Synthesis, processing and characterization of nanoscale multi functional oxide films V

Resume : Metalorganic vapor phase epitaxy and molecular beam epitaxy are exclusively used for fabricating semiconductor quantum structures, although they require large amounts of capital cost. Conversely, sputtering is a cost-effective approach for depositing large-area amorphous or polycrystalline thin films. We have been developing a novel epitaxial growth technique by combining the virtues of these technologies: helicon-wave-excited-plasma sputtering epitaxy (HWPSE) [Chichibu et al., JAP 91, 874 (2002)] so that large-area epitaxial growth can be realized in a simple system at low cost. In this presentation, HWPSE of reduced donor concentration Zn-polar (0001) ZnO homoepitaxial films exhibiting a step-and-terrace surface structure with the terrace width as wide as 0.85μm and a monolayer height of 0.26 nm will be demonstrated. Using a crystalline ZnO target prepared by the hydrothermal technique, instead of the target synthesized by the chemical vapor transport, residual concentrations of B, C, Cr, Li, and Si in the epilayers underran the detection limits of secondary-ion-mass spectrometry. Because the present target do not contain Ga or In, low temperature photoluminescence (PL) spectra were dominated by sharp emission peaks originating from the recombination of free excitons and excitons bound exclusively to a neutral Al, of which concentration was 2x10^16 cm-3. The full-width at half-maximum value of the near-band-edge emission at room temperature became as narrow as 65 meV

Resume : In the field of multiferroic (MF) materials several systems have shown the coexistence of electric and magnetic order with coupling between them. However, direct evidences of spintronic functionalities in presence of magnetoelectric coupling are still not systematically reported. We present direct demonstration of spintronic functionalities: anisotropic magnetoresistance (AMR) and tunnel magnetoresistance (TMR) in several MF systems. We will focus on the occurrence of AMR at the ferroelectric domain walls of an archetypical MF, i.e. BiFeO3 (BFO), showing that BFO conductive domain walls display hysteretical AMR. This effect results from the ferromagnetic nature of domain walls magnetically coupled to the antiferromagnetic domains of BFO. [1] We have also studied a MF La1-xSrxMnO3 (LSMO)/ PZT epitaxial bilayer. We have observed that the electronic doping of LSMO is modified by the electric field generated by the adjacent ferroelectric, and that it produces significant changes on AMR stemming from the change on LSMO magnetic properties. [2] Focusing on TMR effects on MF structures, we have found that spin valve functionality naturally appears in a MF LSMO/PbTiO3/Co magnetic tunnel junction. This implies that the system shows memory functionality on top of the TMR effect, upgrading the junction performance. [3] [1] J. H. Lee, I. Fina, et al. Adv. Mat. 26, 7078 (2014). [2] D. Preziosi, I. Fina, et al. Phys. Rev. B 90, 125155 (2014). [3] A. Quindeau, I. Fina, et al. Submitted.

Resume : Ga-doped ZnO (GZO) is promising candidate as sensing materials for hydrogen sensor operated at low temperature. In semiconductor gas sensors, adsorption and desorption at surface or grain boundary have been considered as operation mechanisms. In this paper, we report characterization of surface and bulk chemical state of GZO films with focused on influences of thermal annealing. The GZO films were deposited by ion-plating with DC arc discharge under the oxygen gas flow rate of 5 (GZO5) and 25 sccm (GZO25), respectively. Considering gas sensing temperature, the films were annealed in nitrogen gas atmosphere. After the annealing, the carrier concentration increased in the GZO25, while it did not change in the GZO5. From the Zn 2p and O 1s spectra measured by surface sensitive soft x-ray photoemission spectroscopy, we only observed desorption of hydroxyl groups and other adsorbate species from surface by annealing in the both GZO films. On the other hand, in the Zn 2p spectra measured by bulk-sensitive hard x-ray photoemission spectroscopy, we observed clear change in the Zn 2p spectra corresponding to decrease of carrier concentration in the GZO25, and nearly no change in the GZO5. These observations are consistent with change of carrier concentration caused by the annealing. From detailed analysis on angle resolved photoelectron spectroscopy on the O 1s, it was suggested that the change of carrier concentration were caused by desorption of chemically adsorbed oxygen.

Resume : Amorphous oxide thin-film transistors (TFTs) have been extensively studied in the last decade due to their better properties compared to amorphous-silicon TFTs. They could be manufactured at low temperatures on inexpensive, light weight and flexible polymer substrates, opening the possibility for space applications. There have been very few studies about their performance and reliability under radiation. We deposited amorphous indium zinc oxide thin films having different In/(In+Zn) compositions by the pulsed laser deposition (PLD) technique. The deposited IZO films exhibited good optical properties in the visible and near infrared range, low resistivity and high mobility. After deposition, the films were submitted to gamma radiation from a 137Cs source up to a dose of 20 kGy (1 Gy = 1 J.kg-1) at a dose rate of 5 Gy/min. The experiments were performed under argon atmosphere and also under air for the sake of comparison. X-ray reflectivity and diffuse scattering investigations were performed to accurately measure the thickness and estimate changes induced by gamma radiation on the mass density and surface and interface roughness. Spectroscopic ellipsometry and optical reflectivity investigations were used to assess changes induced by the irradiation on the optical and electrical properties of the films. The results showed that amorphous films could tolerate higher doses than polycrystalline layers without a marked decrease of their properties.

Resume : Perovskite materials with ABO3 formula present interesting properties depending on their composition, and have been studied for their potential applications as gas sensors, fuel cells or catalyst. Perovskite ABO3 based on Rare Earth cation associated with 3d transition metal (A= La, Pr, Nd, Sm, and B=Co, Ni, Mn, Fe) can present thermochromic properties, it means a reversible change of optical and electrical properties with temperature. This transition, where a semiconducting behavior is observed at low temperature while metallic state is observed at high temperature, is directly dependent of the 3d element electronic structure, and the A cation size. The electronic structure of anion plays also a key role in structural and physical properties, and oxygen substitution by nitrogen can lead to modification of these properties. Due to higher energy of nitrogen 2p orbital, it gives thus an additional way to tune perovskite properties. In this work, several perovskites deposited by reactive magnetron sputtering are studied. Rare earth (RE= La, Pr, Nd, Sm) cobaltites (RECoO3) and Rare earth ferrite (REFeO3) films are deposited on (100) undoped Si single crystal and fused silica substrates, from two metallic targets RE and Fe or Co. The RE and Fe contents inside the growing films were controlled by the current applied to the targets. Oxygen or Oxygen/Nitrogen mixture is used as reactive atmosphere to form corresponding oxide or oxinitride. The chemical stoechiometry of the deposited material was checked by energy dispersive X-ray analyses. The amorphous films were then annealed to crystallize the perovskite, and the corresponding crystallized structure was checked by XRD measurements. Optical measurements were performed in UV, Visible and IR range (determined by UV-Visible and FTIR spectroscopy), and resistivity was determined by four probes methods at different temperatures (from 25°C up to 600°C), thanks to Linkam® heating device. This work presents the link between cation and anion elements and their direct influence on the perovskite properties.

Resume : Spinel zinc ferrite ZnxFe3-xO4 (0.1

Resume : Chemical vapor deposition (CVD) is a simple, low cost and easily transferred method to large scale for the growth of various deposition layers. In addition, deposition parameters such as the kind and the amount of precursors, deposition time and temperature, can simply be controlled. However, a small change in one of the above parameters can lead to different vanadium oxidation states with consequently different properties. In this paper, vanadium oxide coatings were fabricated using a chemical vapor deposition at atmospheric pressure (APCVD) on SnO2 pre-coated glass substrates using vanadyl (IV) acetylacetonate as vanadium precursor at 500 oC and O2, 2-propanol and ethanol as oxygen sources. The samples were characterized by x-ray diffraction, Raman spectroscopy, scanning electron Microscopy (SEM), UV-Vis-NIR spectroscopy measurements at temperatures below and above Tc, transmittance measurements as a function of temperature at an incident radiation of 1500 nm and cyclic voltammetry. The effect of oxygen source through the reactor on the properties of the samples is discussed.

