Multifunctional binary and complex oxides films and nanostructures for nanoelectronics and energy applications - II
Metal oxides films, heterostructures or nanostructures are key materials for nanoelectronics and energy applications. This symposium will focus on recent advances in synthesis and characterization of functional oxides (binary and complex oxides) and on their various functionalities for emerging key technologies.
This symposium is aimed at bringing together and bridging scientists working on different areas of synthesis, structural / physical characterization and integration of functional metal oxides for application in information and energy technologies. Materials in the form of thin films, heterostructures and nanostructures (nanocrystals, nanowires and nanotubes) of binary and complex oxides (dielectrics, ferroelectrics, ferroics, electro-optics, piezoelectrics) will be considered. Their integration on various substrates such as oxides, semiconductors or 2D materials (graphene, chalcogenides) will be addressed.
In this perspective, recent developments in the synthesis of oxides using either chemical routes (for low temperature deposition, deposition on non planar substrates…) or physical routes will be presented. Materials challenges such as composition control, strain engineering, defect tailoring and the integrity of the material after processing will be addressed. Recent progresses in advanced structural and physical characterization such as nano-imaging and spectroscopy will be featured.
Current realizations in nanoelectronics (advanced CMOS, new switches for low power operation), non-volatile memories (ReRAM…), piezotronics, embedded sensors and actuators will be reviewed. As the scalability is an important aspect of the integration, the effect of the size reduction in nano-scaled devices on the physical properties will be discussed. This is particularly relevant for ferroics oxides for which domains affect strongly the properties.
This symposium should be an interdisciplinary forum for scientists working in the field of oxide heterostructures for integration on semiconductors and an opportunity to discuss challenges and future trends in this area.
Proceedings will be published in a special issue of Thin Solid Films. Submitted manuscripts will be considered for publication after a regular peer-reviewing selection.
Hot topics to be covered by the symposium:
- Thin film, multilayer and nanostructure growth (sputtering, PLD, MBE, CVD, ALD, CSD…)
- Monolithic integration of oxides on silicon
- Dielectrics for future ultimate CMOS technologies – new materials, integration challenges
- Oxides for non-volatile memories: Redox Resistive RAM, FeRAM, FE tunnel junctions…
- Piezoelectrics, ferroelectrics, multiferroics: processing, properties and applications
- Advanced characterization of oxide films - Atomic scale imaging and spectroscopy
- Complex oxide electronics
- MEMS, NEMS, piezotronics, or electro-optic applications
- Oxides for energy materials (films, superlatiices…)
- Marin Alexe, University of Warwick, UK - Photoelectric effects in Oxides
- Alexander Demkov, The University of Texas at Austin, USA - MBE/ALD of complex oxides on semiconductors and ab initio study of their interfaces
- Maryline Guilloux-Viry, ISCR, University of Rennes, France - Ferroelectrics growth and characterization for RF tunable devices
- Andrei Kholkin, CICECO, Portugal - Nanoelectromechanics in oxides: from piezoelectricity to local electrochemistry
- Jens Kreisel, CRP Gabriel Lippmann, Luxembourg - Interaction of photons with the model multiferroic BiFeO3
- Patrycja Paruch, University of Geneva, Switzerland - Dual-function devices combining carbon nanotubes and ferroelectric materials
- Matthew Rosseinsky, University of Liverpool, UK - Chemical routes for oxide nanostructure synthesis
- Jennifer Rupp, ETH Zürich, Switzerland - New materials and methodology to probe diffusion kinetics in memristive anionic-electronic switches
- Florencio Sanchez, ICMAB, Spain - Monolithic integration of complex oxides on silicon
- Sabina Spiga, CNR-IMM, Agrate Brianza (MB), Italy - Material engineering and bottom up fabrication approaches for nanoscaled memristive devices
- Ilia Valov, Peter Grünberg Institute, Jülich, Germany - Recent progress on redox-based resistive switching
- Anke Weidenkaff, University of Stuttgart, Germany - Oxides thermoelectrics
- Tao Wu, KAUST, Saudi Arabia - Photovoltaic effect and solar cells
- Adrian Carretero-Genevrier, INL, Ecully, France
- Hans Christen, Oak Ridge National Laboratory, USA
- Paul Hurley, Tyndall Institute, Cork, Ireland
- Nathalie Lemée, LPMC, University of Amiens, France
- Vijay Narayanan, IBM T.J. Watson Research Center, USA
- Beatriz Noheda, University of Groningen, The Netherlands
- Thomas Schroeder, IHP Frankfurt Oder, Germany
- Susan Trolier-McKinstry, The Pennsylvania State University, USA
- Dirk Wouters, IMEC, Belgium
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Photoeffects in complex oxides II : Tom Wu
Authors : Marin Alexe, Akash Bhatnagar, Mingmin Yang
Affiliations : University of Warwick, Department of Physics, CV4 7AL Coventry, UK
Resume : In the recent past, the entire field of photo-ferroelectrics has been revitalized by the reports of photovoltaic (PV) effect in BiFeO3 (BFO). Unlike traditional semiconductors the open circuit voltages in non-centrosymmetric materials such as BFO are not limited by band gap, they can exceed the band gap of the material by orders of magnitude. The microscopic origins of this effect are still under debate. This talk will address the electronic origin of the anomalous bulk photovoltaic effect in BiFeO3. We will show that the existence of the abnormal photovoltaic effect in BFO single crystals is directly correlated to the presence of photoelectric active sub-band gap levels situated around 2.2 eV. We will also show that the PV effect can be largely tuned by modifying the occupancy (pumping) of these levels demonstrating that that these sub-band levels are at the electronic origin of APV effect in BFO. Additionally, we will discuss characterization methods, such as thermally stimulated current and variable temperature photoelectric characterization, able to provide valuable information on electronic structure of material under investigation, respectively shallow/deep levels in the band gap, which proved to affect the dark and photo-conduction mechanism.
Authors : V. Fridkin 1, K. Maksimova 2, Yu. Matveyev 3 and A. Zenkevich 3
Affiliations : 1 Institute of Crystallography, Russian Academy of Sciences, 59 Leninskii prospekt, Moscow, 119333, Russia; 2 Deutsches Electronen Synchrotron, 85 Notkestraße, Hamburg, D-22607, Germany; 3 Moscow Institute of Physics and Technology, 9 Institutskiy per., Dolgoprudny, Moscow region, 141700, Russia
Resume : The origin of the so-called Bulk Photovoltaic Effect (BPE) in non-centrosymmetric crystals is fundamentally different from that of classical PE. Irrespective of particular microscopic mechanism, as the photo-excited hot carriers thermalize in the conduction band, they get a shift in space lo. Although the voltage generated in BPE can be much higher than the band gap of a crystal, the energy conversion efficiency (e.c.e.) is extremely low. However, the situation can radically change at the nanoscale, when the thickness of the crystal is comparable to lo, typically in a 10 nm range. To measure BPE in thin non-centrosymmetric films, we used Pt/BaTiO3/Pt heterostructures comprising 20 or 50 nm thick epitaxial ferroelectric BaTiO3 layer, grown on a single crystalline MgO(001) substrate. The set of light-emitting diodes with the emission band around ~360 nm (Eg ~ 3.4 eV) and the controlled light power density on the sample surface up to 0.5 W/cm2 was used for illumination. By analyzing the set of the obtained I-V curves, we get e.c.e. ~ 0.6%, which is 4.5 orders of magnitude larger as compared to the bulk crystals. This value is still much lower than the commercial solar cells. However, the calculations indicate that for alternative thin film materials with non-centrosymmetric crystal structure (e.g. LiNbO3:Fe) the BPE efficiency can be further enhanced, and this might provide a viable alternative for the effective use of BPE in photovoltaic applications.
Authors : Ignasi Fina[1,2], Fanmao Liu, Diego Gutiérrez, Greta Radaelli, Riccardo Bertacco, Josep Fontcuberta
Affiliations : Max Planck Institute of Microstructure Physics, Weinberg 2, Halle Germany. Mail: email@example.com; University of Warwick, Department of Physics, Coventry CV4 7AL, United Kingdom; Institut de Ciènca de Materials de Barcelona (ICMAB-CSIC), Campus UAB, Bellaterra 08193, Catalonia, Spain; LNESS Center - Dipartimento di Fisica del Politecnico di Milano, Como 22100, Italy
Resume : Transition metal oxides can present a plethora of interesting coupled functionalities including the coupling between transport properties and light, traditionally exploited making use of semiconductor materials. A particular subclass of transition metal oxides are ferroelectric (FE) materials, which are insulating in nature and in most cases with large bandgaps that make them rather transparent to visible light. However, in thin films, due the presence of defects, interface and electrode effects, visible light can generate photocarriers. We will report on the photoresponse of BaTiO3 thin films, where remarkable photoinduced effects have been observed at appropriate wavelengths. More specifically, we have explored the dependence of the induced photocurrents on the direction of the polarization and the strength of the imprint field. We show that the measured short-circuit photocurrent resembles the FE retention properties of the studied material. We argue that this fact results from the dependence of both parameters on the depolarizing electric field, therefore it is stated that depolarizing electric field is the main driving force for the generated photocurrent. Interestingly, it is observed that the FE imprint fielddoes not importantly collaborate in the generation of photocurrent. The present study suggest that: photocurrent is univocally determined by the depolarizing field, which is promising in terms of electro-optic read-out of information on FE based memories.
Ferroelectrics : Marin Alexe and Wilfrid Prellier
Authors : M. GUILLOUX-VIRY1, A. WAROQUET1, F. CISSE1,2, A. LE FEBVRIER1, V. DEMANGE1, S. DEPUTIER1, V. BOUQUET1, X. CASTEL2, R. BENZERGA2, R. SAULEAU2, P. HAMOUMOU3, B. GAUTIER3
Affiliations : 1 ISCR, UMR-CNRS 6226/Université de Rennes 1, Campus de Beaulieu, 35042 RENNES, FRANCE ; 2 IETR, UMR-CNRS 6164/IUT de Saint-Brieuc/Université de Rennes 1, 18 rue Henri Wallon, 22004 SAINT-BRIEUC, and Campus de Beaulieu, 35042 RENNES, France ; 3Institut des Nanotechnologies de Lyon, INSA de Lyon, 7, avenue Capelle, Villeurbanne Cédex 69621,France
Resume : Ferroelectrics are attractive to design agile devices thanks to the large electric field dependence of their dielectric permittivity. Device performance depends on the ferroelectric characteristics of the integrated thin films. During the last decade, intensive studies were focused on BaxSr1-xTiO3, which is a quite low loss perovskite compound, for which TC can be monitored by choosing an adequate composition. Alternative multifunctional materials were also investigated, such as KTa1-xNbxO3 which also offers to tune TC. This solid solution shows high tunability at a moderate electric field, but its use is still limited because of significant dielectric losses. For the different materials, various approaches are investigated in order to obtain low loss agile materials, such as the screening of composition, doping, the control of high quality epitaxial films, the association with dielectrics in composites. The challenge is to find the best trade-off in order to reduce the losses without drastically damaging the tunability. It was also shown that the deposition conditions strongly influence the final performance of the materials. In this way, it has been evidenced that strain effects can give access to the monitoring of ferroelectric properties in nanostructured composite films. Deposition conditions can also give access to new materials, with specific nanostructuration, obtained by a phase diagram approach. New piezoelectric epitaxial niobates films were obtained by this way.
Authors : E Buixaderas, C Kadlec, D Nuzhnyy, I Rychetsky, J Petzelt, H Ursic, B Malic,
Affiliations : Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic Department of Electronic Ceramics, Joef Stefan Institute, Ljubljana, Slovenia
Resume : The evaluation of the dielectric response in thick films of dielectric materials and in mixtures of dielectric and metals is not as straightforward as in bulk materials, due to the presence of porosity. To obtain the effective dielectric function of these films, porosity can be taken into account using the Lichtenecker model, but a more generalized effective medium model with percolation threshold and critical percolation exponents was proposed by McLachlan. The case of a mixture of a ferroelectric with a metal, is very interesting because the dielectric response can be greatly enhanced, and near the percolation threshold the permittivity diverges. This effect is discussed for a set of thick Pb(Zr,Ti)O3 films and composite films Pb(Zr,Ti)O3 −xPb2Ru2O6.5 . Films were prepared by screen printing on sapphire substrates, and their homogeneity and phonon response were studied by Raman spectroscopy and Fourier-transform infrared (FTIR) reflectivity. The dielectric response below phonons was measured using time-domain terahertz transmission spectroscopy. The compositions, up to 25 vol% Pb2Ru2O6.5, are below and above the electrical percolation threshold, known to be about 17% in the bulk composites. Using the dielectric functions of bulk PZT ceramics and Pb2Ru2O6.5 single crystals, the effective dielectric functions can be compared with those obtained using the theoretical models.  D Nuzhnyy, E Buixaderas et al, J. Physics D: Appl. Phys 47 (2014) 495301 (2014).
Authors : Qiang LIU1, Simon MARTIN2, Nicolas BABOUX2, David ALBERTINI2, Brice GAUTIER2, Bertrand VILQUIN1, Yves ROBACH1
Affiliations : (1)Universite de Lyon, Ecole Centrale de Lyon, Institut des Nanotechnologies de Lyon, CNRS UMR5270, 36 avenue Guy de Collongue, 69134 ECULLY Cedex, FRANCE (2) Université de Lyon, INSA de Lyon, Institut des Nanotechnologies de Lyon, CNRS UMR5270, 7 avenue Capelle, 69621 VILLEURBANNE Cedex, FRANCE
Resume : Lead zirconate titanate (Pb(Zr1-xTix)O3, PZT) is well known for its excellent piezoelectric and ferroelectric properties and its subsequent applications. Tunable composition makes it versatile and morphotropic phase boundary (MPB, x=0.48) is especially attractive for the large piezoelectric constant, considerable remnant polarization and great dielectric constant. Despite the fact that lead in not environment friendly, the study based on PZT continues intensively along with other complex oxides due to the lack of equivalent substitutes. PZT(52/48) films with thickness from 33 nm to 200 nm have been deposited on SrTiO3 substrate, with an SrRuO3 interlayer as bottom electrode, by two methods: a) sol-gel, which is low cost and has short fabrication cycle; b) sputtering, producing high homogeneous, large scale, precise thickness controlled thin film. X-Ray Diffraction indicates single crystalline PZT is epitaxially grown on the substrate. Surface roughness is less than 1 nm (root mean square), characterized by Atomic Force Microscopy. At nanoscale, piezoresponse force microscopy shows the inverse piezoelectric effect. At macroscale, electrical properties of the PZT thin films were measured through current-voltage (I-V), capacitance-voltage (C-V) and PUND (Positive Up Negative Down). These characterizations allowed to discriminate between the differents conduction models and also between the ferroelectric domaisn switching behaviour.
