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

Resume : Strontium ferrite (SrFeOx, SFO) exhibits a variety of x-dependent electronic and magnetic states, ranging from an antiferromagnetic insulating to a ferromagnetic metallic phase. By decreasing x (or the oxygen vacancy concentration) from nominal 3.0 (perovskite) to 2.5 (brownmillerite), the valence state of Fe changes from 4+ to 3+, which greatly influences the material’s crystal and electronic structures. In this talk, we focus on x = 2.5 phase of SFO. The brownmillerite structure can have an inversion symmetry breaking due to a specific ordering of rotated FeO4 tetrahedral units. This might lead to a structural ferroelectricity in the material, which can be confirmed by different experimental approaches. We further suggest tuning of the ferroelectric properties by controlling the tilting orientation using an electric field.

Resume : A novel concept to obtain ferroelectric material with enhanced piezoelectric properties is proposed. This approach is based on the combination of two pathways: (i) the evolution of a ferroelectric monoclinic phase and, (ii) the coexistence of different types of ferroelectric domains leading to polarization discontinuities at the domain walls. Each of these pathways enables polarization rotation in the material which is responsible for giant piezoelectricity. Targeted incorporation of anisotropic epitaxial lattice strain is used to implement this approach. The feasibility of our concept is demonstrated for K0.9Na0.1NbO3 epitaxial layers grown on NdScO3 substrates where the coexistence of (001)pc and (100)pc pseudocubic oriented monoclinic domains is experimentally verified. This coexistence results in a complex periodic domain pattern with alternating emergence of ferroelectric in-plane a1a2 and inclined MC monoclinic phases, which differ in the direction of the electrical polarization vector. Our approach opens the possibility to exploit ferroelectric properties in both vertical and lateral directions and to achieve enhanced piezoelectric properties in lead-free material caused by singularities at the domains walls.

Resume : Among the perovskites ferroelectric materials, lead-free BaTiO3 (BTO) is intensively studied, in a wide range of applications: MEMS devices, non-volatile memories, electro-optical devices, and piezoelectric and electro-optical properties. Many authors have discussed thin films of BTO as well. In this work, BTO thin film deposited on different substrates by RF magnetron sputtering were investigated. Three templates representative of different types of materials system were selected: 1) SrRuO3 buffered SrTiO3 (STO) single crystals as an oxide reference material, 2) Silicon on oxide (SOI) as a semiconductor with SrRuO3 and Pt/TiO2 bottom electrodes. After BTO crystallization, the structural characterization and crystalline quality were investigated by X-ray diffraction (XRD). Whatever the substrate used, the BTO thin films are c-oriented and strained with elongated c-axis, without any a-domain. Electrical and ferroelectric measurements were performed at room temperature: the C-V characteristics with a butterfly shape indicate the ferroelectric nature of BTO tetragonal films. The relative permittivity were determined using parallel-plate capacitor equation and found to be ε_r= 115 for all the samples. The ferroelectric properties of BTO films were confirmed by hysteresis loops and the corresponding remnant polarization value is P_r = 2.5μC/〖cm〗^2(E_c=170 KV/cm). Whatever the substrate, the same crystalline perovskite structure was obtained for BTO films with a tetragonal structure. Moreover, the BTO films have state-of-art P-E hysteresis loops and C-V characteristics. We can conclude that, due to the texturation of the BTO films, the choice of the substrate (STO or SOI) seems to have no influence on the BTO films properties.

Resume : The evolution of the structural and magnetic properties of Co doped ZnO has been investigated over an unprecedented concentration range above the coalescence limit. ZnO films with Co concentrations from 10% to 60% of the cationic sublattice have been grown by reactive magnetron sputtering. At low Co concentrations, the films which are devoid of metallic Co precipitations exhibit anisotropic paramagnetism [1]. With increasing Co content, the films become antiferromagnetically ordered with increasing order temperature [2]. Uncompensated spins, coupled to the antiferromagnetic dopant configurations, lead to a vertical exchange-bias-like effect [3], which increases with increasing Co concentration. In parallel, the effective magnetic moment per Co atom and the single-ion anisotropy is gradually reduced [2]. The obtained phase diagram of the magnetic order deviates significantly from theoretical predictions of coalescence-induced magnetic order in Co-doped ZnO [4]. Finally, the transition from 60% Co-doped ZnO to the Zn-Co-spinel demonstates that antiferromagnetism also persists despite the p-type carrier background in the spinel [5]. [1] A. Ney et al., Phys. Rev. B 81, 054420 (2010) [2] V. Ney et al. Phys. Rev. B 94, 224405 (2016) [3] B. Henne et al., Phys. Rev. B 93, 144406 (2016) [4] S. K. Nayak et al., J. Phys.: Condens. Matter 21, 064238 (2009) [5] B. Henne et al., Sci. Rep. 5, 16863 (2015)

Resume : Transition metal oxides having a perovskite structure form a wide and technologically important class of compounds. In these systems, ferroelectric, ferromagnetic, ferroelastic or even orbital and charge orderings can develop and eventually coexist. In practice, these orderings can be tuned by external electric, magnetic or stress field and the cross couplings between them enable important multifunctional properties such as piezoelectricity, magneto-electricity or magneto-elasticity. Recently, it was proposed that, additionally to typical fields, the chemical potential that controls the concentration of ion vacancies in these systems might reveal an efficient alternative parameter to further tune their properties and achieve new functionalities. Here, concretizing this proposal, we show that the control of the content of oxygen vacancies in perovskite thin films can indeed be used to tune their magnetic properties. Growing PrVO3 thin films epitaxially on a SrTiO3 substrate, we reveal a concrete pathway to achieve this effect. We demonstrate that monitoring the concentration of oxygen vacancies through the oxygen partial pressure or the growth temperature can produce a substantial macroscopic tensile strain of a few percents. In turn, this strain affects the exchange interactions, producing a non-trivial evolution of the Neel temperature in a range of 30 K.

Resume : At low temperatures quantum mechanical corrections to the resistivity of metals and doped semiconductors lead to a minimum and a subsequent increase of the resistance. Such effects are attributed to weak localization effects, due to the backscattering of phase coherent electrons interfering constructively or destructively, or to electron-electron interactions, which occur when the screening of diffusive electrons is enhanced compared to the conventional Fermi liquid model. These phenomena have been widely investigated in nonmagnetic materials of all dimensions and provide insight into the fundamental properties of a given material, mainly concerning phase coherence. These two phenomena are typically disentangled by exploring magnetoresistance. Researchers have recently investigated such phenomena in magnetic materials but in colossal magnetoresistance (CMR) manganites the interplay between electronic, magnetic and structural degrees of freedom can complicate the interpretation. Here we investigate the resistivity minimum in manganite devices patterned by electron beam lithography and ion beam etching, which allow the control of the physical dimensions and the transport direction. We explore the 3- to 2-dimensional in terms of both electron-electron interactions and weak localization. Our main results are the estimation of the phase coherent time for La0.33Sr0.7MnO3 and the reduction of weak localization in the presence of domain walls.

Resume : Transition metal oxides present multiple advantages for environmental-friendly applications. They are indeed non-toxic and abundant on earth, and their electronic properties can moreover easily be tuned by doping or alloying processes: such oxides can display a rich phase diagrams as a function of their cationic constituents. (Co,Mn)3O4 compounds have recently been suggested as good candidates for photovoltaic and photocatalysis applications. Intermediate between antiferromagnetic cubic spinel Co3O4 and ferrimagnetic tetragonal spinel Mn3O4, they can indeed exhibit complex magnetic structures and tunable electronic properties, strongly linked with the structural phase transition appearing as a function of the composition. We will present a complete description of the atomic, magnetic and electronic structure variations for the whole (Co,Mn)3O4 solid solution. All the results, calculated from first principles using density functional theory based methods, will be discussed by comparison with experimental measurements performed on thin films obtained by dip-coating techniques.

Resume : The electrical, crystallographic and magnetic properties of ultra-thin magnetite (Fe3O4) have been studied in detail, using a novel approach of employing superlattice structures of Fe3O4/MgFe2O4 and Fe3O4/MgO on various substrates. By careful analysis of their properties the influence of substrate stoichiometry, Fe3O4 thin film thickness, antiphase boundaries on the magnetic properties can be separated. In particular the origin of the controversial enhanced magnetic moment in ultra-thin films can be assigned to the substrate stoichiometry, in particular the migration of oxygen vacancies into the Fe3O4 thin film. The multi-layer concept can be employed to many other such systems and offers new methods of tuning the properties of a magnetic thin oxide.

Resume : In amorphous solids structural disorder can lead to an insulator–metal transition on account of Anderson localization, i.e. the electronic states below the mobility edge are localized. If the Fermi energy passes through the mobility edge the material changes from an insulator to a metal. In addition, large deviations from the ideal stoichiometry of an oxide, that is, high defect concentrations, provide a high concentration of electronic defects (self-doping). We will consider examples of highly disordered oxides that were prepared by pulsed laser deposition and discuss their electronic conductivities and their application in resistive memory devices. In amorphous GaOx thin films we found non-filamentary memristive switching based on bulk oxide ion conductivity. We directly observed reversible enrichment and depletion of oxygen ions at the blocking electrodes responding to the bias polarity by using photoemission and transmission electron microscopies. The shape of the hysteresis I-V curves is tunable by the bias history, as found in the mathematically derived memristor model. This dynamical behaviour can be attributed to the coupled drift and diffusion of oxygen ions and the oxygen concentration profile acting as a state function of the memristor. L. Nagarajan, R.A. De Souza, D. Samuelis, I. Valov, A. Börger, J. Janek, K.-D. Becker, P.C. Schmidt, M. Martin, Nature Mater. 6 (2008) 391-398. M. Liu, Th. Leichtweiß, J. Janek, M. Martin, Thin Solid Films 539 (2013) 60-64. T. Leichtweiss, R.A. Henning, J. Koettgen, R.M. Schmidt, B. Holländer, M. Martin, M. Wuttig, J. Janek, Mater. Chem. A 2 (2014) 6631-6640. Y. Aoki, C. Wiemann, V. Feyer, H.-S. Kim, C.M. Schneider, H.-I. Yoo, M. Martin, Nat.Commun. 5:3473 doi: 10.1038/ncomms4473 (2014). Ch. Kura, Y. Aoki, E. Tsuji, H. Habazaki, M. Martin, RSC Advances 6 (2016) 8964-8070.

Resume : Nanocomposites of nanocrystalline metal oxides and carbon nanomaterials have great potential for energy and environmental applications. The nanocomposite thin films with a large specific surface area are preferable as electrode materials in electrochemical energy conversion and storage, and chemical sensors for applications in portable electronics, microelectronics devices and microelectromechanical systems. However, the cost-efficient manufacturing of nanocomposites thin films has been a significant challenge for conventional chemical and physical techniques. Herein we report a novel approach to rapid (within a couple of minutes) photoinitiated synthesis of nanocrystalline metal oxides-reduced graphitic oxides (rGO) in-situ nanocomposite thin film through pulsed white light irradiation of photosensitive metal-organic precursor films made by chemical solution deposition. The instantaneous photoinitiated pyrolysis of photosensitive precursor occurs in the first couple pulses of irradiation and results in metal oxides-graphitic oxides composite thin film with a 3-D nanostructure that includes a porous top dendritic layer and a dense bottom layer. Subsequent pulsed light irradiation improves the crystalline quality of metal oxides nanograins and leads to the reduction of graphitic oxides. This novel approach has been applied to synthesize 3-D nanostructured TiO2-rGO [1], Co3O4-rGO [2] and Fe2O3-rGO [3] in-situ nanocomposite thin films. We also successfully fabricated Co3O4-rGO and Fe2O3-rGO nanocomposite thin films on Si substrates for Si-based micro-supercapacitor application. Measuring them as electrode materials in a three-electrode cell in 2M KOH electrolyte, Co3O4-rGO as cathode material exhibited a specific areal capacity as high as 50 mF/cm2 at 2 mA/cm2 and a great rate capability of 60 % retention from 0.1 mA/cm2 to 10 mA/cm2 after stable cycling more than 100,000 times [2], while Fe2O3-rGO as anode material showed a specific areal capacity as high as 100 mF/cm2 at 5 mA/cm2 after stable cycling more than 10,000 times [3]. This straightforward and scalable nanotechnology opens a new pathway to the manufacturing and practical application of nanocrystalline metal oxides-reduced graphitic oxides nanocomposite thin films for thin-film based batteries and sensors. References [1] S. Luo, S. Zhang, B. B. Bourgeois, B. C. Riggs, S. Adireddy, K. A. Schroder, Y. Zhang, J. He, K. Sun, J. T. Shipman, V. Puli, R. Tu, L. Zhang, S. Farnsworth and D. B. Chrisey. Instantaneous photoinitiated synthesis and rapid pulsed photothermal treatment of three-dimensional nanostructured TiO2 thin films through pulsed light irradiation. Submitted to Journal of Materials Research, (2017) Invited paper [2] S. Luo, W. Liu, M. Oguntoye, B. B. Bourgeois, J. He, B. C. Riggs, S. Adireddy, J. Shipman, S. Zhang, L. Zhang, N. Pesika and D. B. Chrisey. Photoinitiated synthesis of Co3O4-reduced graphitic oxides in-situ nanocomposite thin film as electrode materials for silicon-based micro-supercapacitor with ultra-long lifetime. Submitted to Nano Lettters, (2017) [3] S. Luo, W. Liu, M. Oguntoye, B. B. Bourgeois, J. He, B. C. Riggs, S. Adireddy, J. Shipman, S. Zhang, L. Zhang, N. Pesika and D. B. Chrisey. Pulsed photoinitiated synthesis of nanocrystalline iron oxides-reduced graphitic oxides in-situ nanocomposite thin film as high performance anode for silicon-based micro-supercapacitor. Submitted to ACS Energy Lettters, (2017)

Resume : Perovskite rare-earth nickelate oxides (RNiO3) are mostly studied for their appealing sharp metal-to-insulator transition (MIT)[1]. Because the latter is affected by the ionic radii of the rare-earth ions (R≠La), nickelates offer the possibility to study one of the most fascinating problems of condensed matter without introducing chemical disorder. However, so far, a comprehensive picture that enables a clear understanding of the MIT is still lacking [2]. In the particular case of NdNiO3 (NNO) synthesized as form of thin films, the straininduced effect at the MIT properties provide (unexpected) dissimilar results. Indeed, a compressive strain state has been found to decrease, increase or completely suppress the MIT [3]. It becomes evident that different aspects need to be considered in the growth process in order to unequivocally describe the transport properties of NNO thin films. By means of pulsed laser deposition two series of NNO thin films have been grown onto LaAlO3 single crystals by using two different ceramic targets, i.e. mixed-phase (mixture of Nd2O3 and NiO oxides from Pi-Kem) and single-phase (mostly NdNiO3 from Toshima). Interestingly in both cases the pre-ablation history (overall number of laser pulses fired prior deposition) of the ceramic targets affected, in different way, the reproducibility of the growth experiments. In-situ XPS and TEM-based analysis indicated cationic off-stoichiometry (prevalent in the case of the mixed-phase target), as the main cause for the lack of reproducibility of the thin films MIT properties. As a consequence, changes in the Ni valence and bandwidth are deduced and discussed [4]. [1] Medarde, M.L., J. Phys.: Condens. Matter., 9, 1679-1707 (1997). [2] Garcia-Munoz, J.L., et al., PRB 52, 13563-13569 (1995). [3] Breckenfeld, E., et al., ACS Appl. Mater. Interfaces 6, 22436-22444 (2014). [4] Preziosi, D., et al., AIP Advances 7, 015210 (2017). This work was supported by the ‘MINT’ ERC Consolidator Grant #615759.

Resume : Ceria is a key component of oxidation catalysts that operate through a Mars-van Krevelen mechanism, with a role in promoting activity. The paradigm example is the VOx–CeO2 system for oxidative dehydrogenation reactions, where a synergy between vanadium oxide species supported on ceria drives the enhanced activity: catalyst reduction is promoted by reduction of ceria. This results in favourable oxygen vacancy formation and hydrogen adsorption energies, which are useful descriptors for the oxidation activity of VOx–CeO2 catalysts. In this contribution we study if this promoting effect holds for other metal oxide modifiers of ceria, focusing on CrOn– and MnOn–CeO2(111) (n = 0 − 4). We show from density functional theory calculations and statistical thermodynamics that the stable species in each case is MnO2– and CrO2–CeO2, similar to the vanadia modifier. The energetics of oxygen vacancy formation and hydrogen adsorption are more favourable than unmodified CeO2, indicating that VO2–CeO2 is not unique in displaying enhanced activity for oxidation reactions. However, the mechanisms involved depend on the modifiers. CrO2–CeO2 shows similar properties to VO2–CeO2 with ceria reduction upon oxygen removal to stabilise the 5+ oxidation state of Cr. In contrast, in MnO2–CeO2, Mn is preferentially reduced. These results shed light on the factors involved in active oxidation catalysts based on supported metal oxides on ceria that should be taken into consideration in a rational design of such catalysts.

Resume : Chemical gas sensors based on metal oxide nanopores and nanotubes are among the most studied structures for the environmental, food quality and health monitoring due to their several advantages such as large surface area, good chemical stability, low cost and simple measuring electronics. Gas sensor technologies are still developing and have yet to reach their full potential in capabilities and usage. Therefore, the improvement of metal oxides’ sensing properties remain challenging issue for fabrication of low power consumption and small size sensors. In this regard, fabrication of mixed and composite structures based on metal oxides could prove to be an effective way to enhance their sensing properties. Recently graphene with its excellent electronic capacity and high specific surface area have been applied as new additive in composite materials to improve their functional properties. In this work, we report the fabrication of a nanocomposite material based on highly ordered TiO2 nanotubes and modified graphene sheets. We prepared the structures combining the electrochemical anodization and modified Hummers methods. The sensing properties of the fabricated nanocomposite were tested towards different, explosive and toxic gases. The morphological, structural and elemental analysis of the composite were performed. Investigations showed that the sensing performance of composite was extremely enhanced compared to pristine TiO2 nanotubes. As the result we prepared a composite material based on metal oxide nanotubes and modified graphene with the substantially improved sensing properties. Meanwhile, we developed a cost-effective and easy growth method for the fabrication of high performance and small size chemical gas sensors.

Resume : Amorphous silicon suboxides exhibit intrinsic resistive switching behaviour which is highly desirable for its use in resistive random access memory (ReRAM) technologies. We have carried out a combination of electrical probing measurements and transmission electron microscopy (TEM) characterisation to gain an insight into how the microstructure of sputter-deposited oxide films can influence their switching behaviour. We characterised three different metal-oxide-metal structures of varying interface roughness. Scanning TEM (STEM) characterisation of pristine oxide films suggests that rougher oxide interfaces result in lower switching voltages and greater device endurance. Rougher oxide interfaces are shown to promote enhanced columnar growth in the oxide films, which is typical of sputter deposition. This results in the growth of intercolumnar void structures. Electron energy-loss spectroscopy (EELS) indicates that on electrical stressing, these structures facilitate the migration of oxygen and lead to enhanced switching behaviour. Our results suggest that columnar microstructure is an important factor to consider in the optimisation of silicon suboxide-based ReRAM technology.

Resume : The need for fast and energy efficient digital memories is driving many efforts now to advance resistive switching device technology, though, its most promising applications will likely be in neuromorphic computing. Most of the efforts now are on memristor-based firing-rate neural networks, such as the ones implementing deep learning algorithms, due to their widespread use in today’s machine learning applications. A potentially more promising are spiking neural network, whose operation is closer to that of biological brain. Such networks are believed to be more energy efficient and naturally suited for coordinated processing of spatial temporal data because of explicit encoding of information in the timing of the signals, which makes some operations, like correlation and coincidence detection, straightforward to implement. In our talk we will show that the TiO2-based memristor is a promising device technology for implementing the synaptic links between neurons in a spiking neural network. Using a 20x20 crossbar array of TiO2 devices, we will discuss experimental demonstration of a simple coincidence detection task performed by an analog spiking neural network with integrate-and-fire neurons and memristive synapses. We will also present some experimental statistics on device variations and simulations of bigger network based on an experimental model of the devices.

Resume : In this study we report the fabrication of solution-based metal oxide (MOX) transistors involving high power xenon flash lamp pulses with pulse durations of several hundred microseconds and energies up to 5 J/cm2. Using this technology we are able to demonstrate the successful realisation of low-voltage In2O3 and ZnO transistors with field-effect mobilities of 1.7 cm2/Vs and 6 cm2/Vs respectively at operating voltages around 2 V for the first time on glass substrates. These performances are comparable to reference devices fabricated by using conventional thermal treatment at temperatures of 250 °C but obtained in just a few seconds and thus in a fraction of time. Besides electrical characterisation the influence of the high intensity flash exposure on the surface topography and elemental composition of the MOX semiconductors is investigated by atomic force microscopy and x-ray photoelectron spectroscopy. Using a numerical model we are able to analyse the temperature profile in time within the thin film stack revealing a remarkable increase of the temperature beyond 1000 °C in less than 1 ms on top of the device surface within the MOX layers during each pulse while the backside of the glass substrate is nearly unaffected. In addition, we will show that this technology enables a facile way to pattern solution-processed In2O3 by selective xenon flash exposure of the MOX films through a shadowmask which is of high importance for the rapid fabrication of (opto-)electronic devices.

