exchange interaction between local magnetic moments, respectively. The spin current-induced magnetic dynamics and switching occur via the spin torque exerting on the local magnetic moments at a critical current density sufficient to overcome the magnetic coercive energy. Due to the intrinsic magnetic structure, the mentioned conditions are most consistent with the multilayer antiferromagnetic (AF) nanostructures, which are characterized by the compensation of magnetic moments with the absence of demagnetization field and the significantly reduced magnitude (with respect to ferromagnetic case) of the critical current density. The torque effect in AF nanostructures, in general, is related to the exchange interaction between the polarized spin density of a reference layer and the staggered local magnetic moments of a spaced adjacent antiferromagnetic layer. The polarized spin density can be caused by both spin polarization of electrons during the current passage and the effective field of a spin-orbit interaction near the interface. In the clean limit, the spin torque effect in AF nanostructures significantly exceeds one in the ferromagnetic case. Impurities leads to violation of the spin torque formation and increasing the spintronics effect, that is most exhibited in AF nanostructures based on spin valves. The microscopic description in the square tight-binding model has shown that the tunnel AF nanostructure are most robustness with respect to influence of impurities [1]. This work was supported by the European project H2020-MSCA-RISE-2017-778308-SPINMULTIFILM". 1. A. Manchon, Condens Matter, 29, 104002 (2017).

Authors : Min-Sang Lee(1), Sung-Hwan Jang(2), Jeong-Mi Lee(3), Kwang-Yeal Lee(4), Dae-Hee Won(5), Young-Ki Lee(6), Yeon-Tae Yu(3)
Affiliations : (1) PLT, 15, Yongji-ro, Gimje-si, 54352, Korea (2) ManuEnC, 30-3, Bonghwanggongdan 2-gil, Gimje-si, 54363, Korea (3) Chonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju-si, 54896, Korea (4) Sewon HF, 257-29, Wanjusandan 2-ro, Bongdong-eup, Wanju-gun, 55318, Korea (5) Wonkwang University, 460, Iksan-daero, Iksan-si, 54538, Korea (6) Uiduk University, 261, Donghae-daero, Gangdong-myeon, Gyeongju-si, 38004, Korea

Resume : In this work we synthesized InZnP alloy quantum dots(QDs). Indium phosphide quantum QDs have shown great potential in next generation display and lighting applications. However, early synthetic methods that involved rapid injection at high temperatures have not been able to reproducibly produce the required optical properties. For achieving high photoluminescence quantum yields (PL-QY), the InP or InZnP core should be covered by a thick shell of a large band gap, chemically stable semiconductor such as ZnS. The synthesis of InP/ZnS in one-pot method by adding a sulfur source during the core synthesis leads to an alloy structure capped with a thin ZnS shell. Due to the large lattice mismatch of 7.7% between zinc blende InP and ZnS it is difficult to obtain a thick shell. ZnSe has a lower mismatch of 3.3% and several works reported the growth of either ZnSe or ZnSexS1−x shells on InP or InZnP. Here we present a synthetic method for InZnP core quantum dots, which reduce the lattice mismatch between the core and shell, and dramatically decreased the FWHM to as low as 40nm with the PLQY up to 90%. Finally, the QDs were made into QD hybrid lighting and QLED. QD hybrid lighting were produced using 4CL PCB and sheets using green, red and deep red QD resin on blue LEDs, and its rendering index was Ra 94 or higher. QLED devide were produced using InZnP green and red QDs and CdSe blue QD, and the peaks of EQE and white efficiency were 2.1 % and 0.6 lm/W.

Authors : Greg Swadener
Affiliations : Mechanical, Biomedical & Design Engineering , Aston University

Resume : Strain layers in Si and Ge can be used to tune the electronic properties of epitaxial films, but because of the 4% lattice mismatch, misfit dislocations frequently occur. However, even with a high density of misfit dislocations and nominal strain relaxation, the strain distribution within thin layers is not uniform. The 3-dimensional strain field for Ge layers 1-2 nm thick sandwiched between Si layers has been calculated using molecular statics and established MEAM potentials. It is found that localised regions of high strain still occur in regions that are less than 10 nm in diameter. The high strain leads to electron traps in the Ge layer and hole traps in the Si layers within 0.5 nm of the interface. The strain field in a film with approximately evenly spaced misfit dislocations is found to provide a high areal density of carrier traps. Results for 2D films will be compared to 3D heterostructures.

Authors : Andris Antuzevics, Meldra Kemere, Anatoli I. Popov
Affiliations : Institute of Solid State Physics, University of Latvia, Latvia; Institute of Solid State Physics, University of Latvia, Latvia; Institute of Solid State Physics, University of Latvia, Latvia

Resume : It is fundamentally important to understand, control and predict the effect of radiation on structure and optical properties of functional materials. Al2O3 is an important technological material with a wide array of applications such as solid-state lasers, substrates for microelectronics and optical windows. Various types of defects such as F-type and V-type centers and interstitials are possible in Al2O3. Depending on the type of center and its creation history defect stability can be vastly different. In this work thermal stability of neutron irradiation induced defects has been investigated experimentally in transparent alumina ceramics. Results of a combined analysis of electron paramagnetic resonance (EPR) and photoluminescence spectroscopy will be provided.

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09:30 Coffee Break    
OXIDES : Eugene Kotomin
Authors : Maxim V. Ananyev
Affiliations : Ural Federal University

Resume : Lanthanum scandate based oxides are promising oxide materials for solid oxide electrochemical devices: protonic ceramic fuel cells (PCFC), electrolysis cells (PCEC) and gas sensors. Generally accepted theory for acceptor doped oxides says that for A(II)B(IV)O3 perovskite substitution of B-site by cation with an effective charge +3 leads to formation of vacancies in oxygen sublattice due to electroneutrality condition. This defect formation is considered as the main mechanism for oxides based on zirconates or cerates of alkali-earth metals. For A(III)B(III)O3 perovskites substitution of A-site by cation with an effective charge +2 causes formation of oxygen vacancies too. Formation of oxygen vacancies as a rule is attributed to a decrease of the local symmetry in close B-cation environment in perovskite structure, since appearance an oxygen vacancy is the reason of existing both 6-coordinated B-cation in the form of structural octahedron, and defected 5-coordinated B-cation. In case of LaScO3, however, we are challenged by the fact that Sc3+ must be 6-coordinated only. Sr-doped LaScO3 oxides possess perovskite-like structure ( Pnma) with two nonequivalent positions of oxygen. In strontium-doped lanthanum scandates, in order to satisfy the electroneutrality condition, the substitution of La3+ lanthanum on strontium Sr2+ should lead to a decrease in the oxygen content in the oxide lattice (which is usually associated with the formation of oxygen vacancies according to generally accepted theory) and be accompanied by a decrease in the local symmetry of the Sc3+ ion. It is known that the Sc3+ scandium ion in oxides can be in only one coordination environment equal to 6, which contradicts the formation of oxygen vacancies in its environment, since their appearance should lead to a change in the coordination number of scandium from 6 to 5. Constriction in coordination number 6 and increasing of the symmetry in lanthanum strontium scandates leads us to refuse an idea of oxygen vacancies formation in lanthanum scandate with lanthanum substitution by strontium, and consider a new mechanisms of defect formation, which excludes an existence of an oxygen vacancy in perovskite structure. In this study, we report the novel defect formation mechanism in strontium doped lanthanum scandate, when with strontium doping a release of oxygen due to electroneutrality condition leads to coupling of the structural octahedrons through a joint edge: 2ScO6 – O = Sc2O11. Since strontium doped lanthanum scandate proton-conducting oxides can incorporate hydrogen from H2O-, H2- and CH4-containing gas phase, a new type of defect formation plays an important and determining part in both protonic defects’ formation, protonic and oxygen ionic transport. We submit a description of H2O incorporation taking into account the novel defect formation mechanism including coupling/decoupling of structural octahedron due to H2O release/uptake process.

Authors : Andrei Chesnokov, Denis Gryaznov, Eugene. A. Kotomin, Juris Purans
Affiliations : Institute of Solid State Physics, University of Latvia, Kengaraga 8, Riga, LV-1063, Latvia; Institute of Solid State Physics, University of Latvia, Kengaraga 8, Riga, LV-1063, Latvia; Institute of Solid State Physics, University of Latvia, Kengaraga 8, Riga, LV-1063, Latvia, Max Planck Institute for Solid State Research, Heisenbergstr. 1, Stuttgart, D-70569, Germany; Institute of Solid State Physics, University of Latvia, Kengaraga 8, Riga, LV-1063, Latvia

Resume : We have applied hybrid density functional theory calculations to the analysis of thermoelectric properties of Ir-doped ZnO. The emphasis of this work is on calculating the Seebeck coefficient and electrical conductivity as functions of Fermi level in order to estimate potential of Ir-doped ZnO for p-type conductivity. In particular, the present study was encouraged by previous experimental results showing the Seebeck coefficient's sign change in response to increasing Ir concentration [1]. We describe several possible ZnO-embedded IrOx complexes with varying number of surrounding oxygen atoms and with different Ir oxidation states, including those involving formation of peroxide fragments. All modelled complexes, regardless of Ir oxidation state, demonstrate potential for p-type conduction for the Fermi level, μ[F] in the range 0 < μ[F] < 0.7 eV. Corresponding values of Seebeck coefficient (S) around 90 µV/K as well as the calculated phonon frequencies of peroxide moiety of 810–942 inverse centimeters are in very good agreement with experimental results. In light of this data, we discuss high sensitivity of calculated S(μ[F]) dependencies to the electronic structure. [1] M. Zubkin, R. Kalendarev, J. Gabrusenoks, A. Plaude, A. Zitolo, A. Anspoks, K. Pudzs, K. Vilnis, A. Azens, J. Purans, Thin Solid Films 636, 694 (2017).

Authors : Longfei Zhao1, Wing H. Ng1, Adnan Mehonic1, Alexander L. Shluger2, Anthony J. Kenyon1
Affiliations : 1 Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK 2 Department of Physics & Astronomy, University College London, Gower Street, London, WC1E 6BT, UK.

Resume : A novel delayed-electroforming process is discovered in defective silicon oxide based ReRAM devices. These devices have simple MIM structure and are CMOS compatible. While most conventional voltage sweep-triggered electroforming occurs at high voltage, this novel electroforming process happens at negligible voltage after pre-stressing with a constant voltage, and allows more energy-efficient switching. A typical delayed-electroforming process consists of three steps: firstly a highly resistive pristine device stressed for hundreds of seconds, then a detection voltage of 10mV is applied across the device to monitor resistance state. The device remains highly resistive (~M?) for minutes after the stress is removed, but abruptly reaches a low resistance state (~100?) under detection voltage. We investigated the effect of charge injection during stressing, and observed this process for devices of different oxide thickness, which indicates that this phenomenon is a common occurrence among various SiOx MIM devices. We also discuss possible causes for this delayed-electroforming.

Authors : Lord, A.M.*(1), Consonni, V. (2), Kepaptsoglou, D.M. (3).
Affiliations : (1) Centre for Nanohealth, University of Swansea, United Kingdom; (2) Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France; (3) SuperSTEM, SciTech Daresbury Science and Innovation Campus, Daresbury, United Kingdom.

Resume : Native point defects such as oxygen vacancies are known to be a culprit in creating low non-ideal Schottky barriers. This is complicated further in ZnO nanowires when defects concentrate near surface and electrical contact interfaces while interacting with adsorbates creating a range of donors and traps. Nanowires grown with Au nanocatalysts overcome complicated electrical contact fabrication to create intimate epitaxial interfaces with the single crystal ZnO resulting in rectifying electrical transport behavior that is dominated by quantum-mechanical tunneling at the contact edge.1 The dominance of the interface edge region results in a high sensitivity to the range of defects at the surface and near the Au interface.2 Here, we discuss comprehensive luminescence spectroscopy, electron microscopy and electrical transport measurements examining the influence of oxygen on the Schottky contacts and show with minor changes to the growth process that high-defect nanowires deviate from the edge-tunneling model producing a range of transport behavior from Ohmic to Schottky. Low-defect nanowires follow the edge-tunneling model and with further oxygen treatment the influence of surface defects is minimized such that high quality Schottky contacts with low leakage current are produced. Through a process of elimination examining the role of oxygen, ZnO polarity and Au structure we identify the major influences on electrical performance. (1) Lord, A. M. et al. Nano Lett. 2015, 15, 4248–4254. (2) Lord, A. M. et al. Nano Lett. 2017, 17, 6626–6636.

Authors : Thomas Schwab (a), Matthias Niedermaier (a), Paolo Dolcet (b), Gregor Zickler (a), Johannes Bernardi (c), Michel Bockstedte (d), Silvia Gross (b) and Oliver Diwald (a)
Affiliations : (a) Chemistry and Physics of Materials, University of Salzburg, 5020 Salzburg, Austria; (b) Chemical Sciences, University of Padova, 35131 Padova, Italy; (c) USTEM, Vienna University of Technology, 1040 Vienna, Austria; (d) Institute for Theoretical Physics, University Linz, 4040 Linz, Austria;

Resume : Stability and functional properties of nanocrystalline mixed metal oxides are sensitively dependent on defect chemistry and interfaces. Control over defect formation at the nanoscale in vapour phase grown non-equilibrium solids and defect evolution by annealing induced ion diffusion provides efficient means to achieve functional material properties, which significantly differ from their extended solid counterparts. Moreover, understanding the underlying transformation processes opens new pathways to ultimately achieve functional ceramics with tailored grain boundaries and intergranular regions. The present contribution discusses the transformation behaviour of diluted transition metals (Fe, Co) in MgO nanocrystals, which were synthesized by metallocene injection into the Mg combustion flame. Subsequent vacuum annealing of as-synthesized particle powders provides means to control impurity localization and to trigger phase separation in these non-equilibrium solids.[1] By combining structural characterization (XRD, TEM) with X-ray absorption and photoelectron spectroscopy investigations, we tracked valence state and local chemical environment changes of admixed transition metal ions inside the MgO based nanoparticles. Whereas Co-Mg-O nanoparticles exhibit a high thermal stability for Fe-Mg-O nanoparticles we obtained evidence for the formation of impurity-Mg vacancy complexes which ultimately undergo surface migration to enable magnesioferrite nucleation.[2,3] Differences in the behaviour between Co and Fe admixtures will be discussed and rationalized by means of ab initio calculations. [1] A. R. Gheisi et al., Part. Part. Syst. Char. 2017, 34, 1700109. [2] M. Niedermaier et al., J. Phys. Chem. C 2017, 121, 24292. [3] M. Niedermaier et al., J. Phys. Chem. C 2019, 42, 25991

Authors : A. Dauletbekova, A. Akylbekova, Z. Baimukhanov, Sh. Giniyatova, A. Kozlovskyi, F. Komarov, L. Vlasukova, A. I. Popov, A.T. Akilbekov
Affiliations : L. N. Gumilyov Eurasian National University, Nur-Sultan, Kazakhstan, Institute of Nuclear Physics, Nur-Sultan, Kazakhstan, Belarus State University, Minsk, Belarus, Institute of Solid State Physics, University of Latvia, Riga, Latvia,

Resume : In our work, a-SiO2/Si (p – and n- type) structures with an oxide layer were irradiated with 200 MeV Xe ions to a fluence of 108 ions/cm2 at DC-60 cyclotron (Nur-Sultan). Subsequent chemical etching of irradiated SiO2/Si samples was carried out in a 4% aqueous solution of HF with the addition of palladium (m(Pd)=0.025 g) at 18°± 1°C. After that, chemical deposition was carried out using two different solutions: chloride and sulfate. By varying the time and temperature of deposition we obtained nanocrystals of ZnSe2O5 and ZnSeO3. The performed X-ray diffraction analysis (D8 ADVANCE ECO X-ray diffractometer) unambiguously showed formation of ZnSe2O5 nanocrystals in a-SiO2/Si (p – and n- type) templates with an orthorhombic crystal structure and space group Pbcn (60) and ZnSeO3 with an orthorhombic crystal structure and space group Pnma (62).

Authors : A. Platonenko, D. Gryaznov, A. I. Popov, E. K. Kotomin
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga, LV-1063, Latvia

Resume : Corundum (sapphire, α-Al2O3) is an important radiation-resistant material with potential applications for components of diagnostic windows and breeder blankets. Radiation-induced changes in structural and optical properties of radiation-exposed α-Al2O3 crystalline materials are mainly associated with aluminum and oxygen vacancies. The vacancies in anion sublattice result in the formation of electronic defects after trapping one or two electrons (so called F and F+ -centers). The vast majority of the experiments on point defects in oxides were performed so far using the optical absorption and luminescence, while such rapidly developing techniques as Raman spectroscopy and neutron scattering methods were used only in very rare cases. Note that the optical absorption method does not work in the region of large defect concentrations due to the optical density saturation. Previously it was shown, that Raman scattering techniques proved to be very useful and promising for a better determination of the electronic structure of defects in alkali halides. Here we analyze by means of ab initio calculations the oxygen sublattice defect induced vibrational modes in corundum, as well anion vacancies in KBr. The aim of this study is to find possible “fingerprint” modes for identification of the anion defects, vacancies and interstitials, in various charge states. Using LCAO approach and hybrid B3LYP functional as implemented in the CRYSTAL17 computer code, the structural and vibrational properties are evaluated for each defect, suggesting possible defect-specific modes for vibrational spectroscopy. Obtained results are compared with available experimental data.

Authors : Ricca, C.*(1), Aschauer, U.(1)
Affiliations : (1)Department of Chemistry and Biochemistry and National Centre for Computational Design and Discovery of Novel Materials MARVEL, University of Bern, CH-3012 Bern, Switzerland

Resume : A complex interplay between magnetism, polarization, strain, and stoichiometry is responsible for the functional properties of transition metal oxides. Furthermore, in materials with a cooperative Jahn-Teller distortion, the orbital order can also couple to the defect chemistry and induce novel material properties, as we illustrate through the study of oxygen-deficient LaMnO3 (LMO). At low temperatures, LMO is an insulating A-type antiferromagnet due to the Jahn-Teller distortion that splits the eg orbitals of the high-spin Mn3 ions, resulting in a distorted orthorhombic perovskite structure with alternating long, short, and intermediate Mn-O bond lengths. Our DFT U calculations show that, as a result of these peculiarities, relaxations around an oxygen vacancy (VO) in LMO depend on which type of Mn-O bond is broken, affecting the d-orbital energies and leading to an asymmetric and hence polar localization of the excess electrons with respect to the defect. This behavior is different compared to other manganites, like SrMnO3 (where the two extra electrons reduce the Mn sites adjacent to the vacancy), and can be tuned through strain. Indeed, isostatic and epitaxial strain affect the Mn-O bond lengths and orbital order and can consequently influence the charge localization and polarity.

Authors : Christophe Avis, Youn Goo Kim, Mohammad Masum Billah, Jin Jang
Affiliations : Department of Information Display and Advanced Display Research Center, Kyung Hee University, Seoul, South Korea

Resume : Alongside indium gallium zinc oxide (IGZO), many oxides have been investigated for the past 16 years. Whether amorphous or polycrystalline, oxide semiconductors have demonstrated their potential use for large area electronics such as Active Matrix Organic Light Emitting Diodes (AMOLED) and other flexible and transparent electronics. Vacuum and non vacuum processes have been investigated for devices including diodes and thin film transistors (TFTs).Nevertheless, because IGZO use scarce and costly materials, and use many atoms, other more simple semiconductors may be viewed as a replacement. We propose tin oxide in its amorphous phase (a-SnOx). The devices combines abundant atom and simple solution process for TFTs reaching high mobilities. We can obtain the field effect mobility over 50cm2/Vs. a-SnOx demonstrate high performance, low subgap states, and high stability among common stressors making it a candidate for future large area electronics.

Authors : K.K.Abgaryan
Affiliations : Federal Research Center "Computer Science and Control" of the Russian Academy of Sciences

Resume : This paper presents a new multiscale computing technology for modeling metal oxide memristive structures with embedded defects used as the basic elements of a resistive memory cell. To study and simulate the patterns and parameters of memristive switching, a multiscale approach is used in which the first principle quantum-mechanical modeling of the atomic-crystalline structure of metal oxide memrist materials is carried out at the level of the atomic structure. It takes into account impurity and artificial structural defects (oxygen vacancies and others). As a result of the calculations, the electronic structure, the density of charge carriers (taking into account their spin polarization), energy zones are determined. Data are generated to identify the potentials of interatomic and ion-atom interactions, which are transferred to the next level to model the dynamics of changes in the structural elements of a resistive memory cell using three-dimensional statistical modeling. This work was supported by the Russian Foundation for Basic Research, project No. 19-29-03051 mk.

12:45 Lunch    
Authors : A. Kanaev (a), E. Feldbach (b), L. Museur (c), V. Krasnenko (b), A. Zerr (a), M. Kitaura (d)
Affiliations : a - Institute of Physics, University of Tartu, 1 W. Ostwald str., 50411, Tartu, Estonia b - Laboratoire de Physique des Lasers, CNRS, Université Sorbonne Paris Nord, 93430 Villetaneuse, France c - Laboratoire des Sciences des Procédés et des Matériaux, CNRS, Université Sorbonne Paris Nord, 93430 Villetaneuse, France d - Faculty of Science, Yamagata University, 1-4-12 Kojirakawa, Yamagata 990-8560, Japan

Resume : Structural modifications of polycrystalline g-Si3N4 spinel sample synthesised via high-pressure method were investigated after irradiation with He+ ions of 150 keV energy and total dose of 10^17 cm^-2. The analysis was based on previous assignment of the PL bands (L. Museur et al., Sci. Rep. 6 (2016) 18523), correlation of their spectral positions and theoretical calculations of the formation energies of cation and anion vacancies in the octahedral and tetrahedral voids. The results indicate strong changes of cathodoluminescence, photoluminescence (PL), PL excitation and Raman spectra. In particular, excitonic PL was significantly inhibited and a new near-IR band appeared with the excitation above the band gap energy of 5.05 eV. This was explained by an effective trapping of photoinduced electrons and holes by charged defects. The spectral shift of PL spectra with the excitation photon energy indicated a heterogeneous nature of the defect sites. The energetic positions of near-IR and visible PL bands correlate, suggesting an interaction with a common cation defect to be an origin. The visible PL of exciton bound to a neutral defect SiVx was red shifted, which was attributed to permutations between empty and occupied octahedral and tetrahedral sites inherent to the spinel structure after collisions with He+ ions. The positively charged cation sites in the spinel structure are compensated by VN''' anion vacancies. The local deformation of the spinel lattice affects PL intensity of the self-trapped exciton at 4.35 eV.