Authors : Alexandru Enesca, Luminita Isac, Anca Duta
Affiliations : Transilvania University of Brasov, Brasov, Romania
Resume : Sustainable removal of organic pollutants from wastewater represents an alternative to the traditional methods and to the mono-component fotocatalytic materials which show sever limitations in terms of production and operation costs and durability. This paper presents the development and properties of high efficient photocatalytic multi-tandem structures based on metallic oxides (SnO2, TiO2) and sulfides (CuxS). The thin films are obtained by spray pyrolysis deposition, using inorganic precursors and alcoholic solvents. Post-deposition annealing is used to improve the crystallinity of the tandem components. The design of the multi-layered structures is done considering the band energy levels to obtain complex multi-tandems activated mostly by Vis radiation, sustainable and stable in the working environment. The compatibility of the crystallization systems (tetragonal for SnO2, TiO2 and body-centered tetragonal for CuxS), the morphology (dense granular for metal oxides and porous granular for CuxS) and the surface energy (dominated by polar component) support the adjustment of the energy levels in bi- and tri-component tandem structures. The photocatalytic tests were doe at two methylene blue (MB) and phenol concentrations (4ppm and 10ppm) and at different pH (3, 5, 7, 8, 9). The results shows significant differences in the photocatalytic efficiency of multi-tandem structures which are correlated with the influence pH influence on the energy levels values. The photocatalytic experiments under UV-Vis irradiation shows that MB degradation using CuxS/TiO2/SnO2 tandem structure reach 60% efficiency in 4h and 80% efficiency after 6h of irradiation.
Authors : VS Teodorescu1, AV Maraloiu1, R Negrea1,2, A Slav1,2, C Palade1, AM Lepadatu1, ML Ciurea1
Affiliations : 1-National Institute of Materials Physics, Bucharest-Magurele, Romania 2-University of Bucharest, Faculty of Physics, Bucharest-Magurele, Romania
Resume : Thin films of Ge-HfO2 were co-sputtered on oxidized Si substrate, having a Ge/HfO2 ratio of 25/75 and 50/50. The Ge-HfO2 film with thickness of 15 nm was covered by a pure HfO2 film of 20 nm thickness, also deposited by magnetron sputtering. The whole as-deposited structure is amorphous, and it was crystallized using a rapid thermal annealing processor at different temperatures between 650 and 850 oC , in argon atmosphere. The film structure was studied by STEM, EDX and HRTEM, using a cross section (XTEM) specimen preparation, before and after the annealing. The RTA annealing induces the crystallization of both HfO2 and Ge-HfO2 films. The sizes of HfO2 crystalline grains are larger than the structure thickness. Generally, any HfO2 crystalline grains are extended from the top surface to the interface with the substrate. The bottom part of all HfO2 crystalline grains has Ge inclusions that are probably amorphous nanoparticles embedded in the crystallized HfO2 matrix. These Ge amorphous nanoparticles were evidenced by STEM observations and have 4 to 5 nm in size. They produce big distortions in the HfO2 crystalline lattice, as evidenced by image processing of the HRTEM images. No crystalline Ge nanoparticles were observed and no traces of any moiré fringes which can results from Ge and HfO2 superposed lattices were evidenced. In our opinion, Ge nanoparticles remain amorphous due to the high rate of HfO2 crystal lattice growth.
Authors : Virginie Théry, Jean-Christophe Orlianges, Alexandre Boulle, Amine Mennai, Annie Bessaudou, Françoise Cosset, Arnaud Beaumont, Aurelian Crunteanu
Affiliations : SPCTS CNRS UMR 7315, Centre Européen de la Céramique, 12 rue atlantis, 87068 Limoges Cedex, France XLIM - CNRS / Université de Limoges, UMR 7252, 123 rue Albert Thomas, 87060 Limoges Cedex
Resume : One of the emerging fields in nano-electronics is the adaptive electronics based on resistive memories integrating functional oxides. In this context, the most promising memories and devices make use of the Mott Metal-Insulator Transition (MIT) in which electric charge injection into a transition metal compound induces a transition from a strongly correlated insulator into a weakly electron correlated metal (Mott or Mott-Hubbard transition). The transition is accompanied by large resistance changes of the material, on very short timescales. Among the possible materials exhibiting a MIT, vanadium dioxide (VO2) is of particular interest since it exhibits a huge resistivity change between the two stable phases (5 orders of magnitude). In this work, pure and W-doped VO2 epitaxial films have been grown on Al2O3 and TiO2 substrates of various orientations using both pulsed laser deposition and electron beam evaporation. The films have been characterized using high-resolution X-ray diffraction, ellipsometry and 4-probe electrical resistivity measurements. We show that there is clear dependence between the magnitude of the MIT and the deposited film thickness. This behavior can be explained by the fact that upon decreasing film thickness the level of strain in the films increases, which results in a lowering of the electrical gap in the insulating state by ~0.1 eV and hence a degraded resistivity and resistivity ratios reduced by 2 orders of magnitude for the thinnest films.
Authors : Reham Abu Amer1, Michel Kazan1, Digambara Patra2, Malek Tabbal1
Affiliations : 1 Department of Physics, American University of Beirut, Bliss St. P.O. Box:11-0236, Beirut, Lebanon 1107 2020 2 Department of Chemistry, American University of Beirut, Bliss St. P.O. Box:11-0236, Beirut, Lebanon 1107 2020
Resume : ZnO nanoparticles were successfully synthesized via simple precipitation method by controlling different parameters of the precipitation process such as solution concentration and calcination temperature. The structural and morphological properties of these samples were investigated by SEM and XRD analysis. SEM images showed uniformity in the particles size and shape for ZnO nanoparticles calcined at different temperatures compared to the other synthesized samples. The average crystallite size increases with increasing the calcination temperature. We used UV-VIS and FTIR spectrophotometers to get the reflectivity data of the selected samples. By using Kramers-Kronig (K-K) method, we then determined the optical constants, n and k with the real and imaginary parts of the dielectric constant in the IR region. The K-K method was then combined with a newly developed technique to compute the optical parameters in the UV-VIS region. A shift in the absorption peak in the extinction coefficients of the samples was observed due to defects by varying the calcination temperature. Green emission was observed from 36 nm grain size ZnO samples and yellow emission was observed from 470 nm grain size ZnO samples. Finally, to verify the validity of our approach, we back calculated the UV-VIS reflectivity spectra from the deduced optical parameters, and good agreement was found between the measured and calculated spectra. This confirms the importance of our approach in developing a new numerical technique for accurate measurement of the optical parameters at the UV-VIS wavelengths. The reflectivity based technique described in this work could be applied to study ZnO nanoparticles of smaller sizes reaching the quantum confinement region.
Authors : Han-Ki Kim, Dong-Ju Kim
Affiliations : Department of Advanced Materials Engineering for Information and Electronics, Kyung-Hee University
Resume : We investigated the electrical, optical, structural, and morphological properties of Ti-doped In2O3 (TIO) films grown by DC magnetron sputtering using 1-, 3-, and 5-wt% Ti-doped TIO targets as a function of film thickness. Compared with the TIO films prepared from 3 and 5 wt % Ti doped TIO targets, the 300 nm thick TIO films fabricated using a 1 wt % TIO target showed a lower resistivity of 2.4 × 10-4 Ohm-cm, an mobility of 49 cm2/Vs, and higher average transmittance of 80% in the near infrared wavelength (800-2000nm) region due to an effective Ti dopant composition. In addition, a different structural evolution of the TIO columnar with increasing thickness significantly influenced on the resistivity and optical transmittance of the TIO films. Based on Hall measurements, UV/visible spectrometer, X-rays diffraction and field emission scanning electron microscopy analysis results, we correlated the properties of TIO films with thickness and TIO target composition
Authors : A.A. Tikhii, V.A. Gritskikh, S.V. Kara-Murza, N.V. Korchikova, Yu.M. Nikolaenko, I.Yu. Reshidova, I.V. Zhikharev
Affiliations : Donetsk Institute for Physics and Engineering named after O.O. Galkin, 83114 Donetsk, Ukraine; Lugansk National Taras Shevchenko University, 91011 Lugansk, Ukraine; Lugansk National Taras Shevchenko University, 91011 Lugansk, Ukraine; Lugansk National Taras Shevchenko University, 91011 Lugansk, Ukraine; Donetsk Institute for Physics and Engineering named after O.O. Galkin, 83114 Donetsk, Ukraine; Donetsk Institute for Physics and Engineering named after O.O. Galkin, 83114 Donetsk, Ukraine; Donetsk Institute for Physics and Engineering named after O.O. Galkin, 83114 Donetsk, Ukraine
Resume : The variation of optical and magnetoresistive properties of La-Sr-Mn-O films at different regimes of annealing procedure is investigated. The films with the thicknesses 40 -100 nm were deposited onto single crystal Gd3Ga5O12 (111) substrates by dc magnetron sputtering of ceramic La0.7Sr0.3MnO3 target in argon-oxygen atmosphere . The optical conductivity investigated in energy spectrum range of 1-5 eV. Magnetoresistance was measured in the temperature range 80310 K. We observed no significant dc-conductivity and no 1 eV polaron feature in the optical conductivity spectra for the unannealed films. The annealing carried out in air at temperature 870 K has small influence on the films properties. When the annealing temperature increased to 1170 K the refractive index and the optical conductivity spectra of the annealed films become similar to the ones of epitaxial La0.7Sr0.3MnO3 films (the 1 eV polaron feature appears). However these spectra are shifted by ~ 0.5 eV to higher energy. The annealed films with thicknesses of more than 60 nm have the temperature maximum of resistance at ~ 180 K and widened temperature range of negative magnetoresistance, which is typical for polycrystalline films . The films with thicknesses of less than 60 nm have no maximum of resistance. 1. Yu.M. Nikolaenko, A.B. Mukhin, V.A. Chaika and V.V. Burkhovetskii, Tech. Phys., 55, 8, 1189 (2010); 2. Abdullah Goktas, Ferhat Aslan, Ibrahim Halil Mutlu, J Mater Sci: Mater Electron, 23, 605 (2012).
Authors : Mark Buckwell, Luca Montesi, Richard Chater, Sarah Fearn, Adnan Mehonic, Steven Hudziak, David McPhail, Anthony Kenyon
Affiliations : University College London, Imperial College London
Resume : With the current trend of decreasing device sizes whilst improving performance, silica-based resistive switches offer the potential for simple fabrication, using existing infrastructures, of high-density, high-efficiency data storage media. Here we present recent work on memory functionality through reversible switching between discrete states of resistance in 37 nm silicon suboxide layers. However, in order for such devices to be optimised and integrated into consumer technologies it is necessary to fully understand the switching mechanism. Current research in oxide-based resistive RAM focuses on the migration of oxygen atoms through an insulating layer under electrical stress. While it has become increasingly clear that oxygen movement plays a major role in device behaviour, there has remained a lack of direct evidence correlating switching behaviour and oxygen motion. Along with pre- and post-switching characterisation of the active material using atomic force microscopy and x-ray photoelectron spectroscopy, we present recent work in which we have successfully observed, using primary and secondary ion mass spectroscopy, the ejection of oxygen-based species from our devices during operation. The novel methods used and subsequent data obtained highlight the dynamic behaviour of our silica memory.
Authors : D. Louloudakis1,2*, D. Vernardou1, E. Spanakis3, M. Panagopoulou4, Y. Raptis4, G. Kiriakidis2,5, N. Katsarakis1,5,6, E. Koudoumas1,6
Affiliations : 1Center of Materials Technology & Photonics, School of Applied Technology, Technological Educational Institute of Crete, 710 04 Heraklion, Crete, Greece; 2Department of Physics, University of Crete 711 00 Heraklion, Crete, Greece; 3Department of Materials Science & Technology, University of Crete 711 00 Heraklion, Crete, Greece; 4School of Applied Mathematical and Physical Sciences, National Technical University of Athens, GR 157 80, Zografou Campus, Athens, Greece; 5Institute of Electronic Structure & Laser, Foundation for Research & Technology- Hellas, P.O. Box 1527, Vassilika Vouton, 711 10 Heraklion, Crete, Greece; 6Department of Electrical Engineering, School of Applied Technology, Technological Educational Institute of Crete, 710 04 Heraklion, Crete, Greece
Resume : Many methods such as magnetron sputtering, atomic layer deposition, spin coating, sol-gel and chemical vapor deposition (CVD) have been used for the deposition of thermochromic vanadium dioxide layers on glass substrates. In this work, vanadium dioxide coatings were fabricated using vanadyl (IV) acetylacetonate as vanadium precursor in an atmospheric pressure CVD (APCVD) system on SnO2-precoated glass substrates. The samples were characterized by x-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV-Vis-NIR spectroscopy at temperatures below and above transition temperature as well as transmittance measurements as a function with temperature at an incident radiation of 1500 nm. The effect of deposition temperature and N2 flow rate through the vanadium precursor on the thermochromic characteristics of the coatings is discussed.