Resume : Integrating functional oxides on silicon substrates is a key issue for future microelectronic devices. However, the controlled epitaxial growth of complex oxides on Si substrates is a challenging task regarding the strong structural, chemical and thermal dissimilitude between these materials [1]. This work describes new strategies to integrate advanced oxide nanowire thin films on Si substrates via a chemical solution deposition approach. Manganese oxides based single crystalline nanowires with the hollandite structure were epitaxially grown on top of Si through a scalable and low cost direct precursor solution process. The nanowire growth mechanism involves the controlled growth of quartz thin films at the Si surface, which allowed the epitaxial stabilisation and crystallisation of nanowires. α-quartz layers were obtained by thermally activated devitrification of the native amorphous silica surface layer, driven by the confined precursor’s solutions containing alkaline earth cations [2]. This innovative growth method offers the possibility to modify the chemical composition, crystallographic structure and hence the physical properties of the grown nanowires [3]. Nanowire films including Ba1+xMn8O16, Sr1+xMn8O16, the doped quaternary oxides (BaSr)1+xMn8O16 and Ba1+xMn8-yXyO16, and a novel crystallographic phase LaSr-2×4 all of them with enhanced ferromagnetic and electrical properties have been effectively integrated on Silicon. 1. J.Vila-Fungueiriño et al, Frontiers in Physics 3, 38, 2015 2. A.Carretero-Genevrier et al, Science 340, 827, 2013 3. A.Carretero-Genevrier et al, Chemical Society Reviews 43, 2042, 2014

Resume : Integration of complex oxides on semiconductor platforms offers a promising perspective to improve or add functionalities on nanoelectronic chips. Recently, few groups studied the growth of the ferroelectric perovskite BaTiO3 on Si or Ge substrates. In order to obtain c-axis growth of the tetragonal BaTiO3 phase, it is necessary to insert a buffer layer such as SrTiO3 on both substrates. We consider here the direct growth of BaTiO3 on Si1-xGex substrates. In order to evaluate the impact of the surface chemistry on the epitaxy, we considered strained-Si1-xGex on Si (100) substrates. The passivation of the starting surface will be discussed. By developing a careful surface preparation, the direct growth of BaTiO3 was achieved on strained Si0.8Ge0.2/Si. From the X-ray diffraction analysis, the films are found to be oriented with <112> directions perpendicular to the substrate's surface and show two distinct in-plane orientations. Aberration-corrected scanning transmission electron microscopy (STEM) was performed to investigate the crystalline domains and the interface with the semiconductor. A detailed study will be presented, including high-angle annular dark-field (HAADF)-STEM imaging and electron energy loss spectroscopy (EELS)-STEM analyses. The cationic and oxygen compositions of the film and interface will be discussed. An orthorhombic epitaxial silicate is formed at the interface with Si0.8Ge0.2 which gives rise to the 112 epitaxial growth of BaTiO3.

Resume : We demonstrate regular-type perovskite solar cells based on vertically grown Ni-doped zinc oxide (ZnO) nanorod arrays as the electron transporting layer (ETL). 1% or 2% Ni elements were doped into ZnO nanostructures during hydrothermal growth of nanorods. Moreover, P3HT doped with bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI) was used as the hole transporting layer. Three types of perovskite materials, including MAPbI3, (MA)x(FA)1-xPbI3, and (MA)y(GA)1-yPbI3, were used as the light absorbers to exploit conversion efficiency of photovoltaic devices. Both Ni-doped ZnO nanorods and perovskite materials were characterized with miscellaneous techniques, including SEM, AFM, X-ray diffraction, and absorption/emission spectroscopies. Regular-type perovskite solar cells with the configuration of ITO/Ni-doped ZnO nanorods/PCBM/perovskite/P3HT Li-TFSI/Au were fabricated and evaluated. All devices were measured under standard AM1.5G illumination condition in the ambient environment without encapsulation. The champion perovskite solar device was achieved using 2% Ni-doped ZnO nanorods as the ETL and (MA)y(GA)1-yPbI3 as the absorber. The device delivered an open-circuit voltage of 0.83 V, a short-circuit current density of 23.73 mA/cm2, a fill factor of 70%, and a power conversion efficiency of 13.8% that was higher than the previous result demonstrated in the 2016 EMRS Spring Meeting.

Resume : We demonstrate a novel carrier transporting combination made of tungsten trioxide (WO3) nanomaterials and Cs2CO3/PCBM buffer bilayer to improve photovoltaic performance of regular-type perovskite solar cells (PSCs). The WO3 nanoparticles and nanorods were prepared by sol-gel process and hydrothermal method, respectively. The Cs2CO3/PCBM buffer bilayer was deposited upon the WO3 layer by sequential coating to form pinhole-free perovskite layer. The prohibited PL emission of the perovskite brought by Cs2CO3/PCBM bilayer indicates more effective carrier extraction and reduced recombination, which facilitates the carrier transfer from the perovskite to WO3 layers. Regular-type PSCs with the configuration of FTO/WO3/Cs2CO3/PCBM/ CH3NH3PbI3/P3HT/Au were fabricated. The optimized device based on WO3 nanoparticles and Cs2CO3/PCBM bilayer showed an open-circuit voltage of 0.84 V, a short-circuit current density of 20.4 mA/cm2, a fill factor of 0.61, and a power conversion efficiency of 10.5%, which were significantly higher than those of PSCs without Cs2CO3/PCBM buffer bilayer. The leakage current of the PSC device containing Cs2CO3/PCBM buffer bilayer was also significantly suppressed.

Resume : Conducting films are the quintessence of modern communication technologies. It is critical for many optoelectronic devices and components. There are most heavily used for electronic applications in devices; for instance, nanowires, nanoparticles and nanohybrid films. Our approach results in silver features of excellent conductivity and, subsequently to prepare the functional mounted on organic/ inorganic nanohybrid solutions with a polymeric dispersant and exfoliated clay which shows the performance to silver nanoparticles (AgNPs) etched on Clay substrates. A scanning electron microscopy showed that the images of the cross-section of synthesized AgNPs were clearly visible, the top white layer of approximately 1 μm thickness corresponds to silver film. Furthermore, thin films of AgNPs were prepared on a 60 μm thick film that were consistent with a sheet resistance as low as 4.12×10-4 Ω/sq through surface migration could be prepared by controlling the temperature sintering on ovan at 250 ℃ to form an interconnected network and by using Clay/ PTT1-B1/ AgNO3 in a weight ratio of 1/10/35 “Ag wt% in 5 wt%” and 1/10/59 “Ag wt% in 8 wt%.” During the sintering process, the color of the hybrid film feature changes from golden to white, demonstrating the possibility of the AgNPs to migrate and form an interconnected network. These nanohybrid requirements have potential for use in a new technology.

Resume : Last years for the synthesis of nanostructures on the surface and in the subsurface region of materials commonly used low-energy ion implantation in combination with the annealing. Special attention is given to nanoscale structures of silicon and metals in SiO2 films. These structures are the prospects for the creation of new electronic, optical, opto-electronic devices. It is known that during ion implantation into the surface layer of material formed various defects and nonequilibrium strained layers, nanoscale structures and boundary areas with different compositions and during the subsequent annealing occurs annealing of defects, diffusion of atoms, the formation of new nanocrystalline phases structural phase transformations etc. The observed effects are strongly dependent on the properties and structure of the matrix, the type, energy and the ion dose, type of annealing and vacuum conditions. In this work first studied the processes occurring in the bombardment of thin films of SiO2/Si with Ar+ ions and subsequent annealing: mechanisms of formation of nanostructures and films, their composition, electronic and crystal structure. The results of experimental investigations of the formation of nanoscale structures of Si by methods of secondary- and photoelectron spectroscopy showed the following: At the bombardment SiO2 with Ar + ions in the surface region of the SiO2/Si at low doses (D ≤ 5 • 1015 cm-2) are formed separate nanocluster areas enriched up to 50 -. 60 at% of atoms Si, and at high doses (D = 6 • 1016 cm-2) - thin layer (d = 25 - 30 Å) "pure" silicon as separate units. After warming observed film disintegration into separate cluster phase of "pure" Si. At T = 700 K, the surface size of these phases consist approximately 200 - 400 nm, and the distance between them approximately 300 - 500 nm. Thickness cluster phases is increased up to 30 - 40 Å. Increasing of temperature up to 900 K leads to evaporation of silicon phases.

Resume : Transparent conducting oxides (TCOs) are used in a wide range of applications, including flat panel displays, photovoltaics, solar cells, gas sensors, and transparent electrodes. TCO films require a low resistivity (ρ ≤10-3 Ω•cm), high optical transmittance (≥ 80%), and a large optical band gap energy (≥ 3.5eV). Sn-doped In2O3 (ITO) and F-doped SnO2 (FTO) are the most widely used TCO materials. However, indium in ITO is scarce and the processing temperature for FTO is too high. A doped ZnO thin film can be an alternative. In this work, we investigated the optical and electrical properties of Sn-doped ZnO thin films grown via RF co-sputtering deposition methods at room temperature. Both ZnO and Sn-doped (10 wt%) ZnO targets were simultaneously sputtered. By varying the relative power ratios of the two targets, the Sn-composition of ZnO:Sn thin films could be controlled. Through annealing, carrier concentrations and mobilities were improved. Carrier concentrations and mobilities of the ZnO:Sn thin films were measured using Hall effect measurements. The ellipsometric angles, Ψ and Δ, of ZnO:Sn thin films was measured via spectroscopic ellipsometry. Dielectric functions were obtained from the ellipsometric angles using the Drude and parametric optical constant models. With an increase in the Sn doping concentration, the Drude model amplitude increased substantially. The Urbach and optical gap energies of ZnO:Sn films were determined using the dielectric functions. The effective mass of ZnO:Sn was estimated to be 0.274 m0 assuming that the carrier concentrations measured via ellipsometry and Hall effect measurements were the same. The lowest resistivity of the ZnO:Sn films was 2.6x10-2 Ω·cm. The largest mobility and carrier concentration values of the ZnO:Sn thin films were 10.63 cm2/V·s and 5.61x1019 cm-3, respectively. Urbach energy increased as the Sn composition increased due to an increase in crystalline disorder. We determined the shift in the optical gap energy of the ZnO:Sn thin films to be a combination of Burstein-Moss effect, electron-electron interaction, and electron-impurity scattering. The total band gap energy shift using the model calculation matched well with the measured optical gap energy shift. The discrepancy between the model and experimental band gap energy shift could be attributed to Sn-alloying effect.

Resume : Interfacial materials with special wettability have attracted tremendous research attention for solving environmental problems.[1,2] Specifically, superhydrophilic and underwater superoleophobic films are promising candidates for oil pollution remediation by selective oil/water separation. The current key research direction for the practical implementation of such materials is to make them affordable, sustainable, multifunctional and stable under a wide range of harsh operation conditions, such as high temperatures and harsh chemicals. Here, we present our recent work on a novel silica nanofiber-based superhydrophilic and underwater superoleophobic mesh that incorporates all the aforementioned important characteristics. The mesh is prepared using waste soda-lime glass as the raw material through a green synthesis route. The resulting mesh shows excellent performance in separating various oil/water mixtures. More importantly, the mesh can maintain the superwettability under various harsh environments, and simultaneously remove multiple water contaminants during the oil/water separation process, leading to the multifunctional water purification. By converting the waste, i.e. waste soda-lime glass, into valuable functional materials, our strategy also helps to mitigate the severe land pollution caused by the accumulation of solid waste. [1] Q. Ma, H. Zhang* et al., Small, 2016, 12, 2186. [2] B. Chen, Q. Ma, H. Zhang*et al., Small, 2015, 11, 3319.

Resume : In this study, we found that the photocurrent of the annealed SnO2 thin films directly relates with the oxygen content in the annealing ambient. XPS results show that the surface oxygen adsorptions of the annealed SnO2 thin films increases with the oxygen content in the annealing ambient. It implies that the increasing of the surface oxygen adsorptions would enhance the photocurrent of the annealed SnO2 thin films. A SCR (surface space charge region) would be formed due to the surface oxygen adsorptions. With the SCR, we speculate that the electron-hole pairs of excitons excited by UV-laser can be separated. A theoretical calculation is used to verify that the SCR can effectively separate the electron-hole pairs. By knowing the width of the SCR, we can study the separation time of the electron-hole pairs by the built-in electric field. Therefore, we use the Poisson’s equation and the oxygen vacancy concentration varying from the surface into the SnO2 thin films to estimate the width of the SCR. The calculated width of the SCR is 4.32 nm and the electrons drifting time to across the SCR is about 3.31E-10 s. We note that the separation time of electron-hole pairs are shorter than the recombination time, which might prove that the SCR of the surface oxygen adsorptions can effectively separate the electron-hole pairs. The separation of the electron-hole pairs can cause excitons transforming to photo-carriers, which further enhances the lifetime of photo-carriers. The calculated lifetime of the photo-carriers from the annealed SnO2 thin films with oxygen annealing ambient matches the lifetime of the photo-carriers from common solar-cells. Therefore, we can conclude that the surface oxygen adsorptions of the annealed SnO2 thin films would enhance the photocurrent by increasing the lifetime of photo-carriers.

Resume : Ti2O3 is an oxide material that demonstrates the metal-insulator transition at about 150-300°C with approximately two orders increase of the electrical conductivity upon the heating. Such functionality could be prospective for different applications, including creating of the controlled plasmonic devices. However, lower titanium oxides are rarely produced and characterized, especially in the form of thin films. In our research, we demonstrate the formation of Ti2O3 films during the arc sputtering of a titanium target in an oxygen atmosphere. The crystal structure of the produced samples was investigated using Raman spectroscopy and X-ray diffraction, the optical properties were studied using ellipsometry, the conductivity of the films was measured using a four-probe method, the surface morphology was examined by atomic force microscopy and the chemical state of titanium atoms was determined using X-ray photoelectron spectroscopy. We show that the formation of the crystalline Ti2O3 films is possible at the process temperatures above 350°C. Produced samples demonstrate metallic properties and their crystalline structure corresponds to the bulk heated to about 170-200°C. Thus, the metal-insulator transition temperature for our films is significantly shifted into the region slightly below the room temperature.

Resume : Pure and manganese doped zinc oxide inks were developed by dispersing the respective nanoparticles in an ethylene glycol based solvent with polymeric stabilizer additive using mechanical milling approach. Nanoparticles were obtained by wet milling commercially purchased powders. For forming the doped nanoparticles, the powders were solid state sintered and then milled. Stable inks with uniform suspension were obtained and the sedimentation time for inks dispersed in different media was compared. Filtered inks using 200 nm pore size filters display stability greater than two months. The ink composition and fluid flow properties were investigated and optimized for proper jettability. Continuous line and drop patterns were deposited on a cleaned glass substrate using a custom built direct writing system. The deposition rate, speed, substrate temperature, and number of passes were varied and their effect on the spatial distribution of particles in printed pattern was characterized. Post annealing the particle continuity was studied using optical and electron microscopy while roughness and thickness were quantified using optical profiler. The optical and electrical properties of the printed patterns were measured and used to optimize the ink preparation route. Our work shows that this synthesis route can be used for preparing a variety of metal oxide based inks for printed electronics applications.

Resume : In this paper the influence of the heat treatment on the structural and optical properties of oxide single-layer and multilayer transparent thin film structures of ITO/Au/ITO, AZO/Au/AZO, TiO2/Au/TiO2 and Bi2O3/Au/Bi2O3 type is studied. The single-layer oxides and respective multilayer structures have been deposited on glass substrates by successive DC magnetron sputtering using metallic targets In:Sn, Zn:Al, Ti and Bi, in reactive (for the oxide films) or inert (for the metallic Au interlayer films) atmosphere. Good quality transparent conducting thin film structures have been obtained, with resistivity  10-4 ·m and transmittance  75%. The wetting surface properties in function of time exposure at UV radiation (254 nm) have been also studied before and after heat treatment performed at 450 °C.

Resume : Synergetic transport properties in 2D material-transition metal oxide heterostructure are studied by examining conductance of monolayer graphene on epitaxial SrTiO3 (STO) thin film grown on Nb-doped STO single-crystalline substrate. [1] Due to the large dielectric constant of STO thin film, we could largely scale down the required gate-voltage in our device compared to a similar device on a silicon substrate. In particular, clear quantum Hall plateaus could be observed within a narrow gate-voltage sweep range. As applying higher gate voltage in our device, a systematic development of hysteretic conductance was observed on top of the quantum Hall behavior. We attributed the hysteresis to the creation and annihilation of oxygen vacancies in STO. Furthermore, a simple capacitor model could be constructed by using the linear behavior of the scale factor with respect to the gate-voltage sweep range, which led to a quantitative relationship among the dielectric properties of STO with oxygen vacancies. We believe that our results suggest that inherent quantum Hall conductance in graphene can serve as a robust and sensitive probe for investigating the ionic and electronic nature of complex transition metal oxides. [1] Park, J., et al., Voltage Scaling of Graphene Device on SrTiO3 Epitaxial Thin Film. Nano Lett., 2016. 16(3): p. 1754-1759.

Resume : In recent years fuel cells became one of the most attractive technology for energy conversion devices. The use of catalyst and more specifically platinum allows to increase the conversion rate, but the high price of this metal requires to find an alternative way. It has been shown that tungsten oxycarbide presents the same electronic behavior as platinum but in the last decades only few studies focused on this compound. Moreover, to increase the surface reactivity and keep the device as compact as possible, the catalyst material has to be porous. In this study, thin films of tungsten oxycarbide were grown by direct liquid injection chemical vapor deposition on silicon wafer covered by native oxide using tungsten hydride as precursor. A two steps process has been developed by depositing a dense tungsten oxycarbide layer on a porous tungsten oxide layer. Surface and cross-sectional morphologies obtained by scanning electron microscopy evidenced that porosity of the tungsten oxide layer is temperature dependent. However, oxycarbide deposits obtained at higher temperature on the oxide do not modify the porosity character. X-ray photoelectron spectra evidenced that oxycarbide deposit completely covers the tungsten oxide.

Resume : New layered perovskites doped with magnetic elements of ACa2MNb3TiO13 (A = K or Rb, M = Mn, Fe, Co and Ni) were successfully synthesized by applying the unique "solid-state templating process" and their ion-exchange and exfoliation behaviors were examined. The target compounds were obtained by calcining a stoichiometric mixture of a typical Dion-Jacobson phase of ACa2Nb3O10 and ilmenite-type oxide of MTiO3 at 1373 K. The Rietveld refinements and chemical analysis indicate the successful formation of ACa2MNb3TiO13. Reaction of a 5 M HNO3 solution promoted the substantial exchange of interlayer alkali ions for protons. The basal spacing was expanded to about 2 nm by the proton exchange accompanied by hydration. Reaction of the protonated samples with a tetrabutylammonium hydroxide aqueous solution produced a turbid colloidal suspension. AFM observation of the samples after deposited on a Si substrate detected micrometer-sized 2D objects with a uniform thickness of about 2.1 nm, suggesting the delamination into unilamellar nanosheets. In-plane and out-of-plane XRD data further confirmed the full exfoliation of the layered perovskite compounds.

Resume : Non-doped ZnO thin films are deposited on glass by spray pyrolysis and spin-coated method by changing the deposition temperature under atmospheric pressure. The supply of precursor and the growth of ZnO are occurred simultaneously in spray pyrolysis, while occurred at separate steps in spin-coated method. Diethylzinc (DEZ) solution and Zinc acetate solution are used as the solvents. Since DEZ reacts actively with water and oxygen at low temperature, ZnO can be generated by DEZ solution at low temperature in comparison with Zinc acetate solution [1]. For the deposited ZnO thin films, the optical and structural properties are characterized with spectrophotometer, X-ray diffractometry and transmittance electron microscopy. The density of each layer is evaluated by X-ray reflectivity. The surface morphological analysis are carried out using scanning electron microscopy and atomic force microscopy. ZnO grows into polycrystalline films with a hexagonal wurtzite-type structure by the deposition over the critical temperature according to the growth method and the solution material. The morphology of deposited films are roughly divided into the columnar and the granular structure. Also grain size is increasing with increasing the deposition temperature. It is found that these structural properties determine the physical properties of ZnO films such as the optical band gap, the overall density of film and the surface roughness. [1] K. Yoshino et al, Jpn. J. Appl. Phys. 50 (2011) 040207

Resume : Vanadium dioxide (VO2) is a strongly correlated electron oxide that undergoes a first-order metal-insulator transition (MIT), coupled with a structural phase transition from a high-temperature tetragonal rutile phase to a low-temperature monoclinic phase at the temperature of approximately 340 K. VO2 nanowires have attracted significant attention due to a variety of potential applications for electronics and optoelectronics using an ultrafast MIT property. Importantly, the MIT property of VO2 nanowires is significantly affected by their stoichiometry, doping, size effect, defects, and strain. In this work, to effectively investigate those issues, we fabricated two-terminal sensor devices which made from single-crystalline VO2 nanowires decorated with Au nanoparticles. First, VO2 nanowires were synthesized and characterized on a SiO2 (1 µm) substrate. Secondly, we investigated sensing properties of hydrogen gas for the two-terminal VO2 devices. This study provides helpful and valuable information on controlling the structural and electrical properties of VO2 nanowires for the sensor applications.

