Nanomaterials and advanced characterizationN
Current trends in optical and X-ray metrology of advanced materials for nanoscale devices VI
Photonic probes are an essential tool to characterize novel materials, since they can be non-destructive and are sensitive to many of the critical characteristics of the materials. This symposium will: i) explore the use of photons from terahertz to x-ray to characterize materials essential for many emerging technologies; ii)give an overview of the current status of optical and x-ray metrology for materials characterization and quality assurance of thin films, layer-structured materials, and one-dimensional nanomaterials, with a particular emphasis on state-of-the-art metrology; iii)promote and encourage the interaction between academic and industrial research to address scientific and technological challenges associated with the improvement of standard analytical methods and qualification of newer techniques with a particular emphasis for ICT, Microwave/Terahertz, Renewable Energy and Energy storage, health and heritage conservation; iv)promoting and encouraging young researches and academics interaction with industry to address scientific and technological challenges associated with the improvement of standard analytical methods and qualification of newer techniques suitable for addressing the needs for the emerging technologies of the future at nanoscale; v)foster networking activities within all these emerging fields of science and technologies that are expected to have a significant societal impact.
This symposium will explore recent advances in photonic characterization of novel materials used in applications as varied as renewable energy, medical applications, and art restoration. Visible photons are very easy to produce and manipulate, and have the proper energy to characterize semiconductor materials, such as might be found in solar cells. Infrared and terahertz photons much lower energy and are harder to produce and manipulate, but give information about lattice vibrations and impurities in materials. X-rays are much higher energy, and therefore can explore material characteristics such as lattice spacing and atom identification. This international symposium is intended to give an overview of the current status and future trends of optical, terahertz, infrared and x-ray metrology used to characterize nanoscale and other materials essential for many emerging technologies such as ICT, Microwave/Terahertz, Renewable Energy and Energy storage, health and heritage conservation. Another emphasis of the symposium will be on the use of larger facilities, such as synchrotrons, which produce x-rays with characteristics beyond the capability of laboratory light sources. An important consideration in this symposium will be on the actual characteristics measured, as well as the limits of the technique. In addition to the scientific objectives, we will promote and encourage the interaction between worldwide academics, National lab scientists and scientific instrument manufacturer to improve standard analytical methods and qualification of newer techniques suitable for addressing the needs for the emerging technologies of the future. A special networking event between Europe and Japan will be organised as part of this symposium.
Hot topics to be covered by the symposium:
- Ellipsometric techniques (Mueller Matrix, Infrared, THz, time-resolved and in-situ)
- X-ray diffuse scattering
- THz spectroscopy
- Spatially resolved optical and x-ray techniques at nanoscale.
- Characterization of complex materials such as halide peroskites, graphene, graphene oxide, 2D semiconductor materials, nanotubes and nanowires, nanoporous materials and composites.
- Emerging novel materials: Catalysts, Nanocarbons, 2D Materials, Thermoelectrics, β-Ga2O3, e-Ga2O3,Perovskites, SiC;
- Bio-related materials (Proteins, Cancer Cells, in-vivo and ex-vivo characterization)
- Materials for New Mobility (Batteries, Supercapacitors, 5G/6G, Fuel cells, CFRPs)
- Nanostructures, photonic crystals, and metamaterials; transparent conductive materials
- Dielectrics and ceramics: low- and high-k materials; transparent semiconductors
- Novel functional materials: Ferroelectrics, ferromagnetics and multiferroics
- Emerging X-ray Techniques: Coherent imaging; Ultrafast timing fs (FEL)
- Novel imaging and mapping capabilities and high spatial resolution: Nanoscale Raman (TERS/ SERS), IR and Photoluminescence Spectroscopies
- Ultrafast Spectroscopy/ Optical Pump-probe techniques
- High Resolution Transmission Electron Microscopy
List of confirmed invited speakers:
- Eva Bittrich, Functional and nanostructured organic thin films for energy harvesting and sensing – From in-situ VIS ellipsometry to X-ray metrology, Leibniz-Institut, Dresden, Germany
- Jacky Even, Halide perovskites, INSA Rennes, France
- Chris Sturm, Optical properties of low symmetry materials and their determination by ellipsometry, Univ. Leipzig, Germany
- Kurt Hingerl, Prediction of the ellipsometric and Mueller matrix response of structured samples for imaging ellipsometers, Johannes Kepler University, Linz, Austria
- Juan Antonio Zapien, NIR to UV Characterisation of Complex Structured Materials in the Visible Far Field: the Measurement and the Modelling Challenges, City University of Hong Kong, China
- Sean Knight, Fabry-Pérot Enhanced Terahertz Mueller Matrix Ellipsometry for Materials Characterization, Univ. Nebraska, USA
- Manfred Helm, Nonlinear THz spectroscopy of nanomaterials, Helmholtz-Zentrum Dresden-Rossendorf, Germany
- Dave Rogers, Beta-Ga2O3 thin films for novel optoelectronic device concepts, NANOVATION, France
- Laurent Lombez, Multidimensional luminescence imaging techniques for the development of advanced concepts of solar cells, CNRS IRDEP, France
- Nicolas Barreau, Epitaxy of CIGS on a GaP/Si(001) platform : towards CIGS/Si tandem solar cells, Univ. Nantes, France
- Takashi Teranishi, Electric Field Response of Ferroelectrics in Microwave Region, Okayama, University, Japan
- Shintaro Yasui, Li-ion thin film batteries with ultra-high speed chargeability: modification of interface by ferroelectrics, Tokyo Institute of Technology, Japan
- Joo-Hiuk Son, Manipulation of biological materials using terahertz radiation for potential cancer treatment, University of Seoul, South Korea
- Takao Shimizu, Epitaxial ferroelectrics materials (to be confirmed) Tokyo Institute of Technology, Japan
- Masayoshi Tonouchi, (TBA), Osaka University, Japan
- Chiko Otani, (TBA), RIKEN, Japan
- Hitoshi Tabata, (TBA) University of Tokyo, Japan
Selectd papers will be published as a special issue in Physica Status Solidi a (pss-a), Wiley.
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N.I Terahertz spectroscopies and applications : T.Kiwa, O.Durand, M.Modreanu
Authors : Masayoshi Tonouchi
Affiliations : Osaka University
Resume : Laser Terahertz (THz) Emission Microscope (LTEM) is our original microscope which enables us to visualize temporal carrier transport of photoexcited electronic materials. LTEM has been proven as a new promising tool in the evaluation platform for semiconductor R&D, which visualizes the temporal photoexcitd carrier transport with a resolution of laser beam diameter. The waveforms of LTEM unveil the nature of carrier dynamics in various materials such as wide-gap semiconductors, and also can tell the type of carriers i.e. p or n without any contacts. In this talk, we will show examples of the application of THz emission spectroscopy to GaN and some nano materials.
Authors : Hitoshi TABATA
Affiliations : The University of Tokyo
Resume : The surfaces of topological insulators contain two dimensional massless Dirac electrons. Plasmon can be excited using coupled electrons of top and bottom surfaces and shows resonance in the terahertz frequency rage with exceptionally large mode indices and long lifetimes. In the range of terahertz wave length, there are a number of important resonance absorption modes caused by intermolecular coupling and it enables us to directly observe the specific binding state of a bio-related molecular system without modifying fluorescent molecules. However, in general, it is necessary to amplify the signal intensity by some techniques. Two-dimensional Dirac plasmons can be excited from these surface electrons. These plasmons are expected to exhibit resonances in the terahertz (THz), a frequency range of interest for bio-medical sensing and chemical identification. Topological insulators (TIs) are materials having a bulk bandgap crossed by linearly-dispersing two-dimensional surface states and are expected to show surface plasmon in the THz wave length range. In addition, TI plasmons should also exhibit spin-momentum locking, leading to a reduction in scattering and an increased plasmon lifetime. In this study, we have focused on TIs of Bi2(Te,Se)3 as topological insulators those generate surface plasmon resonance in the terahertz range, and fabricated thin films on sapphire substrates by a pulsed laser deposition (PLD). Crystallographic, nano-micro structural properties are discussed. And their physical, electrical and optical properties are also presented in a view point of the terahertz plasmonics.
Authors : M. Helm, I. Fotev, L. Balaghi, D. Lang, R. Rana, S. Winnerl, H. Schneider, E. Dimakis, A. Pashkin
Affiliations : Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
Resume : We study the plasmonic response of free charge carriers in GaAs/InGaAs core/shell nanowires by means of THz spectroscopy. In the first set of experiments, we generate an electron-hole plasma in an ensemble of nanowires using photoexcitation by a femtosecond optical pump pulse. Fitting the plasmon peak measured in the linear low-field regime allows us to deduce room-temperature mobilities around 4000 cm2/Vs. Besides that, we drive the plasmon in nanowires with intense THz pulses generated in an organic DSTMS crystal. In a THz field of >MV/cm the plasmon peak is red shifted, indicating intervalley transfer of the electrons. In the second experiment, we investigate a single, highly electron doped nanowire by scattering infrared near-field infrared microscopy (s-SNIM). Here we observe a red shift of the mid-infrared plasma resonance from 125 meV to 95 meV at a peak power of 0.5-1 kW (pulse energy of 2-3.5 nJ) from our free-electron laser, which can be explained by heating the electron system in the nonparabolic conducting band. We gratefully acknowledge contributions from S. Shan, J. Schmidt, R. Hübner, S. C. Kehr, and L. M. Eng
Authors : Joo-Hiuk Son, Hwayeong Cheon, Donggun Lee, Seo-Yeon Jeong
Affiliations : Deparment of Physics University of Seoul
Resume : Carcinogenesis involves DNA methylation which is a primary alteration in DNA in the development of cancer before genetic mutation. Because the abnormal DNA methylation is found in the most of cancer cells, assessment of DNA methylation using terahertz radiation can be a novel optical method to detect and control cancer. The methylation has been directly observed by terahertz spectroscopy at around 1.6-1.7 THz and this epigenetic chemical change could be manipulated to the state of demethylation using high-power terahertz radiation. Demethylation of cancer DNA is a key issue in epigenetic cancer therapy and our results may lead to the treatment of cancer using electromagnetic waves. In the presentation, the manipulation of biological molecules and cells toward cancer treatment using intense terahertz radiation will be explained in detail.
Authors : Hiromichi Hoshina, Shota Yamazaki, Masaaki Tsubouchi, Masahiko Harata
Affiliations :  RIKEN Center for Advanced Photonics, Sendai, 980-0845, Japan;  Kansai Photon Science Institute, National Institutes for Quantum and Radiological Science and Technology, Kyoto, 619-0215, Japan;  Laboratory of Molecular Biology, Graduate School of Agricultural Science, Tohoku University, Sendai, 980-0845, Japan
Resume : Our recent experimental research on THz irradiation experiment by two different THz sources, a THz-FEL and a gyrotron, targeting actin filaments, which serve as representative biopolymer materials, will be presented. The THz-FEL produces pulsed THz waves in the 3–6 THz frequency range with a duration of 2 ps. In early studies, morphological changes were observed in the macromolecules after THz irradiation, and these phenomena were believed to be the result of the THz photons acting on the molecular dynamics. However, our recent study revealed that the pulsed THz waves with energy density of ~10−4 J/cm2 (~108 W/cm2 at the peak) generate acoustic waves efficiently in the aqueous media. These acoustic waves propagated deeply into the water and demolished the actin filaments in living HeLa cells that were submerged into the cell culture medium. The results implied that THz pulsed irradiation affects the biomolecules in the tissues, even if these molecules are located a few millimeters away from the body surface. These results must be considered when the safety guidelines for use of THz radiation are determined in the future. In contrast, irradiation experiment using a gyrotron with lower peak power of the order of ~W/cm2 induces the elongation of the actin biopolymer without thermal or acoustic effects. The polymerization of monomeric actin into filaments plays pivotal roles in cell motility, growth, differentiation and gene expression. Therefore, techniques for manipulation of actin polymerization have been developed to aid in understanding and regulation of multiple biological functions. THz irradiation technology, instead of actin-binding chemicals, should provide a safe and novel approach for regulation of the dynamics of actin polymerization and depolymerization in living cells. Our findings indicate the possibility of use of THz waves for artificial manipulation of biological phenomena through modulation of the functions and dynamics of various biomolecules.
N.II. Advanced nanoscale characterisation of material and devices : O.Durand, J.Even
Authors : Shimizu, T.*(1,2), Mimura, T.(2), Tashiro,Y.(2), Sakata O.(1), & Funakubo H.(2)
Affiliations : (1)National Institute for Materials Science, Japan (2)Tokyo Institute of Technology, Japan
Resume : The HfO2-based ferroelectric materials have gathered much attention due to their excellent compatibility with state-of-the-art semiconductor technology because the HfO2-based materials are employed as alternate gate dielectrics for field-effect transistors. The ferroelectricity in HfO2 is considered to originate from the metastable orthorhombic structure. On the other hand, it has been scarcely reported that the ferroelectric phase transition of HfO2 ferroelectric materials because most polycrystalline HfO2-based ferroelectric film transforms into the most stable monoclinic phase upon heating. We have developed the epitaxial film of HfO2 ferroelectric materials by substituting Y and investigated the fundamental properties of the materials. In this study, we investigate the phase transition of HfO2-based ferroelectric materials with epitaxial film by means of X-ray diffraction including synchrotron X-ray source. In addition, we also study the phase formation of the orthorhombic ferroelectric phase in epitaxial film. As a result, the tetragonal phase stabilized at high temperature transition to the orthorhombic phase during the cooling process.
Authors : Shintaro Yasui
Affiliations : Laboratory for Advanced Nuclear Energy, Tokyo Institute of Technology
Resume : Piezoelectric microelectromechanical-systems (MEMS) are widely used for actuators, sensors and other devices. Pb-contained piezoelectric materials such as Pb(Zr,Ti)O3 [PZT] and Pb(Mg,Nb)O3-PbTiO3 [PMN-PT] with superior piezoresponse and electromechanical properties are commonly used in piezo-MEMS. However, Pb-based materials are toxic, and there is an urgent need to replace those materials. In this work, we propose Pb-free (Bi,Sm)FeO3 [BSFO] which has a perovskite structure. Epitaxial BSFO films prepared on (100)cSrRuO3//(100)SrTiO3 substrates by pulsed laser deposition display robust piezoresponse at the morphotropic phase boundary composition. The origin of piezoelectricity is investigated by in-situ synchrotron-high resolution x-ray diffraction under pulsed applied electric field. We find that the large piezoresponse in BSFO at this composition originates from an extrinsic effect of field-induced phase transition from an antiferroelectric phase to a ferroelectric phase. Maximum longitudinal piezoresponse (d33) of approximately 240 pm/V was detected based on displacement of diffraction peaks measured under electric field.