Authors : A.Dvurechenskii, A.Kacyuba, G.Kamaev, V.Volodin, A. Krupin.
Affiliations : A.Dvurechenskii; A.Kacyuba; G.Kamaev; V.Volodin. Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, 630090, Novosibirsk. A. Krupin. Novosibirsk State Technical University, 630073, Novosibirsk

Resume : The CaF2– Si(111) pair has a small lattice mismatch of about 0.6% at room temperature, and the fluorite-like structure of CaF2 is similar to the diamond-like structure of Si. These features allow growing the crystalline pseudomorphic insulator films of CaF2 on Si surfaces instead of SiO2 films which are always amorphous and have a number of intrinsic defects on SiO2 –Si interface. The experiments were made in ultra-high vacuum on the Katun-100 molecular-beam epitaxy (MBE) facility equipped with a CaF2 effusion source having a graphite crucible. In the experiments were made on Si(111) substrates. For all samples, before the growth, the standard procedure of substrates chemical preparation for MBE was used. The aim of experiments was to study the MBE growth of CaF2 films on Si(111) under electron-beam irradiation with the electron energy 20 keV and current density 50 μA/m2. The samples structure and elemental content were studied by reflection high-energy electron diffraction (RHEED) atomic force microscopy (AFM) and Raman spectroscopy. It was found that, during the CaF2 growth on Si, the area exposed to the electron beam undergoes strong modifications, such as in the surface morphology and film chemical composition. With reflection high-energy electron diffraction, atomic force microscopy and Raman spectroscopy, it is shown that the electron beam action leads to the CaSi2 layer synthesis at the interface of the silicon substrate and epitaxial growing CaF2 film. The radiation-induced epitaxial СаSi2 film growth on Si(111) takes place at substrate temperatures above 300 °C. The crystal structures of thin CaSi2 films were found to depend on the deposited СаF2 film thickness: it is the trigonal rhombohedral modification 3R for thin (<20nm) СаF2 films and the trigonal rhombohedral modification 6R for thicker films. This study was supported by the Russian Foundation for Basic Research and by the RosAtom Corporation (Project No. 20-21-00028).

Authors : D.V. Andreev1, G.G. Bondarenko2, V.V. Andreev1, A.A. Stolyarov1
Affiliations : 1) Bauman Moscow State Technical University, the Kaluga branch, 2, Bazhenov st., Kaluga, 248000, Russia; 2) National Research University Higher School of Economics, Myasnitskaya st. 20, Moscow, 101000, Russia

Resume : In the work, we have studied the influence of high-field field injection of electrons on the formation and subsequent evolution of the radiation-induced defects in thin nano-scale dielectric films of MIS devices. One of main effects caused by the irradiation of MIS devices, influencing on efficiency and determining reliability of these, is the changing of the dielectric charge state and the interface resulting in structural change of the materials. We demonstrate that under the concurrent influence by radiation and high-field injection of electrons the accumulation of positive charge in the bulk of the gate dielectric is defined by 1) generation of holes caused by the radiation and high-field ionization, 2) annihilation of a fraction of the trapped charge as a result of interaction with injected electrons, 3) redistribution of local electric fields in the dielectric bulk. We have studied the influence of high-field injection modes on changing of the charge state and defectiveness of MIS structure after the radiation influence. We show that after the radiation influence of MIS structures the high-field injection of electrons can result in erasing of a fraction of the positive charge trapped in the oxide because of its annihilation at interaction with injected electrons. However, the annihilation of positive charge commonly causes an increasing of surface state density. The study of the charge effects, taking place in thermal dioxide films of MIS structures under the concurrent influence of Fowler-Nordheim electron injection and ionizing radiation, is a subject of great interest not only from the perspective of utilization of MOS but besides from the perspective of utilization of radiation MOS sensors.

Authors : Tobias Vogel 1*, Thomas Kämpfe 2, Nicolas Guillaume 3, Anna Lisa Serra 3, Nico Kaiser 1, Gauthier Lefèvre 3, Maximilian Lederer 2, Ricardo Olivo 2, Tarek Ali 2, David Lehninger 2, Eszter Piros 1, Gabriele Navarro 3, Christelle Charpin-Nicolle 3, Stefan Petzold 1, Christina Trautmann 4, Lambert Alff 1
Affiliations : 1 - Advanced Thin Film Technology Division, Institute of Materials Science, TU Darmstadt, Alarich-Weiss-Str. 2, 64287 Darmstadt, Germany; 2 - Fraunhofer IPMS, Dresden, Germany; 3 - CEA LETI, Grenoble, France; 4 - GSI Helmholtzzentrum, Darmstadt, Germany & Institute of Materials Science, TU Darmstadt, Darmstadt, Germany.

Resume : Emerging memory classes such as oxide-based resistive, ferroelectric and phase-change random-access memory (OxRAM, FeRAM, PCRAM) are facing more and more interest in the field of memory technology and are discussed as possible successors of flash technology for highly-scaled memory cells. Thereby, radiation hardness [1] is of particular interest, enabling applications in harsh radiation environments, e.g. space. Additionally, there is a scientific interest in the failure mechanisms of the stored memory induced by ion exposure, to better understand the physical background for future improvements. The information storage mechanisms of resistive random-access memory devices are mainly based on the movement of ions, the crystalline structure and, in contrast to flash technology, not directly on charge. In ferroelectric and phase-change memories, where the information storage mechanisms are strongly connected to the crystalline structure (including a missing long-range order) of the active layer, a possibly induced phase change by ionizing irradiation has to be considered. In this study, we compare the effects of heavy ion irradiation on the properties of different emerging memory classes: Phase Change Memory based on germanium-antimony-telluride (GST), OxRAM and FeRAM [2] based on HfO𝑥. We demonstrate the crystallinity changes in these material systems exposed to heavy ion radiation and the relation to defects, as well as the correlation to the electrical properties of full memory devices. Our investigations lead to a better understanding of ion-induced failure mechanisms. This is especially related to oxygen-deficiency in HfOx, the limits of irradiated transistors compared to HfO𝑥-based memory cells and an ion-induced ferroelectric to antiferroelectric phase transition in HfO𝑥-based ferroelectric devices. [1] S. Petzold et al., Heavy Ion Radiation Effects on Hafnium Oxide-Based Resistive Random Access Memory, IEEE Trans. Nucl. Sci. 66, 1715 (2019). [2] T. Kämpfe, T. Vogel et al., Heavy Ion Irradiation Effects on Structural and Ferroelectric Properties of HfO2 Films, 2020 Joint Conference of the IEEE International Frequency Control Symposium and International Symposium on Applications of Ferroelectrics (IFCS-ISAF). IEEE, 1-3 (2020).

Authors : N. Klingner, K.-H. Heinig, D. Tucholski, W. Möller, R. Hübner, G. Hlawacek, S. Facsko
Affiliations : Helmholtz-Center Dresden-Rossendorf, Dresden, Germany

Resume : Broad ion irradiation of nanoobjects can considerably change their shape. Examples are ion-beam hammering [1], ion-induced shaping of buried particles [2], and ion-induced viscous flow of nanopillars [3]. Such shape changes are mainly driven by the kinetics of defects generated by binary collisions of ions and recoils. Here we report a new kind of ion-induced structure evolution. Sub-micrometer Sn spheres were irradiated with 30 keV He+ ions in a Helium Ion Microscope (HIM). Above a He+ fluence of 1017/cm², Sn extrusions appeared on the surface of the spheres and were imaged with the HIM. Initially, small, pyramid-like facetted extrusions form at the equator of the tin spheres (north pole pointing to the ion source). Later, each sphere becomes completely covered with tin and appears like a facetted single-crystalline cube. No Sn extrusions were observed for tin spheres with diameters smaller than 100 nm. Transmission electron microscopy and Auger electron spectroscopy studies show that the single crystalline tin spheres are covered with a few-nm-thick SnOx skin and that the extrusions grow epitaxially on the exposed tin surface. A model was developed which assumes that the He+ ions generate 70 Frenkel pairs per ion in the body-centered tetragonal lattice of tin. The implanted helium atoms, interstitials and vacancies are confined by the SnOx skin. Some He atoms will occupy vacancies which will partially inhibit their recombination with interstitials. This results in an increasing pressure of the “interstitial gas”. Furthermore, the He+ ion irradiation will cause erosion of the SnOx skin. The sputter coefficient increases with the angle of incidence, so that openings in the SnOx skin will form in the equator regions first. The interstitials can now escape from the interior of the Sn sphere and form an epitaxial regular Sn lattice on the outside. Computer simulations were performed based on this model. The Frenkel pair generation and the SnOx skin sputtering are simulated with dynamical programs based on the Binary Collision Approximation TRI3DYN [4]. Reaction-diffusion dynamics as well as nucleation and extended defect growth were simulated with a 3D kinetic lattice Monte Carlo program [5] using an RGL-potential for tin. The formation of cavities and their filling with He reproduces the experimentally observed tendency for cube formation. [1] Snoeks et al., Nucl. Instr. Meth B 178 (2001) 62 [2] Schmidt et al., Nucl. Instr. Meth. B 267 (2009) 1345 [3] Xu et al., Semicond. Sci. Technol. 35 (2020) 15021 [4] Möller, Nucl. Instr. Meth. B 322 (2014) 23 [5] Strobel et al., Phys. Rev. B 64 (2001) 245422

Authors : A. Burko, K. Girel, N. Khinevich, S. Zavatski, H. Bandarenka
Affiliations : Applied Plasmonics Laboratory, Belarusian State University of Informatics and Radioelectronics

Resume : Metallic nanostructures grown on porous silicon (PSi) have attracted great attention due to their prominent plasmonic properties, high stability, and cost-effective fabrication compatible with basic steps of Si technology. These nanomaterials open disruptive perspectives for photovoltaics and biosensing. The last one is mostly realized through surface-enhanced Raman scattering (SERS). Si chips covered with metalized PSi have been widely used as SERS-active substrates, which allow detecting substances at low concentrations down to the single-molecule level. Outrageous performances of such SERS-active nanomaterials have been praised but the effect of defects in Si wafer on the morphology of PSi and further deposited metallic nanostructures have not been considered. These defects lead to poor reproducibility of SERS-signal across the substrate’s surface limiting the reliability of SERS-analysis. Here we present a study of repeatability of morphology, optical properties, and SERS-activity of metallic nanostructures on PSi depending on defects in parent Si induced by irregular dopant level. The defects resulted in the formation of spiral areas in the PSi layer with a porosity deviation up to 30%. This strongly affected SERS-activity of upper metallic nanostructures. This was shown a lower porosity promotes detecting small molecules while a higher porosity is more favorable to find macromolecules. Explanation and discussion of the nature of this phenomenon were given considering simulation of electric field strength distribution and measurement of light absorption in SERS-active substrates. An original approach to avoid non-uniformity in properties of SERS-active substrates based on PSi was developed.

16:00 Coffee Break    
Authors : Vladimir Pankratov
Affiliations : Institute of Solid State Physics, University of Latvia, Kengaraga iela 8, LV-1063 Riga, Latvia

Resume : Luminescence nanoparticles and nanomaterials (nanophosphors) are relevant in all applications as bulk luminescence materials. However, nanophosphors have found their most notable applications as luminescent markers in molecular biology and medical diagnosis and therapy. These range from non‐invasive in vivo whole‐body diagnosis to in vitro examination of individual organs or cells. It is well known that luminescence properties of nanophosphors suffers from surface defects of nanoparticles. In the current talk unique surface‐dependent properties have been reviewed in popular nanophosphors (Y3Al5O12:Ce; LaPO4:Ce,Tb; YVO4:Eu; ZnWO4; CaF2:Pr,Mn; etc.). The experimental results have been obtained by means of luminescence and VUV excitation spectroscopy technique utilizing synchrotron radiation excitations. The advantages of the experimental methods elaborated in two European synchrotron facilities at DESY (Hamburg, Germany) and MAX IV (Lund, Sweden) will be discussed in details. It is also demonstrated that size-dependent luminescence properties of nanophosphors are significant if the electron thermalization length or the length of free electron pass becomes larger than the size of nanoparticles. Both surface and size-dependent properties play a crucial role in energy transfer processes in nanophosphors.

Authors : L. Bruno (1,2), G. Franzò (2), F. Priolo (1,2), S. Mirabella (1,2)
Affiliations : (1) Dipartimento di Fisica e Astronomia “Ettore Majorana”, Università di Catania, via S. Sofia 64, 95123 Catania, Italy; (2) CNR-IMM, via S. Sofia 64, 95123 Catania, Italy

Resume : The effect of Au nanoparticle (20 nm in size) decoration on the UV and visible luminescence of ZnO nanorods is studied. ZnO nanorods (100 nm wide, 700 nm long) were synthesized by chemical bath deposition while decoration with small Au nanoparticles (density of 10^10 nanoparticles/cm2) was achieved by immersing the sample in a colloidal solution of nanoparticles. Au decoration has been quantitatively investigated by Scanning Electron Microscopy and Rutherford Backscattering Spectrometry, while the emission properties of the bare and decorated samples have been studied by photo- and cathodo-luminescence. Au decoration of ZnO nanorods causes a significant depletion of free electrons below the surface, leading to a reduction of UV photoluminescence and an increase of visible-UV intensity ratio. The visible emissions are generally ascribed to the presence of surface states and deep levels in ZnO nanostructures. The visible defect components are characterized by blue, green, and orange states with energies at 2.52 eV, 2.23 eV, and 2.03 eV, respectively [1]. The formation of a nano-Schottky junction under the Au nanoparticles decorating ZnO nanorods has been investigated and modeled pointing out a relevant 2D bending of energy bands in the nanorods, leading to a strong electric field beneath the metal-semiconductor interface and parallel to the surface. These data are presented and discussed. [1] E. G. Barbagiovanni, R. Reitano, G. Franzò, V. Strano, A. Terrasi and S. Mirabella, Nanoscale, 2016, DOI:10.1039/c5nr05122c.

Authors : Ivan A. Aleksandrov (1), Konstantin S. Zhuravlev (1,2)
Affiliations : 1) Rzhanov Institute of Semiconductor Physics, Novosibirsk 630090, Russian Federation;. 2) Novosibirsk State University, Novosibirsk, 630090, Russian Federation

Resume : Point defects in crystals have attracted a great attention in recent years due to the possibility of using such centres as the basic elements for quantum computing and quantum telecommunications. AlN is an important material for optoelectronic devices operating in ultraviolet spectral range. The study of defects in AlN is of fundamental importance and is in demand in many fields of application of this material. Optical methods, such as photoluminescence and absorption spectroscopy are effective instruments for investigation of energy structure of defects. For identification of defect luminescence bands it is necessary to consider theoretically the local electron-phonon coupling determining luminescence line shape and its dependence on the temperature. In experiments, luminescence bands with donor-acceptor nature are often observed. Therefore, calculations of the luminescence line shapes of donor-acceptor transitions taking into account lattice relaxations for deep-level defects is necessary for the luminescence bands identification. In this work we have investigated theoretically the energy structure and electron coupling with local lattice vibrations for deep centres in AlN [1]. Using hybrid functional density functional theory, we have calculated local phonon energies, Huang-Rhys parameters, formation energies, charge state thermodynamic transition energies, and luminescence line shapes for different defects in AlN. The defects for luminescence line shape calculations were selected based on their formation energies considering intrinsic defects in AlN, defects and defect complexes containing most common unintentional impurities of carbon, oxygen and silicon. Luminescence line shapes of band to deep centre transitions in AlN have been calculated in dependence on temperature for most abundant defects in AlN. Donor-acceptor luminescence line shapes for shallow donor to deep acceptor and deep donor to deep acceptor transitions have been considered theoretically. Configuration diagrams of oxygen and silicon DX-centres have been calculated, and peak energies of optical transitions of an electron from the DX-centres to deep acceptors have been estimated. Possible assignments of the experimental luminescence bands in AlN based on the calculations have been discussed. [1] I.A. Aleksandrov, K.S. Zhuravlev, Journal of Physics: Condensed Matter, 32, 435501, (2020).

Authors : Ankit Goyal, Peter Schall, Katerina Newell
Affiliations : University of Amsterdam, Institute of Physics, Science Park 904, 1098XH, Amsterdam, The Netherlands

Resume : Lead halide perovskites are well-known for their attractive light emission properties with quantum yield approaching ~95%. Rare-earth ions have been used in the past to alter the photonic properties of semiconductor nanocrystals because their electronic transitions in near-infrared region and can lead to quantum yield beyond 100% due to multi-exciton generation. Doping perovskites with rare-earth ions like Yb3+ can therefore further boost their optical properties. However, the low doping concentrations of Yb3+ have so far restricted the increase in quantum yield. Mechanochemistry is a powerful tool to create defects and achieve higher dopant concentrations. Mechanochemistry also allows the production of such complex materials at a gram scale in a green way, without the use of toxic solvents that could be useful for practical purposes. In this study, we use a custom-built high-energy ball mill to synthesize Yb3+ doped CsPb(Cl0.5Br0.5)3 with higher Yb3+ loading. The effect of milling duration is studied on the incorporation of Yb in perovskite nanocrystals and photophysical properties. We find that by optimal milling, we can incorporate ~5 % Yb3+, giving rise to PL emission at ~980 nm. We will discuss material and photophysical properties obtained from experimental analysis of these materials, such as photoluminescence quantum yield, X-ray diffraction, electron microscopy, to uncover effects that are accessible at high doping levels.

Authors : J. Cardoso1, N. Ben Sedrine1, M. C. Sequeira2, P. Jozwik2, M. S. Relvas1, C. Wetzel4, C. Grygiel5, K. Lorenz2,3, T. Monteiro1, and M. R. Correia1
Affiliations : 1 Departamento de Física e i3N, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal 2 IPFN, Instituto Superior Técnico, Campus Tecnológico e Nuclear, Estrada Nacional 10, P-2695-066 Bobadela LRS, Portugal 3 Instituto de Engenharia de Sistemas de Computadores-Microsystems and Nanotechnology (INESC-MN), Rua Alves Redol, 1000-029 Lisboa, Portugal 4 Department of Materials Science and Engineering & Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180, United States of America 5 CIMAP, CEA-CNRS-ENSICAEN-UNICAEN Caen 5, France

Resume : Group III nitrides are wide-bandgap semiconductors mainly used in optoelectronics and high power electronics. Currently, blue InGaN/GaN light-emitters are well established with efficiencies up to ~80 %. However, efficiency is known to decrease with increasing emission wavelength due to polarization effects and Auger losses. The introduction of In compositional gradient in InGaN/GaN multi-quantum wells (MQWs) is expected to reduce these effects, and therefore improve the efficiency of these emitters. Swift-heavy ions (SHI) are high energy (tens of MeV) ions that lose their energy mainly by electronic excitation instead of elastic collisions when passing through the material. Thus, SHI irradiation is suggested to be a solution to achieve intermixing in MQWs with a reduced density of lattice defects typically generated by ion irradiation. In this work, the effects of SHI irradiation on the luminescence of III-N structures (layers and MQWs) grown on sapphire substrates are studied by optical transmission, µ Raman, photoluminescence (PL), PL excitation (PLE), and time-resolved PL (TRPL). In this study, the influence of different parameters is considered, namely the SHI energy loss and fluence.

Authors : D. M. Esteves [a], M. Peres [a,b,c], B. M. S. Teixeira [e], L. C. Alves [a], E. Alves [a,b], Zhitai Jia [d], Wenxiang Mu [d], N. A. Sobolev [e], M. R. Correia [e], T. Monteiro [e], N. Ben Sedrine [e], K. Lorenz [a,b,c]
Affiliations : [a] Instituto Superior Técnico (IST), Campus Tecnológico e Nuclear, Estrada Nacional 10, P-2695-066 Bobadela LRS, Portugal; [b] IPFN, IST, Portugal; [c] INESC-MN, Lisboa, Portugal; [d] State Key Laboratory of Crystal Materials, Shandong University, Jinan, 250100, China; [e] i3N, Physics Department, University of Aveiro, 3810-193 Portugal

Resume : b-Ga2O3 is an emerging wide bandgap semiconductor with promising applications in transparent conducting films for optoelectronic devices, solar-blind ultraviolet photodetectors, photocatalysts and gas sensors [1]. Its wide bandgap and high transparency make b-Ga2O3 is a good host material for optically active centres in the spectral region spanning from the infrared to the ultraviolet. In this context, besides the intrinsic ultraviolet/blue luminescence of undoped b-Ga2O3, Cr-doping has been shown to provide efficient light emission in the red/infrared spectral region. In this work, we present an ionoluminescence study performed with protons and alpha particles with energies from 600 keV to 2.2 MeV of Cr-doped Ga2O3 single crystals co-doped with Si-donors and/or with Mg-acceptors. In particular, along with the quenching of the ultraviolet/blue emission, we observe the enhancement of the Cr3 luminescence yield in Si-doped samples by more than one order of magnitude for a fluence of 1.5E15 protons/cm2 with 2 MeV energy. The observed luminescence by ionoluminescence and photoluminescence at room temperature is dominated by two sharp lines overlapped on a broad band associated, that can be assigned to the 2E -> 4A2 and 4T2 -> 4A2 Cr3 transitions, respectively. On the other hand, in Mg co-doped samples, the yield of the Cr3 emission is high already in the as-grown samples, and no further increase is observed upon irradiation. Additionally, by complementary electrical characterization we present a strong evidence that the pinning of the Fermi level, due to the formation of deep levels, should be the main process responsible for the observed increase of the Cr3 luminescence yield. An annealing study from 500 to 800 ºC of the samples co-doped with Si-donors was also carried out, showing that for temperatures higher than 550 ºC the influence of the irradiation defects on the luminescence properties are removed, and the Cr3 luminescence yields return to their initial values before irradiation. In short, this study contributes to a better understanding of the defect levels that can act as sensitizers for Cr3 luminescence in b-Ga2O3. Furthermore, these results reveal the potential of Cr doped b-Ga2O3 for radiation sensors such as radiation dosimeters, allowing the optical detection and measuring ionizing radiation both in- and ex-situ with high reproducibility and reusability potential. [1] Higashiwaki M and Jessen G H 2018 Guest Editorial: The dawn of gallium oxide microelectronics Appl. Phys. Lett. 112

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09:30 Coffee Break    
Authors : Janis Timoshenko, Beatriz Roldan Cuenya
Affiliations : Department of Interface Science, Fritz-Haber Institute of the Max-Planck Society, 14195 Berlin, Germany

Resume : The unique structural motifs of nanoparticles (NPs) enable many of their technologically important applications, e.g., in the field of heterogeneous catalysis. X-ray absorption spectroscopy (XAS) is one of a few experimental techniques that allow one to characterize such motifs, and to track their in-situ transformations in small (<3 nm) NPs. Unfortunately, the same reasons that are responsible for the NPs unique functionality (enhanced disorder, heterogeneous environments of metal atoms, low coordinated surface sites and interactions with support and ligands) make XAS data analysis for NPs much more challenging than for their bulk analogues. Here we demonstrate that this problem can be addressed by machine learning methods, which allow us to incorporate into the interpretation of experimental XAS data the insights from theoretical modeling of NPs structure and ab-intio XAS calculations.