Resume : Methane is an extremely important clean fuel source; however, its activation is extremely difficult due to the large energy required to break the first CH bond. This contribution presents a density functional theory investigation of doping of cerium dioxide (111) with (1) alkaline earth metals and (2) divalent Cu and Zn metals to examine their effect in promoting methane activation. The incorporatation of these metal dopants in the surface results in spontaneous formation of charge compensating oxygen vacancies, and also enhances surface reducibility. This effect from substitutional doping of the ceria surface greatly improves the adsorption, and the stablity of the CH3 + H dissociation products compared to undoped ceria. The enhanced stabilisation of the products drives the thermodynamics towards dissociation. The calculated kinetic barriers show that for the alkaline earths, Mg and Ca doping lower the kinetic barrier compared to the undoped surface, while for Sr the activation energy is higher. Zn substantially lowers the activation barrier, while Cu makes little difference. We examein correlations between the thermodynamics and kinetics and the cation dopant size. Alkaline earth doping shows that the dissociation products become more stable with a larger dopant ionic radius while the kinetic barriers are reduced with increasing cation size up to the limit of the Ca cation. Sr, Cu and Zn appear to show little correlation which we trace to the particular surface structures induced by each dopant. Finally, oxidation of methane on these divalent doped surfaces shows that the dopant can control the selectivity of products, with Zn promoting formaldehyde formation and Mg doping promoting CO2 formation. Support from the European Commission through the 7th Framework Project BIOGO (www.biogo.eu), grant number 604296, is acknowledged

Resume : Ti/TiOx and W/WOx multilayered thin films have been deposited by DC reactive sputtering using the reactive gas pulsing process. It is implemented to produce regular alternations of metal-oxide compounds at the nanometric scale [1, 2]. Structure and growth have been investigated by XRD, XPS and Transmission Electron Microscopy with associated analytical techniques. Conventional TEM has been performed to determine the thickness of the periodic metallic and oxide layers from 3 to 50 nm. HRTEM experiments have been used to propose a growth model. Chemical information was obtained from energy dispersive spectroscopy and electron energy loss spectroscopy. Regularity of metal and oxide alternations, quality of interfaces as well as oxygen diffusion through the multilayered structure have been examined and linked to the growth conditions. Electrical measurements have been also carried out with the van der Pauw method to determine resistivity changes with temperature. Relationships have been established between in situ growth conditions, structural and chemical parameters and electrical properties in periodic multilayers. The knowledge of the structural parameters has allowed determining a first relation between the elaboration conditions (control of the pressure value) and the structural parameters. Electrical and structural results have also been related to propose a law linking the resistivity values to the structural parameters as total thickness etot, metal met and oxide ox layers thickness and metal elemental composition Cmet. [1] A. Cacucci et al, Acta Mater., 61 (2013) 4215-4225 [2] V. Potin et al, Superlattices and microstructure (10.1016/j.spmi.2016.10.071)

Resume : Metal oxide semiconductors have recently been of high interest due to their excellent electrical performance combined with optical transparency and mechanical flexibility. Thin-film transistors implementing a number of metal oxides semiconducting channels have been demonstrated already. They have excellent performance that is superior to that of amorphous silicon (a-Si:H). Amongst them, Indium Zinc Oxide-based materials constitute the most promising next-generation TFT materials of choice, due to their high mobility caused by direct overlap of the isotropic s orbitals of its Indium atoms. One remaining issue, however, is the formation of oxygen vacancies that destabilize the material’s electronic properties. To address this issue, Ga doping has been used in an effort to suppress the oxygen vacancies. This work reports on the physical properties of an alternative metal oxide material-Indium Zinc Oxide thin films doped with yttrium (IZO:Y). The IZO:Y films were processed from solutions at 400 oC in air by spray pyrolysis of b-diketonates and chlorides and characterised by UV-Vis absorption spectroscopy, FTIR, AFM, x-ray diffraction, spectroscopic ellipsometry and field effect measurements. Analyses revealed very smooth polycrystalline films with wide band gaps in the order of 3.5 eV. TFTs employing Al2O3 gate dielectrics and IZO:Y semiconducting channels exhibit excellent operating characteristics for the optimal Y doping content of 0.4 mole i.e. a high electron mobility in excess of 20 cm2/Vs and current modulation ratio in the order of 10^6.

Resume : Recently, a large number of In2O3-based oxide semiconductors (mainly Indium Zinc Oxide - IZO and Indium Gallium Zinc Oxide - IGZO) have been extensively investigated for use as the semiconducting channels in thin film transistors (TFTs). IZO has a large amount of deep defect states that can be attributed to oxygen deficiency states resulting in instability in such TFTs. To resolve this issue, the addition of gallium has been utilised to reduce the oxygen deficiency state density making a-IGZO a suitable semiconducting material for TFTs. There is some evidence however that gallium doping leads to an increased device photosensitivity to visible light, a rather undesirable effect when they are used in flat panel displays. In order to address the above-mentioned stability issues we have investigated TFTs employing solution processed tungsten-doped Indium Oxide (In2O3:W). The films were deposited by spray coating at 350 oC from InCl3 and WCl5 blends in methanol and characterised by X-ray diffraction, AFM, UV-Vis absorption spectroscopy and field effect measurements. TFTs that employed Al2O3 gate dielectrics, In2O3:W semiconducting channels (with various W content) and gold source and drain contacts underwent negative bias stress for 6000 s, and showed excellent stability characteristics such as a small decrease of the threshold voltage (from 2.3 V to 2.0 V) without significantly decreasing the electron mobility - decreased for 16 to 14 cm2/Vs.

Resume : Solution processed ZrO2 and its implementation as the active channel material in TFTs has already been demonstrated. The use however of substrate temperatures compatible with flexible glass substrates i.e. up to 500 oC resulted in ZrO2 dielectrics of a monoclinic structure (the “distorted” phase of a cubic structure) limiting its dielectric constant to 15. The desired “high-temperature” ZrO2 with a tetragonal cubic phase can readily be stabilized, at lower temperatures by the use of different dopant elements (or compounds such as CaO, MgO, Y2O3). This can also be achieved by reducing the crystallite size. Because of its high dielectric constant, in theory in excess of 24, yttria-stabilized zirconia (YSZ) has thus been suggested as a promising gate dielectric candidate Here, we report on the deposition and characterisation of yttria-stabilised zirconia (YSZ) gate dielectrics grown by spray coating in air at moderate temperatures of about 450 oC from yttrium and zirconium b-diketones in methanol. The YSZ films of various yttrium content were investigated by means of UV–Vis absorption spectroscopy, x-ray diffraction, AFM, admittance spectroscopy, spectroscopic ellipsometry, and field-effect measurements. Analyses of the YSZ films reveal smooth films (RRMS<2 nm) of a tetragonal (fluorite) phase with dielectric constant in the range between 16 and 21. TFT transistors employing YSZ deposited with an optimal Y content of about 4 % mole, reveal excellent operation characteristics in terms of low voltage operation, low leakage currents, high electron mobility in excess of 35 cm2/Vs and high on/off current modulation ration in the order of 10^7. These performance enhancements may be attributable to the large band offsets and small lattice mismatch between the YSZ dielectric and ZnO.

Resume : It is well-known that grain boundaries in doped transparent conducting oxides exhibit potential barriers, which reduce the carrier mobility due to thermally activated transport across the barriers. According to the Seto model, which is typically used to describe the phenomena and to derive the density of trapped charges at grain boundaries, the potential barrier heights should decrease with increasing carrier concentration and are expected to vanish at the highest concentrations. We have performed Hall effect measurements of In2O3 thin films either undoped or doped with different concentrations of SnO2, ZrO2, GeO2, and with H2O. The films were prepared by magnetron sputtering at different substrate temperature and with varying oxygen or water content in the process gas. These measurements reveal that grain boundary scattering is mostly pronounced for Sn-doped samples and increases with increasing Sn concentration. The effect is related to the segregation of Sn dopants to the grain boundaries, which is in-line with segregation of dopants to the surface as demonstrated by XPS measurements. A significant reduction of carrier mobility is observed even for films with carrier concentrations of 1021 cm-3. The dependence of grain boundary scattering on dopants is also observed from the determination of barrier heights using temperature dependent Hall effect measurements. Comparing samples with similar carrier concentrations shows that the highest barriers are obtained with Sn-doping while H2O (H) doping results in the lowest barrier heights.

Resume : A prompt and inexpensive glucose level detection is a key issue for human health and biotechnological applications. Nanostructured nickel hydroxide has shown notable activity for amperometric non-enzymatic glucose sensing [1]. Here, we present the room-temperature synthesis of a hierarchical combination of Ni(OH)2 nanoflakes electrodeposited onto ZnO nanorods grown by chemical bath deposition. The shape features (height and lateral size) of ZnO NRs were varied by changing the chemical bath deposition parameters. ZnO NRs provide a large surface area substrate for the pulsed electrodeposition of nanostructured Ni(OH)2. The correlation between the synthetic parameters and the electrochemical behavior of Ni(OH)2/ZnO nanostructures is reported. The non-enzymatic oxidation of glucose at the surface of electrodeposited Ni(OH)2 is demonstrated in 0.1 M NaOH electrolyte, revealing a glucose sensitivity up to 1.85 mA/(mM cm2), with a linear detection range of 0.04–2.10 mM [2]. All the samples show a fast response time (less than 1 s), resistance in chloride solution, selectivity in the presence of common interfering electroactive species and excellent long-term stability. All these features, combined with the ease of the fabrication method, make Ni(OH)2/ZnO nanostructures an ideal alternative for inexpensive amperometric glucose sensing applications. [1] K. Iwu, S. Mirabella et al. Sens. Actuators B 2016 [2] V. Strano, S. Mirabella, RSC Advances 2016.

Resume : Non-enzymatic glucose sensing is based on the direct catalytic oxidation of glucose and typically allows very high sensitivity at the expense of high fabrication cost, low selectivity and poor stability. By using low-cost method we fabricated a novel Ni oxide based nanostructure for non-enzymatic glucose sensing [1]. A high surface area (25 m2/g) Ni nanofoam is obtained by room-temperature chemical bath deposition followed by 350 °C reducing annealing, and by cyclic voltammetry (CV). Several glucose sensor electrodes, on flexible and on rigid substrate, were fabricated, showing sensitivity up to 3 mA/cm2mM, linear range of 0.01–0.7 mM, limit of detection (LOD) of 5 M, resistance to chloride poisoning, excellent long-term stability (4% decrease in sensitivity after 64 days) and selectivity in the presence of common interfering species. The growth kinetics of the nanofoam is presented and modeled in terms of NiOOH nucleation and subsequent Ni(OH)2 precipitation. In addition, a full device was realized with a miniaturized electrochemical cell, based on a silicon chip with planar microelectrodes, connected to a PCB board (for the electrical driving and reading). The sensing electrode was based on NiOOH and glucose testing was performed in human blood and saliva [2]. The device sensitivity decreases with decreasing the electrolyte pH, with still some activity also at the physiological pH of 7.4. [1] Iwu et al., Sensors and Actuators B 224 (2016) [2] S. Petralia et al., submitted

Resume : The present work is devoted to the elaboration and characterization of undoped and tin doped ZnO deposited onto glass substrates by spray pyrolysis technique. The influence of Sn dopant on structural, optical and electrical properties of ZnO thin films were characterized by X-ray diffraction (XRD), UV–Vis spectroscopy and Hall Effect measurements using Van Der Pauw’s method. The atomic percentages of dopant in the starting solution were 0%, 1%, 3% and 5%. Structural analysis confirmed the hexagonal wurtzite structure of all deposited films with a polycrystalline nature. By applying scherrer formula to the preferential orientation, the grain size decreased from 49.1 nm for undoped ZnO to 30 nm with increasing Sn content up to 5 at.%. It was also observed that the peak position of the (002) plane shifted slightly to the high 2θ value with increasing Sn doping. The deposited thin films are highly transparent with an average transmittance above 80% in the visible region and the band gap decreased from 3.25 to 3.19 eV with increasing Sn content in the spray solution from 0 to 3 at.%. The lowest electrical resistivity of the as deposited Sn doped ZnO films (71 Ω.cm) combined with the highest carrier concentration (6×1016 cm-3) and mobility (1.22 cm2.V-1.s-1) was noted at 3 at.% Sn Doping. In addition, an improvement of the electrical properties was seen after post annealing under argon atmosphere at 350 C°. It was noticed that the electrical resistivity of the annealed films decreased sharply, by three orders of magnitude, due to the increase of both carrier concentration and mobility.

Resume : One of the important problems of physics of nanostructures is a research of dynamics of deactivation of interacting particles on the inhomogeneous surface. The kinetics of photoprocesses in such media doesn’t correspond to formal-kinetic model. The correlated pairs fade away and spatially distributed structures form in the systems, in whiсh annihilation processes have a place. Efficiency of these processes on a porous surface depends on its structural characteristics (pore size, degree of heterogeneity). Convenient way for gathering of information about modification of reagent distribution and cluster formation is a registration of delayed fluorescence, which is accompanied by triplet excitation annihilation at the different temperatures or ratio of reagent concentrations. Kinetics of photophysical processes gives information about kinematics of approaching reactants, features of distribution of cooperating particles in the structured environments. Annihilation delayed fluorescence of reagents became excited by second harmonic of laser IAG:Nd3+ (λ=532 nm, τ0,5=10 ns, pulse energy ~50 mJ) and were registered with time resolution 300 ns at wave-lengths 570 nm and 410 nm. Luminescence measurements are performed in vacuum-processed dish at the temperature range 153-293 K. Molecules of dye (rose bengal) and aromatic hydrocarbon were sorbed on a porous surface of silicon dioxides at various anthracene concentrations. Anthracene concentration in the solution is changed from C=5·10-5 mol/l to C=10-4 mol/l, dye concentration is 5·10-5 mol/l. Experimental kinetic dependences are compared to computer modeling results of hetero-annihilation processes in the systems, which have multifractal distribution of reagents on a surface. The degree of order, which is a criterion of structure self-organization and allows to determine degree of structure symmetry breakdown, is used for the description of reagent distribution on a surface. The degree of matrix microscopic heterogeneity is determined by parameter Δ. It relates with topology of space, in which annihilation processes have a place that leads to formation and growth of interstitial molecule clusters and exerts influence on kinetics of processes. Degree of order dependence on the temperature has the same nature as dependences of quenching sphere radius on the matrix temperature. The analysis of experimental results based on the multifractal formalism allows explain phenomena: change of order parameter in temperature range, chaos burning. Such simple models like cellular automata allow understand processes of complex kinetic phenomena on the solid state surface.

Resume : Carbon nanotubes were prepared by CVD assisted continuous CO2 laser ablation. The experimental system is composed of a laser ablation chamber, a furnace and a deposition chamber to assure long time of flight for plasma precursors and to keep the relatively high temperature for growth of carbon nanotubes. Solid targets were prepared by size-selected mixed carbon and Fe based oxides catalyst nanopowders obtained by laser pyrolysis. Different concentrations of catalysts in the carbon targets as well as different buffer gases and gas pressures have been used in order to study their influence on the formation of carbon nanotubes. Transmission electron microscopy and Raman spectroscopy were used to investigate the effect of various parameters effect on the growth and diameter distribution of the tubes.

Resume : In this work, we present a fabrication of SERS-active substrates by applying pulsed laser deposition. The substrates are based on Ag/ZnO nanostructures and can be repeatable used in Raman experiments without losing their sensitivity. The samples were prepared at process parameters usually used for deposition of smooth and dense thin films. Ag was incorporated into ZnO nanostructures during the growth by using of composite or mosaic target. Methylene blue (MB) was used as a SERS-active molecule. The UV-assisted cleaning cycles were applied for analyte degradation. It was demonstrated that MB undergoes rapid photodegradation and removes after each cleaning cycle. The SERS response before each cleaning cycle was highly reproducible and the substrates were characterized by a long shelf life. The results obtained demonstrate that Ag/ZnO nanostructures can be used as efficient, cheap and recyclable SERS-active substrates.

Resume : The application of laser-induced self-organized processes allows the large-area surface nanostructuring. In this study, the periodic surface nanostructuring of fused silica and sapphire is shown. For this purpose, the ripple formation was combined with an IPSM-LIFE (laser-induced front side etching using in-situ pre-structured metal layer) process. The dielectric substrates covered with a 10 nm thick Mo layer were irradiated by a fibre laser with a wavelength of 1064 nm and selectable pulse duration from 1 ns to 600 ns. At particular laser parameter, the irradiation causes the formation of ripple structures in the thin film with a periodicity similar to the laser wavelength. The further laser irradiation (IPSM-LIFE) of the ripples results in the modification of the linear ripples into periodic nano-scaled droplet structures. The formed metal droplet structures can be transferred into the dielectric substrate with an additional laser irradiation almost maintaining the lateral geometry of the metal droplets. The characteristics of the achieved metal and dielectric structures can be varied with the laser processing parameters and were analysed by atomic force (AFM) and scanning electron microscopy (SEM).

Resume : The pulsed laser deposition of pure or doped (Nd or Fe) ZnO films on (001) oriented MgO substrates was investigated as a function of the substrate temperature and oxygen pressure. Polar (alternate Zn and O planes) and non-polar ZnO films were obtained depending on the precise growth conditions and epitaxial films were observed in both cases. For the epitaxial non-polar films various epitaxial relationships were observed, and the domain matching epitaxy was used in order to describe the in-plane orientation of the film with respect to the MgO substrate. Differences appear in the epitaxial relationships between pure and doped ZnO films on MgO substrates. The main reason is due to the defects induced by the doping in the ZnO matrix, which limit the size of the crystallites. In the doped films, the minimum size of the epitaxial domain is lower than that in the pure ZnO, and accordingly the in-plane orientations of the crystallites are different. The precise epitaxial relationships will be presented and discussed in comparison with the results previously reported.

Resume : Zn-doped FeO (wustite phase) films were obtained by pulsed–laser deposition of a spinel target. The nearly pure wustite phase was obtained for growth in the 200 - 350°C range under a residual pressure of 5x10-7 mbar, or at room temperature in the 10-8-10-7 mbar range. A low proportion of the Zn:Fe3O4 spinel phase may coexist with this wustite phase. Very differently, an increase in the oxygen pressure and/or substrate temperature leads to the stabilisation of the spinel phase alone. All the wustite films grown on c-cut sapphire substrate are epitaxial, even those grown at room T. The epitaxial relationship is : (111)Zn:FeO // (00l)Al2O3 and [10-1]Zn:FeO // [210]Al2O3 The optical, electrical and magnetic properties of these nanocomposite films were measured and correlated to their structural and microstructural characteristics. In particular, the coexistence of the antiferromagnetic Zn:FeO phase and of the Zn:Fe3O4 ferrimagnetic phase in the films leads to very specific magnetic properties (magnetic exchange bias) which will be presented and discussed.

Resume : Due to a high practical importance of ZrO2 it was intensively studied during last several decades in forms of crystals, nanostructures and thin films [1,2]. As a result the procedures of synthesis and structure modification of zirconia are well elaborated. At the same time, some opportunities to make this oxide even more attractive for applications, in particular as optical material, are still under consideration. It is known a doping with rare-earth (RE) ions greatly improve luminescence properties of zirconia. However, RE elements belong to so-called critical raw materials and therefore decreasing of their using in devices is important problem of science and modern technology. This problem can be partly solved by ZrO2:RE doping with “abundant” element ions that should improve RE luminescence intensity. In this work we show that fluorination is a suitable way to improve luminescence intensity of Eu3+ ions in zirconia. A row of co-doped with fluorine and europium zirconia nano-ceramics were synthesized by solid state route. Obtained compounds were characterized with powder XRD, scanning electron microscopy and luminescence spectroscopy. It was found the studied samples of ZrO2:Eu,F are mixture of monoclinic and cubic zirconia with particles sizes about 50-150 nm. Doping with 8 mol. % of F leads to increase of ZrO2:0.5%Eu red luminescence intensity in about 6 times. [1] L. Kumari, et al., Cryst. Growth Des. 9 (2009) 3874. [2] X. Wang, et al., J. Alloys Compd. 556 (2013) 182.

Resume : In future thermonuclear fusion devices D+T reaction will be operated whose high release of energy requires plasma facing components (PFCs) to withstand extreme environment. Owing to its favorable physical properties tungsten is used for PFCs receiving highest fluxes in operating tokamaks (ASDEX-upgrade, JET-ILW) and will compose the ITER divertor. The high temperature of PFCs associated with the possible presence of oxygen impurities or accidental scenarios e.g. cooling system leakage or an emergency shutdown of the divertor may cause oxidation of the W-PFCs whose surface properties would then be altered. This work presents characterization studies carried out on samples that mimic the W-oxide that will possibly form in ITER. Films of WO3 with thicknesses between 20 and 230 nm were grown by thermal oxidation of tungsten substrates at 400° C and oxygen pressures of 5 Torr and 590 Torr. Previously, the effects of the substrate, oxygen pressure and oxidation time on the structure and thickness of the oxides formed and their thermal stability in the 400 - 800° C range were studied by Raman microscopy, X-ray diffraction, SEM and spectroscopic ellipsometry. We investigated the evolution of the specular reflection coefficient with wavelength between 200 and 800 nm and we correlated the respective colors of the films with the corresponding thickness and extinction wavelength as derived from the ellipsometry modelling. Acknowledgments: PN-Ctr 5N 2016 Romania and Be PAProMITER, France

Resume : Nanocomposite oxide films with both wurtzite (Fe:ZnO) and spinel (Zn:Fe3O4) phases have been obtained by pulsed-laser deposition of mixed (ZnO-Fe3O4) targets. The growth conditions (temperature, oxygen pressure and target composition) were studied in order to obtain these nanocomposite films. Both phases were found epitaxially grown on c-cut sapphire substrates. The epitaxial relationship of the wurtzite phase was the same as that observed for pure ZnO on sapphire. Differently, for the spinel phase in addition to the classical in-plane orientation of the pure spinel on sapphire, other epitaxial relationships were observed, due to the Zn doping and/or presence of the wurtzite phase. The optical, electrical and magnetic properties of these nanocomposite films were measured and correlated to their structural characteristics.