Authors : Yu. A. Mastrikov1, E. A. Kotomin1,2, R. Merkle2, M. M. Kuklja3, and J. Maier2
Affiliations : 1Institute of Solid State Physics, University of Latvia, Kengaraga str. 8, Riga, Latvia 2Max Planck Institute for Solid State Research, Heisenbergstr.1, Stuttgart, Germany 3Materials Science and Engineering Dept., University of Maryland, College Park, USA
Resume : AABBO3-delta-type complex perovskites with a large oxygen deficiency deltaexhibit a perceptible ionic conductivity, leading to their use as electrolytes ((La,Sr)(Ga,Mg)O3-delta) or materials for oxygen permeation membranes and solid oxide fuel cell (SOFC) cathodes ((La,Sr,Ba)(Mn,Fe,Co)O3-delta) [1,2]. The oxygen migration in these materials occurs by the vacancy mechanism with the migration through a critical triangle formed by one B- and two A site cations, as the bottleneck . Oxygen ionic conductivity is important not only for its transport though the cathode body, but also for the surface chemistry. Oxygen vacancy formation and migration energies were found to be the major factors determining the surface oxygen reduction rate . These two quantities were analyzed for a series of complex (Ba,La,Sr)(Co,Fe)O3-delta (BSCF and LSCF) perovskites by means of first principles DFT calculations . The atomic relaxation, electron charge redistribution, and transition states energies for oxygen ion migration are obtained and discussed in detail with special emphasis on the vacancy formation and migration at the surface. . M. Kuklja, E.Kotomin, R. Merkle, Yu, Mastrikov, J.Maier, Phys. Chem. Chem. Phys. 15, 5443 (2013).  R. Merkle, Yu.A. Mastrikov, E.A. Kotomin, M.M. Kuklja, J. Maier. J Electrochem.Soc. 159, B 219 (2012).  Yu.A. Mastrikov, R. Merkle, E.A. Kotomin, M.M. Kuklja, J. Maier, Phys. Chem. Chem. Phys. 15, 911 (2013)
Authors : N. Guillaume, E. Puyoo, M. Le Berre, D. Albertini, N. Baboux, C. Chevalier, B. Gautier, F. Calmon, J. Grégoire, K. Ayadi
Affiliations : Lyon Institute of Nanotechnology (INL), UMR 5270 INSA de Lyon, Université de Lyon, Villeurbanne, France
Resume : TiOx layers are implemented in various devices ranging from metal/insulator tunnel transistors to Memristors. Nevertheless the Ti/TiOx interfaces lack a thorough characterization towards a better understanding of occurring phenomena. We report here on the behavior of lateral MIM structures fabricated by Local Anodic Oxidation (LAO) of Ti thin films. The samples are composed of a thin Ti channel, a few µm wide and 5-10 nm thick fabricated by means of optical lithography. A transverse oxide line is then patterned by LAO lithography to define the Ti/TiOx /Ti planar structure. Using PtSi tips in contact mode, 85nm wide and 8nm thick junctions are obtained. Under air, the TiOx junctions exhibit evolving I(V) characteristics with a continuous increase in resistance at each cycle. After several cycles the devices invariably gets in a high resistance mode, consistent with a continuing oxidation process of the Ti electrode induced by the electrical stress, the Ti/TiOx interface being open to the environment. This self-limiting process leads to a junctions width of around 1 µm. Structural and chemical analysis performed by EELS and EDX via HRTEM before and after the electrical stress highlight the growth of a rutile TiOx phase initiated at the amorphous oxide line. This transformation mechanism is totally suppressed if the electrical stress is applied in a vacuum environment, thus indicating the role of ionic motion in the process. Further issues will be discussed in the final paper.
Authors : K.Maksimova (1), S.Medvedeva (2), D.Novikov (1), A.Zenkevich (3)
Affiliations : (1) Deutsches Electronen Synchrotron, 85 Notkestraße, Hamburg, D-22607, Germany; (2) Immanuel Kant Baltic Federal University, 14 Nevskogo str., Kaliningrad, 236000, Russia; (3) Moscow Institute of Physics and Technology, 9 Institutskiy per., Dolgoprudny, Moscow region, 141700, Russia
Resume : Ultrathin ferroelectric (FE) films have recently got much attention in the context of the non-volatile memory devices. Over the last decade, the rapidly improving expertise in the fabrication of the structurally perfect complex oxide FE layers have led to the fabrication of heterostructures with intriguing physical and functional properties. In particular, ultrathin heteroepitaxial BaTiO3 (BTO) films have been utilized as a storage medium in the FE tunnel junctions , and exhibited giant bulk photovoltaic effect . Pulsed Laser Deposition (PLD) has recently emerged as an excellent tool to grow epitaxial oxide heterostructures, particularly comprising ultrathin FE BTO and SrTiO3 (STO) layers. In this work, we report on the effect of PLD growth conditions of BTO and STO on MgO and Si substrates on their structural and FE properties. We show that the structural properties of the oxide layer strongly depends on a precise control over the partial O2 pressure in the growth chamber, substrate temperature and laser ablation parameters. The structure of 3-100 nm PLD grown layers was monitored in situ by RHEED, and further analyzed ex situ by XRD, XRR, AFM and TEM. The ferroelectric properties were investigated by piezoresponse force microscopy. BTO and STO thin films grown at the optimized conditions are monodomain ferroelectrics with the polarization direction perpendicular to the substrate. 1. A. Zenkevich et al. APL 102 062907 (2013). 2. A. Zenkevich et al. PRB 90 161409 (2014)
Authors : J. More-Chevalier,1 A. Ferri,2 C. Cibert,1 R. Desfeux,2 R.Bouregba,1 G. Poullain 1
Affiliations : 1 Université de Caen Basse-Normandie, ENSICAEN, CNRS, UMR 6508 CRISMAT, F-14050 Caen, France 2 Université dArtois, Unité de Catalyse et de Chimie du Solide-UCCS, CNRS UMR 8181, F-62300 Lens, France
Resume : Tb0.3Dy0.7Fe2/Pt/PbZr0.56Ti0.44O3 (Terfenol-D/Pt/PZT) artificial multiferroic structure was sputtered on Pt/TiO2/SiO2/Si substrate. An intermediate platinum layer of 80 nm was used to minimize atomic diffusion between magnetostrictive Terfenol-D layer and piezoelectric PZT films. Ferroelectric and magnetic properties were characterized at room temperature. Then, direct and converse magnetoelectric coupling was evidenced in the synthesized heterostructure. A direct magnetoelectric voltage coefficient of 1.27 V/cm Oe was measured, which is a large value for thin films considering the clamping effect of the substrate. The magnetic domain patterns were locally imaged by magnetic force microscopy, and strong changes were observed when a dc electric field was applied to the ferroelectric layer. A reversible control of the ferromagnetic domains in the multiferroic heterostructure was obtained by removing the external electrical field. This significant finding was explained by the residual tensile stress imposed by the clamping effect of the silicon substrate. These results emphasize that the combination of Terfenol-D and PZT materials in thin films form is very promising to design integrated magnetoelectric devices operating at room temperature.
Authors : P. Prepelita, V. Craciun, F. Garoi, M. Filipescu, T. Tozar, D. Cristea *
Affiliations : National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Street, PO Box MG-36, 077125 Magurele, Ilfov, Romania *Department of Materials Science, Transylvania University, 500036 Brasov, Romania.
Resume : Several TCO thin films (ITO, AZO, SnO2), with thickness in the range 200400 nm, have prepared onto unheated glass substrates, using rf magnetron sputtering and vacuum thermal evaporation. Using the two sputtering targets during the rf magnetron sputtering deposition, the surface of the substrate was heated at 350 - 375 K, which resulted in a good adherence of the thin film on the respective substrate. After deposition, the samples were annealed in air at temperatures up to 750 K. The structural and optical properties of both as-deposited and annealed samples were investigated. The morphological and structural characteristics of the obtained structures were investigated by AFM, SEM and XRD respectively. The transmittance spectra, in double beam were recorded in the 1903000 nm wavelength range and the electrical conductivity was measured with four points method. The samples surface morphology appeared as granular and polycrystalline with high optical transparency and have a good electrical conductivity. Depending on the preparation conditions and the annealing temperature, value of the optical bandgap, Eg, of the corresponding thin films ranged between 3.36 eV and 3.45 eV. The obtained results are discussed in correlation with the structure of the thin films and the role of doping materials in oxide thin films.
Authors : A. Kiazadeh, J. Martins, A. Rovisco, J. V. Pinto , A. Correia, P. Barquinha, H. L. Gomes , R. Martins and E. Fortunato
Affiliations : CENIMAT/I3N Departamento de Ciência dos Materiais, Faculdade de Ciências e Tecnologia (FCT),Universidade Nova de Lisboa (UNL), and CEMOP/UNINOVA, 2829-516 Caparica, Portugal Algarve University, Electronics department, Campus Gambelas, Faro, Portugal
Resume : High-κ gate dielectric implementation is one of several strategies to allow further miniaturization of amorphous oxide-based thin film transistors (TFTs) . Gate dielectrics play a crucial role in decreasing subthreshold slope and operating voltage due to their large capacitive coupling between the active layer and gate. However, achieving an equivalent thickness reduction with a reasonably small leakage current and obtaining the intended threshold voltage coexisting with good electrical stability under stress are still big challenges. Therefore, all the reliability issues must be understood and minimized for producing High-κ/metal gate stacks. Throughout this investigation, we employ the IGZO-TFTs using different gate dielectric configurations of a high-κ, amorphous Ta2O5 mixed with SiO2 in multicomponent films and/or multilayer structures. The dynamic of gate positive bias stress (PBS) and recovery time is studied for each TFT. At the initial stages of PBS experiment, all TFTs exhibit anomalous negative threshold voltage shift (ΔVth). However, the negative ΔVth is smaller for cosputtered Ta2O5/SiO2-IGZO devices compared to Ta2O5-IGZO TFTs. Interestingly, inserting silicon layers into the cosputtered Ta2O5/SiO2 dielectric suppresses the negative ΔVth and with increasing stress time, the shift direction switches to the positive side. Note that SiO2-gated IGZO-TFTs show normal positive ΔVth, so this unusual shift cannot be caused by the channel layer exclusively. Two possible reasons can be the origin of this negative ΔVth: (i) ion migration within the gate dielectric or (ii) charge trapping/detrapping in dielectric. The ion drift is an irreversible process while all the TFTs show a reasonable fast recovery time after PBS. Therefore, this hypothesis is discarded. However, it is hard to believe that holes can be generated in the n-channel device without light illumination. In addition, it is already reported that hole current cannot be injected into the dielectric by the carrier separation technique on leakage current . Therefore, it can be concluded that the negative shift is not due to hole trapping, but due to electron detrapping from Ta2O5. In order to clarify an instability model, positive bias stress temperature instability (PBTI) process is applied for devices showing only negative ΔVth. The negative shift increases with increasing temperature. The time evolution of negative ΔVth is given by a power law with almost the same exponent 0.7 for all TFTs. We suggest that negatively charged defect that releases electrons is a negatively charged interstitial oxygen defect. Such interstitial oxygen defects are easily generated as already reported for the HfO2 gate dielectric, a close relative of Ta2O5 . References:  L. Zhang, J. Li, X. W. Zhang, X. Y. Jiang, and Z. L. Zhang, High-performance ZnO thin film transistors with sputtering SiO2/Ta2O5/SiO2 multilayer gate dielectric, Thin Solid Films, vol. 518, no. 21, pp. 61306133, Aug. 2010.  M. Sato, K. Yamabe, T. Aoyama, Y. Nara, and Y. Ohji, Origin of the Hole Current in n-type High- k /Metal Gate Stacks Field Effect Transistor in an Inversion State, Jpn. J. Appl. Phys., vol. 46, no. No. 44, pp. L1058L1060, Nov. 2007.  C. Kaneta and T. Yamasaki, Oxygen-related defects in amorphous HfO2 gate dielectrics, Microelectron. Eng., vol. 84, no. 910, pp. 23702373, Sep. 2007.
Authors : M. Esro1, R. Mazzocco2, G. Vourlias3, A. Krier2, W. I. Milne4,5, O. Kolosov2, and G. Adamopoulos1*
Affiliations : 1 Lancaster University, Engineering Department, Lancaster LA1 4YR, UNITED KINGDOM; 2 Lancaster University, Physics Department, Lancaster LA1 4YB, UNITED KINGDOM; 3 Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, GREECE; 4 Department of Engineering, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, UNITED KINGDOM; 5 Kyung Hee University, Display Research Laboratory, Department of Information Display, Seoul 130701, SOUTH KOREA;
Resume : High-k dielectrics are extensively studied as alternatives to SiO2 as gate dielectrics for the next generation of field-effect transistors employing metal-oxide semiconducting channels. Amongst the wide range of high-k dielectrics LaAlO3 combines the advantages of the high permittivity of La2O3 with the chemical and thermal stability of Al2O3 and exhibits desirable chemical and electrical properties without the shortcomings of each individual material retaining at the same time a relatively high permittivity and large band gap. LaAlO3 films have been deposited by a variety of techniques including MBE, PLD, magnetron sputtering, sol-gel, ALD and MOCVD. Here, we report the deposition of a-LaAlO3 thin films as a function of the aluminium to lanthanum atomic ratio using spray pyrolysis, a simple and large-area-compatible deposition technique. The films were studied by means of atomic force microscopy, X-ray diffraction, impedance spectroscopy, UVVisible absorption spectroscopy, spectroscopic ellipsometry, and field-effect measurements. Analyses reveal amorphous LaAlO3 that exhibit wide band gap (6.2 eV), low roughness (1.3 nm), high dielectric constant (17), and high breakdown voltage in excess of 3 MV/cm. Thin film transistors based on a-LaAlO3 gate dielectrics employing spray coated ZnO channels exhibit excellent electron transport characteristics with negligible hysteresis, high on/off current modulation ratio (>10^7) and electron mobility in excess of 12 cm^2 V−1 s−1.
Authors : M. Esro1, O. Kolosov2, G. Vourlias3, A. Krier2, W. I. Milne4,5, and G. Adamopoulos1*
Affiliations : 1 Lancaster University, Engineering Department, Lancaster LA1 4YR, UNITED KINGDOM; 2 Lancaster University, Physics Department, Lancaster LA1 4YB, UNITED KINGDOM; 3 Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, GREECE; 4 Department of Engineering, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, UNITED KINGDOM; 5 Kyung Hee University, Display Research Laboratory, Department of Information Display, Seoul 130701, SOUTH KOREA;
Resume : The fundamental material requirements for alternative gate dielectrics to provide performance comparable to SiO2 to be achieved, constitute a very challenging topic. Rare earth oxides (REO) are among the potential candidates for the next generation of gate oxides, because of their high relative permittivity, large bandgap, high crystallisation temperature and thermodynamic stability in contact with a number of semiconducting materials. A wide range of techniques has been used for the deposition of rare earth oxide films including, ion-beam and magnetron sputtering, MBE, PLD, solgel, MOCVD and ALD. Here, we report on the deposition and characterisation of high-k neodymium oxide (Nd2O3) dielectrics grown by spray pyrolysis in air at moderate temperatures. Nd2O3 films on ITO were investigated by means of X-ray diffraction, AFM, admittance spectroscopy, UVVis absorption spectroscopy, spectroscopic ellipsometry, and field-effect measurements. Depending on the deposition temperature (between 400 oC and 600 oC), analyses reveal smooth films (RRMS<2 nm) of amorphous, cubic or hexagonal phase with high dielectric constant in the range between 12 and 19 and high breakdown voltage (>2.9 MV/cm). Thin film transistors employing Nd2O3 gate dielectrics employing spray coated ZnO semiconducting channels exhibit excellent electron transport characteristics with electron mobility in excess of 30 cm^2 V−1 s−1, high on/off current ratio (10^6) and hysteresis-free operation.