Authors : Takashi Teranishi, Shinya Kondo, Akira Kishimoto
Affiliations : Okayama University
Resume : The frequency response of the complex permittivity in oxides is described by the dielectric dispersion of four contributions: the interfacial, dipole, ionic, and electronic polarizations. Two methods, i.e., the micro-sized planar electrode and ring resonator techniques, were developed to measure the microwave dielectric properties of specimens having a large permittivity. The modified Kohlrausch–Williams–Watts (KWW) model was used for the dipole relaxation function. Using mentioned technique, the complex permittivities of various dielectric oxides were determined up to a few GHz. For instance, the dipole polarization contribution to the dielectric response under a DC electric field in BaTiO3 based ferroelectrics was investigated [1, 2]. The apparent tunability of BST was determined by the domain wall density; a higher domain wall density resulted in a larger dipole polarization. The origin of colossal polarization of doped TiO2 based compounds were also discussed via microwave dielectric spectroscopy . Ionic polarization in THz was analyzed by the four-parameter semi-quantum (FPSQ) phonon dispersion model. Broadband dielectric spectroscopy from low to THz was consequently determined via combining dielectric relaxation function and mentioned FPSQ relation. The dipole and ionic polarizations and electronic contributions were simultaneously quantified for various perovskite ferroelectrics, in attempt to analyze the microscopic behavior in dipole polarizations [4-8]. The broadband conductivity spectrum of 8 mol% yttria-stabilized zirconia (8YSZ), a fast oxygen-ion conductor, was also acquired to quantify all conduction contributions, i.e., interfacial, grain boundary, and bulk contributions .  T. Teranishi et al., Jpn. J. Appl. Phys. 52, 09KF06 (2013).  T. Teranishi et al., Jpn. J. Appl. Phys. 58, SLLC03 (2019).  N. Delegan, T. Teranishi et al., J. Appl. Phys. 125, 205103 (2019).  T. Tsurumi et al., Appl. Phys. Lett. 91, 182905 (2007).  T. Teranishi et al., J. Appl. Phys. 105, 054111 (2009).  T. Teranishi et al., Appl. Phys. Lett. 100, 242903 (2012).  T. Teranishi et al., IEEE Trans. Ultrason. Ferroelectr. Freq. Contr. 57, 2118 (2010).  K. Miyata, T. Teranishi et al., J. Chem. Phys. 152, 084704 (2020).  T. Teranishi et al., Jpn J. Appl. Phys. 51, 011102 (2012).
Authors : Leonid Goray*, Alexei Bouravlev^
Affiliations : *Alferov University, St. Petersburg, 194021 Russia ^Ioffe Institute, St. Petersburg, 194021 Russia
Resume : We are developing A3B5 superlattices (SLs) grown by the molecular beam epitaxy with sharp heterointerfaces, constancy of composition, good homogeneity and a large number of periods (up to 1000) and thickness of up to 15 μm. Such semiconductor structures can be used for creation of tunable laser sources of far infrared and terahertz radiation using the formation of corresponding minibands and sequential tunneling of carriers through many periods. To synthesize such super-multiperiod (SMP) SLs with an accuracy of layer thickness at the atomic level and roughness/diffuseness of interfaces at the subatomic level, it is necessary to create new methods for precision control of composition and structural parameters: rigorous theoretical methods (Deep X-Ray Reflectometry – DXRR) and valid extended data obtained, particularly, with synchrotron radiation sources with high brilliance. A key future of the considered technique is matched investigation using DXRR, XRR, and XRD which is applicable for analysis of SMP SLs of various designs and allows one to characterize samples and determine with high reliability and accuracy the morphology and composition of layers. It was demonstrated using the laboratory equipment, the XRR results for Design I semiconductor superlattice (SL) grown by molecular-beam epitaxy (MBE) provide overestimated values of σ for several interfaces. In contrast, with Design II & III SLs, the inaccuracy of the derived results for σ = 0.35 nm is only about 1% for all the layers studied. This value of σ is close to the critical (before an overestimation) one and the usual XRR study with σ ≈ 0.3 nm provide accurate results for all correlation lengths and incidence angles under study. However, in the general case, such a value depends on the correlation length (roughness statistics), angle of incidence, and radiation wavelength and can be determined only using the rigorous theory of scattering. The range of grazing incidence angles was ~ 0–3° for Cu Kα diffractometer radiation and the thickness of SL was ~ 1 μm. To investigate with the same accuracy SLs with thicknesses of ~ 10 μm and more, like as super-multiperiod (SMP) structures, higher grazing angles, higher radiation energies and much higher source brightness are required. First, we use XRD to find the SL period and thicknesses of individual layers in the period by the envelope shape of the satellites and their positions and fitting a theoretical curve. To verify the XRD model and to determine the absolute errors for this structure, the XRR & DXRR methods were used. In the resulting model of XRR, exact values of layer thicknesses, as well as rms roughnesses can be obtained for the best agreement with the experimental data. Then, applying successively XRD after XRR we finally obtain perfectly matched XRD curves, which are also matched in the best way to XRR data. The next step in the matched procedure is to determine the proportion of some material in the solid semiconductor solution. It can be done, for example, using rocking curves obtained near specific reflexes. Such a methodology can be (and should be) applied to any design of such SMP SLs.
Authors : Burkovsky, R. G.* (1), Lityagin, G. A. (1), Kniazeva, M. A (1), Gao, R. (2), Dasgupta, A. (2), Andronikova, D. A. (3).
Affiliations : (1) Peter the Great Saint-Petersburg Polytechnic University, Russia (2) University of California, Berkeley, USA (3) Ioffe Institute, Russia
Resume : Functionality of thin films often depends on phase transitions, which either occur during device operation or reside nearby in the space of thermodynamic variables, thereby maximizing the essential characteristics. Characterizing the critical dynamics, associated with the transition in films was always challenging, especially the dynamics of inhomogeneous order parameters, which are described by finite wavevectors and can be probed only by short-wavelength radiation scattering. Practically important example are antiferroelectric (AFE) films, where the transition is related to inhomogeneous (staggered) dipole arrangement. We report on the first measurements of critical diffuse scattering (DS) in PbZrO3 AFE epitaxial thin films. The sample heterostructures PbZrO3 (100 nm)/SrRuO3 (20 nm)/SrTiO3 were grown by pulsed laser deposition at UC Berkeley. The measurements were performed at ID03 beamline of the ESRF. Using grazing-incidence setup we were able recording the critical DS distributions in the large regions of the Brillouin zone and tracing the temperature dependence of the signal. The results rule out the possibility of first- to second-order change of the transition character, suggested by recent studies, and point out towards near-interface structural heterogeneity as the origin of observed differences in phase transition scenarios in the film and bulk forms.
Authors : Jamil E. Flores Gonzales (1), Alexander E. Ganzha (1), Daria A. Andronikova (1), Alexander F. Vakulenko (1), Arvind Dasgupta (2), Ran Gao (2), Carlsten Richter and Roman G. Burkovsky (1)
Affiliations : 1. Peter the Great St.Petersburg Polytechnic University (SPbPU), St.Petersburg, Russian Federation. 2. Materials Science and Engineering, University of California, Berkeley, Berkeley, CA, United States.
Resume : Ferroic materials possess regions (domains) with defined orientations of the order parameter (spontaneous polarization for ferroelectrics) that together form its domain configuration which influences the functional behavior of the material. Modifications in the domain configuration may be introduced through dimensional and epitaxial effects, therefore, domains of bulks will be arranged differently than films of the same material. In the case of domains outside the capability of the polarized-light optical microscopy, research in domain configurations is usually carried out using electron diffraction and piezo-response force microscopy. Those methods exhibit some limitations, such as the need for the material to be polar in the case of PFM, or the demand for high-vacuum and charge issues in electron techniques. The objective of this work is the development of an alternative non-destructive method for characterizing the domain configuration of films and its changes when external stimuli are applied, such as high temperatures or electric fields. For this purpose, we adapt the relatively new method of X-ray nanoscopy, which consists of scanning the surface of the film with an ultra-sharp-focused synchrotron X-ray beam and monitoring the diffracted intensities. We have tested a 1000-nm-thick PbZrO3 epitaxial film, grown at UC, Berkeley. The experiment was carried out at the beamline ID01 – ESRF. Measurements were made at room temperature, where the material resides in the antiferroelectric phase. Aiming to interpret the data, a statistical analysis was developed based on the calculation of the covariance and variance between intensity distributions coming from different domain orientational states. Four 3D-maps (Z–domain intensity distribution, X-Y–translational shifts of the sample) corresponding to a different domain orientational state were obtained. Distributions do not have regular patterns, contrasted to bulk samples, and have a rather chaotic spatial domain distribution, with no visible traces of domain walls oriented in usual high-symmetry directions. Domains, apparently, often have sizes smaller than the spot size (about 100 nm), due to spatial overlapping of different domains under the spot, smearing of the intensity distribution takes place. To find the reason behind the smearing of intensity distributions, mutual covariances were calculated and compared against an ideal case with no domain overlap and absolutely sharp contrast. The experimental covariance was close to 50% of the ideal case, which we attribute to the large sample thickness, finite spot size and non-perpendicular angle of incidence. X-ray nanoscopy showed its capability to study the domain configuration of antiferroelectric thin films. We assume that if thinner samples are used, results will be more deterministic, thus allowing the exact determination of the domain configuration and the consequent characterization of its changes when external stimuli are applied.
Authors : C. Romanitan* , K. Mouratis [2,4], I.V. Tudose [2,5,6], I. Bratosin [1,7], O. Tutunaru , C. Pachiu , E. Koudoumas [2,3] and M. Suchea* [1,2]
Affiliations :  National Institute for Research and Development in Microtechnologies-IMT Bucharest, Romania, 126A, Erou Iancu Nicolae Str., 077190 Voluntari, Romania  Center of Materials Technology and Photonics, School of Engineering, Hellenic Mediterranean University, 71410 Heraklion, Crete, Greece;  Department of Electrical and Computer Engineering, School of Engineering, Hellenic Mediterranean University, 71410 Heraklion, Crete, Greece;  Physics Department, University of Patras, 26500 Patras, Greece;  Chemistry Department, University of Crete, Heraklion, Greece;  Institute of Electronic Structure and Laser, Foundation for Research & Technology-Hellas, Heraklion, Crete, Greece;  Faculty of Physics, University of Bucharest, 405 Atomistilor Street, 077125, Magurele, Romania
Resume : It is well known that the materials to be used for electrochromic applications must fulfill many of the same criteria as battery electrodes and they must be able to react very fast with small cations such as hydrogen or lithium and totally reversibly. Vanadium oxides have gained a constantly growing interest in this field, because of their varying material properties according to oxidation state. For example, vanadium pentoxide V2O5 exhibits both anodic and cathodic coloration, and thus the reversible lithium-ion insertion/extraction processes in V2O5 lead to not only reversible changes in optical parameters but also multicolor changes for esthetics in the voltage range of ± 1 V [1,2]. Herein, orthorhombic α-V2O5 nanostructured thin films grown by spray deposition technique were investigated. Further details can be found in our previous work [3,4]. In particular, the focus of interest is the strain and the associated relaxation processes, that lead to the occurrence of the structural defects. X-ray diffraction investigations showed that the thin films are highly oriented along the (001) preferential plane perpendicular to c-axis, which is very useful for intercalation of hosts for Li-ions, as happens in rechargeable batteries and electrochromic devices. To have a quantitative evaluation of the strain processes, Rietveld refinement and Williamson-Hall plot were employed in XRD data analysis. The presence of dislocations can be also observed from Raman spectroscopy, where a broadening of the main Raman peak A1g was happening accompanied by an asymmetricity of the shape. In addition, the relationship between the structural defects and electrochromic/storage performances was studied. Using cyclic voltammetry measurements results in correlation with the XRD and Raman studies one can conclude that the dislocations seem to govern both Li-diffusion in our samples and redox reactions. The results clearly prove a strong dependence between the strain/dislocations and the device performances; thus, the strain engineering approach may be considered a valuable method for a further development of energy storage electrodes applications. Acknowledgments: This research was partially co-financed by Romania through PN-III-P4-ID-PCE-2020-1712 project within PNCDI III, Greece and the EU (European Social Fund—ESF) through the Operational Program “Human Resources Development, Education and Lifelong Learning” in the context of the project “Strengthening Human Resources Research Potential via Doctorate Research—2nd Cycle” (MIS-5000432), implemented by the State Scholarships Foundation (IKΥ).  Tong, Z., Lv, H., Zhang, X., Yang, H., Tian, Y. & Li, N. (2015). Sci. Rep. 5, 16864.  Chernova, N. A., Roppolo, M., Dillon, C. & Whittingham, M. S. (2009). J. Mater. Chem. 19, 2526–2552.  Mouratis, K., Tudose, I. V., Bouranta, A., Pachiu, C., Romanitan, C., Tutunaru, O., Couris, S. & Koudoumas, E. (2020). Nanomaterials. 10, 2397.  Mouratis, K., Tudose, V., Romanitan, C., Pachiu, C., Tutunaru, O., Suchea, M., Couris, S. & Vernardou, D. (2020). Materials (Basel). 13, 3859.
N.III Current trends in spectroscopic ellipsometry I : M.Losurdo, M. Modreanu, O.Durand
Authors : Kurt Hingerl
Affiliations : Center for Surface- and Nanoanalytics, Johannes Kepler Universität Linz, 4040 Linz, Austria,
Resume : Rayleigh and Abbe derived formula for the diffraction limit, which is due to the finite width of each imaging system, because the optical near fields cannot be transmitted through it. The intensity overlaps on the screen and it cannot be any more unambiguously decided if the image stems from one or from two distinct points or areas. With the appearance of spectroscopic imaging ellipsometers (SIE) especially applied to structured samples, and capable of imaging the ellipsometric angles or Mueller Matrix elements the problem above cannot be solved in direct way, i.e. the angular resolution cannot be changed. However, with a slight reformulation the number (and size) of the contributing points or areas can be determined with an imaging ellipsometer on a field of view of e.g. 50 x 50 µm area with resolution of a few µm by a few µm (for numerical purposes we assume 2 x 2 µm). In our contribution we will first discuss, how ellipsometric measurements with an imaging ellipsometer shall be interpreted in the case of no depolarisation and with depolarisation. Then it is shown with numerical techniques based on finite element methods or rigorous coupled wave analysis. 1) that the presence of subwavelength defects or structures (Au) of an areal size of e.g. 50 x 50 nm and 10 nm height on Si can be easily detected by SIE, provided the two ellipsometric angles and are measured with an accuracy of 0.01°. This result proves that the well known sensitivity of ellipsometry on the thickness of vertical overlayers can be extended also to the horizontal dimensions. 2) Knowing that there is more than one structure with the given size in the real plane even closer than the Abbe formula can resolve in the image plane, SIE will immediately determine this number by measuring and 3) In addition we show that extremely high precision SIEs will allow to estimate the approximate distance between the different structures. The ellipsometric response depends, due to the existence of evanescent fields in plane , on the distance between the single structures. A matrix of in total 9 structures (i.e. a field of 3 x 3) of 20 nm x 20 nm structures a distance p apart will yield different SEI responses depending on the distance.