Resume : Lithium titanate (Li4Ti5O12, LTO) is a promising anode material for the next generation of lithium ion batteries. Its physical properties and morphology (which consequently affect its electrochemical performance) highly depend on its synthesis method. FSP is an attractive process for the controlled one-step synthesis of functional multicomponent oxides from low cost precursors1. During FSP the liquid precursor is sprayed and dispersed into the flame zone with the aid of an oxidizing gas, combusted and converted into nanoparticles through droplet evaporation, nucleation, sintering and agglomeration. The main aim of this study is to control the growth process of LTO in order to maintain the desired particle properties. LTO nanoparticles of different sizes are synthesized by variation of the FSP processing conditions and characterized accordingly. By varying the O2 dispersion gas flow rate (20-50l/min), LTO nanoparticles’ size decreases from 21 to 14nm due to decrease of droplet concentration in the flame. However, as the interaction of the aforementioned physical processes is hard to investigate only by experiments2, numerical simulations based upon computational fluid dynamics techniques are implemented in order to examine the process steps and the effect of the FSP processing conditions on the particle size. 1 H.Torabmostaedi, T.Zhang, Chem. Eng. Res. Des. 92, 2470, 2014. 2 A.J.Gröhn, S.E.Pratsinis, A.Sánchez-Ferrer, R.Mezzenga, K.Wegner, Ind. Eng. Chem. Res. 53, 10734, 2014

Resume : Owing to their specific optical and electronic properties, ZnO thin films offer a promising alternative to indium tin oxide for applications in photovoltaics and transparent electronics. ZnO thin films were grown at room temperature by pulsed electron beam deposition under different growth parameters. Dense and smooth films are formed on SiO2 / Si wafer, large area glass or flexible substrates, and their stoichiometry and physical properties were controlled by the deposition geometry, nature and pressure of the gas during deposition. Electrical and optical properties of these large area ZnO thin films were mapped in each point by four point probes, optical transmittance in UV-visible-near infrared region and photoluminescence spectroscopy. Large variations of the O/Zn ratio were evidenced over a range of several centimeters thus allowing for the above mentioned measurements to be performed for various compositions. Transparent ZnO thin films show tunable resistivity and carrier density up to few orders of magnitude, making them interesting for low-cost transparent electronics, such as single step fabrication of thin film transistors or resistive random access memory devices.

Resume : The aim of this work is to investigate the expansion of an oxygen low-pressure microwave plasma. By measuring electron density and electron temperature, using Langmuir probe, we search the optimal parameters such as pressure and microwave power, to use in titanium and manganese films oxidation and surface modification. Titanium and manganese films were grown on Si (100) substrates by sputtering of a metallic titanium target and Pulsed Laser Deposition of a manganese target respectively. The effect of operating parameters such as substrate temperature, chamber pressure and plasma activation on the oxidation of these films was studied using GIXRD technique. We find that the electron density increases with the injected power into the plasma while the electron temperature keeps a constant value. In addition, the two quantities show a decrease when the plasma expands in the reactor. Moreover, electron density shows maximum value at low pressure (5mTorr – 20 mTorr) and high microwave power (300 – 400W) which led us to work at these conditions in the remote plasma assisted oxidation of titanium and manganese films. At a substrate temperature of 500 C and without plasma activation, we got a multiphase titanium oxide film with a predominantly TiO2 anatase phase. With plasma activation at this temperature, a pure phase of anatase was formed. In parallel, the exposure of manganese films to oxygen remote plasma led to the formation of a mixture of two phases of manganese dioxide (Ramsdellite and Pyrolusite), while the exposure to an oxygen gas without plasma activation led to the formation of Hausmanite (Mn3O4).

Resume : The van der Waals surfaces (0001) of InSe and GaSe layered semiconductors were for the first time used as substrates for growing Zn0.5Cd0.5O oxide films. It is shown that surface morphologies of the nanostructured oxide films deposited by means of radio-frequency magnetron sputtering onto InSe and GaSe substrates are different. The n-Zn0.5Cd0.5O/p-InSe heterojunctions showed diode-like behaviour. The atomic force microscopy characterization of the oxide films revealed that the nanostructures have domelike shapes and are distributed uniformly over the surface. Their lateral density is relatively high (~10^10 cm^-2) and they are the centres of light scattering. It was established that the nanostructurization of the oxide surface results in emergence of an additional photosensitivity band of the heterojunctions in infra-red region. The oxide films under investigation have defects caused by mechanical strain at the heterointerface. It was revealed that these defects induce shunt currents of the heterojunctions. We demonstrated that vacuum annealing of the samples can be successfully used to decrease the influence of the shunt currents. The changes in electrical properties were investigated by analyzing temperature and frequency dependences of current-voltage and capacitance-voltage characteristics, respectively. In addition, we established that vacuum annealing affects the band-structure of Zn0.5Cd0.5O and the band-gap-energy can be tuned by a value in the range of ~0.14 eV.

Resume : Using surface x-ray diffraction in combination with ab-initio calculations we have studied the atomic structure of ultra thin ZnO films deposited on Fe(110). In contrast to expectation that ZnO adopts the "graphitic" hexagonal Boron-nitride structure the Wurtzite (WZ) structure is observed. Its formation is related to oxygen impurities in Fe(110) hollow sites inducing an anisotropic charge redistribution within the film which is characterized by a metallic surface. Our results provide a deeper understanding of depolarization mechanisms in ultra thin polar films at the atomic scale.

Resume : Chemical spray pyrolysis (CSP) is a solution based deposition method that allows precursors to be mixed in varied ratios before deposition giving a wider degree of freedom in doping thin films for different applications. Doping TiO2 with zirconium improves the gate dielectric properties and its stability with a silicon substrate for metal-oxide-semiconductor based technologies. Zr-TiO2 films with different Zr concentrations (0 ? 40 mol%) were deposited at 450 oC onto quartz and Si substrates by CSP; followed by annealing at temperatures between 500 and 900 oC. The structural, morphological, optical and electrical properties of sprayed Zr-TiO2 films were studied. As-deposited Zr-TiO2 films showed an increase in smoothness and a decrease in the thickness, while the optical band gap (Eg) increased from 3.1 to 3.4 eV with increasing Zr amount. As-deposited TiO2 films exhibited anatase phase while the Zr-TiO2 samples were amorphous and anatase structure formed by annealing at 500 oC. Upon annealing at 600 oC, the mean crystallite sizes of Zr-TiO2 remain between 28 and 22 nm while the Eg increased to 3.4 eV irrespective of the Zr amount. Zr-TiO2 films annealed at 900 oC showed a mixture of anatase and rutile phases and decrease in Eg from 3.2 to 3.0 eV with increasing the Zr amount. The electrical properties of Zr-TiO2 were investigated in the metal-oxide-metal configuration, showing a strong dependence on the doping level.