Resume : The aim of this work was to produce thin films of Mg-Al and Zn-Al layered double hydroxide (LDH) with organic chromophores guest intercalated in layered double hydroxide host via pulsed laser deposition (PLD). The capacity to intercalate organic anions into the interlayer space due to their high anionic exchange ability is characteristic to the clay materials. The organic chromophore was a commercial dye named coumarin-343. Powders of intercalated coumarin in Mg-Al and Zn-Al layered double hydroxide with Mg/Al and Zn/Al of 2.5 and Mg/Al and Zn/Al of 3 were prepared by co-precipitation and then pressed and used as targets for thin film deposition. For powder characterization, we used: X-ray diffraction (XRD) for the structural analysis, thermal analysis (TG-DTA). Three different wavelengths of a Nd:YAG laser (266, 532 and 1064 nm) working at a repetition rate of 10 Hz and pulse duration of 5 ns have been tested. After deposition, the thin films were thermal treated at different temperatures and characterized by X-Ray Diffraction (XRD) and optical spectroscopy. The optical response and the thermo-optical stability of the obtained thin films were investigated.

Resume : Zinc Oxide (ZnO) is a transparent conductive oxide and wide band gap semiconductor with a direct band gap, large exciton binding energy and diversity of nanostructure shapes interesting for applications such as the optically transparent electrodes. We study the effect on the optical and electrical properties of hydrogen plasma treatment of the nominally undoped, nanocrystalline ZnO thin films deposited by DC reactive magnetron sputtering of Zn target in the gas mixture of argon and oxygen plasma. After hydrogen plasma treatment, the increase of the electrical conductivity and the increase of the infrared optical absorption was detected and related to the increase of the free carrier concentration. To confirm this relation, the mobility and carrier concentration were measured by temperature dependent electrical resistivity and Hall effect using the van der Pauw method. We also investigated the localized defect states below the optical absorption edge using optical absorption spectroscopy and photoluminescence in a broad spectral range from near UV to near IR. We conclude that the increase of the electrical conductivity is indeed confirmed to be related to the increase of the free carrier concentration and thus we prooved that the controlable post-deposition hydrogen plasma doping od ZnO thin films is possible. We acknowledge the Czech Academy of Sciences project KONNECT-007 and the Czech Science Foundation project 16-10429J.

Resume : Transparent conductive oxides (TCOs) are a class of materials which combines high optical transmittance in the visible spectrum with a resistivity below 10-3 Ωcm. Indium tin oxide (ITO) is the most used TCO. It is widely applied as transparent electrode for various applications due to possibility to prepare a transparent film with low resistivity at wide range of deposition parameters. The AZO is considered as a cheap and non-toxic alternative to ITO, but the process window for sputtering of AZO with suitable properties is narrower than for ITO. The subject of the present work is replacing the preferably-used ITO by an AZO in ZnO-nanorod-based devices. These devices usually use a 100 nm-thick ITO layer as TCO and a ZnO film as a seed layer for nanorod growth. Our main aims are to eliminate rare indium from the process and combine the role of the seed layer for nanorod growth with a sheet resistance lower than 100 Ω/sq in a single ZnO-based thin film. The investigated AZO films with thickness up to 300nm were deposited on PET substrate at temperatures up to 100°C. The study was focused on the relation between electrical properties and film structure. Electrical properties, namely sheet resistance, Hall mobility and carrier concentration were determined by the by Hall measurement. The surface morphology were investigated by the SEM. The properties of the generator containing AZO were compared to the one containing ITO.

Resume : II-VI oxides such as zinc oxide and tin dioxide are wide band gap semiconductors which have unique applications in both opto-electronic and optical devices. They exhibits interesting optical properties that could be applied in quantum confined structures and light emitting devices. In this work, we report a chemical technique for synthesis of one dimensional nanostructures in a horizontal furnace with alumina tube. ZnO and SnO2 with different morphologies (nanowires and nanorods) and sizes (from 20nm to 10μm) are grown on different substrates by thermal evaporation of source materials and gas transport in cold zone of furnace using a carrier gas. The effect of substrate, additional metal sputtering, gas flow flux and vacuum conditions are investigated on the structural and morphological studies by means of the field emission SEM, EDX and XRD. Photoluminescence spectra of the nanostructures show high intensity optical emission at room temperature around UV and blue wavelength which is very interested for LED applications.

Resume : In about 20 years, various types of oxide nanosheet were prepared by using soft-chemical process. And, these materials have studied as photocatalytic, magnetic, dielectric materials and so on. We focused on a problem about the elution of metal ion from framework structure of layered oxides in ionic-exchange process of interlayer using strong acid. In this study, we tried to prepare Ti0.8Zn0.2O2 nanosheet prevented metal ion elution using various kinds of acid solutions. Lepidocrocite-type K0.8Zn0.4Ti1.6O4 powder was prepared using solid state reaction method. Acid solutions for ionic-exchanging used hydrochloric acid, acetic acid, carbonated water and boric acid. From chemical analysis using ICP-AES measurement, the use of hydrochloric acid was made not only ionic-exchange from K+ to H+ (H3O+) but also elution of Zn2+ from framework structure. On the other hands, the other weak acids made only ionic-exchange reaction. As a result, it was found that these ionic-exchange and elution mechanism of K0.8Zn0.4Ti1.6O4 had correlation pH and pKa values of each acid solution. Then, TiO2 and Ti0.8Zn0.2O2 nanosheet thin film were prepared by spin coating method. In case of photoinduced hydrophilicity, Ti0.8Zn0.2O2 nanosheets were found to be superior to TiO2.

Resume : Using a fast and eco-friendly radio frequency magnetron sputtering (rfMS) method, In2O3:Sn (ITO) thin films with thickness values in the range 270 – 450 nm, were deposited on glass substrates. After deposition, the samples were subjected to rapid thermal annealing (RTA) in air at temperatures up to 723 K. Surface morphology of the rapid thermally annealed samples appeared as granular and polycrystalline with high optical transparency and good electrical conductivity. In this study, a stylus profilometer (Ambios, XP–2) was used to measure the thickness of the oxide thin films. The structural, optical and electrical properties of both as-deposited and annealed samples were investigated. A comparative analysis of the structure and properties of these oxide films was then carried out. The surface morphology of the obtained films was investigated by AFM and SEM techniques. Influences of post deposition thermal treatment on structural properties of these oxides were discussed based on XRD and XPS results. Transmittance spectra, in a double-beam configuration, were recorded in the 190 nm – 3000 nm wavelength range and, from these, optical constants were obtained for the ITO films. Optical properties of these oxide films in the near infrared (NIR) range were described by the Drude free electron model. An algorithm for oxide thin films using computational models (i.e. Swanepoel and Wemple DiDomenico models) was developed and optical properties were obtained. The dispersion of the refractive index follows the usual behavior and it is well described by a single oscillator model. Depending on the annealing temperature, the value of the optical bandgap, Eg, of the corresponding thin films ranged between 3.35 eV and 3.65 eV. The electrical conductivity was measured using the four points method. An electrical analysis of the conduction mechanisms specific for different voltage ranges was also performed. The obtained results are discussed in correlation with the optical properties of the thin films and the role of annealed treatment in oxide thin films. This research is supported by the National Authority for Research and Innovation in the frame of Nucleus programme - contract 4N/2016.

Resume : Zinc oxide doped with manganese attracts much attention due to its possible application in the field of spintronics. The luminescent properties of this material are less requested mainly because of weak emission. The reason of this effect is not clear now. Here we present the results of combined investigations of diffuse reflection, photoconductivity (PC) and photoluminescence (PL) of ZnO ceramics doped with Mn. The concentration of Mn (NMn) varied from 1019 to 1021 cm-3. The X-ray diffraction did not reveal the presence of other Mn-related phases in the samples. In the diffuse reflectance spectra, Mn doping produced a broad structureless absorption band in the range of 400-600 nm. The band emerged as the shoulder and transformed into well-defined band as the Mn content increased. This was accompanied by appearance of extrinsic PC maxima in the same spectral range. The onset of PC band corresponded to the onset of the broad absorption band. Both bands can be assigned to charge-transfer transition from Mn 3d shell to the conduction band. As a result of Mn doping, the quenching of all self-activated PL bands and the appearance of a new PL band peaked at 645 nm were observed. The band at 645 nm became dominant in PL spectrum at NMn =1021 cm-3 and was assigned to Mn intra shell transition. The model which explains the quenching of PL bands, low intensity of Mn-related emission side by side with intensive exctrinsic PC is proposed.

Resume : The increasing interest in ultrasensitive, low-cost and miniaturized electrochemical biosensors has promoted the use of nanostructured oxide surfaces for their enhanced surface-to-volume ratio, favorable electronic properties and electrocatalytic activity. In the frame of biosensors that are integrable with the standard silicon technology, complementary metal-oxide-semiconductor (CMOS) compatible processes are suitable and provide many potential advantages (e.g. low cost and high throughput). Indium tin oxide (ITO) is a transparent CMOS-compatible material with good conductivity that is recently being considered as a suitable substrate for biosensing purposes. Out of all available growth methods of ITO nanostructures, electron beam evaporation has been the most popular due to its low cost, precisely controllable parameters and flexibility. In the present study, self-catalytic vapor-liquid-solid (VLS) growth of ITO was studied under a multivariate experimental design. Parameters such as indium oxide/tin oxide ratio, growth temperature, deposition rate and oxygen partial pressure were tuned in an attempt to probe the combination of parameters that results in highest electrochemical performance. In this respect, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were performed, and the electrochemical area available for redox reactions in the surface/electrolyte interface was calculated under the Randless-Sevcik approach.

Resume : We present the first simultaneous observations of both electronic and structural temperature-induced insulator-to-metal transition (IMT) in VO2 ultrathin films, made possible by the use of broad range transmission infrared spectroscopy. Thanks to these techniques, the infrared phonon structures, as well as the appearance of the free carrier signature, were resolved for the first time. The temperature-resolved spectra allowed the determination of the temperature hysteresis for both the structural (monoclinic-to-rutile) and electronic (insulator-to-metallic) transitions. The combination of these new observations and DFT simulations for the monoclinic structure allows us to verify the direct transition from monoclinic (M1) to rutile and exclude an intermediate structural monoclinic form (M2). The delay in structural modification compared to the primer electronic transition (325 K compared to 304 K) supports the role of free charges as the transition driving force. The shape of the free charge hysteresis suggests that the primer electronic transition occurs first at 304 K, followed by both its propagation to the heart of the layer and the structural transition when T increases. This study outlines further the potential of VO2 ultrathin films integrated on silicon for optoelectronics and microelectronics.

Resume : Nanorices fluorine doped tin oxide (nr-FTO) was successfully synthesized using only FTO substrate in hydrothermal process. This method combining with novel recipe of hydrothermal solution managed to synthesis homogenous film of nr- FTO and spherical nr-FTO. The samples were characterized using FESEM, EDS, XRD and solar simulator measurements. The FESEM results show the grain size of FTO nanorice which is 54.8nm along with diameter of 21.0nm. Nanorices fluorine doped tin oxide were prepared at 5 h, 10 h, 15 h and 20 h, respectively. Finally, power conversion efficiency of Dye-Sensitized solar cell were measured and 2.77% was the highest which was prepared at 10 h of hydrothermal process

Resume : ZnMgO alloys provide an optically tunable family of wide bandgap materials in the range of 3.37–7.85 eV. This opens wide prospects for their application in devices operating in the UV to deep-UV spectral range. In this work, optical properties of screen-printed Zn0.8Mg0.2O films sintered at TS=400-1000°C in the air were investigated by micro-Raman and photoluminescence (PL) methods. In the Raman spectra, the increase of TS value resulted in shifting of the E2high phonon mode to lower frequencies and appearance of additional phonon bands at about 102.2 and 610 cm-1 ascribed to the E2low and quasi-LO modes of hexagonal ZnMgO solid solution, respectively. The PL spectra showed the exciton-related bands in the UV region and wide defect-related bands in the visible spectral range. At TS>600 °C a pronounced increase of defect-related PL bands, the decrease of ZnO exciton PL and appearance of ZnMgO excitonic transitions were found. The Raman spectra as well as PL and PL excitation spectra demonstrated that formation of ZnMgO alloy began at TS=700 °C and reached Zn0.8Mg0.2O at TS=1000 °C. However, the ZnO phase was also observed. The intensity of ZnMgO exciton PL is found to be strongly reduced at the film surface. Additional annealing of these films in the N2 flow allowed this effect to be ascribed to the intense Zn evaporation.

Resume : Pulsed electron beam deposition (PED) has been used to grow indium oxide thin films on c-cut sapphire single crystalline substrates between room temperature and 500° C under oxygen gas. The composition, structure and microstructure of these films were correlated to their electrical (resistivity, mobility and carrier density) and optical (UV-VIS-NIR absorption) properties. These studies show that a simple way to tune the physical properties of indium oxide thin films is given by a precise control of the PED growth conditions. In fact, a slight difference in oxygen pressure during the growth has strong effects on the electrical film properties. Depending upon the precise oxygen composition of the thin films, semiconductor, metal-insulator transition or metallic behavior can be observed in the temperature dependent resistivity curves. These results will be presented and the correlation between the film composition, structural phases and their physical properties will be discussed.

Resume : Rare earth doped titanium oxide thin films are potentially interesting for photovoltaic applications. In this work we have studied the role of rare earth elements (Tm and Yb) on the growth and physical properties of TiO2 thin films obtained by pulsed electron beam deposition method. These films were grown on Si and c-cut sapphire single crystal substrates under oxygen or argon gas at temperatures between room temperature and 500 °C. Composition, surface morphology and structure of films were correlated to their UV-visible optical transmission and electrical properties. These results will be presented and discussed, in particular the correlation with photoluminescence studies.

Resume : The optical properties of amorphous indium gallium zinc oxide (a-IGZO) thin films with various In:Ga:Zn ratios were investigated. a-IGZO, commonly used as channel in thin film transistors, can be employed also as transparent conductive oxide when the cations stoichiometry is changed. Thin films on Si and quartz substrates were obtained at room temperature by pulsed laser deposition technique using an ArF laser (193 nm), by ablating targets with various stoichiometries in reactive atmospheres. Grazing incidence X-ray diffraction investigations showed that the films were amorphous for all chemical compositions investigated, without any long-range order. The films thickness results, obtained from simulations of X-ray reflectivity (XRR), spectroscopic ellipsometry (SE) and Rutherford backscattering (RBS) data, were very similar. The chemical composition of the deposited films was investigated by RBS and energy dispersive X-ray analysis. The dependence of density on stoichiometry resembles the corresponding dependence of the refractive index in the transparency range. A free carrier absorption was noted in the visible spectral range for certain samples, indicating the conductive character of such thin films.

Resume : Undoped and lithium doped nickel oxide thin films have been prepared onto glass substrates at 500°C by the spray pyrolysis process using the nickel nitrate [Ni(NO3)2 6H2O] and lithium chloride (LiCl2) solutions. The effects of the Li-doping concentration on the structural, surface morphological, optical and electrical properties were investigated. The X-ray diffraction (XRD) pattern of undoped and NiO:Li films showed polycrystalline nature with cubic structure phase related to NiO structure. Further, the preferred orientation growth was along (111) plane. Although the crystallite size values exhibited a decreasing with increasing Li doping level from 0 to 5%. Morphological analysis showed that the films reveals nanocrystalline grains with spherical shaped particles and different sizes distributed randomly over surface of substrate. The composition analysis was carried out by (XRF) and the obtained result proves successfully the presence of nickel, oxygen and lithium with different atomic percent. Optical transmittance spectra of the films showed transparency more than 63% in the visible region. The optical band gaps were found to be decreased according to the Li-doping concentration increases. Hot point probe methods (Seebeck effect) show that all deposited films have a p-type semiconductor behavior. The electrical measurements indicate that the conductivity was increases behavior depends on the lithium concentration.

Resume : Two types of polymer / liquid crystal composite materials were studied: • Classic PDLCs • PDLC doped with TiO2 nanoparticles The systems studied are TPGDA / E7 and GPTA / E7. A comparative study of the opacity of these materials was carried out using an electro-optical bench by measuring the transmissions to the initial state "Toff". The results obtained were correlated with those of optical microscopy with polarized light and infrared spectroscopy "FTIR". The doped PDLCs are elaborated by injection of TiO2 nanoparticles in the initial mixture followed by photo polymerization under UV radiation. An investigation of the morphology and the state of dispersion is made with the aim of highlighting the differences and improvements brought by this load on the optical and electro-optical properties of these materials.

Resume : The great potentialities of graphene can be enhanced thanks to the functionalization of its surface, which make it suitable for different application fields. In this work the changes in electronic structure of graphene after the deposition of TiO2 and the influence of graphene in TiO2 photocatalytic activity were studied. Different thicknesses of TiO2 were grown on graphene films by Atomic Layer Deposition at 200 °C using water and TiCl4 as precursors. The changes in electronic structure of graphene were investigated by means of Raman spectroscopy and the TiO2 stoichiometry was studied by X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of TiO2/Graphene material was tested under a UV-Visible irradiation (generated by a solar simulator) using UV-Vis. spectrophotometry. The results indicate that inhomogeneity and intrinsic stain effects are present within the same sample. A study on undecorated graphene showed pre-existent strain and nonintentional self-doping caused by the mismatch and the presence of charged impurities on the underlying substrate respectively. The deposition of TiO2 films with thickness ≤ 10 nm led graphene to be p-doped, while strain becomes the dominant effect increasing film thickness. Oxygen vacancies, detected by XPS, decreased exponentially increasing the thickness of the TiO2 films to reach a stoichiometric O/Ti atomic ratio above 10 nm thickness where anatase phase signal appeared. The combination of TiO2 and graphene enhanced the efficiency of the electron-hole separation of TiO2 under UV-Visible light, which gave rise to a higher photocatalytic activity tested for methyl red molecule degradation.

Resume : Here we report the synthesis of ZnO nanodisks by simple, cheap and low temperature method of electrodeposition. Depositions were carried out in a three-electrode electrochemical cell at 80 °C. ZnO nanodisks were deposited onto ITO/glass substrates from aqueous solutions containing 0.2 mmol/l solution of ZnCl2 in the presence of H2SeO3 microadditive. Different concentrations of microadditive were tested. It was observed that disks dimentions can be controlled by changing the concentration of microadditive. For example, ZnO disks with dimensions of 1 μm in diamether and 100 nm thick were obtained in the presence of 0.05 mmol/l H2SeO3 in working solution. The ZnO discs were characterized using field emission scanning electron microscopy (SEM), X-ray diffraction (XRD) and optical measurements (UV-Vis) methods.

Resume : In this work, we report the fabrication of indium tin oxide free organic solar cells and demonstrate the ability of niobium doped titanium dioxide (TNO) layers produced by sol-gel as feasible alternative electrode. The conductivity of the TNO were tailored by changing the layer thickness and the post-annealing conditions. Later, the crystal structure was revealed by X-ray diffraction. The post-annealing treatments were performed in a rapid thermal processing furnace under different gas atmospheres, temperatures and times. The conductivity of the samples was measured using a four-point set-up and the transparency through a UV-VIS spectrophotometer. A good sheet resistance of 181 Ω/Sq. is achieved when the electrode was heated in an nitrogen/hydrogen atmosphere mixture at 1000 °C for 10 minutes. TNO based organic solar cells were manufactured and their performance was evaluated by current-voltage measurements. A power conversion efficiency of 0.71 % was attained.

Resume : Indium-Gallium-Zinc oxide has enticed substantial interest in the last years for use as channel films for transparent thin film transistors (TTFT). IGZO TTFTs with top gate – bottom contacts geometry were fabricated by pulsed laser deposition (PLD). Amorphous IZO thin films were grown for the source-drain and gate contacts. A study concerning the dependence of these thin films transport properties on the working gas pressure has been performed. Various IZO films with In/(In+Zn) values of 50%, 70% and 90% and IGZO (In:Ga:Zn ratios 1:1:1 or 1:1:2) target stoichiometries were used. HfO2 thin films were used as gate insulator. The leakage currents and breakdown field of the gate insulator films were measured, and the structure and thickness for all films were investigated by XRD, X-ray reflectiometry and ellipsometry techniques for various PLD working gas pressures. The source-drain and gate contacts were patterned using metallic shadow masks produced by electro-erosion technique. The study presented here concerns the influence of the PLD working conditions (gas type and pressure, the target-substrate distance and the laser pulse energy) on the films interfaces quality and their electrical properties in order to obtain the optimal performance in a TTFT.

