Synthesis, processing and characterization of nanoscale multi functional oxide films VIII and 6th E-MRS & MRS-J bilateral symposium

Resume : Heterostructuring functional oxide thin films with two-dimensional layered materials via van der Waals interactions can open up the possibility of broadening the device applications. We report a universal thin film growth of vanadium dioxide (VO2) with rutile structure, magnetite (Fe3O4) with spinel structure, nickelate (NdNiO3) with perovskite structure on chemically inert and insulating single-crystalline hexagonal boron nitride (hBN) flakes of a two-dimensional layered material. Transition metal oxides exhibits attractive functionalities such as metal-insulator transition (MIT) with an orders-of-magnitude change in resistivity across room temperature in VO2, ferro/ferrimagnetism in Fe3O4, hydrogen sensing in SmNiO3 for electronic/photonic/chemical device applications, with advancement in thin film growth techniques. Thin films of functional oxides were commonly grown on crystalline oxide substrates, but the use of transferrable materials as the growth substrates can provide versatility in applications, including flexible devices. We employ single-crystalline hBN, which is an insulating layered material, as a substrate for oxide thin film growth. VO2 thin films in the polycrystalline form are grown onto hBN thin flakes exfoliated onto Si with a thermal oxide, with grains reaching up-to a micrometer in size, with the preferentially (110) orientated surface of the rutile structure, which is the most energetically favorable. The VO2 film on hBN shows a MIT at approximately 340 K, across which the resistivity changes by nearly three orders of magnitude, comparable to VO2 films grown on common substrates such as sapphire dioxide. The VO2/hBN stack can be picked up from the supporting Si and transferred onto arbitrary substrates such as paper, polymer metal foil. Furthermore, we discovered that the Fe3O4 and NdNiO3 thin films also could be grown on hBN with the energetically favorable [111] orientation, on the (001) plane of hBN. The Fe3O4 thin films and NdNiO3 films on hBN exhibit MIT at 115 K and 160K, respectively, and the transition temperature was independent of the film thickness. Our results can open up a way for new possibilities for practical and versatile applications of functional oxides in flexible electronics, photonics, spintronics, iontronics. References: H. Tanaka et al, Appl. Phys. Lett. 120 (2022) 053104, ACS Appl. Electron. Mater. 3(2021)5031, Sci. Rep. 9 (2019) 2857

Resume : Novel and multifunctional materials are required within the energy transition framework to reduce electronic device consumption and overall materials usage. Within this context oxynitrides are a relevant class of materials. Ferroelectric materials such as barium titanate (BaTiO3) are very well suited to realize opto-electronic sensors especially if their band gap can be tuned. The insertion of nitrogen, less electronegative than oxygen, into the lattice of an oxide causes an increase in the covalent nature of the chemical bonds. This leads to a decrease of the optical band gap value Eg and thus to a modification of the absorption properties of the compound, as well as doping by charge carriers making it possible to envisage new transport properties. Producing epitaxial oxynitride thin films is however highly challenging. In this study, we have grown single crystalline N-doped oxides by atomic nitrogen plasma assisted molecular beam epitaxy on SrTiO3 (001) substrates. Different conditions of nitrogen insertion in the perovskite lattice of BaTiO3 were studied, and the doped films are compared with epitaxial undoped films of identical thickness realized with atomic oxygen plasma. Deposits were made on several types of substrate depending on the nature of the characterization techniques intended to be carried out. Structural properties of the samples were investigated in-situ by electron diffraction (RHEED) and ex-situ by synchrotron radiation X-ray reflectivity (XRR) at beamline DiffAbs (Synchrotron SOLEIL). The chemical composition was analyzed by photoelectron spectrometry (XPS) at beamline TEMPO (Synchrotron SOLEIL). Ferroelectric characterizations were studied by Piezo Force Microscopy (PFM) and ferroelectric measurements at C2N laboratory. Optical properties were examined by differential transmittance microspectroscopy. Structural and ferroelectric characterizations are observed to be similar for N-doped and undoped barium titanate thin films. Thanks to XPS measurements, the presence of substitutional nitrogen in the oxynitride thin films has been confirmed and quantified. This small quantity (⁓1%) of nitrogen in the films leads to a significant decrease of the optical band gap value. This new class of oxynitrides compounds is expected to allow new applications based on visible light absorption.

Resume : Rare-earth nickelates RNiO2 adopting an infinite-layer phase show superconductivity once La, Pr or Nd are substituted by a divalent cation. Either in the pristine or doped form, these materials are reported to adopt a high symmetry, perfectly symmetric, P4/mmm tetragonal cell. Nevertheless, bulk compounds are scarce, hindering a full understanding of the role of chemical pressure or strain on lattice distortions that in turn could alter magnetic and electronic properties of the 2D nickelates. We perform a complete analysis of the structural and magnetic properties of these nickelates, combining Density Functional Theory (DFT) with fully correlated configuration interaction (CI) techniques. We reveal that these compounds are prone to exhibit O4 group rotation with the amplitude depending on the R-to-Ni cation mismatch. These rotations can be tunned by applying pressure or strain. Moreover, they are enhanced by the presence of H impurities that can be intercalated during the reduction process from the RNiO3 to RNiO2 phase. Regarding the magnetic properties, we show that nickelates magnetic interactions are dominant over the highly localized 4f electrons, these having a marginal effect. Furthermore we show that the low temperature phase is a C-type antiferromagnet for all compounds, characterized by an antiferromagnetic exchange coupling of 60 meV in the 2D plane and an out of plane ferromagnetic interaction of 20 meV.

Resume : The recent discovery of a zero-resistance state in nickel-based compounds[1] has generated new excitement about one of the most studied, yet undisclosed, problem in condensed matter physics. Indeed, in light of possible analogies with copper-based compounds, it was already anticipated[2] that the study of infinite-layer nickelates could have helped to shed light on the still puzzling underlying mechanism(s) of unconventional superconductivity. From the preparation standpoint, an SrTiO3 (STO) layer was firstly used as capping layer to obtain the superconducting state in Nd0.8Sr0.2NiO2 films[1], and beyond the assumption that it could allow for a better stabilization of the infinite-layer phase during topotactic reduction, its role is still unclear. Indeed, superconductivity was reported also for non-capped films, suggesting that it is not due to the presence of the capping layer[3]. On the other hand, some properties of capped and uncapped samples are different, in particular the low energy excitation spectra. Magnetic excitations around 200 meV energy loss could be observed only for STO-capped samples, while the uncapped ones showed a peculiar charge order that seems to enter in competition with superconductivity[4–6]. Here, we will present, out-of-plane angular magnetotransport measurements acquired for both capped and uncapped infinite-layer nickelate thin films at different Sr-doping levels. Capped samples exhibit a much larger magnetoresistance (MR) signal if compared to the uncapped ones and present also a modified two-fold anisotropic MR signal. We suggest a possible correlation between the modified magnetic properties between capped and uncapped samples and the observed variation in the angular magnetotransport data. 1. Li, D. et al. Superconductivity in an infinite-layer nickelate. Nature 572, 624–627 (2019). 2. Rice, T. M., M., A. V. & D., B. Electronic structure of possible nickelate analogs to the cuprates. Phys. Rev. B - Condens. Matter Mater. Phys. 59, 7901–7906 (1999). 3. Zeng, S. et al. Phase Diagram and Superconducting Dome of Infinite-Layer Nd1-xSrxNiO2 Thin Films. Phys. Rev. Lett. 125, (2020). 4. Tam, C. C. et al. Charge density waves in infinite-layer NdNiO 2 nickelates. (2021). 5. Lu, H. et al. Magnetic excitations in infinite-layer nickelates. Science (80-. ). 373, 213–216 (2021). 6. Krieger, G. et al. Charge and spin order dichotomy in NdNiO 2 driven by SrTiO 3 capping layer. (2021).

Resume : Magnetic materials are the key elements for the development of the spintronic and particularly the control of magnetic anisotropy in ferromagnetic thin films. In this context, Lanthanium Strontium Manganite (La0.7Sr0.3MnO3) attracted much attention because of its ferromagnetic, half-metallic behavior and high curie temperature above 300 K [1]. The tunability of its properties has been extensively investigated in the last decades; however, most of these studies is done on monocrystalline substrates having a specific crystallographic orientation. Combinatorial substrate epitaxy approach is a low cost alternative that open the access to a library of orientations. This polycrystalline substrate is a sintered and mirror polished ceramic [2], where at the surface, each grain is considered as a local monocrystal allowing grain on grain local epitaxy [3]. In our work, La0.7Sr0.3MnO3 thin film has been grown on polycrystalline SrTiO3 using pulsed laser deposition. We show that the nature of the polycrystalline film induces interesting macroscopic magneto transport properties tunable by the grain size (2 to 40 µm) not present in monocrystalline substrate. In order to understand the influence of the microstructure on the magnetic properties, we investigate the polycrystalline films with electron back scattered diffraction (EBSD) for the grain size and crystallographic orientations. For the study of the local magnetic domains structure, we use magnetic force microscopy (MFM) in different configurations AC and DC mode, in air and under vaccum. Effect of orientation and grain boundaries on the local magnetic properties will be discussed further. References 1. Kumari, S. et al. Effects of Oxygen Modification on the Structural and Magnetic Properties of Highly Epitaxial La0.7Sr0.3MnO3 (LSMO) thin films. Sci. Rep. 10, 1–11 (2020). 2. Lacotte, M. et al. Growth of Ca2MnO4 Ruddlesden-Popper structured thin films using combinatorial substrate epitaxy. J. Appl. Phys. 116, (2014). 3. Woo, S. et al. Surface properties of atomically flat poly-crystalline SrTiO 3. Sci. Rep. 5, 1–7 (2015).

Resume : The accelerated pace of the society’s development has led to several problems, such as dramatic climate changes, pollution and lack of sustainable energies [1,2]. Therefore, a lot of research has been done on sustainable environmental technologies [3]. Photocatalysis is a green technology with great potential in the treatment of pollutants and remediation of water, with the possibility of using solar energy, which makes the catalytic processes economically viable for large scale applications, while acquiring additional environmental value [4–8]. Among the various photocatalysts studied, TiO2 is one of the most studied semiconductors for the decomposition of several pollutants, due to its strong oxidation potential to decompose organic pollutants, physical and chemical stabilities, excellent optical properties, low cost, non-toxicity and earth abundance. Despite this, one major difficulty is the recovery and recycling of nano TiO2-based materials in powder form. In addition, TiO2 possesses a wide band gap, absorbing thus in the UV region [9]. In consequence, its photocatalytic activation is limited under visible light, which represents ~ 45% of the solar spectrum [10]. Regarding this last limitation, several approaches have successfully been employed and include doping with metal and non-metal elements, surface modification and combining TiO2 with other semiconductor materials [11–13]. Over the last few years, a new category of photocatalysts, the “floating photocatalysts”, has emerged with great potential to overcome the drawback of recovery and recyclability of nanopowders. The benefits of using floating photocatalysts include flexibility and lightness, while their “floating” characteristic offers the advantages of maximizing the utilization of light, as well as the oxygenation of the photocatalyst, due to the proximity of air/water interface. Moreover, it is easy to collect from water and it does not need special equipment or stirring during the photocatalytic reaction. Under these circumstances, an optimization of illumination and oxygenation should hence improve the radical formation rate and oxidation efficiency [9][14]. In terms of natural floating materials, cork presents several advantages, which makes it suitable in photocatalytic experiments, like earth-abundance, compressibility, resilience, thermal stability and corrosion resistance, non-toxicity, large surface area and hydrophobicity. Hydrophobicity is an important feature of this material, since it can be more predisposed of attaching organics from water on its surface, thus leading to an improvement of their removal and oxidation capability [9]. Although cork provides a lot of potential for photocatalytic applications, only few studies have reported cork’s use as a support in photocatalytic tests. On that account, our aim is to provide insights on the behavior of TiO2-based materials synthesized with different acids, directly grown by a low-cost and green microwave irradiation technique on cork platforms, at a low temperature. To the best of our knowledge, a similar study has never been reported before. Keywords: TiO2, nanostructures; cork substrates; photocatalysis; microwave irradiation. *Corresponding Authors: Daniela Nunes and Rodrigo Martins, CENIMAT|i3N, Department of Materials Science, School of Science and Technology, NOVA University Lisbon and CEMOP/UNINOVA, Caparica, Portugal, e-mails: daniela.gomes@fct.unl.pt (D. Nunes) and rm@uninova.pt (R. Martins). References 1. Hu, X.; Yip, A. C. K. Heterogeneous Catalysis: Enabling a Sustainable Future. Frontiers in Catalysis 2021, 0, 3, doi:10.3389/FCTLS.2021.667675. 2. Xu, Y.-J. Promises and Challenges in Photocatalysis. Frontiers in Catalysis 2021, 0, 6, doi:10.3389/FCTLS.2021.708319. 3. Urbonavicius, M.; Varnagiris, S.; Sakalauskaite, S.; Demikyte, E.; Tuckute, S.; Lelis, M. Application of floating tio2 photocatalyst for methylene blue decomposition and salmonella typhimurium inactivation. Catalysts 2021, 11, doi:10.3390/catal11070794. 4. Neena, D.; Kondamareddy, K. K.; Bin, H.; Lu, D.; Kumar, P.; Dwivedi, R. K.; Pelenovich, V. O.; Zhao, X. Z.; Gao, W.; Fu, D. Enhanced visible light photodegradation activity of RhB/MB from aqueous solution using nanosized novel Fe-Cd co-modified ZnO. Scientific Reports 2018, 8. 5. Rani, S.; Aggarwal, M.; Kumar, M.; Sharma, S.; Kumar, D. Removal of methylene blue and rhodamine B from water by zirconium oxide/graphene. Water Science 2016, 30, 51–60. 6. Schneider, J.; Matsuoka, M.; Takeuchi, M.; Zhang, J.; Horiuchi, Y.; Anpo, M.; Bahnemann, D. W. Understanding TiO2 Photocatalysis: Mechanisms and Materials. Chemical Reviews 2014, 114, 9919–9986. 7. Borges, M. E.; Sierra, M.; Cuevas, E.; García, R. D.; Esparza, P. Photocatalysis with solar energy: Sunlight-responsive photocatalyst based on TiO2 loaded on a natural material for wastewater treatment. Solar Energy 2016, 135, 527–535. 8. Rajeshwar, K.; Osugi, M. E.; Chanmanee, W.; Chenthamarakshan, C. R.; Zanoni, M. V. B.; Kajitvichyanukul, P.; Krishnan-Ayer, R. Heterogeneous photocatalytic treatment of organic dyes in air and aqueous media. Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2008, 9, 171–192. 9. Sboui, M.; Nsib, M. F.; Rayes, A.; Swaminathan, M.; Houas, A. TiO2–PANI/Cork composite: A new floating photocatalyst for the treatment of organic pollutants under sunlight irradiation. Journal of Environmental Sciences 2017, 60, 3–13, doi:10.1016/J.JES.2016.11.024. 10. Reda, S. M.; Khairy, M.; Mousa, M. A. Photocatalytic activity of nitrogen and copper doped TiO2 nanoparticles prepared by microwave-assisted sol-gel process. Arabian Journal of Chemistry 2020, 13, 86–95. 11. Humayun, M.; Raziq, F.; Khan, A.; Luo, W. Modification strategies of TiO2 for potential applications in photocatalysis: A critical review. Green Chemistry Letters and Reviews 2018, 11, 86–102. 12. Nunes, D.; Pimentel, A.; Branquinho, R.; Fortunato, E.; Martins, R. Metal oxide-based photocatalytic paper: A green alternative for environmental remediation. Catalysts 2021, 11. 13. Zhao, J.; Chen, C.; Ma, W. Photocatalytic Degradation of Organic Pollutants Under Visible Light Irradiation. Topics in Catalysis 2005, 35, 269–278. 14. Machado, L. C. R.; Torchia, C. B.; Lago, R. M. Floating photocatalysts based on TiO2 supported on high surface area exfoliated vermiculite for water decontamination. Catalysis Communications 2006, 8, 538–541, doi:10.1016/J.CATCOM.2005.10.020.

Resume : Titanium dioxide (TiO2) is a reference standard material for photocatalysis, not only for its properties, which have been widely studied over the years, but also for its low cost, which makes it easily available and industrially attractive. In photocatalysis, the properties of greatest interest are the light absorption and the sample morphology. Several chemical and physical techniques allow a control of the defectiveness and morphology of the titanium dioxide thin films. Among them, a very common physical technique, which allows high quality film fabrication with less external contamination, as well as, an easy control of film growth, is the thermal oxidative synthesis. This method permits not only to realize a TiO2 bulk, but also TiO2 nanowires (NWs) through a simple pre-treatment of the titanium surface. NWs shows a greater exposed surface to volume area than the flat TiO2 film, strongly increasing the photocatalytic activity compared to a bulk sample. This advantage, combined with an easy and robust TiO2 NWs synthesis on an industrially Si wafer substrate, make the realization of TiO2 NWs photocatalytic platform an excellent alternative even to the already high performant TiO2 nanoparticles. The present work reports a study on the realization and optimization of TiO2 NWs substrate for photocatalytic activities. Indeed, we report how the material composition in terms of doping, defects, and surface morphology affect the photocatalytic activity of TiO2 NWs. TiO2 film and NWs were synthesized by seed assisted growth and thermal oxidation at 750°C in presence of a O2 environment. The sample surface is pre-treated by depositing a thin (3-5 nm) of gold layer which, through the annealing process, leads to the formation of nanoparticles and induces the growth of nanowires. This approach permitted the production of stable TiO2 NWs in the rutile phase with a low chemical contamination. Two categories of samples were prepared: reduced and Fe doped ones. Reduced samples were prepared by a post-annealing in forming gas (95% N2, 5% H2). It leads to a partial reduction of the oxide (TiO2-x) equivalent to a self-doping with vacancies. Samples doped with Fe were prepared by a pre-treating titanium substrate with ion implantation. The doping through the implantation didn’t affect the morphology and the structure of both TiO2 film and NWs, according to Raman spectroscopy and SEM images. We monitored the photocatalytic activity trough the degradation of the methylene blue (MB), under UV and visible radiation. Along with the results obtained by these three type we further optimized the performances by introducing a Pt nanoparticle decoration. All these results, allows us to trigger the photocatalytic performances of these TiO2 NWs and show how their performances can be optimized. Indeed, Pt deposited samples shows an increase of photoactivity in the UV region and Fe doping are used to enhance the activity in the visible region.