Authors : A. Lappas (1,*), G. Antonaropoulos (1,2), M. Vasilakaki (3), K.N. Trohidou (3), V. Iannotti (4), G. Ausanio (4), I.K. Robinson (5,6) and E.S. Bozin (5)
Affiliations : (1) Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, Vassilika Vouton, 71110 Heraklion, Greece; (2) Department of Chemistry, University of Crete, Voutes, 71003 Heraklion, Greece; (3) Institute of Nanoscience and Nanotechnology, National Center for Scientific Research Demokritos, 15310 Athens, Greece; (4) CNR-SPIN and Department of Physics "E. Pancini", University of Naples Federico II, Piazzale V. Tecchio 80, 80125 Naples, Italy; (5) Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA; (6) London Centre for Nanotechnology, University College, London WC1E 6BT, UK.

Resume : The quest for nanoscale crystals that surpass the performance of a single magnetic core is motivated by the design-concept of controlling the spatial distribution of chemical composition within a single motif [1]. Here, we combine nanochemistry, detailed characterization and Monte Carlo simulations to explore the relation of size and shape on nanoscale surfaces and interfaces emerging in core-shell iron-oxide nanocrystals, while we also discuss those imperfections that assist magnetic properties relevant to nanobiotechnology [2]. Connecting compositional complexity and nanomagnetism allows us to gain insights on how controlled cation vacancy-induced disorder tailors physical properties, including exploitable thermal energy transfer for small-size magnetic nanocarriers. Synchrotron X-ray total scattering experiments corroborate our idea that size-dependent evolution of the metal-cation valence state, produces pinning defects which promote favorable magnetic exchange interactions at subcritical sizes (< 10 nm), and importantly beyond the limitations of finite-size effects alone. We offer a description of atomic interaction effects and knowledge of the different length-scale mechanisms required to facilitate the performance of single-crystal nanoscale particles as functional nanoheaters. [1] J.-H. Lee et al., Nat. Nanotechnol. 6, 418, (2011). [2] A. Lappas et al., Phys. Rev. X 9, 041044 (2019).

Authors : Jagodar, A.*(1), Kovacevic, E.(1), von Wahl, E.(1), , Strunskus, T.(2), Cvelbar, U.(3), Santhosh, Neelakandan M.(3), Ammar, M.R.(4), Boulmer-Leborgne, Ch.(1), Berndt, J.(1), Brault,P.(1)
Affiliations : (1) GREMI UMR 7344, CNRS&University of Orleans, France (2) Institute for Materials Science, Christian Albrechts Universitaet zu Kiel, Germany (3) Jozef Stefan Institute, Slovenia (4) CNRS, CEMHTI UPR3079, Univ. Orléans, France

Resume : The interest in the novel, often carbonaceous materials with large effective surfaces, high conductivity, stability, is growing due to the downsizing of electrical devices and the demand for low-cost new materials. These materials show great potential applications for electrochemical devices, transistors, and biosensors, or as even as analog materials in laboratory astrophysics. In this work, we present plasma synthesized carbon-based nanomaterials (CBNs) and their analysis. CBNs are produced by low temperature plasma procedures, and examples are given for different processes: for example volume and surface processes, catalyst-free or catalyst driven processes. All these processes result often in conductive nanostructures, like free-standing graphene, vertically aligned graphene nanosheets, thin films, or nanoparticles. These materials are either pure carbons, hydrocarbons, or nitrogen-containing carbons. Nitrogen introduction can be obtained either by growth in the nitrogen-containing atmosphere or plasma post-treatment. These processes finish often in both doped and functionalized materials. A popular technique to simulate plasma-surface interactions is molecular dynamics (MD). MD simulations can provide insight into fundamental mechanisms like the formation of different kinds of bonds. The interplay between doping and functionalization can be advantageous and can result in different functional groups of interest which can be useful e.g. for the synthesis of carbon-based parts of FET biosensors.

Authors : Yung-Chang Lin, Jeyakumar Karthikeyan, Yao-Pang Chang, Shisheng Li, Silvan Kretschmer, Hannu-Pekka Komsa, Po-Wen Chiu, Arkady V. Krasheninnikov, Kazu Suenaga
Affiliations : National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan; Department of Applied Physics, Aalto University, P.O. Box 11100, 00076 Aalto, Finland; Department of Basic Sciences and Humanities, Rajiv Gandhi Institute of Petroleum Technology, Jais, Amethi- 229304, Uttar Pradesh, India; Department of Electrical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan; International Center for Young Scientists (ICYS), National Institute for Materials Science (NIMS), Tsukuba 305-0044, Japan; Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany; Microelectronics Research Unit, University of Oulu, P.O. Box 8000, 90014 Oulu, Finland

Resume : In 2D materials with a high surface-to-volume ratio, such as transition metal dichalcogenides, various post-synthesis approaches to doping have been demonstrated, but doping beyond the solid solubility limit is difficult to achieve, especially in the metal sublattice. Moreover, control over the spatial distribution of dopants remains a challenge. Here, we present a post-growth two-step doping method, which includes annealing followed by deposition of dopants together with Se or S. The Ti, V, Cr, and Fe impurities at W sites are identified by using transmission electron microscopy and electron energy loss spectroscopy. We observe a high density (6.4–15%) of various types of impurity atoms, that are largely confined within nanostripes embedded in otherwise pristine WSe2. With the help of density functional theory calculations, we reveal a novel doping mechanism based on a dislocation climb mechanism in the presence of excess doping atoms. These special 1D heterostructures embedded in 2D planes are promising spatially controlled tailoring of the electronic structure and magnetic properties.

Authors : I. Jénnifer Gómez, Manuel Vázquez Sulleiro, Anna Dolečková, Naděžda Pizúrová, Jiřina Medalová, Rajarshi Roy, David Nečas, Lenka Zajíčková
Affiliations : Faculty of Science (FoS), Masaryk University, Brno, Czechia; IMDEA Nanociencia, Faraday 9, 280 49 Ciudad Universitaria de Cantoblanco Madrid, Spain; FoS, Masaryk University, Brno, Czechia; Institute of Physics of Materials, Žižkova 22, 616 62 Brno, Czechia; FoS, Masaryk University, Brno, Czechia; CEITEC - Central European Institute of Technology, Masaryk University, Brno, Czechia; CEITEC, Brno University of Technology; CEITEC, Brno University of Technology & FoS, Masaryk University, Brno, Czechia;

Resume : Carbon dots (CDs), usually defined as carbon nanoparticles with a diameter below 10 nm, are amazing class of fluorescent nanomaterials. This family of materials includes graphene quantum dots (GQDs), zero-dimensional graphene nanoparticles. GQDs with tunable near-infrared (NIR) fluorescence emission promise an excellent bioapplication potential, especially in bioimaging. However, the synthesis of GQDs exhibiting fluorescence emission in near-infrared (NIR) region, in which living systems do not present autofluorescence, is rare and they are synthesized from expensive and even poisonous chemical reagents, using time and energy-consuming approaches and complicated or inefficient purification techniques. Here, we report a facile and fast synthesis of nitrogen-doped GQDs (N-GQDs) emitting from near-ultraviolet to NIR. We reconstruct the different recombination pathways to explain this broadband emission focusing in particular on the NIR band using steady-state and time-resolved photoluminescence measurements. Furthermore, we proved excellent biocompatibility of synthesized N-GQDs by exposure to human vascular smooth muscle cells and demonstrated their potential for in vitro bioimaging applications by confocal fluorescence microscopy.

Authors : Arseny Kiryakov, Anatoly Zatsepin, Dmitry Zatsepin, July Shchapova, Nikolay Gavrilov
Affiliations : Ural Federal University, Yekaterinburg, Russia; Institute of geology and geochemistry UB RAS, Yekaterinburg, Russia; Institute of electrophysics UB RAS, Yekaterinburg, Russia

Resume : Pulse ion implantation of 30 keV MgAl2O4 optical ceramics by Cu2 ions was performed. A comprehensive analysis of the spectroscopic properties of ceramics before and after implantation (XRD, XPS, Raman, ESR, optical absorption, luminescence) was performed. Detected modification spinel matrix luminescent properties as a result of ion bombardment. Besides, it was found that, as a result of pulsed ion implantation, there is a complex relationship between the ion fluence and the concentration of intrinsically optically active centers, due to competing processes of radiation annealing and radiation formation of intrinsic F and F centers. As a result, pulsed copper ion implantation into the surface layer of the ceramic formed «core-shell» nanostructure copper exhibiting surface plasmon resonance. One of the possible channels for the relaxation of energy absorbed by the nanoparticle by the mechanism of localized surface plasmon resonance was observed. It was found that the thermal annealing of implanted ceramics leads to the activation of copper nanoparticles' growth. Heating at temperatures above 200 Celsius initiates the oxidation of copper nanoparticles, presumably by the Valenci-Carter mechanism.

Authors : Kurt Klauke [1], Bugra Kayaalp [1], Mattia Biesuz [2], Alessandro Iannaci [2], Siwon Lee [3], Massimiliano D'Arienzo [4], Vincenzo M. Sglavo [2], WooChul Jung [3], and Simone Mascotto[1]
Affiliations : [1] Institute of Inorganic and Applied Chemistry, University of Hamburg, Germany; [2] Department of Industrial Engineering, University of Trento, Italy; [3] Department of Materials Science and Engineering, Korean Advanced Institute of Science and Technology, Republic of Korea; [4] Department of Materials Science, University of Milan-Bicocca, Italy;

Resume : Confinement of charge carriers in nanoscopic systems has revealed to be an effective strategy to confer ceramic materials unconventional conductive properties by exploiting particle size effects and interfaces characteristics. Strontium titanate (SrTiO3) is a piezoelectric oxide that requires to be doped by acceptor redox species in order to acquire substantial chemical reactivity. In the present work, we show how chemically inert SrTiO3 and donor-doped SrTiO3 ceramics can be turned into active materials by improving the concentration and reactivity of the oxygen defect species using electric-field-assisted treatments [1,2]. The consolidation of hydrothermally prepared perovskite nanoparticles in presence of an electric field arrested the grain growth, retained the specific surface area and enhanced the concentration of Sr vacancies and O─ species. Moreover, the confinement of such ionic defects in mesoscopic particles contributed to a significant improvement of the charge carrier mobility. The effect of these electric-field-induced properties was tested with respect to the total catalytic oxidation of methane. Field-treated materials exhibited more than 95% of methane conversion at 800 °C, with performance over 3 times higher than for the conventionally treated material and other donor-doped perovskites. [1] K. Klauke, B. Kayaalp, M. Biesuz, A. Iannaci, V. M. Sglavo, M. D’Arienzo, S. Lee, S. Jongsu, W. Jung, S. Mascotto, ChemNanoMat 2019, 5, 948–956. [2] B. Kayaalp, K. Klauke, M. Biesuz, A. Iannaci, V. M. Sglavo, M. D’Arienzo, H. Noei, S. Lee, W. Jung, S. Mascotto, J. Phys. Chem. C 2019, 123, 16883–16892.

Authors : Utkarsh Ahuja (, Bo Wang ( and Katerina E. Aifantis (, Pu Hu (
Affiliations : (1) Mechanical and Aerospace Engineering, University of Florida, USA (2) Wuhan Institute of Technology, P.R. China

Resume : Numerous experiments suggest that the capacity decay of Si porous electrodes is related to the significant fracture experienced during the lithiation/de-lithiation process. In this work modeling and surface engineering of nanosized Si is employed to synthesize nanocomposites with enhanced stability. Initially, a multiphysics model is applied to predict the size of Si particles that limit damage formation. The model is experimentally verified against scanning electron microscopy (SEM), which shows for the first-time fracture of Si microparticles after the first cycle. Particles less than 100 nm are predicted to be mechanically stable, and to further increase stability, a facile one step in-situ polymerization process is used to synthesize Si/polydopamine (Si/DPA) nanocomposites, in which ~2 nm of polydopamine (DPA) uniformly coat the surface of the Si. The as-prepared electrodes exhibit higher capacity than previously reported Si/DPA composites: 2000 mAh g-1 at ~700 mA g-1 , with a 66% retention after 100 cycles. A 15% higher capacity retention is observed herein for the Si/DPA nanocomposite electrode compared with the pure Si electrode. The enhanced capacity retention of the nanocomposite electrode can be attributed to the engineered polymeric layer which buffers the expansion upon alloying and enhances adhesion within the nanocomposite electrode.

Authors : Katerina Dohnalova Newell(a), Prokop Hapala(b), Ivan Infante(c)
Affiliations : (a) University of Amsterdam, Science Park 904, 1098XH Amsterdam, The Netherlands; (b) Czech Academy of Sciences, Na Slovance 1999/2, 182 21 Prague 8, Czech Republic; (c) Department of Nanochemistry, Italian Institute of Technology, via Morego 30, 16163, Genova

Resume : Surface is for most semiconductor nanocrystals (NCs) considered a passive or undesired feature that needs to be protected from oxygen to prevent degradation. In semiconductor NCs with purely covalent chemistry, such as silicon, carbon or germanium based NCs, surface species dramatically alter the opto-electronic properties through a direct contribution to the density of states of the NC core. Hence, surface can be an additional powerful tunability tool that can tailor and even enhance the optical properties via (i) strain, (ii) charge transfer and (iii) orbital displacement. In this density functional theory (DFT) study, we test surface tunability of ~2nm silicon NCs (SiNCs), with almost 50 % of constituent atoms residing on the surface, directly covalently linked to a ligand. Silicon is one of the most important materials for industry - used in almost all technologies nowadays, from microelectronics to photovoltaics and light detectors. However, it is lacking efficient light emission due to its inherent indirect bandgap and there is still no Si light source available up to date. Enhancing optical capabilities of silicon is therefore of great interest and importance. We simulate SiNCs with various electronegative ligands (organic, halides) to analyze influence of such ligands onto the radiative rate and general density of states, visualized using the "fuzzy" band-structure approach [1]. We found [2] enhanced radiative rates, but with a lower magnitude than reported before from similar system via tight binding [3,4] and DFT [5]. [1] P. Hapala et al., Phys. Rev. B 87 (2013) 195420; [2] K. Dohnalova, P. Hapala, K. Kusova and I. Infante, Chem. Mater. 32 (2020) 6326; [3] A. N. Poddubny and K. Dohnalova, Phys. Rev B 90 (2014) 245439; [4] K. Dohnalova et al., Light: Science & Applications 2 (2013) e47; [5] K. Kusova et al., Adv. Mater. Interfaces 1 (2014) 1300042.

Authors : Sigitas Tamulevicius, Mindaugas Juodenas, Domantas Peckus, Tomas Tamulevicius
Affiliations : Institute of Materials Science, Kaunas University of Technology, Barsausko St.59, Kaunas 51423, Lithuania

Resume : When plasmonic nanostructures are arranged in periodic lattices, their scattered light can interact with adjacent nanoparticles via diffraction. Such 1-D, 2-D nanostructures including nanoparticles may be used as building blocks for sophisticated optical devices. There, we describe the method of self-assembly – capillary assisted particle assembly to produce high area and high assembly yield 2-D nanostructures of silver nanoparticles. We observed surface lattice resonances with a high Q factor, which demonstrated the quality of our assembly as well as prooved single-particle positioning accuracy. Our arrays are exposed to air, but that did not destroy the surface lattice resonance phenomenon, so this left space to introduce different materials to the system, e.g. fluorophores for lasing or functionalization of nanoparticles for biosensing applications. Furthermore, our method is not limited to Ag nanoparticles that we had used – self-assembly may be used to pattern a variety of different materials and nanoparticle shapes.

12:45 Lunch    
SEMICONDUCTORS : Sebastian Kruss
Authors : Alexei Bouravleuv
Affiliations : University associated with IA EAEC Institute for analytical instrumentation RAS St.Petersburg Electrotechnical University

Resume : Nanoscale ferromagnetic semiconductor (FS) structures are one of the most promising objects for the control over spin interactions by means of different methods, e.g. electrical or optical, and as a result for the creation of new spintronic devices, such spin-LEDs. Usually FS layers grow at relatively low temperatures to avoid phase separations, but nanostructures seem to be formed at higher temperature range. We have elaborated the novel techniques for the MBE growth of (In,Mn)As quantum dots [1-3] at relatively high growth temperatures. (In,Mn)As quantum dots have been grown by molecular beam epitaxy using Mn-atom selective doping. The detailed investigation of the structures obtained demonstrates, that despite relatively high growth temperature, the (In,Mn)As quantum dot structures have a high crystalline quality. Based on (In,Mn)As quantum dots used as active layers, p-i-n diodes were created, which optoelectronic properties were investigated using both optical and electric pumping. References [1] A. Bouravleuv et al., Semiconductors, 47 (2013) 1037-1040. [2] A. Bouravleuv et al., Appl. Phys. Lett., 105 (2014), 232101. [3] A. Bouravleuv et al., Nanotechnology, 27 (2016) 425706.

Authors : Tadas Paulauskas,1 Vaidas Pačebutas,1 Jan Devenson,1 Vytas Karpus,1 Mária Čaplovičová,2 Xiaoyan Li,3 Mathieu Kociak,3 Arūnas Krotkus1
Affiliations : 1 Center for Physical Sciences and Technology, Vilnius, Lithuania 2 STU Centre for Nanodiagnostics, Slovak University of Technology, Bratislava, Slovakia 3 Laboratorie de Physique des Solides, University of Paris-SUD, Orsay, France

Resume : The dilute bismide GaAs1-xBix alloy has experienced an extensive amount of research and represents the emerging class of bismuth-containing group III-V semiconductors. Incorporation of large Bi atoms into the lattice produces perturbations mainly to the valence band states, which leads to the bandgap bowing, as well as large spin-orbit band splitting. The interest in this alloy arises from its potential and already implemented applications in near- to mid-infrared range optoelectronics − lasers, photodetectors, solar cells. The distribution of alloyed atoms in semiconductors often deviates from the expected random distribution and can have significant effects on the properties of the materials. Previous studies of the spontaneous atomic ordering of bismides focused primarily on their atomic and microstructure analysis. The study presented here examines the influence of the CuPt-type ordering on GaAsBi optoelectronic properties, and is the first study that reports the optical anisotropy in GaAsBi alloys. Atomic and bulk-scale structural, chemical, as well as optical study of the dilute GaAsBi alloys was carried out. The optical anisotropy was revealed in samples grown on exact and offcut (001) GaAs substrates via polarized photoluminescence and transmittance spectra, as well as by birefringence and linear dichroism measurements. The observed polarization dependence in all the optical measurements agreed with theoretical predictions for the CuPt ordering. No optical anisotropy was observed in the bismide sample composed of anti-phase domains grown on (001) Ge, in which the anisotropy is not expected. Multiple sample surface and bulk characterization techniques, including SEM, AFM, XRD, and cross-sectional STEM, were employed to exclude other possible sources of structural anisotropies that may cause these optical effects. Atomic-scale HAADF and EDX analysis of Bi atom distribution and XRD suggests that the ubiquitous CuPt ordering is responsible for the optical anisotropy. Further work will be needed to clarify the magnitude of the ordering-induced valence-band splitting in GaAsBi alloys, and to better understand the reasons for such pronounced effects at dilute Bi concentrations. Polarization anisotropy is an important factor to consider for future development of GaAsBi-based lasers and photodetectors. These findings elucidate spontaneous ordering effects in GaAsBi and encourage its further investigations. References: 1. T. Paulauskas et al „GaAs1-xBix growth on Ge: anti-phase domains, ordering, and exciton localization“, Scientific Reports 10, 2002, (2020). 2. T. Paulauskas et al „Polarization dependent photoluminescence and optical anisotropy in CuPtB-ordered dilute GaAs1–xBix alloys“, Journal of Applied Physics 128 (19), (2020). 3. T. Paulauskas et al „Atomic-resolution EDX, HAADF, and EELS study of GaAs1-xBix alloys“, Nanoscale Research Letters 15 (121), (2020).

Authors : D. Verheij [1,2], M. Peres [2], S. Cardoso [1], L.C. Alves [3], E. Alves [2], C. Durand [4], J. Eymery [5], J. Fernandes [6], K. Lorenz [1,2]
Affiliations : [1] Instituto de Engenharia de Sistemas e Computadores - Microsistemas e Nanotecnologia, Rua Alves Redol 9, 1000-029, Lisboa, Portugal; [2] IPFN, Instituto Superior Técnico (IST), Campus Tecnológico e Nuclear, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal; [3] C2TN, Instituto Superior Técnico (IST), Campus Tecnológico e Nuclear, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal; [4] Université Grenoble Alpes, CEA, IRIG, PHELIGS, NPSC, 17 avenue des Martyrs, 38000 Grenoble, France; [5] Université Grenoble Alpes, CEA, IRIG, MEM, NRS, 17 avenue des Martyrs, 38000 Grenoble, France; [6] Instituto de Engenharia de Sistemas e Computadores – Investigação e Desenvolvimento, Rua Alves Redol 9, 1000-029, Lisboa, Portugal;

Resume : GaN is expected to have a high resistance to radiation damage and good stability in extreme environments due to the large displacement energies of the atoms in the crystal lattice and its dynamic annealing properties. For this reason, it is a very interesting material for applications in the field of semiconductor radiation detectors and electronics. In this work we use GaN core-shell p-n junction microwires as building blocks for radiation sensors. In comparison to their thin-film counterparts, the microwires do not only present a superior crystalline quality but may also provide a higher flexibility and compactness. Single wire devices are fabricated through optimized microfabrication steps and electrical characterization is performed under 2 MeV proton and UV radiation. At room temperature, the detectors show a leakage current as low as 1 pA in reverse bias which leads to high signal-to-noise current ratios. At the same time, transient I-V measurements reveal rise and decay times below 25 ms. Besides the electrical signal, the effect of the induced damage by the ionizing irradiation was studied by transient IBIC measurements and IBIC maps. We observed that the electrical signal remains stable even after irradiation with a total proton fluence of 1x10^16 protons/cm^2. On the other hand, irradiation with this fluence led to a small increase of the leakage current, reducing the signal-to-noise current ratio, coupled with a decrease of the forward bias current of the sample, indicating a rise in the resistivity of the device. Finally, we show that the sensor works both in reverse bias and in self-powered mode. Merging this characteristic with the aforementioned flexibility and compactness, this indicates that these devices may be a solution in radiation applications where size limits and low power consumption are key requisites.