Resume : Continuous monitoring and controlling of humidity have wide range of industrial and domestic applications. Present day humidity monitors are mostly polymer dielectric based capacitors, which have poor long term stability and are difficult to integrate with CMOS substrate. In this paper, we are demonstrating a highly sensitive resistive humidity sensor employing metal oxide thin film as sensing layer. Hierarchical Cu doped NiO nanostructure was synthesized by surfactant mediated hydrothermal route to fabricate humidity sensors at room temperature. The transition metal oxides (e.g. NiO) are found to be less sensitive towards humidity with a poor response and recovery. The optimum sensing was achieved for a doping percentage of 10% Cu. The sensors show a response of 225% at 90% relative humidity at room temperature. The sensing material was found to be coral like in nature which provides large surface area within small volume and also defect sites. Along with this, metal doping has played a crucial role for good humidity sensing. The material also showed good repeatability and reproducibility in performance thereby making it a reliable material for humidity sensor application. The novel in-situ doping can be achieved at room temperature with low cost environmentally friendly chemical route and hence can be extended for large scale manufacturing. Thus, Cu doped NiO can be a useful material for cost efficient fabrication of future commercial humidity sensors.

Resume : The formation and nanoparticles and their incorporation dynamicss during nanosecond-laser PLD has never been well understood. Here we report the intentional formation of nearly-pure fluxes of ultrasmall (~3 nm) amorphous nanoparticles (UANPs) by gas-phase condensation in laser ablation, and demonstrate their advantages when deposited as metastable "building blocks" for the catalyst-free growth of crystalline nanostructures of different morphology and phase by the process of crystallization by particle attachment (CPA). This process is quite general, and although we concentrate on the formation of anatase, B-phase, and rutile (as well as "black anatase") TiO2 nanostructures and films, we will show the formation and integration of other oxide nanostructures (e.g. MgO, SnO2) as well as atomically-thin 2D materials (e.g. GaSe, MoSe2) by PLD of UANP precursors. Although the formation of crystalline nanostructures by dynamic particle attachment processes is well accepted in liquid-phase synthesis, such assembly processes by gas phase condensation and deposition are far less understood. Temporally- and spatially-resolved gated-ICCD imaging and ion probe measurements are employed as in situ diagnostics to understand and control the plume expansion conditions for the synthesis of nearly pure fluxes of ultrasmall amorphous TiO2 nanoparticles in background gases and their selective delivery to substrates. We describe the separation and propagation of nanoparticles from the atomic/molecular plume. These amorphous nanoparticles assemble into loose, mesoporous assemblies on substrates at room temperature but dynamically crystallize via the Ostwald-Lussac Law by sequential particle attachment at higher substrate temperatures (~400-800 oC) to grow a variety of nanostructure phases and morphologies. Molecular dynamics simulations indicate that nanoparticles arrive to the underlying nanorod to crystallize and template their crystalline orientation within nanoseconds at 600°C, then sinter between laser pulses. This work demonstrates that PLD of amorphous nanoparticles as metastable "building blocks" for attachment and crystallization is a versatile new method to explore and control the growth of thin films and nanostructures with desirable crystalline phases, nanostructure, and mesoporosity tailored for energy applications. Research sponsored by the U.S. Dept. of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Div. (synthesis science) and Scientific User Facilities Div. (characterization science).

Resume :
The ferromagnetic semiconductor EuO is amongst the most interesting compounds for spintronics devices and applications [1,2]. The high spin polarization, magnetic properties [3,4], and the possibility to integrate EuO with Si [1], GaAs [5], GaN [1] and many others technologically significant semiconductors, makes this material fascinating from basic and applied standpoints.
In this work we present a new methodology for preparing high quality textured EuO thin films in high vacuum at room temperature. The EuO textured nanocrystalline thin films are obtained by in-situ reduction from a pure Eu₂O₃ bulk ceramic target [6] by pulsed laser deposition (PLD) on Si(100) substrates, at 10^-7 mbar and without any additional gas pressure. X-ray photoelectron (XPS) spectroscopy studies prove the presence of Eu²⁺ , and the analysis of X-ray diffraction (XRD) spectra reveals only the pattern corresponding to the EuO crystalline phase with a texture along the (110) direction. The analysis of the peaks width according to the Scherrer equation points at an average crystallite size of 16 nm. Our findings indicate that PLD from Eu₂O₃ is a highly efficient method to prepare this relevant material.

[1] A. Schmehl, V. Vaithyanathan, A. Herrnberger, S. Thiel, C. Richter, M. Liberati, et al., Epitaxial integration of the highly spin-polarized ferromagnetic semiconductor EuO with silicon and GaN., Nat. Mater. 6 (2007) 882–887. doi:10.1038/nmat2012.
[2] A. Melville, T. Mairoser, A. Schmehl, D.E. Shai, E.J. Monkman, J.W. Harter, et al., Lutetium-doped EuO films grown by molecular-beam epitaxy, Appl. Phys. Lett. 100 (2012). doi:10.1063/1.4723570.
[3] B.T. Matthias, R.M. Bozorth, J.H. Van Vleck, Ferromagnetic interaction in EuO, Phys. Rev. Lett. 7 (1961) 160–161. doi:10.1103/PhysRevLett.7.160.
[4] J. Lettieri, V. Vaithyanathan, S.K. Eah, J. Stephens, V. Sih, D.D. Awschaiom, et al., Epitaxial growth and magnetic properties of EuO on (001) Si by molecular-beam epitaxy, Appl. Phys. Lett. 83 (2003) 975–977. doi:10.1063/1.1593832.
[5] A.G. Swartz, J. Ciraldo, J.J.I. Wong, Y. Li, W. Han, T. Lin, et al., Epitaxial EuO thin films on GaAs, Appl. Phys. Lett. 97 (2010). doi:10.1063/1.3490649.
[6] A. Quesada, A. del Campo, J.F. Fernández, Sintering behaviour and translucency of dense Eu₂O₃ ceramics, J. Eur. Ceram. Soc. 34 (2014) 1803–1808. doi:10.1016/j.jeurceramsoc.2013.12.034.

Resume : Cobalt ferrite (CoFe2O4) adopts an inverse spinel structure with ca. 90% of the Co2+ ions located in the octahedral sites. The strong interaction between the cobalt ions confers to the material an important anisotropy 1, which makes this material interesting in the field of spintronics, in particular as a pinning layer 2. Cobalt ferrite is the subject of renewed interest thanks to the possibility to modulate its anisotropy. One possibility to achieve this modulation is to substitute iron for a rare earth element leading to a competition between the anisotropy of the 4f element and the anisotropy of the Co2+. CoFe2O4 thin films were epitaxially grown by pulsed laser deposition on (100) MgO at 400°C in O2/N2. The cell undergoes important distortions depending on the deposition pressure. For high pressures (> 0.1 mbar), it shows tensile strain with an out of plane cell parameter smaller than bulk (8.392 Å). For lower pressures (< 0.03 mbar), the tetragonalization is stronger and reversed with out of plane and in plane cell parameters higher (8.60 Å) and smaller (8.23 Å) than bulk, respectively, yielding an interesting out of plane easy axis of magnetization. In order to fully tune the magnetization easy axis, rare-earth (RE = Nd, Gd, Tb, Dy, Er) doped thin films were elaborated. The films grow epitaxially on MgO substrates and the insertion of the RE into the spinel lattice was proved by resonant diffraction experiments performed on the CRG-BM02 beamline at the ESRF (Grenoble). 1 K. Yosida, Theory of Magnetism, Springer Science & Business Media, 1996 2 Wohlfarth E. P. (Ed.) Ferromagnetic Materials, 3, Elsevier Science Publishers B.V., 1982

Resume : Multifunctional oxide thin films from the lead-free system (K,Na) ? (Nb,Ta) ? O (KNN) are of great interest for several applications, due to their piezoelectric and ferroelectric properties. In particular, their high dielectric permittivity that can be driven by an external DC electric field enables the fabrication of tunable and miniaturized microwave devices. In this frame, KNN thin films have been grown by Pulsed Laser Deposition (KrF excimer laser) on sapphire substrates. The influence of the deposition parameters was studied in view to control the composition of the thin films and consequently the behavior of the resulting devices. Thin films were characterized by scanning electron microscopy, atomic force microscopy and X-ray diffraction before being integrated into coplanar waveguide (CPW) devices (stub resonators and transmission lines). The dielectric permittivity and dielectric loss were retrieved from microwave measurements on transmission lines whereas the tunability and the global loss were computed from the stub resonator measurements. The influence of the K/Na content on the thin films characteristics will be shown. The microwave properties will be compared to those of K0.5Ta0.5Nb0.5O3 (KTN) thin films that we have previously studied. Whereas first experiments showed a higher tunability with KTN compared to KNN, the global loss remains lower with KNN, which is a promising result for further studies.

Resume : We have grown by multi-target Pulsed Laser Deposition nanostructured YBa2Cu3O7 superconducting films with artificial pinning centres using various approaches: substrate decoration [1], quasi-multilayers [2], multilayers, targets with secondary phase nanoinclusions [3], and combinations of the above mentiones [4], involving various architectures and nanoinclusions (Ag, BaZrO3, LaNiO3,). From DC magnetization loops and AC multiharmonic susceptibility measurements we have studied the critical current densities and pinning potentials, and correlated the results with TEM images. We have found that both Jc and Up depend strongly on the types of material(s) used for the nanoengineered pinning centres and on the architectures used in the nanostructures. [1] A. Crisan, S. Fujiwara, J.C. Nie, A. Sundaresan, H. Ihara, Applied Physics Letters 79 (2001) 4547 [2] T. Haugan, P.N. Barnes, R. Wheeler, F. Meisenkothen, M. Sumption, Nature 430 (2004) 867 [3] J.L. MacManus-Driscoll, S.R. Foltyn, Q.X. Jia, H. Wang, A. Serquis, L. Civale, B. Maiorov, M.E. Hawley, M.P. Maley, D.E. Peterson, Nature Materials 3 (2004) 439 [4] P. Mikheenko, V.-S. Dang, M. M. Awang Kechik, A. Sarkar, P. Paturi, H. Huhtinen, J. S. Abell and A. Crisan, IEEE Transactions on Applied Superconductivity 21(3) (2011) 3184 Acknowledgment: Financial support from Romanian Ministry of Research through POC Project P-37_697 nr. 28/01.09.2016 is gratefully acknowledged.

Resume : Despite the immense scientific literature regarding the oldest known magnetic material, magnetite has magnetic and structural properties still unveiled. Specifically, in the nanometric scale, many efforts are being developed in order to obtain high quality thin film layers with a preferred crystalline orientation [1]. This aspect is crucial for spintronic devices for optimal spin-polarized current in a metal/semiconductor heterojunction. In this sense, a positive spin polarization at the (111) surface of magnetite has been recently observed [2]. The chemically layered polar nature of the junction Fe3O4(111)/SrTiO3(111) might be employed as a scenario for studying spin injection from half metals into semiconductor materials. Therefore, aiming to discover the possible spin-polarized current effects, high quality Fe3O4(111) epitaxial thin films (~30 nm) are grown on SrTiO3 substrates by Pulsed Laser Deposition (PLD) as a function of temperature deposition (300-900 ºC). Depending on the different temperature stages, a homogeneous thin film or triangular Fe3O4 terraces as a single phase are formed. The structural properties and chemical composition of the epitaxial thin films are characterized by surface X-ray diffraction (SXRD), X-ray photoelectron spectroscopy (XPS) and confocal Raman microscopy (CRM). Apart from this, the magnetic properties of the samples are examined by a magneto-optic Kerr effect (MOKE) system in ultra-high vacuum (UHV). With this study we present not only a broad characterization of these epitaxial Fe3O4 samples, but also investigate the correlation between magnetic, morphological and structural properties as a function of the temperature deposition and how this could affect for the progress of future spintronic devices. References [1] A. Muñoz-Noval, J. Rubio-Zuazo, E. Salas-Colera, A. Serrano, F. Rubio-Marcos, G. R. Castro, Appl. Surf. Sci., 355, (2015), 698-701. [2] A. Pratt, M. Kurahashi, X. Sun, D. Gilks, and Y. Yamauchi, Phys. Rev. B, 85, (2012) 180409.

Resume : TSST has developed a large area PLD system with which oxide thin film growth on 4” silicon wafers is investigated and optimized, obtaining highly crystalline heterostructures with atomically sharp interfaces. We present the results from this system on the growth of La0.67Sr0.33MnO3 (LSMO) thin films on high quality YsZ//CeO2//SrRuO3 buffer layers on 4'' silicon wafers. Film quality is investigated with X-Ray Diffraction and magnetic characterisation. Rocking curve measurements around the LSMO (002) Bragg reflection show values of ~1degree, which is comparable to the quality of films grown in <1” small scale experiments. A growth temperature dependence in the crystallinity of LSMO is shown. With the introduction of the SRO layer LSMO films show single phase crystallinity and magnetic response for temperatures as low as 250C. When this SRO layer is lacking, fully amorphous film growth is observed at higher temperatures up to 550C. We speculate that the occurrence of this LSMO high quality crystal growth at these low growth temperatures could be understood by an improved surface diffusion induced by the SRO buffer layer, where studies have shown the dependence of surface diffusion on crystal plane termination. Recent work on BiFeO3 growth show qualitatively similar behaviour, were a drastic change in growth kinetics is understood by improved growth kinetics on A-site terminated SRO.

Resume : It is well known that Pulsed Laser Deposition (PLD) is a very flexible and versatile technique allowing fast optimization of new and complex material thin films. The unique features of PLD allow for the integration of “Beyond Moore” materials in CMOS and new devices. Among these are Pb(Zr,Ti)O3, PMN-PT, BaTiO3, LiNbO3 and other materials of interest for applications in ferroelectrics. Within the scope of the PETMEM project [1] a new ground-breaking beyond CMOS computer technology will be developed that has the potential of no less than 50 to 100 times reduction of power consumption compared to current state-of-the-art. This novel Piezoelectric Transduction Memory (PETMEM) device uses a radically different switching mechanism in order to go beyond the power limits of current devices. High strain and long term stability of the piezoelectric material are key ingredients for successful commercialization of the piezoelectronic transduction memory. These properties are generally achieved in epitaxial films of PZT or PMN-PT. Integration of epitaxial piezo layers on silicon forms therefore an essential ingredient for the realization of these memory devices. Using Solmates PLD platform, wafer-level integration of epitaxial thin films on silicon is demonstrated. The robust and reliable hardware allows uniform thin film deposition up to 200 mm diameter with high process reproducibility. In this contribution the deposition of epitaxial PZT and PMN-PT thin films on silicon wafers by means of buffer layers will be presented. The piezoelectrical and piezomechanical properties in relation to their crystalline quality will be discussed. The results of this work are the first milestone in the development of the piezoelectric memory.

Resume : Amorphous indium zinc oxide (IZO) and indium gallium zinc oxide (IGZO) films have excellent opto-electronic properties that have been used in thin film transistors and display devices. Pulsed laser deposition (PLD) is one technique that can be easily used to grow thin films of IZO and IGZO thin films having various structures and compositions to investigate their properties. We used the PLD technique to grow thin films of IZO with In/(In+Zn) values from 0.1 to 0.9, In1-xGaxZnO4, HfO2 and ZrO2 that are used to fabricate transparent thin films transistors on Si and glass substrates from room temperature up to 200 °C. The grown films and devices were irradiated by gamma and UV radiation to investigate the effects of radiation on their structure and properties. The surface morphology of the deposited films, investigated by atomic force microscopy, was very smooth with rms values below 1 nm, allowing for the use of surface sensitive characterization techniques such as X-ray reflectivity (XRR) and X-ray diffuse scattering to investigate the interface morphology. In addition, we also used optical reflectometry and photoluminescence (PL) to characterize the changes of the optical properties caused by the irradiation. The results showed that after gamma irradiation, the surface morphology slightly changes, the rms values increasing from 1 nm to 2-3 nm. Also, the films density, extracted from simulations of the acquired XRR curves, decreased by a few percentage points, which resulted in a small thickness increase. The refractive index values, estimated from spectroscopic ellipsometry measurements, also decreased by 1-2 percentage points, consistent with the observed changes in density. The optical band gap values, extracted from Tauc plots, slightly decreased by few tenths of eV, while the resistivity was almost unchanged. PL measurements for different ratios of In/(In+Zn) showed that the light emission increased dramatically due to defect formation after gamma radiation. The emission peaks, however, deviated from the normal expected defect emission peaks. Interesting was that a regular shift in the wavelength of peak positions was also observed during measurements at different spots on the films due to changing film thickness. PL can be heavily distorted by interference. One reason for the pronounced interference may be the low reabsorption of the PL emission that typically occurs below the band gap. The results showed that these amorphous transparent oxide films could tolerate a high level of radiation without adverse effects upon their structure, stoichiometry or optical and electrical properties.

Resume : We have developed molecularly thin 2D oxides in diverse compositions and structures by delaminating appropriate layered compounds via the massive hydration-driven swelling in aqueous amine solutions [1,2]. The process promotes the total disintegration into unilamellar oxide sheets, laterally extending up to several tens micrometers, which exhibit a range of useful electronic, magnetic and chemical properties. The nanosheets are colloidal polyanionic 2D crystals dispersed in aqueous media, and we can apply solution-based processes via sequential adsorption and Langmuir-Blodgett transfer to assemble them layer-by-layer as a building block into designed nanostructures [1]. Particularly, we constructed superlattice films of multiple nanosheets and developed intriguing functionalities [3]; ferroelectricity and multiferroic behavior in hetroassemblies of dielectric and ferromagnetic nanosheets, accumulation of photogenerated carriers in systems of Ti and Mn oxide nanosheets and graphene. [1] R. Ma, T. Sasaki, Adv. Mater. 22, (2010) 5082. [2] L. Z. Wang, T. Sasaki, Chem. Rev. 114 (2014) 9455. [3] R. Ma, T. Sasaki, Annu. Rev. Mater. Res. 45 (2015) 111.

Resume : One-dimensional (1D) systems offer a useful platform for studying low-dimensional phenomena often associated with the onset of critical quantum phase transitions. While exactly solvable models, such as Luttinger liquid theory, are thought to describe 1D systems very well, only a few naturally occurring materials with intrinsic 1D structure are available for experimental studies. Here we present a new approach of synthesizing 1D quantum systems by creating dimensionally-confined stripe-superlattices from in-plane oriented 2D layered oxides. We have used this method to synthesize 1D IrO2 stripes using a-axis oriented superlattices of Sr2IrO4 and insulating (La,Sr)GaO4, both are of the K2NiF4 symmetry. The dimensional confinement of our 1D superlattices has been confirmed by structural characterizations. Optical spectroscopy shows clear anisotropic characteristics and one-dimensional electronic confinement of the spin-orbit split Jeff= 1/2 band. Spin and orbital excitations observed in resonant inelastic x-ray scattering spectra suggest larger exchange interactions and more confined orbital excitations in the 1D IrO2 stripes as compared to its 2D counterpart. The observed electronic confinement and localized spin-structure are quite consistent with density functional theory calculations. This method of transforming layered materials into 1D striped structures is a viable technique for obtaining dimensional-crossover phase transitions while tuning from two- to one-dimension.

Resume : Gallium based liquid metal alloys are known to possess unique low melting points which allow them to remain liquid at ambient temperatures. Furthermore these liquid metals are known to feature ultrathin interfacial oxide layers of exceptional quality.[1] We recently demonstrated that these oxide layers can be deposited onto substrates, forming atomically thin layers with extraordinary lateral dimensions.[2] In this work we investigate the effect of co-alloying small quantities (up to 1%) of reactive transition and post-transition metals. We demonstrate that metals with a higher propensity to react with oxygen dominate the surface oxide. Thus a simple, scalable printing process can be devised that allows depositing atomically thin oxide layers onto substrates. In this initial work we report the large scale deposition of ultrathin nanometre thick HfO2, Al2O3, Gd2O3, ZrO2, Ga2O3 and ZnO, directly onto wafers. In a second part we developed methods to delaminate these oxide sheets and collect them in liquid suspensions. 2D oxide nanosheets are obtained exceeding 50 micron in lateral dimension while being 1 – 2 nm thick. Study of the fundamental principles underlying the oxide growth suggests that many further 2D oxides may be accessible using this technique. 1 M. J. Regan et al. X-ray study of the oxidation of liquid-gallium surfaces Physical Review B 1997 55, 16, 10786 – 10790 2 B. J. Carey et al. Wafer Scale 2D Semiconductors from Printed Oxide Skin of Liquid Metals Nature Communications 2017 (just accepted)

Resume : Two-dimensional (2D) materials have activated tremendous interests due to their fascinating physical and chemical properties and the promising applications in nano-electronics, where thermal transport plays a vital role in determining the performance of devices. In this paper, we present a first-principles study of thermal transport properties of monolayer zinc oxide (ZnO), which is emerging with potential applications in nano-electronics and thermoelectrics. The thermal conductivity of monolayer ZnO is found to be as low as 4.5 Wm-1K-1 at 300 K, which is dramatically lower than those of bulk ZnO and lots of other 2D materials. Detailed analysis is performed in the framework of Boltzmann transport theory and electronic structure to understand the low thermal conductivity. Most surprisingly, the thermal conductivity of monolayer ZnO nonmonotonically and slowly decreases with temperature and does not follow the conventional 1/T law. This unusual phonon transport behavior arises from the dominant contribution of optical phonon modes to the overall thermal transport in monolayer ZnO, which has been rarely reported in literature, and the significantly increased specific heat of the high frequency (optical) phonon modes with temperature increasing. Our study highlights the abnormal thermal transport properties of the new 2D material and we anticipate that this research will motivate the experimentalists to further study other physical and chemical properties of monolayer ZnO for emerging applications such as such as thermoelectrics, thermal circuits, and nano-/opto-electronics.