Resume : Research of external action influence processes on the evolution of materials structures is one of the fundamental tasks with important applied significance. There are nonlinear processes in real systems. One of the perspective methods for description of such structures is the method of fractal analysis. The calculations of fractal parameters based on the geometric characteristics of the system, therefore spatial pictures of investigated structures can be obtained by the computer modeling of the nonlinear processes by the usage of cellular automata. The structure of solid describes its physical and chemical properties, any changes in material structure affect its mechanical, optical, electrical and other properties. In this work the influence of fractality of clusters forming on the heterogeneous surface of silicium oxide SiO2 on the photophysical processes are studied. General information about photoprocesses mechanisms are obtained based on model system investigation, for example, luminescent dye molecules applying on a solid surface. The components of system were organic dye Bengal Rose (BR) and aromatic Hydrocarbon Anthracene (An). Dye molecules are sorbed from spirit solution on the surface of SiO2 adding An dissolved in hexane. After laser irradiation electronic subsystem of BR molecules is exciting, particles of BR become donors of triplet energy and molecules An become acceptors. As a result of donor-acceptor interaction annihilation delayed fluorescence (ADF) is observed. The methods of computer modeling and multifractal analysis are used for study of the change of two-component system properties. The character of luminescence kinetics on the SiO2 surface depends on the interacting particles distribution at the initial moment of time. At the modeling of energy transfer processes confirmed that the multifractal structure can be formed as a result of accidental chaotic structure destruction. The phenomenon of ?burning out? of chaos occurs at accidental chaotic distribution of reagents molecules on the SiO2 at initial moment of time. The analysis of experimental results of kinetic processes on the SiO2 surface based on the multifractal formalism allows to establish the correlations between fractal properties of system and efficiency of electron excitation energy transfer. The ratio of the reagents molecules concentrations and the temperature of SiO2 surface are control parameters of processes occurring in the system. In the region of low temperatures the system tends to maintain its multifractal parameters independently from the concentration of donors and acceptors. The increase of the matrix temperature leads to loss of the system stability, to the change of the mechanism of energy transfer.

Resume : Among advanced materials for clean energy, non-stoichiometric BaxSr1−xCo1−yFeyO3−δ (BSCF) and LaxSr1−xCo1−yFeyO3−δ (LSCF) are considered as promising materials for cathodes in solid oxide fuel cells (SOFC) and oxygen permeation membranes. BSCF exhibits the best oxygen exchange performance among similar materials, mixed ionic and electronic conductivity, high oxygen vacancy concentration, and low diffusion activation barrier, which largely define the oxygen reduction kinetics. However, it tends to decompose at low temperatures into a mixture of cubic and hexagonal perovskite phases, which strongly affects its practical applications. To understand the mechanism(s) of this unwanted process, the first principles quantum mechanical calculations of BSCF and LSCF crystals with different non-stoichiometry were performed and possible decomposition scenarios were studied. It is shown that formation energies of oxygen vacancies in the cubic and hexagonal phases of BSCF differ considerably and also behave in quite different ways depending on non-stoichiometry; in fact, it is the oxygen non-stoichiometry that makes the cubic phase more stable than the hexagonal phase. In comparison, LSCF is shown to be much more stable with respect to both the phase transformation and phase decomposition. The first principles calculations are accompanied with a thermodynamic analysis of the conditions under which a cubic phase is stable, in good agreement with experimental data.

Resume : Zinc oxide is considered as a promising conductive oxide for photovoltaic and photonic applications due to its wide bandgap, mechanical stability and intense UV and green-orange emission. At the same time, the doping of ZnO with rare-earth (RE) ions offers fine monitoring light absorbing and emitting properties of the materials in required spectral range. In this work, screen-printed ZnO films doped with Sm3+ and/or Ho3+ ions were studied by means of photoluminescence (PL), Raman scattering and X-ray diffraction methods versus sintering conditions and doping level. All the films were found to be polycrystalline of a wurtzite structure. The increase of sintering temperature caused the enlargement of ZnO grains. The films sintered at temperatures below 700°C showed the UV emission only, whereas the films fabricated at higher temperatures also demonstrate the visible (540-600 nm) defect-related PL band. The doping of ZnO films with Sm ions resulted in broadening of the defect-related PL band towards the red spectral range, whereas the doping with Ho ions stimulated its widening towards the blue spectral range. Simultaneous codoping with both these ions caused the quenching of the UV and “native” visible PL bands as well as an enhancement of Sm3+ - and Ho3+ - related emission. The effect of RE doping on PL and PL excitation spectra is discussed in terms of energy transfer from ZnO host to RE ions as well as the formation of RE complexes.

Resume : Sputtered ZnO thin films mostly exhibit a strong preferred orientation of crystallites in the [001] direction perpendicular to the substrate surface (c-axis orientation). The preferred orientation of crystallites in the [100] direction (a-axis orientation) is obtained when the sufficient substrate voltage is applied during the deposition. Nevertheless, ions accelerated by voltage of tens or hundreds Volts damage the growing film and thus the post-deposition annealing is needed. We report about structural analysis of sputtered a-axis ZnO films annealed up to 900°C. The film structure was primarily observed by X-Ray Diffractometr equiped with high temperature vacuum chamber. We focus on the effect of the annealing temperature on the size, quality and preferred orientation of crystallites. We found that, while at up to 500°C the ratio between a-axis and c-axis phase is almost constant and only the structure is enhanced, at temperature higher then 500°C transformation from a-axis to c- axis orientation occurs.

Resume : Gd-doped ceria (GDC), one of the most studied oxygen ion conductors, was recently shown to exhibit electrostriction of 6.5?10-18 [m2/V2]. GDC is completely inert with respect to Si, which makes it very attractive for integrated MEMS applications. Using only Si-compatible processes, we fabricated large area (3-4 mm2) self-supported films (300-500 nm) of GDC with top and bottom Al contacts. We have developed a simple process to achieve complete strain relaxation in the GDC films, which permitted fine control of the buckling type and mode in the self-supported structures. Application of alternating voltage (AV) induces electromechanical response at the double frequency, which is typical for electrostriction. The amplitude of the vertical displacement is a few ?m and, surprisingly, the response persists till at least 1 MHz. Applying 2.5 AV (50 kV/cm) @ 100 kHz for a period of 17 hour (~6?109 cycles) does not cause to detectable degradation or fatigue. Using a proximity sensor, we determined that the amplitude of the displacement at the 2nd harmonic is linearly proportional to the applied electric field squared at least till 200kV/cm. This implies that the saturation field for GDC is above this value. Our results strongly suggest that GDC is a very promising material for electromechanical actuation in MEMS, in particular for mechanical switches and tunable capacitors.

Resume : Disordered materials (with modulation of the refractive index comparable with wavelength of light) are deeply studied in order to achieve a better understanding of light transport in photonic media. Here we study the light transmission properties of one dimensional photonic structures in which the disorder is due to a random variation of the layer thickness. The photonic structures, made by silicon dioxide and titanium dioxide, have been fabricated by radio-frequency sputtering and characterized by spectrophotometry and electron microscopy. The light transmission properties of the disordered structure has been simulated by taking into account the dielectric constant dispersion of silicon dioxide and titanium dioxide, resulting in a very good agreement between the simulations and the experimental data. With respect to a periodic photonic crystal, the transmission of the photonic structure, in the range 300 – 1200 nm, is significantly lower [1]. Such study envisages the use of disordered one dimensional photonic structures for the modelization and realization of broad band filters. [1] A. Chiasera, F. Scotognella, L. Criante, S. Varas, G. Della Valle, R. Ramponi, M. Ferrari, Science of Advanced Materials, DOI: 10.1166/sam.2015.2249

Resume : For years, materials are competing for the best thermoelectric properties through the enhancement of the figure of merit ZT. After metals and semiconductors, oxides and polymers are today in the front. In the same time, the way to evaluate the ZT property is often a problem because of the plural techniques and systems of measurement. The last development in the laboratory consists in a complete setup for the simultaneous evaluation of the Seebeck coefficient, electrical and thermal properties of the thermoelectric material, that we call ZT-meter. With this microscale device, we performed a deeply analysis of the thermoelectric behaviour of concerned materials. Evolving in a national project, called Tours2015, we are actually studying different sputtered PEDOT-Tos polymer thin films deposited on silicon, in order to correlate the growth parameters with the thermoelectric properties. With ZT values expected above 0.2, these materials could be serious candidates to be used later on as a new micro-source of energy.