Authors : M. A. Curado1,2, H. V. Alberto2, R. C. Vilão2, J. M. Gil2, J. M. V. Cunha1,3,7, T. S. Lopes1,4,5,6, J.P.Teixeira1, K.Oliveira1, P. A. Fernandes1,7,8, O. Donzel-Gargand1,9,M.Monteiro1, Ana G.Silva10 ,J. Leitão3,6, P. M. P. Salomé1,3
Affiliations : 1INL - International Iberian Nanotechnology Laboratory, Avenida Mestre José Veiga, 4715-330 Braga, Portugal 2 - CFisUC,Departamento de Física, Universidade de Coimbra, 3004-516 Coimbra, Portugal 3 - Departamento de Física, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal 4 - Institute for Material Research (IMO), Hasselt University (partner in Solliance), Agoralaangebouw H, Diepenbeek, 3590, Belgium4 5 - Imec division IMOMEC (partner in Solliance), Wetenschapspark 1, 3590 Diepenbeek, Belgium. 6- EnergyVille 2, Thor Park 8320, 3600 Genk, Belgium 7 - I3N, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal 8 - CIETI, Departamento de Física, Instituto Superior de Engenharia do Porto, Instituto Politécnico do Porto, Porto 4200-072, Portugal 9 - Solar Cell Technology, Department of Material Science and Engineering, Uppsala University, SE-751 21 Uppsala, Sweden. 10 - CeFiTec, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516, Caparica, Portugal

Resume : In this study we implement a passivation layer between Cu(In,Ga)Se2 and CdS to perform a fundamental study and to understand the impact of these layers on morphological, structural and optoelectronic properties of CIGS based solar cells. To evaluate the morphological impact of the Al2O3 on CIGS, Raman spectroscopy, X-ray diffraction (XRD), grazing incident X-ray diffraction (GI-XRD) and transmission electron microscopy (TEM) was performed. The structural analysis show that CIGS maintain the same morphological properties. GI-XRD confirmed the non-crystalline nature of Al2O3. The chemical composition is identified by X-ray Photoelectron Spectroscopy (XPS) and TEM-EDS maps. There are evidences of Cu diffusion to the CdS layer when an Al2O3 layer is not present. However, such effect is not visible with the Al2O3 on top of the CIGS, which indicates that the Al2O3 is working as a diffusion blocking layer. TRPL and PL analysis show a very complex behaviour of the recombination channels and are not in agreement, demonstrating that there are several changes when a dielectric layer is placed in between the CIGS and the CdS. Admittance measurements are used to identify equivalent AC circuits and to extract interface defect density (~10^11 cm-3). We also present Muon spin spectroscopy (µSR) results, which suggest that CIGS has a surface-defect region which is reduced when a CdS capping layer is added. However, the introduction of a thin (3nm) Al2O3 layer strongly reduces this effect.

15:45 Coffee Break    
POSTER SESSION 2 : Symposium Organizers
Authors : R. I. Eglitis, J. Purans, J. Gabrusenoks, A. I. Popov
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV1063

Resume : We analyze the systematic trends in the ABO3 perovskite bulk and (001) surface F-center calculations. For example, we recently performed ab initio calculations for the F-center in the BaTiO3 and SrZrO3 bulk and on the BaO and ZrO2-terminated (001) surface using a supercell model and a hybrid B3PW exchange-correlation functional [1-3]. We find that two Ti atoms nearest to the bulk F-center in BaTiO3 are repulsed, while nearest eight oxygen and four barium atoms relax towards the oxygen vacancy (by 1.06, 0.71 and 0.08% of the lattice constant a0, respectively). The magnitudes of atomic displacements around the F-center located on the BaO-terminated (001) surface in most cases are larger than those around the bulk F-center (0.1, 1.4 and 1.0% of a0). The bulk and BaO-terminated (001) surface F-center bands are located only 0.23 and 0.07 eV under the conduction band bottom, indicating that the F-center is a shallow donor. Our calculations demonstrate considerable increase of the chemical bond covalency between the BaTiO3 bulk F-center and its nearest Ti atoms equal to 0.320e, and even larger increase for BaO-terminated (001) surface F-center and its nearest Ti atom 0.480e, in comparison to relevant Ti-O chemical bond covalency in the perfect BaTiO3 bulk 0.100e. The difference between F-center formation energy in BaTiO3 bulk (10.3 eV) and on its BaO-terminated (001) surface (10.2 eV) trigger the segregation of the F-center from the bulk towards the BaO-terminated (001) surface. We also performed ab initio calculations for BaTiO3/SrTiO3 and PbZrO3/SrZrO3 (001) interfaces [4] as well as ReO3 polar (001) nano-surfaces. For BTO/STO and PZO/SZO heterostructures, we found that the number of interface layers do not influence much the electronic structure of studied structures, while termination of deposited BTO and PZO (001) thin film atop of STO and SZO substrates considerably shift the band edges with respect to the vacuum level and thus reduce the band gap. References: [1] R.I. Eglitis and S. Piskunov, Comput. Condens. Matter 7, 1-6 (2016) [2] M. Sokolov, R.I. Eglitis et al., Int. J. Mod. Phys. B 31, 1750251 (2017) [3] R.I. Eglitis and A.I. Popov, J. Nano-Electron. Phys. 11, 01001 (2019) [4] S. Piskunov and R.I. Eglitis, Solid State Ionics 274, 29-33 (2015)

Authors : Agata Fularz, Sawsan Almohammed, James H. Rice
Affiliations : Agata Fularz - School of Physics, University College Dublin, Belfield, Dublin 4, Ireland; Sawsan Almohammed - School of Physics, University College Dublin, Belfield, Dublin 4, Ireland, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland; James H. Rice - School of Physics, University College Dublin, Belfield, Dublin 4, Ireland

Resume : Surface enhanced Raman spectroscopy (SERS) is a sensitive and nondestructive technique used for the detection of biological and chemical molecules. Here we outline how semiconductor substrates can be used as platforms for SERS in place of or as a way to further enhance the performance of noble-metal nanomaterials. We demonstrate a universal approach of oxygen incorporation into metal oxide nanowire/metal nanoparticle templates that allows for greater SERS enhancement due to localized surface plasmon resonance excitation, point defect induced optical gap shrinking as well as wettability change of the substrate. We report up to five-fold Raman relative peak intensity enhancement after annealing-induced interstitial oxygen introduction. This approach is applied to defect formation in metal oxide semiconductor nanowires such as ZnO, WO3, TiO2, and NiO and is applicable for a wide variety of probe molecules, making the method suitable for medical, security and environmental applications.

Authors : Gusakov, V.E.*(1), Gusakova, J.V.(2), Tay, B.K.(3)
Affiliations : (1)Scientific-Practical Materials Research Center of NASB, Belarus (2)Novitas Center, Nanyang Technological University, Singapore (3) CINTRA UMI CNRS/NTU/THALES, Singapore

Resume : In many aspects, MoS2 can be considered as prototypical transition metal dichalcogenide (TMD) for which first principal studies are performed to study TMDs. It is well known that defects significantly alter the electronic properties of semiconductors, and thus affect their practical applications. We present a theoretical study of the formation, diffusion and electronic properties of intrinsic points defects (vacancy and interstitial atom) in monolayer and bulk MoS2. All calculations have been performed using a crystal supercell method (the supercell of 96 and 48 atoms was used for bulk and monolayer MoS2 respectively). Quantum Espresso implementation of the DFT was used for the computation of the structure and electronic properties. We used PAW pseudopotentials and PZ LDA and PBE GGA approximations of the exchange-correlation energy. We present the general approach to the calculation of the energy formation of intrinsic point defects in TMDs based on the calculation of the energy formation of Frenkel pair (vacancy interstitial atom) without using chemical potentials. We also, for the first time, present complete calculation of the diffusion coefficient (pre-exponential factor and activation barrier) of intrinsic defect and analyzed the influence of the defect charge states on the diffusion coefficient. So for monolayer MoS2 we have obtained the energy formation of Frenkel pair equal to 12.38 eV and 3.95 eV for Mo and S respectively.

Authors : Domantas Peckus (1), Erika Rajackaitė (1), Rimantas Gudaitis (1), Mindaugas Andrulevičius (1), Tomas Tamulevičius (1,2), Šarūnas Meškinis (1), Sigitas Tamulevičius (1,2)
Affiliations : (1) Institute of Materials Science, Kaunas University of Technology, K. Barsausko St. 59, LT-51423 Kaunas, Lithuania (2) Department of Physics, Kaunas University of Technology, Studentu St. 50, LT-51368 Kaunas, Lithuania

Resume : Graphene and its derivatives have attracted great scientific interest because of their chemical, physical and electrooptical properties. One of them, vertical graphene nanosheets (VGNs) look very promising for future sensor and other applications because of high surface area, unique morphology, optical, chemical, electrical and physical properties. Similarly, to planar graphene, the accurate defect control is crucial for their practical use. Despite intensive recent research performed on planar graphene defectiveness and its relation to the electrooptical properties, the defect analysis of VGNs is still quite modest. In our research, we have tried to contribute to these studies analysing various height VGNs on fused silica substrate produced by microwave plasma enhanced chemical vapour deposition technique. We have studied how the height of VGNs influences their structural, morphological and electrooptical properties and compared them with the features of high quality planar graphene's. The analysis was performed employing XPS, SEM, AFM, Raman scattering spectroscopy, absorption and fluorescence spectroscopy. Defectiveness influence of VGNs on the excited state relaxation dynamics of the film was measured by transient absorption spectroscopy. We demonstrate a clear correlation between the excited state of graphene relaxation dynamics and graphene defect density. We believe that such kind of relation might lead to the effective quality control method of VGNs.

Authors : R.A. Redko a,b, G.V. Milenin a, V.V. Shynkarenko a, V.B. Neymash c, V.Y. Povarchuk c, S.M. Redko a
Affiliations : a V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, 03680, Kyiv, Ukraine b State University of Telecommunications, 7, Solomenska str., 03680 Kyiv, Ukraine c Institute of Physics, NAS of Ukraine, Kyiv, 03028, Ukraine

Resume : The effect of 4 MeV electron irradiation on the photoluminescence (PL) properties of Si-doped GaN was investigated. MOCVD grown GaN thin films were irradiated at different doses 1·107, 2.5·107 and 1·108 rad (samples A, B and C, respectively). Photoluminescence (PL) measurements were carried out at room temperature in the 350–650 nm wavelength range using a Perkin-Elmer LS55 PL spectrometer, with an error below 0.5 nm. A source of excitation was light with wavelength λ=315 nm and emittance of 5 μW/cm2. It was obtained that PL spectra from irradiated samples have been changed during long-term period after treatment. The shift positions for near band gap photoluminescence peak as well as its intensity change were detected. After electron irradiation, the shape of PL spectra for samples A-C is almost same. Integral PL intensities of samples B and C have been decrease due to electron irradiation but not dramatically. For Sample A an increase of the integral PL intensity was observed. Small radiation dose (107 rad) results in the increase of integral intensity while larger doses (2.5·107 and 108 rad) results in its decreasing. One can think that that electron irradiation with larger doses results in non-radiative recombination channel magnification. While the treatment with dose of 107 rad, on the contrary, results in its decrease. The last fact is well-known as low doses effect. It is meaning that low doses of external influences result in improvement of useful characteristics (i.e. structural perfection, emission properties, homogeneity and so on).

Authors : V. Pankratov1, A.P. Kozlova2 and A.I. Popov1
Affiliations : 1 Institute of Solid State Physics University of Latvia, Kengaraga iela 8, LV-1063 Riga, Latvia; 2 National University of Science and Technology “MISiS”, Leninsky Prospekt 4, 119049 Moscow, Russia

Resume : Silicon carbide (SiC) is a wide band gap semiconductor suitable for high-voltage, high-power, and high-temperature devices from dc to microwavefrequencies. However, elementary processes of multiplication of electronic excitations under irradiation by synchrotron radiation have not been studied yet in these types of the materials. The aim of the present research is to report on the investigation of multiplication of electronic excitations processes and luminescence in cubic 3C-SiC crystals with theoretically well-studied electronic structure. Another goal of current study is comparative investigation of electronic structure of virgin and neutron irradiated 3C-SiC. The influence of the radiation-induced damage on the electronic structure has a particular interest. For these reason the luminescence and excitation spectra of as grown and neutron 3C-SiC as well as the appropriate reflection spectra were studied under ultraviolet (UV) and vacuum ultraviolet (VUV) synchrotron radiation. Two synchrotron facilities have been utilized for the examination of luminescence and reflection properties: SUPERLUMI station of DORIS III storage ring at DESY (Hamburg, Germany) and FINESTLUMI setup of FinEstBeAMS beamline of MAX IV synchrotron (Lund, Sweden). Results obtained demonstrate that there is clear difference between as grown and neutron-irradiated crystals. Luminescence mechanisms and the appropriate role of neutron-induced defects will be discussed in details.

Authors : V. Pankratova, J. Purans, V. Pankratov
Affiliations : Institute of Solid State Physics, University of Latvia, Kengaraga iela 8, LV-1063 Riga, Latvia

Resume : Scandium fluoride (ScF3) is a wide-band gap material (Eg≈10eV) belonging to perovskite-type compounds. ScF3 demonstrates strong negative thermal expansion (NTE), which is more pronounced than that of most known NTE materials. Taking into account that luminescence method is very sensitive to lattice structure and symmetry changes the study of intrinsic luminescence properties is extremely important for dipper understanding and analysis of NTE in ScF3. In this study luminescence properties of the single crystal as well as a polycrystalline ScF3 (99.99% Aldrich) have been investigated in wide spectral (1.5-40 eV) as well as temperature (10-300 K) range. Vacuum ultraviolet luminescence excitation spectroscopy technique has been applied. The experiments have been carried out at FINESTLUMI endstation using synchrotron radiation from 1.5 GeV storage ring of MAX IV synchrotron. Emission and excitation spectra as well as their temperature dependencies of ScF3 have been successfully obtained. The origin of luminescence centres will be elucidated and preliminary proposed. The behavior of thermal evolution of excitation spectra in the range of excitonic and/or band-to-band transitions will be discussed in respect of NTE in ScF3. The possibility of non-radiative relaxation of self-trapped exciton in ScF3 with creation of radiation defects will be discussed.

Authors : A. Lushchik (1), V.N. Kuzovkov (2), A.I. Popov (1,2), G. Prieditis (1), V. Seeman (1), E. Shablonin (1), E. Vasil’chenko (1,2), E.A. Kotomin (2)
Affiliations : (1) Institute of Physics, University of Tartu, W. Ostwald Str. 1, 50411 Tartu, Estonia; (2) Institute of Solid State Physics, University of Latvia, Kengaraga 8, Riga LV-1063, Latvia

Resume : Sapphire (a-Al2O3) is a technologically important material, in particular, widely used in optical applications such as radiation dosimeters, scintillators and being considered as a promising candidate for windows in fusion reactors. Its optical and mechanical properties are controlled by presence of radiation- (predominantly, neutron) induced defects. In this study, we analyze thermal stability and recombination kinetics of primary anion Frenkel defects - the F-type electronic centers and interstitial oxygen atoms in fast-neutron-irradiated a-Al2O3 single crystals. Theory was developed taking into account neutral and charged Frenkel defect pair formation, defect migration, Coulomb attraction and recombination. Based on ab initio calculations and new theoretical kinetics analysis, we have demonstrated for the first time а co-existence in comparable concentrations of two interstitial types – neutral O atoms and negatively charged O- ions (with attributed absorption energies of 6.5 eV and 5.6 eV, respectively) and have obtained their diffusion parameters, necessary for the prediction of secondary defect-induced reactions and defect stability.

Authors : N.V. Krainyukova (1), V.O. Hamalii (1), A.I. Popov (2), L.L. Rusevich (2), and E.A. Kotomin (2)
Affiliations : (1) B. Verkin Institute for Low Temperature Physics and Engineering of NAS of Ukraine, Kharkiv, (2) Institute of Solid State Physics, University of Latvia, Riga

Resume : The smooth (001) surfaces of SrTiO3 (STO) single crystals were investigated by the reflection high-energy electron diffraction (RHEED) method in the temperature range from 5 to 300 K. We have found five structural anomalies depending on temperature [1]. The anti-ferro-distortive phase transition from the cubic structure to tetragonal observed in the STO bulk at 105 K extends on the surface from 70 to 120 K. The found anomalies below 7 K and about 35 K are similar to those in the bulk considered as a crossover between the growth of the ferroelectric atomic displacements with decreasing temperature and quantum-mechanical stabilization of this growth due to the zero-point atomic motion. The other two anomalies are related only to a surface. Differentiation of lattice parameters depending on the depth from a surface revealed their changes, which showed a distinct effect of in-plane contraction on the (001) surface of STO confirmed by the theoretical analysis performed by the DFT method [1,2]. This effect is imposed by the surface symmetry and energetics differences as compared with the bulk. [1] N.V. Krainyukova, V.O. Hamalii, A.V. Peschanskii, А.І. Popov, and E.A. Kotomin, Low temperature structural transformations on the (001) surface of SrTiO3 single crystals, Fiz. Nizk. Temp./Low Temp. Phys. 46, 877-888 (740-750), (2020). [2] V.O. Hamalii, A.V. Peschanskii, А.І. Popov, and N.V. Krainyukova, Intrinsic nanostructures on the (001) surface of strontium titanate at low temperatures, Fiz. Nizk. Temp./Low Temp. Phys. 46, 1377-1385 (1170-1177), (2020)

Authors : Youya Wagatsuma 1, Md. M. Alam 1.2, Kazuya Okada 1, Michihiro Yamada 3, Kohei Hamaya 3, Kentarou Sawano 1
Affiliations : 1 Adv. Res. Lab., Tokyo City Univ.; 2 Univ. of Barishal; 3 CSRN, Osaka Univ.

Resume : Strained SiGe/Ge heterostructures with the (111) surface orientation are attracting attentions owing to their applicability to high mobility nMOS and spintronics devices [1], whereas crystal growth and defect structures of the SiGe/Ge(111) have not been explored sufficiently. Recently we systematically investigated critical thickness of the strained SiGe/Ge-on-Si(111) [2], and found that unusual line-shaped ridge roughness appears on the SiGe surface at the initial stage of strain relaxation. In this study, we clarify an origin of the ridge formation and drastically suppress it by patterning Ge-on-Si substrates as a new approach. In experiments, a Ge layer was grown on a Si(111) substrate with MBE, followed by line & space patterning via photolithography process. Subsequently, a strained SiGe layer was grown on the patterned Ge-on-Si. TEM observations revealed that cracks are generated in the ridge region for the sample without the patterning. By contrast, it was shown that the surface was free from such ridges for the sample with the patterning, which indicates the crack formation can be completely avoided by the patterning. Therefore it can be said that this method can increase critical thickness and highly widen the applicability of the strained SiGe(111) heterostructures to spintronics and high performance electronic devices. This work was partially supported by JSPS KAKENHI (Nos. 16H02333, 19H02175 and 19H05616). [1] K. Hamaya et al., J. Phys. D: Appl. Phys. 51, 393001 (2018). [2] Md. M. Alam et al., Appl. Phys. Express 12, 081005 (2019).

Authors : Yuwa Sugiura1, Youya Wagatsuma1, Koudai Yamada1, Yusuke Hoshi1, Michihiro Yamada2, Kohei Hamaya2, Kentarou Sawano1
Affiliations : Adv. Res. Lab., Tokyo City Univ.1, CSRN, Osaka Univ.2

Resume : In recent years, information and communication technologies and associated encryption technology has become more and more important, and the use of the circular polarized light for optical communications has been proposed. In particular, spin LEDs are expected as on-chip circular polarized light generating devices. As a material, we have been focusing on a Ge because it can be monolithically integrated on a Si substrate and can emit lights in telecommunication wavelength bands. Moreover, an employment of a surface orientation of (111) enables epitaxial over-growth of high-quality ferromagnetic materials on the Ge(111), and spin injection from the ferromagnetic materials into the Ge(111) has been realized [1]. Based on these spin-injection technologies, we are aiming to create a spin LED devices with a ferromagnetic electrode. So far, EL emission from Ge has been reported only for Ge with the surface orientation of (100), but EL emission from Ge-on-Si with the (111) orientation has not been explored. In this study, a Ge(111) p-i-n structure is grown on a Si(111) substrate, where both reduction of defects and high-density doping in the epitaxial Ge are issues of great importance to achieve efficient light emission. For the purposes, two-step growth method is employed to reduce such defects and low-temperature growth is partly used for n-type in-situ doping with high-precision. And then, a vertical diode with a mesa structure is fabricated to reduce defect-related leakage currents. As a result, we successfully obtain strong EL emission at room temperature. The sample was grown by using a solid source molecular beam epitaxy (MBE) system. First, an undoped Ge buffer layer of 40 nm was grown on a p-type Si (111) substrate at a temperature of 350℃. Subsequently, a B-doped Ge layer of 500 nm was grown at 700℃, and an undoped Ge layer of 40 nm and a P-doped Ge layer of 300 nm were grown at 300℃. After the growth of the p-i-n structure, a growth of an ultra-thin (UT) Si layer (2 monolayers), P delta doping (2×1014 cm-2) and 7 nm Ge capping were performed to obtain a low resistivity Ohmic contact [2]. An optical active area (125μm×75μm) was mesa-defined by the photo-lithography and following reactive ion etching (RIE) process. As top and back metal contacts, Au and AuGa were deposited, respectively, where the top metal contact area (90μm×40μm) was defined by lift-off process. From the fabricated Ge(111) p-i-n diode, we obtained strong EL emission at room temperature. A clear EL spectrum appeared with an injected current of 220 mA and the EL intensity drastically increased with the injected current increase. We can consider that the EL emission comes from the direct transition owing to the tensile strain induced in the Ge-on-Si. In the future, we can expect the realization of circularly polarized light generating Ge-spin LEDs by replacing metal electrodes with ferromagnetic material ones. This work was supported in part by Grant-in-Aid for Scientific Research (19H02175, 19H05616, 20K21009) from MEXT, Japan. [1] K. Hamaya et al., J. Phys. D: Appl. Phys. 51, 393001 (2018). [2] M. Yamada et al., Appl. Phys. Lett. 107. 132101 (2015).