Authors : Pasquale Morvillo, Rosita Diana, Eugenia Bobeico, Rosa Ricciardi, Carla Minarini
Affiliations : ENEA, P.le E. Fermi 1, 80055 Portici, Italia
Resume : The architecture of a polymer solar cell (PSC) plays a crucial role on its stability because some of the materials used to build the device can suffer from degradation when exposed to air. In the inverted device configuration, the indium tin oxide (ITO) electrode, covered by a n-type metal oxide is used as the cathode and an air-stable high-work-function metal (e.g. Ag) is used as the anode. Such structure doesnt suffer from the top metal contact oxidation and ITO/PEDOT:PSS interface stability of the conventional structure. In this work, we report the application of low-temperature solution processed zinc oxide or titanium oxide as ETLs in inverted PSCs. The metal oxide thin films were deposited on ITO/glass substrates by spin coating. Photovoltaic devices with the configuration ITO/ETL/blend/MoOx/Ag were then realized in order to investigate the performance of the metal oxides. The photoactive layer is a blend of Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th) and [6,6]-phenyl C71 butyric acid methyl ester (PCBM) (1:1.5 w/w). We made a comparative study of the photovoltaic behavior of devices realized using different ETLs. All the devices were characterized by UV-VIS spectroscopy, IV light, IV dark and quantum efficiency measurements. The best polymer solar cells reached a power conversion efficiency up to 9.5%.
Authors : José M. Vila-Fungueiriño1, A. Carretero-Genevrier2, B. Rivas-Murias1, R. Moalla2, R. Bachelet2, G.Saint-Girons2, F. Rivadulla1
Affiliations : 1 Centro de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS), Campus Vida, Universidade de Santiago de Compostela, 15782-Santiago de Compostela, Galicia, Spain 2 Institut des Nanotechnologies de Lyon (INL) CNRS - Ecole Centrale de Lyon, 36 avenue Guy de Collongue, 69134 Ecully France
Resume : Complex functional oxides exhibit a fascinating range of properties: from colossal magnetoresistance and high-temperature superconductivity to ferroelectricity and multiferroicity. Oxides can therefore potentially provide solutions to many of the technological challenges facing human society, including lower energy consumption devices and transition to renewable sources of energy. In addition, silicon is nowadays the most fundamental technological material in electronic industry. Therefore, it is highly desirable to integrate monolithically oxide films and nanostructures on silicon, since it could open the way to the fabrication of efficient devices applications. In this regard, the presented work takes advantage of all the benefits of soft chemistry to overcome the main challenges for the monolithic integration on silicon of a high temperature ferromagnetic-metallic material . In this work we describe the polymer assisted deposition (PAD)  of epitaxial La0.7Sr0.3MnO3 (LSMO) thin films on SrTiO3/Si. A buffer layer of crystalline STO was previously deposited on top of Si (001) with Sr-passivated surface by molecular beam epitaxy (MBE). The transport and magnetic properties of ultrathin films of LSMO show that it is possible to integrate functional thin films of complex oxides on silicon substrates by exploiting the possibilities of this soft chemical technique.  A. Carretero-Genevrier et al. Nanoscale, 6, 14025 (2014)  Q. X. Jia et al. Nature Mat. 3, 529 (2004)
Authors : Daniel E. E. Deacon-Smith, David O. Scanlon, C. Richard A. Catlow, Alexey A. Sokol, and Scott M. Woodley
Affiliations : University College London, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom
Resume : KTaO3, a I-V ABO3 perovskite, is attracting substantial interest following the discovery of a two-dimensional electron gas (2DEG) on its (001) surface . Little is, however, known of its surface structure unlike the widely studied II-IV, SrTiO3 counterpart . The polar (001) KTaO3 surface, with alternating +1 and -1 charged terminating planes must undergo a reconstruction to become stable. Here, we reveal a new stabilisation mechanism which involves K enrichment of the surface in agreement with experiment . Reconstructions of the TaO2 terminated surface with inter-planar cation exchange result in stable configurations, in which highly charged Ta is fully co-ordinated and only K is exposed on the surface. A global optimisation yields a number of low-energy minimum (2 x 2) reconstructions mediated by this mechanism. We propose that this mechanism is general to polar I-V perovskite surfaces and that it will give rise to novel surface electronic properties.  King, P. D. C. et al. Subband structure of a two-dimensional electron gas formed at the polar surface of the strong spin-orbit perovskite KTaO3. Physical review letters 108 (2012).  Enterkin, J. A. et al. A homologous series of structures on the surface of SrTiO3 (110). Nature Materials 9, 245248 (2010).  Szot, K. et al. Chemical inhomogeneity in the near-surface region of KTaO3 evolving at elevated temperatures. Journal of Physics: Condensed Matter 12, 46874697 (2000).
Authors : D. Afouxenidis1, O. Kolosov2, G. Vourlias3, A. Krier2, W. I. Milne4,5, and G. Adamopoulos1*
Affiliations : 1 Lancaster University, Engineering Department, Lancaster LA1 4YR, UNITED KINGDOM; 2 Lancaster University, Physics Department, Lancaster LA1 4YB, UNITED KINGDOM; 3 Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, GREECE; 4 Department of Engineering, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, UNITED KINGDOM; 5 Kyung Hee University, Display Research Laboratory, Department of Information Display, Seoul 130701, SOUTH KOREA
Resume : Transparent oxide materials have drawn considerable attention due to their unique electrical and optical properties, such as high electron mobility, and optical transparency. In particular, thin film transistors (TFTs) employing amorphous oxide semiconducting channels seem to constitute promising candidates for large-area electronics such as AMOLED displays because of the superior device characteristics over their polycrystalline counterparts or a-Si. Several amorphous oxide semiconductors (AOS), such as gallium indium zinc oxide (GIZO) and Indium zinc oxide (IZO), have been reported as alternative channel materials and fundamental electronic circuits have already been realised. Despite their attractive properties, however, AOS TFTs are usually realised using stringent and potentially costly manufacturing techniques. Here we demonstrate how spray pyrolysis, a simple and large-area-compatible deposition technique, can be used for the processing of high quality GIZO semiconducting channels. The GIZO semiconductors were spray coated onto thermal SiO2 substrates at temperatures in the range between 300 and 600 oC from soluble precursor solutions with varying the Ga, In, and Zn composition. At the optimum deposition temperature and composition, TFTs employing spray coated GIZO semiconducting channels exhibit excellent electron transport characteristics with negligible hysteresis operation, electron mobility in excess of 40 cm^2 V−1 s−1, and high on/off current ratio (10^6).
Authors : Junsoo Kim, Wonchul Choi, Soojung Kim, Taekwang Kim, Hyundal Jung, Dongsuk Jun, Taehyoung Zyung, Eun-su Nam, Seungen Moon, Seung-Min Lee
Affiliations : Energy Harvesting Devices Research Section, ETRI, Daejeon 305-700, Korea; Energy Harvesting Devices Research Section, ETRI, Daejeon 305-700, Korea, Department of Electrical Engineering, KAIST, Daejeon 305-701, Korea; Energy Harvesting Devices Research Section, ETRI, Daejeon 305-700, Korea, Department of Advanced Device Technology, UST, Daejeon 305-350, Korea; Energy Harvesting Devices Research Section, ETRI, Daejeon 305-700, Korea; Energy Harvesting Devices Research Section, ETRI, Daejeon 305-700, Korea; Energy Harvesting Devices Research Section, ETRI, Daejeon 305-700, Korea; Energy Harvesting Devices Research Section, ETRI, Daejeon 305-700, Korea, Department of Advanced Device Technology, UST, Daejeon 305-350, Korea; Energy Harvesting Devices Research Section, ETRI, Daejeon 305-700, Korea; Energy Harvesting Devices Research Section, ETRI, Daejeon 305-700, Korea; Hanbeam co., Suwon, 443-270, Korea
Resume : Thermal property of gate dielectric in MOSFETs is crucial and fundamental information for managing the heat to avoid performance drop or device failure come from the released heat of the devices. The electric devices are getting smaller until few nano meters to maximize the degree of integration, therefore the nano scale thermal properties should be also provided to design the heat dissipation system properly. However, the bulk properties of material cannot be applied because most properties of nano scale films are not same as that of well-known bulks value owing to the phonon scattering at the boundary or phonon confinement effects. Furthermore, the measuring the thermal conductivity of thin film is very hard due to the fact that the measuring the difference of temperature between films cross section is too small and difficult to detect. Here, we introduce the 3ω method that can measure the thermal conductivity stably with small errors less than 10% and report the thermal conductivity of thin film Al2O3 grown by atomic layer deposition (ALD) which is the representative high-k material generally used as a gate dielectric material. The film is also characterized by XPS, RBS to investigate the film quality, such as density and composition of the Al2O3. Our study provides more accurate value of thermal properties which was changed in nano scale so we expect it can help designing the heat managing in integrated circuit more efficient.
Authors : J. Frascaroli (1,2), S. Brivio (1), F. G. Volpe (1), E. Cianci (1), S. Spiga (1)
Affiliations : (1) Laboratorio MDM, IMM-CNR, via C. Olivetti 2 - 20864 Agrate Brianza (Italy); (2) Physics Department, University of Milano, Via Celoria 16 - 20133 Milano (Italy).
Resume : Resistive switching memories (RRAM) are promising candidates for future non-volatile memory applications. Doping of the functional oxide provides an additional degree of freedom for the engineering of the device performance, in particular addressing the switching variability. In this work, we investigate the role of Al concentration up to 7% in Pt/Al:HfOx/TiN RRAM through endurance, retention and random telegraph noise (RTN) characterization. Endurance experiments tested on more 1k DC cycles proved the beneficial effect of the Al introduction on the variability of the resistance levels and switching voltages. However, the increase of the doping concentration determines a deterioration of the high resistance state (HRS) retention, inspected over more than 1 Ms at temperatures up to 180°C. Retention analysis additionally gives an original insight into the oxide properties. We determined a reduction of the effective activation energy for the retention failure process as a function of increasing doping concentration. This finding can be related to an enhanced oxygen species diffusion out of the filament region and different oxide structures of the doped films. The analysis of the RTN additionally reveal the role of the Al doping on the effective number of the electrically active electron traps in the same oxide region. We demonstrate that by tailoring the oxide doping concentration it is possible to achieve the best trade-off between the memory performance and retention behavior
Authors : Laura Begon-Lours, J. Trastoy, L. Phillips, V. Garcia, R. Bernard, E. Jacquet, C. Carretero, K. Bouzehouane, S. Fusil, S. Xavier, C. Ulysse, C. Deranlot, S. Collin, M. Varela, M. Bibes, A. Barthelemy, J. E. Villegas.
Affiliations : Unite Mixte de Physique, CNRS-Thales, 1 Av. Augustin Fresnel, 91120 Palaiseau, France; Laboratoire de Photoniques et Nanostructures, Route de Nozay, 91460 Marcoussis, France; University Complutense of Madrid, Spain
Resume : We study the tunneling resistance of superconductor/ferroelectric/normal-metal vertical junctions based on ultrathin (4 to 8 nm thick) BiFeO3-Mn grown on YBa2Cu3O7 by pulsed laser deposition. The junctions are defined via a series of nanofabrication steps which include e-beam lithography, normal-metal deposition (NbN or Co capped with Pt) and lift-off. We use conductive-tip atomic force microscopy and Piezoresponse Force Microscopy to characterize the transport across the barrier as a function of its ferroelectric state. The observed electro-resistance is discussed in terms of different microscopic mechanisms and variable electric-field screening in the normal and superconducting states. Work supported by DIM Oxymore
Authors : V. Dimza, A.I. Popov, L. Kundzina, M. Kundzins, K. Kundzins, M. Livins, M. Antonova
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga, LV-1063, Riga, Latvia
Resume : Typical ABO3 perovskite type - PLZT (Perovskite Lead Lanthanum Zirconate Titanate) ceramics have attracted great interests in manufacturing electrical capacitors and micro-actuators due to their excellent piezoelectric and ferroelectric properties. In this presentation the results of Mn doping on the the dielectric properties of Perovskite Lead Lanthanum Zirconate Titanate (PLZT, 8/65/35) ceramics are reported. The complex dielectric permittivity measurements as a function of Mn ion concentration were performed in the wide temperature range of 20 to 400 oC at frequencies within the range of 100 Hz 1 MHz. Essential changes caused by the Mn doping in the behavior of dielectric permittivity with frequency and temperature were observed. In particular, at room temperature and electric fields 30 kV/cm it was found that the increase of the Mn concentration leads to the appearance of the following changes to polarization hysteresis loops P(E): firstly, slim (restricted) loops in pure PLZT, then double loops (like antiferroelectric) and then rectangular (like ferroelectric). Thus, if non-doped PLZT corresponds to the typical relaxor behaviour (for example, for pure PLZT is fulfilled the Vogel-Fulcher law), then Mn doping restrain relaxor behaviour and Debye and Maxwell-Wagner type dispersion components appear. The mechanisms of Mn doping and Mn-induced change of vacancy concentration on dielectric and aging properties are discussed.
Authors : David Mora-Fonz, Richard Catlow
Affiliations : University College London; University College London
Resume : ZnO is an important wide-gap n-type semiconductor. Accurate characterisation of surface structure and properties is therefore of vital importance. Recently, ZnO wurtzite films with non-polar surfaces have attracted attention as new materials which show higher emission efficiency for blue or ultra-violet LEDs. Two of the most important issues to address in the study of the non-polar surface structural properties of ZnO are the character of the atomic relaxation at clean surfaces compared to bulk and the electronic structure of such surfaces. Structurally, both: the (10-10) and the (11-20) ZnO surfaces have been investigated extensively using both theoretical and experimental techniques; however, the nature of surface relaxations remains controversial. We will discuss the structure of these surfaces using interatomic potential and ab-initio methods and the stability of features such as steps, dimer vacancies and grooves. The electronic structure of the non-polar ZnO surfaces was predicted using ab-initio methods. A correct positioning of the band edges of ZnO is essential to calculate a great variety of physicochemical properties, which are crucial in the design of electronic devices. We employed a method recently developed by Logsdail et al., which gives a better approximation to the experimental bulk ionization potential values. The last point we will discuss will be the band bending of the VBM and CBM across the surface on the ZnO non-polar surfaces.