Resume : Due to the waste heat in ever more compact microelectronic devices, the harvesting of thermal energy has become interesting for self-powering small devices. Pyroelectric materials, which couple a change in temperature to a change in electrical polarization, can be used for the conversion of the thermal energy to an electric energy [1]. According to recent reports, single-crystalline pyroelectric films should provide an enhanced conversion energy efficiency with respect to bulk or polycrystalline materials [2]. Here, we show the monolithic integration of flat single-crystalline pyroelectric complex oxides (Ba1-xSrxTiO3 and PbZr1-xTixO3) on silicon via a thin SrTiO3 buffer layer grown by molecular beam epitaxy. In order to obtain a MIM heterostructure, an epitaxial bottom electrode (SrRuO3 or La0.7Sr0.3MnO3 layer) is used between the buffer layer and the pyroelectric film. Ferroelectric hysteresis loops at different temperatures give pyroelectric coefficients slightly higher than the bulk value (~400 µC.m-2.K-1 for PbZr0.52Ti0.48O3), and provide an estimation of the harvested pyroelectric energy (~50 mJ.cm-3.cycle-1). Effects of the different structures and compositions on lattice parameters, remnant polarization and pyroelectric coefficients will be discussed. The pyroelectric efficiency of single-crystalline films will be also compared to that of poly-crystalline ones. [1] S.B. Lang, Phys. Today 58, 31 (2005) [2] G. Sebald et al., Smart Mater. Struct. 18, 125006 (2009)

Resume : Resistive switching has been intensively investigated in oxide thin films, and it has been proved that oxygen vacancies (OVs) play important roles in the switching. However, OVs are always inevitably introduced into the oxide thin films during the deposition. That raises challenges in terms of the precise control of switching properties. Moreover, the coexistence of grain and grain boundaries in the polycrystalline oxide thin films grown on metal bottom electrodes makes it complicated to explore the transport behavior during the switching, which remains a large obstacle to understand the fundamental mechanism of the resistive switching. In the present work, ion-exfoliated single crystalline LiNbO3 (LNO) thin films with a thickness of 600 nm was bonded to Pt/SiO2/LNO substrates, and circular Au top electrode was sputtered to form Au/LNO/Pt capacitor structures. PFM results indicate that the thin film has a single domain structure without any domain boundaries or grain boundaries. The pristine LNO thin film shows high resistivity of Giga ohm, and no I-V hysteresis has been observed. However, after a vacuum annealing with a pressure of 1×10-3 Pa for 3 hours a forming step has been observed at a voltage of +24 V, and the thin film shows resistive switching behavior in the subsequent voltage cycles. This can be ascribed to the oxygen vacancies generated by annealing, which form conductive filaments in the LNO thin film. This work excludes the influence of randomly introduced OVs by traditional thin films deposition techniques, which benefits to a better control of the filaments formation and to a deep understand of the underline mechanism of the resistive switching in oxide thin films in the future work.

Resume : Ferroelectric oxides integrated on semiconductor substrates are of particular interest for various silicon-based electronic and photonic devices. Among them, the perovskite BaTiO3 is an attractive candidate for integrated photonics and low power logic devices. The control of the crystalline orientation of the ferroelectric tetragonal cell (c- versus a-axis orientation) as a function of the processing parameters is a key issue. In order to support the MBE growth strategy on SrTiO3-buffered Si of epitaxial BaTiO3 thin films with the desired orientation, high-resolution transmission electron microscopy (HRTEM) and high angle annular dark-field (HAADF) atomic structure images of various films were acquired and treated quantitatively using geometric phase analysis. Different deposition conditions were investigated (temperature, oxygen pressure, annealing). In this work, maps of the strain in the BaTiO3 films with respect to the Si substrate are determined at the nanometric scale (1-2nm) to evidence the local tetragonality (orientation and c/a ratio) of the BaTiO3 films. Correlations with the local cation composition are also proposed on the basis of electron energy loss spectroscopy (EELS) performed at the atomic scale. HRTEM work is performed on an image corrected Hitachi HF3300S microscope (I2TEM-Toulouse) and HAADF-EELS on a FEI Titan Low-Base 60-300 (Zaragoza).

Resume : Chemical characterization of surface and interface are crucial in materials science in order to understand the underlying physical properties. This is particularly true for strongly correlated electron systems like perovskite based materials where electronic correlations, structure, strain, intermixing, oxygen deficiency, surface reconstructions, are the means to control the properties of oxide thin films and heterostructures. XPS spectroscopy gives information about the chemical composition and the chemical environment of the atoms situated at surfaces and is a direct measurement of band offsets. Nevertheless , surface contaminants (water, adsorbed molecules) at the surface could provide a non-negligible contribution which modifies the analysis. In order to obtain clean surface, ion bombardment is used to clean and profile the surfaces. Nevertheless, the traditional ion etching with mono-atomic argon ions tends to modify the materials, challenging the analysis. We will present a new method for surface cleaning and profiling with cluster ion gun where the energy per atom is much less important. Consequently, this last etching appears to be much more gentle for any surfaces and doesn’t seem to change binding energies of the elements. The capacity to remove only the carbon contamination and then to control a progressive etching atoms by atoms is really promising to investigate various ultrathin films. First results based on model system based on SrTiO3 will be presented.

Resume : The study of epsilon-Fe2O3 nanoparticles has aroused significant attention in recent years due to their promising properties such as giant coercive field (around 2T at room temperature), magneto-resistance or millimeter wave ferromagnetic resonance (FMR) [1]. Thus, epsilon-Fe2O3 nanoparticles are good candidates for the development of applications in fields as electronics, RF devices, hydrogen production [2] or new magnetic materials. In the present work we describe different synthesis routes of epsilon-Fe2O3 particles embedded in SiO2 films on Si(100) by an easy one-pot sol-gel method. We were able to modify the size and morphology thanks to addition of Barium nitrate, CTAB and Glycerol. Also, a Raman spectrum of a single epsilon-Fe2O3 nanoparticle without additional contributions from other iron oxides phases is presented for the first time. Moreover, low-temperature Raman study and output laser dependence have been performed in the range from 80 K to 600 K, observing anomalies in the intensity, bandwidth and band position when undergoing a ferromagnetic - paramagnetic transition located around 500 K. References [1] L. Machala, J. Tucek, and R. Zboril, Chem. Mater., 23, 3255?3272 (2011). [2] G. Carraro, C. Maccato, A. Gasparotto, T. Montini, S. Turner, O. I. Lebedev, V. Gombac, G. Adami, G. Van Tendeloo, D. Barreca, and P. Fornasiero, Adv. Funct. Mater. 24, 372?378, (2014)

Resume : In the last 10 years there has been growing interest in investigating the impact of non-centrosymmetry of piezo or ferroelectric materials for energy harvesting devices. The range of devices that are being investigated include those that can convert kinetic energy into electrical energy and the conversion of sunlight into fuels, known as solar fuels, or produce electrical energy such as in a photovoltaic device. The fundamental principle and area of interest, behind these energy conversion processes are related to the breaking of crystal symmetry that is found in a piezo or ferroelectric material. This breaking of the crystal symmetry intimately influences the physical properties within the material and leads to some very specific behaviour. In this talk I will show how the domain structure of a ferroelectric material effectively separates photoinduced carriers. This leads to regio-specific photochemistry where oxidation and reduction occur on predefined areas of the photocatalyst surface, separated by tens to hundreds of nanometres. We will then discuss how the dipole of the ferroelectric crystal lattice can be used to produce enhanced photocatalytic efficiency and how these dipoles can retard the recombination of photoinduced carriers. We have recently measured carrier lifetimes in BaTiO3 using transient absorption spectroscopy at 1-2 seconds without any external applied field, which exceeds values for traditional semiconductors under a strong applied electric field. The same fundamental phenomena is responsible for the 50% increase in power conversion efficiency in a ZnO based photovoltaic device when music is played and also enables us to effectively convert vibration into an electrical output. I’ll end by drawing a picture of how the breaking of crystal symmetry may influence energy conversion in the future.