Authors : G. Zvejnieks-1, L. L. Rusevich-1, E. A. Kotomin-1,2 , M. Maček Krzmanc-3
Affiliations : 1- Institute of Solid State Physics, University of Latvia, Riga, Latvia; 2- Max Planck Institute for Solid State Research, Stuttgart, Germany; 3-Jožef Stefan Institute, Ljubljana, Slovenia

Resume : Ferroelectric layered perovskites as Bi4Ti3O12 (BTO) are important technological materials due to their physical properties [1]. In particular BTO based structures are promising catalysts for photochemical reactions [2,3]. Therefore, development of physical models that explain the driving mechanisms behind this behavior could further facilitate the development of next generation materials. In this work, we use first principles linear combination of atomic orbitals (LCAO) approach with hybrid density functional theory (DFT) formalism as implemented in CRYSTAL17 code [4] to model BTO in different orthorhombic symmetries, including Fmmm and B2cb. We find that BTO initial geometry within orthorhombic Fmmm symmetry reduces to a tetragonal one, where both in-plane lattice constants coincide. This result qualitatively disagrees with a number or experimental studies that reported Fmmm phase of BTO [5,6]. First principle calculations demonstrate that in order to obtain orthorhombic BTO lattice geometry with different in-plane lattice constants the symmetry should be further reduced, e.g., to B2cb space group. [1] N.A. Benedek et al., Dalton Trans., 44, 10543 (2015). [2] J. Wu, et al., CrystEngComm, 20, 3084 (2018). [3] M. M. Kržmanc, et al., ACS Appl. Mater. Interfaces, 13, 370 (2021). [4] R. Dovesi, et al., CRYSTAL17 User’s Manual, University of Torino, Torino, 2017. [5] B. Aurivillius, Arkiv foer Kemi, 1, 499 (1949). [6] A. V. Knyazev, et al., J. Therm. Anal. Calorim., 122, 747 (2015).

Authors : N.A. Kalanda*, G. Suchaneck**, E.A. Artiukh*, G. Gerlach**
Affiliations : *Scientific-Practical Materials Research Centre of the NAS of Belarus 220072 Minsk Belarus, **TU Dresden Solid State Electronics Laboratory 01062 Dresden Germany

Resume : Recently, scientists are increasingly using the sol-gel technique, which allows a synthesis of the strontium ferromolybdate (SFMO) nanosized powder. The interest in this synthesis method is also due to the fact that with the help of the sol-gel technique, it becomes possible to develop new materials, including the SFMO-(superconductor, semiconductor, dielectric) nanocomposites for a creation of a new spintronic devices generation. However, despite a large number of publications, many issues related to the optimization of the sol-gel technique for the obtaining of nanosized single-phase powders of SFMO double perovskites with magnetic properties required for industry remain unclear, and the obtained experimental data are contradictory. Strontium nitrate, iron nitrate, ammonium molybdate, and high purity citric acid monohydrate in aqueous solution have been used as starting reagents for the synthesis of nanosized SFMO compound by the citrate-gel technique (a kind of the sol-gel technique). The synthesis of SFMO was carried out in several stages, and at the final stage it was annealed at T = 1120 K for 4 h in a continuous flow of a 5%H2/Ar gas mixture. As a result, the single-phase SFMO nanopowders with crystal lattice parameters a = b = 0.55629 nm, c = 0.78936 nm, and antisite defect concentration (occupation of Fe sites by Mo and vice versa) of 6%, and an average grain size of 69 nm were obtained. For a polydisperse powder with a log-normal grain size distribution, the temperature dependences of magnetization in both the field cooled and the zero field cooled mode indicate a two-phase magnetic state of the nanopowder SFMO with a mixture of superparamagnetic and ferrimagnetic particles. The presence of the two-phase magnetic state has also been confirmed by the Mössbauer spectroscopy. It was found that the temperature dependence of the nanopowder magnetization is well approximated by an equation consisting of constants, a Bloch-law spin wave ​term, a higher order spin wave correction, and a superparamagnetic term including the Langevin function. Volume fractions and magnetizations of ferrimagnetic and superparamagnetic particles in SFMO nanopowder were determined. Using the law of approach to the saturation magnetization consisting of an Akulov law term and a superparamagnetic term, the magnetic anisotropy constants of superparamagnetic and ferrimagnetic particles have been calculated based on the experimental data of the field dependences of the SFMO nanopowder magnetization. This work was supported by the European project H2020-MSCA-RISE-2017-778308-SPINMULTIFILM.

Authors : Nikolskaya, A.A., Korolev, D.S., Konakov, A.A., Mikhaylov, A.N., Belov, A.I., Marychev, M.O., Pavlov, D.A., Tetelbaum, D.I.
Affiliations : Lobachevsky University, Nizhny Novgorod 603950, Russia

Resume : Silicon optoelectronics is a rapidly developing field of research due to the demand in increased speed of signal transmission in integrated circuits. The main problem of creating such silicon-based circuits is the insufficient luminescence efficiency of cubic silicon (c-Si). To cope with this problem, hexagonal modifications of silicon can be used. In the present work, the possibility of synthesis of light-emitting inclusions of the hexagonal 9R phase (9R-Si) in c-Si substrates by ion irradiation of SiO2/Si system followed by high-temperature annealing has been demonstrated. It is assumed that the relaxation of mechanical stresses arisen upon ion implantation into SiO2 film (provided that the average projected range of ions is smaller than the film thickness) leads to the restructuring of atomic plane packing with the formation of 9R-Si modification during annealing. Such synthesized samples reveal the photoluminescence band at ~ 1235 nm, which corresponds in the photon energy to indirect interband transition in the 9R-Si band structure expected according to our calculation. The influence of 9R-Si synthesis conditions on the luminescent properties is studied and discussed. The work was supported by RFBR (Grant No. 20-32-90204) and Grant of the President of Russian Federation (MK-4092.2021.1.2).

Authors : Doroshkevich A.S.1,2, Oksengendler B.L.3,4, Lyubchyk A.I.5,6, Zakharova A.S.1,7, Tikhonova N.S1,7, Gridina E.A.1,7, Nikiforova N.N.3, Suleymanov S.X.4 , BALASOUI Maria1,8 , Stanculescu Anca9, CHICEA Dan10
Affiliations : 1Joint Institute for Nuclear Research, Dubna, Russia, е-mail:; 2Donetsk Institute for Physics and Engineering named after O.O. Galkin, Kiev,Ukraine, e-mail:; 3Ion-plasma and laser technologies Institute after U.Arifov,Uzbekistan, Tashkent, е-mail:; 4Materials Science Institute of SPA “Physics-Sun” Uzbekistan, Tashkent, е-mail:; 5Lusófona University, IDEGI, Campo Grande, 376 1749-024 Lisboa, Portugal,е-mail:; 6Nanotechcenter LLC, Krzhizhanovsky str., 3, Kyiv 03680, Ukraine; 7Dubna State University, Dubna, Russia, 19 Universitetskaya street, Dubna, Moscow region,141982 e-mail:; 8Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering (IFIN-HH), Bucharest Romania, e-mail:; 9National Institute for Materials Physics (NIMP) Strada Atomiștilor 405, Măgurele 077125, Romania; e-mail:; 10UNIVERSITY «LUCIAN BLAGA» of SIBIU (Str. Dr. Ion Ratiu 7-9, Sibiu, 550012, Romania) e-mail: *E-mail:

Resume : At present stage of scientific development, an extremely urgent task is to introduce the technology of effects of the nanoscale state of matter. A promising area of research is the effects of contact interaction of chemically homogeneous nanoparticles / nanoleers. The quantum mechanical transport effect of the appearance of negative differential resistance (NDR [1]) is known. A resonant tunneling diode (RTD) and a two - layer tunneling transistor (DELTT) are under development, in which the resonant quantum effects of electron penetration through the barrier perform the functions of voltage rectification and, even, signal amplification [2]. The structural elements of such devices have the size of quantum dots of 1-3 nm. However, as the experiment and theoretical calculations show, similar effects can also occur on larger objects. Monodisperse particles in the form of compacts (1grams) obtained using high hydrostatic pressure (P = 300MPa) were brought into contact with the side faces by a mechanical force of the order of 10N. The electrical properties of the resulting linear contact were studied at constant (U ϵ [- 6V- +6V]) and alternating current (excitation signal amplitude I = 150mV, operating frequency range ω ϵ [10 Hz - 2 MHz]) by voltammetry (Potentiostat P30, "ELINS") and impedance spectroscopy (Device Z – 1500, "ELINS") methods. To ensure electrical continuity, the surface of the compressed nanoparticles was hydrated with amospheric moisture for 4 hours (used air humidity range 50-90%). For the first time, the rectifying properties of the contact of hydrated nanoparticles of the same chemical composition (ZrO2 – 3mol%Y2O3) but of different sizes (7.5 nm, 10 and 14 nm) were experimentally established. The dependence of the degree of hydration and amount of dopants were studied. The possibility of obtaining of functional semiconductor heterostructures for electronics and energy of adsorption [3] based on linearly ordered hydrated multi-dimensional oxide nanoparticles of the same chemical composition was shown, An empirical physical model of the established effect was obtained. The study was performed in the scope of the Project H2020/MSCA/RISE/SSHARE number 871284 project and RO-JINR Projects № 268/2020 item 57, 59 and № 269/2020 item 62, 60. [1] [2] [3] A.S. Doroshkevich and al.// Applied Nanoscience. 9(8), 1603-1609 DOI 10.1007/s13204-019-00979-6.

Authors : L.L. Rusevich, D. Gryaznov, E.А. Kotomin, V. Krasnenko
Affiliations : Institute of Solid State Physics, University of Latvia, Riga, Latvia

Resume : Two-dimensional materials exhibit new electronic structure properties when the thickness becomes comparable to interatomic spacing. These electronic states are controlled by s and p electrons which are weakly interacting. On the other hand, transition metal oxides (TMO) have strongly interacting d electrons, with narrow bands where the Coulomb repulsion is poorly screened. This gives rise to the wide multiplicity of correlated states occurring in these materials showing almost any electronic ground state of condensed matter. TMO can be metals, insulators, superconductors, ferromagnets, multiferroics and display collective magnetic (spin density waves) and charge (charge density waves) excitations interacting strongly with electrons giving rise to exotic quasiparticle states. In this study, we report on large scale first-principles (ab initio) computer simulations of oxygen vacancies in ultrathin SrTiO3 (STO) and BaTiO3 (BTO) (001) perovskite films. The atomic and electronic properties of this films, as well as formation energy of vacancies were examined within the linear combination of atomic orbitals approximation, with using of the B1WC advanced hybrid exchange-correlation functional of the density-functional-theory (DFT), as implemented in CRYSTAL17 computer code. Various possible spin states of the defective systems were considered by means of unrestricted (open shell) DFT calculations. The systems were studied using a two-dimensional slab model with different number of layers (5–9) and the periodic supercell approach. The defects were considered both inside the films and on the (001) surface of the slabs with TiO2 termination. Dependence of vacancy formation energy on the thickness of slab and position of vacancy in a slab was investigated and compared with results obtained for the bulk STO and BTO. In order to estimate the dependence of defect formation energy on the defects concentration, the calculations were performed for supercells of two different size (2x2 and 3x3). These calculations will be used for prediction of the free-standing this film conductivity at different conditions.

Authors : Laura Basiricò1,2, Andrea Ciavatti1,2, Ilaria Fratelli1,2, Giorgio Pacioni1, Francesco Maccaferri1, Beatrice Fraboni1,2
Affiliations : 1Department of Physics and Astronomy, University of Bologna 2INFN-Bologna, Bologna, Italy

Resume : Trap-assisted photoconductive gain has been observed in organic/hybrid thin films since the early 90’s, providing a route for organic semiconductors to be employed as active layer in highly sensitive UV-vis photodetectors while preserving the advantages of organic materials. [1,2] More recently, we demonstrated direct X-rays photoconversion based on photoconductive gain in flexible organic thin film devices operated below 1V. [3,4] These devices are characterized by an unexpected high X-ray sensitivity that we justified by interpreting the detection mechanism as a photo-modulation of the semiconductor conductivity due to charge accumulation during X-ray exposure. We proposed that, during X-ray irradiation, additional free carriers are generated and accumulate in the organic thin film and to derive a model for such accumulation’s impact on photocurrent we considered the differences in hole and electron carrier transport in organic materials. In fact, the additional electrons and holes generated by the interaction with the X-ray follow a different fate: holes drift along the electric field until they reach the collecting electrode while electrons remain trapped. To guarantee charge neutrality, mobile holes that are collected at the collecting electrode are continuously re-injected from the injecting electrode, i.e. for each electron-hole pair created, more than one hole contributes to the photocurrent, leading ultimately to a photoconductive gain. Crucial for the amplification in this mechanism is the slow recombination dynamics of X-ray generated carriers, resulting here from the presence of deep trap levels which remove free electron carriers from the recombination process. In a very recent work [5] we investigated further the origin of the physical processes and parameters controlling the minority carrier traps that assist the photoconductive gain effect in X-ray detectors based on organic field effect transistors. We demonstrated that by reducing the grain size and increasing the number of grain boundaries, we can increase the density of electron trap states within the material, enhancing the photoconductive gain for the X-ray induced photocurrent. Further, by adding polystyrene to the semiconductor solution, we can reduce the interface hole trap density and consequently the charge carrier mobility is enhanced, as well as the device sensitivity. This study gives an insight on the understanding of the crucial parameters and physical processes that control the X-rays detection performance of organic polycrystalline thin-film semiconductors, fundamental steps to implement real-life applications of direct high-energy radiation detection based on organic thin films. [1] Hiramoto, M. et al., Appl. Phys. Lett. 64, 187–189 (1994). [2] Chen, HY et al., Nature Nanotech 3, 543–547 (2008). [3] L. Basiricò et al., Nat. Commun., vol. 7, 13063, (2016). [4] Ciavatti, A. et al. Appl. Phys. Lett. 111, 183301 (2017). [5] Temiño et al., Nat. Commun., vol. 11, 2136, (2020).

Authors : Arpita mukherjee
Affiliations : University of Gothenburg

Resume : Photonic devices stand to benefit from the development of chromophores with tunable, precisely controlled spontaneous emission lifetimes. Here we demonstrate a method to continuously tune the radiative emission lifetimes of a class of chromophores by varying the density of electronic states involved in the emission process. In particular, we examined the peculiar composition-dependent electronic structure of copper doped CdZnSe quantum dots. It is shown that the nature and density of electronic states involved with the emission process is a function of copper inclusion level, providing a very direct handle for controlling the spontaneous lifetimes. The spontaneous emission lifetimes are estimated by examining the ratios of emission lifetimes to absolute quantum yields and also measured directly by ultrafast luminescence upconversion experiments. We find excellent agreement between these classes of experiments. This scheme enables us to tune spontaneous emission lifetimes by three orders of magnitude, from ~ 15 ns to over ~ 7 s that is unprecedented in existing lumophores.

Authors : István Székely, Endre-Zsolt Kedves, Monica Baia, Zsolt Pap,
Affiliations : Faculty of Physics, Babeș–Bolyai University, M. Kogălniceanu 1, 400084 Cluj–Napoca, Romania, Centre of Nanostructured Materials and Bio-Nano Interfaces, Institute for Interdisciplinary Research on Bio-Nano-Sciences, Treboniu Laurian 42, 400271 Cluj-Napoca, Romania; Faculty of Physics, Babeș–Bolyai University, M. Kogălniceanu 1, 400084 Cluj–Napoca, Romania, Centre of Nanostructured Materials and Bio-Nano Interfaces, Institute for Interdisciplinary Research on Bio-Nano-Sciences, Treboniu Laurian 42, 400271 Cluj-Napoca, Romania; Faculty of Physics, Babeș–Bolyai University, M. Kogălniceanu 1, 400084 Cluj–Napoca, Romania, Centre of Nanostructured Materials and Bio-Nano Interfaces, Institute for Interdisciplinary Research on Bio-Nano-Sciences, Treboniu Laurian 42, 400271 Cluj-Napoca, Romania; Faculty of Physics, Babeș–Bolyai University, M. Kogălniceanu 1, 400084 Cluj–Napoca, Romania, Centre of Nanostructured Materials and Bio-Nano Interfaces, Institute for Interdisciplinary Research on Bio-Nano-Sciences, Treboniu Laurian 42, 400271 Cluj-Napoca, Romania, Department of Applied and Environmental Chemistry, University of Szeged, Rerrich Béla tér 1, Szeged, HU-6720, Hungary

Resume : During the synthesis of several semiconductors, the salts present play a crucial role in the crystallization process, while this issue is rarely considered in these studies. Therefore, it is crucial to enlighten the impact of different anionic and cationic species on semiconductor oxides' morpho-structural properties. In this paper, the impact of different halides, respectively their electronegativity (NaX, KX –salts, and HX – as acids) was investigated upon WO3 structure, surface, morphology, and photocatalytic activity (in composite systems with commercial TiO2). Three series of samples were investigated, which were obtained from sodium tungstate dihydrate applying sodium or potassium salts as shaping agents – WO3-NWH-NaX/WO3-NWH-KX, and from ammonium metatungstate hydrate and hydrohalic acids – WO3-AMT-HX. The halide anions' presence did not influence the crystal phase composition – Na and K halide salts led to a 100% hexagonal partial hydrate. However, hydrohalic acids' addition yielded both hexagonal partial hydrate (HPH) and monoclinic (MC) WO3 crystal phases. The presence of W+5 centers were evidenced by Raman spectroscopy and X-ray photoelectron spectroscopy. W+5 and W+6 species affected the band gap values of the NaX and KX series; a higher percentage of W+5, respectively W+6 caused a redshift, while regarding the HX series, it led to a blue shift. Increased electronegativity of the halide anions used during the synthesis has an unfavorable effect upon the composites' photoactivity, while in the case of hydrohalic acids, it had a positive effect. Two composite systems (WO3-AMT-HF+P25 and WO3-AMT-HCl+P25) yielded higher conversion rates (87.7 and 84.6%) than P25 (82.8%). Correlations were found between several Raman peaks ratio, electronegativity, and the composite systems' photocatalytic activity.

Authors : Saszet Kata 1*, Almási Enikő Eszter 2, Pap Zsolt 3, Hernádi Klára 4, Baia Lucian 1
Affiliations : 1. Faculty of Physics, Babeș-Bolyai University, Cluj-Napoca, Romania; 2. Department of Mineralogy and Geochemistry, University of Szeged, Szeged, Hungary; 3. Institute of Interdisciplinary Research in Bio-Nano Sciences, Babeș-Bolyai University, Cluj-Napoca, Romania; 4. Department of Applied and Environmental Chemistry, University of Szeged, Szeged, Hungary; *;

Resume : Oxide minerals are natural compounds found in Earth’s crust, some of them, such as cuprite (Cu2O) being often encountered and mined. Synthesized Cu2O nanoparticles are largely researched semiconductors with several application fields: pigment, fungicide, solar cell, catalyst, photocatalyst, gas sensor etc. In the present research the lesser-known cuprite is investigated, to chart the preparation process, the properties and possible applicability of copper (I) oxides mineral counterpart. Cuprite minerals were obtained from the mountain range of Rudabánya, Hungary. As part of the processing, the minerals were crushed with pestle and mortar, submitted to micro grinding in a planetary ball mill and finally were grinded into nanopowders in a wet-type bead mill, using different grinding times, resulting in different size ranges of nanoparticles. Additionally, commercial Cu2O and CuO were purchased (Acros Organics, Sigma-Aldrich), to which the properties of the cuprite minerals were compared. All materials were submitted to thorough investigation of the structural, morphological and optical properties, with the aid of XRD, XPS, Raman spectroscopy, SEM and DRS. Based on powder diffractograms, the raw microgrinded cuprite mineral is majorly composed of Cu2O, with cubic crystal structure typical for cuprite. With the increasing grinding time of the minerals, beside the Cu2O reflections also appear at least two additional reflections on their diffractogram – these belonging to CuO. This structural alteration is corroborated by photoelectron spectroscopic finds: due to high-energy bead milling, cupric ion species appeared on the surface of all nanogrinded cuprites. The success of the milling procedure is proven not only by the broadened Cu2O reflections on the X-ray diffractograms, but also by the SEM micrographs. Raman and diffuse reflectance spectroscopic measurements are in agreement with previous characterization outcomes. CuO having a narrower band gap and being generally more responsive to visible light, than Cu2O, the outcome of the mineral processing can be considered doubly useful: the material was not only reduced to a nanosize more suitable to application, but also its structure was altered to contain possibly more active species. The possible applicability of the μM materials was investigated by adsorption and photocatalytic tests under UV-A light (λmax=365 nm). The used model pollutants in both cases were aqueous solutions of methyl orange, salicylic acid and paracetamol. The preliminary results show various properties when it comes to application in the field of photocatalysis: adsorption phenomena and also possible photocatalytic activity can be observed. These properties are mainly influenced by the preparation process of the nanominerals and the induced defects in their structure eg. the mineral with the longest grinding time, smallest particle size and highest cupric ion content shows adsorption properties in each pollutant case. Acknowledgements. K. Saszet acknowledges the financial support of the Collegium Talentum scholarship provided by the Sapientia Hungariae Foundation.

Authors : D. Kenbayev (1), A. Dauletbekova(1), E. Polisadova (2), Sh. Giniyatova (2), A. Shalayev(3), A.I. Popov (4,5)
Affiliations : (1) L.N. Gumilyov Eurasian National University, Nur-Sultan, Kazakhstan (2) Tomsk Polytechnic University, Tomsk, Russia (3) Vinogradov Institute of Geochemistry SB RAS, Irkutsk, Russia (4) Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV-1063, Latvia (5) Institute of Physics, University of Tartu, W. Ostwald Str. 1, 50411 Tartu, Estonia

Resume : Layered halides of alkaline earth metals BaFBr, doped with Eu ions, are used in efficient storage image plate devices for different types of ionizing radiation. Based on the rather high radiation sensitivity of BaFBr, they are interesting for damage creation and energy-storage studies under swift heavy ion irradiation and further development of image plate detectors for ion beam detectors. In this work , we have studied optical absorption spectra of BaFBr single crystals irradiated by 147 MeV Kr ions up to fluences (1010 - 1 1013) ions/cm2 at room temperature. The absorption spectra were measured several times over a fairly long period of time. From the results obtained, it follows that the dependence of the concentration of F centers on the density of absorbed energy passes through a maximum. A decrease in the F (Br -) concentration with an increase in fluence is most likely associated with the aggregation process. Additional investigations of the luminescence of irradiated crystals showed that its intensity depends on the fluence.

