Metal oxide- and oxyhydride-based nanomaterials for energy and environment-related applications

Resume : Photocatalysis is an established phenomenon in splitting water into hydrogen and oxygen. Several researchers have been working on the basic understanding, new and novel materials and a variety of conventional and emerging applications. The available literature is vast. Our laboratory has been working on the concept of generating oxygen in the human blood (lung assist device) using the principles of oxidative photocatalysis on the conventional materials : tin doped indium oxide (ITO) and titanium oxide (TiO2) nano thin films. The basic principle of the lung assist device is that when human blood is subjected to photocatalysis, with the water like content available in the blood (plasma) is split and oxygen is produced; this oxygen being in the immediate vicinity, the haemoglobin can pick up this oxygen. Several experiments conducted in our laboratory have clearly shown the proof of concept. We could enhance the oxygen saturation (SaO2) in the blood to about 6% (in about six hours) over the base level; this consistent result is a remarkable achievement and a firm first step towards a lung assist device. The most important boundary conditions of this application, which has been validated positively, are that no reactive species of the oxygen be produced by the photocatalytic process and the chemical nature of the human blood should not be affected even after subjecting for six (or more) hours of photocatalysis (with UV light of 254 nm). The important result of the experiment conducted so far is: 6% increase in SaO2 level in the human blood.

Resume : A partial overview of the research activity carried out at IMEM-CNR on Si(O)(C) and ZnO nanostructures chemically functionalized for energy and nanomedicine applications will be presented. As for energy applications, it will be demonstrated the outstanding electro-catalytic performance and stability of a hierarchical cobalt oxide (Co3O4)-functionalized vertically-aligned SiC NW array electrode for use in the oxygen evolution reaction of water splitting. The excellent electrochemical behavior, high specific capacitance and high areal power and energy of MnOx-decorated carbonized porous Si NW arrays are also shown. An asymmetric hybrid supercapacitor has been designed showing a large operational potential window and a good capacitance retention (>80% after 10000 CV cycles)). The effect of residual sulfur atoms on the optical properties of highly porous wurtzite ZnO for photocatalysis are reported. Sulfur related intra-gap states are found to be responsible for an optical emission at 2.36 eV, preferentially associated to substitutional sulfur atoms in oxygen position, in porous ZnO nanostructures. The nanoscale mapping of plasmons and excitons in ZnO tetrapods coupled with Au nanoparticles evidences that the Au plasmon resonance is localized at the Au/vacuum interface, rather than presenting an isotropic distribution around the nanoparticle. This result paves the way for innovative devices like e.g. hybrid solar cells. As for nanomedicine applications, it will be reported that by exciting directly the fluorescence of CeF3 NPs in CeF3-ZnO nanocomposite by UV radiation, ZnO is photo-activated in cascade, producing reactive oxygen species that are known to induce necrosis in cancer cells. Our composite nanostructure is stable in aqueous media with excellent optical coupling between the two components and presents good cell viability, with very low intrinsic cytotoxicity in dark. It will be also reported that SIC-NWs can support cardiac bioelectric propagation over distance in-vitro via an intrinsic physiological gap junction conductance. Further, in vivo injection SIC-NWs in an ischemic area favours the elimination of ventricular ectopic activities and re-instate bioelectric conduction, recovering the time interval between the beginning of the ventricular depolarization and the end of the ventricular repolarization as well as the depolarization complex of the ventricles prolongations. Finally the use of SiC/SiO2 NWs for the reconversion of medical X-rays to light to activate an in-situ deep solid tumor treatment will be presented. It will be shown how the in vivo injection of SiC/SiO2 NWs into a lung cancer improves of about 40% the efficacy of radiotherapy without NWs. The concurrent use of SiC/SiO2 NWs with an innovative monoclonal antibody- pthalocianine conjugate for pancreatic and liver cancer treatments under soft X-ray irradiation will be also illustrated.

Resume : Development of polydopamine (PDA) based composite nanomaterials is an actual subject. PDA is a biocompatible synthetic polymer, which has strong affinity to a wide range of surfaces due to the existence of multiple functional groups (such as indole, catechol, quinone, and indolic/catecholic ?-system), which can be attached to organic and inorganic materials. Among a number of different inorganic functional materials, ZnO is well known and interesting due to its structure (different architectures), electrochemical (high isoelectric point (IEP) (pH~9.1)) and optical properties (high exciton binding energy and high PL at room temperature). The combination of ZnO with PDA layers could improve optical, electronic and sensitive properties of ZnO/PDA towards target molecules. In the present work, 1D ZnO nanowires (ZnONWs) were coated with PDA film via chemical bath deposition. PDA is derived from self-polymerization of dopamine in alkaline aqueous solutions (in our study, TRIS buffer solution was utilized). Structure, optical and electronic properties of ZnONWs/PDA core/shell nanostructures were analyzed by TEM, XRD, Raman and FTIR spectroscopy, photoluminescence measurements, and diffuse reflectance spectroscopy. The TEM measurements confirmed the conformal coating of PDA with different layer thicknesses. To confirm the PDA formation EELS was performed. Correlation between structural and optical properties of the prepared nanostructures was shown. The obtained results were discussed.

Resume : Heavy metals contamination is becoming one of the most serious problems due their toxicity for the environment and the human health, even at low concentrations. In this regard, considerable efforts have been devoted to the development of a simple and inexpensive method for the selective and sensitive detection of heavy metal ions. In the present study, an optimized and finely controlled three-step approach was used to develop a fluorescent amine-modified silica-based platform for selective sensing of metal ions in aqueous solution. Silica films of controlled thickness and wettability were prepared by an optimized combination of sol-gel method and spin-coating technique. Tetraethoxysilane (TEOS) was used as silica precursor on silicon substrates. Subsequently, a monolayer of aminosilanes (APTES) was grafted on the silica surface. Finally, fluorescein isothiocyanate (FITC) was covalently bonded on the surface of the amine-modified silica platform. These materials were systematically characterized by water contact angle, diffuse reflectance, atomic force microscopy (AFM), and photoluminescence spectroscopy. The stability of the silica-based functionalized platforms in water was assessed prior to sensing experiments. Photoluminescence titration experiments successfully demonstrated that this system can be used as for selective sensing of metal ions in aqueous solution.

Resume : Organometallic halide perovskite solar cells (PSCs) have been attracting extensive research interests due to their excellent photovoltaic performance and potential for low cost and scale-up fabrication. In a common PSC architecture, electron and hole transport layers play an important role in achieving high power conversion efficiency besides the perovskite layer. Metal oxide semiconductors are among the most promising candidates for charge carrier transport layers due to their suitable energy alignment for charge extraction and blocking, considerable chemical stability and spectral transparency, as well as low cost and easy fabrication. Further improving the electrical properties of intrinsic metal oxides and metal-oxide/perovskite interfaces are critical to boost the overall efficiency of the PSCs. In this work we demonstrate low-temperature solution processible metal oxide transport layers for both conventional and inverted planar PSCs, including NiOx as the hole transport layer and SnO as the electron transport layer. The metal oxide layers are further optimized by doping with inorganic (Cu, Sb) or organic molecule (F6TCNNQ) dopants to enhance the charge extraction while suppress the interfacial recombination loss. Various characterization results indicate that the carrier concentration and carrier mobility of the metal oxide transport layers can be effectively increased with reduced energy level offset, which implement the achievement of highly efficient and stable PSCs.

Resume : Because of the high electrical conductivity and transparency to visible light, PEDOT:PSS has found applications in a number of photovoltaic devices. Incorporation of nanosized inorganic semiconductors to the polymer is suggested to enhance performance. In this work, anatase TiO2 nanoparticles have been synthesized and incorporated into PEDOT:PSS [1]. Optical and electrical properties of TiO2 can be modified by controlling the size of the nanoparticles and by doping. Firstly anatase TiO2 nanoparticles were synthesized via hydrolysis using Ti(OBu)4 as precursor. Two different dopants, Ni and Li, in a variable cationic concentration were introduced adding NiCl2 6H2O or LiCl, respectively. Large amount of nanoparticles has been obtained with high crystallinity and homogeneity in sizes around 10 nm, as confirmed by x-ray diffraction (XRD) and transmission electron microscopy (TEM). Changes in the TiO2 vibrational modes and luminescence were observed as a function of the doping, as shown by Raman spectroscopy and Photoluminescence X-ray photoemission spectroscopy (XPS) shows changes on the O 1s core level due to dopant inclusion. Hybrid composites have been prepared via spin coating of PEDOT:PSS funcionalized with a variable amount of the nanoparticles, among other wettability and conduction enhancers (DMSO, EG, Triton X-100) over n-type Si substrates. Homogeneous microsized dispersion has been obtained, with layer thickness around 120 nm. Lifetime values in the range of 200-400 us were measured by PL-QSSPC. [1] M García-Tecedor, S. Z. Karazhanov, G. C. Vásquez, H. Haug, D. Maestre, A. Cremades, M. Taeño, J. Ramírez-Castellanos, J.M. González-Calbet, J. Piqueras, C.C. You, E. S. Marstein, Nanotechnology, 29, 035401 (2018)

Resume : Metal oxide carrier transporting layers have been investigated widely in organic/inorganic lead halide perovskite solar cells (PSCs). Tin oxide (SnO2) is a promising alternative to the titanium dioxide commonly used in the electron transporting layer (ETL), due to its tunable carrier concentration, high electron mobility, amenability to low-temperature annealing processing, and large energy bandgap. In this study, a facile method was developed for the preparation of a room-temperature-processed SnO2 electron transporting material that provided a high-quality ETL, leading to PSCs displaying high power conversion efficiency (PCE) and stability. A novel physical ball milling method was first employed to prepare chemically pure ground SnO2 nanoparticles (G-SnO2), and a sol?gel process was used to prepare a compact SnO2 (C-SnO2) layer. The effects of various types of ETLs (C-SnO2, G-SnO2, composite G-SnO2/C-SnO2) on the performance of the PSCs are investigated. The composite SnO2 nanostructure formed a robust ETL having efficient carrier transport properties; accordingly, carrier recombination between the ETL and mixed perovskite was inhibited. PSCs incorporating C-SnO2, G-SnO2, and G-SnO2/C-SnO2 as ETLs provided PCEs of 16.46, 17.92, and 21.09%, respectively. In addition to their high efficiency, the devices featuring the composite SnO2 (G-SnO2/C-SnO2) nanostructures possessed excellent long-term stability?they maintained 89% (with encapsulation) and 83% (without encapsulation) of their initial PCEs after 105 days (>2500 h) and 60 days (>1400 h), respectively, when stored under dry ambient air (20 ± 5 RH %).

Resume : The incorporation of dopants in metal-oxide semiconductor photocatalysts can be used to red-shift the optical absorption edge and to enhance the photocatalytic activity under solar irradiation. However, the dopant-induced energy levels and the spectral dependence of photoactivity are not yet fully understood. We tackle this problem using a combination of femtosecond-resolved transient absorption spectroscopy in the UV-visible range [1] and high energy resolution x-ray absorption spectroscopy under differential illumination [2]. This last approach, recently developed within our group exploiting the unique features of high-brilliance synchrotron sources, provides the chemical sensitivity necessary to identify element-specific photoexcitation paths. The focus of our study are vanadium-doped TiO2 nanoparticles (V-TiO2 NPs) prepared by gas-phase condensation [3], that exhibit both photocatalytic activity for -NO2 reduction and photoelectrochemical water splitting in the visible spectral range, where undoped TiO2 NPs are completely inactive. We explain the material?s behavior, relevant to energy and environment-related applications, by determining the position of the dopant-induced intra-gap level and by studying the photoelectron excitation and trapping dynamics with elemental sensitivity. [1] G. Rossi et al, Appl. Catal. B ? Environmental 237, p. 603 (2018) [2] G. Rossi et al, Phys. Rev. B 96, p. 045303 (2017) [3] G. Rossi et al, J. Phys. Chem. C 120, p. 7457 (2016)

Resume : Nowadays, the implementation of flexible devices and the light weight are on the rise. We attempted to implement solar cells that can be used in flexible devices by using carbon paper as a substrate. In addition, ZnO/Ag was combined as a back reflector to improve the performance. However, when carbon is used as a substrate, it can diffuse into the Ag layer in the subsequent p-i-n process range of 200 to 400 ° C. To prevent this, we added a metal oxide layer, SiO2 or SnOx, as a carbon diffusion barrier between the carbon substrate and the back reflector. Further, we confirmed the optical characteristics and the effect of preventing carbon diffusion with and without the oxide layer. Experimental results showed that the back reflector bonded to the metal oxide layer showed better performance, and the SnOx bonding showed the best performance. First, the surface of the carbon paper was cleaned, and each film was deposited using an RF magnetron sputter. The thickness of the back reflector of Ag was 350 nm and that of Zn was 100 nm. For the carbon diffusion barrier, an oxide layer of 100 nm was first deposited, followed by the back reflector layer. The optical properties were examined using ultraviolet-visible spectroscopy, and cross sections were confirmed through transmission electron microscopy. The diffusion characteristics of carbon were evaluated using time of flight-secondary ion mass spectrometry after 200?400 ? heat treatment process in a dry furnace.