Resume : A d-orbital electron has an anisotropic electron orbital and is a source of magnetism. The realization of a 2-dimensional electron gas (2DEG) embedded at a LaAlO3/SrTiO3 interface surprised researchers in materials and physical sciences because the 2DEG consists of 3d-electrons of Ti with extraordinarily large carrier mobility, even in the insulating oxide heterostructure [1]. To date, a wide variety of physical phenomena, such as ferromagnetism [2] and superconductivity [3], have been discovered in this 2DEG system, demonstrating the ability of the d-electron 2DEG systems to provide a material platform for the study of interesting physics. However, because of both ferromagnetism and the Rashba field, long-range spin transport and the exploitation of spintronics functions have been believed difficult to implement in the d-electron 2DEG systems. In this presentation, the experimental demonstration of successful room-temperature spin transport in the d-electron-based 2DEG at a LaAlO3/SrTiO3 interface by using dynamical spin pumping [4]. The spin relaxation length at room temperature is estimated to be ca. 300 nm from the gap length dependence. Calculations using two different theoretical models supported the claim. The detail of the experimental concept, control experiments and theoretical analyses are discussed in the presentation. References [1] A. Ohtomo et al., Nature 427, 423 (2004). [2] A. Brinkman et al., Nature Mater. 6, 493 (2009). [3] N. Reyren et al., Science 317, 1196 (2007). [4] R. Ohshima, M. Shiraishi et al., to appear in Nature Mater.

Resume : Metal-Organic Frameworks (MOFs) provide an interesting class of materials in which metal-oxide substructures (0D nodes, 1D chains or 2D sheets) are linked through organic molecules. This provides the MOFs the ability to combine/link multiple physical properties (e.g. luminescence, sorption, mechanical, chemical,?). In this work, we study the class of breathing MOFs and investigate how different physical properties influence one another. More specifically, we focus on the role of the spin-configuration of the 1D metal-oxide chains in MIL-47(V) MOFs. In case of the MIL-47(V), we show there is a clear link between the spin-configuration and the mechanical properties, predicting the breathing-transition-pressure in excellent agreement with experiment[1]. We also compare the physical properties between the large-and narrow-pore geometries of the structure and discuss their evolution.[2] The flexibility of this MOF, even though it is considered as relatively stiff within this topology group, presents many challenges for its theoretical study [2]. It also proves to behave slightly different in powder and monocrystalline form, with subtle differences which can be pinpointed on its spin-configuration using high-accuracy theoretical approaches.[3] [1] Beilstein J. Nanotechnol. 5, 1738-1748 (2014), doi: 10.3762/bjnano.5.184 [2] J. Phys. Chem. C 119(41), 23752-23766 (2015), doi: 10.1021/acs.jpcc.5b06809 [3] Cryst. Eng. Comm. 17(45), 8612-8622 (2015), doi: 10.1039/C5CE01388G

Resume : Transition-metal oxide heterostructures are attractive for functional device applications because electronic and magnetic phases that are inaccessible in the bulk can be stabilized by epitaxial strain, confinement, charge doping, or interface effects. We use resonant elastic x-ray scattering to investigate ordering phenomena of spin, charge and orbitals in nanoscale complex oxide multilayers. As a model system we have investigated perovskite-type RNiO3-based heterostructures (R = rare-earth ion) grown by molecular-beam epitaxy and pulsed-laser deposition on various substrates. In my talk I will present results of our studies of the layer-resolved orbital occupations, the unusual antiferromagnetic order observed in the ultra-thin limit, and the quantitative investigation of the bond-order parameter.

Resume : In recent years donor doped strontium titanate (n-STO) has gained a lot of attention as model material for various applications, such as gas sensing or resistive switching. In addition, it is widely used as a quasi-metallic substrate material for functional all oxide electronic devices. For this purpose, n-STO is often referred to as a degenerate n-type semiconductor. However, recent research on n-STO also indicated the existence of a surface space charge layer. In this study, we investigated the electronic surface structure of n-STO thin films. 0.5 wt% Nb-doped STO homoepitaxial thin films were analyzed by in-situ near ambient pressure XPS at a temperature of 770 K and a pO2 which ranged from ultra high vacuum conditions up to 5 mbar. Upon exposure to O2 gas at elevated temperatures, we detected a rigid shift of up to 0.6 eV for the binding energies of all characteristic STO core level peaks and the valence band maximum. The rigid shift is attributed to a relative shift of the Fermi level towards the valence band due to a negative charge accumulation at the surface and hence, an electron depletion layer in the near surface area. The negative surface charge may be provided by the formation of cation vacancies or the formation of charged oxygen adsorbates at the surface. Our results clearly indicate a pO2-dependent surface space charge formation in donor doped STO under oxidizing conditions at temperatures as low as 770 K.

Resume : A competitive spin transfer torque (STT) MRAM element combines a high TMR ratio with a low critical current density to flip the free electrode magnetization orientation using STT. Yet, if the tunnel barrier height of intrinsic MgO were involved, then no STT could take place at an applied bias below that leading to voltage breakdown [1]. Conversely, how do MTJs with MgO that isn’t intrinsic nevertheless yield high TMR? An oxygen vacancy picture of spin- and symmetry-polarized solid-state tunneling across MgO has recently been proposed to reconcile these contradictions [2-3]. On the basis of ab-initio theory and magnetotransport experiments, we will discuss how double oxygen vacancies called M centers can, compared to the case of single oxygen vacancies called F centers, sustain TMR. To study these aspects within the same device, we’ve designed MTJs that integrate a MgO composite barrier: the lower 1.5nm segment is sputtered from a MgO target in pure Ar, while the top segment is sputtered in a Ar/O2 plasma. We unexpectedly observe a switchover to negative TMR at ~-1V (fig. a). Referring to panel b, thermally assisted tunneling spectroscopy [1-3] enables us to correlate this spintronic feature with a localized state positioned ~1eV from EF which has, in previous work [1-3], been identified as the F center located below EF. Considering the sign of applied bias and our electrical hookup, our results are consistent with a picture of hole tunneling[4] onto the F center located in the O2-augmented segment of the MgO barrier. Since this feature is not observed at positive bias, we infer that inserting O2 into the Ar plasma converts M centers to F centers by reducing the absolute density of oxygen vacancies. The sign inversion of TMR is, in turn, the result of modifying the MTJ’s spatial potential profile [5]. We will also discuss the impact on magnetotransport of altering the concentration of O2 in the plasma. Our work constitutes the first explicit proof that hole tunneling onto the localized states of oxygen vacancies is taking place. Looking ahead, our work also demonstrates the addressing of localized states that are positioned solely on one side of the MTJ’s tunnel barrier. [1] Oxygen-vacancy driven tunnelling spintronics across MgO;U. Halisdemir et al. Proc. SPIE 9931, Spintronics IX, (2016) and ref. therein. [2] Localized states in advanced dielectrics from the vantage of spin- and symmetry-polarized tunnelling across MgO, F Schleicher et al., Nature Communications 5, 4547 (2014) [3] MgO magnetic tunnel junctions of enduring F-type upon annealing; F Schleicher et al, Journal of Physics D Applied Physics 48, 435004 (2015) [4] Observation of Fowler-Nordheim hole regime across an electron tunnel junction due to total symmetry filtering; M. Bowen et al Phys. Rev. B, 73, 140408(R) (2006). [5] Tunnel barrier parameters and magnetoresistance in the parabolic band model; F. Montaigne, M. Hehn and A. Schuhl, Phys. Rev. B 64, 144402 (2001)

Resume : The quasi two-dimension electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community [1]. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. Another is the extreme sensitivity of its transport properties to electrostatic boundary conditions. First- principles calculations have suggested that the critical thickness could be reduced to just 1 uc by covering the LAO film with specific metals [2], an effect we recently demonstrated experimentally for Co [3]. However, the underlying mechanism leading to the formation of the q2DES in these Co/LAO(1 uc)/STO samples remains unclear. In this presentation, we show the chemical, electronic and transport properties of several LAO(1-2 uc)/STO samples capped with different metals (Ti, Ta, Co, Ni80Fe20, Nb, Pt, Pd and Au) grown in a ultra-high vacuum (UHV) system combining pulsed laser deposition (to grow the LAO), sputtering (to grow the metal) and in situ X-ray photoemission spectroscopy (XPS). Magnetotransport measurements were performed at low temperatures (2K) and high magnetic fields (9T) and analyzed with a current-dependent (2+1)-band model in order to extract the carrier density, mobility and number of populated bands of the q2DES at the interface. We performed a systematic XPS study, since the presence of a q2DES in the STO is associated with a valence change of the Ti 3d ions from 4+ (in the 3d0 bulk insulating state) towards 3+. Additionally, XPS shows that the appearance of interfacial conductivity is accompanied by a partial oxidation of the metal, a phenomenon that is strongly linked with the q2DES properties and with the formation of defects in this system. The results confirm that for several metals a q2DES forms at 1-2 uc of LAO. In contrast, for noble metals, the q2DES does not form at low LAO thicknesses and instead the critical thickness is increased above 4 unit cells. We discuss the results in terms of a hybrid mechanism that incorporates both electrostatic and chemical effects [4]. [1] S. Gariglio, M. Gabay, J. M. Triscone, APL Mater. 2016, 4, 60701 [2] R. Arras et al., Phys. Rev. B 2012, 85, 125404 [3] E. Lesne, et al., Nature Commun. 2014, 5, 4291 [4] D.C. Vaz et al., submitted

Resume : Ferroelectric tunnel junctions (FTJs) have emerged as promising candidates for novel memory devices. The success of this approach relies on the ability to build ferroelectric tunnel junctions with large electroresistance (ER) response. In ferroelectric tunnel junctions, ER can be understood on the basis of the change of the tunnel barrier height upon polarization reversal in presence of asymmetric electrodes. However, other mechanism may also contribute to the electroresistance, such as space-charge effects or ionic motions, their combination determining the magnitude and sign of the electroresistance (ER=(Rup-Rdown)/Rdown, where Rup and Rdown are the resistance values for polarizations with opposite sign). Understanding the thickness and time-dependent response of ER in FTJs is crucial to fully understand the origin of ER with different sign and magnitude. Here, we report on the systematic investigation of ER dependence on ferroelectric sample thickness and writing time (tw) of Pt/ BaTiO3/La0.7Sr0.3MnO3/ SrTiO3 Ferroelectric Tunnel Junctions. Our results reveal that the different conductance states of the barrier have a radically different sign, magnitude and dependence on the writing time (for writing times longer than 1s) depending on sample thickness. Having all the samples the same top and bottom electrodes and consequently similar ferroelectric/metal interfaces, we can conclude that ER results from a combination of a fast FE polarization switching and a slower process, which origin will be discussed. We believe that the presented results will help to the better understanding of the ER phenomena in thin ferroelectric films.

Resume : In recent years, the thickness of ferroelectric thin films has been pushing the limit of a few unit cells to enable a new type of ferroelectric-based devices, such as ferroelectric tunnel junctions (FTJs). The FTJ device structure is analogous to the traditional ferroelectric capacitors. However, the major difference is that the reading process is performed non-destructively through the electronic tunneling current measurements, which makes the FTJs faster and energy efficient. Conventionally, a polarization state in ferroelectric devices is controlled by an electric bias. In this study, we demonstrate an alternative way to switch the polarization using optical excitation of hybrid BaTiO3-based FTJs where we used a narrow-bandgap 2D semiconductor, molybdenum disulfide (MoS2), as one of the electrodes. Bulk MoS2 has an indirect bandgap of 1.2 eV, while monolayer MoS2 is a semiconductor with a bandgap of 1.8 eV. As an initial step, we investigated the electrically-induced switching mechanism and polarization stability in MoS2/BaTiO3 hybrid heterostructures. Next, we demonstrated the UV light-induced polarization switching of the same heterostructures. It has been shown that the polarization switching direction of the BaTiO3 layer strongly depends on the ambient due to the altered type of the screening charges in MoS2. Polarization switching and retention behavior of the bare BTO films under UV illumination was used as a reference. The obtained results open a possibility for optical control of the electronic transport in memory and logic devices composed of 2D materials and ultra-thin ferroelectrics allowing reduced operation power and response time.

Resume : In a ferroelectric field effect device, the carrier density in the conducting channel is tuned with a ferroelectric gate. Depending on the ferroelectric polarization direction, either charge accumulation or charge depletion is obtained, corresponding to an increase or decrease, respectively, of the channel resistance. This effect has been used to control the physical properties of complex oxides acting as conducting channel. On the other hand, this field effect can also be taken advantage of to detect the polarization state of a ferroelectric thin film, by monitoring the electrode resistance in capacitor geometry. In this picture, we report on the resistance variation of a SrRuO3 (SRO) film in the 1-10 nm thickness range, with either BaTiO3 or PbTiO3 as ferroelectric thin film in order to tackle different polarization values. All perovskite heterostructures were grown by pulsed laser deposition on SrTiO3 substrates. The devices were fabricated combining optical lithography, ion beam etching of the oxide layers and lift-off process for the Pt top electrodes. The resistance variation of the SRO electrode was systematically measured upon switching the ferroelectric polarization, ranging from 0.4% (10 nm-thick SRO) to 25% (1 nm-thick SRO). The thickness and polarization dependences are discussed in terms of the charge screening at the ferroelectric/electrode interface.

Resume : In this study we report the results of high quality Pb(Zr, Ti)O3 PZT thin films that have been successfully deposited by two different methods, pulsed laser deposition (PLD) and sol-gel on (001) Si substrate. In order to perform PLD depositions of PZT a SrTiO3 (STO) buffer layer was deposited by molecular beam epitaxy (MBE) on Si substrate, this acting as a template for PZT deposition and as a barrier for Pb diffusion into Si. Additionally, 20 nm of SrRuO3 were grown by PLD on top of the STO in order to act as back electrode. Suspended pyroelectric elements on Si wafers have been fabricated by sol-gel method and Reactive Ion Etching (RIE) technique was used to release the PZT membranes. Electrical and pyroelectric measurements have been performed. Their ferroelectric properties were tested by performing C-V and P-V measurements at room temperature. For the pyroelectric measurements two different sources of IR radiation were used (a laser diode with wavelength of λ = 800 nm and a blackbody used for different temperatures, e.g. 500°C and 700°C). The pyroelectric coefficient is estimated from the frequency dependence of the pyroelectric signal measured in the voltage mode, where the top electrode is exposed to the infrared radiation. The removal of the substrate allows the active pyroelectric material a grater variation of the temperature, leading thus to superior pyroelectric properties.

Resume : With the advances on both deposition and structural characterisation techniques, a new light has been shed on the physics of multiferroic thin films. For example, it is now possible to investigate not only the tilt system of nickelate or vanadate thin films but also the amplitude of the rotation along the out-of-plane and both in-plane directions. This, in turns, enables to better understand how the symmetry of substrate modifies the tilt patterns with respect to the bulk. Another possibility offered by these advances is the control over the domain structures of ferroelastic thin films which have a dramatic influence over the performances of such thin films. Not only is it possible to favour the formation of a particular domain pattern through deposition conditions, but it is also possible to induce a reversible interchange between cross-hatched and stripe domain patterns e.g. in ferroelectric PZT and multiferroic La/BFO thin films. Strain-engineering has been shown a very effective tool to control the structure (orientation, distortion) of ferroic thin films with a particular interest for properties strongly coupled to the lattice. This is generally achieved through a proper transfer of the misfit strain through the interface between the film and the substrate. This approach suffers several limitations, mainly related to the compatible substrates and their availability. An interesting alternative is to use thickness as a way to tune the misfit strain. Finally, with a more exquisite control of the interface quality enables the design of heterostructures mimicking at the nano-scale bulk bimorphs with the dramatic improvement of strain-mediated properties such as piezoelectric/magnetostrictive heterostructures.

Resume : Due to the remarkable possibilities of epitaxially growing strontium titanate (SrTiO3 or STO) on silicon, this oxide is widely used as a buffer layer for integrating other perovskite oxides which allows for the development of various functional electronic devices on silicon. Moreover, STO is known to be an incipient ferroelectric in bulk but may become ferroelectric when in the form of strained ultrathin films. Given the importance of the potential applications for electronics if this property is demonstrated, we performed a spectroscopic study of STO on Si(001) templates coupling experimental and ab initio investigations. Their infrared spectra show that both the mechanical stress and the thickness play major roles: higher energy modes evolve as soft modes in thinner strained films. In order to support these observations, the dynamical ab initio calculations allowed deriving the conditions for STO films to become ferroelectric at room temperature as shown by the development of a soft mode and the divergence of the in-plane dielectric constant.

Resume : Composite multiferroics can be created by strain coupling at the interface between a ferromagnetic and a ferroelectric material. Application of an electric field is then observed to alter the magnetic properties. Such an induced magnetoelectric coupling is strongly depending on the structural and chemical features at the interface. The isotope-sensitive technique of nuclear resonant scattering of synchrotron radiation is used to selectively study the chemistry and magnetic state of the Fe/BaTiO3 interface. An electric polarity-dependent modification of the metal/ferroelectric oxide interface has been systematically observed. The results show that the interface can be oxidized or reduced by inverting the polarity of the electric field applied across the interface above a threshold field value of ±400 kV/m. Remarkably, the final interface state depends on the polarization history of the system. Based on these results, a model for the electric field induced ion transport at the Fe/BaTiO3 interface has been suggested. Subtle structural changes at the interface (oxidation, formation of a magnetically dead layer) deteriorate the magnetoelectric coupling.

Resume : Multiferroics have been widely focused because potential applications in novel multifunctional devices such as sensors, memories and spintronics. However, since the scarcity of single-phase multiferroic magnetoelectric (ME) materials, ME composite systems, such as ferroelectric-ferromagnetic multilayer structure, have been studied in recent years. In these ME composite systems, the ME coupling effects come from of altering polarization or magnetization by transferring strain which is induced by magentostriction in the ferromagnetic or by the piezoelectric effect in the ferroelectric in on component to the other component. In this study, thin composite systems or Pb(Zr,Ti)O3-CoFeO3-Pb(Zr,Ti)O3 systems were grown by pulsed laser deposition (PLD). The strain-mediated ME coupling effect according to the thickness of CoFeO3 layer was systematically investigated. The ME properties of thin composite system were characterized by P-E measurements for electric property, VSM for magnetic property and especially, ME coupling coefficient measurements using precise ME characterization set-up. In this presentation, a volumetric influence of CoFeO3 on the magnetoelectric properties and magnetic properties of trilayer thin film system will be addressed in detail.

Resume : During the last decade, in the field multiferroic materials, several systems have shown the coexistence of electric and magnetic order with coupling between them (so-called magnetoelectric coupling). In the particular class of composite multiferroics, where magnetoelectric coupling takes place owing to mechanical coupling between a ferroelectric material and a ferromagnetic material, the sign of the net magnetization in the ferromagnet can not be selected uniquely by an electric field, whatever is its sign or magnitude. This is because piezoelectricity and magnetostrictive effects are both even functions of electric field and strain, respectively. Without overcoming this fundamental issue, we will show that magnetic memory effects present in the antiferromagnetic to ferromagnetic transition of FeRh can help to circumvent it. For this we have characterised a PMN-PT/FeRh structure. PMN-PT is a relaxor ferroelectric with record piezoelectric coefficient, and FeRh presents a large change in its lattice parameters while crossing the antiferromagnetic to ferromagnetic phase transition. Thus, one can tune the magnetic order by means electric-field, by modifying the magnetic transition temperature on FeRh via strain coupling between the piezoelectric substrate and the magnetic layer. First, we will show that FeRh phase transition shows clear memory effect. After FeRh magnetization is oriented in the ferromagnetic phase by an external magnetic field and FeRh is bring to the antiferromagnetic phase by cooling it; if one measures the orientation of the magnetization again in the ferromagnetic phase it partially recovers its initial state. This result is revealed by micro- and macro- magnetic characterization. Second, we also show that by the application of low electric field, we can isothermally manipulate a large amount of magnetization, owing to the magnetic memory effect.

Resume : Lead zirconate titanate (Pb(Zr1-xTix)O3, PZT) is well known for its excellent piezoelectric and ferroelectric properties and its subsequent applications. Tunable composition makes it versatile and morphotropic phase boundary (MPB, x=0.48) is especially attractive for the large piezoelectric constant, considerable remnant polarization and great dielectric constant. Despite the fact that lead in not environment friendly, the study based on PZT continues intensively along with other complex oxides due to the lack of equivalent substitutes. PZT(52/48) films with thickness from 33 nm to 200 nm have been deposited on SrTiO3 substrate, with an SrRuO3 interlayer as bottom electrode, by sol-gel process, which is low cost and has short fabrication cycle. X-Ray Diffraction indicates single crystalline PZT is epitaxially grown on the substrate. Surface roughness is less than 1 nm (root mean square), characterized by Atomic Force Microscopy. At nanoscale, piezoresponse force microscopy shows the inverse piezoelectric effect. At macroscale, electrical properties of the PZT thin films were measured through current-voltage (I-V), capacitance-voltage (C-V) and PUND (Positive Up Negative Down). These characterizations allowed to discriminate between the differents conduction models and laso between the ferroelectric domains switching behaviour.