Authors : L. Khomenkova1,5,*, P. Normand2, P. Dimitrakis2, E. Kapetanakis2, M. Carrada3, F. Gourbilleau1, A. Slaoui4 and C. Bonafos3
Affiliations : 1) CIMAP, CEA/CNRS/ENSICAEN/UCBN, 6 Blvd Marechal Juin, 14050 Caen Cedex 4, France; 2) INN/ NCSR Demokritos, 153 10 Aghia Paraskevi, P.O.Box 60228, Athens, Greece; 3) CEMES/CNRS, Université de Toulouse, 29 rue J. Marvig 31055 Toulouse Cedex 4, France; 4) ICube, 23 rue du Loess, BP 20 CR, 67037 Strasbourg Cedex 2, France; 5) V.Lashkaryov Institute of Semiconductor Physics, 45 Pr.Nauky, 03028 Kyiv, Ukraine
Resume : Charge-trapping memories such as SONOS and MONOS have attracted considerable attention as promising alternatives for next-generation flash memories due to dielectric layers scalability, process simplicity, power economy, operation versatility. Nevertheless, the continued miniaturization of the devices forces an application of high-k dielectrics. In this work high-k stacked dielectric structures based on the combination of Hf-based and SiNx materials were fabricated. Their structural and electrical properties versus deposition conditions are studied by means of FTIR-ATR and high-resolution TEM techniques. Front- and back-side Al contacts were deposited by thermal evaporation and patterned by photolithography in order to fabricate MIS memory capacitors for electrical characterization. All samples demonstrated smoothed surface (with a roughness below 1 nm) and abrupt interfaces between the different stacked layers. No crystallization of Hf-based layers was observed after annealing at 800°C for 30 min, demonstrating their amorphous nature and phase stability upon annealing. Uniform C-V characteristics were measured along the wafers for all stacks. Besides, after round-voltage sweep they demonstrate significant Vfb hysteresis due to charging of the stack caused by carrier injection from the substrate. These phenomena were found to be more pronounced for the structures with pure HfO2 layers. The associated mechanisms and their tuning parameters will be discussed in details.
Authors : R. Moalla1, Q. Liu1, G. Saint-Girons1, B. Vilquin1, N. Baboux2, G. Sebald3, C. Dubourdieu1, R. Bachelet1
Affiliations : 1 INL-CNRS, Ecole Centrale de Lyon, Ecully, France; 2 INL-CNRS, INSA de Lyon, Villeurbanne, France; 3 LGEF, INSA de Lyon, Villeurbanne, France
Resume : Due to the waste heat in ever more compact microelectronic devices, the harvesting of thermal energy has become interesting for self-powering small devices. Pyroelectric materials which couple a change in temperature to a change in electrical polarization can be used for the conversion of the thermal energy to an electric energy with temperature temporal variation . According to recent reports, single-crystalline pyroelectric films should provide an enhanced conversion energy efficiency with respect to bulk or polycrystalline materials . Here, we show the integration of pyroelectric PbZr0.52Ti0.48O3 thin films by sol-gel process on Si(001) via a thin SrTiO3 buffer layer grown by molecular beam epitaxy (MBE) and a sputtered SrRuO3 bottom electrode. These heterostructures are compared with the same ones grown on SrTiO3(001) substrate. The structural characterizations by RHEED, XRD and AFM show that the heterostructures are epitaxial with flat surfaces and with mixed c/a domains. Ferroelectric hysteresis loops at different temperatures give pyroelectric coefficients close to the bulk value (~250 µC.m-2.K-1), and provide an estimation of the harvested pyroelectric energy of 50 mJ.cm-3.cycle-1. Direct pyroelectric measurements are done and compared to the indirect ones, and the pyroelectric efficiency of single-crystalline films are also compared to that of poly-crystalline ones. : S.B. Lang, Phys. Today 58, 31 (2005) : G. Sebald et al., Smart Mater. Struct. 18, (2009)
Authors : Li Tao, Qin Wei Wei, , Hu Xue Feng, Huang Shengming, and Wei Zhang
Affiliations : State Key Laboratory of Material-oriented Chemical Engineering and School of Chemical Engineering, Nanjing Tech University, Nanjing, Jiangsu 210009, PR China
Resume : Recent discovery in ZnO nanogenarator has spurred tremendous interest in micro-sensor power application. The fundamental principle of ZnO nanogenarator is to utilize the environmental mechanical energy, which is available everywhere from irregular vibrations, light airflow, noise and human activity with a wide spectrum of frequencies and time-dependent amplitudes. The first prototyping of a nanogenarator by means of ZnO piezoelectric nanowire (NW) arrays have demonstrated to able to drive sensor network nods in micro-power range. ZnO piezoelectric thin films have also been successfully transferred onto flexible substrates for stretchable energy harvesting, which suggests new possible applications of piezoelectric nanomaterials. However so far the fundamental mechanism from thin film piezoelectric generator is still unclear. To further clarify the effect of stress-induced and nonsymetry charge center promoted electrical potential is critical for large power output from ZnO nanogenerator. Power output from NW nanogenarator is still in the power range micro watt, which is still far way from milli-power output source requested by most applications of individual sensor and sensor network system. The lacking of high power output in current ZnO NW generator is partially attribute to non-well c-axis oriented crystalline of ZnO NW material and low yield in NW device, both are synthesized by chemical method. Therefore to explore new approach for ZnO NW material synthesis to enhance piezoelectric effect is desirable. In this paper, the effects of the stress on piezoelectric response for ZnO film grown by pulsed-laser deposited (PLD) are investigated. To promote differerent film stress, the ZnO films are deposited at different thcknessa and different temperature. Structurally, special emphasis is placed on XRD characterizations of the films. Additional characterizations using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) will be detailed at a later date. The piezo-electric properties of these films are characterized by Piezoelectric Force Microscopy (PFM). The observed corresponds of piezoelectric (PE) property to stress is also theoretically investigated.
Authors : S. Schamm-Chardon1,3, C. Magen2,3, L. Mazet4, R. Cours1, R. Bachelet4, G. Saint-Girons4, M. Hÿtch1,3, and C. Dubourdieu4
Affiliations : 1- CEMES-CNRS, Université de Toulouse, 31055 Toulouse, France 2- LMA-INA, Universidad de Zaragoza and Fundación ARAID, 50018 Zaragoza, Spain 3- Transpyrenean Associated Laboratory for Electron Microscopy, CEMESINA, CNRSUniversity of Zaragoza, Spain 4- INL, UMR CNRS 5270, Ecole Centrale de Lyon, 69134 Ecully, France
Resume : Ferroelectric oxides integrated on semiconductor substrates are of particular interest for various silicon-based electronic and photonic devices. Among them, the perovskite BaTiO3 is an attractive candidate for integrated photonics and low power logic devices. The control of the crystalline orientation of the ferroelectric tetragonal cell (c- versus a-axis orientation) as a function of the processing parameters is a key issue. In order to support the MBE growth strategy on SrTiO3-buffered Si of epitaxial BaTiO3 thin films with the desired orientation, high-resolution transmission electron microscopy (HRTEM) and high angle annular dark-field (HAADF) atomic structure images of various films were acquired and treated quantitatively using geometric phase analysis. Different deposition conditions were investigated (temperature, oxygen pressure, annealing). In this work, maps of the strain in the BaTiO3 films with respect to the Si substrate are determined at the nanometric scale (1-2nm) to evidence the local tetragonality (orientation and c/a ratio) of the BaTiO3 films. Correlations with the local cation composition are also proposed on the basis of electron energy loss spectroscopy (EELS) performed at the atomic scale. HRTEM work is performed on an image corrected Hitachi HF3300S microscope (I2TEM-Toulouse) and HAADF-EELS on a FEI Titan Low-Base 60-300 (Zaragoza).
Authors : Adrián Carretero-Genevrier1, Judith Oró-Solé2, Jaume Gázquez2, Teresa Puig2, Xavier Obradors2, Clément Sanchez3, Etienne Ferain4, Juan Rodríguez-Carvajal5, Narcís Mestres*2
Affiliations : 1 Institut des Nanotechnologies de Lyon (INL) CNRS- Ecole Centrale de Lyon, 36 avenue Guy de Collongue, 69134 Ecully, France; 2 Institut de Ciència de Materials de Barcelona ICMAB, Consejo Superior de Investigaciones Científicas CSIC, Campus UAB 08193 Bellaterra, Catalonia, Spain; 3 Laboratoire Chimie de la Matière Condensée, UMR UPMC-Collège de France-CNRS 7574. Collège de France, 11 place Marcelin Berthelot, 75231 Paris, France; 4 it4ip sa, 1 avenue Jean-Etienne Lenoir, 1348 Louvain-la-Neuve, Belgium; 5 Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9, France
Resume : Selective synthesis for integrated nanomaterials with controllable morphology and composition represents an emerging research area in nanoscience and nanotechnology because the intrinsic properties behind nanostructures are generally phase-, shape-, and size- dependent. In this direction, the present work shows the capabilities of nanoporous organic and inorganic template systems directly supported on different substrates for the confined growth of epitaxial ferromagnetic complex oxides nanostructures. In particular, we describe the versatility and potentiality of sol-gel precursor solutions combined with nanoporous templates  to synthesize i) polycrystalline La0.7Sr0.3MnO3 nanorods on top of single crystal perovskites, ii) single crystalline manganese based octahedral molecular sieves (OMS) nanowires on silicon [2,3], and iii) epitaxial directional grown single crystal OMS nanowires on fluorite-type substrates . The influence of the distinct growth parameters on the nanostructural evolution of the resulting nanostructures and their magnetic properties are studied in detail. We demonstrate that the combination of soft-chemistry and epitaxial growth opens new opportunities for the effective integration of novel functional complex oxides nanomaterials. . 1 A Carretero-Genevrier et al Chem.Soc.Rev 43 2042 (2014) 2 A Carretero-Genevrier et al JACS 133 4053 (2011) 3 A Carretero-Genevrier et al Chem.Mater 26 1019 (2014) 4 A Carretero-Genevrier et al Chem.Comm 48 6223 (2012)
Authors : Baba WAGUE1, Qiang LIU1, Simon MARTIN2, Nicolas BABOUX2, David ALBERTINI2, Brice GAUTIER2, Pedro Rojo-Romeo1, Bertrand VILQUIN1, Yves ROBACH1
Affiliations : (1) Universite de Lyon, Ecole Centrale de Lyon, Institut des Nanotechnologies de Lyon, CNRS UMR5270, 36 avenue Guy de Collongue, 69134 ECULLY Cedex, France (2) Université de Lyon, INSA de Lyon, Institut des Nanotechnologies de Lyon, CNRS UMR5270, 7 avenue Capelle, 69621 VILLEURBANNE Cedex, France
Resume : Barium strontium titanate (BaxSr1-xTiO3, BST) is a well known ferroelectric material. Moreover this environmentally friendly material - thanks to its lead-free composition - is attractive for microwaves applications, energy harvesting, and electro-optics. In this work, 200nm-thick BST (70/30) has been deposited using two methods: a) sol-gel, which is low-cost and has short fabrication cycle; b) sputtering, producing high homogeneous, large scale, thickness precisely controlled thin film. Two types of bottom electrode were used and their influence on ferroelectric properties and domains switching was investigated: SrTiO3 (STO) substrate, with a SrRuO3 (SRO) interlayer as bottom electrode to get epitaxial BST film; platinum buffered silicon, which is the classical industrial template. Diffraction indicates crystalline BST is c-axis oriented on both substrates. Moreover on SRO-buffered STO the film is epitaxially grown. At nanoscale, the samples were characterized by piezoresponse force microscopy. At macroscale, BST thin films show different behaviors with respect to the different bottom electrodes, measured through current-voltage, capacitance-voltage and PUND (Positive Up Negative Down). These characterizations will be compared with those performed with 200nm-thick PZT films deposited by sputtering and sol-gel on SRO-STO and Pt buffered silicon templates.
Authors : Julien PEZARD1, Jeremy LHUILLIER1,2, Zakarya EL-FRIAKH1,2, Veronique SOULIERE3,Pedro ROJO-ROMEO2, Bertrand VILQUIN2, Mihai LAZAR1
Affiliations : (1) Universite de Lyon, Ecole Centrale de Lyon, Laboratoire AMPERE, CNRS UMR5005, 36 avenue Guy de Collongue, 69134 ECULLY Cedex, France (2) Universite de Lyon, Ecole Centrale de Lyon, Institut des Nanotechnologies de Lyon, CNRS UMR5270, 36 avenue Guy de Collongue, 69134 ECULLY Cedex, France (3) Universite de Lyon, Université Claude Bernard Lyon 1, Laboratoire des MultiMatériaux et Interfaces, CNRS UMR5615, 22 avenue Gaston Berger, 69622 VILLEURBANNE, France
Resume : Graphene is a semiconductor with zero band gap, linear energy dispersion, and linear density of electronic states. One of its most important properties is a strong electric field effect which leads to an electrostatically tunable carrier density in the range of n < 1e14 cm-2. Together with high carrier mobilities for both electrons and holes (as high as 10000 cm2/V.s at room temperature), this attracts a lot of attention to graphene as a possible material for a future high-speed field effect transistor (FET). Graphene layer was synthetized from silicon carbide wafers (SiC) by evaporating Si atoms from 4H-SiC surface at high temperature thanks to a high energy electron beam in UHV. The formation of single layer graphene has been confirmed by Raman spectroscopy: peaks at 1580 cm-1 (G-peak) and 2690 cm-1 (2D peak), originated from graphene in-plane vibrational modes. After deposition of SiO2 functional oxide, the whole layers were patterned to realize a FET device. The graphene channel has width about 40µm and length between 2µm and 16µm. The application of voltage up to 9V at room temperature on the binary oxide gate leads to on-off working operation with a variation about 600% of the drain current.