Resume : Many functional materials are traditionally synthesized by slow reaction processes that are energy and time consuming. In the present world there is strong demand on development of modern materials and materials processing methods that could offer rapid reaction rates, energy efficiency and be environmentally safe. Complex metal oxide ceramics have found wide applications in energy storage capacitors, electromechanical transducers, piezoelectric, and ferroelectric devices. The conventional method to prepare complex metal oxide ceramics is ceramic-powder-based processing, i.e., through solid-state reaction at high temperatures. This process has several disadvantages, such as high-temperature reaction, limited degree of chemical homogeneity, and low sintering ability. Therefore, during past years, several chemical-based processing routes, including freeze-drying, spray-pyrolysis, sol? gel, spray-drying, and pyrolysis of complex compounds, have been developed to prepare powders with more homogeneous composition, improved reactivity, and sintering ability at low temperatures. Recently, non-conventional processing methods such as mechanical alloying and mechano-chemical approaches have been used to create reactions between species. However in this method the reaction kinetics is very slow and processing time long. The objective of the present study is to investigate the application of an Electro-Mechano-Chemical (EMC)[1] technique to synthesize various metal- oxide ceramics, in particular formation of nano-phases and characterize the structural, physical, and optical properties. By using EMC, high purity single phase multi-element oxides can be formed in as little as 0.1% of the processing time required in conventional solid-state techniques. An even more important feature of EMC is that the crystallite size of the synthesized compound is able to be reduced to nanometer size, by careful selection of electrical (voltage, current, total power) and mechanical (vibration frequency and amplitude) experimental parameters. We use EMC for (i) synthesis of metal oxides from elemental powders by oxidation in oxygen plasma and for (ii) synthesis of single phase multi element oxides from pre-mixed oxides as starting materials. This presentation provides an overview of recent development of EMC method and it?s application in rapid synthesis of Perovskite ABO3 type oxide ceramics such as BaHfO3, BaTiO3, MnTiO3, PbZrO3, other complex metal oxides and metal oxyhydrides and others. References 1. A.Calka and D.Wexler, Nature, 419,(2002)147-151

Resume : Here, we report room temperature growth of the continuous layers consisting plate-like WO3.2H2O on a large area of indium doped tin oxide (ITO) coated glass substrates with excellent adhesion by using liquid phase deposition (LPD) technique. Electrochromic properties of the continuous WO3.2H2O 350 nm thick films were evaluated by cyclic voltammetry and chronoamperometry. During cyclic voltammetry experiments at negative currents reduction process occurs via intercalation of equal numbers of protons and electrons into the film working electrode. The films change their color from colorless to dark blue. Conversely, in positive currents oxidation process occurs and the color of the films changes back to its original color via deintercalation of protons and electrons back to the electrolyte. The bleaching and coloration time were determined based on chronoamperometry experiments about 3.2 and 14.1 s. These results indicate that coloration is a slow process whereas bleaching is kinetically a fast process. The cycling performance of the film was evaluated with a two electrode system using a square wave with 1 V amplitude and 30 s period time. Visually, the film constantly was transformed to colored and bleached states within about 900 cycles which afterwards the film was detached from the substrate.

Resume : Electrochromic (EC) materials being among chromogenic materials have the area of usage increasing day by day. The most common areas of usage of the EC materials are glasses, sensors and display panels. With the applied potential differences, little ions such as Li+ and H+ inserted to the film and material changes its optical state. Electrochemical impedance spectroscopy (EIS) is one of the best technique to determine the electronic properties of thin films. Explication of EIS data gives useful information about electrolyte resistance, charge transfer resistance, capacitance of the sample. It is also very common to determine an equivalent circuit model to reach information about the density of states and bandgap electronic structure of thin films. In this study, organic/inorganic EC materials such as WO3 and PANI were coated on ITO with several technics such as electrodeposition, chemical bath deposition and spin coating. EC behaviors of these films were measured with the 3-electrode system and cyclic voltammetry (CV), chronoamperometry (CA) analysis was done in order to monitor its ion exchange. Electronic properties of films were obtained with the EIS measurements. Band gaps were calculated and compared with the literature and experimentally obtained.

Resume : Noble metal (Au, Ag, and Pt, etc.) micro and nanostructures (M-Ns) have being received exceptional attention during the last decades, due to their unique structural, electronic and catalytic properties. Especially, the incorporation of these M-Ns with wide-bandgap semiconductor metal oxides such as titanium oxide (TiO2) has been shown to enhance their (photo)catalytic activity in the visible and ultraviolet (UV) irradiation due to plasmonic and non-plasmonic enhancement. (Photo)catalytic properties of hybrid structures can be finely tuned by controlling the shape and size of Au M-Ns.[1,2] In the literature, there are various studies about the synthesis of M-Ns well-defined size and morphology. However, it is still a challenge to achieve good adhesion between M-Ns and metal oxide surface. Therefore, some approaches (seed-mediated growth, etc.) have been published to enhance the adhesion of Au M-Ns on metal oxide by using some binder molecules (thiols and silanes, etc.). Mostly organic molecules are used for binding Au M-Ns with a solid substrate. However, these may decrease the surface conductivity and affect the catalytic activity of the Au M-Ns. Similarly, electrodeposition methods can also be used to prepare Au M-Ns on the solid substrates. But the electrodeposition process works only on the conductive substrate such as indium tin oxide (ITO). Therefore, there is a need to prepare stable Au M-Ns on metal oxide thin films without using any organic molecules (binders) or a conductive electrode. Here, we demonstrate a novel photocatalytic deposition approach for preparing Au M-Ns on metal oxide surface by UV illumination with strong chemical adhesion. This method allows the controlling the geometry, size, and distribution of such Au M-Ns on metal oxide thin film by simply changing the deposition solution, photocatalytic activity of metal oxide, UV illumination intensity and time. [1] S. Veziroglu, M. Z. Ghori, M. Kamp, L. Kienle, H. G. Rubahn, T. Strunskus, J. Fiutowski, J. Adam, F. Faupel, and O. C. Aktas, Adv. Mater. Interfaces, 2018, 5, 1800465. [2] S. Veziroglu, M. Z. Ghori, A.-L. Obermann, K. Röder, O. Polonskyi, T. Strunskus, F. Faupel and O. C. Aktas, Phys. status solidi, 2019, 1800898.

Resume : GaFeO3 (GFO) oxides are of great interest due to their magnetoelectric properties that can be exploited in multiferroic devices [1-3]. Pulsed laser deposition can be used to deposit high quality films, but it is difficult to be extrapolated to industrial facilities. We have explored electrodeposition and thermal oxidation as alternative growth processes. Electrodeposited layers show evidences of partial oxidation for Ga, whereas Fe seems to keep its metallic state. The electrolyte composition enables to achieve flat films, whereas the Fe/Ga ratio can be tuned by the applied growth potential. For thermal oxidation, we have monitored the evolution of sputtered uncapped Fe70Ga30 thin films with temperature. The treatment in oxygen atmosphere promotes the formation of Ga-rich aggregates at 500 °C. At 600 °C there are evidences of Ga oxidation but not for Fe, and at 700 °C Ga evaporates [4]. A better strategy for the oxidation seems the use of Mo capping layers to reduce the formation of Ga aggregates. Annealing at lower temperatures, between 200 °C and 400 °C, also seems to decrease the surface damage. A further optimization of the thermal oxidation process is the use of appropriate substrates for the FeGa layers that are eventually oxidized. [1] J. Atanelov, P. Mohn, Phys. Rev. B 92 (2015) 104408. [2] S. Mukherjee et al., Phys. Rev. Lett. 111 (2013) 087601. [3] H. Niu et al., J. Am. Chem. Soc. 139 (2017) 1520. [4] P. Alvarez-Alvarez et al., J. Alloys Compnd. 713 (2017) 229.

Resume : Gallium oxide (Ga2O3) is an interesting wide bandgap material having either insulating or semiconducting properties depending on the concentration and type of the impurities as well as intrinsic defects. The interest to Ga2O3 is because of its exceptional fundamental properties, specifically promising for power electronics, and of potential use in a range of other applications, e.g. in solar blind photodetectors, scintillators for medical diagnostics, transparent and passivating layers in solar cells, detectors tolerating high radiation/temperature, etc. For power electronics, among other materials, Ga2O3 possess most superior properties (humbled by diamond only), as such ranking it increasingly high among other ?energy? materials. One of the issues slowing down the use of Ga2O3 is the lack of fundamental understanding and difficulties in controlling electrically active point defects and defect complexes. Indeed, starting from ?simplest? point defects, due to the low symmetry of typically used monoclinic ?-Ga2O3, there are two different configurations of Ga in the unit cell (tetragonal and octagonal, GaT and GaO, respectively) and three different environments in the O sub-lattice in ?-Ga2O3. Such complexity results in equally many different vacancy configurations and sites for extrinsic impurities to reside, provoking a number of electronic states in the bandgap. Further, taking into consideration potential extrinsic impurities and corresponding defect complexes, the result is a plethora of potential localized electronic states. Some initial understanding has been accounted recently, not least by provoking defect formation induced by irradiation. In this presentation, upon discussing the perspectives and challenges, the results of our recent investigations of electrically active levels in ?-Ga2O3 will be highlighted [1] and set in the context of the present understanding [2]. Our approach is to use electron and ion irradiation for controllable introduction of the intrinsic defects into the material. In its turn, the methodological strength is in using a combination of the deep level transient spectroscopy (DLTS), secondary ion mass spectrometry (SIMS), and hybrid functional calculations for guiding the experimental work. [1] M.E. Ingebrigtsen, et al. APL, 112 42104(2018); M.E. Ingebrigtsen, et al., APL Mater., 112, 42104 (2019); M.E. Ingebrigtsen, et al. JAP, in press (2019). [2] Irmscher, K., Z. Galazka, M. Pietsch, R. Uecker, R. Fornari. J. Appl. Phys., 110 63720(2011); Zhang, Z., E. Farzana, A.R. Arehart, S.A. Ringel. Appl. Phys. Lett., 108 52105(2016); Gao, H., S. Muralidharan, N. Pronin, M.R. Karim, S.M. White, T. Asel, G. Foster, S. Krishnamoorthy, S. Rajan, L.R. Cao, M. Higashiwaki, H.v. Wenckstern, M. Grundmann, H. Zhao, D.C. Look, L.J. Brillson. Appl. Phys. Lett., 112 242102(2018).

Resume : We report on the growth of metastable (Mg,Zn)O oxide alloys and Ga2O3 polymorphs by plasma-assisted molecular beam epitaxy (PAMBE). The achievable maximum concentration of Mg in polar (Mg,Zn)O thin films is limited by the onset of phase separation into wurtzite and rock salt structure. Depending on the growth method, the substrate material and the applied growth conditions the reported incorporation limit varies between 4% and around 40%. The highest concentrations in MBE-grown layers were achieved for non-equilibrium growth conditions at low temperatures around 270°C. Thermal annealing of thin films with Mg concentrations of 28% and 38% grown on c-plane sapphire results in a transition from a pure wurtzite phase to the coexistence of wurtzite and rock salt phases. Transmission electron microscopy revealed a vertical equilibration of the (Mg,Zn)O film into a complex heterostructure, consisting of alternating rock salt and wurtzite layers. In the second part we show that the growth window of beta-Ga2O3, usually limited by the formation of volatile gallium sub-oxide in the Ga-rich regime, is expanded by the presence of tin during the growth process. By application of various analytic techniques we demonstrate that the presence of tin results in the formation of phase-pure metastable epsilon-Ga2O3 when Ga-rich growth conditions are applied. A growth model based on the oxidation of gallium sub-oxide using tin as a catalyst is suggested and the incorporation characteristics of tin are assessed. We will show that the catalytic growth process presents a promising technology platform for the synthesis of epsilon-Ga2O3 nanostructures.

Resume : Gallium oxide is attracting a lot of interest due to both its optical and electrical properties. Its wide band gap (4.9 eV) provides applications in UV-blue photodetectors. On the other hand, the huge breakdown field (8 MV/cm) makes Ga2O3 a competitive alternative to diamond or SiC materials for power device applications. Most of the reported work is based on thin films. In this work, we report the synthesis of undoped and doped ?-Ga2O3 nanowires of high crystalline quality by thermal evaporation methods. The approach allows for shape engineering by suitable selection of impurities. Ge and Sn are used as n-type dopants and their incorporation in the monoclinic phase is discussed. In addition, the formation of branched, crossing wires and particle decorated NWs is explored. Finally, we report the luminescence and light confinement properties in Cr doped nanowires.

Resume : Bulk vanadium dioxide (VO2) is an archetypal strongly-correlated electron material exhibiting a first-order metal-insulator transition (MIT) at T(MIT)~68°C. This transition is characterized by a drastic resistivity change and a structural transformation from an insulating monoclinic phase at room temperature (RT) to a metallic tetragonal rutile-like phase above T(MIT). This makes VO2 an interesting candidate for integration in energy-related devices, such as passive radiators or thermochromic windows. The fact that VO2 is usually in the form of films opens the way for easily tuning its MIT characteristics directly via the synthesis conditions. We hereby present a structural and spectroscopic study of a VO2 film grown on Al2O3(0001) by reactive sputtering. We combined High-Resolution X-Ray Diffraction and Raman spectroscopy to address the crystallographic phases present during the MIT. We established two structural models to account for the possible epitaxial relationships and demonstrate that their respective signatures in reciprocal space allow to easily differentiate them by diffraction. At RT, the phase is similar to the monoclinic M1 bulk phase. Above 66°C, it transforms into a M2-like polymorph. Upon further temperature increase, this latter partially turns into the rutile R-like polymorph. The coexistence of M2 and R phases is attested well above the transition temperature, questioning the importance of interfacial strain in the M2 phase stability.