Authors : Y. O. Suchikova (1), A. A. Konovalenko (2), I. S. Konovalenko (2), A.I. Popov (3)
Affiliations : (1) Berdyansk State Pedagogical University, Berdyansk, Ukraine (2) Benemérita Universidad Autónoma de Puebla,4 Sur 104 Centro Histórico C.P. 72000 Puebla, Mexico. (3) Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV-1063, Latvia

Resume : The continuing interest in porous semiconductors, in particular, in porous indium phosphide (InP), is associated with the simplicity of their preparation and the morphological diversity of structures. We have synthetized the porous wires having the ladders-like pattern on the n-InP (111) substrate with the use of electrochemical etching in a water-alcohol solution of hydrofluoric acid. The morphological characteristics of the fabricated microstructures were studied using scanning electron microscopy, while chemical analysis of surface was performed using of the lithium silicon energy dispersive detector (INCA Energy). It was found that the obtained wires have a porous structure. The periodicity of these structures is related to the segregation phenomena that arise during the growth of a InP monocrystal by the Czochralski method. The irregularity of etching of the indium and phosphorus sublattices is connected with the chosen crystallographic orientation of the substrate. The formation of a nanoporous oxide over the surface allows us to consider the obtained structures as ferroelectrics.

Authors : Anna Lavie1, Sergey Khodorov1, Tal-El Hajbi1, Ellen Wachtel1, David Ehre1, Yishay Feldman2, and Igor Lubomirsky*1
Affiliations : 1Dept. Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel 2Dept. Chemical Research Support, Weizmann Institute of Science, Rehovot, Israel

Resume : The electrostrictive strain coefficient of RExCe1-xO2-x/2 (RE= Gd or Sm, x ≤ 0.2) undergoes Debye-type relaxation with characteristic relaxation time less than 1 sec. Anelastic behavior of thin films of these materials has been observed during the course of weeks/days, posing the question of the possibility of monitoring electric field- induced dimensional changes on an intermediate time scale ranging from minutes to hours. We were therefore motivated to develop a method for in situ monitoring of electric-field induced strain in ceramic pellets using a laboratory X-ray diffractometer (Rigaku Ultima III, 40 kV, 40 mA, div slit: 1 mm by 5mm). The diffractometer was run in parallel beam mode with a strip detector (Dectris). Diffraction patterns were accumulated every 180 s in “sliding average” mode. For Sm- and Gd- doped ceria, the (422) diffraction peak (2θ=88°) was monitored. A patch of electrolytically-deposited copper on the upper surface of the pellet served as an internal reference ((311)-peak at 2θ=90°). A custom-made BN ceramic sample holder prevented sample heating. The sensitivity of this arrangement to longitudinal strain is better than 20 ppm. Using this setup, we found that the Sm- and Gd- doped ceria ceramics tested expand under the influence of DC bias (approx. 20kV/cm) with a response time of 5-10 hrs . Field-induced changes persist for at least 24 hrs. The origin of this behavior will be discussed elsewhere.

Authors : Y. O. Suchikova (1), A. A. Konovalenko (2), I. S. Konovalenko (2), A.I. Popov (3)
Affiliations : (1) Berdyansk State Pedagogical University, Berdyansk, Ukraine (2) Benemérita Universidad Autónoma de Puebla,4 Sur 104 Centro Histórico C.P. 72000 Puebla, Mexico. (3) Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV-1063, Latvia

Resume : We report our recent study of the nonlocal dielectric response of a three-dimensional homogenized crystal composed of an InP semiconductor inclusion embedded in a silica glass matrix. The inclusion of InP have the planar ladder-like pattern. Since the conduc-tivity and the plasma frequency of InP depends on temperature, the band structure of a homogenized crystal will undergo significant changes upon cooling and heating. The dependence of the effective averaged plasma frequency on temperature along with the structural anisotropy of the crystal provides additional opportunities for controlling the propagation of electromagnetic modes. The nonlocal permittivity, as the function of frequency and wave vector, is calculat-ed with the use of homogenization theory [1, 2], which is based on the Fourier formal-ism and form-factor division approach. Using the nonlocal effective permittivity, the complex dispersion relation for photonic modes propagating in a periodic semiconduc-tor–dielectric array is described even beyond the long-wavelength limit. In addition, we study the temperature dependence of the nonlocal effective parameters for photonic crystals composed of InP ladders embedded into a silica glass host matrix. In the case of infinitely long ladders, the photonic crystal shows plasma-like behavior with a tempera-ture-dependent effective plasma frequency in the far infra-red range. For the case of isolated InP ladders, the photonic crystal demonstrates a typically dielectric behaviour in the lowest frequency band, whose width can also be tuned by changing the temperature. [1] Cerdán-Ramírez V, Zenteno-Mateo B, Sampedro M P, Palomino-Ovando M A, Flores-Desirena B and Pérez-Rodríguez F. Anisotropy effects in homogenized magnetodielectric photonic crystals. J. Appl. Phys. 106, 103520 (2009). [2] Konovalenko A and Pérez-Rodríguez F. Nonlocal response of tunable photonic metamaterials with semiconductor inclusions. J. Opt. Soc. Am. B 34 2031-40 (2017).

Authors : Marina Romanova1, Stanislav Cichon2, Yuri Dekhtyar1, Premysl Fitl3, Joris More-Chevalier2, Michal Novotny2, Lenka Volfová2
Affiliations : 1 Institute of Biomedical Engineering and Nanotechnologies, Riga Technical University, Riga, Latvia; 2 Institute of Physics of the Czech Academy of Sciences, Prague, The Czech Republic; 3 University of Chemistry and Technology, Prague, the Czech Republic

Resume : Black metals are metals with a sponge-like nanoporous surface. Their surface appears black because light enters the pores and does not exit back due to multiple reflections. Black metals can be used as heat-absorbing coatings in thermal detectors or pyroelectric devices. In this research, 500 nm and 1000 nm thick black aluminium (B-Al) films were deposited on 1 mm thick fused silica substrates using pulsed DC magnetron sputtering in a mixed atmosphere of argon and nitrogen of 94% and 6% respectively. The resulting B-Al films had a soft surface which was easily susceptible to scratching. It was found that aluminium nanowires grew from scratches and small abrasions on the film surface when the films were annealed in the vacuum of 10-3 Pa at a substrate temperature of 350 °C. Energy-dispersive X-ray analysis confirmed that the atomic percentage of aluminium was 70–80% both in the film and the nanowires, and the remaining elements were carbon, nitrogen, and oxygen. Longer nanowires grew in the case of a thicker film. Some nanowires had a spiral shape that suggested that their growth was driven by a screw-dislocation mechanism. Scanning electron microscopy did not reveal any visual changes in the shapes of mechanically intact pores after annealing of the B-Al films.

Authors : Marina Romanova1, Regina Burve2, Yuri Dekhtyar1, Vera Serga2, Aleksandr Vilken1
Affiliations : 1 Institute of Biomedical Engineering and Nanotechnologies, Riga Technical University, Riga, Latvia; 2 Institute of Inorganic Chemistry, Faculty of Materials Science and Applied Chemistry, Riga Technical University, Riga, Latvia

Resume : MgO is as an efficient emitter of exoelectrons. In this research, electron capture in Si/SiO2 substrate during thermally stimulated exoelectron emission (TSEE) measurements of MgO thin films was studied. Si/SiO2 is a substrate commonly used in microelectronics. The substrate consisted of an amorphous 1 µm thick SiO2 layer thermally grown on a Si wafer. Nanocrystalline MgO films were prepared on the substrate by the extraction-pyrolytic method. TSEE from the films was measured and strong TSEE peaks were observed at temperatures of 450 ºC and 525 ºC. Also, photoelectron emission (PE) from the films was measured before and immediately after TSEE measurements. PE was excited by UV photons of 4–6 eV energy and it was found that the registered photoelectrons were emitted both from the film and the substrate. PE spectra recorded after TSEE measurements had several distinct PE maxima that were associated not with MgO but with electrons trapped in the defect centres of the SiO2 layer. We attribute the origin of the defect centres to the SiO2 layer since the same PE maxima were observed in PE spectra of a bare Si/SiO2 substrate after its irradiation with weak electrons with energies up to 1.5 keV emitted by a hot cathode source. Presumably, the defect centres already existed in the as-fabricated SiO2 layer and they could capture exoelectrons emitted by MgO films. To check whether the substrate was charged during TSEE measurements of MgO films, the bare Si/SiO2 substrate was also subjected to TSEE measurements. PE spectra of the bare substrate recorded after its TSEE measurements did not demonstrate any PE maxima. Therefore, our findings suggest that the defect centers that already existed in the SiO2 layer were filled with electrons emitted from MgO film during its TSEE measurements.

Authors : N. Mironova – Ulmane*, A.I. Popov, G. Krieke, A. Antuzevics, V. Skvortsova, E. Elsts, A.Sarakovskis
Affiliations : N. Mironova – Ulmane Institute of Solid State Physics, University of Latvia, Kengaraga Street 8, LV-1063 Riga, Latvia; A.I. Popov Institute of Solid State Physics, University of Latvia, Kengaraga Street 8, LV-1063 Riga, Latvia; G. Krieke Institute of Solid State Physics, University of Latvia, Kengaraga Street 8, LV-1063 Riga, Latvia; A. Antuzevics Institute of Solid State Physics, University of Latvia, Kengaraga Street 8, LV-1063 Riga, Latvia; V. Skvortsova Institute of Solid State Physics, University of Latvia, Kengaraga Street 8, LV-1063 Riga, Latvia; E. Elsts Institute of Solid State Physics, University of Latvia, Kengaraga Street 8, LV-1063 Riga, Latvia; A.Sarakovskis Institute of Solid State Physics, University of Latvia, Kengaraga Street 8, LV-1063 Riga, Latvia;

Resume : Use of Cr3 ions in the study of the structure in the Mg-Al spinel N. Mironova – Ulmane*, A.I. Popov, G. Krieke, A. Antuzevics, V. Skvortsova, E. Elsts, A.Sarakovskis Institute of Solid State Physics, University of Latvia, Kengaraga Street 8, LV-1063 Riga, Latvia Due to it's a high radiation resistance to radiation damage, magnesium aluminum spinel MgAl2O4 was proposed as a very promising material for RF windows in a fusion reactor. In this work, we present original results on the EPR and optical spectroscopy Cr3 ions in natural and synthetic single crystals (grown by Verneuil method) magnesium aluminium spinel (MgAl2O4) at temperature 10 K. It has been known that cations Mg2 and Al3 in the MgAl2O4 spinels may be differently distributed between the lattice sites. In MgAl2O4 normal spinel unit cell Mg2 occupy 8 tetrahedral (Td) and Al3 16 octahedral (D3d) sites of the unit cell, respectively. The partial occupation of tetrahedral sites by Al3 ions and of octahedral sites by Mg2 is usually referred to as inversion spinel. The chromium ions in the crystal structure of the spinel always occupy octahedral positions. In this position local symmetry of its environment sites is the D3d point symmetry. The EPR and photoluminescence spectra of Cr3 ions are a good indicator of the inversion of the spinel MgAl2O4 lattice. The photoluminescence spectra of Cr3 ions of the natural crystal which we can see efficient red emission R-lines (684.7 and 684.5 nm) due to the 2Eg → 4A2g spin-forbidden transition of Cr3 ions located at the sites with D3d local symmetry. The photoluminescence spectrum of the synthetic single crystal of a stoichiometric spinel MgAl2O4 has lines broader than R - zero-phonon lines in the luminescence spectrum of natural spinel. Besides R- and N-lines which are due to zero-phonon transitions, in the photoluminescence spectra of Cr3 ions wide electronic structures at low temperatures are located at long-wavelength side zero-phonon lines. Dominant contribution in EPR spectra comes from the axial centre, which is formed by Cr3 substitution of Al3 sites in the spinel structure. The line width of the EPR spectra of Cr3 ions in the synthetic stoichiometric single crystals spinel MgAl2O4 is observed to depend on the angle between the direction of the magnetic field and the <111> axis, while for the natural spinel MgAl2O4 this dependence is not observed. The results of studying the effect of heat treatment and radiation on the structure of natural and synthetic stoichiometric MgAl2O4 are discussed.

Authors : A. Burko1, N. Khinevich1, S. Zavatski1, H. Bandarenka1,2, S. Dubkov3, D. Gromov3
Affiliations : 1 Applied Plasmonics Laboratory, Belarusian State University of Informatics and Radioelectronics, Minsk, Belarus 2 The Polytechnic School, Arizona State University, Mesa, AZ, USA 3 MIET National Research University of Electronic Technology, Moscow, Russia

Resume : Discovery and explanation of surface-enhanced Raman scattering (SERS) phenomena have passed a trail to confident detection of submolar amounts of chemical compounds, which is not possible by ordinary Raman scattering spectroscopy. A variety of SERS-active materials have been fabricated and characterized including colloidal solutions and solid substrates of nanoparticles of noble metals. The latter one is usually presented by an array of metallic nanostructures immobilized on a sculpted host material defining their ordered location. Unique features for SERS-spectroscopy are possessed by grainy metallic coatings on macroporous silicon template that pores have equivalent diameters and the depth varied in a range from 0.5 to 2 microns. The pore geometry provides a concentration of the electromagnetic field in its center due to internal bounces of the excitation light while percolating morphology of metallic film facilitates an additional enhancement between nanograins of metal. However, defects (e.g. uneven pore sizes’ distribution) typical for macroporous silicon, which is fabricated by electrochemical etching (anodization) of silicon wafers, strongly affect the reproducibility of the SERS-signal intensity. In this work, we studied such an effect with SERS-active substrates based on macroporous silicon coated with a layer of silver nanoparticles depending on structural parameters of pores (diameter, depth), the molecular weight of analyte, and regimes of the SERS-measurements (laser wavelength, power density, spot diameter). Structural irregularities of macroporous silicon were found to be critical for reproducibility of SERS-spectra from macromolecules (molecular weight is over 0.5 kDa) resulting in (i) signal deviation up to 25% and (ii) 14% of similar spectra pattern if the laser spot does not overlap or goes much beyond pore boundaries. In contrast, SERS-spectra of the chemical compounds with low molecular weight were not greatly affected by the imperfection of the macroporous template. The observed behavior of the SERS-active substrates was discussed in terms of electric field distribution of the pores under different conditions basing on simulation in COMSOL Multiphysics.

Authors : Tigran G. Akopdzhanyan1, Anna P. Kozlova2, Sergei Rupasov2, Kirill Chernenko3, Vladimir Pankratov3
Affiliations : 1 ISMAN, 8 Academician Osipyan str., Chernogolovka, Moscow Region, 142432, Russia; 2 NUST MISIS, Leninskiy prospekt 4, Moscow, 119049, Russia; 3 MAX IV Laboratory, Lund University, PO BOX 118, 221 00 Lund, Sweden 4 Institute of Solid State Physics, University of Latvia, 8 Kengaraga, LV-1063, Riga, Latvia

Resume : Aluminum oxynitride (AlON) ceramics reveal an excellent combination of thermomechanical and optical properties in UV, VIS, and IR spectral range. Thus, AlON can be a good alternative to tempered glass and sapphire single crystals and it is also prospective material for high-temperature applications in aerospace engineering and power industry. Lattice defects strongly affect the optical and thermomechanical properties of AlON ceramics and must therefore be understood. In current study we report luminescence properties of nominally pure and europium-doped AlON ceramics prepared by a self-propagating high-temperature synthesis method. Luminescence experiments were carried out under vacuum ultraviolet excitations of synchrotron beam at 1.5 GeV storage ring of MAX IV synchrotron facility (Lund, Sweden). Nominally pure AlON ceramics reveal two broad emission bands in UV spectral range which were attributed to oxygen centers in AlN and oxygen vacancies in Al2O3. The intensity of the last band is strongly dependent on the synthesis parameters. Both emissions are poorly exited in VUV spectral range demonstrating an effective trapping of charge carriers by non-radiative centers, presumably surface loss centers of the ceramics’ grains. The europium-doped AlON ceramics exhibit europium related emission band at about 410 nm. Examining excitation spectra of this emission the multiplication of electronic excitations processes have been successfully observed and analyzed.

Authors : Anna P. Kozlova1, Oleg A. Buzanov2, Vladimir Pankratov3
Affiliations : 1 NUST MISIS, Leninskiy prospekt 4, Moscow, 119049, Russia; 2 JSC Fomos-Materials, Moscow 107023, Russia; 3 Institute of Solid State Physics, University of Latvia, 8 Kengaraga, LV-1063, Riga, Latvia;

Resume : La3Ga5SiO14 (LGS, langasite), La3Ga5,5Ta0,5O14 (LGT, langatate) and Ca3TaGa3Si2O14 (CTGS, catangasite) single crystals belong to the class of functional synthetic materials found their application due to their superior laser, piezoelectric, and electro-optic (EO) properties. The luminescent properties of langasite, langatate and catangasite single crystals have been studied by means of the vacuum ultraviolet excitation spectroscopy utilizing synchrotron radiation from 1.5 GeV storage ring of MAX IV synchrotron facility. The results obtained for the catangasite single crystal are reported for the first time, while the results obtained for langasite and langatate single crystals have been used as references. The catangasite single crystal exhibits two emission bands at 320 nm (3.87 eV) and 445 nm (2.78 eV). Examining excitation spectra in vacuum ultraviolet spectral range, the 320 nm emission band was explained as the emission band of self-trapped exciton in CTGS single crystal. Its atomic structure is discussed. It is also proposed that the 445 nm (2.78 eV) emission in the CTGS is due to the F-centers, which have shown a well-resolved excitation (absorption) band at 5.1 eV (243 nm). The luminescence data for all three compounds are summarized and analyzed.

Authors : A.I. Popov, V.N. Kuzovkov, A. Platonenko, E. Elsts, A.Moskina, E.A. Kotomin
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV-1063, Latvia

Resume : We present here an overview of recent results obtained on the modeling and analysis of the thermal annealing of dose-dependent characteristics of radiation damage of several scintillation materials, such as PbWO4, ZnO, BaF2, CaF2, PbF2, Y3Al5O12, Gd3Ga5O12, CsI and KBr. Where possible and where there is sufficient experimental data, we will demonstrate whether the Meyer - Neldel rule for thermal annealing of radiation defects works or not, and we will show whether there is a connection between the migration-recombination properties of defects and the radiation type/fluence. This work has received the funding from Latvian Council of Science via Project LZP-2018/1-0214 “Radiation damage studies in scintillator materials for high-energy physics and medical applications”.

Authors : H. Klym (1), I. Karbovnyk (2), L. Calvez (3), A.I. Popov (4)
Affiliations : (1) Lviv Polytechnic National University, Lviv, Ukraine (2) Ivan Franko National University of Lviv, Lviv, Ukraine (3) Equipe Verres et et Céramiques, UMR-CNRS 6226, Institute des Sciences chimiques de Rennes, Université de Rennes 1, Rennes Cedex, France (4) Institute of Solid State Physics, University of Latvia, Riga, Latvia

Resume : Free-volume defects in the Ge-Ga-S/Se (80GeS2-20Ga2S3 with CsCl and 80GeSe2-20Ga2Se3 after crystallization and gamma-irradiation) glasses were studied using positron annihilation lifetime spectroscopy. It is shown that void fragmentation in (80GeS2-20Ga2S3)85(СsCl)15 glass can be associated with loosing of their inner structure. Full crystallization of these glasses corresponds to the formation of defect-related voids. These trends are confirmed by positron-positronium decomposition algorithm. It is established that changes in defect-related component in the fit of experimental positron lifetime spectra for nanocrystallized glasses testifies in a favor of structural fragmentation of larger free volume entities into smaller ones in 80GeSe2-20Ga2Se3 glass. After irradiation of 80GeS2-20Ga2S3 glasses nanovoids with different size are created as intrinsic structural defects associated with topologically uncoordinated negative-changed centers. These defect centers form additional energy levels both near the bottom of the conduction band and in the vicinity of the valence band, as well as additional intrinsic electric fields.

Authors : H. Klym (1), A.I. Popov (2)
Affiliations : (1) Lviv Polytechnic National University, Lviv, Ukraine (2) Institute of Solid State Physics, University of Latvia, Riga, Latvia

Resume : The positron annihilation lifetime (PAL) spectroscopy method based on the fact that the unstable positron-electron system (positronium Ps) is repelled from ionic cores of atoms and tends to location in open pores. In the case of spinel ceramics, two channels of PAL should be considered – the positron trapping and o-Ps decaying. However, if trapping sites will appear in a vicinity of grain boundaries neighbouring with free-volume pores and extended defects, they can become mutually interconnected resulting in a significant complication of the measured PAL spectra. This occurs provided the input of one of the above annihilation channels will be significantly changed. It is established that lifetimes of the defect components increase with sintering temperature of ceramics. These changes correspond to the increased defects near gnain boundaries of ceramics, nanopore size and smaller amount of nanopores. To apply positron-positronium trapping algorithm it was shown that the chemical-adsorbed water vapor modifies structural defects located at the grain boundaries in a vicinity of pores, this process being accompanied by void fragmentation during water adsorption and agglomeration during water desorption after drying. The physical adsorbed water not modified grain boundaries in oxide MgAl2O4 ceramics located only in nanopores.