Authors : Eva Bittrich (1), Petra Uhlmann (1), Mahmoud Al-Hussein (2), Jari Domke (3), Torsten Fritz (3), Marieta Levichkova (4), Karsten Walzer (4)
Affiliations : (1) Leibniz Institute of Polymer Research Dresden, Hohe Str. 6, 01069 Dresden, Germany; (2) Physics Department and Hamdi Mango Center for Scientific Research, University of Jordan, Amman 11942, Jordan; (3) Institute of Solid-State Physics, Friedrich-Schiller-Universität Jena, Helmholtzweg 5, 07743 Jena, Germany; (4) Heliatek GmbH, Treidlerstr. 3, 01139 Dresden, Germany
Resume : Structural templating is one of the strategies for controlling the orientation of small molecule absorbers in the photoactive layer of an organic solar cell to increase its power conversion efficiency. A pi-stacked crystalline template layer is deposited below the photoactive layer to induce flat-lying (“face-on”) growth in the absorber phase by pi-pi-interactions. For improvement of the solar cell efficiency template molecules with suitable HOMO level alignment have to be found. We report on the template molecule ellagic acid, a polyphenol present in numerous fruits, and its effect on the morphology of thin films of the oligothiophene DCV4T-Et2. By differential reflection spectroscopy and photoluminescence spectroscopy we find J-aggregation in the monolayer regime. In “bulk” films of 30 nm we confirm the change from “edge-on” to “face-on” orientation of the DCV4T-Et2 phase by grazing-incidence wide angle X-ray scattering (GIWAXS) and spectroscopic ellipsometry. Finally, we show that the short circuit current density and the fill factor of corresponding organic solar cells with a templated photoactive layer are significantly improved.
Authors : Sean Knight(1), Steffen Richter(1), Vallery Stanishev(1), Philipp Kühne(1), Megan Stokey(2), Tino Hofmann(3), Mathias Schubert(2), Vanya Darakchieva(1)
Affiliations : Department of Physics, Chemistry and Biology, Linköping University, Sweden(1), Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, U.S.A.(2), Department of Physics and Optical Science, University of North Carolina at Charlotte, U.S.A.(3)
Resume : Terahertz Mueller matrix ellipsometry is a powerful technique for materials characterization, which has been used to determine the complex dielectric tensor of thin films and substrates in the spectral range of 0.1 THz to 1 THz[1,2]. Its sensitivity can be greatly enhanced by utilizing Fabry-Pérot interferences that occur between multiple reflections off of the sample's interfaces for samples containing THz-transparent substrates. Further enhancement is possible by creating an external Fabry-Pérot cavity via adding a reflective metal surface behind such samples. These techniques, for example, have enabled the detection of optical Hall effect signatures in two-dimensional electron gases, and recently, were used to detect the electron paramagnetic resonance (EPR) signal in Ce-doped lutetium oxyorthosilicate.  Philipp Kühne, et al., IEEE Trans. Terahertz Sci. Technol 8, 257 (2018).  Sean Knight et al., Sci. Rep. 9, 1353 (2019)  Sean Knight et al., Opt. Lett. 40, 2688 (2015).
Authors : Biwas Subedi, Indra Subedi, Prakash Uprety, Dipendra Adhikari, Niva Jayswal, Marie Solange Tumusange, Maxwell M. Junda, Kiran Ghimire, Prakash Koirala, Robert W. Collins, Yanfa Yan, and Nikolas J. Podraza
Affiliations : University of Toledo
Resume : Opto-electronic devices like photovoltaics (PV) depend on both optical response of component materials to control how incident light is collected as well as material electronic transport properties to utilize that absorbed light. Millimeter (THz) to ultraviolet range spectroscopic ellipsometry measures the complex optical response of materials for and within solar cells. Layer thickness, interfacial formation, structure, electronic transitions, bandgap, Urbach tails, and relative defect density are identified optically for components of silicon wafer, polycrystalline organic-inorganic lead halide perovskite, and other thin film PV technologies. THz optical Hall effect measures majority and minority carrier transport properties of semiconductors within solar cells. Open circuit voltage and fill factor simulated using those transport properties agree with direct measurement. Spectroscopic ellipsometry measurements of complete single and tandem junction PV generate structure and optical property input parameters for simulations of external quantum efficiency (EQE) and short circuit current density. Sources of optical and electronic losses are identified through quantification of parasitic absorption in non-current generating layers and carrier collection profiles of PV devices. Non-contacting optical measurements provide a means of full PV device property prediction and loss diagnosis.
Authors : C. Sturm (1), K. Hingerl (2), V. Zviagin (1), R. Schmidt-Grund (1,3), T. G. Mayerhöfer (4), M. Grundmann (1)
Affiliations : (1) Felix Bloch Institute for Solid State Physics, Universität Leipzig, Germany (2) Center for Surface and Nanoanalytics, Johannes Kepler University Linz, Austria (3) now at: Institute for Physics, Universität Ilmenau, Germany (4) Leibniz-Institut für Photonische Technologien e.V., Germany
Resume : Wide-bandgap materials, which are interesting for opto-electronic devices, like Ga2O3, exhibit often a low crystal symmetry. Here, we present the determination of the optical properties of such materials by spectroscopic ellipsometry. For the investigation of the nature of the underlying excitations, we present a general approach for the decomposition of the dielectric function by taking into account the dipole orientation distribution of each excitation into account. The application of this approach is demonstrated exemplary on an orthorhombic KTiOPO4, monoclininc Ga2O3 and triclinic K2Cr2O7. Without making any assumptions, we show that the tensor elements of the dielectric function in general are not independent of each other. The dielectric function can be described by a superposition of electronic transitions. For each transition an eigensystem exists in which the contribution to the dielectric function is given by a diagonal susceptibility tensor. The relative magnitude of these tensor elements is given by the dipole orientation distribution of the corresponding transition. In the limiting case, the oriented dipole approach is obtained as well as the tensor for uniaxial and isotropic materials. It is also shown that the imaginary part of the non-diagonal tensor elements can become negative, which is forbidden in scalar systems.
Authors : Gerald E. Jellison Jr, Raphael P Hermann, Lynn A Boatner, T Zac Ward, Andreas Herklotz
Affiliations : Oak Ridge National Laboratory
Resume : Several bulk and thin-film crystals of SnO2 were grown and examined using generalized ellipsometry techniques. The bulk samples were grown using the chemical vapor transport technique and resulted in two different habits of the crystals, depending on the processing parameters: 1) Needles of SnO2 crystals were obtained that were 1-2 cm long, less than 1 mm wide and oriented with the optic axis (OA) along the long crystal axes. 2) Using a different set of growth parameters, larger crystals were obtained, but the crystals were twinned to adjoining crystals. Thin films of SnO2 were grown using the pulsed laser deposition technique - one set on sapphire and another on rutile. Two different generalized ellipsometry techniques were employed to examine these samples. The normal-incidence two-modulator generalized ellipsometry microscope (2-MGEM) operating at 577 nm measures the diattenuation N = (Ra - Rb)/(Ra + Rb) where Ra and Rb are the reflectivities for light polarized along two mutually perpendicular directions - where Ra is the maximum reflectivity. The 2-MGEM also measures the direction of the principal axis. Spectroscopic generalized ellipsometry measurements were also preformed using the two-modulator generalized ellipsometer (2-MGE) which measures the standard ellipsometric parameters including cross-polarization terms. The 2-MGEM measurements on the bulk needle-like samples determined that the maximum diattenuation was 0.0611 ± 0.0008, which is related to the birefringence at 577 nm. Similar measurements on the bulk sample showed that the OA was at an angle of ~75° with respect to the normal to the sample surface. The 2-MGE measurements of the larger bulk SnO2 sample were used to determine the ordinary and extraordinary complex dielectric functions of the SnO2 crystal. The 2-MGE measurements of the two thin-film samples showed no cross polarization, which indicates that the samples were either isotropic or that the OA was perpendicular to the sample surface. The films grown on sapphire were fit best using a Tauc-Lorentz model for the thin film. This is consistent with X-ray measurements that showed that the film consisted of very small crystallites aligned with the OA in the plane of the sample surface but otherwise randomly oriented. According to X-ray measurements, the films grown on rutile had the OA perpendicular to the sample surface. The model of the 2-MGE data that fit best consisted of the structure: air/roughness/SnO2/interface/rutile, where the roughness and interface layers were modeled using the incomplete Beta function, and the optical functions of the SnO2 layer were determined from the bulk measurements.
N.IV Advance nanoscale characterization : Bittrich Eva, G.E.Jellison
Authors : Daniela Dragoman, Sorina Iftimie
Affiliations : (1) Univ. of Bucharest, Physics Faculty, P.O. Box MG-11, 077125 Bucharest, Romania
Resume : The talk will focus on the emerging area of metasurfaces, which are increasingly replacing conventional optical components in optics and optoelectronics applications due to their miniature size and flexibility in design. In particular, the talk will concentrate on the design of metasurfaces for imaging applications in the infrared spectral region. Different configurations of all-dielectric metasurfaces will be presented, the emphasis being on providing solutions for imaging/focusing devices with variable focus and reduced aberrations and/or for handling partially coherent light fields. Limitations imposed by implementations of the designed metasurfaces will be also addressed. The research leading to these results has received funding from the EEA Grants 2014-2021, under project no. EEA-RO-NO-2018-0438 - ElastoMETA
Authors : Coline Bretz, Andrea Vaccaro
Affiliations : LS Instruments, Fribourg, Switzerland, http://www.lsinstruments.ch
Resume : Static (SLS) and Dynamic (DLS) Light Scattering are among the most powerful techniques to study nanostructures. These technologies have been widely employed for more than 30 years, and are still undergoing constant improvement. While SLS and DLS are well-established characterization techniques, several completely new light scattering methods have gained significant traction among material scientists over the past decade. Among these, Diffusing Wave Spectroscopy (DWS) can be used to characterize the viscoelasticity of materials on a wide frequency range using low sample volumes if compared to classical mechanical rheometers. This presentation will feature a review of the scientific fundamentals of the techniques mentioned above, and take a closer look at some of the recent advancements, including Depolarized Dynamic Light Scattering (DDLS) and Modulated 3D Cross-Correlation.  Weitz & Pine, Diffusing-Wave Spectroscopy. In Dynamic Light Scattering; Brown, W., Ed.; Oxford University Press: New York, 652-720 (1993).  Balog & al., Characterizing nanoparticles in complex biological media and physiological fluids with depolarized dynamic light scattering, Nanoscale, 2015, 7, 5991-5997  Block & Scheffold, “Modulated 3D cross-correlation light scattering: Improving turbid sample characterization”, Rev. Sci. Instrum. 81, 123107 (2010).
Authors : Alexander Ebner (1); Robert Zimmerleiter (1); Jakob Kilgus (1); Christoph Cobet (2); Kurt Hingerl (3); Christian Rankl (1); Markus Brandstetter (1);
Affiliations : (1) RECENDT – Research Center for Non-Destructive Testing GmbH, Science Park 2, Altenberger Str. 69, 4040 Linz, Austria; (2) Linz School of Education, Johannes Kepler Universität, Altenberger Str. 69, 4040 Linz, Austria; (3) Center for Surface and Nanoanalytics, Johannes Kepler Universität, Altenberger Str. 69, 4040 Linz, Austria;
Resume : Conventional optical techniques applied in the fingerprint region of the mid-infrared (MIR) spectral range typically rely on thermal emitters. Such sources are characterized by low brightness, which finds expression in poor signal-to-noise ratios (SNR), long acquisition times and insufficient spatial resolution. By exploiting high-brightness broadband MIR laser sources, however, the limits of conventional instruments can be exceeded by orders of magnitude. The application of a spectrally tunable MIR quantum cascade laser (QCL) for spectroscopic ellipsometry is presented. The QCL based ellipsometer is outperforming state-of-the-art FTIR ellipsometers in terms of SNR by a factor of 290. This exceptional noise performance allows to acquire high-resolution (1 1/cm) broadband (900 1/cm – 1204 1/cm) ellipsometry spectra in less than a second (887 ms), which designates a reduction in acquisition time by a factor of 66,000 compared to reference measurements performed with a state-of-the-art instrument. The great benefit of this approach is illustrated by monitoring molecular reorientation during the stretching of a 6 µm Polypropylene film at sub-second temporal resolution. In addition, we demonstrate the advanced investigation of semiconductor materials by means of spectroscopic transmission ellipsometry measurements at continuously varying angle of incidence and sample orientation – likewise enabled by the available brightness of the applied QCL.
Authors : Teguh Citra Asmara, Claribel Dominguez, Wenliang Zhang, Jennifer Fowlie, Yi Tseng, Eugenio Paris, Jonathan Pelliciari, Andi Barbour, Ignace Jarrige, Steven Johnston, Marta Gibert, Valentina Bisogni, Jean-Marc Triscone, Thorsten Schmitt
Affiliations : Paul Scherrer Institute, Switzerland; University of Geneva, Switzerland; Paul Scherrer Institute, Switzerland; University of Geneva, Switzerland; Paul Scherrer Institute, Switzerland; Paul Scherrer Institute, Switzerland; Brookhaven National Laboratory, USA; Brookhaven National Laboratory, USA; Brookhaven National Laboratory, USA; University of Tennessee, USA; University of Zurich, Switzerland; Brookhaven National Laboratory, USA; University of Geneva, Switzerland; Paul Scherrer Institute, Switzerland
Resume : In recent years, correlated transition metal oxides (TMOs) have attracted significant attention due to their remarkable structural, electronic, magnetic, and optical properties that provide many ways to finely tune their functionalities. An example is the rare-earth nickelates (RNiO3), which are unusual among other TMOs due to their negative charge-transfer behaviour with an electronic configuration of Ni 3d8L (L = oxygen ligand hole) in their paramagnetic metallic state. Most RNiO3 (except for R = La) undergo metal-insulating (MIT) and antiferromagnetic (AFM) transitions at low temperatures accompanied by a breathing distortion in their crystal structure. This breathing motion leads to a bond disproportionation where expanded NiO6 octahedra (Ni 3d8 configuration, no holes on oxygen, and high spin) alternate with collapsed NiO6 octahedra (Ni 3d8L2 configuration, average of two holes on oxygen, and low spin), resulting in an AFM ordering vector of Q = (1/4 1/4 1/4)pc (pc = pseudocubic). This close relationship between breathing distortion and electronic configurations suggests that electron-phonon couplings (EPC) lie at the heart of the MIT in RNiO3. Recent progresses in both theory and instrumentation have allowed the use of high-resolution resonant inelastic x-ray scattering (RIXS) to probe this EPC. Here, we use high-resolution RIXS to track the momentum- and temperature-dependent evolution of the EPC across the phase transitions of RNiO3 thin films for R = La, Nd, and Sm. We find that the EPC of the phonon mode related to the breathing distortion of NdNiO3 reduces significantly by ~20% at the onset of its MIT just below 180 K. This drastic change of EPC is consistent with the polaronic condensation scenario, which proposes that the MIT of RNiO3 is caused by the condensation (melting) of polaronic carriers at low (high) temperatures. Furthermore, we also find that the momentum-dependent EPC of insulating NdNiO3 becomes maximum at half of the AFM ordering vector, signifying a strong magneto-elastic coupling in this material. These results reveal the intimate connection between electronic, lattice, and spin degrees of freedom in RNiO3 that can be exploited for future advanced functional devices, and demonstrate the capability of high-resolution RIXS in probing and even quantifying the electron-phonon interactions in advanced materials.