Resume : The influence of the strain on the oxygen-ion conductivity is investigated for ways to enhance the ionic conduction. Within the currently most accepted scenario, tensile strain is expected to lead to a decrease in the activation energy. Crystalline thin films are used as model systems to evaluate this effect, but reports are highly controversial. Doped ceria is a typical oxygen ion-conductor used as electrolyte in solid oxide fuel cells. Pulsed laser deposition allows the very controlled growth of epitaxial films. Tensile strain is induced in 15% samarium doped ceria by using a growth platform which provides a lattice mismatch of 1.4% and which is also suitable for electrical characterisations. This platform consists of a buffer layer of SrTiO3 on BaZrO3 on a MgO substrate. A Multi-beam Optical Stress Sensor is employed as a valuable tool to monitor the stress in situ via the substrate curvature during growth of such films. Simultaneously, the growth mode is monitored with Reflective High Energy Electron Diffraction. This so far unique combination can lead to a better understanding of the stress evolution during the growth. The strain is characterised additionally ex situ with x-ray diffraction and the tensile strain values are in agreement with the in situ stress measurement. Electrical characterisations of strained and relaxed films will be presented and the observed stress evolution will be compared with established models for thin films.

Resume : NiO has great potential applications in organic photovoltaics and catalysts. The performance strongly depends on the orientation of NiO, as the discrepant electronic structures in polar {111} and non-polar {100} surfaces. This presentation aims to investigate the controlling growth orientations of NiO thin films on glass substrates by reactive magnetron sputtering at room temperature. In the first part, the influence of total sputtering pressure and oxygen flow rate on the structure, crystallization and growth orientation of single layer NiO thin films is presented. Since the internal stress decreases with the increase of the total pressure, an improvement of the NiO crystallinity is evidenced. Then, a two-step deposition procedure (growth of bilayer thin film) is shown to tune the film growth orientation independently of the deposition conditions. It is observed that the growth orientation of the top layer is determined by that of the bottom layer. For instance, a < 100> oriented NiO seed layer will set the top layer to be < 100> orientation, regardless of its intrinsic growth conditions. Moreover, highly < 111> oriented NiO thin films on glass substrates have been attained by using a < 111> textured Cu2O seed layer. This growth behavior is detailed by high resolution transmission electron microscopy (HRTEM) analyses. The well-matched atomic structures between NiO {111} and Cu2O{111} planes may be the driving force to promote the growth of < 111> oriented NiO.

Resume : The most efficient multifunctional piezoelectric materials are lead-based (PZT [(PbZrO3)1-x(PbTiO3)x] and PMN-xPT [(PbMg1/3Nb2/3O3)1-x(PbTiO3)x] and therefore are about to be banned by European RoHS directive. Their piezoelectric coefficients peak in the vicinity of the so-called morphotropic phase boundary (MPB) separating two ferroelectric phases with different structures : one is rhombohedral (once poled for PMN-xPT) and the other is tetragonal [1,2]. Thus alternative lead-free materials are required and an obvious direction is to look for MPBs in other ferroelectric solid solutions. BiFeO3 (BFO) being a ferroelectric (TC~1100K) with record polarization (100µC.cm-2) and a rhombohedral structure is a good starting point. Indeed MPBs have been found in ceramic solid-solutions of BFO with tetragonal ferroelectric perovskite phases with a strong increase of d33 (up to 140 pm/V for BaTiO3) [3]. However, MPBs can also be induced by chemical substitution in new systems for which the end member of the phase diagram does not need to be a ferroelectric perovskite. In this work, we report the exploration of the (BiFeO3)1-x(GaFeO3)x system, where GaFeO3 is piezoelectric and crystallizes in a non-perovskite orthorhombic structure. Composition spread epitaxial Ga-doped BFO (BGFO-x) films were pulsed laser deposited onto La0.8Sr0.2MnO3 electrodes. Composition gradients were characterized by WDX, RBS and XPS while structure and phase analysis was realized by X-Ray micro-diffraction and TEM. Piezoelectric properties were characterized at various length scales with PFM and laser interferometry. All compositions were found to exhibit typical hysteretic ferroelectric behavior with a slight reduction of ferroelectric domain sizes upon Ga doping. A change of symmetry associated with rapid lattice parameters variation has been evidenced just below 6% of Ga doping and is correlated with a sharp enhancement of d_33^eff , probably resulting from the presence of a MPB. The maximum〖 d〗_33^eff (55pm/V for a film thickness of 135nm) shows no extrinsic domain wall contribution and compares to the best PZT value for the same film thickness.

Resume : Ultrathin films of Fe3O4 have been grown epitaxially on nearly lattice matched MgO(001). The stability of 4 nm thick films in ambient air and under annealing in an oxygen atmosphere at 570K has been studied. By magneto optical (MOKE) and Raman measurements, we can confirm the presence of the Fe3O4 phase and the formation of a maghemite top layer, passivating the magnetite thin film. In a second step, we are able to demonstrate that this top layer oxidation in ambient air can be prevented by a 2 nm thick magnesium ferrite passivation layer, while a thicker 20 nm MgO layer prevents oxidation even at elevated temperatures. First results of employing the ultrathin Fe3O4/MgFe2O4 layers as building blocks for novel magnetic nanolaminate materials will be presented.

Resume : The demand for stretchable electronics has increased drastically in recent years, owing to the growing popularity of wearable and compact devices such as smart watches and fitness gear. However, these devices use conventional rigid technology in a flexible housing. Here, we demonstrate precursors for fully stretchable devices by integrating high quality oxide thin films into a rubber substrate. We show a universal process for transferring planar, transparent indium tin oxide (ITO) thin films on to elastomeric polydimethylsiloxane (PDMS) substrates. This process overcomes the challenge of incorporating high-temperature-processed crystalline oxide materials with low-temperature organic substrates by using the weak adhesion at the platinum-silicon interface. We demonstrate control over film thickness and show feature sizes down to 2.5 µm by using standard micro fabrication techniques. Counterintuitively, the ITO thin film electrodes on PDMS are shown to withstand uniaxial strains of 15%. We explore the capabilities of the electrodes by characterising the devices using resistance vs. strain measurements and in situ scanning electron microscopy, revealing a novel surface structure called micro-tectonics which is responsible for the high stretchability of the oxide thin films. We show that the ITO layer forms overlapping plates that can move independently from each other forming a fully functional stretchable surface. Reference: P. Gutruf et al. "Transparent functional oxide stretchable electronics: micro-tectonics enabled high strain electrodes." NPG Asia Materials 5 9 e62 (2013).