Resume : Multiferroics featuring magneto-electric coupling bring high promises for the future of spintronics and especially electronic memories.To overcome the lack of intrinsic materials, combining a ferromagnet and a ferroelectric inan artificial multiferroic system is an elegant solution. However in order to control the system properties, understanding the magneto-electric coupling mechanism(s) is mandatory. In this work we investigated bilayers composed of a BaTiO3 ferroelectric film and of a ferromagnetic (CoFe2O4, NiFe2O4) film deposited subsequently by atomic oxygen molecular beam epitaxy. We used piezoresponse force microscopy (PFM) to define µm-sized ferroelectric domains and spectromicroscopy data (local XAS and XM(C,L)D spectra and associated images at Co, Ni, Fe, O and Ti edges) were acquired by X-ray PhotoEmission Electron Microscopy. In this way it is possible to clarify the link between the BaTiO3 ferroelectric state and (i) chemistry modifications of the ferromagnet, (ii)(anti)ferromagnetism behavior and (iii) charge anisotropy. In particular we noticed a coupling between the ferroelectric pattern and the magnetic and charge anisotropy properties of the ferrites, also entangled with chemical modification of the latter (e.g. Fe reduction). By tuning the PFM writing parameters and studying ferrites with different magnetostrictive and ferromagnetic properties, this contribution brings new insights about the magneto-electric coupling in these artificial multiferroics.

Resume : Thin films of the lead-free Na_xK_1-xNbO_3 (NKN) compound have been intensively researched due to their strong ferroelectric parameters and their environmentally friendly character. Here we focus on the change of optoelectronic properties of NKN films in the amorphous-to-microcrystalline transition region at deposition temperatures between 450 and 600 oC. Film growth was performed by pulsed laser deposition method (PLD), ablating sintered targets by the ultraviolet line of a Nd:YAG laser system (wavelength 266 nm, pulse duration of 5 ns, repetition rate of 5 Hz, and energy density 0.1 J/cm2), while varying the oxygen background pressure. The films were then analyzed by scanning electron microscopy (SEM), Rutherford backscattering (RBS), optical transmittance (OT), spectral ellipsometry (SE), Raman spectroscopy, capacitance-voltage characteristics (C-V), and admittance spectroscopy (AS). Low-temperature films showed high surface roughness in SEM, poorly defined optical band gap by OT, and poor ferroelectric properties as measured by hysteresis loops. For high-temperature films (600 oC) the SEM micrographs showed clear microcrystalline features of typically 200 nm size. Good stoichiometry was verified by RBS with calibration obtained from a ceramic target. The bandgap obtained from SE was 3.69 eV, in accordance with optical transmission results. We also could monitor weak photosensitivity in the UV region, leading to non-exponential decays after pulsed laser excitation, with typical initial decay time of 5 microseconds, which is an indication of the existence of a broad distribution of deep trap states. Taking essential film parameters into account (dielectric constant 1.300, remnant polarization 6 microC/cm2, coercive field of 24 kV/cm), we found optimal deposition conditions at 0.2 mbar oxygen pressure and 600 oC deposition temperature. (This work was supported by Fundação para a Ciência e a Tecnologia (FCT) through projects PTDC/FIS/108025/2008 and PTDC/CTM-CER/115085/2009).

Resume : The Multiferroic materials are currently the subject of intensive experimental and theoretical investigation, motivated by their potential applications in spintronics, multiple-state memories and others [1]. Bismuth ferrite (BiFeO3 or BFO) is the most studied multiferroic until now due to the coexistence of ferroelectric and magnetic order at room temperature. BFO thin film presents a polarization of about 100µC/cm2 in (111) oriented films and also considered as an alternative to lead based materials for electromecanical applications. Rare earth substitution of Bismuth (Bi1-xRExFeO3) (RE: Sm, Gd, Dy, La) leads to improved physical properties of thin films such as reduction of leakage current which is an obstacle for practical applications [2]. Important piezoelectric properties were observed for some compositions (Sm, Gd, La) and were correlated to a morphotropic phase boundary (MPB) between a rhombohedral R3c phase and an orthorhombic Pnma phase [2]. To better understand the origin of this induced MPB we investigate in the present work the effect of strain and substrate orientation on the structural interaction between BFO and LaFeO3 (LFO) in (BiFeO3)xΛ/(LaFeO3)(1-x)Λ superlattices (SLs). SLs have been grown using pulsed laser deposition on different substrates (SrTiO3,MgO, DyScO3) buffered by a conducting layer of SrRuO3 and studied by x-ray diffraction (Ɵ/2Ɵ, reciprocal space maps and phi scan), transmission electron microscopy (TEM) and Raman spectroscopy. (110), (100) and (111) STO substrate orientations were also used. The composition was varied, 0.20 ≤x≤ 0.90, while the modulation period Λwas kept constant at about 10nm.Our SLs investigations revealed a nanoscale mixture that depends strongly on the BFO thickness (PbZrO3like versus Pnma like state) and the substrate orientation. A PbZrO3 antiferroelectric like state is discovered in BFO and a peculiar domain state was revealed using a combination of XRD, TEM and Raman spectroscopy investigations. [1] M. Bibes, A. Barthélémy, Nat. Mater. 7 425 (2008). [2] D. Kan, C.-J. Cheng, V. Nagarajan, and I. Takeuchi, J. of Appl. Phys. 110, 014106 (2011).

Resume : Investigations of magnetoelectric coupling have been intensively performed on inorganic multiferroic materials. On the other hand, organic multiferroics have been much less studied, despite an increasing demand for flexible material-based applications. Polymer-based multiferroic materials can be prepared by the nanocomposite approach, which is an attractive way to tailor multiferroic materials through the choice of shape, size and microstructure of the constituents. Using rationally designed nanoscale building-blocks with properly-designed interfaces may enhance the magnetoelectric coupling between magnetic and ferroelectric components with potential applications for new multifunctional devices. Our work thus seeks to develop and optimize new hybrid two-phase nanocomposites, comprising inorganic ferromagnetic and organic ferroelectric components. In addition, because most studies have been concentrated on the electric control of the magnetism, we focus our efforts on the magnetic control of the electric polarization, much less reported coupling properties even for inorganic multiferroics. Our organic-inorganic thin films consist of ferromagnetic CoFe2O4 nanostripes embedded in a matrix of organic piezo-and-ferroelectric poly(vinylidene fluoride-ran-trifluoroethylene) copolymer (P(VDF-TrFE)). To reach this, CoFe2 nanostripes were fabricated by electrodeposition within a poly(methyl methacrylate) (PMMA) template fabricated by nanoimprint lithography, and further oxidized to form CoFe2O4 stripes after template removal. In a final step, P(VDF-TrFE) was embossed in the magnetic line grating acting as mold, thereby forming a continuous composite layer. The effect of the annealing treatment on the oxidation of CoFe2 nanostructures was first investigated. The M(H) magnetization curves and the magnetic properties of the ferromagnetic nanostructures (coercive field, saturation magnetization, saturation field) were investigated by Alternating Gradient Magnetometry (AGM). Local ferroelectric characterization was then performed on the nanocomposite using Piezo Force Microscopy (PFM). The local magnetoelectric coupling in these layers was also investigated, by measuring the local ferroelectric properties under a magnetic field using PFM, and attempts were performed to influence the electric polarization of the polymer by a magnetic field. We show that using proper design of a nanoimprinted organic-inorganic composites layer, offers the possibility to manipulate the electric polarization at room temperature, aided by an electric field, under a magnetic field.

Resume : Integration of crystalline oxide thin films with semiconductors has attracted considerable attention in recent years. Compared to Si, GaAs have a higher saturated electron velocity and electron mobility, transistors based on GaAs can function at a much higher frequencies. In this talk, SrTiO3 films were grown on GaAs (100) substrates as an intermediate buffer layer for the epitaxial growth of oxide thin films including multiferroelectric Mn-doped BiFeO3 and semiconductor ZnO by laser molecular beam epitaxy (L-MBE). The properties of the multilayers in terms of growth modes, strain and interface structures were characterized by the in-situ reflective high energy electron diffraction (RHEED) pattern. The crystalline quality and surface morphology of the oxide/GaAs heterostructure were investigated respectively by a combination of X-ray diffraction (XRD) and atomic force microscopy (AFM). These heterostructure exhibit good functional properties such as ferrelectrisity and resistive switching. Furthermore, theelectrical transport properties of these heterostructure with an emphasis on the interface strain effect were discussed in relation with the electrical properties. The results provide an understanding of the integration of oxide/GaAs heterostructure with full control over the interface structure at the atomic-scale.

Resume : Two-dimensional electron gas (2DEG) at the perovskite oxide interfaces such as LaAlO3/SrTiO3 interfaces has intrigued numerous researchers due to its versatile characteristics such as magneto resistance, gas and light sensitivities, resistance switching, and transistor operation. In this presentation, the diode-type functionality of the Pt/a-Al2O3/ SrTiO3 (a-AO/STO) system, where 2DEG at a-AO/STO interface plays the role of bottom electrode, was reported. The sample shows highly useful diode characteristics (F/R ratio of 10^4 @1.5V) and non-linearity in the forward direction (current ratio of 10^3 between 0.5 and 1.0V). These performance endures up to 1,000cycles with no noticeable change. Also the pulse based characterization was adopted to carefully examine the volatile resistance degradation when positively biased. The resistance of the samples degraded during the applying positive bias and recovered during the removal of bias. The origin of resistance change is movement of oxygen vacancies in a-AO layer, of which detailed kinetic model could be setup based on the Fick’s second law.

Resume : Perovskite-type metal oxides possess attractive features, including high conductivity (ionic, electronic, or mixed), electrocatalytic activity, and chemical/structural stability, which make them suitable for use in solid oxide fuel cells (SOFCs). Electrodeposition has attracted significant attention as a promising approach to synthesizing high-quality metal oxides. This method allows the preparation of various oxide materials, including perovskite oxides, with tailored physicochemical properties suitable for their specific applications by controlling deposition parameters. In this study, we demonstrate the fabrication of perovskite-type LaMO3 (M = Mn, Co) thin films and nanostructures via a facile electrochemical route. The proposed method involves the "chemically assisted electrodeposition" of hydroxide (electrochemical nitrate reduction and in-situ hydroxide co-precipitation), followed by thermal conversion of hydroxide to oxide. Our experimental results demonstrate that the composition, nanostructure, and morphology of the perovskite metal oxides strongly depend on the electrodeposition parameters, such as the precursor concentration, applied current density, and solution pH. The materials and electrochemical properties of the fabricated perovskite oxides are studied, and then, their feasibility in SOFCs is discussed.

Resume : Due to new research efforts in the field of thermoelectrics with a focus on size effects, there is a growing need for measurement setups dedicated to samples with small geometrical dimensions like thin films and nanowires with considerably different physical properties than bulk material. The characterization of these samples is important to learn more about their structure and conduction mechanism but also important for technical applications e.g. in the semiconductor industry. We report on the development of a new system to simultaneous measure the electrical and thermal conductivity, the Seebeck Coefficient and the Hall Constant of a thin film sample in the temperature range from liquid nitrogen up to 300°C. Due to the nearly simultaneous measurement at only one sample, errors caused by different sample compositions, different sample geometries (thickness) and different heat profiles can be avoided. The system consists of two main parts, a structured Si-wafer and a suitable measurement setup. To measure the el. conductivity and the Hall constant, the wafer owns a structure with four electrodes to use the Van-der-Pauw method. For the Seebeck measurement an additional temperature gradient can be applied on a membrane Setup. The temperatures for the Seebeck calculation are measured with resistance thermometers on the chip. The thermal conductivity can be measured in plane using the Völklein Method, doing a steady state or transient measurement. Therefore a small heating/sensing stripe is deposited on a very thin nitride membrane. Depending on the material of investigation (organic or inorganic), the sample can be deposited on the front side or the backside of this membrane. To get a correct result, the measurement has to be done under vacuum (no heat transfer by conversion) in a thermal stabilized and controlled chamber (to avoid heat transfer by radiation, the ambient temperature has to be identical with the chip temperature). In order to meet these requirements a suitable vacuum chamber with sample holder and necessary ports has been designed. The sample holder can be cooled with liquid nitrogen and heated by joule heating on both ends to create either a constant temperature or a defined temperature gradient. To measure the Hall constant, the chamber is put between two spools of an electro magnet to apply a variable magnetic field with a maximum of +/-1 T. As proof of concept, a showcase study of Bi87Sb13 thin films in varying thickness has been performed and compared to previously published data [1]. References: [1] Linseis, V., Völklein, F., Reith, H., Woias, P. and Nielsch, K. (2016) ‘Platform for in-plane ZT measurement and Hall coefficient determination of thin films in a temperature range from 120 K up to 450 K’, Journal of Materials Research, 31(20), pp. 3196–3204. doi: 10.1557/jmr.2016.353.

Resume : Chrome oxide (Cr2O3) is a corrosion-resisting material, has a magnetoelectric effect and high mechanical strength. Chrome oxide thin films are used as an optical filter, a coating for eliminating electric charge in the X-ray tubes. The paper presents the research results of the structure and electrical conductivity of chrome oxide thin films obtained by electron-beam evaporation of a target of pressed chrome oxide powder. The film structure was investigated by the methods of low-energy electron diffraction, infrared spectroscopy and the electron paramagnetic resonance method. The film composition was studied by x-ray microanalysis. The performed investigations resulted in the following: - a technology for formation of a chrome oxide target for electron-beam evaporation is developed; - the chrome oxide film structure was investigated; - the electrical conductivity of chrome oxide films was investigated; - temperature coefficient of the film electrical conductivity, the activation energy of electrical conductivity and contact electromotive force were defined: - it was established that the film electric conductivity corresponds to the electronic conductivity type; - the influence of vanadium oxide and silicon oxide additives on the structure, electrical conductivity of chrome oxide films is investigated; - the research made it possible to develop the technology for the production of chrome oxide films with stable and reproducible parameters.

Resume : Nanoscale tungsten oxide WO3 with the particle size of 20-200 nm has good application prospects in photocatalysis, photovoltaics (perovskite solar cells), for creation of functional materials and coatings for various purposes. Traditional methods of nanoscale WO3 synthesis are complicated for control of WO3 particle size. The processes are expensive. The paper presents a new method of electrochemical synthesis of nanoscale tungsten oxide providing the ability to control WO3 particle size in wide range. The method is based on the cathode reduction reaction of alkali metals tungstates. It is shown that WO3 particle size can be effectively controlled by changing the cathodic current density. The data of the experimental studies, including the particle size dependence on the cathodic current density, temperature and electrolyte pH, dependence on the current output from the synthesis conditions is presented. The conditions for electrochemical synthesis of tungsten oxide content with less stoichiometric WO2.5 - WO2.7 oxygen content (blue tungsten oxide). SEM-images of the tungsten oxide samples obtained under different conditions are given. It is shown that the new synthesis method provides narrow particle size distribution, and the distribution structure approximates to Gaussian distribution. The described new electrochemical method of synthesis can be widely used as an industrial method of nanoscale WO3 synthesis.

Resume : In recent years, multilayer thin films have attracted much attention due to their potential applications [1-3]. These applications may be used over a wide temperature and frequency range which may deteriorate the properties of multilayer thin films. In addition, the interface number has an important influence on the temperature and frequency dependence of the multilayer thin films. Therefore, it is very important to study the effects of interface number on the temperature and frequency dependence of the multilayer thin films. In this paper, PbZr0.52Ti0.48O3 (PZT) and Ba(Mg1/3Ta2/3)O3 (BMT) thin films were prepared by sol-gel method and aqueous solution-gel method, respectively. PZT/BMT thin films with different interface numbers were prepared and the effects of interface number on the temperature and frequency dependence of PZT/BMT thin films were investigated. The dielectric properties were measured with the amplitude of 0.5V from 100Hz to 1MHz by precision impedance analyzer and the ferroelectric properties were measured by precision workstation in the range from 25 to 145 °C. As the temperature increases, there is a decrease in the remanent polarization for the PZT/BMT thin films due to the increase in the degree of disorder. The interface number can improve the temperature stability of PZT/BMT thin films. As the frequency increases, the remanent polarizations for the PZT/BMT thin films decrease and the decline rate of remanent polarizations slows with the interface number increasing, indicating that interface number can improve the frequency stability of PZT/BMT thin films. Keywords: Interface number, temperature dependence, frequency dependence, PZT/BMT thin films References: [1] Z. Xu, D. Yan, D. Xiao, et al. Ceram. Int., 2013, 39, 1639-1643. [2] B.D. Lee, R.L. Hong, K.H. Yoon, et al. J. Am. Ceram. Soc., 2005, 88, 1197-1200. [3] F. Yan, G. Chen, L. Lu, et al. Appl. Phys. Lett., 2013, 103, 042906.

Resume : Hafnium-zirconium silicate (HfZr-silicate, (HfZrO4)1-x(SiO2)x) thin films were developed for advanced gate stack applications by incorporating Si atoms into virgin HfZrO4 via atomic-layer deposition (ALD), yielding films with varying levels of SiO2 content (x = 0.10, 0.15, and 0.20). Electron conduction behavior was responsible for a reduction in the gate leakage current of HfZr-silicate compared to pure HfZrO4 films and was clearly explained by a conduction-electron generation model. Furthermore, HfZr-silicate-based structures exhibited less charge trapping and featured an improved interfacial stability when in contact with Si compared to virgin HfZrO4, although they experienced both bias and thermal stress. These phenomena were associated with the formation of an interfacial layer (IL) between virgin HfZrO4 and the Si substrate while there was no IL for the HfZr-silicate. With regard to the electrical properties of the films with varying SiO2 incorporation, film with 15% SiO2 content was recommended as a high-k candidate due to its superior electrical properties and outstanding durability.

Resume : The effect of annealing atmosphere on photovoltaic effect of multiferroic BiFeO3 (BFO) thin film fabricated on Pt(111)/Ti/SiO2/Si(100) substrate by spin coating technique is reported. X-ray diffraction analysis revealed that BFO film annealed in air atmosphere is single-phase perovskite structure. Whereas, BFO film annealed in O2 and N2 showed impurity phase in it. Microstructure of BFO annealed in air atmosphere showed well defined grains. The presence of a single BFO phase leading to lower leakage current and superior photovoltaic (PV) effect. The photovoltaic study shows the open circuit voltage Voc = - 0.47 V and short circuit current Isc = 3.56 µA/cm2 for positive polling and Voc = 0.44 V , Isc = -3.41 µA/cm2 for negative polling for air annealed BFO film. On the other hand, the BFO films annealed in O2 and N2 atmosphere showed poor PV effect and was difficult to switch the polarization. Hence, we revealed that the BFO film annealed in air atmosphere can be useful for practical atmosphere such as, nonvolatile digital memories, spintronics, and data storage media.

Resume : Oxide thin films are the subject of intensive both experimental research and development for a long time because of their potential usefulness as spintronic devices. Most of the technologically important oxides crystallize in systems having more than one cationic site, such as the perovskite, spinel, garnet or hexaferrite systems. It is well established that different cationic distributions or different crystallographic position will result into different magnetic properties or electric ones. If both cationic distribution and crystallographic position can be easily determined in bulk materials using classical methods such as X-rays or neutron diffraction, they are extremely tricky to determine in thin films owing to the relatively small amount of material to probe. Anomalous scattering experiments have shown over the past ten years their capabilities for locating metal atoms on different sites, even in cases of small occupancies, and even in mixed metal situations. 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. DANES experiments can be recorded at different edges between 5keV and 25 keV using the BM02 beamline of the ESRF allowing thus to map almost all atoms. For data analysis, a software, “FitREXS”, has specially been developed for this purpose using the Python language and may be easily adapted to any system. Simulation as well as refinement of the different crystallographic parameters can be easily done thank to this code. Moreover, additional parameters such as the orientation of the cells along the growth direction for polar unit cell can also been taken into account and will be discussed.

Resume : In 2011 ferroelectricity was discovered in a binary oxide: Si-doped HfO2 [1]. Thereafter, it has been demonstrated that a ferroelectric phase (f-phase) appears for a larger sort of cation dopants (Zr4+, Y3+, Al3+, La3+, Gd3+ or Sr2+) [2], with the Pca21 space group. Most of the articles use electrodes to stabilize the f-phase. In this context, the stack TiN/Hf0,5Zr0,5O2/TiN have been particularly studied. And in 2015 the first Negative Capacitance Field Effet Transistor (NC-FET) has been fabricated using this stack on the top of the NC-FET gate [3]. TiN is frequently fabricated by sputtering [4], whereas ferroelectric HfO2 is made by Atomic Layer Deposition (ALD). It could be interesting to have only one optimized process for the entire fabrication. But few articles have been dedicated to doped (and undoped) ferroelectric HfO2 by sputtering [5-7]. In this context, we compare different aspects of the two deposition technics for ferroelectric doped and undoped HfO2. References [1] T.S. Böscke et al., “Ferroelectricity in Hafnium Oxide Thin Films Ferroelectricity in Hafnium Oxide Thin Films,” Applied Physics Letters 102903, no. 2011 (2011): 0–3, doi:10.1063/1.3634052. [2] Min Hyuk Park et al., “Ferroelectricity and Antiferroelectricity of Doped Thin HfO2 -Based Films,” Advanced Materials, 2015, 1811–31, doi:10.1002/adma.201404531. [3] Kai-shin Li et al., “Sub-60mV-Swing Negative-Capacitance FinFET without Hysteresis,” 2015, 620–23. [4] Patrick Polakowski and Johannes Müller, “Ferroelectricity in Undoped Hafnium Oxide Ferroelectricity in Undoped Hafnium Oxide” 232905, no. 2015 (2016), doi:10.1063/1.4922272. [5] Lun Xu et al., “Ferroelectric Phase Stabilization of HfO2 by Nitrogen Doping,” Applied Physics Express 9, no. 9 (September 1, 2016): 91501, doi:10.7567/APEX.9.091501. [6] T. Olsen et al., “Co-Sputtering Yttrium into Hafnium Oxide Thin Films to Produce Ferroelectric Properties,” Applied Physics Letters 82905, no. 2012 (2016), doi:10.1063/1.4747209. [7] Tomonori Nishimura et al., “Ferroelectricity of Nondoped Thin HfO2 Films in TiN/HfO2/TiN Stacks,” Japanese Journal of Applied Physics, n.d.