Authors : L. Znaidi*, T. Chauveau, A. Tallaire, F. Liu, M. Rahmani, V. Bockelee, D. Vrel, P. Doppelt
Affiliations : Université Paris 13, Sorbonne Paris Cité, Laboratoire des Sciences des Procédés et des Matériaux (LSPM), CNRS - UPR 3407, 99 avenue Jean-Baptiste Clément, 93430 Villetaneuse, France
Resume : ZnO is both a piezo-electric and electro-optic material, and a semiconductor which possesses a wide band gap (~3.3 eV)  with as its most unique property an exciton binding energy of 60 meV . However, the properties of ZnO thin film depend greatly on the crystallographic texture, and the control of the crystallization and growth direction is therefore essential. For example, (002)-oriented ZnO have practical applications such as light emitting diodes and sensor arrays . Similarly, other specific orientations may exhibit different interesting properties and the precise control of the final texture of the films is therefore a key parameter for their wider development. With significantly lower investment costs and a highly-controlled way for ZnO thin films elaboration, the sol-gel process has emerged as being very attractive compared to other deposition methods. Zinc acetate dihydrate, ethanol and monoethanolamine were used as starting materials, solvent and stabilizer, respectively. The multi thin layers are prepared by spin-coating onto glass substrates, and are transformed into ZnO upon annealing at 500°C. The structural, morphological, and optical properties of the thin films as a function of precursor concentration have been investigated using X-Ray Diffraction (XRD, Rietveld and texture analysis), Scanning Electronic Microscopy (SEM), Atomic Force Microscopy (AFM) and Cathodo-Luminescence (CL). The results obtained from the different characterization techniques will be presented and discussed. ω 2 θ scans and texture measurements were performed by XRD. On all samples, the different analyses show two main texture components (fibers) <00.2> and <05.2>. From the ODF (Orientation Distribution Function), volume fractions of these two components were calculated. Keywords: Sol-gel, ZnO thin films, Spin-coating, Texture, ODF, Volume fractions  A.B.M.A. Ashrafi, Y. Segawa, K. Shin, J. Yoo, T. Yao, Appl. Surf. Sci. 249 (2005) 139144.  K.K. Kim, J.H. Song, H.J. Jung, S.J. Park, J.H. Song, J.Y. Lee, J. Vac. Sci. Technol. A 18 (6) (2000) 28642868.  C.S. Lao, Q. Kuang, Z.L. Wang, M.C. Park, Y. Deng, Appl. Phys. Lett. 90 (2007) 262107.
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Resistive switching in oxides I : Sabina Spiga
Authors : Ilia Valov
Affiliations : Research Centre Juelich, Electronic Materials PGI 7
Resume : Redox-based resistive switching memories are key factor for development of the future nanoelectronics and information technology fulfilling the demands for low power consumption, high information density, fast read and write speeds and non-volatility. These two electrode electrochemical systems also demonstrate great promise as building units for memrisitve and neuromorphic operations, paving the way for beyond von Neumann computing. The present talk will focus on the interface dynamics of nanoscaled memristive devices emphasizing the different interactions at the atomic scale. The importance of local charge concentration and distribution, and the generic relevance of the counter charges will be highlighted. The nanobattery effect and its implications on both memristors theory and device stability and performance will be discussed on theoretical and experimental level. Strategies for improving the memristive devices will be pointed out
Resistive switching in oxides II : Rainer Waser
Authors : Jennifer L. M. Rupp1, Felix Messerschmitt1, Sebastian Schweiger1, Rafael Schmitt1 and Markus Kubicek1
Affiliations : 1) ETH Zurich, Department of Materials, Electrochemical Materials, Honggerbergring 64, 8093 Zurich, Switzerland
Resume : Bipolar resistive switches were recently proposed as a new class of non-volatile switches capable of reading, writing and erasing memory information by switching non-linearly between low- and high-resistance values by application of mV voltage pulses in the ns range. In the last years, resistive switching has been reported for various classes of materials ranging from sulfides to oxides. Despite their promises oxide-based resistive switches are rarely connected in their diffusion kinetics and constants to the memristive device performance characteristics under bias. In particular, models to describe the mixed anionic-electronic defect contributions for two-carrier systems are missing; this difficults the material selection criteria for best performing devices beyond classic gate oxide selection. Firstly, we report on how to probe carrier diffusion characteristics and memristance for mixed anionic-electronic resistive switches and their oxide materials for the newly proposed Memristor-based Cotrell analysis. For this, we fabricated 2-terminal Pt|SrTiO3-δ|Pt cross-bar array structures as a model system in terms of its mixed defects which show stable and reproducible resistive switching. Secondly, new material engineering of oxides are discussed to control resistive switching device properties like retention, Ron/Roff ratios and power consumption by "interfacial strain engineering of mixed conducting oxide" is reported. Lattice strain engineering using heterostructures at internal interfaces can be used to tune material properties in micro-dots as new resistive switching archiectures far beyond the change accessible by doping. We exemplify the switching characteristics based on either comprsively or tensily strained Gd0.1Ce0.9O2-x heterolayers by Er2O3 or Sm2O3 monolayer modulation, respectively. Thirdly, the role of grain boundaries is discussed for epitaxially and nm-roughness grown LaFeO3 thin film resistive switches with controlled defect levels. We compliment classic resistive switching tests characterizing the near order Raman vibrational (ionic bonding), direct and non-linear optic spectroscopy techniques (electronic contributions).
Authors : Luca Montesi, Mark Buckwell, Leon Garnett, Adnan Mehonic, Steve Hudziak, Tony Kenyon
Affiliations : Department of Electronic & Electrical Engineering - University College London.
Resume : Modern digital computers are inefficient at reproducing the behaviour found in biological neuronal networks that arises from extreme parallelism and the complex and dynamic nature of neuronal plasticity and synaptic signaling. Despite dissipating megawatts, not even supercomputers can emulate a relatively simple neuronal network in real-time. On the other hand, memristors and ReRAM devices have exhibited synapse-like behaviour under pulsed electrical stimulation. Such analogue neuronal networks have been shown to function while dissipating only a few watts. Here we show that a ReRAM TiN/SiOx/TiN device characterized by intrinsic switching is capable of neuromorphic behaviour. Conductance can be increased or decreased by means of subsequent potentiating or depressing pulses. In particular, long and short-term memory phenomena occur at nanosecond time scales. This will allow for fast and power efficient emulation of mammalian-brain-like biological networks. Our device is also fully compatible with CMOS technology, allowing for cost-effective design and fabrication of networks involving billions of devices.
Authors : Yao Shuai, Xin Ou, Wenbo Luo, Arndt Mücklich, Danilo Bürger, Shengqiang Zhou, Chuangui Wu, Yuanfu Chen, Wanli Zhang, Manfred Helm, Thomas Mikolajick, Oliver G. Schmidt, & Heidemarie Schmidt
Affiliations : State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China; Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, P. O. Box 510119, Dresden 01314, Germany; Technische Universität Dresden, Institut für Angewandte Physik, 01062 Dresden, Germany; Namlab gGmbH, Technische Universität Dresden, Institute of Semiconductors and Microsystems, Nöthnitzer Strasse 64, Dresden01187, Germany; nstitute for Integrative Nanosciences, IFW Dresden, Helmholtzstraße 20, Dresden 01069, Germany; Technische Universität Chemnitz, Department of Materials for Nanoelectronics, Faculty of Electrical Engineering and Information Technology, Chemnitz 09126, Germany
Resume : Bipolar resistive switching has been observed in the Au/BiFeO3/Pt/Ti capacitor-like structures [1-3]. From the energy filtered transmission electron microscopy and Rutherford backscattering spectrometry it is observed that Ti diffusion occurs if the deposition temperature is above 600 °C. The current-voltage (I-V) curves indicate that resistive switching can only be achieved where this Ti diffusion occurs. The effect of Ti diffusion is confirmed by the BiFeO3 thin films deposited on Pt/sapphire and Pt/Ti/sapphire substrates. The resistive switching needs no electroforming process, and is incorporated with rectifying properties which is potentially useful to suppress the sneak current in a crossbar architecture. After low-energy Ar+ irradiation, the retention of the structure is significantly improved, which is due to the stabilization of the trapping charges inside the thin films. Those specific features open a promising alternative concept for nonvolatile memory devices as well as for other memristive devices like synapses in neuromorphic circuits. References 1.Shuai, Y., et al., Appl. Phys. Express 4, 095802 (2011). 2.Shuai, Y., et al., J. Appl. Phys. 109, 124117-124114 (2011). 3.Shuai, Y., et al., Appl. Phys. Lett. 98, 232901-232903 (2011). 4.Shuai, Y., et al., IEEE Electron Dev. Lett. 34, 54-56 (2013). 5.Shuai, Y., et al., Sci. Rep., 3, 2208 (2013).
Authors : R. Dittmann, N. Raab, C. B?umer, R. Waser
Affiliations : Peter Gr?nberg Institute (PGI 7), Forschungszentrum J?lich GmbH, J?lich, Germany; Institut f?r Werkstoffe der Elektrotechnik, RWTH Aachen, Aachen, Germany
Resume : Resistive switching oxides are promising candidates for the next generation of non-volatile memories. It is generally assumed that defects have a strong impact on the resistive switching properties of transition metal oxides. However, the correlation between different types of defect structures and the switching performance is still elusive. In a first step, we deposited single-crystalline SrTiO3 thin films with various cation stoichiometry by pulsed laser deposition in order to modify their defect structure and investigated the influence on the resistive switching properties. We observed differences in initial states, forming steps, and switching characteristics, which are analyzed taking into account both point defects and extended defects. In particular, we observed a significant correlation between the presence of extended defects and the increase of the retention time at low currents. Besides internal interfaces provided by extended defects, we investigated the impact of heterointerfaces between SrTiO3 and different insulating oxides. We could clearly demonstrate that the retention time of SrTiO3/Au thin film devices is strongly improved by inserting oxide interlayers such as SrO, Al2O3 and ZrO2 of only one nm. We will present a consistent explanation for the modified properties observed in non-stoichiometric thin films and discuss the modification of the retention times in the framework of the presence of space charges and modified oxygen transport at internal and external interfaces.
Authors : C. M. Orfanidou1, C. N. Mihailescu1, 2, V.H. Mai3, V. S. Nguyen4, O. Schneegans4, G. E. Stan5 and J. Giapintzakis*1
Affiliations : 1Nanotechnology Research Center and Department of Mechanical and Manufacturing Engineering, University of Cyprus, 75 Kallipoleos Avenue, PO Box 20537, 1678 Nicosia, Cyprus 2National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Street, PO Box MG-36, RO-077125 Magurele, Romania 3CEA, LIST, 91191, Gif Sur Yvette Cedex, France 4Génie Électrique et Électronique de Paris, CNRS, UPMC and Paris-Sud Universities, Supélec, 11 rue Joliot-Curie, 91192 Gif-sur-Yvette, France 5National Institute of Materials Physics, 105bis Atomistilor Street, PO Box MG-07, RO-077125 Magurele, Romania
Resume : LixCoO2 is a very well known material as it has been used as a cathode material in commercial Liion batteries during the last decades. Recently, resistive switching (RS) phenomena have been reported for polycrystalline LixCoO2 thin films grown on highly doped silicon wafers [p++ Si (111)] using conducting probe atomic force microscopy (CP-AFM) [1,2]. We have fabricated metal-insulator-metal (MIM) devices based on LixCoO2 thin films grown by pulsed laser deposition (PLD) on p++ Si (111) and used two-probe I-V measurements to investigate the effect of SiO2- and LixCoO2-layer thickness on the resistive switching behavior of the devices. In this presentation, we will discuss a plausible mechanism that governs the RS behavior of MIM devices based on LixCoO2 thin films. Unraveling the mechanism governing these RS phenomena could lead to the usage of LixCoO2 thin films in new technological applications, such as resistive random access memories (RRAM) and neuromorphic systems.  A. Moradpour, O. Schneegans, S. Franger, A. Revcolevschi, R. Salot, P. Auban-Senzier, C. Pasquier, E. Svoukis, J. Giapintzakis, O, Dragos, V. C. Ciomaga, P. Chrétien, Adv. Mater. 23, 4141-4145 (2011)  V.H. Mai, A. Moradpour, P. Auban Senzier, C. Pasquier, K. Wang, M.J. Rozenberg, J. Giapintzakis, C.N. Mihailescu, C.M. Orfanidou, E. Svoukis, A. Breza, Ch. B. Lioutas, S. Franger, A. Revcolevschi, T. Maroutian, P. Lecoeur, P. Aubert, G. Agnus, R. Salot, P.A. Albouy, R. Weil, D. Alamarguy, K. March, F. Jomard, P. Chrétien, O. Schneegans, Sci. Rep., Accepted
Advanced characterization of oxides : Jennifer Rupp and Anke Weidenkaff
Authors : M.C. Weber1,2, Mael Guennou1, Constance Toulouse3, Maximilien Cazayous3, Yannick Gillet4, Xavier Gonze4, Jens Kreisel1,2
Affiliations : 1 Luxembourg Institute of Science and Technology 2 University of Luxembourg 3 LMPQ, Université Paris Diderot-Paris 7 4 Université Catholique de Louvain
Resume : Knowledge of the electronic band structure of materials is a cornerstone of modern technology. In functional dielectric and multiferroic oxides, traditionally seen and used as insulating materials, electronic structures have been much less explored than in semiconductors. However, today, they gain importance with the growing interest for interactions of ferroic materials with light, namely in the view of photovoltaic or photoelectric properties. Here, we show how resonant Raman spectroscopy enables to probe electronic levels of the model multiferroic BiFeO3 (BFO). Using twelve different excitation wavelengths ranging from the deep blue (442 nm = 2.8 eV) to the infrared (785 nm = 1.6 eV), we show that both the first- and second-order Raman signatures of the crystals differ significantly for different laser wavelengths. Careful analysis of the intensities allows the discussion of oxygen electronic defect levels and both the direct and indirect band-gaps. Notably, temperature-dependent experiments provide the first experimental indication that the reported strong variations of the optical band-gap in BFO originates from a decreasing indirect electronic gap. More generally, our study suggests that Raman scattering at various wavelengths offers a well-adapted probe for the investigation of electronic excitations in multiferroic functional oxides.