Resume : The facile synthesis of graphene oxide (GO), which also possesses a band gap, can overcome some limitations of graphene in technological applications. On the other hand, current research mainstreams dealing with advanced luminescent materials are related to the achievement of white light emission using carbon derivatives [1]. Different synthesis routes were used to prepare GO composites with Li doped SnO2 nanoparticles [2] for evaluation of its performance for applications as anodes in Li-ion batteries (LIBs) and as luminescent materials. Galvanostatic charge and discharge cycling in CR2032-type half-cells showed that SnO2-based anodes have a high capacity in the charge/discharge process up to 100 cycles, while an intermediate capacity for the GO/SnO2 composite was observed. The capacity remains stable after the 200th cycle, showing that the materials can be used as a promising alternative anode material for LIBs. The composites exhibit photoluminescence related to functional groups and surface defects in GO. As a general trend the composites with a higher amount of oxygen functional groups exhibit lower PL intensity, whereas the presence of Li as well as formation of SnO and reduced GO induces higher PL signal. Moreover, the intensity of the luminescence from the composites is larger than from pure GO, while maintaining a nearly white emission. 1. Félix del Prado, María Taeño, David Maestre, Julio Ramírez-Castellanos, José María González-Calbet and Ana Cremades, J. Phys. and Chem. of Solids 129, 133?139 (2019) 2. Félix del Prado Hurtado, Ana Cremades, David Maestre, Julio Ramirez-Castellanos, José M González-Calbet and Javier Piqueras, Journal of Material Chemistry A 6, 6299-6308 (2018)

Resume : Modern photovoltaic energy converters based on the use of wide absorption spectrum, including near infrared range is currently of increased interest. We present a study of an original nanomaterial, namely, a thin multilayer nanostructured film consisting of metal oxide Ni or Ta nanoparticles (2-15 nm in diameter) with the spatial ordering of nanoclusters by size as a potential photovoltaic material. The system is an ensemble of densely packed metal nanoclusters with a gradient size distribution of nanoparticles deposited on the surface of silicon oxide. A key feature of the system is that the presence of the size dependence of the Fermi energy leads to the spatial redistribution of the charge in the system as a whole. That means that the average size of metal nanoparticles in the conducting system of nanoparticles in contact with each other monotonically changes in the selected direction, the potential difference is observed in the same direction. The appearance of a photoelectron in this system leads to the flow of the electron in the direction of the potential gradient. Since nanoclusters are metal, this provides the ability to detect photons of different wavelengths and provides a wide spectrum of radiation absorption. Nanocluster layers are formed using magnerton sputtering method with built-in mass filtration of nanoclusters that provide layer-by-layer formation of monodisperse layers made of different nanocluster sizes. The obtained preliminary results on the formation and study of the chemical, electron, and optical properties of the obtained multilayer nanocluster films are discussed.

Resume : With the rapid growth of wearable electronics, flexible and high-performance power sources has attracted increasing attention. Among various energy harvester, triboelectric nanogenerator (TENG) is highly promising owing to its light weight, easy fabrication, broad material selection, and high conversion efficiency. However, many traditional TENG are based on hard materials, which decreases the effective contact between the triboelectric pair and the output performance. Although more and more flexible TENG have recently been developed, they still show confined deformability and are hardly used in shape-adaptable devices. Herein, by employing graphene oxide (GO) dispersion as the liquid electrode while PDMS as the electrification layer, novel liquid single-electrode TENG (LS-TENG) with simple structure and high deformability, is firstly developed. The output performanceof this device is remarkably improved by adding a small amount of GO dispersion, where its open-circuit voltage and short-circuit current density are 123.1 V and 18.61 mA?m-2, respectively. This is much better than the reported LS-TENG based on NaCl solution and liquid metal. Moreover, Its maximum power density achieves 4.95 W?m-2 at a contact frequency of 3 Hz, which is higher than that of reported GO solid single-electrode TENG (3.13 W?m-2, 5 Hz). When palm taps the device with an electrode size of 2×2 cm2, 87 green LEDs in series can be lit up. Tests, such as robustness, durability, and repeatability, all indicate its high stability and potential in practical application. Minute body movement inputs on skin and clothes, indicate its high sensitivity and potential use in highly-flexible and highly-deformable wearable electronics.

Resume : Silicon heterojunction (SHJ) solar cells that combine advanced thin-film hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) technologies are a promising architecture that already demonstrated records-high values of open-circuit voltages that successfully enabled to high power conversion efficiencies even at the industrial production level [1]. For instance, SHJ solar cells feature high open-circuit voltages, generally well above 730 mV, world-record fill factor (FF) of 84.9% and power conversion efficiency of 26.7% as demonstrated in 2017 by Kaneka Corp [2]. Moreover, SHJ layers are typically deposited below 200 °C, which lowers considerably the thermal budget in production of the solar cell and at the same time allows for high throughput production machinery [2]. Due to the low conductivity of a-Si:H, transparent conductive oxide (TCO) needs to be used as a front contact layer on top of a-Si:H in order to collect photogenerated currents. However, TCOs must feature simultaneously high electrical conductivity, low contact resistance with the adjacent layers, and an appropriate refractive index for maximal light in-coupling into the device. In this work, we report on the optoelectronic properties of ITO layers deposited by DC sputtering, using different oxygen to total flow ratios [r(O2) = O2/Ar, ranging from 1% to 8%], for silicon heterojunction (SHJ) solar cell application. The depth profiling of the various elements throughout the thicknesses and interfaces of the ITOs and thin films forming the SHJ device was determined by time-of-flight secondary ion mass spectrometry. Finally, the photovoltaic performance of the fabricated SHJ cells was evaluated with respect to the r(O2) into the ITO layers. Lower r(O2) was found to yield the best PV performance which is attributed to lower parasitic resistive losses. [1] M. Zeman, D. Zhang, ?Heterojunction Silicon Based Solar Cells. Physics and Technology of Amorphous-Crystalline Heterostructure Silicon Solar Cells,? ed: Springer, (2011). [2] K. Yoshikawa, H. Kawasaki, W. Yoshida, T. Irie, K. Konishi, K. Nakano, T. Uto, D. Adachi, M. Kanematsu, H. Uzu, K. Yamamoto, ?Silicon heterojunction solar cell with interdigitated back contacts for a photoconversion effciency over 26%,? Nat. Energy 2, 17032 (2017).

Resume : One of effective approaches to obtain high performance water splitting device is to form desirable band bending at the interface between the charge generation material and electrolyte. For this purpose, ferroelectrics materials can be promising candidate, attributed to the induced polarization by applying high electric field. In this way, the modulated band bending along with desired direction overcomes the intrinsic property of anode or cathode in water splitting. Herein, we selected semiconducting and ferroelectric zinc oxide (ZnO) nanomaterials by doping with lithium and vanadium. The modulated spontaneous polarization in doped ZnO as photoanode was systematically investigated, varying the valence band bends upward or downward at the electrolyte interface. Consequently, the solar-tohydrogen (STH) efficiency using positively-polarized photoanode improved up to up to ~200 %, thanks to the favorable band bending for the generated hole transfer to electrolyte in comparison to the negatively-polarized one. The approach introduced using ferroelectric ZnO is simple, effective, and suitable way to design the high performance photoelectrochemical device. For the future work, also, the ferroelectric ZnO in core-shell design can be easily adopted by combining desirable anode material.

Resume : It was aimed to study the photocatalytic activity of polyaniline (Pani)/iron doped titanium dioxide (Fe-TiO2) composites for the degradation of methylene blue under UV light irradiation. For this purpose, TiO2 nanoparticles were doped with iron ions (Fe) and the doped photocatalyst nanoparticles were introduced into Pani by using an in situ polymerization technique. Pani composites, including 10, 20 and 30 wt.% Fe-TiO2 and undoped TiO2, were prepared via this technique. FTIR, XRD, SEM, EDX and UV?Vis spectroscopies were utilized to characterize the photocatalyst and the composites. According to SEM images, both Fe-TiO2 and TiO2 nanoparticles in aggregated form were distributed homogeneously within Pani matrix. UV-Vis spectroscopy revealed that the band gap of TiO2 widened to 3.18 eV with iron doping and Pani extended the absorption of TiO2 nanoparticles to the visible light region. When compared with undoped TiO2 and its composites, Fe-TiO2 and Pani/Fe-TiO2 exhibited improved photocatalytic activity under UVC light irradiation. Doping the photocatalyst with iron ions might improve the photocatalytic activity through hindering the recombination of the photoinduced charge carriers on TiO2 nanoparticles. The highest dye removal value (28%) was obtained with Pani composite, containing 30 wt.% Fe-TiO2 nanoparticles. In addition, the discoloration rate of the model dye, methylene blue, for the composite sample was 0.0025 min-1.

Resume : The method of sensitization of semiconductor materials, in particular TiO2, polymethine dyes, is a promising approach to the creation of high-performance photocatalytic systems with an extended range of photosensitivity. In this work, the anionic symmetrical polymethine dye 9-ezenyl-2,4,5,7-tetranitro- [2- (2,4,5,7-tetranitro-9H fluorene-9-ezenyl) ethylidene] triethylammonium 9-H- Fluorene (D), which contains three conjugate chromophores, is used to sensitize titanium dioxide. The analysis of the spectral, electrochemical and energy characteristics of the investigated dye shows the possibility of using it as an effective titanium dioxide sensitizer. The method of cyclic voltammetry has been used to determine the oxidation and renewal potentials of the dye and to calculate their redox potentials in the excited state. It is found that they are sufficient for sensitization by transferring electrons to the conduction band TiO2. New light-sensitive heterostructures D/TiO2 (HS) were created. Their photocatalytic activity in the oxidation reaction of iodide ions is determined depending on the irradiation conditions and the concentration of the dye-sensitizer. The energy diagrams of possible electronic processes caused by the action of light absorbed by both a semiconductor and a dye-sensitizer are investigated. An explanation of the found laws is offered.

Resume : NiO, with cubic structure, belongs to the family of p-type wide band gap semiconductor oxides, demonstrating potential applicability in gas sensors, electrochemical supercapacitors or catalysis, among others [1]. Using an appropriate synthesis method can lead to optimize most of these applications by reducing the size and selecting proper chemical composition. In this work, NiO nanoparticles undoped and doped with Sn content between 3 and 30% atomic, have been synthesized by a soft chemistry route based on hydrothermal process, using Ni (NO3)2·9H2O and SnCl2·2H2O as starting materials. The incorporation of Sn can modify the NiO optoelectronic response. In addition, formation of NiO/SnO2 p-n heterojunctions can be also promoted, with applications in photocatalysis or solar cells. The as-grown nanoparticles, with rock-salt structure, show good crystallinity in all cases, and homogeneity in size with dimensions between 7-15 nm. An increase in Sn content leads to a decrease in the particle size and finally to the stabilization of SnO2 phase with rutile structure, as confirmed by X-ray diffraction (XRD). The characterization of the nanoparticles was performed by Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDS), Raman Spectroscopy, Cathodoluminescence (CL), Photoluminescence (PL) and X-Ray Photoelectron Spectroscopy (XPS) at the Elettra synchrotron. CL and PL results show two main emissions centered at 2.3 and 2.8 eV, and a weak emission around 2 eV. XPS measurements show changes in the Sn4+/Sn2+ ratio as a function of Sn content in the nanoparticles, which also involves variable Ni3+/Ni2+ ratio. [1] M. Wang, J.Han, Y.Hu, R. Guo, Y.Yin. App.Mat & Interf. 8, 29511-29521 (2016)

Resume : Solar cells are devices using renewable energy to solve global environmental problems and limited natural resources problems in recent years, and further cost reduction and higher photovoltaic performance are required for their widespread use. Oxide semiconductor-based thin-film solar cells represented by n-ZnO/p-Cu2O heterojunction type solar cells have been attracting attention as low-cost and environmentally friendly solar cells that can be manufactured by aqueous-solution processes and general purpose metals, such as Zn and Cu, as raw materials.[1-4] The aqueous-solution process that does not use a vacuum process or high temperature heat treatments enables the use of plastic substrates. The fabrication of flexible and lightweight oxide solar cells can also be expected to find new applications by taking advantage of its superior characteristics. In this study, ZnO/Cu2O heterojunction has been prepared on a conductive oxide-coated flexible plastic substrate using electrochemical deposition in aqueous solution. We adopted Al-doped ZnO as a conductive oxide and polyethylene naphthalate as a flexible substrate, and investigated the effect of ZnO/Cu2O deposition conditions on the photovoltaic performance. By controlling the deposition rate and the film thickness, photovoltaic performance comparable to that using conventional glass substrates was achieved. [1] M. Izaki, T. Shinagawa, K. T. Mizuno, Y. Ida, M. Inaba, A. Tasaka, J. Phys. D: Appl. Phys. 2007, 40, 3326. [2] A. T. Marin, D. Muñoz-Rojas, D. C. Iza, T. Gershon, K. P. Musselman, J. L. MacManus-Driscoll, Adv. Funct. Mater. 2013, 23, 3413. [3] T. Shinagawa, K. Shibata, O. Shimomura, M. Chigane, R. Nomura, M. Izaki, J. Mater. Chem. C 2014, 2, 2908.

Resume : One of the most promising approaches to increase the Si Solar Cell (SC) efficiency is its combination with frequency conversion layers, which spectrally redistributes irradiance to obtain a larger spectral overlapping with the Si-SC absorptivity. Therefore, conversion efficiency increases at the expense of the thermalization of photogenerated carriers. Down Conversion (DC) and Down Shifting (DS) processes are achieved by means of absorption and emission Rare Earth (RE) ions, such as Tb3+-Yb3+ for DC and Tb3+ for the DS. Major disadvantages of RE ions are their low excitability and their host matrix low chemical compatibility with Si SC. We present in this paper the study of DC (DS) layers, consisting in a Si-based matrix doped with Tb3+-Yb3+ (Tb3+) ions fabricated by a sputtering approach and structurally and optically characterized. The role of RE concentration on cooperative energy transfer (CET) in rare earth ions solid solution was investigated by growing mixed RE thin film and multilayer thin film constituted of an alternation of SiNx:Yb3+ and SiNx:Tb3+ sublayers of few nanometers thick. The resulting DC (DS) conversion efficiency was investigated experimentally and by means of a Monte-Carlo model allowing to explain the role of RE ions interdistances on the CET mechanism and consequently on the efficiency of the conversion. Finally, we successfully integrated our SiNx Tb3+-Yb3+ DC layers on a silicon based SC and determined a relative efficiency improvement up to 1.34%.