Resume : Bimetallic decoration of semiconductor electrodes typically improves catalytic and sensing performances because of a well-claimed synergistic effect. A microscopic and quantitative investigation of such an effect on energy bands of semiconductor can be really useful for further exploitation. Au, Pd and Au@Pd (core@shell) nanoparticles were synthesized through chemical reduction method and used to decorate Ni-based nanostructured thin films. Scanning Electrochemical measurements quantitatively investigated the effect of decoration with mono or bimetallic nanoparticles. Decorated electrodes show higher redox currents than bare ones and a shift in redox peaks, which can be ascribed to a more efficient electron transport and improved catalytic properties. These effects were satisfactorily modeled employing a nano Schottky junction at the nanoparticle-semiconductor interface, pointing out a larger energy band bending (0.4 eV) and a higher localized electric field (108 V/m) in bimetallic decoration [1]. Sensing test of the decorated Ni oxide electrodes were performed with glucose and H2O2 to confirm our model. The presence of bimetallic nanoparticles enhances enormously the electrochemical performances of the material in terms of sensitivity, catalytic activity, and electrical transport. The modification of energy band diagram in semiconductor is analyzed and discussed also in terms of electron transfer during redox reactions. [1] Bruno, L.; Scuderi, M.; Falciola, L.; Priolo, F.; Mirabella, S. Enlightening the Bimetallic Effect of Au@Pd Nanoparticles on Ni Oxide Nanostructured films with Enhanced Catalytic Activity (submitted)

Resume : Material damage related to heavy X-ray irradiation has always been a big concern for synchrotron experiments, both for organic and inorganic materials. Recently, the possibility has emerged to turn this problem into an opportunity and the local tailoring of the electrical properties by means of hard X-ray irradiation has been investigated in many studies [1,2,3]. Specifically, a study performed on rutile single crystals has demonstrated the possibility of not only locally increasing the electrical conductivity of the material upon irradiation, but also of pinning and guiding the electroforming process needed for the fabrication of memristive devices. These modifications are most probably related to a local increase in the concentration of oxygen vacancies, which act as n-dopants in rutile. These observations were made possible by a multi-technique analysis involving X-ray Fluorescence (XRF), X-ray Excited Optical Luminescence (XEOL) and electrical monitoring, together with post irradiation Conducting-Atomic Force Microscopy (C-AFM) imaging[4]. Actually, during this experiment both rutile TiO2 and Fe doped SrTiO3 have been investigated, which were irradiated both at room temperature and at low temperature (8K). To gain more insights about the origin of these modifications, computer simulations have been performed for both materials both at room temperature and at the cryogenic temperature. Firstly, the deposited energy density has been evaluated via Monte Carlo simulations considering the avalanche of relaxation processes induced by the beam, which has turned out to be practically temperature independent. Secondly, the heat propagation in the materials has been evaluated by means of temperature-dependent finite element thermal simulations. These thermal simulations have taken into explicit account the pulsed time structure of the synchrotron beam in addition to the time-averaged flux behaviour. The results show very short temperature spikes corresponding to the synchrotron pulses. The temperature in the material locally increases by tens of degrees above the starting temperature, with higher spikes for Fe:STO due to the smaller X-ray attenuation length with respect to rutile, and a stronger effect at 8K for both materials because of the lower heat capacity at low temperature. These results indicate the possibility for rapid thermal dilation and contraction cycles to take place in the materials, with corresponding shock waves induced by the extreme temperature gradients (10^9 K/m) and heating rates (10^12 K/s). The possibility that local melting occurred in Fe:STO irradiated at low temperature is suggested by AFM images showing surface bumps with a spatial distribution similar to the one of the beam impact points. [1] A. Pagliero et al., Nano Lett. 2014, 14, 1583−1589 [2] M. Truccato et al., Nano Lett. 2016, 16, 1669−1674 [3] L. Mino et al., Adv. Electron. Mater. 2019, 5, 1900129 [4] A. Alessio et al., Phys. Status Solidi RRL 2021, 15, 2100409

Resume : When devising advanced devices, applications designers of different areas are limited by choice of materials. Often, researchers need to adapt their applications to available materials at the cost of lower performance and increased production costs. Thus, more efficient ways to study and develop Value-Added materials imply a paradigm shift. Here we explore Nanolaminates, a low dimensional concept created from multiple layers of two or more materials with nanometric thicknesses, which allows to achieve specific properties, otherwise unattainable by single layer materials. This work explores the possibility to develop customized Selective Contacts (SC), based on nanolaminates, to be implemented on optoelectronic devices. Diverse multilayer systems of dielectric materials, SiOx, SiNx, TiOx, ZnOx, and HfOx, were developed and studied, as well as their single layer counterparts, to evaluate their applicability as selective carrier layers. We conducted an in-depth fundamental study of structural, elemental composition, optical, electronic, and electrical properties, using X-Ray Diffraction, Scanning Transmission Electron Microscopy, X-Ray and Ultraviolet Photoelectron Spectroscopy, Ellipsometry, Reflection Electron Energy Loss Spectrocopy, home-made devices, among others techniques. The obtained results clearly indicate the possibility of tailoring properties to match technological requirements, when varying the nanolaminates’ architecture. Furthermore, a TiOx-ZnOx nanolaminate showed promising optical properties and electronic potential to be tailored, in order to achieve selective electron contact in Cu(In,Ga)Se2 (CIGS) solar cells.

Resume : Functional inks are dispersions of nanoparticles potentially enabling improved fabrication processes of particle based materials and composites bridging several size ranges and properties from the nanoscale to the macroscale. The assembly of nanoparticles on the substrate is pivoted by the deposition methodology and by the surface chemistry of the particles, determining the resulting microstructure of the assembled layers. In this scenario, luminescent particles can be applied in a wide field of technologies such as lighting, display or scintillator technologies. In this work, the electrophoretic deposition (EPD) and its applicability for the assembly of nanoparticles towards functional films. Titanium and hafnium dioxide nanoparticles with a size of few nm were synthesized by a non-aqueous sol-gel route. The doping with europium was used to activate the fluorescence of HfO2, making it suitable for phosphor and scintillator applications. After obtaining stable aqueous dispersions, the influence of several EPD parameters on the film thickness, transparency, relative density and morphology were studied. Depositions of particle based assemblies, with thickness spanning from few tens of nm up to several microns, were performed on flat substrates, as well as on structured substrates, to explore the potential of EPD for the fabrication of complexly shaped multifunctional materials.

Resume : Gallium oxide Ga2O3 has recently attracted a lot of scientific attention as a prospective ultra-wide bandgap semiconductor. It has five different polytypes α, β, δ, γ and ε among which the most studied and thermodynamically stable phase is β-Ga2O3. However, corundum-structured α-Ga2O3 with 5.2 eV bandgap is a better alternative for power electronics and ultraviolet optoelectronics applications. α-Ga2O3 is a metastable phase and it cannot be obtained as bulk crystals used for homoepitaxial growth. On the other hand, sapphire (α-Al2O3) is a convenient substrate for heteroepitaxy since some of its crystalline planes have a small lattice mismatch with α-Ga2O3, but there are only few and recent reports on the use of other orientation sapphire substrates than c-plane. In this work, we demonstrate growth of α-Ga2O3 thin films on a- and m-plane cut sapphire wafers at various substrate temperatures via two different methods – reactive magnetron sputtering and pulsed laser deposition. Crystalline structure, elemental composition, surface morphology and optical properties were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, atomic force microscopy and UV-VIS measurements. α-phase stability dependence on film thickness was also investigated. Such epitaxial stabilization of high-quality thin films with commonly used deposition methods is a perspective way how to integrate α-Ga2O3 on available substrates. The financial support of Latvian Council of Science FLPP project LZP-2020/1-0345 is greatly acknowledged.

Resume : Excellent hydrogen sensing response of Cu doped ZnO thin film (Cu:ZnO) by co-sputtering with substrate heating is presented. The Cu:ZnO thin film have been deposited by varying the power toward Cu target from 0 to 25 W and the power toward ZnO target is constant at 120 W. There is an additional substrate heating of 150 C during the deposition process. It is found that the Cu:ZnO thin film with power of 15 W exhibits highest H2 gas response ability compared to the undoped ZnO thin film resulting in a ~3 fold enhancement in the gas response. The sensing response value is defined as S%=[(Ig-Ia)/Ia]100%, where Ia is the current of the sensor in the air and Ig is the current in the presence of certain H2 concentration. The sensing response of the undoped ZnO thin film is 147% and a high sensing response of 445% is obtained at the 15 W deposited-Cu:ZnO thin film at 1000 ppm hydrogen concentration at 300 C. The 15 W deposited-Cu:ZnO thin film also shows shorter response time of 13 s than that of undoped ZnO thin film of 23 s. The improvement of sensing response of the Cu:ZnO thin film is due to the ZnO grain size is modified by the Cu doping and leads to increase of the specific surface area of smaller grains to improve the sensing ability.

Resume : In this work were elaborated thin films of Zinc Magnesium Oxide (ZnMgO) by ultrasonic spray pyrolysis. Zn1-xMgxO is a wide bandgap compound semiconductor with useful properties for optoelectronic devices, mainly ultraviolet “solar-blind” detectors, as an active layer, and solar cells where it can be used as a buffer layer. The main difficulties related to the elaboration of Zn1-xMgxO using solution-based and spray pyrolysis techniques are the wide miscibility gap between MgO and ZnO and the use of toxic and unsafe solvents such as methanol. In this study, we were able to elaborate Zn1-xMgxO with varying Mg content up to 70% with water-based solutions only. The difficulty using only water-based solutions is related to the inherent unfavorable properties such as strong hydrogen bonds with high boiling point. However, we managed to optimize the precursors solution concentration, the number of scans, the flow rate, the pressure and the temperature, to obtain homogeneous and good quality films. The solid composition in the thin films was measured using X-ray fluorescence to assess the Mg solubility limit in Zn1-xMgxO and its incorporation efficiency. High transmittance of about 90 % in the visible region was obtained in all the films with a very small variation with the thickness, suggesting a highly controlled process of the elaboration. The bandgap and the Urbach energy variation with the composition were investigated and linked to the morphology and structural properties. A miscibility limit of 30 % of Mg was obtained, confirmed by the X-ray fluorescence measurements and correlated to the bandgap variation with the Mg composition extracted from the transmittance spectra analysis. The structural properties were investigated using confocal micro-Raman spectroscopy which permitted to identify the wurtzite structure as the only phase in all the films with composition less than 30 %, with a phase separation occurring beyond this limit. The electrical properties were characterized using the van der Pauw and Hall effect technique using indium to form the ohmic contacts. The n-type carrier concentration dramatically decreases from about 2×1019 to 5×1015 cm-3 when increasing Mg composition from 0 % to 7 %. The thin films become semi-insulating for Mg composition higher than 7 %. The correlation of the electrical results with the optical and structural properties suggests that, in addition to the increase of the bandgap, a compensation mechanism related to the defects introduced in the alloy plays a central role in the decrease in the carrier concentration. The mobility slightly increases with the Mg composition suggesting that the films crystal quality was not significantly degraded by the increase of the magnesium composition in the considered range. The modulation of the conductivity, in addition and partially related to the modulation of the bandgap, is of high interest to the detector or the solar cell device.

Resume : In the past years there has been a paradigm shift regarding the industrialization of certain technologies. Pulsed Laser Deposition (PLD) is at a crossroads in terms of usability and implementation in industrial production as it is understood now. The existent experimental solutions can be difficult to replicate and offer very specific recipes for producing high quality thin films, which are strongly linked to the particularities of the laser beam, deposition geometry and working atmosphere. The work presented here involves research performed towards developing new high-quality low–dimension oxide semiconducting materials for solar cells. Several oxide films (e.g., SnO2, ZnO, ZrO2, HfO2) are produced by PLD technique. Various deposition conditions (laser fluence, repetition rate, O2 pressure, substrate temperature, etc.) are used in order to created the deposition maps of the investigated materials. Based on our recent published data, the angular distribution of the ablated particles kinetic energy has an important effect on the composition and structure of the deposited film. To highlight this novel feature, we have implemented a new deposition geometry that will monitor the angular distribution and allow for the deposition on and off axis. Each deposition was monitored by optical emission spectroscopy to investigate if the formation of new oxide phases also occurs inside the plasma volume and not only at the surface of the deposited film. Comparisons will be made with films produced by rf – magnetron sputtering in order to investigate the importance of plasma particle energy during the deposition process. The deposited films were investigated with a wide array of tools such as Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), X-ray reflectivity (XRR), X-ray Photoelectron Spectroscopy (XPS) and electrical measurements. This work was supported by Romanian Ministry of Education and Research, under Romanian Natl. Nucleu Program LAPLAS VI –n. 16N/2019, ELI-RO_2020_12 and PD 145⁄2020. We acknowledge the Operational Program Research, Development and Education financed by European Structural and Investment Funds and the Czech Ministry of Education, Youth and Sports SOLID21.

Resume : Room temperature deposited amorphous indium zinc oxide (a-IZO) is an excellent material due to its high conductivity, electron mobility (~50 cm2/V-1s-1) and optical transmittance. The electrical and optical properties of IZO films were found to depend on the In/(In+Zn) ratio. Therefore, in order to optimize the parameters of TFTs devices using a-IZO channels and a high-k gate material such as HfO2, it is necessary to measure the dependence of the valence band discontinuity and conduction band offset on a-IZO composition. Amorphous IZO films with variable In/(In+Zn) composition and HfO2 films were deposited at room temperature by pulsed laser deposition (PLD) technique. The valence band discontinuity (ΔEV) of pulsed laser deposited HfO2 on a-IZO heterostructures was obtained from X-ray photoelectron spectroscopy (XPS) measurements. The HfO2 and IZO thin films bandgaps were also measured by XPS, while their density and thickness were determined from modeling of their X-ray reflectivity curves. Taking into account the XPS measured HfO2 and IZO bandgap values, the conduction band offset ΔEC in the HfO2/IZO various heterostructure was also obtained. The estimated values of ΔEV and ΔEC were depending on the In/(In+Zn) value as well as the oxygen pressure used during the deposition of HfO2.

Resume : The discovery of the ferroelectric orthorhombic phase in doped HfO2 gave a major boost to the interest for integrated ferroelectric oxides in the CMOS industry [1]. Given its low crystallisation temperature, the Hf1-xZrxO2 solid solution, i.e Hf0.5Zr0.5O2 (HZO), is an excellent candidate for both front and back-end of line integration of advanced ferroelectric memories. Unveiling the origin of the conduction mechanisms through HZO is crucial for applications where they should be suppressed (e.g. ferroelectric capacitors) and applications where they should be leveraged (e.g. Ferroelectric Tunnel Junctions). Here, we report a low temperature electrical study of HZO down to 4.2 K on two series of ferroelectric capacitor structures: TiN/HZO/TiN and TiN/HZO/AlOx/TiN embedding 11 nm of HZO deposited by reactive magnetron sputtering [2]. Polarisation and current–voltage measurements (Figure 1b) were carried out at each temperature step to get insights on the polarisation switching and leakage currents in our samples. A systematic study of possible charge transport regimes including tunnelling, thermally and trap-assisted mechanisms was then conducted in order to elucidate the origin of leakage currents and the impact of the interfacial layers in both samples. References: [1] Böscke, T. S. et al., Applied Physics Letters 2011, 99, 10102903 [2] Bouaziz, J. et al., ACS Applied Electronic Materials 1 (9), 1740 (2019).