Authors : H. Klym (1), I. Karbovnyk (2), A. Luchechko (2), Yu. Kostiv (1), A.I. Popov (3)
Affiliations : (1) Lviv Polytechnic National University, Lviv, Ukraine (2) Ivan Franko National University of Lviv, Lviv, Ukraine (3) Institute of Solid State Physics, University of Latvia, Riga, Latvia

Resume : The BaGa2O4 ceramics are materials for secondary electron emission coatings in plasma display panels, for proton ceramic fuel cells, etc. Doping of BaGa2O4 ceramics by rare-earth ions results in modification of their structural properties and results in formation of defects near grain boundaries. In this work we analyzed transformation of defect-related free volumes formed by addition phases near grain boundaries of ceramics. Samples of BaGa2O4 ceramics were obtained by solid-state reaction method from BaCO3 and Ga2O3 components with purity of 99.99%. Powders with 0, 1, 3 and 4 mol.% of Eu2O3 (99.99%) were mixed in an agate mortar for 6 h with further pressing in a steel mold. Prepared pellets were annealed at 1200 ºC for 12 h in air. After that, the annealing of ceramic samples was carried out at 1300 ºC for 4h. It is shown that un-doped BaGa2O4 ceramics contain three phase, samples with 3 and 4 mol.% of Eu2O3 are two-phases (BaGa2O4 and Eu3GaO6 phases), while BaGa2O4 ceramics with 1 mol.% of Eu2O3 contain only one (Ba,Eu)Ga2O4 phase on own structural type. Defect-related free volume and nanopores were investigated by positron annihilation lifetime spectroscopy method using three- and four component fitting procedures. It is established that amount of free volumes correlates with addition phases near grain boundaries.

Authors : H. Klym (1), Yu. Kostiv (1), I. Karbovnyk (2), A.I. Popov (3)
Affiliations : (1) Lviv Polytechnic National University, Lviv, Ukraine (2) Ivan Franko National University of Lviv, Lviv, Ukraine (3) Institute of Solid State Physics, University of Latvia, Riga, Latvia

Resume : The Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics are known materials for negative temperature coefficient thermistors, in-rush current limiters, etc. Typically, structural properties of such materials re studied using different traditional method of structural characterizations. The quantity of the additional defect-related phase and its distribution in bulk and on the surface of ceramics are influenced by temperature-time sintering regimes. It is established that the amount of additional NiO phase in these ceramics extracted during sintering play a decisive role. The process of monolitization from the position of evolution of grain-pore structure was studied in these ceramics using positron annihilation lifetime spectroscopy within two-component fitting procedures. The NiO phase results in transformation of free-volume defects in the inner structure of ceramics. To study free volumes formed by NiO and nanopores in Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics three-component fitting procedures and using positron-positronium trapping algorithm was used this work.

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09:30 Coffee Break    
ELECTRONIC MATERIALS 1 : Vladimir Pankratov
Authors : Hanna Bishara*, Lena Formmeyer, Subin Lee, Tobias Brink, Matteo Ghidelli, Gerhard Dehm
Affiliations : Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany

Resume : Grain boundaries (GBs) are the most significant defects influencing electrical properties of materials. However, the relationship between GB types and the nanoscale electrical behaviour is not fully understood yet, hindering the development and the design of novel electronic materials with a better performance, e.g. conductors, photovoltaics, and thermoelectrics. Here, we provide a systematic study to correlate directly-measured resistivity of well-defined Cu GB segments with their structural characteristics investigating the effect of plane, misorientation and curvature. To this aim Cu thin films are sputtered on c-sapphire substrates and annealed to obtain abnormal grain growth and a variety of [111] tilt GB types, namely ?3, ?7, ?19b, ?21a, ?37c, and low angle GBs in misorientation range of 7°-18°. Then, we create local bi-crystals by focused ion beam (FIB), isolating a single GB. Electron backscatter diffraction (EBSD) is used to identify the GB plane/orientation/inclination, while high resolution transmission electron microscopy (TEM) is exploited to unravel the atomic structures. Subsequently, electrical resistivity measurements are conducted with in-situ Scanning Electron Microscopy (SEM) through four scanning probes using micro-manipulators and a nV sensitive voltage-meter. This methodology enables a direct resistivity measurement for different coincidence site lattice (CSL) and low angle GBs. We found that the resistivity values span for more than one order of magnitude matching the predicted trend by simulations. The GB resistivity can be correlated with excess free volume and energies of the interfaces as found by molecular dynamics simulations (MD). Our results indicate that resistivity is highly dependent on the ?-type of the GB. However, it does not noticeably change for structural variations of GB plane, misorientation deviation from ideal ?-type and inclination within the same ?-type. Nevertheless, GB curvature increases resistivity by 80% due to high density of defects, while large resistivity values are observed for GBs which are not described by a uniform equilibrium atomic structure. Overall, our novel results contribute to a better understanding of the structure-resistivity relation in GBs.

Authors : J.M.M. Andrade(1), C.M.M. Rosário(1), S. Menzel(2), R. Waser(2,3), N.A. Sobolev(1)
Affiliations : (1) Physics Department and I3N, University of Aveiro, 3810-193 Portugal (2) Peter Grünberg Institute and JARA-FIT, Forschungszentrum Jülich GmbH, Jülich, 52428, Germany (3) Institut für Werkstoffe der Elektrotechnik II, RWTH Aachen University, Aachen, 52074, Germany

Resume : Redox-based resistive random access memories (ReRAMs) are promising candidates in fields like the memory market and neuromorphic computing. However, the fundamental mechanisms that rule the conduction in these devices are still heavily debated. The present work focuses on studying one model for the conduction, the quantum point contact (QPC) [1], and specifically a single subband approximation (SSA) to this model [2]. With this intent, Pt(20 nm) / Ta(15 nm) / Ta2O5(5 nm) / Pt(20 nm) resistive switching devices were studied, and current-voltage (I-V) curves for both resistance states were obtained. The original QPC model has been found to be hard to apply, as the starting parameters had a strong influence on the fitting results, and the algorithm was not robust. On the other hand, the SSA proved its ability to provide good fits to the data, and to do so better than other conduction mechanisms considered. However, its physical basis is criticized, and it is concluded that, in the devices studied, multiple subbands likely contribute to the conduction, in direct opposition to the assumptions made in such an approximation. A reinterpretation of the SSA’s parameters is proposed, to reconcile the increased performance with a greater physical accuracy. Beyond that, the main challenges and difficulties regarding the application of the QPC to the case of valence change-based ReRAM will be discussed. [1] Miranda, E. and Suñé, J. in 2001 IEEE International Reliability Physics Symposium Proceedings 367 (2001) [2] Miranda, E. A., Walczyk, C., Wenger, C. and Schroeder, T. IEEE Electron Device Lett. 31, 609 (2010)

Authors : Evgeniy Makagon, Maximilian Felix Hoedl, Rotraut Merkle, Eugene Kotomin, Joachim Maier, Igor Lubomirsky
Affiliations : Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel; Max Plank Institute for Solid State Research, Stuttgart, Germany; University of Riga, Institute of Solid State Physics, Riga, Latvia;

Resume : Acceptor-doped BaZrO3 is a promising electrolyte for protonic ceramic fuel cells as it combines high bulk proton conductivity with good chemical stability. The protonic conductivity is achieved by dissociative water incorporation into oxygen vacancies formed by acceptors on Zr4 sites. We have investigated the influence of dopants, oxygen vacancies, and protons on the macroscopic elastic and electromechanical properties of acceptor-doped BaZrO3 ceramics. Ceramics of BaZr(1-x)X(x)O(3-x/2 δ)H2δ with X = Al, Ga, Sc, In, Y, Eu and 0.05 < x < 0.2 were prepared by solid state reactive sintering and hydration. Ultrasonic pulsed echo time of flight measurements were used to infer the Young’s and the shear moduli. Both moduli decrease by up to ~20% due to the presence of dopants and oxygen vacancies that cause local lattice distortions [1,2]. Water incorporation into the vacancies decreases the moduli even further. An unexpectedly large electrostriction coefficient (M33 ~10E-15 m2/V2) was detected with a capacitive proximity sensor for all dopants introducing a new class of non-classical electrostrictors. M33 of the hydrated ceramics exhibits a Debye-type relaxation with the relaxation frequency exponentially increasing with the ionic radius closely matching dielectric relaxation measured by impedance spectroscopy. This implies that the protons are associated with the dopants, and the binding strength decreases from Al to Y. [1] M. F. Hoedl, E. Makagon, I. Lubomirsky, R. Merkle, E. A. Kotomin, J. Maier, Acta Mater. (2018) 160, 247 [2] E. Makagon, R. Merkle, J. Maier, I. Lubomirsky, Solid State Ionics (2020) 344, 115130

Authors : Eric Vandermolen (a,b), Philippe Ferrandis (c), Frédéric Allibert (b), Massinissa Nabet (d), Martin Rack (d), Jean-Pierre Raskin (d), C.H. (Kees) de Groot (e), and Mikaël Cassé (a)
Affiliations : a CEA, LETI, Univ. Grenoble Alpes, 38000 Grenoble, France; b SOITEC, Parc technologique des fontaines, 38190 Bernin, France; c Université de Toulon, Univ. Grenoble Alpes, CNRS, Institut Néel, 38000 Grenoble, France; d ICTEAM, Université catholique de Louvain, 1348 Louvain-la-Neuve, Belgium; e School of Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ, UK

Resume : An important family of silicon-based substrates used for radio frequency (RF) applications relies on the introduction of a large concentration of traps to prevent the formation of a parasitic conduction layer, detrimental to RF substrate performance. Effective resistivity and harmonic distortion (HD) measurements allow the suitability of the substrate for RF applications to be assessed, but to engineer their values, information on trap properties are required. Those properties are difficult to characterize with conventional capacitance techniques due to the combination of high resistivity and large trap density which induces a Fermi-level pinning. In this work, we used photo-induced current transient spectroscopy to generate a transient current by thermal de-trapping after light-induced trap-filling. The signal was then processed to obtain, over a temperature range, a spectrum depending on the trap energy levels and capture cross-sections. This technique was applied to gold-implanted silicon substrates, thus enabling the detection of four main traps. Quantitative evaluation of the defect concentration was achieved by a fitting of measured and simulated HD results. Finally, information obtained about traps was compared with secondary ion mass spectroscopy measurements and an explanation of the role of each introduced defect on RF behavior was proposed. This work opens the way to the understanding trap behaviour in other RF substrates such as trap-rich silicon-on-insulator substrates.

Authors : Daniel J. Mannion, J Li, Francisco V. Ramirez, Mark Buckwell, Wing H. Ng, Adnan Mehonic, Anthony J. Kenyon
Affiliations : University College London

Resume : Thin film oxide capacitors have been shown to exhibit complex current transients in response to step potentials. These involve a sharp initial increase in current followed by a slower decay, resulting in a distinctive peak in device current. They have been observed in materials such as barium strontium titanate (BST) [1,2] and titanium dioxide [4] capacitors as well as in our own amorphous silicon dioxide devices where they were used to carry out edge detection [5]. It is argued these transients are the result of oxygen vacancy defects drifting under the applied potential and that their timing is an indicator of vacancy mobility. However, such mobility values are derived from a space charge theory which appears to break down when characterised from a relaxation perspective. In this talk we present results which suggest an alternative model based on a combination of field- and charge-driven processes. In addition, we will also comment on the role of light in accelerating the rates of such transients. [8] In previous studies, mobility values were determined from the timing of the peak in current and its proportionality to the applied voltage. [1,2,6,7] Space-charge limited current theory suggests this is the point at which vacancies have traversed across the device and begun collecting at the opposite electrode, resulting in Coloumbic repulsion. Underlying this analysis is an assumption that the transients are defined by a single cause, and that both the rise and fall in conduction are the result of a field-driven redistribution of oxygen vacancies. The vacancies act as donors, forming an n-type region at the negative electrode that modulates electronic conduction. [3] In this way, the two processes may be described with a single state variable – the distribution of vacancies at a given moment. However, the relaxation characteristics of these transients reveal two separate processes. The initial increase in current is volatile on the order of hundreds of milliseconds, whereas the later decrease in current is much more persistent and resets on a scale of tens of minutes. The behaviour seems not to be described by one single process, but instead by two. The timing of the peak is therefore dependent on the rates of both processes, something which is overlooked in the existing literature on this topic. Here, we analyse the current transients by separating them into their two respective processes and attempt to identify their properties separately. From relaxation experiments, combined with the rectifying nature of our devices, we can say with confidence the latter process is a field driven effect, suggesting the drift of charged defects. On the other hand, when using optical measurements, we are able to inject charge across the interface barrier without modulating the applied potential, in turn accelerating that initial increase of device current. This suggests the initial process is instead driven by the injection of charge and not by field. These observations support our hypothesis that transients are the result of two separate processes whose timings are defined not just by field but also the conditions of charge injection. This throws into question the accuracy of mobility values previously determined via current transients, which assume the process to be entirely field driven. [1] S. Zafar, et al. “Oxygen vacancy mobility determined from current measurements in thin Ba0.5Sr0.5TiO3 films,” Appl. Phys. Lett., vol. 73, no. 2, p. 175, Jul. 1998. [2] S. Saha et al. “Transient analysis in Al-doped barium strontium titanate thin films grown by pulsed laser deposition,” J. Appl. Phys., vol. 90, no. 3, pp. 1250–1254, Aug. 2001. [3] R. Meyer, et al. “Oxygen vacancy migration and time-dependent leakage current behavior of Ba0.3Sr0.7TiO3 thin films,” Appl. Phys. Lett., vol. 86, no. 11, p. 112904, Mar. 2005. [4] N. Zhong, et al. “Transient Current Study on Pt/TiO 2- x /Pt Capacitor,” Jpn. J. Appl. Phys., vol. 49, no. 4, p. 04DJ15, Apr. 2010. [5] D. J. Mannion, et al. “Memristor-Based Edge Detection for Spike Encoded Pixels,” Front. Neurosci., vol. 13, p. 1386, Jan. 2020. [6] J. Wang et al. “Oxygen vacancy motion in Er-doped barium strontium titanate thin films,” Appl. Phys. Lett., vol. 89, no. 17, p. 172906, Oct. 2006. [7] S. Zafar, et al. “Measurement of oxygen diffusion in nanometer scale HfO2 gate dielectric films,” Appl. Phys. Lett., vol. 98, no. 15, p. 152903, Apr. 2011.2011. [8] J. Lee, et al. “Charge Transition of Oxygen Vacancies during Resistive Switching in Oxide-Based RRAM,” ACS Appl. Mater. Interfaces, p. acsami.8b18386, Mar. 2019. [9] Y. Li, et al. “Visible-light-accelerated oxygen vacancy migration in strontium titanate,” Sci. Rep., vol. 5, no. 1, p. 14576, Nov. 2015.

Authors : R. I. Eglitis, J. Purans, A. I. Popov and Ran Jia
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV1063, Latvia

Resume : The atomic displacement magnitudes of nearest neighbour atoms around the (001) surface F-center in ABO3 perovskites are considerably larger than the related displacement magnitudes of nearest neighbour atoms around the bulk F-center. In the ABO3 perovskites the electron charge is considerably better localized inside the bulk F-center than in the (001) surface F-center, where the oxygen vacancy charge is more delocalized over the nearest neighbour atoms than in the bulk F-center case. The (001) surface F-center formation energy in the ABO3 perovskites is smaller than the bulk F-center formation energy, which triggers the F-center segregation from the ABO3 perovskite bulk towards its (001) surface. In most cases the (001) surface F-center induced defect level in the ABO3 perovskites is located closer to the (001) surface conduction band bottom than the bulk F-center induced defect level to the bulk conduction band bottom [1-3]. In contrast to the ABO3 perovskite bulk and (001) surface F-centers, the CaF2, BaF2 and SrF2 bulk and surface F-center charge is very well localized inside the fluorine vacancy. The atomic relaxation magnitudes around both bulk and surface F-centers in CaF2, BaF2 and SrF2 crystals, as a rule, are considerably smaller than the relevant atomic displacement magnitudes around bulk and (001) surface F-centers in ABO3 perovskites [4,5]. References: 1. R.I. Eglitis and A.I. Popov, J. Nano-Electron. Phys. 11, 01001 (2019) 2. R.I. Eglitis and S. Piskunov, Comput. Condens. Matter 7, 1-6 (2016) 3. M. Sokolov, R.I. Eglitis et al., Int. J. Mod. Phys. B 31, 1750251 (2017) 4. H. Shi, R.I. Eglitis and G. Borstel, Phys. Rev. B 72, 045109 (2005) 5. H. Shi, R. Jia, R.I. Eglitis, Solid State Ionics 187, 1-7 (2011)

Authors : Lorenzo Bottiglieri (1), João Resende (2), Odette Chaix-Pluchery (1), Carmen Jiménez (1), Jean-Luc Deschanvres (1)
Affiliations : 1 Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France; 2 AlmaScience, Campus da Caparica, 2829-516 Caparica, Portugal;

Resume : In the hot topic of the synthesis of highly performing p-type TCOs, copper chromium oxide (CuCrO2) presents promising optical and electrical properties suitable for a wide variety of optoelectronic devices. Nevertheless, this material suffers from relatively high resistivity (ρ > 102 Ω.cm) for stoichiometric thin films at room temperature. Cu vacancies or oxygen interstitial are considered the principal source of p-type doping, with small polaron or band conduction mechanism suggested to interpret the electrical transport mechanism in this material. Furthermore, recent studies reported great electrical performances and adequate transparency for non-stoichiometric CuCrO2 thin films (ρ < 0.01 Ω.cm). In this work, we show that the control of the composition of CuCrO2 thin films allows the synthesis of highly conductive and transparent oxides thin films, by a low-cost and non-vacuum deposition technique. We successfully deposited CuCrO2 thin films out of stoichiometry by Aerosol Assisted CVD at atmospheric pressure. The compositional, structural, and morphological properties were analyzed to understand the effect of the incorporated cationic ratio in the film, Cu/(Cu+Cr), on electrical and optical properties, while addressing the doping mechanism. The incorporated cationic ratio is generally higher than the one in the starting precursor solution, leading to a higher film growth increasing Cu content. The deposition of CuCrO2 out of stoichiometry without any detectable secondary phase is achieved up to a composition of Cu/(Cu+Cr) = 65%. Cu-rich CuCrO2 thin films are characterized by high crystallinity degree, through the formation of large nanocolomnar grains with a strong vertical orientation. The resistivity, the transparency, and the bandgap are reduced with the increase of the Cu/(Cu+Cr) ratio in the film. The greatest electrical and optical properties were found for Cu-rich CuCrO2 thin films with Cu/(Cu+Cr)=65%, resulting in a resistivity of 0.05 Ω.cm, and an average transmittance around 58%, culminating in a Gordon’s Figure of Merit (FoMg) of 2.2 mS. Electrical measurements with temperature under different oxygen partial pressure, together with Raman spectroscopy and XPS revealed a crucial role of oxygen atoms in interstitial sites over the electrical properties, with an enhancement of the conductivity for films annealed in oxygen-rich atmosphere. This is attributed to the creation of defects within the crystal lattice during the thermal treatment. Besides, greater Cu incorporation leads to the synthesis of a composite film formed by Cu2O and CuCrO2. These films present improved carrier mobility and reduced energy gap, with a resistivity around 0.02 Ω.cm, a transmittance of 52%, resulting in a FoMg of 1.4 mS. Finally, the tuning of the optical and electrical performances through a simple chemical approach offers two appealing candidates, Cu-rich CuCrO2 and the composite Cu2O+CuCrO2, for the integration in transparent electronic devices.

Authors : Ya-Ru Wang,1 Alessandro Senocrate,1 Gee Yeong Kim,1 Algirdas Dučinskas,1,2 Jovana V. Milić,2 Davide Moia,1 Michael Grätzel2 and Joachim Maier1
Affiliations : 1 Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany 2 Laboratory of Photonics and Interfaces, EPFL, 1015 Lausanne, Switzerland

Resume : Mixed halide perovskites are promising materials for solar cells, light-emitting diodes and other opto-electronic devices due to their tunable bandgaps. However, under light, these systems show segregation into two phases with different halide compositions (photo-demixing). Interestingly, these two phases tend to remix back in the dark (dark-remixing)1. This phase instability is undesirable when aiming to solar cells with stable output, while it opens opportunities towards new device architectures.2 The observed light induced evolution of different phases involves significant ion transport. Therefore, improved understanding of the underlying defect chemical mechanisms involved in the photo-demixing (and dark remixing) can help both preventing and controlling this effect. While several studies have characterized photo-demixing in 3D mixed halide perovskites, the role of decreasing dimensionality on this process has not yet been fully clarified. In the case of two-dimensional (2D) lead halide perovskites, increased resilience against intrinsic and extrinsic degradation routes has been attributed to the suppression of ion migration in these materials with respect to the 3D counterparts.3,4 It is therefore interesting to probe how the photo-demixing relates to the structure and composition of these mixed halide perovskite systems. Here, we demonstrate for the first time that also 2D mixed halide perovskites show reversible demixing under light. The kinetics of the process is slower for the 2D systems compared with their 3D counterpart. We investigate the evolution of optical and structural properties of 2D perovskite thin films under different light bias conditions, providing information on the thermodynamics and the kinetics of the photo-demixing and dark-remixing processes. These techniques, combined with in-situ conductivity measurements, also allow us to assess the influence of light intensity, thin film composition, substrate, and encapsulation on the ionic properties and phase behavior of these systems. Lastly, we propose a model that describes photo-demixing and dark-remixing in 2D mixed lead halide perovskites based on our previous analysis of the 3D systems.5Our study contributes to defining the thermodynamic picture of 2D mixed halide perovskites, which will aid compositional engineering of optoelectronic devices where photo-demixing is controlled. 1. Hoke ET, Slotcavage DJ, Dohner ER, Bowring AR, Karunadasa HI, McGehee MD. Reversible photo-induced trap formation in mixed-halide hybrid perovskites for photovoltaics. Chem Sci. 2015;6(1):613-7. 2. Mao W, Hall CR, Bernardi S, Cheng YB, Widmer-Cooper A, Smith TA, et al. Light-induced reversal of ion segregation in mixed-halide perovskites. Nat Mater. 2020. 3. Cho J, DuBose JT, Le ANT, Kamat PV. Suppressed Halide Ion Migration in 2D Lead Halide Perovskites. ACS Materials Letters. 2020. 4. Grancini G, Nazeeruddin MK. Dimensional tailoring of hybrid perovskites for photovoltaics. Nature Reviews Materials. 2019;4(1):4-22. 5. Kim GY, Senocrate A, Wang Y-R, Moia D, Maier J. Photo-Effect on Ion Transport in Mixed Cation and Halide Perovskites and Implications for Photo-Demixing**. Angewandte Chemie International Edition. 2021;60(2):820-6.