Resume : In recent years the study of hybrid solar cells has increased and one of the research lines includes the incorporation of new material to enhance their properties1. Nanocrystalline transparent conductive oxides (TCO) within PEDOT:PSS are being studied for this kind of solar cells in order to improve their stability and electrical behaviour, as well as obtain enhanced tunability of their optical and electrical properties. In this work, we study the characteristics of PEDOT:PSS with embedded ?-Ga2O3 or ?-Ga2O3 nanoparticles2. Structural, morphological, optical and electrical characterization has been carried out with X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), photoluminescence excitation (PLE), cathodoluminescence (CL) and Raman spectroscopy. The effect that the ?- and ?- nanocrystals phases induce on the performance of the hybrid system will be discussed. 1. Jäckle S, Mattiza M, Liebhaber M, et al. Junction formation and current transport mechanisms in hybrid n-Si/PEDOT:PSS solar cells. Sci Rep. 2015;5:1-12. doi:10.1038/srep13008 2. García-Tecedor M, Karazhanov SZ, Vásquez GC, et al. Silicon surface passivation by PEDOT: PSS functionalized by SnO2 and TiO2 nanoparticles. Nanotechnology. 2018;29(3). doi:10.1088/1361-6528/aa9c9e

Resume : In recent years, application of heterogeneous photocatalysts, especially environmentally friendly oxide semiconductors have proven to be a highly efficient and economical approach for toxic organic pollutants degradation. In this regard, many efforts have been made to modify bandgap structure and extend the range of light absorption through metal and nonmetal doping. However, Doping can reduce photocatalytic performance of semiconductor nanoparticles by introducing defects and trapping centers which increase recombination rate of photogenerated electrons and holes. Instead of the traditional idea of changing the bandgap, we have tried to enhance photocatalytic properties of Aurivillius phase layered structure Bi2SrTa2O9 through ?Exfoliation/Restacking? process. This new approach not only can increase the specific surface area of the photocatalyst, but also shorten the charge transport pathways which leads to less chance for electron-hole recombination. AFM measurements have shown that Individual nanosheets are similar in thickness (approximately 2 nm) but different in lateral dimension ranging between 200 nm to as large as one micron. Comparing data obtained from BET analysis reveals that specific surface area for restacked nanosheets is almost 13 times higher than the original layered perovskite. Besides, negatively charged surface of the nanosheets enhances adsorption of cationic dyes such as RhB on the surface of catalyst. Comparing photocatalytic activity of original layered perovskite (Bi2SrTa2O9) with that of restacked [SrTa2O7]2- nanosheets under UV light irradiation has shown significant reduction in reaction time for photocatalytic degradation of Rhodamine B from 180 min to 20 min.

Resume : Lead-free piezoelectric nanofiber sheets were prepared by the electrospinning method, and then the piezoelectric nanofibers in the shell parts were twined around a conductive thread (the inner electrode layer) in the core parts. The outer electrode layers were made by braiding the core-shell piezoelectric nanofiber yarns with conductive thread, and the core-shell piezoelectric nanofiber yarns with external electrodes were then directly stitched onto the fabric. The stitching patterns of the core-shell piezoelectric yarns were optimized as long as possible with a stitching interval of 0.15 cm inside an effective area. Energy could be harvested from various garments (a glove, a guard, and a shoe insole) directly stitched with the core-shell piezoelectric yarns according to various bending and pressing body movements.

Resume : Using the sun?s energy to generate hydrogen from water is probably the cleanest and most sustainable source of fuel that we can envisage. Unfortunately, catalysts that do this are currently whether too expensive or low in efficiency.In this research we employed Atomic Layer Deposition (ALD) technique to deposit Metal oxide nanocluster on TiO2 nanoparticle surface. The results show improved photocatalytic activity in the visible range and increased hydrogen evolution efficiency.

Resume : Study of thermoelectric properties of model materials made from the d-metals nanoclusters is presented. Semiclassical thermoelectric transport coefficients was obtained from the non-empirical band structure calculated by DFT. Transport coefficients calculated in bulk limits showed coincidence with the reference ones and obeyed the Lorentz ratio for bulk metals. Up to 50 times increasing of the Seebeck coefficient was obtained numerically for nanoclustered model materials with respect to the bulk one. It stays in agreement with the experimentally observed trends of nanoclusters properties. Relationship of structural, electronic and thermoelectric properties of nanoclusters and structures, formed from it, is discussed in order to developing of highly efficient thermoelectric materials.

Resume : Wide-band semiconductors as SnO2 have demonstrated potential applications [1] in diverse fields ranging from catalysis, optoelectronic devices or energy storaging as batteries. During the last years increasing attention has been focused on the use of SnO2 nanoparticles in ion-Lithium batteries (LiB), for which controlled morfology and size of the nanaoparticles as well as appropriate doping is necessary. In this work, rutile SnO2 nanoparticles have been synthesized by means of a hydrolysis method using SnCl2 2H2O as precursor. Ni or Li doping have been achieved adding a controlled ratio of NiCl2 6H2O or LiCl, respectively. With this method we have obtained rutile SnO2 nanoparticles with high crystallinity and sizes around 20 nm, as measured with X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The cationic concentration of the dopants, ranging from 0.1 to 3.6 at. %, has been measured with energy dispersive X-ray spectroscopy (EDX) and plasma Spectroscopy (ICP-OES). Raman spectroscopy measurements show variations in the vibrational modes as a function of the dopant. Also photoluminescence (PL) has been studied using a He-Cd (325 nm) laser as excitation source. Changes in oxygen vacancies related bands have been observed as a function of the dopant. X-ray photoemission spectroscopy (XPS) acquired at the Elettra synchrotron shows variable Ni3 /Ni2 as a function of the doping. Furthermore, undoped and Li or Ni doped SnO2 nanoparticles were used as anodes in Li ion cells showing an initial capacitance around 700 mAh/g and good stability over 100 cycles. [1] F. del Prado, A. Cremades, D. Maestre, J. Ramírez-Castellanos, J.M. González-Calbet and J. Piqueras, J. Mater. Chem. A, 2018, 6, 6299-6308

Resume : Hybrid solar cells combining organic and inorganic materials have recently become of great interest not only in photovoltaic applications [1], but also as sensors and in microelectronic devices. However, despite the promising efficiencies reported for hybrid composites so far, several aspects still require to be further addressed to overcome some limitations of these compounds and improve their applicability. In this work hybrid composites formed by a conductive polymer PEDOT:PSS functionalized with SnO nanoparticles (1 wt. %) have been investigated. A preliminary study of bare PEDOT:PSS and romarchite SnO nanoparticles synthesized by hydrolysis were firstly carried out. The composites were deposited on n-Si or glass substrates by spin-coating, leading to layers with a thickness around 120 nm and an average surface roughness of 3.5 +- 0.5 nm, as measured by AFM. Electrical and photoluminescence measurements were also performed in these samples. The influence of a piranha pre-treatment on the Si surface has been evaluated. Besides, the stability of the polymer under irradiation has been analyzed by Raman spectroscopy using a UV laser as excitation source. Changes in the region 1200-1500 cm-1 characteristic from the PEDOT:PSS were observed after continuous irradiation. Finally, the composites including SnO nanoparticles were used for n-Si surface passivation. Lifetime values around 350 us were measured by PL-QSSPC, which confirms good passivation behaviour even without pre-treatment of the Si substrate. [1] M García-Tecedor, S. Z. Karazhanov, G. C. Vásquez, H. Haug, D. Maestre, A. Cremades, M. Taeño, J. Ramírez-Castellanos, J.M. González-Calbet, J. Piqueras, C.C. You, E. S. Marstein, Nanotechnology 29, 035401 (2018)

Resume : A novel TiO2 nanoparticles (TNP-Cat) synthesized by chelating with catechol derivatives have been demonstrated. These synthesized TNP-Cats are highly dispersive in organic solvents and form dense film with small roughness. Various analysis including X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) have been conducted to investigate physical, chemical and electrical properties of TNP-Cats. Analysis results showed that chelating the catechol derivatives on the TiO2 alter the energy level of the TiO2 nanoparticles. These TNP-Cats were utilized an electron transporting layer of organic photovoltaic (OPV) devices. In this presentation, characteristics of TNP-Cats and solar cell performances of OPV devices utilizing Cat-TPNs will be discussed.

Resume : The hybrid organic-silicon solar cell concept has started to attract attention in the scientific community. This is due to an attractive combination of potentially simple device fabrication and competitive efficiency compared to other silicon-based solar cell architectures. It has recently been demonstrated that spin-coated poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (hereafter PEDOT:PSS) on silicon wafer is a promising material due to its good optical and electrical properties. However, degradation caused by atmospheric exposure and relatively poor passivation properties limit implementation of PEDOT:PSS?silicon devices. Functionalization of PEDOT:PSS by inorganic nanoparticles is a possible solutions, as was shown for TiO2 and SnO2 nanoparticles. In this work we present our study of the optical and passivation properties of PEDOT:PSS, as well as the effect of its functionalization by NiO nanoparticles on these properties and material durability. The influence of nanoparticles on the electrical properties of the heterojunction PEDOT:PSS/n-Si will be also demonstrated.

Resume : In recent years, many basic principles have been developed to improve and optimize TiO2-based materials as photocatalysts. Herein, we demonstrated new solvothermal oleate approach for the fabrication of TiO2 1D anodized nanotubes decorated with Fe3O4 nanoparticles. The as-prepared samples revealed enhanced photocatalytical activity in photodegradation of methylene blue under visible light irradiation. According to recent studies [1, 2], double-walled nanotubes, containing secondary layer of electrolyte deposition, display lower degradation rate in comparison to single-walled samples. Therefore, single-walled TiO2 nanotube composites were shown to have the highest rate constants, namely, 0.41??? 10-2 and 0.48 10-2 min-1, compared to non-decorated nanotubes. Increase in concentration of the Fe3O4 nanoparticles in 3 times leads to growth of particle size from 20 to 30 nm and formation of bunches and beads. For these samples, the photocatalytic activity reduced due to unavailable surface area. Based on these data, we can conclude, that the resulted TiO2 composite materials produced with a low amount of Fe3O4 nanoparticles could perform as promising magnetically-guidable, low-cost, environmentally-friendly photocatalysts [3]. 1. Mirabolghasemi H., Liu N., Lee K., Schmuki P. Chem. Commun. 2013, 49, 2067?2069. 2. Motola M., Sopha H., Krbal M., Hromadko L., Olmrova Zmrhalova Z., Plesch G., Macak J.M. Electrochem. Commun. 2018, 97, 1-5 3. D. Beketova et al., Ms in preparation.

Resume : Thin film CeO2-based electrolytes are usually fabricated by physical and chemical vapour deposition techniques, such as electron beam evaporation, pulsed laser ablation, magnetron sputtering, spray pyrolysis, metal-organic vapour deposition, and others. It is considered that relatively low deposition rates and high equipment cost are characteristic of the vacuum deposition methods in comparison with traditional methods of ceramic layers? formation (screen printing, electrophoretic deposition, tape casting, and etc.). Despite this, vacuum methods have a number of unique advantages, where very thin and fully dense layers may be fabricated at low temperatures. In this work, gadolinia-doped ceria (GDC, Gd0,1Ce0,9O1,95) multilayer sandwich system (4 ? 12 layers) were deposited on Si (111) substrate by direct current reactive magnetron sputtering in O2/Ar gas mixture. Deposited GDC thin films were annealed at 700 °C for 1 h in air. After the deposition process GDC thin films had a columnar structure, but the dense structures were formed after the annealing process. The structural, morphological, and phase compositional properties of sputtered GDC thin films were investigated using X-Ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). Phase composition results revealed the presence of fluorite microstructure. GDC thin film thickness was ~700-900 nm was evaluated from SEM results. The diffusion of Ce and Gd in multi-layered gadolinia-ceria systems was observed by Rutherford Backscattering spectroscopy (RBS).

Resume : Electrochromic (EC) materials being among chromogenic materials have the area of usage increasing day by day. The most common areas of usage of the EC materials are glasses, sensors and display panels. With the applied potential differences, little ions such as Li+ and H+ inserted to the film and material changes its optical state. Electrochemical impedance spectroscopy (EIS) is one of the best technique to determine the electronic properties of thin films. Explication of EIS data gives useful information about electrolyte resistance, charge transfer resistance, capacitance of the sample. It is also very common to determine an equivalent circuit model to reach information about the density of states and band gap electronic structure of thin films. In this study, organic/inorganic EC materials such as WO3 and PANI were coated on ITO with several techniques such as electrodeposition, chemical bath deposition and spin coating. EC behaviors of these films were measured with the 3-electrode system and cyclic voltammetry (CV), chronoamperometry (CA) analysis was done in order to monitor its ion exchange. Electronic properties of films were obtained with the EIS measurements. Band gaps were calculated and compared with the literature and experimentally obtained.

Resume : More recently, there has been a growing interest on electrochromic devices (ECD) that is able to control the throughput of visible light into buildings that provides the control of energy efficiency by using a small electrical voltage. A great deal of previous research focused on tungsten oxide that is the most studied inorganic electrochromic material due to its better coloration efficiency. In the recent years, extensive research has been carried out on not only the inorganic chromogenic materials, but also the organic ones. This study provides a novel approach to quantifying fabrication and characterization of the all-solid-state electrochromic (EC) devices made up with different electrolytes (Nafion, gel electrolyte LiClO4-propylen carbonate- poly (LiClO4-PC-PMMA), etc) are reported in this study. Herein, organic and inorganic hybrid systems are considered to be produced. These devices consist of electrolyte, inorganic working (tungsten oxide) and organic counter electrode thin films deposited on Indium-tin oxide substrates.