Resume : Ga2O3 based heterojunctions are promising candidates for photodetector applications, their parameters being highly influenced by the preparation technology. n-Ga2O3/p-GaSe heterojunctions have been prepared by air annealing of GaSe micrometric lamella, the latter have been cleaved from single crystalline plates. Depending on annealing regime two type of structures have been prepared having beta-Ga2O3 as a thin layer on GaSe substrate and having beta-Ga2O3 layer formed along to GaSe lamella edge perimeter. The beta-Ga2O3 layer’s physical properties have been jointly investigated by XRD, SEM, EDX and Raman scattering. The beta-Ga2O3 deposited onto GaSe substrate represents a dense set of nanoformations such as β-Ga2O3 nanofibers and nanostrips (being present on lamella edge as well). β-Ga2O3 direct bandgap is 4,75 eV as determined from the analysis of the reflection spectrum by using the Kubelka-Munk function. n-Ga2O3/p-GaSe photoresponse spectral distribution is determined by nonequilibrium charge carriers generation in β-Ga2O3 layer (in the spectral range of 200 – 300 nm) as well as in GaSe substrate. An alternative Ga2O3 based photodetector is formed by use of aerosol deposition for Ga2O3 preparation onto CSS deposited GaSe. A comparison data is presented. Acknowledgements: NARD (ANCD) projects: 20.80009.5007.12; 20.80009.7007.05; 20.80009.5007.02

Resume : Hydrogen doped indium oxide thin films with high near-infrared transmission and high electron carrier mobility have shown their advantages for perovskite photovoltaic technology [1, 2]. In this work, indium oxide thin films were grown by pulsed electron beam deposition on Si, glass and c-cut sapphire single crystal substrates at different substrate temperatures under oxygen or argon gas at pressures around 0.01 mbar. The parameters used during the growth of indium oxide thin films had strong effects on the electrical and optical properties, without evidencing large differences in the structure and film stoichiometry. Post-deposition, a hydrogen glow plasma treatment was used to functionalize as grown indium oxide thin films. Hall effect and optical measurements were performed for both as-grown and plasma-treated films. A significant decrease in film resistivity was obtained as a result of plasma treatment, maintaining the high optical transparency. Comparative X-ray photoelectron spectroscopy measurements showed the correspondence between surface and functional properties of films. The results revealed that the properties of as-grown indium oxide films can be tuned by hydrogen glow plasma treatment for application as transparent conducting electrodes in solar cells with reduced electrical and optical losses. [1] S. Moghadamzadeh et al., ACS Appl. Mater. Interfaces 2021, 13, 46488; [2] T. Koida, Phys. Status Solidi A 2017, 214, 1600464

Resume : Betta-Ga2O3 has been quickly promoted on the top amid wide-gap semiconductor oxides owing to the high carrier mobility, large critical field strength, and native substrate availability. Almost the whole range of oxide growth technologies, from the vacuum-based physical vapour depositions to the various chemical methods, were applied for the fabrication of epitaxial thin films. Here we show that Ga2O3 thin films of a device quality can be produced by the vacuum-free, cost-effective technique of metalorganic aerosol deposition, which was earlier designed for the epitaxial growth of complex oxides. In addition to the sub-monolayer accuracy of layer-by-layer growth and precise composition control, the main advantage of metalorganic aerosol deposition consists in the possibility to use non-volatile metalorganic precursors. We fabricated epitaxial Ga2O3 films on Al2O3(0001) substrates and polycrystalline ones on SiO2/Si substrates using Ga(III) acetylacetonate as a precursor. The substrate temperature, deposition rate, and solution molarity, which are most important for liquid-assisted deposition methods, were optimized to obtain the synthesis of a single-phase betta-Ga2O3. By combining X-ray diffraction analysis with scanning electron and atomic force microscopies, we had demonstrate a high crystalline quality of (201)-oriented betta-Ga2O3 film grown on Al2O3(0001) substrates and the formation of smooth surface morphology (RMS=0.8 nm) for the nanocrystalline one deposited on amorphous substrates. We expect that further optimizations of metalorganic aerosol deposition may offer alternative technological support for the development of various Ga2O3-based oxide heterojunctions. Acknowledgements: NARD (ANCD) projects: 20.80009.5007.12; 20.80009.5007.02

Resume : Pulsed electron beam deposition (PED) is a well-established method to grow oxide thin films, superlattices or heterostructures on rigid or flexible substrates. Besides this classical aspect, PED, working under low oxygen pressure, can control the oxygen incorporation and therefore the stoichiometry of oxide films. Oxygen deficient thin films can be thus grown presenting new microstructures and specific electrical properties. The non-stoichiometry (cation-to anion ratios) is presented in a particular case of zinc oxide thin films grown on c-cut sapphire single crystal substrates at a substrate temperature of 300°C in relation to their structure, electrical and optical properties. The role of pulsed aspect of the growth on the film properties is discussed as a function of the growth parameters. A narrowing of the film band gap is reported together with complementary valence band X-ray photoelectron spectroscopy measurements. A comparison will be made with other results on the growth-induced non-stoichiometry in oxide thin films and density functional calculations on the electronic structure.

Resume : A cathode active material with high charge-discharge capacity is expected for lithium-ion battery (LIB) to be applied to hybrid and electric vehicles, etc. Crystalline LiCoO2 and LiFePO4 have so far been utilized as the cathode active material. The latter is known to have a discharge capacity of 160 mAh/g. It is expected that more Li+ ions could be stored in glassy materials since they have larger specific volume [1]. In this study, cathode active materials of lithium iron vanadate glasses containing CrIII were prepared by the melt-quench method as expressed by 15Li2O‧10Fe2O3‧5P2O5‧xCr2O3‧(70-x)V2O5　and 15Li2O‧(10-x)Fe2O3‧5P2O5‧xCr2O3‧70V2O5　glasses (x=0, 3 and 5). Annealing of the glass sample was conducted at 500 oC for 90 min. Charge-discharge capacity was investigated at room temperature using a half-cell of coin type. X-ray diffraction studies of as-quenched samples showed a halo peak, indicating the successful formation of glasses. After annealing, several crystalline peaks were observed, indicating the formation of glass-ceramics. Very high discharge capacity of 250-300 mAh/g was achieved when discharged from 3.5 to 1.5 V. Detailed information on the local structure will be presented at the conference. References [1] S. Kubuki, H. Masuda, K. Matsuda, K. Akiyama, A. Kitajo, S. Okada, T. Nishida et al., Hyperfine Interact., 226, 765-770 (2014).

Resume : High-power laser systems (HPLS) (i.e., ELI-NP, 2 ×10 PW) require the development of large optical components with outstanding optical quality. One of the most important parameters of the optical components is the laser induced damage threshold (LIDT). Any optical component must be tested before being inserted into a high-power laser system. We proposed an experimental system capable of determining in real time optical properties such as: (I) nonlinear coefficients (nonlinear refractive index, nonlinear absorption coefficient [1]), (II) LIDT using a long working distance imagining system (LWDIS), (III) spectral broadening associated with self phase modulation in solid transparent materials. The proposed experimental assembly uses a chirped pulse amplification laser system based on Ti: Sapphire amplification (800 nm, 10 Hz) delivering pulse with 60 fs duration and energies up to mJ range. It was adapted to perform LIDT measurements in transmission and in reflection (dedicated to coated surfaces) and is completely automatized. The measured values were compared to other measurements using the Langmuir probe and microscopy investigations of the surface morphology. Acknowledgements: work was supported through IFA project ELI-RO 4/2020 LPTC. [1] I. Dancus, V. I. Vlad, A. Petris, T. Bazaru Rujoiu, I. Rau, F. Kajzar, A. Meghea, A. Tane, Z-scan and I-scan methods for characterization of dna optical nonlinearities, Romanian Reports in Physics, 65(3) (2013),966-978

Resume : To construct low carbon society and highly information society more and more in the world, it is necessary to develop a high performances new conponets anddevice such as a solar cell, a lithium battery, a power semiconductor, and post-5G technologies and so on. Metal oxides are expected to be key materials which are used for a new device by controlling metal composition, a crystal structure, orientation or multilayer of the film, a carrier, a spin, etc. In order to fabricate the new devices, their parameters controllable process would be effective. Particularly, thin films with a gradient structure exhibit unprecedented function, so it is essential to construct a new process. For these purpose, we have developed the photo-induced chemical solution process such as excimer laser-assisted metal organic deposition (ELAMOD), and photo reaction of hybrid solution(PRHS) for the preparation of the various kind of metal oxide thin films on organic, glass and single crystalline substrates. In this presentation, we demonstrate a crystallization mechanism for thin film by photoreactions and, a preparation of flexible ceramics thin films on plastics substrates and epitaxial oxide thin film by using a photo reaction process. 1.Epitaxial and flexible VO2 film for the sensor applications To prepare epitaxial oxide films at room temperature; it was found that the direct excimer laser irradiation was effective for the improvement of the crystallinity and electrical properties at low temperature. epitaxial VO2 film on TiO2 substrate was prepared by the KrF laser irradiation at 60 to 100mJ/cm2 at 25℃. By controlling the ingredient crystallinity and oxygen contents of the films, high temperature coefficient of resistance (TCR) of the VO2 film(=32%/K) with non-hysteresis was obtained. Also, by using the photoreaction process, M-I transition temperatures of VO2 was controlled without metal doping. 2.Fablication of the Flexible oxide film by photoreaction process By using the photo reaction of hybrid solution(PRHS) process, flexible RuO2 thin films were successfully obtained on ceramics and plastics substrates at low temperature for the SiC power modules. The resistivity of the RuO2 film was 9.0×10-5Ωcm. The resistance change was less than 100ppm/K at the temperature range from 300 to 25oC. The developed flexible resistor would be expected to relax the crack that comes from the difference in the thermal mechanical properties for the high temperature in SiC modules. In addition, we developed flexible transparent conductive thin films with the highly work function and low resistance for OLED application. Moreover, high luminescent phosphor film on PET was also obtained by the PRHS. By using these process, we propose the new circulating manufacturing of the high-performance materials, thin films, and devices for circulating economy.

Resume : We have been investigating LaFeO3 (LFO) / CaFeOx (CFO) superlattices (SLs) and multilayers (MLs) for an electric field driven low consumption and involatile magnetic memory devices. LFO and CaFeO3 (CFO3) are anitiferromagentic (AFM) materials. For short description, the [nL/nC]m notation is defined to indicate the synthesized SLs and MLs, where nL units LFO / nC units CFO deposition is repeated for m times. As the number of m is one, the film is ML. The synthesized SLs were of nL = nC = 3, 5, 7 with m=14, [5/5]20 and [3/3]33. Those SLs thickness is almost same. The MLs were also prepared with nL = 3~7, 10, 15 with fixed nC = 3 and m = 1. The LFO / CFO SLs and MLs were deposited by pulsed laser deposition method. Since CFO3 is unstable and CFO2.5 is stable, it is easily expected that the CFO3 is transferred to be CFO2.5 as CFO layer get thicker, where a mixture area of CFO3 and CFO2.5 is present, and then only CFO2.5 grows. Previously we confirmed the mixture thickness was almost nC = 3 by observing surface morphology, then we chose nC = 3 in ML. Obtained X-ray reflection (XRR) was fitted assuming [LFO / CaFeO2.5(CFO2.5) / CFO3] for one cycle in order to obtain composition ratio of CFO3 in CFO layer. Magnetic property was measured using SQUID magnetometer. From the illustration of saturation magnetization per cm2, Mst, at 300K depending on composition ration of CFO3 in CFO layer, maximum Mst was obtained at nearly 40% in SLs and 54% in MLs, although LFO and CFO3 are AFM. More than 70% of CFO3 in CFO layer, the Mst was almost zero in MLs. In addition, magnitude of the Mst was surprisingly almost same in SLs and MLs. From the results mentioned above, magnetization was induced at the LFO / CFO3 interface and the mixture area of CFO3 and CFO2.5. In both cases, ferromagnetic (FM) interaction is expected between Fe3+ (3d5) and Fe4+ (3d4). Furthermore almost all of the appeared Mst is expected from the first interface. From the Mst depending on the nL in MLs, increasing the number of nL, the Mst showed abrupt jump up to 4.4 μB / Fe. It is expected that the electron transfer at the interface occur to introduce the FM interaction between Fe3+ (3d5) and Fe4+ (3d4).

Resume : Transparent conductive oxide (TCO) thin films have been used to opt-electronic devices such as liquid crystal or organic electroluminescent displays and solar cells since TCO has high transparency in visible region and high electrical conductivity. The TCO thin films is heat treated during or after deposition process to modify the optical/electrical properties. Here, low-temperature process applicable to heat-sensitive materials has been required due to increasing the demand of flexible devices. Flash Lamp anneal (FLA) is the candidate of the post-treatment process with low heat-damage1). Additionally, FLA is known as a fast and low-cost process. Here, the detailed mechanisms of the characteristic improvement remain unclear, although some modification of TCO films by using FLA process were reported. In this study, we fabricated Al-doped ZnO (AZO) films by using magnetron sputtering and irradiated with light using the strong xenon flash lamp as a post-treatment process. Here, AZO expected for suitable substitution of ITO since AZO has high abundance and nontoxicity. We evaluated the optical and electrical properties of the fabricated sample and clarified the mechanisms of the characteristic improvement by FLA process. AZO films were deposited on the synthetic quartz glass by rf magnetron sputtering with an AZO (Al2O3: 3.0 wt%) target. Thickness of the films were adjusted to 300 nm. The films were post-treated by the FLA system (Ushio Inc.). The irradiation energy was controlled by changing the charging voltage of the capacitor from 2700V to 4200V. In addition, the FLA process was carried out under four conditions: “UV” (wavelength range 200-300 nm), “UV400” (200-400 nm), “VIS” (350-580 nm), “long-VIS” (530-800 nm), by using corresponding band-pass filters. Note that the number of incident photons was made constant each condition by controlling the irradiation energy. Hence, results of each condition can be quantitatively compared by estimating the quantum yield as the increasing number of the free carriers with increasing the number of incident photons. As results of electrical properties measurement, the resistivity was improved from 1.7×10-3 to 5.2×10-4 Ω･cm with irradiation power increasing. The improvement was due to increasing carrier density from 3.5×1020 to 7.3×1020 cm-3. As results of optical properties measurement, the transmittance at 550 nm improved from 83% to 90% by FLA. Furthermore, the reflectance at near-infrared regime was increased due to increasing the carrier concentration. These results shows that the FLA can be improvement the optical and electrical properties of TCO thin films. In the results with the band-pass filters, carrier density in the “UV400” condition was relatively larger than in the “UV” condition. The result indicates that the visible light with energy lower than the band gap may affect the performance improvement of TCO thin films. The details of these results will be present on that day.

Resume : The present work offers insight into the existing models of temperature-dependent charge transport by tailoring the defects-induced disorder into the lattice by swift heavy ions (SHIs) irradiation. Temperature-dependent charge transport properties of the single-phase and nanocomposite doped ZnO thin films were studied using four-probe resistivity measurements in the wide temperature range of 10K-300K. Moreover, the SHI irradiated films demonstrated interesting phenomena of tuning in temperature coefficient of resistance and transition temperature upon increasing fluence of irradiation. These irradiation effects are discussed in terms of irradiation-induced defects/disorders into the lattice. The change in the nature of temperature-dependent resistivity in pristine and irradiated films has been envisaged with a quantitative fit of experimental data by invoking quantum correction to conductivity. Our results are consistent with this model, which essentially depends on weak localization and renormalized electron-electron interactions. Thus, this work extends the validity of the weak localization model from single-phase materials to nanocomposite materials.

Resume : Since many decades’ cuprous oxide is a very popular candidate as a solar cell absorber, as it is a low-cost, non-toxic, abundant alternative compared to popular silicon. However, solar cells realized with Cu2O absorbers so far are way below their Shockley-Queisser limit. The reason for this gap could be to an extent due to the absorber material than heterojunction problems. In our work, we have prepared Cu2O thin films via different popular techniques namely Magnetron Sputtering, Thermal Oxidation, and Pulsed Laser Deposition, and studied in detail the absorber properties via different structural, optical, and transient characterization techniques. The deposition conditions for all the methods are optimized to obtain phase pure Cu2O with the best electrical properties. The Cu2O films showed characteristic Raman peaks of T1u mode at 145 cm-1, second-order Eu mode at 216 cm-1. Rutherford Back Scattering analysis also confirmed the stoichiometry with an O/Cu ratio of 0.5. Surface Photovoltage measurement using Kelvin Probe Microscopy of thermally oxidized films revealed much higher values compared to other techniques which explains the reason why all the current highest efficiency Cu2O solar cells are using oxidized Cu2O foils. We will describe in detail the fabrication methods, detailed characterization of Cu2O via different advanced characterization techniques, and discuss the potential of the films as an absorber for photovoltaic applications.

Resume : Solid-state Li batteries are promising energy storage devices due to their high energy densities and improved safety. However, the large interface resistance at the interface of solid-electrolytes and electrodes hinders the development of solid-state Li batteries. We fabricated thin-film Li batteries with electrolyte-electrode interface resistance below ~ 5 Ohm cm2 [1,2]; the value is smaller than that observed in liquid-electrolyte-based Li-ion batteries. These studies strongly encourage solid-state Li battery research by demonstrating the very low interface resistance leading to the fast charge and discharge. In addition, the study contributes to understanding the properties of oxide-oxide interfaces. Here, we introduced oxide thin-film technologies into solid-state battery research. Thin-film Li batteries with controlled interfaces are ideal for detailed investigations of resistance at electrolyte-electrode interfaces because they enable us to define the interface area and atomic arrangements. We demonstrate a very low interface resistance at a Li3PO4 solid electrolyte and LiNi0.5Mn1.5O4 [3, 4] and LiNi0.5Mn1.5O4 [5] electrode. Furthermore, the talk covers the latest studies on sulfide solid electrolytes and LiCoO2 electrodes. References: [1] M. Haruta, S. Shiraki, T. Suzuki, A. Kumatani, T. Ohsawa, Y. Takagi, R. Shimizu, and T. Hitosugi, Nano Lett. 15, 1498 (2015). [2] S. Shiraki, T. Shirasawa, T. Suzuki, H. Kawasoko, R. Shimizu, and T. Hitosugi, ACS Appl. Mater. Interfaces 10, 41732–41737 (2018). [3] H. Kawasoko, S. Shiraki, T. Suzuki, R. Shimizu, and T. Hitosugi, ACS Appl. Mater. Interfaces 10, 27498 (2018). [4] H. Kawasoko, T. Shirasawa, K. Nishio, R. Shimizu, S. Shiraki, and T. Hitosugi, ACS Appl. Mater. Interfaces, 13, 5861 (2021). [5] R. Nakayama, K. Nishio, D. Imazeki, N. Nakamura, R. Shimizu, and Taro Hitosugi, Nano Lett. 21, 5572 (2021)

Resume : Among the energy sources alternative to fossil fuels, solar energy attracts great interest. Though the solar cells have already reached conversion efficiency of 25.6%, to make solar energy a primary energy source, it is necessary to further overcome some limiting factors. A main aspect is the electron-hole recombination, that can be reduced by the use of selective membranes, that permit the transmission of one type of charge and block the opposite charge. In the current Silicon Hetero-Junction solar cells a p-type doped hydrogenated amorphous silicon film (a-Si:H) combined with an intrinsic a-Si:H provide selectivity and good surface passivation. However, this approach has also some drawbacks, such as parasitic absorption in the UV-Vis region due to the a-Si:H bandgap of about 1.7 eV, a low band bending at the interface with the absorber layer and the use of toxic gases in the production process. An interesting alternative is represented by molybdenum trioxide in its substechiometric form (MoO3-x). The wide band gap of about 3 eV, with the high work function (higher than 6 eV), determines the creation of an efficient electron energy barrier and simultaneously permits the holes conduction. Moreover, it has a high transparency in the UV-Vis region and toxic gases are not used during the fabrication process. The oxygen vacancies in the lattice generate defect levels in the energy gap which act as donor centers, thus increasing the free carriers concentration but influencing the absorption spectra. Also the electron barrier is ruled by the MoO3-x work function that is strongly dependent on oxide stoichiometry. Therefore, the challenge is to find the right stoichiometry to balance transparency and conductivity to maximize MoO3-x efficacy as hole selective contact. In this work, we have deposited MoO3-x thin films with different stoichiometries by RF magnetron sputtering of a stoichiometric molybdenum trioxide target. By changing just the argon pressure the value of x has been varied between 0.4 and 0 as measured by Rutherford Backscattering Spectrometry. The correlation between stoichiometry and the optical and electrical properties will be discussed. By optical measurements in UV-vis-NIR region we will demonstrate the dependence of transparency on stoichiometry. In particular, we will discuss the characteristic absorption at about 800 nm that is associable to defect levels in the MoO3-x energy bandgap due to the oxygen vacancies in the films. While the transmission is higher by decreasing x value, at the same time we will observe the conductivity increase by increasing the x value due to the increasing free carriers concentration. Thus, the optimal stoichiometry for selective contact application will be discussed. Moreover, we will analyze the performances of different prototypes of solar cell containing MoO3-x films as selective contacts coupled with a thin Indium Tin Oxide layer and by comparing the role of different stoichiometries.