Authors : James A. Hillier (1), Sophie Camelio (2), Wayne Cranton (3), Alexei V. Nabok (3), Christopher J. Mellor (4), Demosthenes C. Koutsogeorgis (1), and Nikolaos Kalfagiannis* (1)
Affiliations : (1) Nottingham Trent University, School of Science and Technology, Nottingham, NG11 8NS, UK (2) Institut Pprime, UPR 3346 CNRS-Université de Poitiers, Poitiers, France (3) Sheffield Hallam University, Materials and Engineering Research Institute, Sheffield, S1 1WB, UK (4) The University of Nottingham, School of Physics and Astronomy, Nottingham, NG7 2RD, UK
Resume : Spectroscopic Ellipsometry (SE) is the primary metrology tool for determining the optical constants of materials, and therefore gaining knowledge of which materials and in which cases we can extract precise information from SE is of great importance. The implementation of semiconductors and Transparent Conductive Oxides (TCO) has enabled the unlocking of the near-infrared and infrared window for plasmonics. As materials with lower carrier concentration (N) become of utmost importance for this regime, so do the optical characterisation techniques that have the capability to deliver the exact optical constants of such materials. In this work, we combine an experimental and theoretical approach to find the precise limits (in terms of N) of SE in the different spectral regimes (from IR to UV: 0.03 - 6.5 eV) for which one can, with confidence, extract the explicit optical constants of materials. We focus our attention to the most common TCO candidates for IR plasmonics: tin-doped indium oxide (ITO), aluminium-doped zinc oxide (AZO) and gallium-doped zinc oxide (GZO). We find regions of carrier concentration where NIR-VIS-UV-SE cannot reliably determine the transport properties and we designate material-dependent and application-specific confidence factors for this case. For IR-SE, the story is more complex, and so we investigate the multifaceted influences on the limitations, such as phonon behaviour, grain size, presence of a substrate, film thickness, and measurement noise. This work is hugely timely to the discipline of photonics as we are on the onset of employing alternative, low-N materials to ensure practical applications for plasmonics. Vitally, the methodology we outline can be readily applied to other materials on a case-by-case basis.
Authors : B. Abad, J. Knobloch, T. Frazer, J. Hernández-Charpak, H. Cheng2, A. Grede2, N. Giebink, T. Mallouk, P. Mahale, N. Nova, A. Tomaschke, V. Ferguson, V. Crespi, V. Gopalan, H. Kapteyn, J. Badding, M. Murnane
Affiliations : B.Abad, J. Knobloch, T. Frazer, J. Hernández-Charpak, H. Kapteyn, M. Murnane: Department of Physics, JILA and STROBE NSF Science & Technology Center, University of Colorado and NIST, Boulder, CO 80309, USA H. Cheng, A. Grede, N. Giebink, T. Mallouk, P. Mahale, N. Nova, Crespi, V. Gopalan: Department of Chemistry, Biochemistry and Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA A. Tomaschke, V. Ferguson: Mechanical Engineering, University of Colorado and NIST, Boulder, CO 80309, USA B. Abad: Current affiliation: Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
Resume : Phononic crystals are periodic arrays embedded in an elastic medium, arranged in a specific lattice symmetry that represent a very promising route for tuning the properties of next-generation nanoelectronics, thermoelectrics, and ultralight materials. Nanofabrication techniques can now produce metalattices, i.e., nanoscale phononic crystals with dimensions <<100 nm, that make it possible to engineer new physical properties . To synthesize these nanostructures, nanospheres are first assembled into a colloidal crystal with face centered cubic order. The interstitial space between the nanospheres is then infiltrated with another material, finally forming the metalattice structure. Measurement of the mechanical properties of such nanostructures to date have focused only on one component of the metalattice—either the template or the etched-out structures, and always for periodicities >100 nm. In this work, we present a nondestructive method to accurately extract, for the first time, the mechanical and structural properties of metalattices with much smaller feature sizes. In particular, we probe silicon metalattices fabricated from sphere diameters of 14 nm and 30 nm that contain feature sizes that are an order of magnitude smaller than opals that have been characterized to date. To investigate their mechanical and structural properties, we deposited a set of metallic gratings with linewidths as small as 50nm on top of the metalattice surface. In a pump-probe experimental setup, we use a 25-femtosecond infrared pump pulse to heat the gratings, which impulsively launch surface acoustic waves (SAW) in the metalattice. The wavelength of the SAW can be tuned by varying the grating periodicity, which also changes the SAW penetration depth into the metalattice and the silicon substrate. We then monitor the SAW frequency from the time-dependent change in diffraction of extreme ultraviolet ultrashort (<20fs) probe pulses, created by high-order harmonic generation , as a function of pump-probe delay time. This method allows us to simultaneously extract the acoustic dispersion, the Young’s modulus, thickness and filling fraction of the metalattice . Interestingly, these measured properties agree well with macroscopic predictions, while the transport properties of the same metalattices do not agree with bulk models. Additionally, the measured metalattice thicknesses agree with scanning electron microscopy images and the extracted Young’s moduli agree with nanoindentation measurements. This technique represents the only approach to date to nondestructively validate the filling fraction of deep-nanoscale metalattices. These results can enable precise fabrication, characterization and understanding of materials with tailored mechanical and transport properties.  Chen, W, et al. ACS Nano 14, 4, 4235-4243 (2020).  A. Rundquist et al., Science 280(5368), 1412–1415 (1998)  Abad, B., et al. Nano Lett. 20, 3306-3312, (2020)
Authors : Irdi Murataj, Marwan Channab, Eleonora Cara, Candido F. Pirri, Luca Boarino, Angelo Angelini, Federico Ferrarese Lupi
Affiliations : 1-2 Irdi Murataj; 1-2 Marwan Channab; 1 Eleonora Cara; 2 Candido F. Pirri; 1 Luca Boarino; 1 Angelo Angelini; 1 Federico Ferrarese Lupi 1 Advanced Materials and Life Sciences, Istituto Nazionale di Ricerca Metrologica (INRiM), Strada delle Cacce 91, 10135, Turin, Italy 2 Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, C.so Duca degli Abruzzi 24, Turin 10129, Italy
Resume : Hyperbolic metamaterials (HMMs) show exotic optical properties unattainable in bulk materials, enabling the opportunity for confinement and propagation of light at the nanoscale. To date, most of the HHMs are fabricated by sequential deposition and growth of alternating metal/dielectric layers. The optical axis of the so-obtained HMMs lies in the out-of-plane direction, thus preventing their exploitation into more complex photonic devices and circuitries. In-plane orientation of the optical axis, in the direction coinciding with the anisotropy of the HMMs, is desirable for a variety of novel applications in nanophotonics and imaging. Here, we introduce a method for creating localized HMMs with in-plane optical axis based on the dewetting of block copolymer (BCP)/homopolymer blend thin films. By exploiting the blend film instability over topographically defined substrates, droplets composed of highly ordered lamellar nanostructures in hierarchical configuration were obtained. The pattern transfer process onto a transparent and flexible substrate, generates a hybrid Au/air HMM with hyperbolic dispersion in broad wavelength range in the visible spectrum, crucial for the realization of novel smart nanostructured materials for future stretchable and wearable devices. A strong reduction in the fluorescence lifetime of defects in nanodiamonds placed on top of the HMM is supported by computed Purcell factor as high as 32 at 580 nm. This fast and low-cost method allows to obtain hybrid metal/dielectric nanopatterned substrates with in-plane optical axis whose orientation can be further tuned through the control of the dewetting process, suitable for on-chip integration.
N.V. Poster Session : O. Durand, M. Modreanu, G.E.Jellison
Authors : I. Stepanova, O. Petrova, G. Korolev, M. Guslistov, M. Zykova, I. Avetissov
Affiliations : D. Mendeleev University of Chemical Technology of Russia
Resume : The ferroelectric crystalline phase Bi2GeO5 has spontaneous polarization value comparable to BaTiO3 ceramics. To date, most researchers consider this phase to be metastable so it can be hardly synthesized by conventional crystal growth methods. We offer a new look at the phase formation in the Bi-Ge-O system, which considers Bi2GeO5 as an oxygen-deficient phase and makes it easy to synthesize from non-stoichiometric compositions. The Bi2GeO5 single phase has been successfully synthesized from Bi2O3-Bi-GeO2 batch when Bi oxide has been partially replaced by metallic Bi to form an oxygen deficiency. The crystallization was made both in solid phase and from melts at different temperatures. The structure of the formed crystal phases have been investigated by XRD. It was found that both the melt temperature rise and metallic Bi amount increase led to the formation of Bi2GeO5 single phase. The optimal initial batch compositions and crystallization conditions to produce a single Bi2GeO5 crystal phase has also been found. The research was supported by the Ministry of Science and High Education of the Russian Federation by the project FSSM-2020-0003.
Authors : Roik N.V., Belyakova L.A., Dziazko M.O.
Affiliations : Chuiko Institute of Surface Chemistry of NAS of Ukraine, 17 General Naumov Str., Kyiv, 03164, Ukraine
Resume : A typical strategy for MCM-41 synthesis consists of acid/base catalyzed sol-gel condensation of silica precursor that takes place in solvent in the presence of template as structure-directing agent. So, variation of synthesis conditions (temperature, stirring rate, aging time, microwave irradiation, hydrothermal treatment etc.) as well as chemical composition of reaction mixture gives great opportunities for regulation of morphology and structural parameters of mesoporous silica nanoparticles. As condensation of structure-forming silanes proceeds around supramolecular surfactant assemblies, template plays extremely important role in directing the formation of arranged mesoporous silica framework. Long-chain quaternary ammonium salts belong to the most widely used structure-directing agents in sol-gel synthesis of MCM-41 type silicas. Incorporation of auxiliary organic compounds into the surfactant aggregates, consisting of hydrophobic core and hydrophilic external surface lined with positively charged quaternary ammonium groups, causes changes in critical micelle concentration and configuration of mixed micelles in comparison with individual surfactant and, as a result, has substantial influence on mesoporous structure of silica materials prepared by template-assisted sol-gel synthesis. Taking into account the ability of organic additives to incorporate into the long-chain cationic surfactant micelles, we focused our attention on the effect of amphiphilic organic compounds (azo dyes, bile acids, cyclic oligosaccharides) as cosurfactants and their alkoxysilane derivatives as structure-forming silanes on mesoporous structure of silica materials obtained by template-assisted sol-gel synthesis. The effect of auxiliary agents on mesoporous structure of resulting silicas was estimated by low-temperature nitrogen adsorption-desorption and x-ray diffraction analysis. It was found that introduction of moderate amounts of amphiphilic organic additives or their alkoxysilane derivatives into sol-gel reaction mixture causes formation of silica materials with higher surface area and more distinct long-range ordering of mesopores. Observed pronounced effect on mesoporous structure of silica materials was explained by tight interactions arising between hydrophobic parts of amphiphilic organic compounds and long alkyl chains of cationic surfactant on the one side and between hydrophilic groups of additives and growing anionic oligomers of orthosilicic acid on the other side. Obtained results open up new opportunities for synthesis of MCM-41-type silica materials with improved structural characteristics.
Authors : A.Dvurechenskii, A.Yakimov, V.Kirienko, A.Bloshkin, A.Zinovieva, A.Nenashev, V.Zinovyev, A. Mudriy.
Affiliations : A.Dvurechenskii; A.Yakimov; V.Kirienko; A.Bloshkin; A.Zinovieva; A.Nenashev; V.Zinovyev Rzhanov Institute of Semiconductor Physics, 630090 Novosibirsk, Lavrentiev Av. 13, Russia. A. Mudriy Academy of Science of Belarus, P. Brovki 19, 220072 Minsk, Belarus.
Resume : The coupling of quantum dots (QDs) heterostructures with regular metal subwavelength gratings on the semiconductor surface was demonstrated to be powerful tool of photocurrent enhancement in mid-IR InAs/(In)GaAs and Ge/Si QDs photodetectors (QDIPs). Besides surface plasmon waves the Rayleigh anomaly are characteristic optical phenomena exhibited by periodic subwavelength grating structures. At present work a hybrid metal-dielectric metasurface is developed to improve the photoresponse of Ge/Si QDIPs. The structure consists of a regular array of silicon pillars protruding through subwavelength holes in a periodically perforated gold film on detector top. Compared with a bare QDIP, the peak responsivity of the hybrid detector at a wavelength of 4.4 µm is increased by a factor of 15. The enhanced sensitivity is supposed to arise from coupling of the surface plasmon resonance and diffractive effect of Rayleigh anomaly. The hybrid structures containing Ag nanoparticles over SiGe QDs layer were developed using self-organization of metal nanoislands on the surface of a strained semiconductor structure. Enhanced photoluminescence from SiGe QDs coupled with Ag nanoislands was found. Ag nanoislands grown on the top of the multilayered structures with SiGe QDs support a surface plasmon resonance that can be tuned to the QDs emission wavelength by changing of Ag nanoparticle parameters. Modeling of surface plasmon resonance allows attributing this effect to the increase of the recombination rate due to electromagnetic field enhancement in QDs layer. This work is funded by Russian Science Foundation, grant No.19-12-00070.
Authors : Butenkov D.A., Shelukhina D.N., Runina K.I., Petrova O.B., Avetisov R.I., Avetissov I.Ch
Affiliations : Mendeleev University of Chemical Technology
Resume : Oxyhalide glasses are used both as luminescent and laser materials and as precursors to obtain glass-ceramics with a halide crystalline phase. The addition of fluorides or chlorides into the composition of glasses makes it possible to change the properties of glasses over a wide range - to expand the transparency range of glasses, to change the mechanical properties and viscosity of melts. Optical halide materials with a low-frequency phonon spectrum, doped with ions of rare-earth elements, are of great interest for IR applications. The transfer from oxofluoride glasses to oxochloride glasses should a decrease in the phonon energy, an expansion of the transparency range, and the production of luminescence in regions of spectra where this is impossible in oxide and oxofluoride systems. Doping with neodymium makes it possible to obtain luminescence both in the near infrared region and in the middle - at 2.6 and 5.2 microns. Moreover, the last band appears only in media with low-energy phonons, for example, in PbCl2. Lead oxochloride glasses, in contrast to oxofluoride glasses, has been much less studied. Based on a very wide field of vitrification in lead oxofluoride systems, in our work we decided to synthesize glasses based on PbF2-PbO-B2O3 (SiO2) systems by partially replacing PbF2 with PbCl2. Synthesized high-quality glass with a maximum PbCl2 content of 50 mol% in both chloroborate and chlorosilicate systems. In experiments with a higher concentration of PbCl2 in the charge, polycrystalline castings were obtained containing the crystalline phases PbCl2, Pb2OCl2, PbFCl. The absorption spectra of glasses doped with neodymium have all absorption bands typical of Nd. A detailed examination of individual transitions showed that for them the wavelength of the maximum shifts to longer wavelengths with the replacement of fluorine by chlorine. The luminescence spectra also show a shift in the maximum of the transition to longer wavelengths by more than 7 nm. In this case, as the chlorine content increases, the intensity of the long-wavelength components associated with transitions to excited sublevels increases. The shift to longer wavelengths depends on the ratio of the concentrations of lead chloride and fluoride; the larger the proportion of PbCl2, the greater the shift to longer wavelengths. The properties of the glasses were modified by heat treatment above the glass transition temperature and by exposure to laser radiation. During the modification, partial crystallization of the glasses is observed. This work was financially supported by the Ministry of Science and Higher Education of the Russian Federation within the FSSM-2020-0005 project.