Resume : Resource and cost limitations for indium, requires a timely development of new thin-film transparent conducting oxides, with aluminum doped zinc oxide (AZO) as one strong candidate. Targeted use include large-area and big-market applications, such as soar cells, touch panels, organic-LED and smart windows. Despite of intensive research, the AZO thin-film growth mechanism by magnetron sputtering is not understood, fact reflected by good optoelectronic properties limited to certain regions over the substrate surface. So far, it was demonstrated that, under certain deposition conditions, the AZO resistivity varies with more than two orders of magnitude over a substrate span below of 10 mm while the transmittance remains above 85%. This work reports on spatially resolved properties of AZO thin films by TOF-SIMS, XPS and XRD in correlation with spatially resolved plasma parameters by probes (electrical and thermal) and optical emission spectroscopy. A 2 mm in diameter gold probe is scanned at the level of substrate surface below a 2 inch sputtering cathode (RF or DC operation) to record plasma density. An optical fiber can also measure the probe surface temperature by fluorescence decay between pulses of violet radiation. The same scanning system is used to record optical emission spectra, revealing the spatial distribution of aluminum, zinc and oxygen. This work was supported by the Innovation Fund Denmark through research project no 6151-0011B: SmartCoating.

Resume : Nickel (II) oxide (NiO) thin films were successfully synthesized via simple pneumatic spray pyrolysis method using nickel acetate precursor. The effects of deposition temperature, volume of spray solution and precursor concentration on structural, optical and photocatalytic properties of the NiO films were investigated. XRD, UV-Vis spectroscopy, water contact angle measurement and photodegradation of methyl orange (MO) under UV irradiation were used to characterize deposited films. XRD patterns reveal that independent of the technological parameters all the films are of cubic NiO. The average crystallite size changes from 2 to 8 nm varying the substrate temperature (Ts) from 260 to 400 °C. The bandgap values (direct transitions) were 3.8 eV for the films grown at Ts of 260 °C and at around 3.3 eV if grown at higher temperatures. The deposition temperature and film thickness were found to be the key parameters that influence the samples wettability and MO degradation efficiency. The water contact angles (CA) are 10° and 30°, MO degradation efficiency values are 80%/3h and 15%/3 h for the films deposited at 300 °C and 400 °C, respectively. Increasing the volume of spray solution from 25 mL to 150 mL decreases the CA values from 25 to 8? and increases degradation efficiency of MO from 32% to 80% for the films deposited at 300 °C.

Resume : Hole-conducting poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a materials receiving increasing interest for use in photovoltaic devices. In this work, we present the results of study of the degradation of the optical and electrical properties of pure PEDOT:PSS pure and PEDOT:PSS doped with Si-nanoparticles. The PEDOT:PSS has been deposited on top of Si wafers by spin coating. We found that incorporation of Si nanoparticles into PEDOT:PSS enhances the surface passivation of the surface of Si wafer by increasing the carrier lifetime measured by PL QSS-PC method from about 320 µs to 420 µs for the injection level at 2*10^15 cm^-3. The sheet resistance of PEDOT:PSS has also been increased. Analysis showed that incorporation of the Si nanoparticles does not change noticeable neither Si surface passivation nor kinetics of degradation of lifetime. We report also current-voltage dependence for Si/PEDOT:PSS.

Resume : It is of a great challenge to seek for semiconductor photocatalysts with prominent reactivity to remove kinetically inert dilute NO without NO2 emission. Complete visible light NO oxidation mediated by O2 is achieved over a defect-engineered BiOCl with high selectivity. Well-designed one-electron trapped oxygen vacancies (VO´) on the prototypical (001) surface of BiOCl favors the possible formation of geometric-favorable superoxide radicals (?O2-) in a side-on bridging mode under ambient condition, which thermodynamically suppresses the terminal end-on ?O2--associated NO2 emission in case of higher temperatures, and thus selectively oxidize NO to nitrate. Differently, two-electron-trapped oxygen vacancy (VO?) on BiOCl(010) surface, a prototypical F center, accomplishes NO oxidation through a two-electron charging (VO? + O2 ? VO?-O22-) and subsequent one-electron decharging process (VO?-O22- + NO ? VO-NO3- + e-). The back-donated electron is re-trapped by oxygen vacancy to breed a new single-electron-trapped VO´, simultaneously triggering a second round of NO oxidation (VO´-O2 + NO ? VO-NO3-). These findings can help us to understand the intriguing surface chemistry of photocatalytic NO oxidation and design highly efficient NOx removal systems.

Resume : Abstract The reactive rf magnetron sputtering using H2:Ar plasma on ZnO targets leads to highly transparent and conducting films [1,2]. In this work, aluminum-doped zinc oxide (ZnO:Al) films have been deposited by rf magnetron sputtering using H2:Ar mixtures at various pressures and temperatures. Significant reduction in the resistivity and increase in the optical properties of the films is observed due to the effect of hydrogen incorporation, increase in pressure and as well as temperature. The aim is to optimize ZnO:Al layers to replace the indium tin oxide (ITO) layers, which is the most widely used transparent conductive oxide (TCO) in the market but is expensive due to indium. Analysis of ZnO:Al films with different doping concentrations of hydrogen, pressure, and temperature will be presented. Electrical characterization by four-point probe measurements and optical transmission spectroscopy are used to assess the suitability of the ZnO:Al structures as TCO, by using the Haacke figure of merit (FOM). Heterojunction silicon solar cells also will be fabricated using ZnO:Al replacing the ITO to study the increase in efficiency and open circuit voltage(Voc) of the cells. References: 1. L. Chen et al., Hydrogen-doped high conductivity ZnO films deposited by radio-frequency magnetron sputtering. Applied Physics Letters 85 (2004) 5628. 2. S.Zhong et al., Exploring co-sputtering of ZnO:Al and SiO2 for efficient electron-selective contacts on silicon solar cells. Solar Energy Materials and Solar Cells 194 (2019) 67.

Resume : One of the methods to improve perovskite solar cells (PSC) performance is to change the mesoporous titania (TiO2) structure to a more ordered one, e.g. to nanorod or nanotube arrays. Oriented nanorod-like materials on transparent conductive oxide (TCO) are known for their efficient charge separation and transport properties and are thus favourable for achieving good device performance. In this work vertically aligned TiO2 nanotube (NT) array thin film based electrodes were prepared and tested for application in perovskite solar cells. A two-step process was employed and optimized for TiO2 NT array thin films preparation. It the first step titanium layer was deposited on TCO (ZnO, ITO) substrate by DC magnetron sputtering using titania target and argon as working gas. In the second step, TiO2 NT array was formed by electrochemical anodization of Ti layer. Anodization process parameters were optimized to obtain transparent TiO2 NT layer. Structural, optical and electrical properties of the prepared TiO2 NT electrodes were analyzed and discussed. Influence on PSC performance was also disused. Acknowledgement: This work has been supported by Croatian Science Foundation under the project IP-2018-01-5246 ?Nanocomposites comprising perovskites for photovoltaics, photo-catalysis and sensing? and Croatia-Austria bilateral project ?Titanium dioxide nanotube array based perovskite solar cells?.

Resume : High-efficiency III?V based multi-junction solar cells for terrestrial concentrated photovoltaics require broadband anti-reflection coatings (ARCs) working on wide angles. For this purpose, Ta2O5 and SiO2 coatings deposited by co-sputtering and e-beam evaporation in glancing angle conditions (GLAD) have been developed and characterized by combining ellipsometry and X-ray reflectivity data. Co-sputtering of Ta2O5 and SiO2 has been applied to obtain a ?mixed-oxide? with n matching any value in the range 1.5-2.2. GLAD evaporation has been carried out to nanostructure SiO2 films, in order to reduce its effective n and improve the ARC behaviour at high incident angles. The coating developed have been eventually deposited on InGaP SJ solar cell, to be used as top cell in a MJ cell structure. The cell short circuit current has then been measured in order to compare the performance of the different coatings.

Resume : P-type transparent conductive oxides (TCOs) to be used as membrane layers in thin film solar cells to extract holes. In this work, we considered their application in monolithic CuInxGa1-xSe2 (CIGS) / hybrid perovskites (HPs) tandem cells. Therefore, materials with energy band gap (Wg) > 1.7 eV, low optical absorption in the energy range between 1.0 and 1.7 eV (the band gap of CIGS) but with high enough concentration of free charge carriers (> 1018 cm-3) were of our primary interest. Additional challenges to solve were mostly technological, they originated from low temperature resistance (TS ? 200°C) and high roughness of CIGS films. The latter is worsened by appearance of deep grain-grooves. The following materials were investigated: Cu2O, CuInO2, NiOx. Their conductivity and charge carrier concentration were measured in the correlation with oxygen content. For the Hall-effect measurements special mask was developed to enhance the accuracy. Reactive Hollow Cathode Gas Flow Sputtering (GFS) process was improved in this work. Monte-Carlo simulations were performed to optimize distribution of gases in a reactive area. A nozzle attachment was compared to the diffuser one in terms of their impact at the frontline of a high pressure drop. Optical Emission Spectroscopy (OES) was used to determine a composition of the GFS-plasma, namely, which species appear depending on conditions, such as the art of power generation, distance from the target, pressure and gas. Additionally, their ionization degree and energy distribution were determined.

Resume : Bi2SiO5 is a wide band gap semiconductor belonging to the aurivillius family.1-2 However, being a wide band gap semiconductor, it is effective for photocatalytic applications under UV light only.3-4 The objective of this work is to improve the photocatalytic activity of Bi2SiO5 by lowering the bandgap so that it can absorb both, UV and visible part of the solar light. In this work narrowing of band gap has been achieved by doping halides and its effect on the electronic and optical properties has been studied. The halide-doped Bi2SiO5 photocatalyst was synthesised via a facile hydrothermal approach. The phase, morphology and surface functionalization of the doped catalysts were retained in comparison to the pristine material which was examined by powder X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy and UV-vis diffuse reflectance spectroscopy. The doped Bi2SiO5 nanoparticles showed improved photocatalytic activity for the degradation of both coloured as well as colourless toxic water pollutants under simulated solar light. A small amount of halide doping lowered the band gap of Bi2SiO5 nanoparticles, broadened the optical absorption towards the visible region and escalated the charge separation of generated exciton pairs leading to reduced recombination rate and enhanced photocatalytic activity. The results obtained here show a rational design of halide doped Bi2SiO5 nanoparticles with an improved photocatalytic response. References: 1. Z. Wan and G. Zhang, Synthesis and facet-dependent enhanced photocatalytic activity of Bi2SiO5/AgI nanoplate photocatalysts, J. Mater. Chem. A 3 (2015) 16737-16745. 2. J. Duan, Y. Liu, X. Pan, Zhang, J. Yu, K. Nakajim, and H. Taniguchi, High photodegradation efficiency of Rhodamine B catalysed by bismuth silicate nanoparticles, Catal. Commun. 39 (2013) 65-69. 3. D. Liu, J. Wang, M. Zhang, Y. Liu and Y. Zhu, superior photocatalytic performance of a novel Bi2SiO5 flower-like microsphere via a phase junction, Nanoscale 6 (2014) 15222-15227. 4. J. Wang, G. Zhang, J. Li, and Kai Wang, Novel Three-Dimensional Flowerlike BiOBr/Bi2SiO5 p−n Heterostructured Nanocomposite for Degradation of Tetracycline: Enhanced Visible Light Photocatalytic Activity and Mechanism, ACS Sustainable Chem. Eng. 6 (2018) 14221−14229.

Resume : Atmospheric pollution has been recognized as one of the major threats for modern society. Among the various manmade air pollutants, nitrogen oxides (NOx) induce the ozone production in troposphere and cause acid rains. In addition, NOx, especially nitric oxide (NO) and nitrogen dioxide (NO2) severely affect respiratory and immune systems [1]. Titanium dioxide (TiO2) is the most widely used semiconductor for the photocatalytic decomposition of gaseous and liquid-phase pollutants. Despite its favorable properties like chemical inertness, long-term stability and low cost, TiO2 has a band gap of 3.2 eV. This large band gap enables the harvesting of UV light only, which accounts for 4-5% of incoming solar energy[2] .There have been numerous attempts to extend the photocatalytic efficiency of TiO2 in the broader solar spectrum via nonmetal doping, metal doping, and surface modifications with polymers. In this study, oleic acid capped CdSe/CdSeTe nanoplatelets (NPLs) were synthesized for the surface functionalization of TiO2. Structural characterizations were carried out by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) , ATR-Fourier-transform infrared spectroscopy, transmission electron microscopy (TEM) to confirm the formation of desired materials. These NPLs/TiO2 composites were then tested in NO photo-oxidation under UVA and visible light, showing a remarkable activity in NOx abatement and a high selectivity for nitrate species as compared to standard benchmark TiO2 photocatalyst. The improved photocatalytic property can be attributed to decrease in bandgap and enhanced photogenerated electron-hole pair separation as a result of incorporation of CdSe/CdSeTe NPLs to TiO2. The stability of composites was investigated by extension of reaction duration. Even though some decrease in photocatalytic activity and selectivity of NPLs/TiO2 composites observed, but their performance was even significantly better than pure TiO¬2¬. This facile synthesis approach in combination with a high performance present a valuable material for next generation technologies for the abatement of harmful gaseous pollutants.