Resume : Since the investigation report of transparent flexible thin film transistors consisting of oxide materials [1], the field of flexible oxide devices has been rapidly developed. In most studies in this field, a polymer film is used as the flexible substrate. Because these polymers have low heat-resistive property, the key of the studies has been to reduce the growth temperature of oxide thin films. To achieve the low temperature process, one of the most conventional studies is to explore an amorphous oxide material with characteristic properties such as high carrier mobility because most amorphous materials can be grown even at room temperature. These studies have brought fruitful results for an application of the amorphous oxide semiconductors to various flexible devices. On the other hand, one of the most “traditional” applications of the oxide materials has been harmonization of the various electronic functions. To realize such application, epitaxial oxide thin films are required because of their remarkable anisotropy. However, the epitaxial growth of the functional oxides is impossible on the flexible polymer film due to its high process temperature as above mentioned. It is obvious that new process is required for the “traditional” applications of the oxide materials to the field of the flexible devices. In this study, we have tried a transfer process of the epitaxially grown functional oxide thin films from original substrates, which is appropriate for the epitaxy, to flexible polymer films [2]. In our transfer process, perovskite type single crystal such as SrTiO3 (100) (STO) was employed as initial substrate for the epitaxial growth of the functional oxides. On the substrate, water-soluble sacrificial Sr3Al2O6 (SAO) [3] was epitaxially deposited. In this talk, the result for a ferroelectric/piezoelectric Pb(Zr, Ti)O3 (PZT) is shown. First, PZT thin film was epitaxially grown on SAO/STO using a pulsed laser deposition. After the deposition of the PZT/SAO/STO, the Pt buffer layer was sputtered on the PZT layer. The Pt/PZT/SAO/STO sample was then bonded on flexible polyimide sheet equipping Cu electrodes using conductive Cu double-sided tape. After this process, the sample was soaked into pure water to dissolve the water-soluble SAO layer. In this step, the Pt/PZT layer was transferred to flexible polyimide sheet. Here, we emphasize that the Pt buffer layer plays an important role to protect the transferred PZT from any serious damages. We have confirmed serious damages on PZT during the transfer process without Pt buffer layer. From X-ray diffraction patterns, the PZT thin film show excellent epitaxy before and after the transfer process. From the result, we have established the excellent transfer process of the epitaxially grown functional oxide thin films to flexible polymer sheet. [1] K. Nomura et al., Nature, 432, 488, 2004. [2] H. Nishikawa et al., Jpn. J. App. Phys., 53, 05FB06, 2014. [3] D. Lu, et al., Nature Mater., 15, 1255, 2016.

Resume : Metal oxide (MO) semiconductors are widely used in electronic devices due to their high optical transmittance and promising electrical performance. However, there is ongoing research to improve their performance by utilizing solution processing, preferably employing environment-friendly techniques. In this work, we present some advances towards an eco-friendly, streamlined method for preparing metal oxide thin-film transistors (TFTs) on large-area substrates via blade-coating. Multi-layer indium oxide (InOx) films and indium oxide/zinc oxide/indium oxide (IZI) heterojunctions were blade-coated from a precursor solution in a green solvent—water—to fabricate metal oxide thin-film transistors (MO-TFTs). Low temperature and relatively short period annealing (300 ℃ for 300 s) of triple-coated indium oxide thin-film transistors (TCIO-TFTs) and IZI-TFTs on a 300 nm SiO2 gate dielectric are realized with an average field effect mobility of 15.8 cm2 V-1 s-1 and 28.4 cm2 V-1 s-1 respectively, an excellent on/off ratio (>10 6), and a threshold voltage close to 0 V when measured in air. Additionally, bias stress tests (positive bias stress (PBS) and light bias stress (LBS)) showed the stability of these devices. When even further reducing the energy budget for the annealing process to annealing at 300 ℃ for only 10 s, IZI-TFTs could still achieve a remarkable average electron mobility of 3.6 cm2 V-1 s-1. X-ray photoelectron spectra (XPS) was used to study the initiation of the Metal-oxygen-metal (M-O-M) networks depending on the annealing time. Preliminary flexible MO-TFTs on polyimide film with a blade-coated AlOx film as dielectric were also successfully fabricated, paving the way towards not only a simple, sustainable, and eco-friendly process on developing high-performance MO films, but also a feasible path to the industrial production of flexible devices for advanced low-power electronics.

Resume : Under-vacuum solid-phase crystallization of amorphous W-doped In2O3 (a-IWO) films was carried out by thermal annealing at 250 ℃ in reactive plasma deposition chamber at a pressure of 5×10-4 Pa without any additional gas for 30 min. a-IWO films with thicknesses ranging from 5 to 50 nm were deposited on non-alkali glass substrates (Corning Eagle XG) at room temperature by reactive plasma deposition with direct current arc discharge. The source materials used was a sintered In2O3 pellet with a WO3 content of 1.0 wt.% (corresponding to 0.6 at. %). When annealed, amorphous films undergo crystallization by nucleation and its growth.[1–4] Out-of-plane and in-plane XRD patterns (RIGAKU SmartLab) showed the directed crystallization, in which the crystallization is favored in <111> directions of crystallites, occurs for the solid-phase crystallization of as-deposited a-IWO films, regardless of film thicknesses (t). The reason we chose W atoms as a better alternative to the conventional donor, Sn atoms, is that W atoms have a higher affinity for O atoms. X-ray reflectivity (XRR) measurement results (RIGAKU SmartLab) demonstrate the absence of interfacial oxide layers between IWO films and glass substrates. On the basis of analysis of the data about the mass density of the films (dm), the roughness of interface (rif), and the roughness of the film surface (rsur) of a- and polycrystalline (p-) IWO films, we found insignificant differences in dm and rif between the films and glass substrates between a- and p-IWO films at any given t. On the other hand, rsur values of postannealed p-IWO films are smaller than those of a-IWO films at any given t. Hall effect measurement results show the typical size effect as follows: After the under-vacuum solid-phase crystallization process, we found an increase in the electrical resistivity of p-IWO films with decreasing t of less than 10 nm. Note that 5-nm-thick p-IWO films showed Hall mobility of 57.7 cm2/(Vs). To study the nature of the carrier transport of p-IWO films with t of less than 10 nm, we applied a classical-size-effect model to those ultra-thin films. In such films, t is almost the same as the mean free path of carrier electrons. The quantitative analysis of the relationship between Hall mobility and the ratio of the mean free path of carrier electrons in the bulk n-type doped material to t proved that the contribution of the scattering at a surface and film/substrate interface to Hall mobility is significantly dominant for p-IWO films at t of less than 10 nm. In such p-IWO films that have very flat surface with rsur of less than 0.78 nm and smooth interface with rif of less than 1 nm, their carrier scattering similar to the specular electron scattering is found, to result in a high Hall mobility. We will deduce what happens at the surface and film/substrate interface.

Resume : Among high temperature superconductors (HTS), YBa2Cu3O7-δ (YBCO) films offer an unparalleled opportunity to be used in large-scale superconducting power applications and high field magnets due to their outstanding ability to carry high critical currents at high magnetic fields. But, its implementation is currently limited by the need of high performance/low-cost manufacturing of epitaxial thin films, for which, chemical-solution deposition (CSD) has become a very competitive cost-effective and scalable methodology [1]. However, CSD growth rates are rather small (0.5-1 nm/s). For this purpose, we have developed a novel growth approach, entitled, Transient Liquid Assisted Growth (TLAG) [2], which is able to combine CSD methodologies with ultra-fast growth rates (100-1000 nm/s) by facilitating a non-equilibrium liquid mediated approach. Critical current densities up to 5 MA/cm2 at 77K are already realized in TLAG-CSD grown thin films, but in order to further improve the current carrying properties, understanding of initial nano phases in pyrolysis process and fine tuning of growth parameters are essential to define a robust process, including thicker layers. Furthermore, a control over microstructure of YBCO films is essential as it determines its critical current-density capabilities, which can be enhanced by the presence of well-controlled nano-defects inside the epitaxial superconducting matrix acting as vortex-pinning-centers. We found that the microstructure of pristine YBCO films could be tuned significantly via TLAG-CSD by optimizing different growth parameters. Besides, the addition of secondary phase nanoinclusions can also increase flux-pinning at high fields by incorporating pre-formed NPs to the metal-organic inks [2]. Therefore, the detailed microstructure of YBCO films, nanocomposites, and coated conductors with varying growth parameters on different substrates, investigated via high-resolution transmission electron microscopy (HRTEM), electron-energy loss spectroscopy (EELS), and using aberration-corrected Scanning TEM (STEM) combined with high-angle annular dark field (HAADF), with a focus on new defects landscape at the atomic-level, secondary phases, and strain-effects, will be discussed. [1] J. Gutierrez, A. et al., Nat. Mat., 6, 367 (2007) [2] L. Soler et al, Nat. Commun., 11, 344 (2020)

Resume : We have designed, produced and tested detectors exploiting the pyroelectric response of the Y-Ba-Cu-O semiconductor material in amorphous structure (a-YBCO hereafter). This material was elaborated in the form of thin films (thickness: 100 to 900 nm, deposition rate: 150 nm/h) by DC reactive cathode sputtering under an Ar-O2 plasma atmosphere (deposition pressure: 250 mtorr) on SiOx-Si substrates at low temperature (150-160 °C). The amorphous state was confirmed by X-ray diffraction, although isolated grains were seemingly immersed in an apparently amorphous matrix, as testified by atomic force microscopy observations. Structuring of the films was then performed by conventional lithography and wet etching techniques. We fabricated trilayer devices (Au:Ti contact / a-YBCO film / Au:Ti contact / SiOx/Si substrate). Current vs. voltage plots exhibited the non-linear Schottky nature of the a-YBCO / metal contacts, which were further analyzed by ultraviolet photoelectron spectroscopy. Infrared response tests of the devices was then performed at 850 nm wavelength. We measured the pyroelectric current delivered in the absence of DC bias, which, in addition to the advantage of simplicity, does eliminate the noise that could originate from this DC source. The pyroelectric signal was amplified by a chain including a low noise trans-impedance amplifier (current input, voltage output) and a synchronous detector locked to the intensity modulation frequency f of the VCSEL source at 850 nm. This frequency was in the 1 Hz to 40 MHz range (this latter value being limited by the bandwidth of the low-noise amplifier connected to the device). The noise level was measured, in the absence of incident radiation, by the synchronous detector operating in the adequate ‘noise level’ mode. The frequency response of the trilayer devices exhibited the following features: pyroelectric response, typically - i.e., exhibiting f^(+1) behavior between 1 Hz and 80 kHz, followed by a plateau extending up to 400 kHz, then by a decrease as f^(-1/2) ascribed to heat diffusion through the substrate thickness. With a noise equivalent power lower than 14 pW.Hz^(-1/2) and a detectivity larger than 5x10^8 cm.Hz^(1/2)/W up to 100 kHz, these detectors prove to be highly competitive, as compared to commercial pyroelectric detectors for instance, with an extremely large bandwidth, to our knowledge unrivalled. This experimental study was comforted by modelling the device response by a purely analytic approach. The inputs of this model only included parameters pertaining to the material and the device, such as e.g. a-YBCO dipolar relaxation frequencies, thermal diffusion cutoff, structure geometry, etc. This model, which was able to reproduce the experimental response of the detector with great accuracy, was included in a graphic user interface, so allowing the design of such infrared thermal detectors with accuracy and flexibility.

Resume : Two-dimensional (2D) nanosheets, which possess atomic or molecular thickness, have been emerging as important new materials due to their unique properties. In particular, the development of graphene has opened the possibility of isolating and exploring the fascinating properties of 2D nanosheets of other layered materials, which upon reduction to single/few atomic layers will offer functional flexibility, new properties, and novel applications. In this talk, we review the progress made in the synthesis, assembly, and properties of 2D oxide nanosheets, highlighting emerging functionalities in electronic/energy applications. A variety of 2D oxide nanosheets (such as Ti1-dO2, Ti1-xCoxO2, MnO2, and perovskites) were synthesized by delaminating appropriate layered precursors into their molecular single sheets via soft-chemical process. These oxide nanosheets have distinct differences and advantages compared with graphene because of their potential to be used as insulators, semiconductors, and even conductors, depending on their composition and structures. Another attractive aspect is that 2D oxide nanosheets can be organized into various nanoarchitectures by applying solution-based layer-by-layer assembly. We utilized oxide nanosheets as building blocks in the LEGO-like assembly, and successfully developed various functional nanodevices such as all nanosheet FETs, high-density capacitors, artificial ferroelectrics/multiferroics, spinelectronic devices, Li-ion batteries/solar cells, actuator crystals, etc. Our work is a proof-of-concept, showing that new hybrid materials/devices can be made from 2D nanosheet architectonics.

Resume : Zinc oxide (ZnO) with has a wide bandgap (~3.37 eV) in the near ultraviolet (UV) region and is expected to be applied for UV detectors. Among various growth techniques for preparing ZnO films, we have paid attention to chemical bath deposition (CBD) because of its simple procedure, cost-effectiveness and low deposition temperature (<100 °C). In our previous paper, CBD growth of vertically aligned ZnO nanorods (NRs) on ion-plated ZnO:Ga (GZO) seed layer and the formation of the heterojunction between the ZnO NRs and poly(3,4-ethylenedioxythiophne) poly(styrenesulfonate) (PEDOT:PSS) have been reported. The resultant PEDOT:PSS/ZnO NRs/GZO junctions exhibited photocurrent (PC) under the irradiation of the UV light [1]. In this paper, generation mechanisms of both the PC and hysteresis characteristics observed on the current-voltage (I-V) curves will be discussed. The GZO seed layers were deposited on alkali-free glass substrates by ion-plating (IP) with a DC arc discharge using a sintered ZnO pellet containing Ga2O3 powder of 4.0 wt.%. The CBD solution for preparing the ZnO NRs layers was a mixed aqueous solution of Zn(NO3)2·6H2O and C6H12N4. The PEDOT:PSS layer was spin-coated on the surface of the ZnO NRs layer at 3000 rpm for 30 sec, followed by thermal annealing in air at 80 °C. Typical I-V curve of the PEDOT:PSS/ZnO NRs/GZO heterojunction exhibited a rectification behavior with hysteresis loops both in forward and reverse bias regions. By the irradiation of the UV light of 360 nm, the hysteresis loop area in the forward bias region decreased, but that in the reverse bias region increased. Fowler-Nordheim (F-N) plots (i.e. ln (I/V2) vs. 1/V) for the forward bias voltages in a dark state can be clearly divided into three characteristic regions (denoted by I, II and III in the order of decreasing 1/V, namely, increasing V) [2]. The I-V curve showed an ohmic characteristic at low bias voltages (region I), whereas the current was approximately proportional to the fourth power of the forward bias voltage at high bias voltages (region III). Therefore, the possible candidates for the dominant transport mechanisms in regions I and III are direct tunneling and F-N tunneling, respectively. At the medium forward voltages (region II), the current was approximately proportional to the square of the forward bias voltage. The increase in repetition number of I-V measurement under the forward bias (0→3→0 V) in a dark state led to the increase in maximum forward current. Moreover, the transition voltage from region I to region II shifted to the lower V side with increasing repetition number. A similar tendency has been observed on the In2O3/ZnO/SnO2:F heterojunctions by Kumar et al. [3]. [1] T. Terasako et al. Thin Solid Films 677 (2019) 109. [2] D.G. Gallach-Pérez et. al, J. Lumin. 191 (2017) 107. [3] M. Kumar et al., ACS Appl. Mater. Interfaces 10 (2018) 34370.