Resume : The development of flexible substrates that are based on polymer films is of critical importance to display and photovoltaic applications. Flexible substrates offer the advantages of mechanical flexibility, design freedom, optical transparency, lightweight, and cost-effectiveness. A number of inorganic functional coatings on polymers have critical properties such as water impermeability and electronic conductance, which are required for display, electrochromics and photovoltaic applications. In this study hybrid transparent conductive oxide films which had the structure of TCO/ AgOx /TCO and TCO/Ag nano wire layers were deposited on a flexible substrate as a function of inter layers thickness and chemical status by using DC roll-to-roll magnetron reactive sputtering system. The influences of the inter layer thickness and oxygen partial pressure on the microstructure, optical properties, flexibilities and electrical properties were studied. The high quality hybrid ITO films were deposited at RT with a resistivity of 1.05x10-4Ωcm and the transparency of batter than 89%. Change of electrical and optical properties according to the inter layers and plasma conditions was also observed with XRD, TEM, and XPS. TCO films deposited at RT showed nanocrystalline phases evolved on the amorphous TCO layer. Very flat surface roughness could be obtained at RT, while surface roughness of the films was increased due to the formation of grains over than 70℃. Consequently, high quality hybridTCO films could be prepared by DC roll-to-roll sputtering with high deposition rate and at low deposition temperature; a specific resistivity of 1.05x10-4Ωcm, and Rp-vand Rrms values of surface roughness about less than 4 nm and 0.5 nm. The mechanical failure of brittle oxide and TCO coatings on flexible polymers is a serious issue. The formation of defects, such as cracks and debonding in TCO films may be inevitable in situations in which bend geometries are required, because of the large difference between the elastic properties of TCO and polymers. The initiation and subsequent developments of defects mainly depend on the coating material, thickness, and interfacial adhesion. Thus, it is important to have a clear understanding of the failure behavior of coatings in the case of bend geometries, in order to prevent the destruction of devices in which they are used. Flexibility of hybrid TCO films was measured as functions of the bending radius and bending cycle in bend geometries and then shown an excellent flexibility. It will be considered that these experimental results can be applied to the TCO substrate of flexible display devices.

Resume : Zinc oxide (ZnO) is a II-VI semiconductor material possessing remarkable electronic and optical properties for optoelectronic applications. Rare earth doping of ZnO is investigated for the fabrication of white LEDs. For instance, the green light can be produced by terbium ions (Tb3 ) and the red emission can be achieved by europium ions (Eu3 ). The contributions of these two rare earth emissions in addition to that of ZnO lead to a white light. The case of Eu doping in a ZnO matrix is interesting since two electronic configurations of ions are generated in ZnO: Eu2 and Eu3 . It results a much lower luminescence efficiency of the Eu3 than expected. In the present study, Eu doped ZnO (Eu:ZnO) films were grown on (100) silicon substrates by radiofrequency (RF) magnetron sputtering using a pure ZnO target. Doping was obtained by arranging calibrated Eu oxides (Eu2O3) pellets on the surface of the ZnO target. Using characterization techniques such as X-ray diffraction, X-ray photoemission spectroscopy, transmission electron microscopy, spectroscopic ellipsometry and photoluminescence spectroscopy, the present work aims at studying the effect of the doping rate on the film structure and its photoluminescence properties. The goal is also to cinfirm the presence of Eu2 and Eu3 in the films and to investigate their localization in the ZnO film. In addition, electrical properties and their evolution with the europium doping rate are reported.

Resume : Ultra-small superparamagnetic Ga1.1Fe1.9O4 nanoparticles have been successfully synthesized using a facile and efficient one-pot solvothermal method. This approach is based on the thermal decomposition of Ga(C5H7O2)3 and Fe(C5H7O2)3 in triethyleneglycol, which acts as both solvent and, capping ligand. The structure, morphology and magnetic properties of the ultra-small superparamagnetic Ga1.1Fe1.9O4 nanoparticles have been investigated by X-ray diffraction, FT-IR, HRTEM, SAED, VSM and SQUID. The XRD investigations reveal the formation of the cubic spinel structure, while TEM images show non-agglomerated spherical nanoparticles with an average particle size range between 4.5 to 9 nm. Magnetization vs temperature, M(T), measurements, performed by SQUID, have demonstrated that the resulting nanoparticles show high saturation magnetization and superparamagnetic behaviour at room temperature. Moreover, ligand exchange has been also carried out in order to produce stable dispersions of Ga1.1Fe1.9O4 nanoparticles in polar media. The preliminary studies on using of as-obtained Ga1.1Fe1.9O4 nanoparticles as magnetic pinning centers in YBa2Cu3O7 thin films are performed. Acknowledgments: This work was supported by the EU - FP7/2007-2013 - Grant Agreement No. 280432, EUROTAPES project and by the Post‐Doctoral Programme POSDRU/159/1.5/S/137516, project co‐funded from European Social Fund through the Human Resources Sectorial Operational Program 2007‐2013 and CNCSIS-UEFISCSU.

Resume : In the past decade semiconductor nanowires have emerged as promising building blocks for nanoscale optoelectronic devices. One of the most interesting materials used for nanostructure fabrication is the wide-bandgap semiconductor ZnO, which is a very attractive candidate for blue and UV optoelectronics. ZnO prepared by evaporation condensation technique in the form of high aspect ratio nanowires and microwires. The photoluminescence emission properties of the nanostructures were analyzed as a function of the surface treatment (plasma etching) and as a function of the nanowire diameter. Nanowires were analyzed both as deposited as a mesh on silicon substrate and dispersed over glass and Si substrate, and single nanowires were precisely designated by mean of EBL. Waveguiding properties have been demonstrated to be dependent on the wire dimensions (microwires) and on the laser wavelength. The ZnO nanowires may be applied as PL optical gas sensor and evanescent optical gas sensor, and in heterojunction with p-type material, for LED applications. The research leading to these results has received funding from the European Communities 7th Framework Programme under the grant agreement NMP3-LA-2010-246334, ‘‘ORAMA’’.

Resume : Nickel oxide (NiO) attracts considerable interest for its photocatalytic properties in applications as battery, electrochromic, chemical sensing, etc. and for its potential applications as p-type transparent semiconductor. High conductivity p type NiO films were fabricated by radio frequency sputtering starting from a Ni target in different Ar+O2 pressures. The effect of the different growth parameters on the structural, chemical, optical and electrical properties of the films was investigated. Film resistivity decreased by increasing the oxygen partial pressure in the sputtering gas and reached the value of 1.6x10-2 Ohmcm for films grown in pure oxygen atmosphere. NiO fibers were produced by electrospinning starting from a solution prepared by dissolving 1 g of polyvinylpyrrolidone (PVP) and 1.5 g of Ni (II) acetate tetrahydrate in 15 ml of ethanol. Fibers were deposited on different substrates, including NiO and Ni thin films grown on quartz substrates. Electrospun mat calcined in air at 600°C consisted of randomly oriented fibers with diameters ranging between 40-100 nm. Phase analysis performed by XRD showed the presence of a crystalline NiO phase. Hybrids NiO fibers/NiO films were fabricated to take advantage of the different microstructure properties and enhance electrodes performances.

Resume : In recently reported works the performance improvement of dye-sensitized solar cells (DSSC) assembled with use of Ti/TiO2 interface is ascribed to its low charge transfer resistance and low recombination rate of charge carriers. It refers to DSSC devices on metal foil substrates where the porous TiO2 electrode is produced using the doctor blade method followed by sintering. However, the production process preceded by sputtering of the Ti film on preheated metal substrate and synthesis of the Ti/TiO2 interface seem too complicated, time consuming and associated with a number of process parameters to be controlled. In this work the nanoporous TiO2 films forming the TiO2-Ti junction obtained by a one-step synthesis using pulsed laser deposition (PLD) at atmospheric pressure are reported. It is shown that reliable interconnection of the film with Ti foil can be produced in air under conditions of standard temperature and pressure and without thermal pre-and post-treatment. Observations performed with both the scanning electron and confocal microscopes confirm the presence of porous TiO2 films. Data on the film composition and crystalline phases obtained from the XRD, EDX and Raman measurements indicate on the relatively high anatase/rutile ratio (>75%) with a small amount of TimNn in dependence on the film preparation conditions. AB and KG acknowledge the National Science Centre of Poland for financial support via grants 2012/07/N/ST5/02134 and 2012/07/N/ST5/02139.