Authors : M.N. Shamis*, P.V. Makushko*, I.D. Biesiedin*, I.E. Kotenko**, S.I. Sidorenko*, T.I. Verbytska* and Yu.N. Makogon*
Affiliations : * Igor Sikorsky Kyiv Polytechnic Institute, Department of Physics of Metals, Peremogy av. 37, 03056, Kyiv, Ukraine; ** L. V. Pisarzhevskii Institute of Physical Chemistry of National Academy of Sciences of Ukraine
Resume : FePt thin films are of high interest as a promising material for ultrahigh density magnetic recording media in data storage and HAMR application due to a high magnetocrystalline anisotropy, high values of saturation magnetization and corrosion resistance of ordered L1₀-FePt phase. The aim of the present work is an investigation of the effect of the additional Au(7.5 nm) layer which located as top, intermediate or bottom of FePt(15 nm) layer on phase formation, A1-FePt→L1₀-FePt transformation and structure in FePt-Au thin films during annealing in situ in the temperature range of 20 °C-700 °C Au/FePt, FePt/Au/FePt and FePt/Au thin films, as well as the reference FePt(15 nm) sample, were deposited by magnetron sputtering (Ar pressure 3.5×10^(-3) mbar) from individual Fe, Au and Pt targets onto Si(001)/SiO₂(100 nm) substrates kept at a room temperature. After deposition films with different location of Au layers, were separated from Si(001)/SiO₂(100 nm) substrates by etching in a mixture of HNO₃ and HF acids. Free films were placed onto Cu grids for TEM and then investigated by HEED method during annealing inside electron diffraction camera. The phase composition and structure of as-deposited and annealed in situ films were investigated by TEM as well. It was established that the location of the Au layer in the as-deposited film composition affects the stress in the FePt layer, parameters of its grain structure and ordering temperature of L1₀-FePt phase formation. In the separated from substrate films, the compressive stresses arise in FePt grains only due to the diffusion of gold along the FePt grain boundaries during annealing in situ. Compressive stresses contribute to the formation of the L1₀-FePt phase in accordance with the Le Chatelier rule, since the unit cell volume of this phase is less than that of disordered A1 – FePt. The lowest temperature (300 °C) of the beginning of L1₀ phase formation is observed in FePt/Au/FePt films with an intermediate Au layer.
Authors : V.Gubanov, A.Naumenko, I.Dotsenko, L.Bulavin
Affiliations : Taras Shevchenko National University of Kyiv
Resume : The projective two-valued representations of spinor states for different points of Brollouin zones of crystalline graphite and single-layered graphene as well as of boron nitride (BN) and nitroborene have been constructed for the first time. Projective classes, which transform spin-dependent electronic wave functions at the points of high symmetry of the Brillouin zone have been determined for the above-mentioned structures. For the establishment of projective classes we found the method of constructing of factor systems, in particular, the correct factor system for spinor representations; the form of standard factor systems and the phase factors for their conversion to standard factor systems for each projective class have been found. The dispersion of the electronic states of these structures has been investigated by using the symmetric theoretical group methods. It is shown that the results of the developed methods of theoretical-group analysis are consistent with the data of experimental and computational studies of energy spectra and multiplicities of degeneration of quantum states of pi-electron zones.
Authors : N.Kornienko1 , A.Naumenko1, V.Gubanov1, L.Kulikov2, O.Kolomys3, A.Nikolenko3
Affiliations : Taras Shevchenko National University of Kyiv, Frantsevich Institute for Problems of Materials Science of NAS of Ukraine, V.E. Lashkaryov Institute of Semiconductor Physics NAS of Ukraine
Resume : Our research is based on two major scientific and technical problems: 1) the use of unique physicochemical properties of two-dimensional (2D) structures of graphene, BN and transition metals dichalcogenides of (TMD) MeX2, where Me - metals of IV, V and VI groups (Ti- Hf, V-Ta, Mo, W), and X = S, Se, Te, as well as 2) enhancing their capabilities during intercalation by impurity atoms and molecules. The results of a detailed study of the Raman spectra of natural MoS2 microcrystal (MC) powder and synthesized graphene-like 2H-MoS2 nanoparticles (NP) with additives 0.5 and 1 wt% of carbon excited by 488 nm and 632.8 nm laser radiation are highlighted here. A detailed numerical analysis of the shape of the observed D and G Raman bands, including their decomposition into spectral components, as well as comparison with the reference spectra of the detonation nanodiamonds of ~ 5 nm, is carried out. This revealed the formation of graphite and diamond-like nanostructures in MoS2 NC and their existence in molybdenite MC. Significant effect of 632.8 nm laser radiation that is in resonance with 2H-MoS2 excitons on synthesis and ordering of diamond and graphite-like structures was established for the first time
Authors : Jose Manuel Sojo Gordillo (a), Jaime Segura Ruiz (b), Valentina Bonino (b), Carolina Duque Sierra (a), Alex Morata (a), Albert Tarancón (a,c)
Affiliations : (a) - Department of Advanced Materials for Energy, Catalonia Institute for Energy Research (IREC), Jardí de les Dones de Negre 1, Sant Adrià de Besòs, 08930 , Spain.; (b) - ESRF, European Synchrotron Radiation Facility, 71 Avenue des Martyrs, 38043, Grenoble, France; (c) - Catalan Institution for Research and Advanced Studies (ICREA), Passeig Lluís Companys 23, 08010, Barcelona, Spain;
Resume : Among Chemical Vapor Depositions techniques, Vapour-Liquid-Solid (VLS) Gold-catalysed processes have been widely used to fabricate bottom-up Si nanowires (NWs). These 1D nanostructures improve the intrinsic thermoelectric (TE) properties of bulk Si and can be integrated into micromachined TE generators (μTEGs) . However, NWs of SiGe alloys have always been more desirable thanks to their reduced thermal conductivity and, consequently, better TE Figure-of-Merit. Nevertheless, so far, these grow processes require relatively low growth temperatures (over 650 K); thus, they are slow and not suitable for integrating NWs into μTEGs. The correct doping of such NWs has resulted in being problematic too. Here we present a novel VLS methodology to grow in-situ heavily boron-doped SiGe NWs up to 15 μm long at a rate higher than 100 nm/min. This is the result of a combination of flows that include the use of borane, chloride acid, relatively low pressures (~ 300 Pa), and temperatures above 900 K. These NWs are easily integrated into μTEGs, and the improvement in the device's performance from Si NWs to SiGe ones have been evaluated. Moreover, the effect of boron impurities in the growth process has been assessed. X-ray fluorescence mapping of these NWs has revealed trends in the compositional properties, likely related to the morphological changes observed. Among those, maximum thresholds in the boron content for this VLS process can be highlighted. Beyond them, the catalyst gold amount trapped into the SiGe lattice dramatically increases, degrading the electrical conductivity and, thus, the TE properties. Additionally, hydrochloric acid's increased presence has shown to have positive effects in avoiding this phenomenon. Understanding this phenomenon is essential to overcome this limit and further improve the already encouraging results showed by this material . References:  G. Gadea et al., "Towards a full integration of vertically aligned silicon nanowires in MEMS using silane as a precursor," Nanotechnology, vol. 26, no. 19, p. 195302, May 2015.  I. Donmez Noyan et al., "SiGe nanowire arrays based thermoelectric microgenerator," Nano Energy, vol. 57, pp. 492–499, Mar. 2019.
Authors : M. Kria(a), J. El Hamdaoui(a), E. Feddi(a), L.M. Pérez(b), D. Laroze(b),
Affiliations : a) Group of Optoelectronic of Semiconductors and Nanomaterials, ENSET de Rabat, Mohammed V University in Rabat, Morocco. b) Instituto de Alta Investigación, CEDENNA, Universidad de Tarapacá, Casilla 7 D, Arica, Chile.
Resume : We study of the nonlinear optical and electronic properties in cylindrical core/shell quantum dots AlAs/GaAs in the presence of a donor impurity under a magnetic field. Our computations were carried out within the effective mass approximations. For the numerical solution of the resulting 3D partial differential equation (PDE) via finite element method. A detailed study of the donor binding energies as a function of the magnetic fields and impurity position is determined. Dipole matrix elements related inter-level optical transitions is investigated in order to analyze the absorption coefficient, second and third harmonic generation. Our results show that the magnetic fields have significant influences on the binding energy and on the linear and nonlinear optical properties.
Authors : L. Nedelcu, C. D. Geambasu, M. G. Banciu, M. Burdusel, M. A. Grigoroscuta, P. Badica
Affiliations : National Institute of Materials Physics, Atomistilor 405A, 077125 Magurele, Romania
Resume : The Zr0.8Sn0.2TiO4 (ZST) ceramics are very attractive for microwave (MW) applications, being successfully employed in dielectric resonator (DR) based devices. However, the use of ZST materials can be limited due to their extrinsic dielectric loss. Therefore, determination of the extrinsic and intrinsic losses is essential to decide when a synthesis cycle should be stopped. In this work, we present and discuss the THz and MW properties of the ZST ceramics obtained by conventional ceramic technology (CCT) and spark plasma sintering (SPS). The ZST-DRs obtained by CCT and SPS have shown relative densities of 96.5 % and 99.5 %, respectively. Structural, morphological, and dielectric characterizations of the samples were performed by X-ray Diffraction, Scanning Electron Microscopy, MW spectroscopy, and Terahertz Time-Domain Spectroscopy (THz-TDS). The ZST samples present no secondary phases and their lattice exhibit an orthorhombic unit cell. The SEM micrographs show that a segregation of pores occurs in the samples when the sintering time increases. The dielectric measurements show a change between extrinsic and intrinsic losses depending on the frequency band: in MWs, a substantial contribution is given by the extrinsic losses, while the THz measurements actually provide mainly information on the intrinsic losses. The intrinsic losses (Q × f ~ 60 THz) of the ZST DRs have been derived from THz data. The THz-TDS is shown to be a very useful technique for estimation of intrinsic losses of MW dielectrics, ensuring a fast screening of new materials. Acknowledgments: This work was supported by a grant of the Romanian Ministry of Education and Research, CCCDI - UEFISCDI, project number PN-III-P2-2.1-PED-2019-3351, within PNCDI III.
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N. VI Novel nanoscale materials : O.Durand, N. J. Podraza
Authors : N. Barreau (1), E. Gautron (1), O. Durand (2), A. Létoublon (2), C. Cornet (2), R. Bernard (2), D. Lincot (3)
Affiliations : (1) Université de Nantes, CNRS, Institut des Matériaux Jean Rouxel, IMN, F-44000 Nantes, France (2) Université de Rennes, INSA Rennes, CNRS, Institut FOTON – UMR 6082, F-35000 Rennes, France (3) CNRS, Institut Photovoltaïque d'Ile de France (IPVF), 18 boulevard Thomas Gobert, 91120 Palaiseau, France
Resume : Fabrication of tandem solar cells by combining mature c-Si and Cu(In,Ga)Se2 (CIGSe) thin film photovoltaic technologies is among the valuable routes to achieve 30 % efficiency within the next decade. This approach can be successful only if (i) devices based on 1.6-1.7 eV bandgap C(I)GSe absorber layers reach efficiencies higher than 15 % (ii) Si/C(I)GSe heterointerface are optimized. So far, the main drawback to CuIn1-xGaxSe2-based devices is the relatively low efficiency achieved with absorbers whoe bandgap is wider than 1.5 eV (i.e. x > 0.7). Many models were proposed during the last decades to explain the origins of those lowered performance; most of them blame detrimental grain boundaries, local inhomogeneities, and recombinative heterointerfaces. To overcome these issues, we propose an orignal approach consisting in growing by coevaporation CuIn1-xGaxSe2 (with x > 0.8) onto epi-III-V/c-Si plateforms. This approch offers at least two advantages, namely minimizing the density of crystalline defects thanks to epitaxial growth, and use the epi-III-V as selective contact to minimize detrimental heterointerface recombinations. For our first attempts, we used epi-GaP/c-Si(001) as plateform and we could achieve epitaxial CuIn0.1Ga0.9Se2 growth. The presentation will give an overview of the process used, the results of characterizations, as well as the first device performance.
Authors : Jacky Even
Affiliations : Univ Rennes, INSA Rennes, CNRS, Institut FOTON - UMR 6082, F-35000 Rennes, France
Resume : The presentation will describe recent experimental and theoretical results for 3D and 2D bulk halide perovskites and QD nanostructures, including symmetry analyses and DFT computations of electronic states coupled with spectrocopy (PL, TRPL) and diffraction (X-Ray, Neutrons) studies. The presentation will adress the ongoing debate about the nature of the exciton ground state in perovskite QD.
Authors : Laurent Lombez,1,3, Adrien Bercegol,1,4, Stefania Cacovich,1,3, Armelle Yaiche,1,2, Guillaume Vidon,1,4, Jean-Baptiste Puel,1,4, Christophe Longeaud,1, Sébastien Jutteau,1,4, Daniel Suchet,1,2,3, Jean-François Guillemoles,1,3, Jean Rousset,1,4, Daniel Ory,1,4
Affiliations : 1 Institut Photovoltaique d’Ile de France (IPVF), 18 boulevard Thomas Gobert, Palaiseau, France; 2 CNRS, Ecole Polytechnique, Institut Photovoltaïque d’Ile-de-France UMR 9006, 18 boulevard Thomas Gobert, 91120, Palaiseau, France; 3 CNRS-Institut Photovoltaique d’Ile de France (IPVF), UMR 9006, 18 boulevard Thomas Gobert, Palaiseau, France; 4 EDF R&D, 18, boulevard Thomas Gobert, 91120, Palaiseau, France;
Resume : The excellent photovoltaic performance of halide perovskites goes along with a high photoluminescence yield (PL) that makes them suitable for a wide range of photonic devices and various optoelectronic applications, such as photodetectors, lasers and light emitting diodes. However, due to the complexity of the materials and the related devices, often traditional macroscopic characterization tools are not able to unveil the physical processes underlying the working principles of the solar cells, especially transport properties. Indeed, electronic as well as ionic transport are still under investigation and can be blurred by photonic effect. Here we quantify in depth transport then in plane transport by means of multidimensional imaging techniques. To go further in the in plane case we investigate electrons, holes and ions transport. We used innovative characterisation methods that combine hyperspectral imaging system (HI) and a time-resolved fluorescence imaging (TR-FLIM) set-ups. We employed these optical techniques to study charge carriers transport in hybrid perovskites and probe a large variety of transport parameters (diffusion length, mobility, lifetimes…) which are often cross-linked. Photonic transport is also observed and the experimental impact will be discussed. Besides, measuring the local variations of time resolved luminescence in the nanosecond scale under lateral electric bias allows a direct access to charge carrier collection and transport properties for each kind of charge carrier –electrons and holes-. At long time scale such experiment allows to probe the ionic transport, especially associated with iodine species. More precisely, the iodine seems to affect the band structure and locally modify the bandgap; it also degrades the local quasi Fermi level splitting (i.e. the internal bias). The novel experimental approach, can thus image and quantify the transport mechanisms occurring within the material (even under aging procedure), providing new insights on these complex transport phenomena.