Resume : Magnetite, Fe3O4, is one of the transition metal oxides studied extensively because of its high Curie temperature, metal–insulator transition (Verwey transition) at ~120 K. While the high-quality nanoscale Fe3O4 samples are required for the application as nanoelectronics devices, the achieving the nanoscale Fe3O4 sample with prominent physical properties is longstanding issue owing to the unintended nanoscale defects typically at the interface between Fe3O4 and the substrate. Nanoscale roughness such as kink and scratch on the base substrate causes defects formation, so that atomically smooth substrate is desirable. In this study, we prepared the MgO(001) substrate, of which surface was atomically flattened by a chemical polishing method of which name is Catalyst-referred etching (CARE), and subsequently grew the Fe3O4 thin films. A Fe3O4 film with a thickness of 50 nm was deposited on a MgO substrate using pulsed laser deposition (PLD) technique (ArF excimer: wavelength of 193 nm). The atomic force microscopy (AFM) observation of the CARE processed MgO substrate showed atomically flat surface and ordered crystal arrangement with atomic step and terrace structure. The reflection high-energy electron diffraction (RHEED) and transmission electron microscopy (TEM) revealed the reduction of the density of defects at the topmost surface of MgO. The AFM, RHEED, and TEM results showing the perfection of the MgO(001) substrate surface indicated that the CARE-flattened surface can maintain the flatness and atomic ordering led to the homogeneous hetero-interface between MgO and Fe3O4 film. To understand the effect from the defect density on the property of Verwey transition, the magnetic resistance (MR) response of Fe3O4 films was evaluated. The MRs of Fe3O4 films CARE processed MgO at a magnetic field of 50 kOe was smaller than that of Fe3O4 films grown on pristine MgO, indicating the decrease in the defects by 68%. The temperature-dependent resistivity (R-T) curves for Fe3O4 films grown on the CARE processed MgO exhibited obvious Verwey transition with higher relative change in resistance, whereas that on pristine MgO showed a weak Verwey transition. The maximum relative change in resistance of 5.8, which is markedly larger than that of the thin film on a pristine MgO. We also observed the shift of the transition temperature toward higher values indicating enhancement of Verwey transition in the Fe3O4 films grown on CARE processed MgO. The MR response and R-T curves indicated that the atomically flat surface of the CARE processed MgO can produce a flat interface with fewer broken bonds and oxygen vacancies than those for pristine MgO, resulting in less off-stoichiometry and a nondeteriorating Verwey transition for the Fe3O4 film.

Resume : The direct integration of crystalline oxide layers into flexible electronic systems requires the development of relatively simple, low-temperature processing routes [1]. Seeding represents a powerful strategy to reach this objective by the generation of preferential sites for the nucleation of crystalline phases with a reduced energy barrier. Here, a novel approach is reported where nanoseeds are generated in-situ from a precursor solution using a solvent-engineering strategy (solvent-antisolvent). The controlled addition of an antisolvent (1,3-propanediol) to a solution of metal salts (Bi/Fe) dissolved in acetic acid results in the formation of nanocrystals (seeds) by supersaturation. The presence of such nanoseeds is also confirmed in the deposited layers, improving significantly the crystallinity of the respective BiFeO3 thin films as complementary deduced by piezoresponse force microscopy. Using this low-temperature strategy, crystalline films are directly grown on flexible polymeric substrates at only 350 ºC showing a remanent polarization of 10.5 μC cm-2 and a clear photovoltaic effect (11.7 µW cm-2) of interest in computer memories and energy harvesters. The flexibility of the BiFeO3 thin films may enlarge the number of applications of this multifunctional, lead-free material in next-generation digital and sustainable electronic devices based on a facile, low-cost fabrication method with a reduced energy consumption. [1] Bretos et al., Adv. Funct. Mater. 2020, 30, 2001897; Bretos et al., Chem. Eur. J. 2020, 26, 9277; Bretos et al., Chem. Soc. Rev. 2018, 47, 291. This work is part of the Spanish Projects PID2019-104732RB-I00 and MAT2017-91772-EXP funded by MCIN/AEI/10.13039/501100011033. Grant RYC-2016-20047 funded by MCIN/AEI/10.13039/501100011033. O. B. acknowledges financial support from Spanish "JAE Intro" Programme (JAEINT_19_01923).

Resume : The stabilization of functional magnetic oxides on flexible substrates is not only appealing for novel flexible electronics, but also allows the detailed study of the influence of bending strain on the magnetic properties of these materials. We are interested in investigating the strain dependence of the magnetic anisotropy in two distinct iron oxides, namely magnetite (Fe3O4) and the high anisotropy metastable epsilon iron oxide (ε-Fe2O3) [1]. Both were stabilized by pulsed laser deposition on synthetic fluorphlogopite mica substrates. Magnetite is a well-known cubic spinel ferrite, while ε-Fe2O3 has a low symmetry Pna21 orthorhombic structure. We will show the optimization of the growth parameters together with a precise microstructural analysis via X-ray diffraction combining standard omega-2theta, pole figures and reciprocal space mapping. We determined that the spinel phase grows with (LLL) texture and the twinning in magnetite is strongly reduced as only one domain could be identified. On the other hand, epsilon iron oxide shows the formation of three distinct in-plane domains, with out-of-plane (00L) texture. The tight bonding of the epitaxial film to the flexible mica substrate allows a simple approach to test the tuneability of the magnetocrystalline anisotropy, by bending the substrate one induces a lattice deformation of the films. Here, we investigate the effect of tensile and compressive bending strain at room temperature and below. We revise the effect of the bending geometry and therefore the film-field orientation by comparing M(T) curves and M(H) hysteresis loops from tensile to compressive strain. The influence on the in-plane and out-of-plane magnetic anisotropy for different measurements is compared for the two iron oxide phases. Interestingly, magnetite thin films show a clear dependence on different bending states displaying changes in the coercive field, remnant/saturation magnetization ratio and Verwey transition. Nevertheless, in contrast other reports [2,3] ε-Fe2O3 thin films only show weak variations of the magnetic properties with bending strain, and no change can be observed in the hysteresis loops nor on low temperature magnetic transitions. We discuss these discrepancies in connection to the geometry of the measurements as a source of artifacts. References [1] Gich et al., Journal of App. Physics (2005), 98, 044307. [2] P. Wu et al., ACS Appl. Mater. Interfaces (2016), 8, 49, 33794–33801. [3] T. Amrillah at al., ACS Appl. Mater. Interfaces (2021), 13, 14, 17006–17012. Acknowledgements: I would like to acknowledge the Severo Ochoa Programme for Centres of Excellence in R&D (FUNFUTURE CEX2019-000917-S) and European Research Council FeMiT project: ERC-CoG 819623.

Resume : Rare earth oxyhydroxides (RE-OOH) present unique luminescent properties that makes them very interesting for optically active applications [1-2]. However, while most practical applications, such as sensors, emitters or displays, require materials in thin film configuration, most reports concerning the synthesis of these materials relate to either bulk materials or powders and thus, the fabrication of RE-OOH films remains a challenge. In this work we present the successful single-step preparation of EuOOH thin films starting from an Eu2O3 target by Pulsed Laser Deposition in an appropriate gas environment. Post-deposition annealing in air at moderate temperatures (<300 ºC) leads to the formation of 2D-microcrystalline EuOOH with a characteristic six-pointed star shape with sizes in the 10 microns and a thickness in the 100 nm ranges that cover all the film surface. The shape points to a dendritic diffusion-limited crystallization process. The results obtained suggest that the gas environment during the deposition, rather than the post deposition annealing process, is the responsible for the formation of the observed EuOOH phase. The optical properties (transparency range and refractive index) and photoluminescence response of EuOOH thin films are finally presented. [1] G. Colombi, T. De Krom, D. Chaykina, S. Cornelius, S. W. H. Eijt, B. Dam, ACS Photonics 8, 709-715 (2021). [2] S. Cornelius, G. Colombi, F. Nafezarefi, H. Schreuders, R. Heller, F. Munnik, B. Dam, J. Phys. Chem. Lett. 10, 1342–1348 (2019).

Resume : Abstract Dielectric materials are well-known for micro and nanoelectronics where their insulation and polarizability are critical properties. However, in the energy storage field, high-k dielectric layers in contact with an active material tends to be considered only as an insulating passivation layer. In microelectronics, this conception has been modified with the study of dielectrics at nanoscale level [1-2] revealing interesting properties scarcely known by other fields [3]. We propose to reconsider the vision of high-k dielectric materials for energy at nanoscale for a micro-supercapacitor electrode application. Based on microelectronic deposition techniques [4], a nanometric-scale layer of dielectric is deposited by Atomic Layer Deposition (ALD). Allowing us to create a nanometric, pinhole-free alumina (Al2O3) layer on complex architectures as Silicon nanowires (SiNW) grown by CVD [5]. Microelectronics measurements on a single SiNW is shown to display thickness dependent tunneling electrical conduction. This result brings a silicon based micro-supercapacitor (µSC) protected by a 3 nm alumina layer exhibits Electrical Double Layer Capacitance (EDLC) by means of tunneling current. This result in aqueous electrolyte is an unprecedented for this material, allowing an outstanding lifetime capacity and retaining almost 99% of its initial capacitance after 2 million cycles. [6]. This new approach of energy storage materials open the field of new possibilities and compatibility with aqueous media. It has been shown in this work that, the addition of a conductive polymer PEDOT-PSS is forming an homogeneous nano-composite that benefits from the properties of the protected SiNWs, enhancing it’s stability during the cycling, reaching up to 500.000 cycles in aqueous media, while maintaing remarquable electrochemical performances [7], pushing forward the deposition of new conductive polymers to better understand this stability phenomenon. References [1] G.D. Wilk, R.M. Wallace, J.M. Anthony, High-κ gate dielectrics: Current status and materials properties considerations, J. Appl. Phys. 89 (2001), 5243, doi: 10.1063/1.1361065 [2] H. Zhang, X. Guo, J. Hui, S. Hu, W. Xu, D. Zhu, Interface Engineering of Semiconductor/Dielectric Heterojunctions toward Functional Organic Thin-Film Transistors, Nano Lett. 11 (2011), 4939-4946, doi: 10.1021/nl2028798. [3] A. S. Asundi, J. A. Raiford, S. F. Bent, Opportunities for Atomic Layer Deposition in Emerging Energy Technologies, ACS Energy Letters. Mater. 4 (2019), 908-925, doi: 10.1021/acsenergylett.9b00249. [4] S.M. George, Atomic Layer Deposition: An Overview, Chem. Rev. 110 (2010), 111-131, doi: 10.1021/cr900056b. [5] D. Gaboriau, M. Boniface, A. Valero, D. Aldakov, T. Brousse, P. Gentile, S. Sadki, Atomic Layer Deposition Alumina-Passivated Silicon Nanowires: Probing the Transition from Electrochemical Double-Layer Capacitor to Electrolytic Capacitor, ACS Appl. Mater. Interfaces 9 (2017), 13761-13769, doi: 10.1021/acsami.7b01574. [6] A. Valero, A. Mery, D. Gaboriau, M. Dietrich, M. Fox, J. Chretien, N. Pauc, P.Y. Jouan, P. Gentile, S. Sadki, Redefining high-k dielectric materials vision at nanoscale for energy storage: A new electrochemically active protection barrier, Electrochimica Acta. 389 (2021) 138727, doi.org/10.1016/j.electacta.2021.138727 [7] A. Valero, A. Mery, D. Gaboriau, P. Gentile, S. Sadki, One Step Deposition of PEDOT–PSS on ALD Protected Silicon Nanowires: Toward Ultrarobust Aqueous Microsupercapacitors. ACS Appl. Energy Mater. 2 (2019), 1, 436–447, doi.org/10.1021/acsaem.8b01470.

Resume : SnO2 is a promising n-type semiconducting material with excellent electrical and optical properties.[1] Its thin films are employed in a broad range of devices comprising photovoltaics[2], thin film transistors (TFTs)[3] and gas sensors.[4] With respect to TFTs, SnO2 as channel layer is attractive due to its high mobility and transparency, while gas sensing applications benefit from the oxygen deficient surface nature of SnO2 which facilitates ideal conditions for reduction-oxidation reactions to take place.[5] As the properties of metal oxide thin films and their surfaces are highly dependent on the employed deposition process, a wise choice must be made to this effect. This is especially valid for chemistry-based vapor phase deposition techniques such as atomic layer deposition (ALD) and chemical vapor deposition (VD) wherein the employed precursor is an important building block and a key aspect to consider. We report on a versatile amino functionalized Sn(IV) alkyl precursor. Thermal analyses rendered the liquid precursor not only as volatile and thermally robust but as suitable to be used in MOCVD and PEALD of SnO2 thin films alike, which enabled to tune the surface nature and electronic properties.[6,7] Hereby, PEALD covered a film growth temperature regime of 60 °C – 150 °C and MOCVD one of 400 °C – 800 °C. For both processes, the relevant growth characteristics were carefully investigated. Structure, morphology and composition were evaluated by a combination of XRD, AFM, SEM, RBS, NRA and XPS. Optical band gaps of films with varying thicknesses were determined to be 3.6 eV - 3.9 eV by UV-VIS measurements. Capitalizing on the different film properties obtained for films grown by the MOCVD and PEALD process, latter was used to fabricate bottom-gate bottom-contact TFTs. Mobilities up to 10 cm2V-1s-1 were achieved at low deposition temperatures (T = 60 °C) thus making this PEALD process very attractive for flexible electronics. The devices also showed a high Ion/Ioff ratio of 107. Contrasting this, SnO2 films from the MOCVD process were subjected to a combinatorial approach comprising temperature-dependent vdP, SEM, AFM and XRD. Here, the impact of surface morphology and roughness on the resistivity of thin (≤ 50 nm) SnO2 films was studied. All investigated films revealed hysteresis-free resistivity performance when heated to temperatures of up to 300 °C in atmospheric environment exhibiting minimum resistivities of 3.12 x 10-5 Ω m, which renders them as highly promising for chemical sensor applications. [1] S. Das, et al., Progress in Materials Science, 2014, 66, 112 [2] C. Beneking et al., Thin Solid Films, 1999, 351, 241 [3] R. Mannam et al., Applied Surface Science, 2017, 418, 414 [4] J. Zhao, et al., Sens. Actuators B, 2010, 145, 788 [5] W. Gopel, Prog. Surf. Sci., 1985, 20, 9 [6] D. Zanders, et al., Adv. Mater. Interfaces, 2019, 6, 1801540 [7] D. Zanders, et al., ACS Appl. Mater. Interfaces, 2019, 11, 31697

Resume : Oxide epitaxy heralds flexible approaches for tailoring and understanding the electronic structure of correlated-electron materials. We consider the correlated d1 metal SrVO3 (SVO) as a case study for early transition metal oxide Mott materials. Films growth was done via molecular beam epitaxy (MBE), a process that allows precise control over the stoichiometry and thickness, in addition to being scalable and industry compatible. A key challenge in the study of the electronic structure is to avoid defects that can obscure the actual physical properties, for example, due to electron scattering. Thus, a systematic study of the different growth parameters is required to achieve high-quality films. In this work, we present low defect and epitaxial SVO films with residual resistivity ratio exceeding 15 and room temperature resistivity in the order of 30 µΩ·cm. We emphasize the necessity of a careful analysis of the SVO structural and electronic properties. These findings are the stepping stone for studying the SVO electronic structure for electronic applications and devices. This work was funded by the Israeli Science Foundation (ISF Grant 375/17).

Resume : Transparent conducting and thermoelectric perovskite oxides of general formula ABO3 are appealing because of their chemical flexibility with abundant and low toxicity elements, property tunability by doping and correlation effects, thermal stability, structural compatibility for epitaxy and direct integration on semiconductors (Si, Ge, GaAs) by molecular beam epitaxy (MBE) [1-3]. Whereas various n-type ABO3 are available, as SrTiO3-based solid solutions exhibiting large transmittance (>60%) in the visible range, low resistivity (10-3 ohm.cm) and large thermoelectric power factors (PF ∼40 µW cm-1 K-2) [4-6], the counterpart p-type ABO3 are much less known. Sr-doped LaCrO3 is one of the few p-type transparent thermoelectric ABO3 exhibiting optimal PF around 25 at.% Sr (La0.75Sr0.25CrO3) [7]. In this communication, we will first show that high-quality Sr-doped LaCrO3 epitaxial films can be elaborated by solid-source MBE [8], and secondly that the transport (electronic and thermoelectric) properties of La0.75Sr0.25CrO3 can be largely tuned by epitaxial strain within ± 2% range [9]. In particular, the electric conductivity can be controlled over two orders of magnitude, ranging from ∼0.5 S cm-1 (tensile strain) to ∼35 S cm−1 (compressive strain). Consistently, the Seebeck coefficient can be finely tuned by a factor of almost two from ∼127 μV K−1 (compressive strain) to 208 μV K−1 (tensile strain). The thermoelectric power factor can consequently be tuned by almost two orders of magnitude. The compressive strain yields a remarkable enhancement by a factor of three for 2% compressive strain with respect to almost relaxed films. ---------------------------- [1] L. Zhang et al., Nature Mater. 15, 204 (2016) ; https://doi.org/10.1038/nmat4493 [2] J. He et al., J. Mater. Res. 26, 1762 (2011); https://doi.org/10.1557/jmr.2011.108 [3] G. Saint-Girons et al., Chem. Mater. 28, 5347 (2016) ; https://doi.org/10.1021/acs.chemmater.6b01260 [4] J. Ravichandran et al., Chem. Mater. 22, 3983 (2010) ; https://doi.org/10.1021/cm1005604 [5] G. Bouzerar et al., Europhys. Lett. 118, 67004 (2017); https://doi.org/10.1209/0295-5075/118/67004 [6] M. Apreutesei et al., Sci. Technol. Adv. Mater. 18, 430 (2017); https://doi.org/10.1080/14686996.2017.1336055 [7] K.H.L. Zhang et al. Adv. Mater. 27, 5191 (2015); https://doi.org/10.1002/adma.201501959 [8] D. Han et al., J. Appl. Phys. 126, 085304 (2019); . https://doi.org/10.1063/1.5101049 [9] D. Han et al., ACS Appl. Electron. Mater. 3, 3461 (2021) ; https://doi.org/10.1021/acsaelm.1c00425

Resume : CaVO3 and SrVO3 are newly discovered transparent conductors, belonging to the group of perovskite oxides with strong electronic correlations [1]. This group of oxides offers also an important interplay between the structure of the material and the transport properties, having its impact on the optical properties through the modification of the charge carrier effective mass [2]. The technological potential of these new transparent conductors is largely related to the possibility of integrating vanadates on low cost substrates and especially on glass. In its amorphous form, vanadates are not conducting [3], imposing a growth approach keeping the crystalline character of the material. In this work, we show the possibility to integrate crystalline CaVO3 and SrVO3 thin films by pulsed laser deposition thanks to Ca2Nb3O10- nanosheets seed layer prepared by exfoliation process of KCa2Nb3O10 and deposited onto glass substrate using the Langmuir-Blodgett method. The seed layer induces the possibility to grow the films at a moderate temperature required for the integration on glass. Finally, by using transport and spectroscopic analysis, we are showing that their functional properties are competing with the best transparent conducting oxides known so far [4]. References [1] L. Zhang et al., Nature Materials 15 (2015) 204. [2] A. Boileau et al., Advanced Optical Materials 7 (2019) 1801516. [3] A. Boileau et al., Appl. Phys. Lett. 112 (2018) 021905. [4] A. Boileau et al., Adv. Funct. Mater. (2021), 2108047.