Resume : Nowadays, the producing of hydrogen for energy storage with low costs and high efficiency is the main concern in the research filed. The photovoltaic devices that are renewable energy sources can be used in the photovoltaic-electrolysis process to produce hydrogen. Extended studies were performed on the wide band gap semiconductor oxides for solar water splitting systems. Therefore, in this work, nanostructured metal oxides based on tungsten are studied and produced as thin films and their properties are tuned by the embedding of nitrogen ions in their contents. These thin films are produced by pulsed laser deposition. The deposition parameters such as laser wavelength, gas composition, and laser fluence influence the nanostructures physical and chemical properties. The morphological, structural, and compositional characterization of the obtained structures was performed. The testing of photocatalytic activity of WO3 and WOxNy thin layers in the photochemical decomposition reaction of the water molecule was pursued.

Resume : Recently, metal oxide nanostructures had great development regarding their synthesis and device integration. Having in mind sustainability of materials and processes as well as multifunctionality, zinc-tin oxide nanostructures are some of the most promising oxide nanostructures being researched. The ternary oxide nature allows for impressive multifunctionality, with applications ranging from catalysis, to electronics, sensors and energy harvesting. Concerning energy harvesting applications ZnSnO3 phase is particularly interesting, due to its high piezoelectric constant. Although a pure phase of ZnSnO3 is hard to achieve due to its metastability, in this work ZnSnO3 NWs produced by a seed-layer free hydrothermal synthesis at only 200 °C are presented.1 In order to produce robust energy harvesters, a composite was fabricated mixing these NWs with a micro-structured PDMS film2. The micro-structured nature enabled a double contribution, enhancing both tribo and piezoelectric effects, resulting in a great performance regarding output voltage, current, and instantaneous power density (up to 200 µW·cm-2). As proof of concept, a demonstration of lighting up multiple LEDs by directly connecting them to the fabricated harvester is also shown, evidencing the great potential for wearables and portable electronics.3 [1] A. Rovisco, et. al., ACS Appl. Nano Mater. 1(8), 3986 (2018) [2] A. dos Santos, et. al., Adv. Electron. Mater. 4(9), 1 (2018) [3] A. Rovisco, et. al., submitted (2019)

Resume : The nanomaterials have attracted enormous attention in the catalysis applications. Particularly, we have concentrated on the synthesis of nanocomposites for an electrochemical sensor with improved electrocatalytic performance. Over the past few decades, a great number of studies have demonstrated that graphene oxide (GO) could be used successfully for the removal of Pb (II) from water. Thus, tungsten oxide (WO3) embellished on reduced graphene oxide could be applied in degradation of water for removing the waste ions in it by electrocatalysis. We report a simple and robust ultrasonic-assisted synthetical route via prepared WO3 nanoparticles decorated reduced graphene oxide nanocomposite (GO-WO3) modified electrode for nitrite detection. The composition and morphological formation were characterized by XRD, XPS, FESEM, and HRTEM. Except for valuable information about the characteristics, our results provide and mechanism of transport of adsorbed heavy metals on GO-WO3 nanomaterials in the aqueous environment and the possible environmental risks when spent GO-based heavy mental adsorbents are discharged into natural groundwater systems.

Resume : Transparent conducting oxides (TCOs), which combine high electrical conductivity and high optical transmission in the visible spectral range, are needed in many modern optoelectronic devices, such as solar cells, flat-panel displays, touch-screen sensors, light emitting diodes and transparent thin film transistors. In this talk, I will highlight our study on the band structure and doping control of TCOs. In particular, I will discuss (i) the fundamental band structures and defect properties for the TCOs; (ii) how to achieve simultaneously high transparency and conductivity in n-type TCOs; (iii) why p-type TCOs are difficult to achieve; (iv) how to modify the band structure or design new materials to achieve p-type TCOs or even bipolarly dopable TCOs. Based on the understanding above, we hope to provide useful guidelines for the rational design of novel TCOs that are critical for the development of the next-generation optoelectronic materials.

Resume : Photocatalytic H2 evolution on virtually any pristine semiconductor surface is characterized by low efficiencies due to trapping and recombination of charge carriers, and due to a sluggish kinetics of charge transfer (1). Thus, co-catalyst metal nanoparticles are typically decorated at the semiconductor surface to reach reasonable photocatalytic yields. For this, most common strategies involve wet chemical methods, e.g. impregnation, chemical reduction or photo-deposition. An intriguing, alternative pathway is ?solid state dewetting?: as-deposited thin (nm-thick) metal films on a given surface are usually metastable and when heated to a certain temperature tend to ?dewet?, i.e. they break up and aggregate into defined metal particles (2). Factors such as the initial metal film thickness and composition, treatment temperature, atmosphere and time, can influence morphological and physicochemical features of the dewetted particles (2,3) (e.g. shape, size, dispersion, composition and crystallinity, among others) that are key for their co-catalytic ability in photocatalytic reactions. This talk discusses the use of dewetting as a precise nanostructuring tool to form functional metal nanoparticles at highly-defined TiO2 nanotube surfaces (4), namely to engineer catalyst/semiconductor platforms for light-driven reactions. In particular, we discuss how metal dewetting, steered in size, order, and composition, and synergistically combined with additional self-ordering principles (e.g. alloying, dealloying), can enable various types of functionalization of semiconductor surfaces for photocatalytic applications (5?8). (1) Takanabe, K. ACS Catal. 2017, 7 (11), 8006?8022. (2) Thompson, C. V. Annu. Rev. Mater. Res. 2012, 42 (1), 399?434. (3) Leroy, F.; Borowik, ?.; Cheynis, F.; Almadori, Y.; Curiotto, S.; Trautmann, M.; Barbé, J. C.; Müller, P. Surf. Sci. Rep. 2016, 71 (2), 391?409. (4) Yoo, J. E.; Lee, K.; Altomare, M.; Selli, E.; Schmuki, P. Angew. Chemie Int. Ed. 2013, 52 (29), 7514?7517. (5) Nguyen, N. T.; Altomare, M.; Yoo, J.; Schmuki, P. Adv. Mater. 2015, 27 (20), 3208?3215. (6) Altomare, M.; Nguyen, N. T.; Hejazi, S.; Schmuki, P. Adv. Funct. Mater. 2018, 28 (2), 1704259. (7) Spanu, D.; Recchia, S.; Mohajernia, S.; Schmuki, P.; Altomare, M. Appl. Catal. B Environ. 2018, 237 (May), 198?205. (8) Spanu, D.; Recchia, S.; Mohajernia, S.; Tomanec, O.; Kment, ?.; Zboril, R.; Schmuki, P.; Altomare, M. ACS Catal. 2018, 8 (6), 5298?5305.

Resume : The growing interest for environmental protection and the pursuit for renewable and clean energy sources have made the TiO2-assisted photoelectrochemical water splitting a very active research area. For such application, TiO2 nanoparticles are commonly used due to their superior performances, with anatase being the most commonly observed polymorph in small particles. The study and characterization of native point defects is of paramount importance for understanding the electronic properties of the material and the impact on the photocatalytic activity. Moreover, native defects play a fundamental role also in doped systems, where they can compensate for the defect-introduced carriers. Although several first-principles studies of native point defects in TiO2 anatase exist, they are mostly consider a few of them at a time. The different levels of theory employed in the literature do not allow for a direct calculation of the equilibrium concentrations as different formation energies are often reported with different functionals and corrections schemes.In this study, we comprehensively investigate the stability of native point defects in TiO2 anatase using the GGA+U approach. All native point defects and their ionized states are considered. We systematically compare state-of-the-art methods for obtaining reliable formation energies and correcting for finite-size-errors. Equilibrium defect and carriers concentrations are then calculated with respect to different growth conditions.

Resume : Semiconductor oxides nanowires (NWs) are an excellent benchmark to produce complex nanostructures, which could lead to novel architectures in a NW-heterostructure morphology with enhanced physical properties. Recently, wide band gap oxides, such as Zn2GeO4, are emerging as potential candidates for applications in high power devices or in ultraviolet-solar blind photodetectors [1]. In this work, we report the synthesis and characterization of complex nanostructures of oxide NWs in which Zn2GeO4 NWs combine with SnO2 particles, in a self-organized manner. The synthesis method is the thermal evaporation of the suitable chemical precursors on a catalyst-free basis via a vapour-solid mechanism. Electron microscopy measurements have been carried out to assess the morphology, the microstructure and determine the orientation of the NWs. The results support a model growth in which the Plateau-Rayleigh mechanism [2] would produce a pattern of germanium oxide amorphous particles along the Zn2GeO4 NW. In addition, under suitable kinetic conditions, these particles act as nucleation sites for well-faceted SnO2 crystals. The luminescence properties have been assessed by means of cathodoluminescence and photoluminescence techniques. In addition, optical confinement effects have been observed, what could be further exploited in the design of optical microcavities. References [1] H. Mizoguchi, T. Kamiya, S. Matsuishi, H. Hosono, ?A germanate transparent conductive oxide?, Nature Communications, 2, 470 (2011). [2] R. W. Day, M. N. Mankin, R. Gao, Y. No, S. Kim, D. C. Bell, H. Park and C. M. Lieber, ?Plateau?Rayleigh crystal growth of periodic shells on one-dimensional substrates? Nature Nanotechnology, 10, 345 (2015).

Resume : Many materials for energy storage undergo phase transformations to store and release the energy in form of hydrogen, ions or electrons involving mass transport. To understand and finally overcome the rate limiting processes detailed understanding of the systems is necessary. This includes the structure of crystalline systems, the reaction pathway with possible metastable phases as well as the mesoscale to identify inhomogeneities and long term effects. Here X-rays, especially synchrotron radiation, can provide a wide range of methods spanning from XRD to characterize the crystalline phases, spectroscopy to characterize chemical species to spatially resolved techniques (X-ray microscopy) or combinations thereof. This presentation will show some examples for different techniques and results from metal hydrides for hydrogen storage, intercalation and conversion materials for Li-ion batteries and catalyst particles. With the advance of X-ray free electron lasers the door has opened to directly study ultrafast phenomena such as i.e. nucleation also in the time domain.

Resume : Multi-Principal-Element Alloys (MPEAs) belong to a new metallurgical paradigm based on the alloying of four or more elements with equal concentrations. Most of reports concerning these alloys describe their structure, microstructure and mechanical properties, whereas functional properties such as, hydrogen sorption, are only scarcely investigated. We present here the study of hydrogen absorption properties of MPEAs based on refractory metals. The TiVZrNbX (X = Mg, Al and Ta) alloys have been synthesized by classical high temperature methods or mechanosynthesis under inert atmosphere. To directly produce hydrides we have employed the reactive ball milling under hydrogen gas starting from the pure metal powders. The properties of materials have been studied by several experimental techniques: X-ray diffraction, electron microscopy, neutron diffraction, pressure-composition-isotherm, thermal desorption spectroscopy. All the alloys are bcc single-phased and undergo one-step reaction with hydrogen. We suggest that the lattice distortion, δ, might play an important role: larger δ would favours a single-step reaction, whereas small δ would favour a two-steps phase, as encountered for conventional bcc alloys. The hydrogen absorption/desorption is completely reversible and the capacities varies between 2 and 3 wt%. In summary, this is an original research topic in the field of solid-state hydrogen storage that might open new routes for the design of multifunctional materials.

Resume : MgH2 is one of the most investigated solid-state hydrides as promising hydrogen storage materials due to its large hydrogen capacity of 7.6 mass% and the high abundance of Mg in Earth's crust. The high thermodynamics (-75 kJ/mol H2) of MgH2 originated from the strong Mg-H binding energy results in the serious issue of high dehydrogenation temperature, i.e. above 300°C for pure MgH2. Forming an alloy with a hydride non-forming transition metal has been approved to be a feasible approach to destabilize MgH2. For example, when alloying with Ni to form a binary Mg2Ni, the hydride transforms from MgH2 to Mg2NiH4, and the enthalpy is reduced from -75 to -64 kJ/mol H2. Ternary alloys like RMg2Ni9 and (Mg,Ca)Ni2 can further destabilize MgH2 and can absorb and desorb hydrogen at room temperature, whereas the gravimetric hydrogen capacity is limited due to the Ni-rich composition. It is hard to produce an Mg-based ternary alloy with a homogeneous elemental distribution by melting process because of the thermodynamic immiscibility of Mg in many systems. This technical issue may be solved by the application of severe plastic deformation using high-pressure torsion (HPT). In this study, a new Mg-rich ternary alloy Mg4NiPd was designed and prepared successfully by HPT. Preliminary results indicate hydrogen absorption and desorption proceed at room temperature, suggesting a new approach to design and prepare Mg-based alloys exceed the scope of known equilibrium phase diagrams for room temperature hydrogen storage.