Authors : Gabriele De Luca, Manfred Fiebig, Morgan Trassin
Affiliations : Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 4 10, 8093 Zurich, Switzerland
Resume : The evidence of the electric field control on the antiferromagnetic ordering in BiFeO3 (BFO) increased interest in low energy consumption logic and memory devices. However, to exploit such functionality for devices it is essential to attain deterministic control of ferromagnetism at the single domain scale. In a recent demonstration of room temperature electric field induced magnetization reversal, a ferromagnet/multiferroic heterostructure has been designed based on the combination of magnetoelectric coupling in BiFeO and exchange coupling between magnetic materials. Understanding the underlying BFO domain architecture is a key parameter towards robust and reliable magnetization rotations. Here we show that second harmonic generation (SHG), can detect the distribution of ferroelectric domains in BFO thin films non-invasively and unimpeded by transport properties. We use epitaxial strain for engineering different types of BFO domain patterns that are characterized by SHG, showing a unique relation between the domain distribution and the film symmetry. We then manipulate the BFO film by voltage poling and demonstrate the sensitivity of the SHG process to this manipulation. The concept applied to BFO is transferable to other multiferroics compounds thus indicating the general feasibility of SHG as a characterization technique for heterostructures in which buried ferroelectricity plays a key role in the emergence of magnetoelectric coupling. 1-Heron et al., Nature. (2014)
Authors : O. Vlasin, B. Casals, D. Guitérrez, N. Dix, F. Sánchez, G. Herranz
Affiliations : Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra 08193, Catalonia, Spain
Resume : The electrical polarization in ferroelectrics can be reversed by the application of electric fields. This property is exploited in nonvolatile memories to achieve bistable operation for digital processing and storage. While the potential of ferroelectrics for data processing and storage is beyond doubt, a deep understanding of the dynamics and the local response is crucial for the comprehension of the mechanisms underlying the endurability, retention and fatigue effects in ferroelectric devices. Here we present a comprehensive methodology that exploits optics as a probe of ferroelectric properties with lateral resolution a few hundreds of nanometers. For that purpose, we adapted a confocal optical arrangement to measure the rotation and ellipticity of the polarization of light at the diffraction limit. We have imaged the birefringence of BaTiO3 thin films and identified the contributions arising from electro-optics linked to ferroelectricity as well as strain arising from converse piezoelectricity, so that both properties were mapped out simultaneously. Remarkably, the optical imaging displayed inhomogeneous spatial distributions of both ferroelectric- and strain-related responses, so that they exhibited significant fluctuations in the scale of the micrometer. While possible scenarios for this non-uniformity are discussed, our work underscores the relevance that these variations may have when ferroelectric devices are downscaled to sizes comparable to the micron.
Authors : Alexandre Boulle, Ingrid C. Infante, Nathalie Lemée
Affiliations : SPCTS CNRS UMR 7315, Centre Européen de la Céramique, 12 rue atlantis, 87068 Limoges Cedex, France SPMS, CNRS UMR 8580, École Centrale Paris-Supelec, Grande voie des vignes, 92295 Châtenay-Malabry, France LPMC, EA 2081, Université de Picardie Jules Vernes, 33 rue Saint Leu, 80039 Amiens, France
Resume : An intrinsic property of materials presenting ferroic orders such as magnetization, polarization and/or deformation is the presence of domains, implying the presence of domain walls. In ferroelectric thin films and multilayers, domains may arrange in the form of periodic 180° stripe-domains of alternating up and down polarization so as to reduce the depolarizing field, hence ensuring charge neutrality at the surface or at the ferroelectric/paraelectric interfaces. These domains give rise to a modulated X-ray diffraction (XRD) signal with satellites near the main Bragg peak. From their position and intensity, both the domain period and relative polarization can be straightforwardly obtained. In this work, we show that a complete simulation of the XRD curves allows the determination of not only the relative polarization and periodicity, but also to have access to the total ferroelectric domain size distribution, as well as to the thickness of the domain wall or the wall roughness and tortuosity. The potential of our model will be illustrated for the case of tricolor PbTiO3/SrTiO3/PbZr0.2Ti0.8O3 superlattices and studied from room temperature up to 900K through ferroelectric transition. We show that the closure of the electric field lines at the ferro/para interfaces is the source of an important ferroelastic strain which can be determined from the XRD curves. We will discuss the possible opening of this model to other ferroic thin films materials presenting structural domains.
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Oxides on semiconductors I : Jens Kreisel
Authors : M. Scigaj, N. Dix, I. Fina, R. Bachelet, V. Skumryev, B. Casals, G. Herranz, J. Fontcuberta, F. Sánchez
Affiliations : Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra 08193, Spain
Resume : Multiferroic materials are appealing for its application in microelectronic devices, but coexistence of ferroelectricity and ferromagnetism in a single material is generally restricted to low temperatures. Artificial multiferroics, combining ferroelectric and ferromagnetic phases are an alternative. High quality multiferroic ferromagnetic/ferroeletric heterostructures can be fabricated on oxide single crystals, but its integration with silicon is still elusive. We show here that high quality epitaxial CoFe2O4/BaTiO3 bilayers can be grown on buffered Si(001). The use of a complex LaNiO3/CeO2/YSZ buffer layer was found key to obtain c-axis orientation of BaTiO3. Consequently, CoFe2O4/BaTiO3/LaNiO3/CeO2/YSZ heterostructures were deposited on Si(001) in a single process by pulsed laser deposition assisted with high energy electron diffraction (RHEED). Atomic force microscopy, X-ray diffractometry, and RHEED confirm high structural quality of the CoFe2O4/BaTiO3 heterostructures. CoFe2O4/BaTiO3 bilayers display good multiferroic properties, with high values of magnetization (> 200 emu/cm3) and polarization (>15 uC/cm2) at room temperature. Remarkably, the polarization of CoFe2O4/BaTiO3 bilayers is enhanced, current leakage is reduced compared with bare BaTiO3 films, and there is no fatigue up to more than E10 cycles.
Authors : Min-Hsiang Mark Hsu1,2, Marianna Pantouvaki1, Clement Merckling1, Salim El Kazzi1, Joris Van Campenhout1, Philippe Absil1 & Dries Van Thourhout2,3
Affiliations : 1 IMEC, Kapeldreef 75, 3001, Leuven, Belgium ; 2 Photonics Research Group, INTEC, Ghent University imec, Ghent, 9000 Belgium; 3 Center for Nano- and Biophotonics (NB-Photonics), Ghent University, Ghent 9000,
Resume : In the purpose to achieve optical modulator devices with high speed and low power consumption, ferroelectric materials with strong Electro-Optical (EO) properties are of high interest. Due to its large Pockels coefficient, BaTiO3 (BTO) is considered as one of the most promising candidates. However, the integration of BTO on Si(001) used for waveguides is still very challenging. This work tackles this problem and describes the co-deposition of BTO molecular beam epitaxy on both Ge-on-Si(001) (GoS) pseudosubstrates and SrTiO3 (STO) on Si(001) pseudosubstrates. We first optimize respectively the growth conditions of 0.5 ML BaO (SrO) at the BTO/GoS (STO/Si) interface which is used to enable the in-plane lattice rotation of 45˚ between BTO (STO) perovskites structure and Ge (Si) substrates to reduce the effective mismatch below 3% between the different lattices. Then, optimal BTO epitaxial conditions for both pseudosubstrates have been characterized physically and optically by reflection high energy electron diffraction, x-ray diffraction, photoluminescence, transmission electron microscope and Rutherford backscattering spectroscopy. At last, EO behaviour and waveguide properties of the BTO epitaxial film onto the Ge/Si and STO/ Si are benchmarked with previous studies.
Oxides for energy applications : Andrei Kholkin
Authors : Anke Weidenkaff, Wenjie Xie, Xingxing Xiao, Denitsa Shopova
Affiliations : Materials Chemistry, Institute for Materials Science, University of Stuttgart, Heisenbergstr. 3, DE-70569 Stuttgart; Germany
Resume : The future application of high temperature thermoelectric converters in sustainable energy technologies requires the development of active, stable, low cost and environmentally friendly materials. Heat from concentrated solar insolation, geothermal or waste heat from power plants could be used to provide electricity in a simple sustainable way, if the thermoelectric energy conversion, i.e. the direct transformation of heat into electricity becomes fast and highly efficient. The Carnot efficiency and energy density of such a conversion process is expected to increase with the applied temperature gradients and to be superior to the state-of-the-art low temperature processes. Semiconductors based on perovskite ? type oxides are very attractive for thermoelectric energy conversion processes in air at high temperatures. Their good performance can be explained based on their suitable band structure, adjusted charge carrier density, mass and mobility, limited phonon transport, strongly correlated electronic systems, etc. High temperature powered thermoelectric generators are being constructed with novel non-toxic, temperature stable and more efficient thermoelectric oxide materials. Tailor made perovskite-type titanates, manganates and cobaltates with strongly correlated electrons are used as prospective thermoelectrics. Calcium manganates and strontium titanates are most promising n-type thermoelectric materials, while cobaltates with large spin-orbit entropy factor are showing
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Authors : J. Santiso1,2, H. Téllez2, A. Gutierrez1,3, J. Zapata1, R. Moreno1, J. Roqueta1, A. Magrasó1, J. M. Caicedo1, J. Druce2, J. A. Kilner2 and T. Ishihara2
Affiliations : 1 ICN2, Institut Catala de Nanociencia i Nanotecnologia, Bellaterra, Barcelona (Spain); 2 I2CNER International Institute for Carbon Neutral Energy Research, Fukuoka (Japan); 3 URJC, Universidad Rey Juan Carlos, Madrid (Spain)
Resume : Functional properties of multicomponent oxide materials with perovskite structure are very dependent on the cation and oxygen chemical composition. In most cases only average values of the cation composition are measured by EDS, WDS or ICP. Distribution of cations in depth is difficult to address in very thin films, because most standard techniques, like XPS, provide information from a few atomic layers. Therefore, any changes produced at the outermost film surface become blurred by the deeper analysed volumes. Low Energy Ion Spectroscopy (LEIS) is one of the few techniques capable of analysing the chemical composition of one single atomic layer at the surface, which in combination with a low energy ion sputtering gives rise to high resolution depth profiling. In this study we have analysed by LEIS high crystal quality PLD-grown epitaxial films of different perovskite oxide materials, like Ba0.5Sr0.5Co0.8Fe0.2O3- and GdBaCo2O5.5+, in order to elucidate the real composition profile of the film surface. The analyses showed in all cases A-site terminated surface. Despite the purity and high crystal quality shown by HRXRD analysis as deposited films presented inhomogeneities of the A-site or B-site occupancies along the film growth direction. Post deposition annealing at temperatures as low as 500°C in 200 mbar O2 induced progressive changes in the composition profile of the outermost surface even after the short time exposure of only 15 min. These changes point to non-negligible kinetics for A or B cation migration at the nanoscale in the outer and sub-surface regions, which is a general trend in a variety of complex oxide materials. The driving forces underlying this phenomenon are discussed in view of the results.
Authors : M. Arrigoni, T. S. Bjørheim, E. A. Kotomin, J. Maier
Affiliations : Max Planck Institute for Solid State Research, Stuttgart, Germany; Center for Mater. Sci. and Technology, Dept. of Chemistry, University of Oslo, Norway; Max Planck Institute for Solid State Research, Stuttgart, Germany; Max Planck Institute for Solid State Research, Stuttgart, Germany.
Resume : ABO3 perovskite oxides comprise a broad family of technologically important materials, which display a wide range of functional properties such as ferroelectricity, piezoelectricity, magnetism, high-temperature superconductivity, mixed ionic-electronic conductivity and electro-optic effects. BaZrO3 membranes have attracted considerable attention for potential applications in electrochemical devices such as solid oxides fuel cells (SOFCs), sensors and hydrogen pumps, due to high proton conductivity and good chemical stability. Doping with trivalent cations (usually Y3+) results in the formation of charge-compensating oxygen vacancies, and subsequent exposure to humid atmosphere leads to incorporation of protons through dissociative absorption of H2O. Although doubly positively charged oxygen vacancies dominate in acceptor doped oxides, vacancies with two trapped electrons (the color F center) are more common in undoped oxides. In addition, these two charge states (+2 and 0) of the oxygen vacancy represent limiting cases in partly ionic and partly covalent perovskites, where electrons are neither fully localized in the oxygen vacancy by the electrostatic field, as in ionic compounds like MgO, nor completely localized on the dangling bonds of the nearest cations, as in covalent materials such as silicates. In this study, we apply two complementary first principles methods: the linear combination of atomic orbitals (LCAO) and the plane-wave method with the projector augmented waves (PAW) approach, employing the hybrid HF-DFT PBE0 functional and different pure DFT functionals, to develop a more accurate and complete approach for investigation of the structural, electronic and vibrational properties of oxygen vacancies in variable charge states in ultrathin films of BaZrO3. We consider non-stoichiometric, symmetrical (001)-terminated slabs, with a number of atomic layers ranging from 3 to 9; corresponding to a free standing film of up to ca. 2 nm thickness. For comparison, we considered both BaO and ZrO2 terminated films, in addition to stoichiometric 6-layer films. Vibrational properties were calculated within the harmonic approximation and the finite displacements method by numerical evaluation of the dynamical hessian matrix elements through the first derivative of the atomic energy gradients. The main focus was on the charge density redistribution in different slab layers, and the defect formation energy with a particular emphasis on the vibrational contributions to the Gibbs formation energy and the confinement effects in general. Finally, we address possible confinement effects on the thermodynamics of oxygen vacancies in ultrathin films.
Authors : Y. Liu1, I.C. Infante1, P.E. Janolin1, XJ Lou2, XB Ren2, W. P. Geng3, A. Q. Jiang3, X. J. Meng4, D.C. Lupascu5, L. Bellaiche6, J. F. Scott7, B. Dkhil1
Affiliations : 1Laboratoire Structures, Propriétés et Modélisation des Solides, UMR8580, CentraleSupélec, CNRS, Université Paris-Saclay, 92290 Châtenay-Malabry, France; 2Multi-disciplinary Materials Research Center, Frontier Institute of Science and Technology, and State Key Laboratory for Mechanical Behavior of Materials, Xian Jiaotong University, Xian 710049, P. R. China; 3State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433, P. R. China; 4National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Yu Tian Road 500, Shanghai 200083, P. R. China, University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, China; 5Institute for Materials Science, University of Duisburg-Essen and Center for Nanointegration Duisburg-Essen (CeNIDE), Essen 45141, Germany; 6Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, 72701 Arkansas, USA; 7Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK and Departments of Chemistry and Physics, St. Andrews University, St. Andrews, Scotland KY16 9ST
Resume : The search for alternative solid-state refrigeration materials to hazardous gases in conventional and cryogenic cooling devices is a very active field of condensed matter. The use of phase transitions is a powerful tool to achieve giant caloric effects in ferroic materials in which magnetization, polarization, strain and/or volume can be strongly tuned under a moderate external stimulus. Here, we explored various phenomena existing in ferroelectrics to reveal their potentialities as solid state coolers. By using Landau-based phenomenological calculations, we studied the elasto- and electro-caloric properties of the model and ecofriendly BaTiO3 in details including bulk and thin film form, the role of the external uniaxial stress, electric field, substrate, film thickness and electrodes. We show that ferroelectrics are natural multicaloric materials in which both giant elasto- and electro-caloric responses can be achieved near room temperature and that the 2nd-order nature of transitions can be beneficial. We also investigated how multiphase points composition can be used to enhance electrocaloric effects. Moreover, in addition to conventional electrocaloric effect, we show that negative effect can be also generated efficiently and thus used as a supplemental tool for designing enhanced caloric responses. As a conclusion, our findings clearly demonstrate promising perspectives for ferroelectrics in solid-state refrigeration.