Resume : To reduce the immense power consumption of current computational methods, approaches such as memory-centric computation and brain-inspired neuromorphic architectures are being investigated. In this respect, neuromorphic computation based on memristors offers an emergent artificial neural network (ANN) that can perform in-memory computation with adaptive learning algorithms on hardware. However, one of the main issues of memristor technology is related to device spatial and temporal variations (SV, TV respectively). These negatively impact classification accuracy in ANN hardware. SV originates in the process of memristor device fabrication, referred to as device-to-device variations. TV are due to the fact of stochastic creation of conductive filaments arising cycle-to-cycle variation. These variations can only be minimized by design of an area-scaling resistive switching device. Towards applications in system-on-panel (SoP) architectures and internet-of-things (IoT) devices on flexible substrates, IGZO memristors are fabricated where eventually the same material can be used both for memristor elements and support thin-film transistor circuits. One of the main principles of building a memristor element relies on an asymmetric structure. This means the resistive switching layer is sandwiched between an ohmic contact and a Schottky-type electrode (usually Pt). Here, we show that oxidized molybdenum can also induce a Schottky barrier to IGZO, associated with the high work function of MoO3. Interestingly, switching characteristics are then governed by modulation of barrier characteristics leading to a forming-free area-dependent performance with an analog control of resistance states. Temperature analysis of the characteristics confirms modulation of the barrier width. A data-driven model is then presented by taking the thermionic emission equation as a basis. References: 1 M.E. Pereira, J. Deuermeier, P. Freitas, P. Barquinha, W. Zhang, R. Martins, E. Fortunato, and A. Kiazadeh, APL Mater. 10, 011113 (2022). 2 G. Carvalho, M. Pereira, A. Kiazadeh, and V.G. Tavares, Micromachines 12, (2021).

Resume : ABO3 perovskite oxides present a wide range of fascinating physical properties and are chemically flexible and thermally stable. SrTiO3 is an archetypal member of this family. Partial substitution of divalent Sr by trivalent La to form Sr1-xLaxTiO3 [1-2] leads to n-type layers with large thermoelectric power factor which enables conversion of an electrical potential difference into a temperature gradient (Peltier effect) or vice-versa (Seebeck Effect) [3]. SrTiO3 can also be epitaxially integrated on silicon [4] for on chip applications as micro-thermoelectric coolers or generators. P-types on the other hand are in low number and the few that are known display low thermoelectric power factor even though it can be largely tuned by epitaxial strain (e.g. La1-xSrxCrO3 [5]), though both n-type and p-type materials are needed to form a complete thermoelectric device. SrTiO3 with B-site partial substitution with a trivalent cation, as SrTi1-xAlxO3, appears as a good p-type perovskite oxide candidate. Its band structure, simulated by ab-initio calculations, seems promising with minor perturbation of the band structure up to x=0.125. In this context, we report here on SrTi1-xAlxO3 epitaxial films grown by Molecular Beam Epitaxy (MBE) with x ranging from 0.1 to 0.5. Structural characterizations by Reflection High Energy Electron Diffraction (RHEED), X-Ray Diffraction (XRD) and X-ray Photoemission Spectroscopy (XPS) indicate that good quality SrTi1-xAlxO3 solid solutions can be obtained with effective Al on B-site. Measurement of its thermoelectric properties are currently ongoing. [1] G. Bouzerar et al., EPL, 118, 67004 (2017); DOI : 10.1209/0295-5075/118/67004 [2] M. Apreutesei et al., Sci. Technol. Adv. Mater., 18, 430 (2017); DOI: 10.1080/14686996.2017.1336055 [3] F.J. DiSalvo, Science, 285, 703 (1999); DOI: 10.1126/science.285.5428.703 [4] G. Saint-Girons et al., Chem. Mater., 28, 5347 (2016); DOI : 10.1021/acs.chemmater.6b01260 [5] D. Han et al., ACS Appl. Mater. Interfaces, 3, 3461 (2021); DOI : 10.1021/acsaelm.1c00425

Resume : Vanadium dioxide (VO2) has attracted an increased attention due to its ability to undergo a reversible metal to insulator transition (MIT) which can be thermally induced at a temperature of 340K or, more interesting, via optical or electrical excitations. The MIT is inducing drastic changes in the material’s optical and electrical properties which have made VO2 an interesting material for integration in different electrical and optical devices (high-speed optical and electrical switches, field-effect transistors, oscillators…). The electrical and optical performances of the obtained films are strongly correlated with the quality, grain size, degree of strain and oxidation of the material. Thus, in order to better control the electrical resistivity or optical transmission changes during MIT (hysteresis and transition width, transition temperature), a good understanding of the film’s growth mechanism is needed. We have investigated the structural, morphological and electrical characteristics of VO2 thin films obtained by DC magnetron sputtering of a vanadium target in Ar/O2 atmosphere, on large area substrates, up to 3”. We examined the impact of the deposition and post-deposition annealing parameters on the structural and electrical properties of VO2 coatings. The films were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy and electrical resistivity measurements. These combined analysis results indicate that the deposition and annealing temperatures along with the oxygen partial pressure are the most important parameters in order to achieve mono oriented VO2 films with state-of-the-art amplitude resistivity changes between the two states (superior to 5 orders of magnitude).

Resume : More and more applications require the photosensing enabling discrimination between emitting or polluting species. The identification and quantification of SO2, NOx, H2S and O3 emission based on photo-absorption/fluorescence techniques can be benefited by detectors with multiple-bandwidth detection. However, the bandgaps of typical diamond and SiC detectors are not tunable, whereas those of AlGaN (composite III-nitrides) can only be varied from 3.4 eV to less than 4.5 eV through bandgap engineering. Therefore, other mterials as ZnMgO oxides can be exploited, where Mg concentration tuning can provide bandgap adjustment. In this work we varied Mg content in the ZnMgO material for producing most effective photodetectors with highest and fastest response, and high UV/VIS rejection ratio. We have grown Zn1-xMgxO layers using molecular beam epitaxy technique, varying x in 0-66 % range. Gradual increase of bandgap was observed with x, as well as shift of photoluminescence peak to shorter wavelengths, indicating effective tuning of bandgap. Ag contacts were deposited for obtaining photoconductive Zn1-xMgxO detectors. Pure ZnO detectors shower low performance due to subbandgap defect absorption and high nonequilibrium doping leading to large dark currents. The detectors with 26, 46 % of Mg provided low dark currents with dark resistivities up to GΩ. That detectors showed best detectivity and UV/VIS rejection ratio up to 100. While optimal 26 % Mg detector showed most intensive fast response down to 100 ps if 10 ps excitation laser pulses at 266 nm were applied. Further increase of Mg led again to appearance of defect absorption and lower UV/VIS rejection ratio. All detectors showed reduction of responsivity from about 5-30 A/W to values by magnitude lower due to saturation of defects. Finally, the device operation was related to its material electronic properties via photoluminescence and light induced pump-probe techniques. Larger concentration of ZnO phase was related to subbandgap absorption and strong defect emission thus leading to poor UV/VIS rejection ratio. Better carrier lifetimes were correlated to stronger exciton emission. The sample with 26 % Mg showed largest diffusion length and excitonic emission verifying its best detector parameters. Thus, we can conclude that simple Zn1-xMgxO detector design allows their application in low cost environmental detection systems.

Resume : Transparent and conductive materials (TCM) constitute key components for many applicative domains such as photovoltaics, smart windows, and transparent heaters. Metallic nanowire networks have recently emerged as a promising TCM due to their remarkable optical, electrical, mechanical properties and low-cost fabrication[1,2]. However, their stability when subjected either to electrical and/or thermal stress appears to be a clear limitation for efficient industrial integration. It has been shown that conformal and thin oxide coating metallic nanowire networks not only drastically improved the stability, but can also be seen as a very promising nanocomposite[3,4]. The design and control of oxide thin films offer great opportunities for further device integration thanks to multiple functionalities. The obtained high-performance nanocomposites are associated with high potential for integration within energy-friendly, electronic, and environmental devices. A brief overview will be provided on these recent topics. A more specific focus will be on the use of a recent method to deposit thin oxide layers, Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD)[5], which exhibits several assets: low temperature, high growth rate, and low cost. We will present the design and characterization, as well as physical modelling, of multifunctional nanocomposites based on SALD-deposited oxide on metallic nanowire networks. The key parameters that can tune the main properties (optical transparency, electrical conductivity, flexibility, stability) and compatibility with integration will be discussed, along with the main next challenges. References: [1] L. Bardet, D. T. Papanastasiou, C. Crivello, M. Akbari, J. Resende, A. Sekkat, C. Sanchez-Velasquez, L. Rapenne, C. Jiménez, D. Muñoz-Rojas, A. Denneulin, D. Bellet, Nanomaterials 2021, 11, 2785. [2] T. Sannicolo, M. Lagrange, A. Cabos, C. Celle, J.-P. Simonato, D. Bellet, Small 2016, 12, 6052. [3] A. Khan, V. H. Nguyen, D. Muñoz-Rojas, S. Aghazadehchors, C. Jiménez, N. D. Nguyen, D. Bellet, ACS Applied Materials & Interfaces 2018, 10, 19208. [4] J. J. Patil, W. H. Chae, A. Trebach, K. Carter, E. Lee, T. Sannicolo, J. C. Grossman, Adv. Mater. 2020, 2004356. [5] D. Muñoz-Rojas, V. H. Nguyen, C. Masse de la Huerta, S. Aghazadehchors, C. Jiménez, D. Bellet, Comptes Rendus Physique 2017, 18, 391.

Resume : Printed electronics answers to the emerging trend of using truly inexpensive and easily accessible techniques to design and fabricate low-cost and recyclable flexible electronic components. However, printing of inorganic semiconductor materials arises some barriers for flexible electronics, as they usually may require high annealing temperatures to enhance their electronic performances, which are not compatible with paper. Here, we report the formulation of water-based, screen-printable inks loaded with zinc-based oxide nanostructures that do not require any sintering process. The inks are used to create the channel in fully printed electrolyte-gated transistors on paper, gated by a cellulose-based ionic conductive sticker (CICS). The high conformability of the electrolyte-sticker mitigates the effect of the surface roughness of the channel, yielding transistors that operate under low-voltage (<2.5 V). In alternative, paper can be replaced by a functional ionic conductive “paper-like” substrate that merges the appealing electrochemical properties of the CICS with the mechanical robustness, thermal resistance, transparency, and smoothness of micro/nanofibrillated cellulose nanopaper. The screen-printed transistors are readily integrated in “universal” logic gates (NOR and NAND) by using ubiquitous calligraphy accessories for patterning of conductive paths and graphitic load resistances. This demonstrates the manufacturing of reliable and recyclable cellulose-based iontronic circuits with low power consumption, paving the way to a new era of sustainable “green” electronics.

Resume : We have grown La0.3Sr0.7CoO3–δ thin films by pulsed laser deposition on (LaAlO3)0.3(Sr2TaAlO3)0.7 substrates with and without a protective LaAlO3 capping layer and investigated their structural and magnetic properties. We have observed that, in the uncapped films, the Curie temperature strongly decreased after annealing in helium atmosphere, and it significantly decreased even in samples stored for several weeks at room temperature. The decrease of the Currie temperature is caused by an increase of the concentration of oxygen vacancies, δ. However, we show that already a 3 nm thin LaAlO3 capping layer can essentially conserve δ at room temperature, and it considerably slows down the formation of oxygen vacancies at elevated temperatures.

Resume : The development of low-cost, stable and active electrocatalysts for the oxygen evolution reaction (OER) is a critical requirement for various applications, encompassing water splitting, CO2 reduction, low-temperature fuel cells, and rechargeable metal-air batteries. In particular, the first kind of processes has received a remarkable attention for the production of hydrogen, a strategically attractive energy vector, from water, a largely available natural resource, with no ecological footprint. Among the possible materials, manganese oxides and, in particular, MnO2 and Mn2O3, have emerged as attractive candidates thanks to their low toxicity, large natural abundance, and rich redox chemistry. In this scenario, functionalization with Au nanoparticles (NPs) even in trace amounts stands as a valuable mean to enhance OER performances, due to the occurrence of a strong interaction at the Au/manganese oxide interface, involving a charge redistribution and the formation of interfacial oxygen vacancies. The tailoring of these effects through a controllable material preparation and processing is of key importance to obtain enhanced OER performances. In the present work, manganese oxide nanomaterials are grown on fluorine-doped tin oxide (FTO) substrates by plasma assisted-chemical vapor deposition (PA-CVD), functionalized with gold NPs by radio frequency (RF)-sputtering under mild conditions, and subjected to ex-situ thermal treatments in air or inert atmospheres to trigger the obtainment of MnO2 or Mn2O3, respectively. The advantages offered by the adopted preparation route provide a versatile toolkit for the mastering of material properties. Characterization results revealed the possibility to achieve the selective formation of manganese(IV) or (III) oxides featuring an open dendritic morphology and a high oxygen defectivity. The combination of these features, along with the introduction of gold species, enabled to modulate and improve material activity towards OER. Specifically, Mn2O3-based systems yielded higher current density values than the corresponding MnO2-based ones, and gold introduction induced a ≈20% improvement, despite its very low amount. Overall, the presently reported data pave the way to the improvement of OER performances of transition metal oxide nanomaterials fabricated by means of controllable strategies, taking advantage on strong interactions between the single components at the nanometer scale. L. Bigiani, A. Gasparotto, T. Andreu, J. Verbeeck, C. Sada, E. Modin, O.I. Lebedev, J.R. Morante, D. Barreca, C. Maccato, Advanced Sustainable Systems, 2021, 5, 2000177.

Resume : In this work, a thermally-assisted chemical vapor deposition (CVD) route was implemented and optimized for the tailored fabrication of α-Mn3O4 (hausmannite) nanostructured films on indium tin oxide- (ITO-) coated glass substrates. Syntheses were carried out in a N2+O2 atmosphere and in the presence of water vapor, adopting Mn(hfa)2TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine) as second generation Mn(II) precursor [1]. The influence of growth temperature and total pressure on the system structural, compositional, morphological and optical properties was throughly investigated by a multi-technique approach involving XRD, XPS, SIMS, FE-SEM, AFM and UV-Vis measurements. Characterization results revealed the obtainment of single-phase and high-purity α-Mn3O4 deposits with tunable thickness, particle size and nanoscale morphology. The obtained electrode materials were hence tested in photoelectrochemical (PEC) water splitting experiements, carried out under simulated sunlight irradiation, paying special attention on the interplay between the adopted synthesis conditions and the resulting functional behaviour. The fabricated hausmannite films exhibited an amphoteric semiconducting behavior, and PEC performances strongly dependent on the deposit nanoscale organization. To the best of our knowledge, this is the first study reporting on the use of single-phase α-Mn3O4 electrocatalysts for water splitting applications. This issue, along with the advantages offered by CVD techniques in terms good conformal coverage even of large-area and porous supports, precise thickness/morphology control, and single-step growth of high quality materials, pave the way for the implementation of the present research in the design of other manganese oxide-based catalytic platforms for sustainable energy generation [2]. 1. D. Barreca, G. Carraro, E. Fois, A. Gasparotto, F. Gri, R. Seraglia, M. Wilken, A. Venzo, A. Devi, G. Tabacchi, C. Maccato, J. Phys. Chem. C 122, 1367-1375 (2018). 2. A. Gasparotto, C. Maccato, A. Petala, S. Bebelis, C. Sada, D. I. Kondarides, D. Barreca, ACS Appl. Energy Mater. 2, 8294-8302 (2019).