Resume : Hydrogen-rich hydrides attract great attention due to recent theoretical [1] and then experimental discovery of record high-temperature superconductivity in H3S (TC = 203 K at 155 GPa [2]). Here we perform a systematic evolutionary search for new phases in the Fe-H [3], Th-H [4], U-H [5] and other numerous systems under pressure [6] in order to predict new materials which are unique high-temperature superconductors. We predict new hydride phases at various pressures using the variable-composition search as implemented in evolutionary algorithm USPEX [7-9]. Among the Fe-H system two potentially high-TC FeH5 and FeH6 phases in the pressure range from 150 to 300 GPa were predicted and were found to be superconducting within Bardeen-Cooper-Schrieffer theory, with TC values of up to 46 K. Several new thorium hydrides were predicted to be stable under pressure using evolutionary algorithm USPEX, including ThH3, Th3H10, ThH4, ThH6, ThH7 and ThH10. Fm3 ̅mThH10 was found to be the highest-temperature superconductor with TC in the range 221-305 K at 100 GPa. Actinide hydrides show, i.e. AcH16 was predicted to be stable at 110 GPa with TC of 241 K. To continue this theoretical study, we performed an experimental synthesis of Th-H phases at high-pressures including ThH10. Obteined results can be found in Ref. [10]. Acknowledgments: Authors thank RFBR foundation № 19-03-00100. This work was supported by RFBR foundation № 19-03-00100 and facie foundation, grant UMNIK №13408GU/2018. References [1] D. Duan et al., Sci. Rep. 2018, 4, 6968. [2] A.P. Drozdov et al. Nature. 2015, 525, 73–76. [3] A.G. Kvashnin at al. J. Phys. Chem. C 2018, 122 4731-4736. [4] A.G. Kvashnin et al. ACS Applied Materials & Interfaces 2018, 10, 43809–43816. [5] I.A. Kruglov et al. Sci. Adv. 2018, 4, eaat9776. [6] D.V. Semenok et al. J. Phys. Chem. Lett. 2018, 8, 1920-1926. [7] A.O. Lyakhov et al. Comp. Phys. Comm. 2013, 184, 1172-1182. [8] A.R. Oganov et al. J. Chem. Phys. 2006, 124, 244704. [9] A.R. Oganov et al. Acc. Chem. Res. 2011, 44 227-237. [10] D.V. Semenok et al. 2019, arXiv:1902.10206.

Resume : Lithium ion batteries, which are the most widely used among the secondary battery types, have high capacities and cycling life. The most important characteristic of the batteries is that they can store electrical energy better than competing technologies, they can be used for a long time, and their energy density are better than other battery technologies. These batteries are widely used in smart devices, laptops, tablets etc. in portable devices, smart home systems, and electrical vehicles. The lithium-ion batteries are mainly composed of positive electrode (cathode), negative electrode (anode), electrolyte and separator. A positive electrode is the lithium ion source which is consisting of transition metal oxides, such as LiCoO2, LiMn2O4. The negative electrode hosts lithium ions. While the electrolyte provides ionic conductivity, the separator is used to separate the electrodes. During the charging process, Li ions are extracted from the positive electrode and form a compound on the negative electrode. The theoretical capacity of lithium ion batteries is expected to remain at the same value in each cycle without changing the ingredients. However, this does not take place as expected and lithium ions in the battery can be produced or consumed by side reactions during charging/discharging. When the capacity stability of the battery deteriorates, there is a loss of capacity and a significant decrease in the performance of the battery occurs in long cycles. Anode and cathode materials of the batteries directly affect the capacity and cycle life. Lithium rich layered metal oxides are a high energy density cathode material for new generation lithium-ion batteries (LIBs). This cathode materials have Li[Li1/3Mn2/3]O2 and LiMO2 (M: Ni, Co, Mn, Al etc.) structure and exhibit higher irreversible capacity and cycle life than conventional cathode materials. Nano-sized Li-rich layered metal oxides shorten the electronic/ionic transfer path, facilitating the diffusion of lithium ions and effectively enhancing performance. The lithium van der walls are placed in the gaps and the material has a performance exceeding 280 mAh/g capacity. The nominal voltage is ~4.2 V. There are transition metals with different properties within the structure. The lithium rich cathode material consists of lithium as well as transition metal layers such as Ni, Co and Mn, and incorporates the beneficial effects of these metals. Nickel increases capacity and Mn increases thermal stability while cobalt improves the capacity retention rate performance of the battery. Apart from this, doping of metals such as Al, Zn, Nb, Mg, Fe etc. is increased to performance. In this study, the stoichiometry of metals in the lithium rich cathode material formulation was investigated by changing Mn, Ni and Co ratios. Li1.2MnxCoyNizAl0.02 (x:0.50;0.51;0.52, y:0.14;0.16;0.18, z:0.14;0.16;0.18) formulation was used and the prepared lithium rich cathode active powders were structurally characterized by XRD and Li-rich cathodes were tested by electrochemical methods.

Resume : Antiferroelectrics have been studied as energy storage capacitors due to their higher energy storage density than ferroelectrics and paraelectrics. Environmental concerns for toxic lead have focused studies on lead-free antiferroelectric materials. Recently, we reported that the 0.92NaNbO3-0.08SrZrO3 (NNSZ8) thin film was fabricated on a (110) SrTiO3 (STO) single crystal substrate by a pulsed laser deposition (PLD).[1] The NNSZ8 film showed a double polarization-electric field (P-E) hysteresis loop. In this study, in order to increase the energy storage density, the NNSZ8 thin films were fabricated on a SrRuO3(SRO)-coated (001) STO substrates. The NNSZ8 films with a thickness of about 1.0 ?m were epitaxially grown on the SRO/(001)STO substrate. SEM observation revealed that the NNSZ8 films had flat surface morphology. X-ray reciprocal space mapping indicated that the films had antiferroelectric domains. Their insulation performance was sufficiently high. The double P-E hysteresis loop could also be observed for the NNSZ8/SRO/(001)STO film at room temperature but also at high temperature of 150 oC. The remanent polarization of the NNSZ8/SRO/(001)STO film was closer to zero. Therefore, the present NNSZ8/SRO/(001)STO film had higher energy storage density than the previously reported NNSZ8/SRO/(110)STO film. [1] I. Fujii, T. Shimasaki, T. Nobe, H. Adachi, and T. Wada, Jpn. J. Appl. Phys., 57, 11UF13 (2018).

Resume : Zinc oxide is one of the best photocatalyst for the UV-light sensitised water treatment technologies. Various dopants allow to narrow its band gap and extends its activity to the visible light spectra but for practical applications its properties must get further improvements. The main objective of the current work was to synthesise and test ZnO oxide doped with Zinc metal. For this ZnO based photocatalyst films were deposited using magnetron sputtering with in-situ control of the physical vapor phase composition. Precise monitoring and control of Zinc, Argon and oxygen content in the plasma phase allowed to identify small range of parameters which led to the formation of samples in the intermediate zone between metallic Zn and completely oxidised ZnO phase. Photocatalytic bleaching of Methylene Blue and Rhodamine B in aqueous solution has demonstrated that in such samples metallic zinc acts as a dopant and up to some extent improves the photocatalytic efficiency of ZnO oxide. The relationship between magnetron sputtering process parameters and film properties (crystal phase, elemental and chemical composition, surface roughness, optical properties) are provided and their influence to the high photocatalytic activity of the films is discussed.

Resume : Nitrogen dioxide (NO2) is a highly reactive, hazardous gas and a prominent air pollutant that should be detected at very low concentrations in the ppb rather than ppm range. Low threshold, highly sensitive and selective detection of NO2 by SnO2 has lately appeared as a particularly important issue [1,2]. In this work, thin-film nano-heterostructures of SnO2/TiO2, highly sensitive to NO2, were obtained in a two-step process: (i) magnetron sputtering, MS followed by (ii) Langmuir-Blodgett, L-B, technique. Morphology, crystallographic and electronic properties of the films were studied by SEM, XRD in glancing incidence geometry, XPS, UV-VIS-NIR spectrophotometry, respectively. It was found that amorphous SnO2 thin films detected relatively low concentrations of NO2 of about 200 ppb. More than two orders of magnitude change in the electrical resistivity upon exposure to NO2 was further enhanced in SnO2/TiO2 to reach a three-fold giant gas response. The best sensor responses were obtained at the lowest operating temperatures of about 120oC which is typical for nanomaterials. National Science Centre, Poland project 2016/23/B/ST7/00894 is acknowledged. [1] A. Sharma et al., Sensors Actuators B. 181 (2013) 735?742 [2] J.H. Bang, et al., Sensors Actuators B. 274 (2018) 356?369. doi:10.1016/J.SNB.2018.07.158.

Resume : Methane dry reforming of is a promising way to convert both greenhouse gases, as well as a model reaction to study the transformation of other fuels. Nickel based catalysts attract attention because of their high activity but the main disadvantage is the rapid deactivation due to carbonization and blocking of the Ni centers. Promising supports of Ni catalysts are oxides with high oxygen mobility for gasification of coke precursors to increase stability. Oxygen mobility and reactivity of Ce-Zr oxide can be increased by introducing additional cations. However, the synthesis of single phase mixed oxides by traditional methods (co-precipitation, Pechini) is a challenge. In this work, samples of catalysts based on Ti and Nb-doped Ce-Zr single-phase oxides were synthesized and characterized in detail. Samples of complex oxides were synthesized in supercritical alcohols in flow-through mode, followed by impregnation with Ni, drying and calcination. Samples were investigated by means of XRD, IR, Raman, TEM, XPS. The catalytic activity was studied in methane and ethanol dry reforming using fixed bed reactors. The introduction of cations changes the electronic properties of oxides, the oxidation state and the concentration of cerium and nickel on the surface. The highest catalytic activity is achieved on a sample doped with Nb, while the sample, jointly doped with Nb and Ti, exhibits the lowest deactivation rate. The study was funded by the Russian Science Foundation (Project 18-73-10167).

Resume : HfO2-based thin films are mostly considered as high-k dielectrics for microelectronics. However, doped with different ions, they can offer promising optical applications. In this work, the effect of doping and processing conditions on structural and optical properties of the HfO2 films doped with different elements (Si, Ge, N) grown by radio-frequency magnetron sputtering was studied by means of spectroscopic ellipsometry, FTIR, SEM, TEM and photoluminescence (PL) methods. It was observed that the film morphology depends significantly on the deposition atmosphere. The films grown in Ar plasma showed the presence of grains with a mean size about 100?nm. Post annealing treatments result in a phase separation process and formation of tetragonal HfO2 and SiOx (or GeOx) phases. The films grown with Ar-N2 plasma were found to be denser and smoother whatever the annealing temperature. Thermal treatments stimulate the formation of tetragonal HfO2 phase as well as the SiOxNy (or GeOxNy) phases that was confirmed by FTIR spectra. The PL spectra of all annealed films showed broad PL band in the UV-visible spectral range. The shape of PL band depends on the contribution of different host defects. Their nature and the mechanism of phase separation are analyzed and discussed in details.

Resume : Enhancing the performance of the omnipresent TiO2 photocatalyst by intercepting the inherent shortfalls that prompt its short-lived charge carriers and poor visible-light sensitization, is a hot topic in solar-driven oxidative water-treatment. Nanoscale heterojunction coupling of TiO2 with semiconductor metal-oxide co-catalysts may offer an advantageous way to tailor its photo-inducible energy harvesting ability and electron-transfer properties via the inclusion of synergistic quantum interactions. Both CeO2 and Bi2O3 in its alpha- and beta- polymorphs, are attractive dopant materials owing to their suitable band-gap edge positions for triggering the visible-light activity and enhancing the charge carrier separation. [1,2] CeO2 may particularly offer room-temperature oxygen storage capacity and rapidly interchangeable oxygen lattice species, through its highly active Ce3 /Ce4 redox couple, allowing thus to improve the overall degradation kinetics. In this context, we demonstrate the in-situ fabrication of novel TiO2-CeO2-Bi2O3 nano-heterojunction structures anchored in open-tubular silica capillaries, which can be simultaneously deployed as microreactors and optical light guides in continuous-flow photocatalysis. The synthesis is accomplished via sol-gel assisted solvothermal growth methodology, using titanium(IV) n-propoxide, cerium(III) and bismuth(III) nitrates as metal-oxide precursors, in addition to stabilizing and structure directing additives. Ti(IV)-rich mixtures, with fixed and varied proportions of cerium and bismuth oxide precursors respectively, are prepared in ice-bath, loaded into pre-activated hollow optical fiber silica capillaries, then subjected to solvothermal treatment at 100 °C for 24 hours, and subsequently carefully dried and calcined up to 350 °C. In this work, we particularly examine the role of the Bi(III)-dopant concentration (0.5-5 %mol) as well as the calcination temperature (300-350°C) and ramp, on tuning the microscopic morphology, crystal structure and optical absorption properties of the photocatalysts for solar-light sensitization. Initial structure-to-performance relationships of elementary photocatalytic reactors are established in correlation with the continuous-flow degradation of model chlorophenol compounds in water. [1] L.T.T. Tuyen et al. J. Environ. Chem. Eng. 6 (2018) 5999. [2] X. Xiao et al. Appl. Catal. B ? Environ. 140-141 (2013) 433.

Resume : Oxyhydrides have attracted great attention in recent years due to their photochromic, magnetic, high temperature superconducting, and photocatalytic properties. In this work, we focused on cerium oxyhidride (CeHO), which may show the same properties as other lanthanide oxyhydrides. Using Bärnighausen tree based spacegroups method, we have predicted possible crystal structures of CeHO. We report that, according to the ab initio calculations, several different structures show mechanical stability at 0K and might coexist at the same conditions. Lattice parameters and X-ray diffraction pattern have been derived. Electronic and optical properties for these stable phases are calculated by first-principles calculations within generalized gradient approximations and hybrid functional. We found that CeHO is a wide band gap material. Spin-polarized spectra detect magnetic properties existing for this oxyhydride. Distinct from CeO2 with Ce-4f located inside the band gap, the Ce-4f orbitals are inside conductive band and are less localized.