Resume : One-dimensional ZnO nanostructures are multifunctional nanomaterials with high potential applications in the field of optoelectronics, photovoltaics, sensing due to their properties and their easy synthesis in the form of nanowires using low-temperature hydrothermal process. We report a method which combines e-beam lithography (EBL) and a low temperature (<100 oC) hydrothermal method to achieve localized growth of ZnO nanowires(ZnO NWs) and microroads on wide range of patterned substrates such as glass, quartz, Si and SiO2/Si and ITO/glass. Our method for ZnO NWs patterned growth consists of the three stages: (1) configuration interdigitated metallic electrodes from Cr/Au of 20/150 nm thickness with distance between electrodes in the range of 1.5 -6 µm using laser photolithography ; (2) coating with PMMA ( hydrophobic polymer layer which inhibits growth) by spinning and defining the growth region using electron-beam lithography ( EBL) ; (3) seeding the substrate with discontinuous dispersed ZnO nanoparticles and growth of ZnO nanowires in aqueous solution of zinc nitrate hydrate and hexamethylenetetramine ([Zn2+]:HMT] =1:1) at 90 oC . The quality of the ZnO NWs synthesized through the hydrothermal process has been characterized by SEM, Raman spectroscopy and XRD. The obtained 1D nanostructures are nanorods and nanowires types, with aspect ratio (length/diameter) ranging from 5 to 50, and well crystallized with Wurtzite-type hexagonal pattern and <002> preferential orientation and electrical connected the two adjacent gold electrodes through forming complex interconnected nanowire networks. Current-voltage characteristics showed a photoconductive behavior and UV radiation and gas sensitivity

Resume : ZnO nanogenarator, to utilize the environmental mechanical energy, which is available from irregular vibrations and human activity with a wide spectrum of frequencies and time-dependent amplitudes, have demonstrated to produce micro-watt power output and to drive micro-sensor. .However so far the power output from NW nanogenarator based on chemical synthesis ZnO nanowire is still far away from a milli-power output source , which requested by most applications of individual sensor. Physical vapor deposition of ZnO can largely improve the crystal graphical property of the grown ZnO but limit with small growth area. To achieve good ZnO piezoelectric property and grow large area with high power output is desirable. In this paper, Sol-gel technology was used to prepare ZnO thin film on Si substrate, the characteristic of the samples was measured by XRD, AFM, and SEM. The XRD patterns showed that ZnO thin film had a high (002) orientation with compact hexagonal wurtzite structure. The AFM and SEM microphotograph showed ZnO thin film had a smooth and dense surface, the thickness of the sample was approximately 80 nm. The grain size gradually increased with annealing temperature. Sol-gel grown ZnO film are then patterned into a micro power source. The power output from ZnO micro-power sourse can reach upto 3mW.

Resume : Manganese oxides octahedral molecular sieves (OMS) with mixed valence frameworks have been widely used as bulk material in catalysis, semiconductor industry, and batteries. Monolithic direct integration of OMS with vertically oriented crystals on a semiconductor platform is challenging due to difficulties on preserving epitaxy, crystalline phase, and composition. Here, we developed a new strategy to produce vertical epitaxial single crystalline manganese oxide OMS nanowires thin films with tunable composition and enhanced ferromagnetic properties on Si substrates by using a chemical solution deposition approach [1]. The nanowire growth mechanism involves the use of track-etched nanoporous polymer templates combined with the controlled growth of quartz thin films at the Si surface, which allowed the epitaxial stabilization and crystallization of OMS nanowires. α-quartz layers were obtained by thermally activated devitrification of the native amorphous silica surface layer assisted by a heterogeneous catalysis driven by alkaline earth cations (Sr2+, Ba2+ or Ca2+) present in the precursor solution [2]. Therefore, the combination of soft-chemistry and epitaxial growth opens new opportunities for the effective integration of novel technological functional complex oxides nanomaterials on Si substrates [3]. 1. A. Carretero-Genevrier et al Chem.Soc.Rev 43, 2042 (2014) 2. A. Carretero-Genevrier et al Science 340, 827 (2013) 3. A. Carretero-Genevrier et al Chem. Mater 26 1019 (2014)

Resume : Recently many functionalities only associated with rigid electronics have been demonstrated on a flexible substrate, indicating that flexible devices have a high potential to operate on par with rigid electronics. Furthermore, flexible electronics offer a distinct advantage by organically conforming to irregular surfaces, this enables a new class of electronics that seamlessly integrates with the human body. Fully stretchable electronics pose a challenge for material science and micro fabrication to create devices with the ability to operate impeccably under various mechanically-stressed states. Here, we introduce a distinctive micro-tectonic effect to enable oxygen-deficient, nano-patterned zinc oxide (ZnO) thin films on an elastomeric substrate to realize large area, stretchable, transparent, and ultra-portable sensors. We harness the unique surface structure to create stretchable gas and ultra-violet light sensors, both of which outperform their rigid counterparts under room temperature conditions. The sensors show a high sensitivity to flammable and toxic gases as well as radiation in the UV-A and B band. We characterise the device performance in undeformed and strained states using customised in situ techniques. We demonstrate full functionality under strain as well as an increased sensitivity through micro-tectonic surfaces by comparison to their rigid counterparts. Additionally we show excellent control over dimensions by embedding nanometre ZnO features in an elastomeric matrix which function as tunable diffraction gratings, capable of sensing displacements with nanometer accuracy.

Resume : Rechargeable solid state battery systems with alternative ion-conductive systems are of great interest in research on novel mobile energy storage concepts. For the promising aluminium ion system the spinel structure of λ-MnO2 offers the appropriate 3D channels for intercalation cathodes. As the chemical synthesis of AlMn2O4 has not been established yet, the compound is formed by electrochemically loading of λ-MnO2 spinel with aluminium ions. The synthesis of metastable λ-MnO2 is attained not on a direct way but through delithiation of spinel LiMn2O4 similar to Xue et al.[1]. Commercial LiMn2O4 powder was etched with 18M H2SO4 at 40 °C. Powder XRD measurements report the lithium reduced spinel structure Li0,04Mn2O4. The quantitative analysis of residual Li content via ICP-OES confirmed a Lithium decrease of a factor of about 10. For the future, cyclic voltammetry measurements in aluminium half cells as well as the aluminium intercalation to produce AlMn2O4 as cathode material are going to be evaluated. In addition to that, further experiments will be conducted to evaluate materials suitably for high-energy-density aluminium ion batteries. [1] Y. Xue et al. – Material Letters, 62, 2008, 3884-3886.