Authors : J.V. Vidal1, I.V. Kubasov2, M.D. Malinkovich2, S.P. Kobeleva2, A.L. Kholkin3, N.A. Sobolev1
Affiliations : 1Department of Physics and I3N, University of Aveiro, 3810-193 Aveiro, Portugal; 2National University of Science and Technology MISIS, 119049 Moscow, Russia; 3Department of Materials and Ceramic Engineering and CICECO, University of Aveiro, 3810-193 Aveiro, Portugal;
Resume : We present a study of the anisotropic direct magnetoelectric (ME) properties of bilayered composites featuring single-crystalline piezoelectric plates of LiNbO3 (LNO) and LiTaO3 (LTO) possessing a bidomain structure with opposite polarization vectors (i.e. a head-to-head domain structure). The latter systems thus behave as bimorph piezoelectrics. Here, a bidomain structure was obtained in LNO and LTO square shaped plates by a stationary external heating method. Thin foils of the magnetostrictive Metglas alloy were then bounded to one face of differently cut unidomain and bidomain piezoelectric crystals. The studied systems included: Z-cut LNO and LTO and 128ºY-cut LNO. The quasistatic ME coupling was found to be only slightly smaller in the bidomain samples. Large ME effects were obtained in resonance corresponding to low-frequency bending and high-frequency contour modes of vibration. Of note is the fact that the contour modes were suppressed in the bidomain systems, whereas the bending modes were enhanced. A bending resonance coefficient as large as 50 V/(cmOe) has been obtained at 30 kHz in the 128ºY-cut LNO bidomain sample. Thus, we have shown that such a system can possibly be used in sensitive, low frequency magnetic and current sensors also offering the possibility to partially reject external vibrational and thermal noises due to its asymmetric bimorphic geometry. A more efficient stress transfer is also achieved by removing the need to bound interfaces in bimorphs.
Authors : P. Homm, L. Dillemans, M. Menghini, B. Van Bilzen, C.-Y. Su, R. R. Lieten, J.-P. Locquet
Affiliations : Dept. of Physics and Astronomy, KU Leuven, Leuven, Belgium
Resume : In this work, we report the structural and the electrical properties of Cr doped V2O3 thin films grown epitaxially on c-Al2O3 by oxygen-assisted molecular beam epitaxy (MBE). The Cr concentration in the samples was varied from 0 to 21%. For the undoped samples, the sharp and well-known metal to insulator transition at about 160K is clearly observed. For the highly doped samples, a regular and monotonous increase of the resistance with decreasing temperature is measured. Surprisingly however, in the intermediate regime (between 1% and 4%) a collapse of the insulating state is determined with a reduction of the low temperature resistivity by up to 5 orders of magnitude. This is likely caused by a small excess of oxygen (1-2%) in the thin films. These results suggest that slightly Cr doped V2O3 films may be interesting for field effect devices.
Authors : A. Gokarna*,1, P. Miska2, K. Nomenyo1, R. Aad1, W.Geng1, C. Couteau1, G. Lerondel1
Affiliations : 1 LNIO, ICD, STMR (UMR 6279), CNRS - Université de Technologie de Troyes, 12 rue Marie-Curie BP2060, 10010 Troyes, FRANCE 2 Institut Jean Lamour CNRS UMR 7198 Université de Lorraine, Faculté des Sciences et Technologies, BP 70239, F-54506 Vandoeuvre les Nancy, France.
Resume : Zinc oxide is one of the most promising electronic and photonic materials due to its wide direct band gap of 3.37eV and large exciton binding energy of 60meV. It has attracted attention as a luminescent material in various applications such as UV-light-emitting diodes , chemical sensors , solar cells  etc. ZnO nanowires (NWs) grown in solution have been extensively however, there are extremely few reports on ZnO microstructures which are naturally formed in the solution as a by-product during the synthesis of the NWs. The aim of this work was to study these highly crystalline ZnO microstructures. Microstructures ZnO were grown at a low temperature (<90°C) in solution by using chemical bath deposition method. These microstructures are observed to be abundantly forming in the solution when the Zinc acetate concentration in the solution is above 0.056M. Interestingly they can get deposited on any substrate and do not require any ZnO nucleation layer as in the case of NWs. The obtained microstructures turn to be micropods with perfect hexagonal shape as observed by SEM. These micropods come with varying number of arms, some have two arms (bi-pods), four arms (tetra-pods) or six arms (hexa-pods) which are again perfectly hexagonal in shape. X-Ray Diffraction studies on these micropods reveal that they have a hexagonal wurtzite structure and are perfectly crystalline. Photoluminescence studies of these as-deposited micropods show extremely efficient excitonic UV-emission with low defect-related emission. This minor defect-related emission can possibly arise from zinc hydroxide present in these structures as was observed from the FTIR studies. Therefore, these as-deposited micropods have been annealed at various temperatures in order to remove zinc hydroxide. Thermal annealing leads to the formation of nanopores in the micropods possibly due to the loss of zinc hydroxide. The as-deposited samples were observed to have a high external quantum efficiency of around 21% against 14% for samples annealed at 900°C. The phonon replica observed on the low temperature photoluminescence spectra further confirmed the high crystallinity of these samples. These highly luminescent nanoporous micropods can be used as chemosensors such as in the case of nanowires  which remain more sensitive to surface defects (bound excitons). References:  W. Park, G.Yi (2004). Adv.Mater. 16: 87-90  Z. Fan, J. Lu (2005). Appl. Phys. Lett. 86: 123510/1-123510/3  M. Law, L. Greene, J. Johnson, R. Saykally, P.Yang (2005). Nat. Mater. 4: 455-459  R. Aad, V. Simic, L. Le Cunff, L. Rocha, V. Sallet, C. Sartel, A. Lusson, C. Couteau, G. Lerondel (2013). Nanoscale 5 : 9176-9180
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Transparent conducting oxides : Mireille Richard-Plouët
Authors : K.Fleischer, D. Caffrey, L. Farrel, E. Norton, D. Mullarkey, E.Arca, I.V. Shvets
Affiliations : School of Physics, Trinity College Dublin, Ireland
Resume : We present an analysis of the Raman spectra of p-type transparent conducting Cr2O3:Mg [1,2] grown by various techniques including spray pyrolysis (SP), pulsed laser deposition (PLD), molecular beam epitaxy (MBE) and reactive magnetron sputtering (RMS). Best performing films show a distinct broad range Raman signature related to defect induced vibrational modes not seen on stoichiometric, undoped material. We will present a comparative study to demonstrate that Raman spectroscopy cannot just quantify unwanted dephasing of the material at high Mg concentrations, but is also sensitive to the Mg incorporation site. By correlating the Raman signature to the optical and electrical properties of the films we will demonstrate how growth processes can be optimised to give the best conducting films at the highest transparency and the importance of the local defect structure in effective p-type doping in general.  E. Arca; K. Fleischer, et al., Appl. Phys. Lett. 99, (2011), 111910  A. Holt; P. Kofstad, Solid State Ionics 100, (1997), 201
Authors : T. Kaneda(1), E. Tokumitsu(1,2), T. Miyasako(1), T. Shimoda(1,2,3)
Affiliations : (1) Japan Science and Technology Agency, ERATO, Shimoda Nano-Liquid Process Project; (2) Green Devices Research Center, Japan Advanced Institute of Science and Technology; (3) School of Materials Science, Japan Advanced Institute of Science and Technology
Resume : We have developed nano-rheology printing (n-RP)  for nano-scale patterning of oxide materials, which applies the direct nanoimprint process for gel-films to make oxide patterns. In this presentation, we propose a new and simple fabrication process for oxide thin film transistors (TFTs), in which channel and source/drain regions are simultaneously formed by utilizing the feature of n-RP process. All-oxide and all-solution-derived bottom-gate-structure TFTs were fabricated by the n-RP without using conventional lithography process. First, solution-derived LaNiO3 bottom electrode was formed by the n-RP technique. Then, ferroelectric Pb(Zr,Ti)O3 film was deposited as a gate insulator. Next, ITO solution was spin-coated and dried. Then, n-RP was performed on the ITO-gel film to pattern the channel and source/drain regions. A mold used in this work has 100μm concave square patterns, separated by 10-μm-wide convex lines. After the n-RP process, ITO regions with two different thicknesses were formed; relatively thick (60-80nm) ITO source/drain regions in the concave square patterns of the mold, and thin (10-20nm) ITO channel regions pressed by the convex line patterns. Note that thin channel regions and thick source/drain regions were simultaneously formed by a single n-RP patterning process. A normal n-channel transistor operation was confirmed with an on/off drain current ratio of more than 10^3.  T. Kaneda et al., J. Mater. Chem. C, 2, 40-49 (2014).
Oxides for solar cells : Wilfrid Prellier
Authors : Mireille Richard-Plouet*, Luc Brohan*, Hélène Terrisse*, Solenn Berson#, Noëlla Lemaitre#
Affiliations : *Institut des Matériaux Jean Rouxel, Université de Nantes CNRS, 2, rue de la Houssinière, BP 32229, 44322 Nantes Cedex 03, France #CEA, LITEN, Laboratoire des Modules Photovoltaïques Organiques, INES 50 avenue du Lac Léman, 73375 Le Bourget du lac, France
Resume : Breakthroughs in the field of solar-to-electricity conversion are intimately related to the progress in materials research and development. In particular, materials obtained using the potential of nanotechnologies should give rise to new advances. The photoactive properties of transition metal oxides are very attractive allowing many applications in the environmental domains (photocatalysis, photovoltaics ). Their integration in hybrid solar cells requires the elaboration of films to optimize harvesting and transport of the photogenerated charge carriers. We develop solvothermal syntheses of nanostructured transition metal oxides leading to stable colloidal solutions. In order to remain compatible with low temperature processes on plastic substrates, the solvent is selected to monitor the physico-chemical properties of the obtained solutions. They can be deposited as thin films by printing processes or by electrodeposition, without annealing at high temperature. Some examples of oxide thin film deposited by solution processes will illustrate the potentials of our approach in the field of organic bulk heterojunction solar cells.
Authors : Young-Joo Lee; Jiwon Wang; Sung-Gyu Park; Dong-Ho Kim
Affiliations : Advanced Functional Thin Films Dept., Korea Institute of Materials Science
Resume : Considering the direct integration of PV technologies into window panes (i.e, BIPV), Si-based thin film solar cells can be one of major photovoltaic technologies due to their advantages of low-cost and large-area manufacturing as well as long-term reliability. The window layer in thin film solar cells is particularly important for the device performance. Since through the window layer light comes into the absorption layer and the photo carriers are collected into the front electrode, it should be optically transparent and electrically conductive. In addition, the built-in potential formed by the junction is crucial for the carrier collection. Transition metal oxides (TMOs) such as WO3, V2O5, MoO3 have promising properties as a window layer including a high optical bandgap, a high work function, and good electrical conductivity. In this presentation, our recent progresses in doping-free a-Si solar cells will be given, especially on V2O5-x window layer. It was found that the deposition of i-a-Si layer on V2O5-x without vacuum-breaking results in higher open-circuit voltage (Voc, ~860 mV). In addition, the annealing of sputter-deposited films prior to the i-layer deposition resulted in the improvement of fill factor (FF, ~0.70). Consequently, the efficiency has improved from 7.0% to 9.8%. The experimental details and properties of the oxide material for our dop-ing-free solar cells will be discussed.
Authors : K. Bouras1*, H. Park2, G. Schmerber3, G. Ferblantier1, D. Areau4, H. Rinnert5, S. Colis2, C. Park2, Jae H. Jung2 , W. K. Kima, A. Dinia3 and A. Slaoui1
Affiliations : 1 ICube, CNRS-Université de Strasbourg, 23 rue du Loess, BP 20 CR, 67037 Strasbourg Cedex 2, France 2 School of Chemical Engineering, Yeungnam University, Gyeongsan 712-749, Republic of Korea 3IPCMS, CNRS-Université de Strasbourg, UMR7504, 23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France 4ILV, Université de Versailles-St-Quentin en Yvelines, UMR 8180, 45 avenue des Etats Unis, 78000 Versailles, France 5IJL, Université de Lorraine-CNRS, UMR 7198, Boulevard des Aiguillettes, 54506 Vanduvre-l`es-Nancy, France
Resume : Tin dioxide is one of the most attractive materials studied in the last decade due to its several applications in optoelectronic devices, LCD screens, gas sensors, and solar cells. This n-type semiconductor combines several advantages such as a large band gap (around 3.6 eV for bulk material at 300 K), a high exciton bending energy of 130 meV, a good conductivity and a high carrier concentration, thanks to the high concentration of native oxygen defects. In addition to the TCO properties, doping SnO2 films with rare earth (RE) elements (such as Yb, Pr, Tb, Nd) can enhance their photoluminescence properties thanks to the optical transitions involving the 4f shell of the dopant. However, the transparency and conductivity properties of such RE doped SnO2 films should not be affected by doping. In this paper, we report on the properties of Neodymium doped SnO2 thin films versus the deposition temperature using a reactive magnetron sputtering. The Nd concentration was kept at 0.62 at. % while the substrate temperature was varied from 25 to 400 °C. The crystalline structure was investigated by XRD measurement and TEM microscopy. The chemical composition of the doped films was carefully studied using XPS spectroscopy. No secondary phases like Nd oxides are detected, which indicates that Nd is successfully inserted into the SnO2 host matrix. The UV-Vis-NIR spectroscopy revealed the decrease of the band gap by increasing the deposition temperature until 300°C and then it increases at 400°C. The investigation of the photoluminescence properties under a 325 nm laser excitation show intense emission peaks at 885, 1065 and 1336 nm. Such strong PL signal indicates that Nd3+ ions are optically active in the SnO2 matrix. The electrical properties of the Nd:SnO2 are found to be sensitive to the substrate temperature. Resistivities as low as 0.03 .cm and mobilities as high as 43 cm2/V.s were measured. The Nd:SnO2 films were further inserted into CIGS/CdS based solar cells to serve as TCO as well as photon down shifter layer. The photovoltaic properties showed an increase in cell efficiency by a factor 5 for samples covered with Nd:SnO2 films deposited at 300°C. Such result shows the great potential of these RE doped SnO2 layers to solar conversion.
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