Resume : The problem of the motion of a domain wall inside a magnetic system is a compelling one. Although different kind of walls in particular magnetic systems have been studied, there is up to date no description of the dynamics of a domain wall in spin spiral systems under the action of an external electric field. Here we focus on a frustrated magnetic system where non collinear spiral order is present. This ordering leads to formation of chiral domains with opposite spin rotation senses, that are separated by chiral domain walls. Spiral order breaks inversion symmetry and induces a ferroelectric polarization, whose sign is determined by the chirality of the domain. Thus the spiral order allows for the manipulation of spins via an external electric field. We use analytical and numerical methods in order to describe the dynamics of the wall. We derive the equation of motion for the domain wall through a general continuous model, and perform atomistic spin dynamics simulations that show the temporal evolution of the spin texture, and the polarization of the system. The analytical results predict a linear dependence of the speed of the wall on the external electric field as well as a finite size effect due to the dimension of the system. The simulations corroborates the predictions both in 1D and 2D geometries.

Resume : Transition metal oxides (TMOs) are fascinating and widely researched compounds, showing a great variety of properties driven by complex interactions. Among first row TMOs, perovskite chromium oxides with general formula RCrO3, with R = Ca, Ba, Sr, remain only vaguely explored. This shortcoming is probably linked to the difficulty to stabilize the rare Cr4+ valence state, typically requiring high synthesis pressures [1, 2]. The properties of SrCrO3 (SCO), in particular, are still controversial and under debate. Interestingly, this compound has been observed to be metallic and antiferromagnetic at the same time [3, 2]. This rare and poorly understood combination of properties is also occurring in thin films [4], although only few reports of this compound in form of thin films have been published [4, 5, 6]. The goal of this study is to uncover the electric behaviour of SCO thin films as function of strain and to address the debate about the properties of chrome perovskite oxides. All epitaxial SCO thin films are grown by off-axis RF magnetron sputtering on a variety of substrate imposing a large range of strain value, going from −1.5% compressive to %3 tensile strain. The quality of the thin films is verified using x-ray diffractometry and atomic force microscopy, the Cr4+ valence state is confirmed by x-ray absorption spectroscopy measurements. Temperature-dependent transport measurements show a clear strain-driven metal-to-insulator transition, as tensile strain is increased. Specifically, SCO thin films are metallic with an upturn at about 100 K when grown under slight compressive strain (−0.68% on LaAlO3) and strongly insulating when a tensile strain is imposed (3.40% on DyScO3). This result is in line with previous work [6] and is also consistent with recent results of DFT calculations. These calculations show that tensile strain is responsible for lifting the degeneracy of the t2g orbitals and promoting orbital ordering, resulting in the opening of an energy gap. The transport properties of SCO will also be explored as the film thickness is reduced to a few unit cells. References [1] B L Chamberland. Solid State Communications, 5, (1967). [2] L. Ortega-San-Martin et al. Physical Review Letters, 99, (2007). [3] A. C. Komarek et al. Physical Review B, 84, (2011). [4] K H L Zhang et al. Journal of Physics: Condensed Matter, 27, (2015). [5] K. H. L. Zhang et al. Nature Communications, 5, (2014). [6] G. Bertino et al. arXiv:2104.02738 [cond-mat], (2021).

Resume : Iron vanadate, FeV2O4 (FVO), displays several physical properties such as ferrimagnetism [1], ferroelectricity [2], multiferroism [3], a possible spin-glass-like state [4] and a rich electrochemical behaviour [5]. Both of FVO cations (Fe2+ and V3+) are Jahn-Teller active and, as a result, the material adopts different crystal structures with varying temperatures, which come along with diverse orbitally ordered states [6]. All of these properties have been widely studied in FVO in the bulk form, but very few studies have treated those of FVO thin films [7,8]. In previous work, we have shown the possibility to grow epitaxial FVO films. Compared to former studies, the deposition conditions and the substrate were changed (MgO), leading to high-quality stoichiometric FVO thin films [9]. The structural and magnetic properties of these films have been thoroughly studied and, differently from bulk FVO, a low-temperature crystal transition seems to be lost. Moreover, and despite the small quantity of matter present in the films, the atomic positions have been evidenced throughout a method of our own [10] based on the FDMNES software [11] for the treatment of Resonant Elastic X-ray Scattering (REXS) data. Just as past studies in bulk FVO [12], this information has been used to identify the crystal distortions and, ultimately, the films’ orbital order as a function of temperature. This is the first wide study on FVO//MgO thin films which, thanks to their intricated physical properties, constitute firm candidates for future generation spintronic and orbitronic thin-film-based devices. [1]. MacDougall, G. J., Garlea, V. O., Aczel, A. A., Zhou, H. D. & Nagler, S. E. Magnetic order and ice rules in the multiferroic spinel FeV2O4. Phys. Rev. B 86, 060414 (2012). [2]. Zhao, K.-H., Wang, Y.-H., Shi, X.-L., Liu, N. & Zhang, L.-W. Ferroelectricity in the Ferrimagnetic Phase of Fe 1− x Mn x V 2 O 4. Chin. Phys. Lett. 32, 087503 (2015). [3]. Eremin, M. V. Coupling of spins with an electric field in FeV 2 O 4. Phys. Rev. B 100, 140404 (2019). [4]. Nishihara, S. et al. Appearance of magnetization jumps in magnetic hysteresis curves in spinel oxide FeV2O4. J. Appl. Phys. 107, 09A504 (2010). [5]. Maggay, I. V. B. et al. Electrochemical properties of novel FeV2O4 as an anode for Na-ion batteries. Sci. Rep. 8, 8839 (2018). [6]. Xie, W., Xing, X. & Cao, Z. Successive orbital ordering transitions in FeV 2 O 4 from first-principles calculation. J. Appl. Phys. 126, 244904 (2019). [7]. Shi, X. et al. Structural and magnetic anisotropy in the epitaxial FeV 2 O 4 (110) spinel thin films. AIP Adv. 5, 117146 (2015). [8]. Zhou, D. et al. Magnetic and Magnetodielectric Properties of Epitaxial Iron Vanadate Thin Films. Adv. Electron. Mater. 3, 1600295 (2017). [9]. Roulland, F. et al. Promoting the magnetic exchanges in PLD deposited strained films of FeV2O4 thin films. Mater. Chem. Phys. 276, 125360 (2022). [10]. Peña Corredor, A. Non-destructive evidencing of oxygen positions in nanosized crystals by Resonant Elastic X-ray Scattering. Journal of Applied Crystallograhy (submitted, 2022). [11]. Bunău, O. & Joly, Y. Self-consistent aspects of x-ray absorption calculations. J. Phys. Condens. Matter 21, 345501 (2009). [12]. Kawaguchi, S. et al. Orthorhombic distortion and orbital order in the vanadium spinel FeV 2 O 4. Phys. Rev. B 93, 024108 (2016).

Resume : Nowadays, strontium vanadate SrVO3 (SVO) perovskite oxide is reported as an emergent transparent conducting oxide [1]. Due to the central role of the modification of the carrier charge effective mass by strong electronic correlations, an important interplay between the structure of the conducting oxide and its transport and optical properties exists [2]. The technological potential of these new transparent conductors is largely determined by the possibility of integrating vanadates on low-cost and/or transparent substrates, for example on glass. In its amorphous form, vanadate perovskite oxides are not conducting [3], therefore this study exposes a growth approach by depositing the vanadate thin films on a glass substrate covered by oxide nanosheets, acting as a seed layer for their crystallization. This 2D [Ca2Nb3O10]- sublayer introduces the possibility to grow the films at a moderate temperature (600°C) required for the integration on glass [4]. This special integration leads to textured films with low resistivity from 200 µOhm.cm to 275 µOhm.cm in a range of 5 K to 300 K and an optical transparency of about 75% at 550 nm for films of 40 nm thickness. The films were analyzed by Atomic Force Microscopy (AFM). With PeakForce Tapping mode, the acquired topography shows a high coverage rate (80%) of the nanosheets with lateral sizes from 100 nm to 1 µm. In addition, the electrical Scanning Spreading Resistance Microscopy (SSRM) mode allows to determine the conductivity mapping of the SVO film. In this mode, using a highly conductive diamond tip, the current flowing from the tip to the SVO film is recorded at each pixel of the mapping. A very low resistance ranging from Log(R) = 3.8 to Log(R) = 6 (i.e. R= 6 kOhm to 103 kOhm) is observed when a VDC bias of +1V is applied to the sample. In order to investigate the resistance variability under the applied voltage of the SVO perovskite film on nanosheets, an advanced AFM multidimensional approach (also called DataCube (DCUBE)) developed by Bruker [5] is used. In DCUBE, with a unique AFM scan, the full spectral conductivity at each pixel of the map as a function of a wide range of applied bias voltage is recorded. This higher-dimensional data can be sliced along any axis or plane enabling the voltage analysis at any point, or a resistivity mapping at any voltage. The results reveal three main conductivity regions of the SVO film: most of the film shows a metallic behavior, but at the boundaries between the nanosheets, a Schottky-type conduction is detected. Furthermore, an intermediate behavior was measured in some pixels, which will be discussed. [1] L. Zhang et al., Nature Materials 15 (2015) 204. [2] A. Boileau et al., Advanced Optical Materials 7 (2019) 1801516. [3] A. Boileau et al., Appl. Phys. Lett. 112 (2018) 021905. [4] A. Boileau et al., Adv. Funct. Mater. (2021), 2108047. [5] De Wolf et al. Microsc. Today (2018), 26 (6), 18–27.

Resume : One of the great challenges in the twenty-first century is the generating, storage, and transmission of electrical energy. In response to the needs of modern society and emerging ecological concerns, it is now essential that new, low-cost, and environmentally friendly energy sources and storage systems have to be found. As a new-era group of smart devices, wearable smart devices are rapidly developing to achieve human health monitoring, movement monitoring, and other functions [1]. The piezoelectric nanogenerators (PENGs) have attracted significant attention due to their unique merits of mechanical energy conversion capability, lightweight, low cost and easy manufacturing, which can harvest various types of mechanical energy by utilizing the piezoelectric effect [2-3]. The main goal in the field of PENGs is to increase devices mechanical flexibility and voltage/current output. We propose an original/innovative approach for the fabrication of highly oriented thin films grown on flexible biaxially textured metallic substrate by novel eco-friendly chemical solution deposition processes. In this work we will focus on different perovskite architectures deposited of flexible metallic biaxially textured substrates by novel chemical solution deposition. The LaNiO3 (LNO) and La0.66Sr0.33MnO3 (LSMO) perovskite compounds will be consider as bottom electrode and Ba(ZrxTi1−x)O3 — BZTO piezoelectric film. In order to determine the thermal decomposition behavior, the precursor powder obtained by drying the precursor solution was investigated by thermogravimetry coupled with quadrupole mass spectrometry (TG-QMS), and differential thermal (DTA) analysis. The kinetics of the thermal decomposition of the precursor powder was studied under oxygen and humid oxygen atmosphere from ambient temperature up to 1000 oC. The fabrication of the piezoelectric architecture films consists in the deposition of the precursor solution on flexible NiW substrate by dip-coating, followed by pyrolysis and crystallization in a control atmosphere. The films have been structurally and morphologically characterized by XRD, AFM and TEM, respectively, and the piezoelectric properties have been determined. References [1] H. Shi, Z. Liu, X. Mei, Energies, vol. 13, pp. 86, 2020. [2] Z. Zhao, Y. Dai, S.X. Dou, J. Liang, Materials Today Energy, vol. 20, pp. 100690, 2021. [3] B.J. Hansen, Y. Liu, R. Yang, ACS Nano , vol. 4, pp. 3647–3652, 2010.

Resume : Lead piezoelectric ceramics, used in ultrasound transducers for their performance associated with low cost, will be banned according to the European RoHS directive. PZT replacement work requires finding a material with the highest coupling factors (kij, kt, kp) and Curie temperature (TC). Two main families of perovskite oxides have been classified: the first contains alkaline elements [ex: Na0.5Bi0.5TiO3 (NBT)], while the second (titanates) does not contain them [ex: BaTiO3 (BT), (Ba,Ca)(Ti ,Zr)O3 (BCTZ)]. The high volatility of the alkaline elements makes it difficult to control the composition during their manufacture, while the BT type titanates are already commercially exploited. The compound BZT-50BCT (TC = 90°C, d33 ~ 490 pC/N comparable to soft PZT) was thus used to produce the first lead-free ultrasound probe[1]. Substitution on A or B site at low concentrations influences significantly the piezoelectric properties and the TC. [2] In this work, we report the exploration of continuously doped BCTZ films (BZT-50BCT) with Y and Ce. Composition spread BCTZ thin films were grown by pulsed laser deposition. Composition gradients were characterized by WDS while phase analysis was realized by X-Ray micro-diffraction (µ-XRD). Electromechanical measurements (d33, kt, kp) were realized in order to identify the most efficient doping. The corresponding ceramics, with optimized electromechanical performance, will then be synthesized to target a medical demonstrator in order to evaluate its ultrasonic performance. [1] X. Yan et al., IEEE Trans. Ultrason. Ferroelectr. Freq. Control 60, 1272 (2013). [2] M. Acosta et al., Applied Physics Reviews 4, 041305 (2017).

Resume : Oxide nanoparticles (NPs) are utilized frequently in the last years for various biomedical applications, including healthcare and infection control. However, such nanomaterials could interfere with beneficial bacteria, such as microbiota components and this may change the health and disease balance. The purpose of this study is to reveal in vitro interactions of oxide NPs and Enterococcus sp strains isolated from gut microbiota, highlighting their potential to impair microbial virulence and antipathogenic behavior. Three types of oxide NPs which are widely investigated for antimicrobial application, namely Fe3O4, CuO and ZnO were analyzed in four Enterococcus sp microbiota isolates. All NPs were physico-chemically characterized by SEM, TEM and FTIR spectroscopy. They showed round shape and variable size, ranging between 10-100 nm, depending on their type. Lowest size was obtained for the Fe3O4 NPs (10-15 nm). The results demonstrated that, while Fe3O4, and ZnO NPs show a low impact in modulating the growth and virulence of microbiota Enterococcus sp. isolates, CuO NPs may seriously impact on these strains, when utilized in very low amounts. Minimum inhibitory concentrations (MICs) were equal or higher than 1mg/mL for Fe3O4, and ZnO, but lower than 0,25mg/mL for CuO NPs. Also, subinhibitory concentrations interfered with virulence and antipathogenic activity of the microbiota strains, demonstrated against Gram-positive and Gram-negative pathogenic bacteria. These results suggest that oxide NPs could interfere with viability, virulence and antipathogenic activity of microbiota isolates, and this could impact also on the progression of some microbiota-dependent metabolic diseases.

Resume : Metal oxide nanoparticles were synthesized by vaporizing metallic wires in air under the action of microwaves. The output of an 800 W microwave generator was coupled through an antenna to a cylindrical wave guide cavity with a metallic thin wire placed in the electromagnetic node, where a high-power density was achieved. The wire strongly absorbed the microwaves, resulting in its rapid heating, vaporization and finally a plasma plume formation. Optical emission spectroscopy investigations indicated that the formed plasma contained excited and single ionized atoms from the wire and the ambient atmosphere. The vaporized material was collected on a piece of Si placed opposite the wire, near the cavity wall. Scanning electron microscopy investigations showed that the deposited material consisted of an agglomeration of nanoparticles having dimensions from few nm up to 100 nm. X-ray diffraction and transmission electron microscopy investigations indicated that the nanoparticles were crystalline, with random orientation. X-ray photoelectron spectroscopy analysis confirmed the formation of stoichiometric metallic oxides. High resolution TEM investigations found that the formed nanostructures were single crystals, with faceted surfaces. This simple method could have many applications for metal oxide nanocrystal synthesis. Acknowledgments: This work was supported by a grant of the Ministry of National Education and Scientific Research by project code PN-III-P2-2.1-PED-2019-2949 and Nucleu programme - contract LAPLAS VI, no. 16N/20.

Resume : Zinc oxide is a multifunctional wide-bandgap semiconductor which makes it an excellent candidate for use in all photonic application as well as in high-power electronics. The low-cost production of large-area-devices and flexible electronics arouses interest in solution-based processes of high quality. A ZnO functional ink can act either a dispersion source of ZnO nanoparticles or a chemical solution of metal salt/alkoxide. The characteristics, such as size and shape of the ZnO particles play an important role in controlling the device performance. The properties of the barrier between Si and GaN is crucial in GaN-based device fabrication. We intend to control the properties of the boundary by embedding nanoparticles in different regions of the GaN/ZnO/Si heterojunctions. This research is related to establishing the efficiency of hydrothermal technology of ZnO layers growth on silicon, their physical properties investigations in order to use them, as buffer layers in GaN/ZnO/Si heterojunctions. The ZnO thin layers were synthesized from the following solvents: water, water + ethanol, water+ methanol, water+ propanol, water+ acetone, ethanol, propanol, methanol. The dihydrate zinc acetate, Zn(CH3COO)2 2H2O was used for to obtain the seed crystal layers. The deposition of the own ZnO layer was carried out by using an aqueous solution of Zn(NO3)2+KOH. The polished silicon wafers, Si(111) of both p-and n- type elctrical conductivity having resitivity of 0.1 Ohm.cm, were used as substrates. GI-XRD and AFM have been used for samples investigations. We have achieved the possibility to control the population of ZnO nanoparticles on the SiOx/Si surface by adjusting the deposition conditions (temperature, concentration of the precursor and type of solvent). GaN layers onto ZnO/Si structures have been prepared were synthesized by using HVPE method as the test GaN/ZnO/Si heterojunctions. The efficiency of ZnO as barrier in GaN/ZnO/Si structures has been proven. Acknowledgements: NARD (ANCD) project: 20.80009.5007.12

Resume : The lattice-mismatch-induced strain in complex oxide heterostructures often leads to the appearance of undesirable effects, such as misfit dislocations or octahedral distortions. In the case of layered Ruddlesden–Popper manganite Pr0.5Ca1.5MnO3/SrTiO3(001) (PCMO/STO) films, we have observed recently (Adv. Mater. Interfaces 2021, 2002049) that misfit strain modifies the epitaxial relationship, to that with caxis lying in-plane, i.e. PCMO(110)//STO(001). However, that is the out-of-plane orientation of the caxis is highly preferable for exploring the 2D structure of PCMO. Strain engineering of heteroepitaxial growth by using appropriate buffer layers provides a forceful way to reduce epitaxial strain and, thus, to enhance functional properties of heterostructures. Here we demonstrate that anatase TiO2 film can serve as an effective buffer layer for epitaxy of the coriented PCMO on the undoped as well as on Nb-doped STO(001) substrates. TiO2 films were grown by a metalorganic aerosol deposition technique using a binary solution containing both Ti and Nb precursors. X-ray diffraction has indicated that TiO2 thin films crystallize in a (001)-oriented anatase structure. However, transmission electron microscopy analysis revealed the presence of a-b twinning with two epitaxial relationships (001)[100] TiO2//(001)[100]STO and (001)[010]TiO2//(001)[100]STO. Using the obtained anatase TiO2(001) buffer, the c-oriented growth of PCMO was achieved. Moreover, we have demonstrated that anatase TiO2(001) buffer can be heavy-doped by Nb, yielding a metallic conductivity, which is highly demanded by PCMO applications. In addition, the structural performance and transport properties of the lattice-mismatched TiO2/STO anatase films were compared with those grown on near-perfectly matched LaAlO3(001) substrates. We expect the subsequent optimization of both growth and doping of TiO2 films may open the way for exploring attractive physical properties of c-oriented PCMO films for various energy and catalytic applications. Financial support from Deutsche Forschungsgemeinschaft via SFB 1073 (TP Z02 and B02) and Moldavian State Program 20.80009.5007.12 is acknowledged.