Resume : Low temperature growth of various structural phases of TiO2 is particularly significant for practical applications. In this work, the deposition conditions for the growth of anatase and rutile phase at low temperature (≤ 300 °C) were optimized. TiO2 films were deposited by RF sputtering of a TiO2 target in argon and argon-oxygen plasma (20 % O2) at various substrate temperatures (Tsub = RT-400 °C). The plasma properties were investigated using OES in wide range values of gas composition (0-50 % O2 in Ar discharge). The structural, optical and chemical properties were studied by mean of XRD, UV-visible-NIR spectroscopy and XPS. The XRD results show the formation of anatase phase for the films grown in Ar-O2 plasma over the whole range of temperature. In contrast, the films deposited in argon discharge largely persist in amorphous phase at temperature ≤ 200 °C and revealed the formation of single rutile phase at ≥ 300 °C. The oxygen vacancies detected by XPS analysis for the films deposited in Ar plasma facilitate the growth of rutile phase at low temperature (∼300 °C). The anatase films have interesting optical characteristics such as high transmittance (∼ 85 %) and wider optical band gap (∼3.25 eV) compared with rutile films (∼78 % and 3 eV). Our results demonstrate that oxygen negative ions, oxygen vacancies and surface energy conditions at the substrate are the key parameters controlling the phase and hence the optical properties of the prepared films at low temperature.

Resume : Intermediate Temperature-Solid-oxide Fuel Cells (IT-SOFCs) has a high potential in the application of clean and efficient electric power generation. Major problems in the field can be addressed by decreasing the operation temperature. In this work the symmetrical cells were developed in order to assess the cathodes performance. The materials with perovskite structure synthesized by “citrate” method were used as targets for thin films deposition by RF assisted pulsed laser deposition system (RF-PLD). The compositions of the targets are as following: Nd0.6Sr0.4Co0.8Cu0.2O3-δ,(NSCC), Pr0.5Ba0.5Cu0.8Fe0.2O5+δ (PBSC) and La0.5Sr0.5Co0.8Fe0.2O3-δ (LSCF), respectively. The electrochemical testing of these materials as cathodes in solid oxide fuel cells were carried out using ceramic disc-shaped electrolytes based on YSZ (8% mol. Y2O3 doped ZrO2). Additionally, Ce0.9Gd0.1O2-δ (CGO) synthesized from hydrated nitrate precursors via a modified Pechini method was used as buffer layer between cathodes and electrolyte. The compatibility of the different cathodes and the electrolyte was investigated by SEM and AFM. Studies on structural properties and surface chemistry were performed by XRD, Raman and XPS techniques. It was found that the porous texture of the films is strongly dependent on the deposition method and composition. The electrochemical tests were performed by impedance spectroscopy (EIS) using systematic variation of temperature in the range 600-900 ºC and O2 partial pressure.

Resume : Tin dioxide is one of the most attractive materials studied in the last decade due to its several applications such as optoelectronic devices, gas sensors, and solar cells. It is n- type semiconductor with a wide band gap (around 3.6 eV for bulk material at 300 K). Doping SnO2 films with rare earth (RE) elements (such as Yb, Pr, Tb, Nd) can enhance their photoluminescence properties thanks to the optical transitions involving the 4f shell of the dopant. However, the transparency and structural properties of the RE doped SnO2 films should not be affected. In this work, we have synthesized undoped SnO2 and Yb doped SnO2 (Yb:SnO2) powders by the sol gel method in order to understand the insertion process of Yb in SnO2 matrix and to produce luminescent materials for photon shifting purpose. SEM and TEM micrographs show that the grain size is homogenous for Yb:SnO2 powders. The crystallinity, structure and particles size of the powders were determined using XRD measurements. We found that the crystalline tetragonal rutile phase is achieved upon an annealing temperature of 700?C. Furthermore, a slight diffraction angle shift toward higher angles is observed with increasing Yb content, indicating Yb incorporation. No secondary phases like Yb oxides are detected. The optical properties were studied by the UV-Visible-NIR spectroscopy and revealed Yb related absorption band in the NIR region. Moreover, a decrease of the absorption threshold energy with respect to the Yb content was observed. The intensity of Raman peaks decreases gradually as the Yb content increases. Finally, the investigation of the photoluminescence properties under a 325 nm laser excitation show intense emission at 980 nm attributed to a transition in the Yb energy level. such strong PL signal indicates that the trivalent Yb3 ions are successfully inserted and optically active. An efficient energy transfer might occur from the SnO2 host to Yb3 ions.

Resume : Magnetoelectric materials open the way toward new applications through controlling magnetic or electric polarization with electric or magnetic field, respectively. Ga2-xFexO3 (GFO) compounds are predicted to be magnetoelectrics with non-zero magnetization at room temperature. High quality GFO thin films with quite similar physical properties as bulk materials have been recently elaborated. Gallium and Iron are distributed in four non-equivalent cationic sites in the structure. The determination of the cationic distribution within the structure is a key point for the knowledge of these phases but extremely tricky to determine owing to the relatively small amount of material to probe. One of the many benefits of synchrotron radiation is the ease of energy adjustment of the X-ray beams that allows discriminating the cations contribution in different sites. Diffraction Anomalous Near Edge Structure experiments have been recorded at the gallium and iron edges using the BM02 beamline of the ESRF. A software, “FitREXS”, has specially been developed for this purpose using the Python language and may be easily adapted to any system. Results clearly demonstrate the efficiency of the method for the determination of sites occupancies. Additional parameters such as the orientation of the cells along the growth direction have also been taken into account and will be discussed

Resume : SnO2-based Transparent Conductive Oxides (TCO) are currently widely used in different applications, e.g. as electrodes for photovoltaic, water splitting and fuel cells, for their high performances in terms of carrier density and mobility, low costs, non-toxicity and high transparency in the visible spectrum. To maximize the performances a proper balance between surface-to-volume ratio, to enhance the active surface, and crystallinity grade, to improve the carriers transport, is required. Despite some SnO2-based TCO porous films have been already realized, hierarchical nanostructured contacts has not been done yet. In this work Pulsed Laser Deposition technique has been adopted for this purpose. The resulting tree-like nanostructured film can be tuned in a wide range of porosity, maintaining excellent electrical properties. Electrodes performances have been analyzed from electrical, electrochemical and optical points of view. A gold contact evaporated on the top of the films has been used to determine the conductive performances. With Electrochemical Impedance Spectroscopy we monitored their behavior in electrochemical cells. UV-vis measurements have proved that the optical path can be engineered altering the porosity of the film. These films are suitable for subsequent doping or functionalization. In the present work a novel thermal doping process with Fluorine precursor has been performed as an efficient and facile technique to produce hierarchical nanostructured FTO films.

Resume : Among solar cells of 2nd generation, i.e. based on thin films, CIGSe solar cells have recently reached a world record above 20 %. CIGSe solar cells are often considered as the most promising alternative to Si-based solar cells, thanks to their intrinsic characteristics. A standard CIGSe-based photovoltaic cell is a stacked-layered hetero-structure on a glass substrate: Mo back contact, CIGSe absorber layer, buffer layer (usually CdS obtained by CBD) and the upper ZnO window layer. In the framework of CIGS solar cell industrialization fully fabricated by magnetron sputtering [1], our buffer layer is constituted by Zn(O,S) instead of CdS. Zn(O,S) is deposited by sputtering from a ZnS target in a reactive Ar-O2 plasma. In this study, Zn(O,S) films were deposited on glass substrate by RF magnetron sputtering and DC pulsed magnetron sputtering. The properties of both types of Zn(O,S) films, i.e. chemical, structural, morphological and optical properties, were investigated by XPS, XRD, SEM, ellipsometry and UV-visible spectroscopy and will be presented. In particular, a minimum energy band gap value of 2.6 eV has been obtained for an S/S+O atomic ratio of 0.4 and an average transmittance close to 90%. Such values appear thus very attractive for photovoltaic applications as part of a window layer [2][3]. [1]R. Meunier et al, submitted; oral communication at COFMER'01 and AVS' 61 (2014) [2]A. Grimm et al, Thin Solid Films (2011) [3]B.K. Meyer et al, Applied Physics Letters (2004)