Authors : Mircea Dragoman (1)*, Daniela Dragoman (2), Adrian Dinescu (1)
Affiliations : (1)National Institute for Research and Development in Microtechnologies (IMT Bucharest), Erou Iancu Nicolae Street 126A, 077190 Voluntari (Ilfov), Romania (2)Univ. of Bucharest, Physics Faculty, P.O. Box MG-11, 077125 Bucharest, Romania
Resume : This talk will be dedicated to the new and emerging area of 2D materials having important applications in nanoelectronics. The discovery of HfO2- based ferroelectrics has as the main impact the CMOS compatible fabrication of high frequency HfO2-based devices such as phase-shifters, antenna arrays or filters with a high degree of tunability and miniaturization. The transfer of 2D materials on HfO2 ferroelectrics has demonstrated new physical effects such as the opening of the bandagap in graphene monolayers of 0.2 eV, very high mobility of FETs based on graphene/HfZrO ,enhanced memory performances and memrsistive effects. The authors acknowledge the financial support via project no.. PN-III-P4-ID-PCCF-2016-0033 –GRAPHENEFERRO.
Authors : C. Corley(1), C. Richter(2), A. Wiciak(1), Y. Liu(2), M. H. Zoellner(1), D. Spirito(1), Y. Yamamoto(1), E. Zatterin(3), T. Schuelli(3), N. W. Hendrickx(4), A. Sammak(5), M. Veldhorst(4), G. Scappucci(4), G. Capellini(1),(6), W. M. Klesse(1)
Affiliations : (1) IHP – Leibniz-Institut für innovative Mikroelektronik, Im Technologiepark 25, D-15236 Frankfurt(Oder), Germany; (2) IKZ – Leibniz -Institut für Kristallzüchtung, Max-Born-Straße 2, D-12489 Berlin, Germany; (3) ESRF – European Synchrotron Radiation Facility, 71, avenue des Martyrs, CS 40220, 38043 Grenoble Cedex 9, France; (4) QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands; (5) QuTech and Netherlands Organisation for Applied Scientific Research (TNO), Stieltje-sweg 1, 2628 CK Delft, The Netherlands; (6) Dipartimento di Scienze, Universita Roma Tre, Roma 00146, Italy
Resume : Hole spins in Ge/SiGe heterostructures are promising for large-scale integration of solid state qubits in a CMOS compatible material system, due to the demonstration of high coherence times and multi-qubit algorithms. From the materials point of view one key requirement for realizing large arrays of qubits with shared gate control is a high degree of homogeneity in strain and crystal quality in the Ge quantum well (QW) hosting the qubits. Local fluctuations of the lattice strain affect the electrostatic potential in the QW and, likely, the qubit properties. Here, we leverage Scanning X-ray Diffraction Microscopy (SXDM) and Raman mapping to investigate non-destructively and with high spatial resolution the strain homogeneity in a SiGe /Ge/SiGe heterostructure housing the quantum processor used to demonstrate fast two-qubit logic with holes in Ge. The layer stack was grown epitaxially on a 100 mm Si wafer by RP-CVD, comprising a plastically relaxed Ge virtual substrate, a step-graded Si1-xGex layer, a plastically relaxed Si0.2Ge0.8 buffer, a 16 nm fully strained Ge QW, a 22-nm-thick SiGe barrier and a sacrificial Si cap (< 2nm). Ti/Pd gate electrodes were fabricated on top of the stack by e-beam lithography and lift-off and isolated electrically with an atomic layer deposited dielectric. SXDM measurements were carried out at ID01/ESRF. The improved brilliance after the EBS upgrade enabled us to map the local lattice constants in the thin QW with a spatial resolution below 100 nm. We chose an X-ray energy of 9.3 keV to measure the 335 Bragg reflection at grazing incidence, ensuring high sensitivity for the QW close to the sample surface. We took maps of multiple reflections from the 335 family in the same region of the device, allowing us to extract quantitative values for lattice strain and rotation by overlapping the maps for the different reflections. From the lattice displacement for each reflection, we calculate relative changes of both in-plane and out-of-plane lattice constants of approx. 0.04 % caused by electrodes and misfit dislocations. This variation is shown to be larger than the fluctuations within the unperturbed QW by at least an order of magnitude. Furthermore, the SXDM data substantiates the results from Raman shift measurements performed at an excitation wavelength of 532 nm with a 500 nm spot. The techniques demonstrated provide locally resolved, non-destructive means of characterizing strain variations in Ge/SiGe heterostructures. Our results give insight on their origin and degree, affecting the local potential experienced between different qubits. Material-related inhomogeneities must be taken into account in the optimization of heterostructure growth and design of qubit architectures for scaled CMOS-compatible quantum computing. Scappucci et al, Nat Rev Mater https://doi.org/10.1038/s41578-020-00262-z, 2020 Hendrickx et al, arXiv:2009.04268, 2020 Hendrickx et al, Nature 577 (7791), 487-491, 2020
Authors : Sara Roman-Sanchez (1), Aida Serrano (1), Jesús Lopez-Sanchez (2,3), Adolfo del Campo (1), Juan Rubio-Zuazo (2,3), Israel Lorite (4), José F. Fernández (1), Alberto Moure (1)
Affiliations : (1) Instituto de Cerámica y Vidrio (ICV), CSIC, E-28049 Madrid, Spain; (2) Spanish CRG BM25-SpLine at The ESRF, The European Synchrotron, F-38000 Grenoble, France; (3) Instituto de Ciencia de Materiales de Madrid (ICMM), CSIC, E-28049, Madrid, Spain; (4) SEG Automotive Germany GmbH, G-70499, Stuttgart, Germany
Resume : Press-fit rectifier diodes have a great importance in the field of semiconductor-based technology. They usually form part of the vehicle alternator, which converts mechanical energy into electrical one, and its main function is to transform the alternating current into direct current, which is the suitable one to provide power to the vehicle electrical system. Under working conditions, diodes can reach high currents with small forward voltages and must be capable of withstand high reverse currents without breaking down. However, they are multicomponent devices, made up with different materials (epoxies, metals and semiconductors, joint by a Pb-Sn solder) that show different physical characteristics (thermal conductivity, elasticity or thermal expansion coefficient) and, thus, different behavior against the temperature increase associated with the high currents reached. These characteristics can lead to the appearance of important effects at the device interfaces, such as mechanical stress, which can cause failures on the system and, therefore, its lifetime reduction. The aim of this work is to understand the behavior at the interfaces between the different components of several press-fit rectifier diodes under usual in-operando conditions, as well as to understand their more common failure modes in order to improve the diode performance. For that, several in-situ experiments on the rectifier diodes with different design and technologies have been carried out using several techniques. Confocal Raman microscopy, grazing incidence x-ray diffraction with synchrotron radiation and infrared thermography have allowed an in-operando study of the diodes both in forward biased and reverse biased conditions. The results show the mechanical stress caused at the device interfaces by the electrical current, changes on the lattice parameter and some system failure modes.
Authors : Ioanna Dimkou1, Enrico Di Russo1, Pradip Dalapati2, Jonathan Houard2, Nevine Rochat1, David Cooper1, Edith Bellet-Amalric3, Adeline Grenier1, Eva Monroy3, and Lorenzo Rigutti2
Affiliations : 1 Univ. Grenoble Alpes, CEA, LETI, F-38000 Grenoble, France; 2 UNIROUEN, CNRS, Groupe de Physique des Matériaux, Normandie Université, 76000 Rouen, France; 3 Univ. Grenoble-Alpes, CEA, IRIG-PHELIQS, 38000 Grenoble, France
Resume : InGaN quantum wells (QWs) and quantum dots (QDs) form the active region of III-nitride LEDs for lighting or display applications. The localization of carriers in intentional (QDs) or unintentional (alloy fluctuations) quantum confined systems plays a crucial role in the optical properties of these devices, since it has an impact on the emission wavelength and eventually the recombination efficiency. To understand and control these processes, it is necessary to visualize their chemical properties at the nanometer scale and obtain a direct correlation of alloy distribution and optical features. In this direction, an advanced version of laser-assisted atom probe tomography (APT) allows to record the variation of the micro-photoluminescence (µPL) spectrum of the specimen, during its evaporation. This innovative approach allows gaining new insight into the correlation between the correlative investigation of the spectral emission of the QDs and their structural and chemical features. This study presents a major challenge, since little is known about their shape, the thickness of their wetting layer and the distribution of indium in the QD wetting layer ensemble. Here, we report the characterization and modelling of a 40-period InGaN/GaN QD superlattice grown by plasma-assisted molecular beam epitaxy on a commercial GaN-on-sapphire template. Combining the result of transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and APT, we obtain a complete description of the QD structure. Thus, TEM and AFM measurements point to a wetting layer around 1.1 nm, a QD diameter of in the range of 12-17 nm, and a QD height above the wetting layer around 0.9 nm. The precise superlattice period (12.6±0.1 nm) is extracted from XRD, and the In content of the QDs and of the wetting layer (13% and 6%, respectively) from APT. The model of the QD structure was validated by the in-situ µPL spectra, presented a multi-peak structure around 411 nm due to in-plane fluctuations of the indium content in the QDs and the dispersion of the QD diameter. The in-situ µPL was analyzed during the APT evaporation of the last 15 QD layers. The QD emission lines present a red shift of around 2 nm during the APT process of the last 9 QD layers, which is assigned to the relaxation of strain. In summary, the excellent agreement between the theoretical calculations and the experimental optical features show that the model extracted from structural and chemical characterization provides a good description of this InGaN/GaN QD system. These results confirm the potential of correlated microscopy studies including APT to provide a complete view of three dimensional nanostructures and nanostructured materials.
Authors : Alexander E. Ganzha (1), Georgiy A. Lityagin (1), Alexander F. Vakulenko (1), Dasgupta Arvind (2), Gao Ran (2) and Roman G. Burkovsky (1)
Affiliations : 1. Peter the Great St.Petersburg Polytechnic University (SPbPU), St.Petersburg, Russian Federation. 2. Materials Science and Engineering, University of California, Berkeley, Berkeley, CA, United States.
Resume : Functional dielectrics occupy a significant niche in modern industry. For a wide class of such materials, practically significant properties are determined by the presence of structural phase transitions. Due to the phase switching in thin-film heterostructures of such materials, it is possible to implement a number of promising electromechanical, electrocaloric, energy storage and memory devices. However, in some materials, such as PbZrO3, when going from bulk to thin films, strong deformations of lattice and defects caused by the difference in the cell parameters of the film and the substrate lead to a smearing of the field-induced phase transition between antiferroelectric and ferroelectric structures. The mechanism of this smearing has not yet been established. Phase transition smearing should lead to some structural changes occurring under the field. To identify these changes we propose the method of X-ray scattering with in-situ application of the field. A diffraction experiment is set up with the simultaneous application of an electric field of up to 225 kV/cm to a thin-film PbZrO3 (50 nm) / SrRuO3 (20 nm) / SrTiO3 heterostructure oriented along (001) grown by pulsed laser deposition at the University of California at Berkeley. The experiment was performed using a SuperNova (Rigaku) single-crystal diffractometer. A new intermediate ferrielectric-like phase was discovered. New phase is forming in this thin-film heterostructure when a sufficiently strong electric field is applied, but not strong enough for the antiferroelectric to ferroelectric transition. The field dependence of the integral intensity at the q ⃗ = (1/4, 1/4, 0), q ⃗ = (1/2, 1/2, 1/2), q ⃗= (1/8, 1/8, 0) and q ⃗ = (3/8, 3/8, 0) wave vectors and observability conditions for superstructural reflexes, indicates that the formation of a new structure is associated mainly with reconfiguration of lead ion displacement pattern while the oxygen octahedra subsystem remains unaffected. After simulating all relevant configurations of the lead ions displacements, the structure of the new phase consists of eight layers of lead ions, ordered as ↑↑↑↑ ↓↑↑↓. New phase plays a role in smearing of the antiferroelectric to ferroelectric transition in such films. It has a nonzero polarization due to its ferrielectric nature, and its gradual formation with increasing field should lead to an accelerated increase in the registered polarization until the critical field is reached.
Authors : Wen-Shan Zhang, Maik Matthiesen, Lutz, H. Gade, Jana Zaumseil, Rasmus R. Schröder
Affiliations : W.-S. Z.; M. M.; J. Z.; R. R. S.: Centre for Advanced Materials, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 225, 69120 Heidelberg, Germany. M. M.; J. Z.: Institute for Physical Chemistry, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany. L. H. G.: Institute of Inorganic Chemistry, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.
Resume : Over the last decades, organic semiconductors have drawn great attention for potential applications in optoelectronic devices. One of the key properties for realizing high-performing devices is a good charge-carrier mobility, which is usually determined from the characteristics of organic thin-film transistors (OTFTs). The measured mobility is, however, a device-dependent value and not only an intrinsic property of the material itself. Defects occurring during thin-film deposition can lead to a significant underestimation of the charge-carrier mobility. This clearly limits the establishment of structure-property relationships and thus the rational design of novel materials with optimized performance. To discover morphological defects, microscopic and spectroscopic methods are commonly employed to provide static information on thin-film morphology, that we believe to give an incomplete picture of the real system, since charge transfer processes are dynamic in nature. Herein, we present a novel dynamical analytic method, using ultra-low voltage scanning electron microscopy (Project Delta-SEM, Zeiss Microscopy) [1,2] to create in-situ charges in the active layer of an OTFT and thus to derive the resulting dynamic information on charge transport. We visualize the flow path of the in-situ generated charges to source and drain contacts and thus distinguish active paths from mute regions resulting from morphological defects. The active paths are taken into account in the recalculation of the effective channel width and the correction of the measured mobility values. These measured mobilities obtained from various OTFT devices built with the same organic semiconductor were corrected accordingly, resulting in a lower standard deviation of the charge mobility than that derived from the raw data. References: 1. Steigerwald, M. et al. Frontiers of Characterization and Metrology for Nanoelectronics 51-55 (2013). 2. Schröder, R. R. et al. Microsc. Microanal. 24, 626-627 (2018).
Authors : Vladimirov Mikhail (1), Ganzha Alexander (1), Burkovsky Roman (1), Pavlenko Anatoly (2), Ter-Oganessian Nikita (3)
Affiliations : (1) Peter the Great St.Petersburg Polytechnic University (SPbPU), St.Petersburg, Russian Federation. (2) Federal Research Centre The Southern Scientific Centre of The Russian Academy of Sciences (SSC RAS), Rostov-on-Don, Russian Federation. (3) Southern Federal University, Rostov-on-Don, Russian Federation.