Resume : Single atom catalysis (SAC) is the new frontier of heterogenous catalysis where the catalyst consists of single metal atoms dispersed on a support [1]. Reducibile oxides, such as, cerium oxides, CeO2-x, and iron oxides, Fe3O4 and ?-Fe2O3, are an explored possibility as possible supports, while the single atoms catalysts are constituted by single noble metal atoms dispersed on the oxides. Density functional calculations (DFT) have been carried out to investigate the oxide surfaces, their stability and reducibility, and the preferred configurations for the noble metal atoms in absorption, and Ce(Fe) substitutional sites. We have found the most stable reconstruction for the maghemite (001) surface, and the increased reducibility of maghemite surfaces compared to the corresponding magnetite ones. The reasons for the increased reducibility have been investigated. Also, our results show a larger stability of absorbed atoms on the surfaces of iron oxides than on ceria oxides. Finally, we have investigated single Ag catalysts for H2 dissociation on ceria, and compared them to Cu and Au. We have found that when a single nobel metal atom is adsorbed on CeO2, the activation energies drop with respect to those of pure ceria, and they are slightly lower for Ag than Au and Cu. Instead, when the noble metals substitute a Ce atom, we have calculated only for Ag a significative decrease of the barrier energy. [1] [1] J. Liu, ACS Catal. 7, 34 (2017).

Resume : The recent discovery of ?non-classical? electrostriction in gadolinium-doped ceria (Ce1-xGdxO2-?) (CGO) [1] attracts a great interest as it opens to a novel generation of biocompatible devices with exceptional electromechanical performances. CGO is a non-piezoelectric material with an electrostriction coefficient that overcomes traditional PZT materials by several orders of magnitude, e.g. Q= 0.02 m4/C2 [2] for Pb(Mg1/3Nb2/3)O3 versus Q= 400 m4/C2 for Ce0.8Gd0.2O2-? [3]. Remarkably, the electromechanical effect is attributed to the oxygen vacancies in the lattice and especially to the O-Ce-Vo complexes interacting with external electric fields along the (111) cell orientation [1,4]. Moreover, grain boundaries and disorder affect the electrostriction properties in the material, heavily hindering the electromechanical performances [3]. In this work, we show electrostriction in epitaxial (i.e. grain boundaries-free) CGO thin film in different crystal orientations and thicknesses. Thanks to highly coherent microstructure we can match theoretical principles with experimental data. We find that the electrostriction effect is highly enhanced in textured structures with exceptional values of Q? 1000 m4/C2 for thin films. References: 1. R. Korobko et al., Adv. Mater. 2012, 24, 5857?5861. 2. J. Kuwata et al., Jpn. J. Appl. Phys., 1980, 19, 2099. 3. A. Kabir et al.,Acta Materialia, 2019, 174, 53-60. 4. Y. Li et al., AIP Advances, 2016, 6, 055320.

Resume : The aim of the current study was to deposit TiO2 thin films by chemical spray pyrolysis method with different titanium isopropoxide (TTIP):acetylacetone (acacH) molar ratios in the solution and determine how acacH increase in starting solution effects the morphology, structure, surface chemical composition and photocatalytic activity of the obtained TiO2 films. TTIP:acacH molar ratio in the spray solution was varied from 1:3 to 1:10. TiO2 films were deposited by the spray pyrolysis method onto the glass substrates at 350°C and heat-treated at 500°C for 1 h. TiO2 films showed the transparency of ca 80% in the visible spectral region, thickness of 400 nm and band gap of ca 3.3 eV irrespective of the TTIP:acacH molar ratio in the spray solution. According to XRD results, TiO2 films consist of anatase crystalline phase with the mean crystallite size in the range of 27-47 nm. Raman results, however, demonstrated that the films deposited from TTIP:acacH molar ratio of 1:5 show the mixture of anatase and rutile phases. Self-cleaning properties of the films were estimated using stearic acid (SA) test. Thin layer of 8.8 mM SA solution was spin coated onto the TiO2 film and the degradation rate of SA as a function of irradiation time was monitored by FTIR. It was found that with an increase in the TTIP:acacH molar ratio from 1:3 to 1:8 the k increases from 0.015 to the 0.314. The increase of SA degradation rate with the rise in acacH amount in the precursor solution will be discussed.

Resume : Zinc oxide (ZnO) is one of the most versatile semiconductor materials and has been extensively investigated due to its remarkable interest from the technological point of view, namely in areas as optoelectronics, biomedicine, catalysis or photovoltaics. This material has the ability to be grown by a large number of techniques, presenting one of the richest varieties of morphologies, which are known to offer different functional behaviours. Therefore, several methods have been employed to control the production of its micro and nanostructures. In this talk, the development of the laser-assisted flow deposition (LAFD) method for the production of highly crystalline ZnO crystals will be highlighted. Moreover, since the crystals produced by this technique evidence excellent optical quality, optical characterisation was selected as the ideal tool to evaluate their potential applications. In fact, luminescence-based techniques constitute a powerful way to assess the presence of defects that may have a strong influence on the performance of ZnO once applied in photovoltaic cells or as a photocatalytic agent, for instance. Additionally, the photoluminescence (PL) signal can be used as a transduction mechanism in optical-based sensors. This is an excellent method to probe material?s surface/interfaces and the PL signals are usually very sensitive to the chemical/biological species that are placed on the semiconductor?s surface, allowing to identify changes in the target analyte concentrations and providing high sensitivity and selectivity to the devices. Thus, the application of the LAFD-produced structures in the mentioned fields will be also discussed.

Resume : ZnO is a direct wide bandgap semiconductor with a broad application potential in UV light-emitting devices and detectors, field-effect transistors, solar cells, piezoelectric nanogenerators, or chemical sensors. Despite a large number of applications, the growth of ZnO from solutions is not well understood and the growth technology mostly relies on empirical results. We investigate the growth of ZnO vertical nanorod arrays on patterned substrates and seed layers in both conventional batch reactors and non-conventional continuous-flow reactors and point out the differences. Unlike the batch reactors, in continuous-flow reactors the solution supersaturation can be accurately controlled, which enables to control the growth rates, the aspect ratio, the incorporation of dopants and impurities, and the density of defects. We further report on fundamental mechanisms of nucleation and growth of the nanorods on the substrates modified by focused ion beam (FIB). Thanks to FIB processing we are able to control the nucleation and positioning of the nanorods. This method enables the nucleation to be uniform even on substrates whose morphology is originally non-uniform. Representative examples of substrates with non-uniform morphology are GaN epitaxial templates, which are commercially widely used as an alternative of expensive GaN monocrystals. Moreover, we present measurements of electronic transport in a single vertically oriented n-type ZnO nanorod on p-type GaN substrate using a nanoprobe in a scanning electron microscope.

Resume : ZnO nanowires (NWs) have recently been widely used in energy and environment-related devices, including gas sensors, piezoelectric nanogenerators, solar cells and UV LEDs. For those applications, intrinsically n-type ZnO nanostructures have intentionally been n-doped by incorporating metal (III) elements, mainly by vapour phase deposition techniques. However, controlling the doping during the growth of ZnO NWs by solution deposition techniques is still a major issue. Here we show that the doping of ZnO NWs, mainly with gallium, can be achieved by the low-cost, low-temperature, and easily implemented chemical bath deposition technique. Gallium nitrate and ammonia are added in various concentrations to the standard precursors [1], to tune not only the crystal structure of ZnO NWs and hence their morphology, but also the gallium incorporation. The formation mechanisms are thoroughly investigated and supported by thermodynamic simulations: the doping only occurs if the pH of the solution favours the formation of charged gallium hydroxide complexes. This further emphasizes the electrostatic origin of doping mechanisms in aqueous media [2]. The incorporation of gallium is eventually investigated by energy dispersive x-ray spectroscopy using scanning TEM. Furthermore, temperature-dependent Raman spectroscopy shows the occurrence of characteristic additional modes, revealing either the doping of ZnO NWs, or the formation of compensating defects. These findings show a simple, thorough way to control the doping of ZnO NWs, which opens the way for their more efficient integration into nanoscale devices. [1] R. Parize et al., The Journal of Physical Chemistry C 120, 5242 (2016) [2] C. Verrier et al., Inorganic Chemistry 56, 3573 (2017)

Resume : Modern magneto-electronic devices are ultimately controlled by electric currents, inherently involving a significant energy loss due to heat dissipation. Substituting electric currents by electric fields, where a voltage-induced ionic motion (magneto-ionics) is utilized for the control of magnetism is expected to provide ultra-low power consumption and could be crucial for energy-efficient applications. By means of positron annihilation spectroscopy and magnetometry techniques we have investigated the electrolyte-gated and defect-mediated oxygen and cobalt ions migration in paramagnetic Co3O4, which allows for voltage-controlled ON-OFF room temperature ferromagnetism [1]. Applying a negative voltage reduces Co3O4 to Co (ferromagnetism; ON) and results in a graded material including Co- and O-rich regions. Subsequently, a positive bias reverses the process oxidizing Co back to Co3O4 (paramagnetism; OFF). We show, that this gate-induced O and Co transport is driven by complex vacancies (clusters consisting of both cobalt and oxygen vacancies). Moreover, the O transport is in addition assisted by grain boundaries, which may act as diffusion channels and allow for an exceedingly large incorporation of oxygen. The steady states as a function of bias as well as kinetics of defect-assisted ion migration will be discussed in detail. [1] A. Quintana, E. Mene?ndez, M.O. Liedke, M. Butterling, A. Wagner, et al. ACS Nano 12, 10291 (2018)

Resume : For several years, the field of physics has witnessed a huge development in the methods proposed to enhance the efficiency of solar cells. The spectral response of a photovoltaic cell doesn?t match with the solar emission spectrum because of the limited absorption of silicon, the main constituent of the active layer. One of the prominent research areas of materials for photovoltaics deals with photonic conversion by optimizing the solar spectrum absorption. In this work, we focus on the feasibility of rare-earth doped oxide matrix (Er3+ in Al2O3) to be an efficient media for up-conversion. Owing to the capability of Er3+ ions to combine two or more lower energy photons into one high-energy photon, they are being considered for the enhancement of the ef?ciency of the solar cells. It has been demonstrated that the spatial distribution as well as the nanostructuring control and the concentration of the active ions have been shown to affect the energy-transfer probability in the Er-doped material. For that reason, we have investigated, using Atom Probe Tomography, the 3D spatial distribution of Er atoms in Al2O3 matrix grown by ALD process. The nanostructure will be discussed and compared to optical properties.

Resume : Surface waters are steadily contaminated with hydrocarbons (HC) due to minor incidents during production, transportation, and handling of petroleum and its products as well as by major disasters like the Deepwater Horizon explosion. To date, sufficient methods for the economically efficient and ? in particular ? thorough remediation of these pollutants from water are missing. We developed a sustainable alternative to SotA oil spill response agents based on alkylphosphonic acid (PA) functionalized magnetite nanoparticles (NP).[1] That functionalization switches NP from hydrophilic to hydrophobic/oleophilic. This oleophilicity combined with the large specific surface area, eventuates in highly selective and efficient adsorption of HC on the NP surface. The superparamagnetic nature, allows for easy extraction of oil-soaked NP by an external magnetic field. We demonstrated the efficient extraction of different crude oils and organic solvents from the water surface under various conditions. Furthermore, we confirmed the excellent re-usability without significant degradation of the developed sorbent material over several cycles, which is attributed to the strong grafting of the PA on metal oxides and its excellent stability. In addition to the efficient adsorption of surface contaminations, we are able to extract different pollutants from the water column by minor adjustments in the sorbent material. [1] doi.org/10.1002/adfm.201805742

Resume : Two low-cost chemical methods of sol?gel and hydrothermal process have been strategically combined to fabricate barium titanate (BaTiO3) nanopowders. This method was tested for various synthesis temperatures (100 °C to 250 °C) employing barium dichloride (BaCl2) and titanium tetrachloride (TiCl4) as precursors and sodium hydroxide (NaOH) as mineralizer for synthesis of BaTiO3 nanopowders. BaTiO3 nanopowders synthesized at different temperatures demonstrated stabilization of hexagonal, cubic, tetragonal, orthorhombic and rhombohedral phases. The study shows that choosing suitable precursor and optimizing pressure and temperature; different meta-stable phases of BaTiO3 can be synthesized. So far, stabilization of rhombohedral phase at room temperature is not reported. Optical, magnetic and non-linear optical properties of different meta-stable phases of BaTiO3 have been studied. In addition, the band structure, Raman and infrared vibrational modes are computed by density functional theory (DFT). Influence of post-annealing on the thermal stability and properties by different dopants such as tin (Sn(II), Sn(IV)), zinc (Zn(II)), etc on rhombohedral phase BaTiO3 was investigated. For example, increase in wt% of Sn(IV) dopant ion doping retained the rhombohedral phase of BaTiO3, while Sn(II) doping stabilized rhombohedral-orthorhombic-tetragonal phases with increase in doping wt%. Zn(II) doped BaTiO3 demonstrated superior second harmonic generation (SHG) properties.

Resume : In this study we investigated the influence of rare earth ion doping on the structural, magnetic and optical properties of CoFe2-xRExO4 (x = 0.01; 0.03; 0.05; 0.1; 0.2; 0.3) ferrite thin films obtained by pulsed laser deposition. The monocrystalline (100) Si substrate was placed at a distance of 5 cm in front of the target during the 60 min deposition. The Nd-YAG laser (532 nm) fluence was kept at 5 J/cm2. The X-ray diffraction and Raman spectroscopy results on the bulk materials, which were used as targets during deposition, revealed the formation of residual phases as the concentration of RE dopant was increased. However, the thin films presented diffraction lines and vibrational modes corresponding only to cobalt ferrite. A lower crystallinity of the deposited samples was observed when higher RE concentrations were used. Due to the substitution of Fe by RE elements which possess large ionic radii, the lattice parameter of the thin films presented a monotonous increase. The magnetic response of the nanostructures was correlated to the magnetic moment of the RE dopant and to the structural properties of the films. The optical bandgaps derived from the reflectance spectra presented an increasing trend as the Yb and Dy concentrations were augmented. Considering the high chemical stability of cobalt ferrite, the thin films analyzed in this study can be adequate for sustainable hydrogen production applications.