Authors : Denis Gryaznov, E. A. Kotomin, A. Platonenko, A. Popov
Affiliations : a) Institute of Solid State Physics, University of Latvia, 8 Kengaraga, LV-1063, Riga, Latvia

Resume : The density functional theory (DFT) calculations are nowadays widely used to investigate defects behavior in materials and, thus, represent an effective complement to experiments. Such calculations can provide us with information inaccessible for experiments and/or suggest an important comparison. It is very much due to improved methods available in modern DFT computer codes (e.g. the hybrid density functionals). We present here several cases when the DFT calculations were particularly useful. The DFT calculations of EPR parameters and atomic and electronic structure were performed for hole-type defects in MgAl2O4. The main focus was placed on the calculation of the so-called V-centers with the single hole trapped on a regular oxygen ion. The calculated hyperfine coupling constants were very consistent with the experimental data, but the atomic and electronic structure established and the thermodynamic stability of such defects confirmed on the basis of calculated formation energies [1]. Another example considered the superoxide defect in -Al2O3. The DFT calculations demonstrated the interstitial oxygen dumbbell could exist in the two configurations, symmetric and asymmetric [2]. However, the relaxation pattern around the hole-type center in the asymmetric configuration shows a good agreement with that found from the measured EPR measurements. In addition, the calculated formation energies confirmed the asymmetric configuration being a ground state one. We emphasize important role of bond lengths, spin density and atomic charges for such calculations to get deeper insight into defects behavior. In addition, the calculated formation energies will be discussed for oxygen vacancies in ABO3 perovskite materials with transition metals (e.g., Fe, Ti) and emphasis on the comparison with experimental data. [1] A. Platonenko et al., Nucl. Instr. Meths. Phys. Res. B 464 (2020) 60. [2] V. Seeman et al., Scientific Report 10 (2020) 15852. [3] D. Gryaznov et al. J. Mater. Chem. A 4 (2016) 13093. [4] D. Gryaznov et al. J. Phys. Chem. C 117 (2013) 13776.

12:30 Lunch    
Authors : Anna Lavie1, Sergey Khodorov1, Maxim Varenik1, Ellen Wachtel1, David Ehre1, Yishay Feldman2, Anatoly Frenkel3, and Igor Lubomirsky1
Affiliations : 1Dept. Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel 2Dept. Chemical Research Support, Weizmann Institute of Science, Rehovot, Israel 3Dept. Materials Engineering, Stony Brook, University, NY

Resume : When magnetic or electric ordering in the solid state is too weak to be retained upon removal of the external field, relaxation occurs without remanent magnetization (super-paramagnetism) or polarization (ferroelectric relaxors). Notably, a “ferroelastic relaxor”, i.e. a solid in which ferroelastic domains produce anomalously large elastic compliance in an otherwise stiff material, has, to date, not been reported. Here we report the observation of elastic domains with relaxor behavior in Sm- or Gd-doped ceria ceramics at <5 mol% dopant concentration. The evidence is the following. Alternating electric field (5-30 kV/cm) with f > 50 mHz produces fully reversible electrostrictive contraction in the direction of the field, while for non-alternating electric field, the material expands. DC bias, irrespective of direction causes cubic lattice elongation by ≤ 90 ppm during a few hours. Following DC field removal, induced strain relaxes to its initial state during a few days at 25 °C or a few hours at 100 °C. The same sample can be cycled many times. This behavior, as well as data on the anelastic and electrostrictive response as a function of frequency, is consistent with the material being a “ferroelastic relaxor”. In situ XAS measurements at room temperature under external electric field suggest the existence of elastic nano-domains with a characteristic size of ~1.5 unit cells (~0.8nm).

Authors : Dominik Voigt, Michael Bredol, Atoosa Gonabadi
Affiliations : University of applied sciences Münster, Department of Chemical Engineering, Stegerwaldstr. 39, 48565 Steinfurt, Germany

Resume : Semiconductor quantum dots (QDs) that exhibit size-dependent optical properties have proven to be suitable materials for many prospective applications in the area of nanotechnology. As the demand for smaller, faster and more efficient electronic devices increases, QDs with tunable properties play an important role in the miniaturization process of nanoengineering (including new catalyst materials, sensitization of solar cells, optoelectronic devices and biomedical applications). Among them ternary chalcogenides like CuInS2 are presently considered as promising alternatives to the good performing, but highly toxic, Cd and Pb based QDs. The most common synthesis strategy to yield CuInS2 nanoparticles involves 1-dodecanethiol (DDT), which serves as solvent, stabilizing ligand and sulfur source. The usage of this ligand is a double-edged sword, since due to its strong bonding it produces high-quality nanocrystals but at the same time leads to a challenging exchangeability with other ligands. Since DDT hasn’t any functional groups, this can limit the fields of application through compatibility issues, which is a major drawback since ligand exchange is often mandatory (e.g. enhance the coupling between QDs and electrodes or substrates in solar cells and aqueous phase transfer for biomedical applications). Our work therefore aims to surmount this problem and consequently obtain a broader field of application by overcoming existing compatibility issues. We present a synthesis route that allows for universal surface modification with thiol-containing molecules. These molecules with various terminal groups were used to functionalize the nanoparticles and stabilize them in different media, making any surface charge and polarity accessible. The success of the ligand exchange was confirmed by FT-IR spectroscopy and pH dependent zeta potential and DLS size measurements. It is further shown that this method is transferable and could be used to functionalize other QDs that crystalize in the zincblende structure (or in derivate of it, like chalcopyrite).

Authors : N. Gächter 1, E. Blundo 2, M. Yukimune 3, I. Zardo 1, F. Ishikawa 3, A. Polimeni 2 and M. De Luca 1
Affiliations : 1 Departement Physik, Universität Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland; 2 Dipartimento di Fisica, Sapienza Università di Roma, P.le A. Moro 5, Roma, Italy; 3 Graduate School of Science and Engineering, Ehime University, 3 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan

Resume : Bandgap engineering in semiconductor nanostructures is usually achieved by varying the growth conditions or by imposing high strain levels. Here, we report post-growth bandgap engineering in nanowires by mere exposition to low-energy ionized hydrogen gas. The GaAs/GaAsN core/multishell nanowires in this study contain only 0.7%, 2% and 3% of N, which is typical for dilute nitrides [1]. At such low concentrations, the N atoms behave as strongly localized and perturbing lattice defects and give rise to a number of counterintuitive effects. Among others, they create a red-shift of the GaAsN bandgap as high as 0.35 eV when increasing N from 0 to 3%. With μ-Raman and μ-photoluminescence measurements on single wires, we demonstrate that these defects can be engineered on demand by controlled hydrogenation. The H atoms are incorporated in N-H complexes and annihilate the electronic perturbation effect of the N atoms [2]. Thereby, we can effectively tune the GaAsN bandgap up to the value of pure GaAs. This giant tuning is accompanied by a photoluminescence signal increase of more than one order of magnitude. Our low energy hydrogenation approach creates new, fast and effective possibilities for tuning the optical properties of nanowires at the nanoscale and forming novel site-controlled quantum dots and quantum rings. [1] M Yukimune et al 2019 Nanotech. 30 244002 [2] F Biccari et al 2018 Adv. Mater. 30, 1705450

Authors : Nikolskaya, A.A., Korolev, D.S., Okulich, E.V., Mikhaylov, A.N., Gogova, D., Trushin, V.N., Chigirinsky, Yu.I., Nikolichev, D.E., Nezhdanov, A.V., Kumar, M., Giulian, R., Tetelbaum, D.I.
Affiliations : Lobachevsky University, Nizhny Novgorod, Russia; University of Oslo, Norway; Indian Institute of Technology Jodhpur, Jodhpur, India; Federal University of Rio Grande do Sul, Porto Alegre, Brazil

Resume : Gallium oxide is one of the most promising materials of future electronics due to its wide bandgap (4.4-4.9 eV) and other advantages. Its properties strongly depend on impurity-defect composition that is sensitive to technological parameters. In this work, the properties of β-Ga2O3 layers obtained by magnetron sputtering and modified by ion implantation are studied. Among the advantages of these methods is their non-equilibrium nature promising for obtaining p-type Ga2O3. Ion implantation also allows the controlled introduction of point defects and impurity atoms to a given depth, which determine the electrical and optical parameters of Ga2O3. The dependence of chemical composition, structure, electrical and optical properties on the deposition and ion-modification conditions is analyzed. Ion implantation is also used for the formation of Ga2O3 nanocrystals in Al2O3 film deposited on Si substrate. The possibility of creating effective UV-range photodetectors is shown for the samples with ion-synthesized Ga2O3 nanocrystals. The solutions proposed here are intended to significantly expand the range of applications of gallium oxide in advanced electronic and optoelectronic devices. The work was supported by RFBR (19-57-80011), Department of Science and Technology (DST/IMRCD/BRICS/Pilot Call 3/ Ga2O3 /2019) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq – Brazil). N.A.A. acknowledges the support of the President of the Russian Federation fellowship.

Authors : Flavio. Y. Bruno (1, 2), Siobhan McKeown-Walker (1), Margherita Boselli (1), Emanuel Martinez (2), Anna Tamai (1), Jean-Marc Triscone (1) and Felix Baumberger (1).
Affiliations : (1) Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland. (2) GFMC, Departamento de Física de Materiales, Universidad Complutense de Madrid, 28040 Madrid, Spain

Resume : The deposition of a thin elemental Al layer on the clean surface of bulk insulating SrTiO3 results in the formation of surface of oxygen vacancies on the oxide. As a result a two dimensional electron system (2DES) with remarkable electronic properties is obtained. The electronic structure of such 2DES has been shown to be directly related with the spin-to-charge conversion process that takes place in devices based on such system [1]. In this work we will present measurements of the electronic structure of the 2DES by means of angle resolved photoelectron spectroscopy (ARPES) together with self-consistent tight binding supercell calculations that are in good agreement with our measurements. Moreover we will show how we can tailor the electronic carrier density by controlling the Al layer thickness and thus the amount of oxygen vacancies induced in the surface. We demonstrate that it is possible to tune the electronic density in Al/STO to match that of the celebrated LAO/STO system and perform a comparative study of the electronic structure in both systems. In conclusion, we show how defects such as oxygen vacancies can be used as an effective tuning knob to tailor a desired electronic structure. [1] D.C. Vaz, et al. Nature Materials 18, 1187 (2019). We acknowledge financial support from Comunidad de Madrid (Atracción de Talento grant No. 2018-T1/IND-10521) and by MICINN PID2019-105238GA-I00.

Authors : H. Klym (1), I. Karbovnyk (2)
Affiliations : (1) Lviv Polytechnic National University, Lviv, Ukraine (2) Ivan Franko National University of Lviv, Lviv, Ukraine

Resume : We discuss defect-related free volumes in raw functional nanomaterials such as chalcogenide GeSe2-Ga2Se3 and GeS2-Ga2S3-CsCl glasses or oxide Cu0.4Co0.4Ni0.4Mn1.8O4 MgAl2O4 ceramics which are caused by different technological and post-technological modifications of these compounds. Positron annihilation lifetime spectroscopy (PALS) method within different approaches is used as a main tool for investigations. In the case of 80GeSe2-20Ga2Se3 glasses it is shown that crystallization process during annealing at 380°C for 25 and 50 h indicates specific fragmentation of larger free-volume nanovoids into a greater number of smaller ones. For GeS2-Ga2S3-CsCl glasses it is established that the addition of CsCl transforms free volume due to the void agglomeration in glasses with 10 % mol. of CsCl. In Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics with 8 % of NiO phase addition, positron trapping defects near grain boundaries are formed. Extended defects in nanoporous MgAl2O4 ceramics were characterized by PALS before and after water-immersion treatment. It is shown that in both cases the same type of positron traps prevails, but positron trapping in defects near grain boundaries occurs more efficiently in the water-moistened ceramics. The water vapor modifies defects in ceramics located near grain boundaries and this process is accompanied by the void fragmentation at water adsorption with further void agglomeration at water desorption after drying.

16:00 Coffee Break    
Authors : Florian A. Mann, Niklas Herrmann, Felipe Opazo, Sebastian Kruss
Affiliations : Ruhr-Universität Bochum, Germany

Resume : Single?walled carbon nanotubes (SWCNTs) are a 1D nanomaterial that shows fluorescence in the near?infrared (NIR, >800?nm). In the past, covalent chemistry was less explored to functionalize SWCNTs as it impairs NIR emission. However, certain sp3 defects (quantum defects) in the carbon lattice have emerged that preserve NIR fluorescence and even introduce a new, red?shifted emission peak. Here, we report on quantum defects, introduced using light?driven diazonium chemistry, that serve as anchor points for peptides and proteins. We show that maleimide anchors allow conjugation of cysteine?containing proteins such as a GFP?binding nanobody. In addition, an Fmoc?protected phenylalanine defect serves as a starting point for conjugation of visible fluorophores to create multicolor SWCNTs and in situ peptide synthesis directly on the nanotube. Therefore, these quantum defects are a versatile platform to tailor both the nanotube's photophysical properties as well as their surface chemistry.

Authors : F. Murphy-Armando, M. Brehm, P. Steindl, M. T. Lusk, T. Fromherz, K. Schwarz, P. Blaha
Affiliations : Tyndall National Institute, University College, Cork, Ireland; Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenberger Strasse 69, A-4040 Linz, Austria; Tyndall National Institute, University College, Cork, Ireland, and Department of Condensed Matter Physics, Faculty of Science, Masaryk University, Kotlářská 267/2, 61137 Brno, Czech Republic; Department of Physics, Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, USA; Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenberger Strasse 69, A-4040 Linz, Austria; Institute of Materials Chemistry, Vienna University of Technology, Getreidemarkt 9/165-TC, A-1060 Vienna, Austria; Institute of Materials Chemistry, Vienna University of Technology, Getreidemarkt 9/165-TC, A-1060 Vienna, Austria

Resume : The lack of efficient group-IV light emitting materials is still a bottleneck for large scale, low cost CMOS-compatible data transmission technologies. The main disadvantage in CMOS-compatible group-IV materials, like Si and Ge, is that their band gap is indirect, leading to very inefficient light emission requiring phonon-assisted electron-hole recombination. In this work we use first-principles calculations to show that the introduction a split-[110]-interstitial defect can be used to enhance the direct band gap emission in Ge. The Ge-Ge split-[110]-interstitial defect, the most common interstitial defect in Ge, affects the electronic structure of Ge in two ways that improve light emission. Firstly, it hybridises the conduction band minimum states at the L point with the conduction band state at the zone centre, enhancing direct electron-hole recombination with the zone-centre valence band maximum. Secondly, it introduces two new states at the valence and conduction bands with Delta character, with its wavefunction pinned at the interstitial defect, offering a new direct transition for light emission. We explore how to further enhance the emission from these two recombination paths by changing the majority carrier population to saturate non-radiative paths, and by introducing Sn-Ge split-[110] interstitials. Finally, we explore quantum confinement to shift the wavelength to key spectral regions for datacom and sensing applications.

Authors : Petzold, S. (1), Zintler, A. (1), Eilhardt, R. (1), Piros, E. (1), Kaiser, N. (1), Vogel, T. (1), Major, M. (1), McKenna, K. P. (2), Molina-Luna, L. (1), & Alff, L.*(1)
Affiliations : (1) Institute of Materials Science, Technische Universität Darmstadt, 64287 Darmstadt, Germany (2) Department of Physics, The University of York, York YO10 5DD, United Kingdom

Resume : A model device based on an epitaxial stack combination of titanium nitride (111) and monoclinic hafnia (11-1) was grown onto a c-cut Al2O3-substrate to target the role of grain boundaries in resistive switching. The texture transfer results in 120 degree in-plane rotated m-HfO2 grains, and thus, in a defined subset of allowed grain boundary orientations of high symmetry. These engineered grain boundaries thread the whole dielectric layer, thereby providing predefined breakdown paths for electroforming-free resistive random access memory devices. Combining X-ray diffraction and scanning transmission electron microscopy (STEM) based localized automated crystal orientation mapping (ACOM), a nanoscale picture of crystal growth and grain boundary orientation was obtained. High-resolution STEM revealed low-energy grain boundaries with facing (-1-1-2) and (-121) surfaces. The uniform distribution of forming voltages below 2 V – within the operation regime – and the stable switching voltages indicate reduced intra- and device-to-device variation in grain boundary engineered hafnium oxide based random access memory devices [1]. [1] S. Petzold et al., Adv. Electron. Mater. 5, 1900484 (2019).

Authors : Natsuhiko Yoshinaga(1,2), Satoru Tokuda(2,3)
Affiliations : (1) WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan; (2) MathAM-OIL, AIST, Sendai 980-8577, Japan (3) Research Institute for Information Technology, Kyushu University, Kasuga 816-8580, Japan

Resume : Partial differential equations (PDE) have been widely used to reproduce patterns in nature, and to give an insight on the mechanism underlying pattern formation. Despite a number of PDE models have been proposed, they rely on pre-request knowledge of physical laws and symmetries, and one has difficulties to develop a model to reproduce a given desired pattern. Here we present a method that estimates the PDE models reproducing given patterns based on the “order parameters”, that is, features considering symmetries of patterns. Our method successfully estimates parameters in a model as well as the best model to make the target pattern from the viewpoint of the inverse problems, especially Bayesian model selection. We apply our method two-dimensional and three-dimensional nontrivial patterns, namely dodecagonal quasi-crystals, double gyroid, and Frank-Kasper structures reproduced by using a family of phase-field crystal models. Our method not only estimates the parameters to reproduce these patterns but also gives an insight on the appropriate number of length scales in the model.

Authors : Yu.A. Mastrikov 1, N. G. Chuklina 2,3, A.I. Popov 1, E.A. Kotomin 1, D.V. Gryaznov 1
Affiliations : 1 Institute of Solid State Physics, University of Latvia, 8 Kengaraga, LV1063, Riga, Latvia 2 Vinogradov Institute of Geochemistry SB RAS (IGC SB RAS), 1A Favorskii str., Irkutsk 664033, Russia 3 Irkutsk National Research Technical University, 83 Lermontov str., Irkutsk, 664074, Russia

Resume : Optical properties of binary lead halides, PbX2 (X=F, Cl, Br) make these materials suitable for optoelectronic devices and radiation detectors. These properties of PbX2 strongly depend on experimentally confirmed presence of self-trapped charge carriers. The hybrid DFT computational modelling was performed for the first time for small radius polarons - self-trapped electrons (STEL) and holes (STH) in PbX2 crystals widely used as scintillators. The atomic, electronic structure, spin and charge distributions and formation energies for both types of polarons were predicted for orthorhombic and STEL for the cubic PbF2, STH structure identified in a controversial case of PbCl2. The positions of STEL/STH energy levels in the band structure were determined. We also confirmed and analyzed in detail experimentally suggested models for other STEL/STH cases in PbX2.

Authors : Gianluca Rengo (123), Clement Porret (2), Andriy Hikavyy (2), Erik Rosseel (2), Mustafa Ayyad (2), Richard J. H. Morris (2), Roger Loo (2) and André Vantomme (1)
Affiliations : (1) Quantum Solid State Physics, KU Leuven, Dept. of Physics, Celestijnenlaan 200D, 3001 Leuven, Belgium; (2) Imec, Kapeldreef 75, 3001 Leuven, Belgium; (3) FWO - Vlaanderen, Egmontstraat 5, 2000 Brussel, Belgium

Resume : The extreme downscaling of logic devices has required optimization of the device architectures and material performance. Miniaturization bottlenecks have emerged with the evolution of technology nodes and have included mobility degradation within the channel and enhanced contact resistances. The latter, caused by the shrinkage of the metal/semiconductor contact areas, has become one of the most critical contributors to MOSFET parasitics [1]. The introduction of Si1-xGex source/drain (S/D) stressors within Si pMOS devices has been successfully shown to improve device characteristics. Thanks to its larger lattice parameter compared to Si, pseudomorphic Si1-xGex allows the transfer of compressive strain to the channel, thereby enhancing the hole mobility. An additional benefit of using Si1-xGex is on the contact resistance, as it enables the Schottky barrier height to be lowered [2] and higher active B doping concentrations within the region adjacent to the metal contact to be realised [3]. However, the smaller covalent radius of B compared to Si and Ge results in a reduction of the Si1-xGex lattice parameter, thereby reducing the amount of compressive strain transferred to the channel [4]. Targeting higher Ge contents may compensate this, but it does increase the risk for unwanted strain relaxation and formation of dislocations. Despite difficulties in precisely quantifying its impact, material relaxation is expected to reduce the strain transfer efficiency and may affect the electrical properties of the material. In this contribution, we have investigated the impact of strain relaxation on the electrical and contact properties of B-doped Si1-xGex layers pseudomorphically grown on 300 mm Si(001) wafers. Three different Ge concentrations (x = 0.25, 0.50 and 0.65) were considered. The specific contact resistivity of subsequently fabricated Ti / Si1-xGex contacts were evaluated using the multiring circular transmission line method [5]. Both the S/D layer and contact resistivity were found to increase with increasing Si1-xGex layer thickness. This is, however, not caused by the (small) increase in electrical bandgap induced by (partial) layer relaxation. Instead, we found that B incorporation during epitaxial growth is affected by the initiation of layer relaxation and decreases with higher degrees of strain relaxation. Besides, to assess the impact of different strain conditions on the boron incorporation, we compared the electrical properties and composition profiles of Si1-xGex:B layers grown on different Si1-yGey strain relaxed buffers (SRBs) i.e. y = 0, 0.25, 0.50 and 0.70. [1] P. Raghavan, et al., 2015 IEEE CICC, pp. 1-5. [2] C-N. Ni, et al., (VLSI-TSA), pp. 1-2 (2016). [3] R. Loo, et al., ECS J. Solid State Sci. Technol., 6(1), P14–P20 (2017). [4] K. W. Shin, et al., Jpn. J. Appl. Phys., 57(6), pp. 065504.1-065504.4 (2018). [5] H. Yu, et al., IEEE Electron Device Letters, 36(6), pp. 600-602 (2015).


Symposium organizers
Anatoli POPOVUniversity of Latvia

Institute of Solid State Physics, Kengaraga 8, Riga LV-1063; Latvia
Flyura DJURABEKOVAUniversity of Helsinki

Helsinki Institute of Physics and Department of Physics, Pietari Kalmink. 2, 00014 Helsinki, Finland

+358 249 150084
Katerina E. AIFANTIS (Main)University of Florida

Mechanical and Aerospace Engineering, 1064 Center Drive, Gainesville FL 32611, USA

+1 352 392 6227
Nikolai A. SOBOLEVUniversidade de Aveiro

Departamento de Física and I3N, Campus de Santiago, 3810-193 Aveiro, Portugal