Resume : In recent years, the attention of many researchers has been attracted by perovskite crystals as promising compounds for high-density energy storage (super-capacitors) and memory applications (FeRAM). The transition from bulk to film samples is interesting because of the emerging epitaxial tensions, which lead to significant modification of many properties, including domain configuration. NaNbO3 (NNO) films are of particular interest because of their environmental friendliness. Bulk NNO is rich for its phase diagram and, at room temperature, ferroelectric Q and antiferroelectric P phases are present. But there is no understanding of the structure and domain configuration in thin films of NaNbO3, which is critical, since all this determines the macroscopic effects and properties. The purpose of the study is to determine characteristics of domain configuration in sodium niobate film. NaNbO3(200nm)/SrRuO3(20nm)/(001)MgO(0.5mm) heteroepitaxial structure was grown by RF sputtering method and characterized using the single crystal diffraction method in grazing incidence geometry on Rigaku SuperNova diffractometer. A 3D reciprocal space mapping approach was used to analyze superstructure reflections and diffuse scattering. Analysis of superstructure reflections made it possible to determine the phase, while diffuse scattering - possible domain configurations in NNO film. Characteristic presence and absence of superstructure reflections confirm that we see ferroelectric Q phase. The only observable superstructural reflections at the R and M positions of the pseudocubic Brillouin zone, due to conditions of their observability, are caused by antiphase and phase tilts of the oxygen octahedra (R5- and M2 modes, respectively, Na corresponds to the center of the unit cell). Cationic dipoles, according to diffraction patterns, are oriented in one direction from unit cell to unit cell, which makes the structure polar, without a center of symmetry. Diffuse scattering indicates that the polarization vectors in the unit cell of film NNO are directed in the ±[-101], ± and ±[0-11], ±, while the domain walls are parallel to x0z, y0z planes and there are no domain walls parallel to x0y plane (normal to film is [0 0 1]). Diffuse scattering is represented by relatively weak, but clearly visible intensity rods stemming from the center of the pseudocubic Brillouin zone in the  and  directions (correspond to y0z and x0z planes, respectively). No intensity rods in the  direction were found (corresponds to x0y plane). The intensity along the rod decreases uniformly with distance from the parent reflection and has no maximum, except there. The approach we used made it possible to determine both the structure and characteristics of the domain configuration in thin-film sodium niobate. The result indicates the promising nature of this method and the possibility of its use as a tool during interaction with thin-film structures.
N.VII Special Session H2020 PHEMTRONICS : Kurt Hingerl, Mircea Modreanu
Authors : Maria Losurdo,1 Wolfram Pernice,2 Kurt Hingerl,3 Christoph Cobet,3 Fernando Moreno,4 Marin Gheorghe,5 Guy Gary,6 Jordi Soler7 and Mircea Modreanu8
Affiliations : 1. Institute of Nanotechnology, CNR_NANOTEC, Bari, Italy 2. Physics Institute / CeNTech, Munster University, Munster, Germany 3. Johannes Kepler University, Linz, Austria 4. Department of Applied Physics, University of Cantabria, Santander, Spain 5. NANOM MEMS srl, Bucharest, Romania 6. TEOX, Paris-Saclay, France 7. VLC Photonics, Valencia, Spain 8. Tyndall National Institute, University College, Cork, Ireland
Resume : Active phase change matter with reliable, reconfigurable and interactively tunable dynamical properties is required for future adaptive photonic signal processing to overcome the bandwidth and speed limitations imposed by conventional carrier-based technology. We have established a European Consortium, PHEMTRONICS, that has the ambitious vision of creating a unique path for translating forefront knowledge in phase-transformation dynamics in “light controllable active matter with reconfigurable and interactively tunable dynamical properties” into extreme broadband reconfigurable and adaptive ultrafast switches, antennas and photodetectors devices The aim is to exploit photon-electron-phonon coupling to enable a new technology paradigm of adaptive optical signal processing with key metrics of the “femtosecond scale switching time”, “ultralow power of femtojoule/bit” and “microwave-to-optical frequencies” broadband capability To accomplish this vision, we use photons from NIR to VISIBLE range to activate phase-transformation dynamics and tune optical properties of two-dimensional phase change materials. In this contribution, we will present recent achievements of the consortium in the synthesis of novel two-dimensional materials such as GaS, MoS2, MoOx, VO2, etc.. by several routes of mechanical exfoliation, chemical vapor deposition, atomic layer deposition and solution-based methods (e.g. chemical/electrochemical/laser assisted deposition). The use of optical probes is threefold: 1) determining the correlation between structural-phase and optical response of those new materials; 2) activate the phase transformation and 3) probe their phase change dynamics. To this regard, multi-scale and complementary characterization techniques such as Raman spectroscopy also spatially resolved, spectroscopic ellipsometry from NIR to UV, Mueller Matrix, infrared imaging, confocal Raman and RAS microscopy, and time resolved spectroscopies will be presented and discussed. Focus is on the dependence of the structural phase and related optical properties on the number of layers of the above 2D materials. Experimental research and material properties rationale is guided and supported by exact electromagnetic and DFT based numerical calculations. Acknowledgement: This work has been supported by the European Union’s Horizon 2020 research and innovation program under grant agreement no. 899598– PHEMTRONICS
Authors : Stefano Dicorato, Yael Gutierrez, Giuseppe V. Bianco, Maria M. Giangregorio, Maria Losurdo
Affiliations : Institute of Nanotechnology, CNR-NANOTEC, c/o Department of Chemistry – University of Bari, Via Orabona 4, - 70126 Bari, Italy
Resume : In recent years, phase-change materials (PCMs) have received increasing attention because of their unique properties, exploited in data storage/processing applications. PCMs require pronounced contrast in optical and/or electrical properties between two different structural state. Alternative PCMs to conventional chalcogenide alloys, containing Ge, Sb, and Te, (GST)1 are being extensively studied. In the rising family of two-dimensional, 2D, materials, group (III) chalcogenides such as, GaS, Ga2S3, GaSe, GaTe, gallium sulfide, GaS2 is interesting as phase-change material in the optical range due to its wide bandgap of approximately 2.4 eV in the bulk form. GaS is a layered van der Waals semiconductor consisting in the stacking of covalently bond S-Ga-Ga-S atomic planes, where the successive tetralayers are held together via van der Waals forces. Few layers of GaS have successfully been produced by mechanical exfoliation3, liquid exfoliation4, chemical vapor deposition2, Atomic Layer Deposition (ALD), and used in field effect transistors (FET), near-blue light emitting devices, photodetectors2, energy storage, gas sensing3, and in hydrogen evolution catalysis4. Here we present characteristics of few layers GaS grown by mechanical exfoliation, ALD and CVD. We establish the interplay between number of layers, from monolayers up to 10 layers, of GaS and its structural, optical and electrical properties. Those characteristics have been determined through an extensive characterization by Raman spectroscopy, run as a function of laser wavelength and number of GaS layers, scanning electron microscopy (SEM) used to image the morphology of the layers and count the number of layers, X-ray photoelectron spectroscopy to determine the chemical Ga:S ratio and hence, stoichiometry of the layers, spectroscopic ellipsometry used to determine the dielectric function and optical gap as a function of number of layers, as well as photoconductivity measurements also depending on number of layers. The effect of thermal processing on those structural, compositional, opto-electronic properties is also thoroughly discussed for the first time to the best of our knowledge. Acknowledgement: This work has been supported by the European Union’s Horizon 2020 research and innovation program under grant agreement no. 899598 – PHEMTRONICS. 1 C. Rios et al., "Controlled switching of phase-change materials by evanescent-field coupling in integrated photonics," Opt. Mater. Express 8, (2018). 2 Y. Lu et al., "Controlling Defects in Continuous 2D GaS Films for High-Performance Wavelength-Tunable UV-Discriminating Photodetectors," Advanced Materials 32, (2020). 3 S. Yang et al., "High performance few-layer GaS photodetector and its unique photo-response in different gas environments," Nanoscale 6, (2014). 4 A. Harvey et al., "Preparation of Gallium Sulfide Nanosheets by Liquid Exfoliation and Their Application As Hydrogen Evolution Catalysts," Chemistry of Materials 27, (2015).
Authors : Yael Gutiérrez,1 Gonzalo Santos,2 Stefano Dicorato,1 Pablo García-Fernández,3 Giuseppe V. Blanco,1 Javier Junquera,3 Fernando Moreno,2 Maria Losurdo1
Affiliations : 1 Institute of Nanotechnology, CNR-NANOTEC, c/o Department of Chemistry – University of Bari, Via Orabona 4, - 70126 Bari, Italy; 2 Departamento de Física Aplicada, Universidad de Cantabria, Avda. de los Castros s/n, 39005 Santander, Spain; 3 Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avda. de los Castros s/n, 39005 Santander, Spain;
Resume : Group(III) layered monochalcogenides such as gallium (sulfide, selenide, telluride), Ga(S,Se,Te) are one of the latest additions to the 2D materials family. Among these monochalcogenides, GaS is of particular interest due to its wide band gap which can fill the discontinuity in the band gap energies ranging between those of transition metal dichalcogenides and insulating 2D materials such as hexagonal boron nitride. GaS is a layered van der Waals semiconductor consisting in the stacking of covalently bond S-Ga-Ga-S atomic planes where the successive tetralayers are held together via van der Waals forces. Therefore, few layers of GaS can be isolated by mechanical exfoliation. Bulk GaS has an indirect bandgap reported to be Eg ≈ 2.4-2.6 eV. However, this value increases with decreasing number of layers reaching a value for the monolayer of Eg = 3.05 eV. Being these emission wavelengths of blue to ultraviolet (UV), GaS has been proposed for a new generation of UV photodetectors and blue light emitting devices.  Although the energy band gap of GaS has been established and studied in bulk and in the 2D regime, its dielectric function has not been yet well established and considerations about the GaS crystalline phases have been ignored. In this contribution, we will present a study on the optical properties of GaS supported by DFT calculations and spectroscopic ellipsometry measurements. We will highlight the importance of the GaS crystalline phase and its impact on the dielectric function and Raman spectra of exfoliated GaS samples. ACKNOWLEDGEMENTS: This work has been supported by the European Union’s Horizon 2020 research and innovation program under grant agreement no. 899598 – PHEMTRONICS.  Wang X, Sheng Y, Chang R-J, Lee JK, Zhou Y, Li S, et al. Chemical Vapor Deposition Growth of Two-Dimensional Monolayer Gallium Sulfide Crystals Using Hydrogen Reduction of Ga 2 S 3. ACS Omega 2018;3:7897–903.  Chen T, Lu Y, Sheng Y, Shu Y, Li X, Chang R-J, et al. Ultrathin All-2D Lateral Graphene/GaS/Graphene UV Photodetectors by Direct CVD Growth. ACS Appl Mater Interfaces 2019;11:48172–8.  Hu P, Wang L, Yoon M, Zhang J, Feng W, Wang X, et al. Highly Responsive Ultrathin GaS Nanosheet Photodetectors on Rigid and Flexible Substrates. Nano Lett 2013;13:1649–54.
Authors : G. Santos¹, F. González ¹, D. Ortiz ¹, J.M. Saiz ¹, M. Losurdo ², F. Moreno ¹* and Y. Gutiérrez ²* *corresponding authors: firstname.lastname@example.org and email@example.com
Affiliations :  Group of Optics. Department of Applied Physics Faculty of Sciences. University of Cantabria.  Institute of Nanotechnology CNR-NANOTEC, Via Orabona 4, 70126 Bari, Italy.
Resume : During the last few years, structural color filtering has experienced a great progress from both theoretical and experimental points of view. Color reflective displays are structural color filters usually based on asymmetric Fabry-Perot cavities (AFPCs) which use surrounding light as a source, from which specific wavelength intervals within the visible spectrum are reflected. For a fixed geometry, most of AFPCs filters generate static color, limiting their potential as actively tunable color devices. This can be overcome by introducing an active layer which usually, corresponds to a phase-change material (PCM). One feature of these materials is that they can be switched between their crystalline and amorphous phases by controlled electrical, optical, or thermal excitation. Several strategies have been successfully employed to change the phase of the PCM, and consequently, the reflective color [1-3]. In this contribution, we propose an AFPCs based on molybdenum oxide in order to achieve a switchable on/off color display. Molybdenum oxide (MoOx) can be considered a non-volatile phase-change material, i.e., it does not require a constant energy supply of energy to keep the switched state. Molybdenum oxide can exist as MoO2, MoO3 and as a wide variety of non-stoichiometric oxides. The change in the oxygen content strongly affects the band structure and, consequently, its optical behavior. This innovation can lead to a wide range of outdoor applications posing an advantage with respect to emissive displays, such as LED and OLED, which need to increase power intensity to guarantee good outdoor visibility. References  Wuttig, M., Bhaskaran, H., & Taubner, T. (2017). Phase-change materials for non-volatile photonic applications. Nature Photonics, 11(8), 465-476.  Bachmann, T., Talagrand, C., Broughton, B., Didewar, K., Bandhu, L., Triggs, G., ... & Bhaskaran, H. (2019). Solid state reflective display (SRD®) with LTPS diode backplane.  Carrillo, S. G. C., Trimby, L., Au, Y. Y., Nagareddy, V. K., Rodriguez‐Hernandez, G., Hosseini, P., ... & Wright, C. D. (2019). A nonvolatile phase‐change metamaterial color display. Advanced Optical Materials, 7(18), 1801782.
N.VIII Advanced material characterization : G.E.Jellison, M.Modreanu,
Authors : Zapien, J.A.*(1), Huqe, M.R.(1), & Foo, Y.(1).
Affiliations : (1) Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong, SAR, PRC. * lead presenter
Resume : NIR to UV characterization strategies have paramount importance because of their simple implementation, non-invasive, non-destructive, fast, and contactless advantages. Among them, spectroscopic ellipsometry (SE), as a self-referenced and phase-sensitive technique, provides superb sensitivity to the sample characteristics. However, information about the sample’s characteristics are only accessible via detailed mathematical modeling. While the Rigorous Coupled-Wave Analysis (RCWA) is the preferred strategy for modeling the optical response of structured 1D periodic structures; as the complexity in size and dimensionality increases, it becomes important to find complementary numerical tools to accomplish this task. The Finite Difference Time Domain (FDTD) method provides attractive advantages that include generality of the method, capacity to model single and non-periodic structures, and natural suitability to address non-linear phenomena. We will discuss the use of the FDTD method as an alternative to model the broad band spectroscopic ellipsometry (SE) data of real structures. Particular attention will be given to the computational demands, time-to-result, and its capabilities and limitations to enable a quantitative search for best-fit parameters of an optical model with spectral density comparable to the experimental data. This work was supported by a grant from the Research Grants Council, University Grants Committee, Hong Kong SAR, PRC (Project No. CityU 11210218).