Resume : Metal-air battery has a very high energy density because it could use atmospheric oxygen as the electrode active material. This rechargeable battery needs bifunctional catalytic materials, which involve effective oxygen reduction (ORR) / evolution reactions (OER) at the air electrode at the discharge/charge process. In this study, a new bifunctional catalytic material for the air electrode has developed using a conductive vanadate glass [1] containing CoII,III. 20BaO･5Fe2O3･5Co3O4･70V2O5 glass was synthesized by the melt-quenching method. The prepared vanadate glass was annealed at 450 °C for various times (0 - 300 min). Pulverized vanadate glass was utilized for the preparation of the air electrode by mixing the powder with 7.5 mass% of poly (tetrafluoroethylene) (PTFE), which was hot-pressed on a gas diffusion layer over a Ni metal mesh. 8M KOH aqueous solution and a Pt mesh were used as the electrolyte and the counter electrode, respectively. An Hg / HgO electrode was used as the reference electrode. Anodic and cathodic polarization measurements were carried out. From the results of ORR and OER performance of 20BaO·5Fe2O3·5Co3O4·70V2O5 glasses annealed at 450 ℃. The vanadate electrode showed excellent bifunctional catalytic activity comparable to that of materials reported in the literature, such as polycrystalline LaNiO3 [2]. This vanadate glass proved to be a highly potential candidate for the bifunctional catalytic material for the rechargeable metal-air battery. [1] T. Nishida, Y. Izutsu, M. Fujimura, K. Osouda, Y. Otsuka, S. Kubuki, N. Oka, Pure and Appl. Chem. 89, 419-428 (2017). [2] M. Yuasa, M. Nishida, T. Kida, N. Yamazoe, K. Shimanoe, J. Electrochem. Soc. 158, A605-A610 (2011).

Resume : Nowadays, the number of electronic devices that each person has is quite impressive and it tends to increase exponentially in the next 30 years. The pursue of more and more comfort in society will lead to a massive increase of internet of things (IoT) nodes, since almost every device has embedded electronics. However, this will induce a high quantity of electronic waste (e-waste) accumulation that will not be recycled and will most likely end in landfills of developing countries. In 2019, 53.6 Mt of e-waste was generated worldwide, and it is expected to reach 74 Mt by 2030. To overcome this serious societal problem, it is necessary to rethink the production process of some electronic devices and to reconsider their life cycle assessment, more specifically their environmental footprint. By adopting more sustainable materials (metal oxides) and processes, electronics waste is reduced, leading to the reduction of the carbon footprint, and paving the way for green electronics. Printed metal oxides fulfil these requirements and have been considered as key to surpass the high production costs, material’s waste and still allow large area production. However, some challenges remain on printing efficient and stable eco-devices using a low thermal budget and high-throughput compatibility. In this work, suitable processes (inkjet, screen, and flexographic printing) and materials (In2O3, IGZO, ZTO, and Al2O3) are developed to assure the scale-up of metal oxide-based devices (thin film transistors, diodes and memristors) to printing industry levels. These devices will lead to great societal impact since they can power up the speed and efficiency of lighter and thinner wearable applications.

Resume : MgSnN2 with an average wurtzite structure (wz-MgSnN2) has recently emerged as a pseudo-III-nitride semiconductor, studied for applications in tandem solar cells, green-light-emitting diodes, and other optoelectronic devices. wz-MgSnN2 films can be regarded as magnesium tin oxynitride (wz-MTNO) films, because a certain amount of oxygen was unintentionally incorporated to the films during the growth. wz-MTNO has only been researched recently, and hence its properties are not investigated well. We have investigated the growth and characterizations of wz-MTNO thin films.[1–3] wz-MTON films were reactively sputtered on GaN (001) templates [1,2] and YSZ (111) single-crystalline substrates [3] at the growth temperature of 400 °C. The films grew epitaxially on both the substrates with the epitaxial relationships of wz-MTON(001)(100) // GaN(001)(100) and wz-MTON(001)(110) // YSZ(111)(110). The films were biaxially oriented polycrystalline films rather than single-crystalline films. The fundamental bandgap (Eg) of the wz-MTON film with the least cation off-stoichiometry was determined to be 2.3 eV. When the cation composition was made Sn-excessive, the optical bandgap became wider.[1] The excessive Sn behave electron donors, and thereby the Sn-excessive wz-MTON films had the electron densities of the order of 1020 cm-3. Therefore, the optical-gap widening was ascribed to the Burstein-Moss effect. The fundamental bandgap of wz-MTON can be tuned by alloying with ZnSnN2 (wz-ZMTON) that also is a pseudo-III-nitrides. Eg was varied from 1.5 to 2.3 eV, when the Mg/(Zn+Mg) ratio was increased from 0 to 1. The alloy films exhibited a green a green-light photoluminescence emission near room temperature.[2] Directgap semiconductors with Eg = 1.8–2.5 eV are eagerly anticipated for the development of green light-emitting diodes (LEDs) and top cells in tandem solar cells. Therefore, wz-MTON and wz-ZMTON would be attractive compounds toward the development of green-LEDs and tandem solar cells. The electron transport properties of the wz-MTON epilayers were examined using direct-current (dc) and infrared methods. The electron effective mass at the conduction-band edge (mc*) was determined from the analysis based on the Drude model to be 0.2 m0 (m0 denotes the free electron mass),[3] which agreed with a first-principles value.[4] The optically derived resistivities were always larger than the dc resistivities. This discrepancy became pronounced as the electron density became lower. These phenomena can be interpreted in terms of the electron scattering at the grain boundaries. These results suggest that the growth of single-crystalline layers will be required toward optoelectronic applications. References [1] Yamada et al., ACS Appl. Electron. Mater. 2021, 3, 1314–1349. [2] Yamada et al., ACS Appl. Electron. Mater. 2021, 3, 4939–4942. [3] Yata et al., J. Appl. Phys. in-press. [4] Greenaway et al., J. Am. Chem. Soc. 2020, 142, 8421– 8430.

Resume : Transparent conductive oxide (TCO) films with high electron mobility (>100 cm2 V−1 s−1) exhibit higher conductivity, lower absorption coefficients, and extended transparency compared to those of conventional TCO films. Polycrystalline In2O3 films, which are solid-phase-crystallized (spc) from amorphous films doped with hydrogen (H) or both H and transition metals (TMs), exhibit considerable mobility, and the specific resistance can be equivalent to 2–3 × 10−4  cm or less, even if the carrier concentration is reduced to one-fifths that of conventional TCO films. Consequently, these films exhibit high transparency even in the near-infrared region without compromising their high conductivity. These films can be formed on various underlying layers and substrates by low-temperature (150–200 °C) processes. Therefore, incorporation of the TCO films in window electrodes could improve the performance of existing optoelectronic devices and enable development of new optoelectronic devices with sensitivity in both the visible and near-infrared regions. Indeed, some materials have already been adopted as a window electrode for a-Si:H/c-Si heterojunction solar cells, which exhibit the highest conversion efficiency among crystalline silicon based solar cells. In this study, In2O3:H and In2O3:TM,H (TM: Ce, Zr, W) were experimentally demonstrated to exhibit significantly higher mobility than that of In2O3:Sn,H at similar carrier concentrations (1–4 × 1020 cm−3). The spc-In2O3:H and In2O3:Ce,H (CeO2: 0.5–2 wt.%) films exhibited high mobility (150–160 cm2 V−1 s−1), spc-In2O3:Zr,H (ZrO2: 1 wt.%) and In2O3:W,H (WO3: 1 wt.%) showed a relatively lower mobility (~100 cm2 V−1 s−1), and spc-In2O3:Sn,H (SnO2: 1 wt.%) exhibited modest mobility (~70 cm2 V−1 s−1). We will discuss the microscopic mechanism that causes the difference in mobility owing to the dopant elements in terms of the effective mass and relaxation time of the free electrons in these films.

Resume : In recent years a special interest was given to the development of p-type semiconductors based on metallic oxides (CuxOy or AgxOy) due to their exceptional optical and electrical properties. To understand the fabrication process in the framework of the pulsed laser deposition (PLD) technique two in situ analysis tools (Langmuir probe, LP) technique and Optical Emission Spectroscopy, OES) were implemented for angular, space and time-resolved measurements of transient plasmas generated in Ar or O2 atmospheres. The work was focused on understanding the inner mechanism of laser ablation plasma oxidation of Cu and Ag using two deposition recipes (starting from pure metallic and from oxide ceramic targets) by investigating the plasma dynamics with the aim of achieving oxidation process control via ionic energy distribution function. The metallic oxide laser plasmas present some complex features of the ionic cloud as observed by unbiased probe analysis used as a time-of-flight measurement tool. Angle-resolved measurements revealed a complex distribution of the ions with the ejection of positive species at wide expansion angles in oxide plasma, attributed to oxygen species presence. Plasma potential and electron temperature values were indicative of the oxidation process. Using a semi-empirical model, estimation of ion acceleration field, neutral temperature and densities were performed. Space- and time-resolved OES investigations confirmed the plume splitting indicated by LP measurements and provided insight into the plasma multiple structuring scenario. All the plasma parameters were investigated in conditions similar to those used for thin films growth and the results are discussed with respect to the PLD technology. Comparison between the properties of the plasma and those of the deposited films under those conditions are made. The nature and pressure of each gas influences the emission in a unique manner, which is correlated with the data from the electrical measurements. Thin films, deposited in conditions identical to the plasma diagnostic ones. were investigated using a wide array of techniques (XRD, XPS, AFM, SEM, optical transmission, etc.) and a relationship is established between the morphology of the films and the ablated ion kinetic energies. This work was supported by Romanian Ministry of Education and Research, under Romanian Nat. Nucleu Program LAPLAS VI –n. 16N/2019, ELI-RO_2020_12 and PD 145⁄2020. We acknowledge the Operational Program Research, Development and Education financed by European Structural and Investment Funds and the Czech Ministry of Education, Youth and Sports SOLID21.

Resume : Observations of strong coupling of light with excitons in semiconductor microcavities (MCs) have attracted attention since it leads to the formation of bosonic quasi-particles, namely cavity polaritons. Because the effective mass of cavity polaritons is smaller than that of free carriers or excitons, the realization of coherent light sources with ultra-low threshold current density based on Bose-Einstein condensation of cavity polaritons has been predicted. Excitons in ZnO are stable at room temperature on the basis of their large binding energy (59 meV), and thereby polaritons in ZnO MCs have a huge Rabi splitting energy. Therefore, ZnO is a preferred choice as an active layer material of polariton lasers operatable at room temperature. Recently, lasing actions of the ZnO MCs have been reported using semiconductor/dielectric hybrid distributed Bragg reflectors (DBRs) and fully dielectric DBRs. However, it is still challenging to combine the high crystalline quality of the ZnO active layer with the high photonic quality of the DBRs. The Rabi splitting values for the ZnO MCs measured by photoluminescence (PL) and reflectance measurements have been as large as 130 meV, which was smaller than the ideal value being 191 meV. Possible reasons limiting Rabi include insufficient reflectivity or stopband width of the mirrors and/or insufficient radiative performance of the ZnO active layer. In this study, detection-angle-dependent energy shifts in the near-band-edge emission peak were observed at room temperature in planar ZnO MCs fabricated by a top-down process that simultaneously maintains the high radiative performance of the ZnO active layer and high-reflectivity of wide-bandwidth DBRs. An approximately 2-thick ZnO active layer with a thickness gradient of 67 nm/mm (i.e., an angle of gradient of 14 arcseconds) over the entire 10  5 mm2 area was formed by thinning a bulk ZnO single crystal grown by the hydrothermal method, of which typical threading dislocation densities were lower than 102 cm-2. The DBRs consisting of 10 and 12 pairs of SiO2/ZrO2 multilayers were deposited as the top and bottom mirrors of the MCs, respectively, by nearly surface-damage-free reactive helicon-wave-excited-plasma sputtering method. The quality factor of a passive cavity consisting of the same DBR stacks ranged from 670 to 720 for a large area of 1 mm in diameter. Angle-resolved PL spectra of the ZnO MCs measured at different positions with a macroscopic spot-size being 80 m in diameter exhibited distinct emissions from the lower branch of cavity-polaritons with apparent detunings ranging from -40 meV to 40 meV at room temperature. The results showed our planar ZnO MCs certainly exhibited a strong exciton-photon coupling regime at room temperature, which is a major step toward the realization of room-temperature ZnO-based polariton lasers.

Resume : The polarization switching in ferroelectrics is supposed to take place via domain formation. It is generally accepted that the first step of switching is the nucleation of domains with opposite direction of polarization compared to the initial state, followed by the domain growth and coalescence until the entire volume changes the orientation of polarization. It is assumed that the nucleation takes place on local structural defects, implying the presence of local electric fields that may favor a certain direction of polarization. But what happens if there are no structural defects in the structure? It is possible nowadays to grow high quality epitaxial films and to compare polarization switching in these layers and in polycrystalline ones. Here it is suggested that the switching in ferroelectric thin films may be all the time homogeneous, the presence of domains being triggered by the structural defects. Moreover, it is hypothesized that the difference between homogeneous and non-homogeneous switching is related to the ability of the system to provide in real time the necessary charges to compensate the depolarization field occurring during switching. Finally, it is suggested that the switching itself may be triggered by the charge injection, under the action of the applied field, charge that can destabilize the initial orientation of polarization. Some explanations are proposed based on the analysis of the current-voltage characteristics recorded during polarization switching and considering the presence of the Schottky contacts at the electrode interfaces. The study is performed on samples of different structural qualities but the suggested mechanism seems to be valid for all the cases: first part of the switching suggest a resistive-like behavior of the sample associated to the disappearance of the potential barriers at the electrodes; second part is the polarization switching forced by the applied filed; third part is the re-appearance of the potential barriers accompanied by the re-distribution of the charges involved in the compensation of the depolarization field. The first and the third part are dependent on the structural quality, with impact on domain formation.

Resume : This work deals with vanadium oxide in highly strained original structures: the metal-insulator transition and the original magnetic phase that appear in vanadium oxide nanoclusters epitaxially-embedded in an MgO matrix [ Appl. Phys. Lett. 115, 262901 (2019) ] are studied via electron transport, magneto-resistance, and X-ray circular dichroism measurements. The metal-insulator transition temperature is observed to be in the range of 1.5–27 K [ Appl. Phys. Lett. 116, 042404 (2020) ]. We observe, from 0.3 K to at least 125 K, a superparamagnetic behavior whereas vanadium oxide, in its bulk phase, is reported as anti-ferromagnetic (AF) at low temperatures. This striking feature is consistent with either ferromagnetic spin pairing or with spin canting in the AF spin order along the 1D vanadium ion chains of the Magnéli phase or for the VO2(A)-like phase. Finally, the observed magneto-resistive effect, which reaches up to 8% at low temperatures, indicates ferromagnetic behavior for some of the nanoparticles. This could make possible their use in spintronic devices that could be combined with metal-insulator switching and MR effects.

Resume : The low power manipulation of magnetization is currently one of the most sought-after objectives. Spin-orbit torque (SOT) platforms offer great expectations in that respect. They consist in ferromagnetic (FM) / heavy metal (HM) heterostructures, in which the magnetization of the FM layer is manipulated by the spin current generated by spin Hall effect in the HM layer. We propose here to use a multiferroic FM in order to add extra functionalities to such SOT platforms, such as the electric field control of the spin current generation. We have studied the spin current transfer processes between Pt and the multifunctional magnetoelectric gallium ferrite Ga0.6Fe1.4O4 (GFO). By performing angular dependent magnetotransport measurements, we have in particular been able to differentiate between magnetic proximity effect-induced anisotropic magnetoresistance and spin Hall magnetoresistance (SMR). We could then evidence that SMR is the predominant phenomenon at all temperatures and the only one to be considered near room temperature, with a magnitude similar to the one observed in Pt/YIG heterostructures. This work demonstrates the potential offered by GFO in the field of low power manipulation of magnetization through SOT effects in spintronic devices.