Authors : Marc Chaigneau
Affiliations : HORIBA Scientific
Resume : 2D transition metal dichalcogenides (TMDCs) materials are considered of very high potential semiconductors for future nanosized electronic and optoelectronic devices. An information-rich nanoscale characterization technique is required to qualify these materials and assist in the deployment of 2D material-based applications. Scanning Probe Microscopy (SPM) is a powerful technique to image physical properties of 2D materials, such as topography, conductivity or other electrical properties. Combining SPM and Raman in a single instrumentation is extremely powerful as it makes imaging of both chemical and physical properties possible. As Raman is diffraction limited, only plasmon enhanced Raman and photoluminescence spectroscopies yield correlated electrical and chemical information down to the nanoscale. In this talk, we will report on Tip-Enhanced Photoluminescence (TEPL) and Tip-Enhanced Raman spectroscopy (TERS) data obtained on single crystal WS2 and WSe2 flakes directly grown on SiO2/Si. TEPL and TERS images will be correlated with contact potential difference and capacitance maps as results of Kelvin force probe microscopy acquisition. In addition, we will show the sensitivity of electronic properties (related to Fermi level and charge accumulation) upon light illumination. Beside these semiconductor/dielectric (SiO2) interfaces, probing TMCD/metal interfaces is also essential to integrate TMCDs in 2D or 3D complex structures of devices. We will show results from WS2 on silver and WSe2 and MoS2 on gold. Such transferred surfaces exhibit nanoscale inhomogeneities observed in correlated CPD and Raman maps. Finally, TEPL together with AFM topography data on a lateral single layer WS2/WSxSe1-x/WSe2 heterostructure grown on SiO2/Si will be presented: nanoscale PL response variations are observed beyond the smooth nano-resolution topography.
Authors : Eleonora Cara 1, Luisa Mandrile 1, Alessio Sacco 1, Andrea M. Giovannozzi 1, Andrea M. Rossi 1, Federica Celegato 1, Natascia De Leo 1, Philipp Hönicke 2, Yves Kayser 2, Burkhard Beckhoff 2, Davide Marchi 2, Alberto Zoccante 2, Maurizio Cossi 3, Michele Laus 3, Luca Boarino 1 and Federico Ferrarese Lupi 1
Affiliations : 1 Istituto Nazionale di Ricerca Metrologica INRiM, Strada delle Cacce 91, Torino, Italy 2 Physikalisch-Technische Bundesanstalt PTB, Abbestraße 2-12, Berlin, Germany 3 Dipartimento di Scienze e Innovazione Tecnologica, Universita` del Piemonte Orientale (UPO), Via T. Michel 11, 15100 Alessandria, Italy
Resume : The enhancement factor (EF), indicating the magnification of the Raman signal of molecules interacting with the surface of plasmonic nanostructures, is a crucial parameter in the field of surface-enhanced Raman spectroscopy (SERS). Metrological calculation of EF requires a careful evaluation of both the signal intensities and the number of molecules in SERS and normal Raman conditions. The determination of the surface density of molecules adsorbed on the substrate is fundamental to estimate the number of active molecules contributing to the enhanced Raman signal on a plasmonic substrate and, for this reason, strongly impacts the estimation of the enhancement factor. A viable methodology for this challenging task is reference-free X-ray fluorescence (RF-XRF). We determined the EF using 7-mercapto-4-methylcoumarin (MMC) as probe molecule on gold-coated silicon nanowires, integrating SERS and normal Raman spectroscopy with synchrotron-based RF-XRF data that provide an absolute quantitative measurement of the molecular surface density . In addition, the surface coverage of MMC on the substrate is modelled by molecular mechanics (MM) and molecular dynamics (MD) simulations. RF-XRF analytical quantification can be extended to other molecules or common analytes for SERS or fluorescence spectroscopy. The adoption of standardized methodologies for the characterization of nanostructured systems promotes inter-laboratory comparison and boosts the applicability and progress of SERS.  Cara, E., et al. 2020 Towards a traceable enhancement factor in surface-enhanced Raman spectroscopy. Journal of Materials Chemistry C, 8(46), pp.16513-16519.
Authors : Christian Castillo Delgadillo, Dr. Hendrik Schlicke, Dr. Jan Steffen Niehaus, Prof. Dr. Horst Weller, Prof. Dr. Alf Mews
Affiliations : Fraunhofer CAN; Fraunhofer CAN; Fraunhofer CAN; Fraunhofer CAN, University of Hamburg; University of Hamburg
Resume : Anisotropic nanomaterials exhibit unique properties, which allow their implementation into new enhanced optical devices. Dot-in-rods (DRs) exhibit polarized emission with high degrees of polarization (DOPs) and high quantum yields. The energy-efficient generation of polarized light is of major interest for display technologies. Aligned DR nanostructures have been reported as photoluminescent light sources for efficient LCD technologies, as well as active emissive layers in polarized-emissive light-emitting diodes (PEQLEDs), which can find applications in future 3D- and head-up displays. One of the main challenges is the alignment of DRs for their use in macroscopic devices. This contribution offers insight into the large-scale fabrication of CdSe/CdS DRs by continuous flow processes and their subsequent alignment. The produced films exhibit high DOPs in ensemble, which allows their implementation into several optical devices, such as PEQLEDs.
N.IX. Advanced nanoscale characterisation of material and devices III : O.Durand, J.Even
Authors : D. J. Rogers1, V. E. Sandana1, P. Bove1, F. H. Teherani1
Affiliations : 1Nanovation, 8 route de Chevreuse, 78117 Châteaufort, France
Resume : The epitaxial layers that constitute the active regions in many electronic/photonic devices are often grown on substrates which are not ideal for integration/use in the targeted end-application. For instance, growth substrates can be too expensive or bring undesired constraints such as poor thermal/electrical conductivity, rigidity, opacity, etc etc. For these reasons lift-off of the active epilayers from the growth substrate, and their subsequent transfer/bonding to alternative substrates, has become a very widespread practice. One of the most elegant approaches to this transfer challenge is a technique called Epitaxial Lift-Off (ELO). In ELO a sacrificial underlayer (which also serves as a crystalline template) is employed so as to release the active epilayers from the growth substrate. The release is performed using a preferential chemical etch/dissolution of the sacrificial layer. A key advantage of this approach is that the released epilayer presents a pristine underside which is suitable for direct/fusion bonding to a substrate of choice (irrespective of crystallographic or thermal expansion mismatches). In practise, however, only a very limited set of substrates, epilayers and sacrificial layers have proven amenable to ELO and many epitaxial material combinations must resort to more complicated/destructive/elaborate approaches such as laser lift-off or smart cut. In this talk we will reveal a novel approach which has the potential to significantly extend the portfolio of materials that can be transferred to alternative substrates using ELO.
Authors : Z. Remes(1), A. Artemenko (1), E. Ukraintsev(1), B. Rezek (2), A. Poruba (3), Hua Shu Hsu (4), J. Micova (5)
Affiliations : (1) Institute of Physics CAS, Cukrovarnicka 10, 162 00 Praha 6, Czechia; (2) Faculty of Electrical Engineering, Czech Technical University, Prague, Czechia; (3) SVCS Process Innovation s.r.o., Valazské Mezirící, Czechia; (4) Department of Applied Physics, National Pingtung University, Taiwan; (5) Institute of Chemistry SAS, Dubravska cesta 9, 84538 Bratislava, Slovakia;
Resume : Due to a high surface-to-volume ratio and related size effects, ZnO nanostructures are perspective for energy conversion or sensing applications such as solar cells, light emitting diodes high performance electrochemical capacitors, biosensors, gas sensors, or highly efficient nano-scintillators. We have developed the technology of hydrothermal growth of nanostructured ZnO from zinc nitrate hexahydrate and hexamethylenetetramine (HMTA) and shown that cold hydrogenation in low pressure hydrogen plasma is an effective way to significantly enhance the electrical conductivity and exciton-related emission in ZnO thin films prepared by reactive magnetron sputtering on fused silica glass substrates as well as free-standing hedgehog-like microstructures [1-3]. The plasma treatment has been done in a novel inductively coupled plasma (ICP) quartz reactor recently developed in the cooperation with the Czech company SVCS Process Innovation s. r. o. in Valazske Mezirici and designed to allow in-situ mixing of powder samples. The reactor operates at the radio frequency 13.56 MHz with up to 300 W discharge power and H2, O2, N2 and Ar process gasses at low pressure about 20 Pa. X-ray photoelectron spectroscopy (XPS) showed contamination of plasma processed ZnO powder surface by silicon (~20 at.%) and fluorine (~9 at.%) from quartz walls and polytetrafluoroethylene (PFTE) sealing that disappeared after reducing a parasitic capacitive coupling between antenna and grounded stainless steel holder. We measure topography and surface potential of ZnO nanorods and monocrystalline ZnO samples after different plasma treatments by atomic force microscopy (AFM) and Kelvin probe force microscopy (KFPM). Preliminary results show similar morphology before and after plasma treatment, but different average surface potential values. This work was supported by the CSF project 19-02858J, the CAS Mobility Plus project SAV-21-06, by the Operational Programme Research, Development and Education project SOLID21CZ.02.1.01/0.0/0.0/16_019/0000760, by CzechNanoLab Research Infrastructure (MEYS CR, no. LM2018110), by the project Strategy AV21, program Diagnostic Methods and Techniques and by the Scientific Grant Agency (VEGA, Slovak Academy of Sciences, Grant No 2/0157/20) and by Ministry of Science and Technology of Taiwan (MOST) under Grant Nos. 107-2119-M-153-001 and 108-2923-M-153-002-MY3 (Hua Shu Hsu).  J. Micova, et al., Synthesis, optical properties and crystal quality of zinc oxide nanostructures, Appl. Surf. Sci. 461 (2018) 190-195.  M. Buryi, et al., Influence of precursor age on defect states in ZnO nanorods, Appl. Surf. Sci. 525 (2020) 146448(1-8).  Z. Remes, et.al., Room temperature plasma hydrogenation – an effective way to suppress defects in ZnO nanorods, Mater. Today: Proc. 33 (2020) 2481-2483
Authors : I. Kochylas, V. Gianneta, V. Likodimos, S. Gardelis, P. Falaras, A. G. Nassiopoulou
Affiliations : National and Kapodistrian University of Athens, Department of Physics, Section of Condensed Matter Physics, Panepistimiopolis, 15784, Greece; NCSR Demokritos, Institute of Nanoscience and Nanotechnology (INN), 15341 Agia Paraskevi, Athens, Greece; National and Kapodistrian University of Athens, Department of Physics, Section of Condensed Matter Physics, Panepistimiopolis, 15784, Greece; National and Kapodistrian University of Athens, Department of Physics, Section of Condensed Matter Physics, Panepistimiopolis, 15784, Greece; NCSR Demokritos, Institute of Nanoscience and Nanotechnology (INN), 15341 Agia Paraskevi, Athens, Greece; NCSR Demokritos, Institute of Nanoscience and Nanotechnology (INN), 15341 Agia Paraskevi, Athens, Greece
Resume : Surface-Enhanced Raman Scattering (SERS) constitutes a powerful tool for sensitive detection down to the level of a single molecule that has been used in many areas such as chemical and biological analysis. In this study, we developed highly sensitive SERS substrates of high surface area, consisting of silicon nanowires (SiNWs) decorated with Ag nanostructures by a facile single-step Metal Assisted Chemical Etching (MACE) process. One-step MACE was performed on p-type Si substrates (5-6 Ωcm) by immersion in AgNO3/HF aqueous solutions resulting in the formation of SiNWs decorated by Ag dendrites. We used two alternative fabrication routes: in the first approach the silver dendrites that formed during SiNWs’ growth were removed in HNO3 aqueous solution. By re-immersion in the initial AgNO3/HF aqueous solution, Ag nanoparticle aggregates were deposited in a controllable way mainly at the SiNWs tips. In the second approach, we used directly the composite structure produced by MACE by adjusting the growth time to achieve the desired density of Ag nanostructures. SERS evaluation was performed using Rhodamine 6G as probe analyte at 514 nm, ensuring near-plasmonic resonance as the reflection measurements demonstrated. Substrates fabricated by the second,resulting in dendritic silver nanostructures,enabled R6G detection down to lower analyte concentrations than those fabricated by the first method. Concentrations lower than 10^-13 M were observed and enhancement factors higher than 10^8 were calculated, demonstrating very high SERS sensitivities for analytic applications.
Authors : Kniazeva M.1, Ganzha A.1, Andronikova D.1, Souliou S.-M.2, 3, Roleder K.4, Burkovsky R.1
Affiliations : 1 Peter the Great Saint-Petersburg Polytechnic University, 29 Politekhnicheskaya, 195251 St. Petersburg, Russia 2 Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany 3 European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France 4 Institute of Physics, University of Silesia, ulica 75 Puıku Piechoty 1, 41-500 Chorzów, Poland
Resume : Antiferroelectric materials are interesting due to a number of useful properties, related to structural phase transitions. Understanding them to a level of predicting-power models is presently rather weak yet strongly demanded. The description of the interaction between different types of antiferroelectric distortions such as in the prototypical crystal of lead hafnate is particularly difficult. After the phase transition from cubic to the low-symmetry phase, the crystal is characterized by two order parameters – one, describing lead atoms displacements, and the other arising due to oxygen octahedra tilts. Recently, this has been identified as a triggered incommensurate transition which takes place without an incommensurate mode softening. The goal of this work is to experimentally assess such a transition concept in a wider case, where different distortions do not form simultaneously and are detached in the thermodynamic parameters space, such as on forming Pb[Hf-Sn]O3 solid solutions. PbHf0.7Sn0.3O3 single crystals were grown using the flux growth method, they had the size of ~ 30×30×30 μm and were characterized by X-ray scattering within a temperature range from 159 to 450 °С on cooling at ID28, ESRF. To characterize the crystal structure in different phases we used the method of single crystal diffraction and the diffuse scattering method, which allows to look at the crystal structure fluctuations from the point of view of the corresponding stiffness behavior. The triggered transition from cubic to incommensurate phase, observed in pure lead hafnate, upon doping with tin, divides into two soft-mode driven phase transitions at TAFD = 200 °C and TIC = 172 °C. One of the soft modes, related to the lead-ion subsystem, is characterized by temperature-dependent butterfly-like diffuse scattering centered at the Brillouin zone center. The second soft mode, associated with oxygen, manifests itself in diffuse scattering in the form of rods along the [0 1 0] and [0 0 1] pseudocubic directions near the Brillouin zone boundary (R-point), which indicates the formation of dynamical O6-group tilts, weakly correlated along those directions. During the cubic-to-intermediate phase transition, the maximum of diffuse scattering shifts from the Brillouin zone center to an incommensurate position in the [1 1 0] direction, which can be linked to the relevant polarization correlation coefficient turning negative due to the interaction with growing in magnitude octahedral tilts. Additionally, even in the cubic phase, which is free from tilts, this constant shows a pronounced temperature dependence. The obtained results are unexpected: two model parameters at once - the dielectric stiffness and the correlation energy constant, describing structural fluctuations in the crystal, both for the cubic and intermediate phases, are temperature-dependent.
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