Resume : Our understanding of how devices operate has matured considerably in recent years. Separately conducted device and materials science studies (see e.g. this first report of clear-cut memristance in a spintronic device[1]) have been superseded in scientific insight by ‘operando’ studies that probe the device’s materials properties after the device has been placed in various states of operation. Of course, this approach equates all atoms in a device with its operation, though generally, only a subset of these atoms is actively involved. As an example, it is desirable to hone in on nanocristallites that form near the electrodes of batteries upon repeated cycling and alter its performance[2]. We propose as a next step in operando studies to focus the materials characterization technique onto only those atoms that drive the device’s operation. To do so, the materials science technique excitation is implemented, but the readout is performed using a device operational parameter. To demonstrate the technique’s interdisciplinary potential, we considered an extreme combination of device class and materials science technique. We’ve chosen magnetic tunnel junctions (MTJs), which are a prototypical spintronics device with industrial penetration toward next-generation memories and bio-inspired computing[3]. Indeed, this device class’s operation is driven by the funneling through the tunnel barrier’s defects (e.g. oxygen vacancies[4]) of the entirety of the junction’s current. As a result, the macroscale device operates using a minute subset of active atoms. To focus on solely these atoms, we deployed synchrotron-grade x-ray absorption spectroscopy, which is capable of resolving the electronic structure of dilute atomic species buried within a heterostructure, with chemical sensitivity. We’ve studied the MgO MTJ magnetotransport spectra upon sweeping the soft x-ray photon energy across the O K edge. RP exhibits changes associated with Fe oxide bonds, while RAP does not. We find that these bonds are not only perpendicular to the interface, as anticipated for an ideal MTJ, but also parallel to the interface. This latter observation suggests the presence astride the tunnel barrier’s hotpots of nanoscale FeOx regions. Although this appears counterintuitive considering the high TMR measured, this association of FeOx at both interfaces with high TMR was predicted theoretically[5]. Finally, we find that reaching the O K edge maximum impacts RAP much more strongly than RP. This suggests that the device operation is altered by the absorption of soft x-rays by the device’s active O atoms. We will discuss a first theoretical attempt at explaining the MTJ’s operation in this ‘excited’ state. Our technique has the potential to considerably simplify progress in device studies spanning a wide interdisciplinary range of research fields. It also strengthens scientific causality between a device’s operation and the materials properties that underscore it, and thus touches upon the philosophy of scientific research itself. [1] Bias-crafted magnetic tunnel junctions with bistable spin-dependent states, M. Bowen et al, Appl. Phys. Lett. 89 103517 (2006). [2] Observation and Quantification of Nanoscale Processes in Lithium Batteries by Operando Electrochemical (S)TEM B. L. Mehdi et al Nano Lett. 2015, 15, 2168. [3] Tunneling path toward spintronics, Miao et al, Rep. Prog. Phys. 74, 036501 (2011) [4] Localized states in advanced dielectrics from the vantage of spin- and symmetry-polarized tunnelling across MgO, F Schleicher et al.Nature Communications 5, 4547 (2014) [5] Oxygen-Induced Symmetrization and Structural Coherency in Fe/MgO/Fe(001) Magnetic Tunnel Junctions, C. Tusche, et al, Phys. Rev. Lett. 2005, 95, 176101.

Resume : Transition-metal-doped ZnO has been widely studied due to promising magnetic and electronic properties. This report presents the results of experimental studies of Zn1-xСoxO (x = 0.01, 0.03 and 0.05) films synthesized for the first time by a simple printed-electronics method at temperature about 1000°C on (0001)-sapphire substrates. The photoluminescence, optical absorption and confocal micro-Raman measurements revealed that Co substituted Zn ions and was incorporated into the lattice of ZnO. Raman spectra showed systematic frequency shift and broadening of the ZnO phonon modes with Co content and appearance of additional Co-induced local vibrational modes in the range of 530 – 550 cm-1 were observed. Electronic transitions of Co in the oxygen tetrahedron were observed in optical absorption. In addition, presence of ZnyCo3-yO4 spinel phase was found by Raman and XRD analysis. Room-temperature magnetic force microscopy (MFM) revealed a clear magnetic contrast in 2D magnetization maps, providing the evidence of in-plane magnetization at room temperature. Variation of the magnetic contrast at different magnetic field polarities of the MFM tip was observed. Combination of confocal Raman and MFM mapping allowed for direct correlation between microstructure and magnetic properties of the Zn1-xСoxO polycrystalline films. In particular, it was shown that secondary Co-related spinel phase is localized on grain boundaries. This work was supported by NATO Grant SfP 984735.

Resume : The YBa2Cu3O6 x (Y123 or YBCO) cuprates encompass the well known high-Tc superconductors for high oxygen content (x > 0.5) in the orthorhombic phase. Decreasing x below 0.5 leads, however, to YBCO in the tetragonal phase, which exhibits semiconducting Fermi-glass like behavior for 0.2 < x < 0.5 at room temperature. Using low temperature (100 to 200 °C) DC hollow cathode sputtering, we have elaborated amorphous YBCO (a-YBCO) semiconducting films (150 to 900 nm thick) on SiOx/(001)Si substrates. Indeed, Si-based substrates are adequate to integrate thermal sensors on a silicon chip bearing already processed readout circuitry. The surface of the films was studied by atomic force microscopy and local electrical resistance mapping; it revealed isolated grains immersed in a seemingly uniform substructure. The cation composition of the films was examined by inductively coupled plasma analysis. The oxygen content was checked by Raman spectroscopy, using previously documented data on both crystallized and amorphous semiconducting YBCO phases. X-ray photoelectron spectroscopy (XPS) was used to identify the Ba and Cu bindings with oxygen; it revealed the presence of the expected Y123 phase mixed with the "green phase" Y2BaCuO5. Besides, XPS allowed to study surface contamination layers at the nanoscale level. This compositional issue will be discussed in relation with the structuration of pyroelectric IR/THz sensors, which is our key application of a-YBCO thin films.

Resume : Transition-metal doped wurtzite ZnO is well known and intensively investigated wide-gap diluted magnetic semiconductor promising for application in spintronic devices. This work studies optical and structural properties of pure and Co-doped ZnO microwires (MWs) synthesized by optical furnace method. The morphology, structure and electronic structure of the samples were characterized by scanning electron microscopy (SEM), confocal micro-Raman spectroscopy, photoluminescence (PL) and optical absorption spectroscopy. SEM microscopy showed that Co-doped MWs has hexagonal facets and cavity inside, thus forming a micrometer-sized tube-like structures with lengths of 1.2 mm and diameter of 50-10 µm. Co-doping does not alter the wurtzite structure of ZnO and there is no evidence of Co secondary phase precipitation within the detection limit of Raman analysis. Incorporation of Co on the Zn site is confirmed by registration of additional vibrational mode at 552 cm-1 observed in the Raman spectra. Tetrahedral coordination of the incorporated Co in a high spin 2+ electronic state is confirmed by observation of spin-allowed 4T1(F)  4A2(F) and 4T2(F)  4A2(F) optical transitions. Variation in related intensity of these absorption peaks along the whole length of the individual MW indicate non-uniform spatial distribution of Co, which is in agreement with EDS data and previous electron paramagnetic study. This work was supported by NATO Grant SfP 984735.

Resume : Free surfaces of ferroelectric thin films with polarization oriented out-of-plane exhibit a surface band bending which is expressed as – ePδ/(ε0*εr), , where e is the elementary charge, P is the polarization (positive when oriented outwards), δ the surface thickness of the ferroelectric layer where the depolarization field is not fully compensated by accumulation of mobile charges near surface, ε0 the permittivity of vacuum and εr the dielectic constant of the material. A theory of low energy electron diffraction (LEED) patterns near a ferroelectric surface yields a surface potential written as – ePδ/(2ε0) [1]. By combining X-ray photoelectron spectroscopy (XPS), LEED and macroscopic ε measurements of the polarization on ultraclean, single crystal ferroelectric thin films one is able to derive all three parameters P, δ and εr. The result obtained on lead zirco-titanate PZT(001) with polarization oriented inwards [2] evidenced the formation of a ‚dead layer’ with low values of P and εr even for free ferroelectric surfaces, together with small values of δ and the evidence of 2D electron gas accumulation on the surface. These results are fundamental for the mechanism of formation of dead layers even in absence of metal contacts or other chemical interactions and also may provide new concepts for electron transport on ferroelectric surfaces. [1] C.M. Teodorescu et al., Sci. Rep., revision submitted (2016). [2] L.C. Tănase et al., Sci. Rep. 6, 35301 (2016).

Resume : Perovskite-type oxides are prospective candidates for energy conversion processes in high temperature solar concentrator and solar photoelectrocatalytic devices. In both applications, the composition, nanostructuration and domains in the crystals play an important role. The relation between sample preparation methods, microstructure, and properties isdiscussed to define design rules for high efficiency materials. Their good performance can be explained based on e.g. their suitable band structures, adjusted charge carrier density, effective mass and - mobility, hindered phonon transport, electron filtering potentials, and strongly correlated electronic systems. These properties are tuneable by changing the composition, structure, crystallites size, interfaces and materials combinations with scalable synthesis procedures. The resulting improved materials are characterised and tested in (photo) electrocatalytic and thermoelectric conversion of concentrated solar radiation heat. The goal of this study is to finally utilize the investigated materials to convert solar energy into electricity or fuels. References 1. Maegli, A.E., Hisatomi, T., Otal, E.H., Yoon, S., Pokrant, S., Graetzel, M., Weidenkaff, A., Structural and Photocatalytic Properties of Perovskite-Type (La,Ca)Ti(O,N)3 Prepared from A-site Deficient Precursors. J. Mater. Chem. 22 (2012) 17906-17913. 2. Thiel, P. Populoh, S., Yoon, S., Weidenkaff, A., Enhancement of Redox- and Phase-Stability of Thermoelectric CaMnO3-δ by Substitution, J. Solid State Chemistry 229, (2015) 62-67.

Resume : Elastic strains in thin films and artificial superlattices composed of alternating layers of ferroelectric compounds provide a new route to enhance the properties of known ferroelectrics and create materials with superior properties for device applications. The series of ferroelectric BaTiO3/Ba1-xSrxTiO3 (BT/BST-x) superlattices deposited on (001)MgO substrate using a PLD technique. The structural parameters of the layers were determined by X-ray diffraction. Near- and sub-Terahertz dynamics of soft and Debye-type central modes was studied by the polarized Raman spectroscopy of the BT/BST-x superlattices in the temperature range of 80-500 K. Due to the stress gradients in these BT/BST-x superlattices the phase transitions in BT and BST-x layers occur at different temperatures and depend on chemical composition of the BST-x layers. It was shown that temperature evolution of the low-frequency Raman spectra can be described within the model of coexisting damped harmonic oscillator and Debye relaxator. The occurrence of the pronounced central mode can explain the recently observed relaxor-like dielectric anomalies in BT/BST-x superlattices. We demonstrate that variation of chemical composition of the BST-x layers allows to tune distortions in alternating layers and to modify the shape of the dielectric permittivity as a function of temperature. We acknowledge financial support from the RSF (grant N 14-12-00258) and FP7-ITN-NOTEDEV.

Resume : Oxide heterostructures have attracted widespread attention due to their novel electronic properties. By accurately controlling the interfacial layers, several exotic phenomena such as two-dimensional electron gas, room-temperature ferromagnetism and superconductivity have been observed in thin film oxide heterostructures such as LaAlO3 and SrTiO3 which are, in bulk form, nonmagnetic insulators. In this work, we have designed a LaAlO3/CaMnO3 superlattice consisting of a polar, normally nonmagnetic oxide LaAlO3 and a non-polar insulating antiferromagnetic oxide CaMnO3. The semi-metallic and ferromagnetic properties have been inferred theoretically using density functional theory. In the n-type MnO2/LaO+ interface, the polar discontinuity facilitates a charge transfer from the LaO layer which results in a double-exchange ferromagnetic interaction between the Mn ions. In contrast, the p-type CaO/AlO2- interface results in G-type antiferromagnetism. We also conduct experiments to realize and understand the different types of magnetism at different interfacial layers predicted in our theoretical calculations. We have successfully grown the LaAlO3/CaMnO3 superlattices on LaAlO3 (100) substrates using a Laser MBE technique at a substrate temperature of 700 ºC and an oxygen pressure of 10-5 Torr. RHEED was used to precisely control the thickness of the superlattice. The magnetic measurements of a superlattice, which made up of alternating layers of 10-unit-cell LaAlO3 and 4-unit-cell CaMnO3 for 7 periods, demonstrate a pronounced hysteresis loops with ferromagnetic signal. We found that the saturation magnetization depends on the thickness of LaAlO3. In addition, the effect of strain and oxygen partial pressure for LaAlO3/CaMnO3 superlattice will also be investigated. These parameters can be manipulated to tune the electron transfer process and create oxygen vacancies during the growth of the superlattice, which will further affect the electronic and magnetic properties. These properties are highly attractive in regards to future spintronic applications and will be discussed in this paper.

Resume : Formation of ferroelectric domains has a large impact on the ferro- and piezoelectric properties of epitaxial oxide films. Of particular interest are periodic domain structures with monoclinic symmetry due to their enhanced piezoelectric coefficients. These monoclinic phases have been predicted for KxNa1-xNbO3 thin films grown under anisotropic in-plane strain. However, understanding and controlling of the ferroelectric domain evolution at the nanoscale is essential for a transfer from fundamental research to technological applications like surface acoustic wave devices. In this study, K0.7Na0.3NbO3 thin films with a thickness range between 10 and 45 nm were grown under anisotropic lattice strain on (110) TbScO3 substrates by metal-organic chemical vapor deposition. Monoclinic Mc domains have been verified and investigated by means of x-ray diffraction and piezoresponse force microscopy. The resulting domain pattern exhibits periodically arranged stripe domains which are aligned along pseudocubic [-110]pc as well as [110]pc direction, while the pseudocubic unit cells are sheared alternatingly in ±[100]pc and ±[010]pc direction. Depending on the film thickness, up to four different superdomain variants with different in-plane orientations are observed. For films with a thickness of 45 nm, the propagation of surface acoustic waves – first and third harmonic – are verified and found to occur only along the [100]pc and [010]pc directions coinciding with the monoclinic shearing directions.

Resume : Corrosion of steel occurs in several forms depending on the species present. Among these forms CO2 corrosion (sweet corrosion) in oil pipelines is by far the most common type encountered in the oil and gas industry. Although phenomenological theories of corrosion have improved the measurement and mitigation of mild corrosion, the lack of understanding, detection and prediction of highly localized severe corrosion leading to the breakdown of passive scales, still causes devastating faults and thus raises the cost of oil and gas production. To fully understand the formation and destruction of the passive sweet corrosion scale, which is crucial in moderating the corrosion rate, a molecular-level study of its nucleation, growth and degradation is required. In this work we therefore utilize density functional theory (DFT) to calculate surface stability and locate the reaction sites of the commonly observed sweet corrosion scales (siderite – FeCO3 and chukanovite – Fe2(OH)2CO3). This enables us to predict their growth mechanisms and model the crystallite morphology under different conditions, which is fundamental to controlling its passivation. The success of this study may help the front line engineers predict the localized high-rate corrosion and further prevent the collapse of passive scales.

Resume : Novel nanocomposites structures including ferroelectric layers have attracted considerable research efforts in recent years because of their prime importance for potential applications in spintronics and energy harvesting applications. The efficient manipulation of the ferroelectric states and domains remains however very challenging. Piezo-response Force Microscopy (PFM) is a very well suited experimental approach to tackle these issues. We report recent PFM investigations revealing different PFM contrasts as a function of the nature of the substrate or of the top oxide layers in BaTiO3 based hetero-structures. Epitaxial BaTiO3 layers were considered as free layer, deposited on Nb doped SrTiO3(001) or Pt(001), or as inner layer in a sandwich structure including another oxide top layer (MFe2O4/BaTiO3 with M = Co, Ni, Fe and Fe2O3/BaTiO3) on Nb doped SrTiO3 [1]. We determined two regimes for the ferroelectric (FE) poling by PFM, one, where only the FE contrast is observed with no contrast in topography (weak poling), and the second one, where besides the FE contrast, the topography contrast appears also, with steps around 1nm (strong poling). The transition between the two regimes depends on the voltage and force on the tip, on the contact quality between the substrate and the ground, on the sample structure (single BaTiO3 layer or heterostructure) and on the nature of substrate (Pt or Nb doped SrTiO3). [1] T. Aghavnian, PhD 2016, Université Paris Saclay

Resume : Nano-crystalline particles of cerium oxide (CeO2) has attracted extensive interests over the last years with rapidly increasing applications in various fields. In order to exploit and expand their applications was made an extensive characterization of physical and chemical properties. The aim of the research was to put in evidence the influence of surfactants on tailored characteristics of the particles of cerium oxide (CeO2) revealed by morphological characterization. In the present paper, cerium oxide (CeO2) nanoparticles were prepared using co-precipitation method in the absence and presence of different surfactants, using cerium nitrate Ce(NO3)3 as a basic material, sodium hydroxide as a precipitator agent, cetyltrimethyl ammonium bromide C19H42BrN (CTAB >99%) and sodium dodecyl sulfate C12H25NaO4S (SDS 99%) as cationic and anionic surfactants. The precursors samples were calcined at 550°C for 3h in air, then the powders were investigated to analyse the structural and morphological characteristics by Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The FTIR spectra exhibits the band below 500 cm-1, which is assigned to the Ce-O stretching mode and it confirms the formation of CeO2 for all samples. The XRD analysis indicated that the particle size decreasing with the introduction of surfactants. Also, the SEM images revealed that the CeO2 samples consist of crystalline particles with the sizes in the range of 10-40 nm, and for the samples prepared with different surfactants decreases the degree of agglomeration and less particle size than powder sample without surfactants. The obtained results indicate that both the addition of the surfactants and the processes parameters (concentration of precipitant, reaction conditions, time and temperature of presintering and sintering) allow to tailor the final properties of the product.

Resume : We report here results of our investigation of oxide nanometric films integrated with silicon substrates for new multifunctional applications. Ultraviolet photons of KrF-laser (248 nm) was used for the synthesis of nanometeric films based on iron and chromium oxides (Fe2O3-X(0≤x≤1) and Cr3-XO3-Y(0≤x≤2; 0≤y≤2)) with variable thickness, stoichiometry and electrical properties. Films deposition was carried out on the silicon substrate Si <100> at the substrate’s temperature ТS = 293°K. Atomic force microscopy methods as well as X-ray diffraction and X-ray reflectometry analysis were used for nanometric films characterization. Fe2O3-X(0≤x≤1) nanometric films demonstrates the negative magnetoresistance in magnetic fields up 0.7 Т. At the same time, for hybrid systems of the alternate layers Fe2O3-X(0≤x≤1)/Cr3-XO3-Y(0≤x≤2; 0≤y≤2) the positive magnetoresistance as well as the magnetic hysteresis and magnetoresistivity switching effect in the low magnetic fields were observed. SPV spectra of multi-component composite structure with several types of surface carriers transporting materials were studied. It was found a significant rise in value and expansion of the spectral range of the surface photo-voltage.

Resume : Multilayered heterostructures formed by alternative layers of thin films of ferroelectric or magnetic ordering materials, are intensive studied this days for their potential magneto-electric couplings and/or multiferroic properties. The electric and dielectric properties of such structures have been investigated in a large number of studies and the results show that the electric and dielectric characteristics of the multilayers are different comparing with the ones of the constituent materials. For a complete understanding of this heterostructures electric properties it is important to have knowledges about the constituent materials electrical properties. If the electric properties of the ferroelectric thin films are intensively studied in literature, the electric properties of the ferrites thin films are less known. Therefore, we investigated the electric properties of an epitaxial thin film of NiFe2O4, obtained by pulsed laser deposition, using SrTiO3 as substrate and SrRuO3 as top and bottom electrode. Electrical characterization includes current-voltage, capacitance-voltage, and capacitance-frequency measurements at different temperatures. The results reveals a hysteresis-like behavior of current and capacitance as function of voltage which could be assigned to a resistive and/or capacitive switching. Experimental results are explained consider a band diagram representation and the presence of a defect with a deep donor-type level in the band-gap of the NiFe2O4 layer.

Resume : Thermal treatment of glass-ceramics dictates various important features such as microstructure, mechanism of glass, degree of crystallization, magnetic properties and biological response etc. In this study, we investigated the heat treatment conditions and the crystallization kinetic of ferro/ferrimagnetic bioactive glass-ceramic by using differential thermal analyser under isothermal and non-isothermal condition. The initial work involves relevant literature survey and selection of based glass system and interesting ferromagnetic materials. Modified incorporation method will be employed in this research, where the solid-state reaction and conventional glass-melting techniques were employed to separately prepare the selected ferro/ferrimagnetic powder and bioactive glass, respectively. The mixture of ferro/ferrimagnetic and base glass was then re-melted to form glass. The important parameters including glass formula, melting temperature, and quenching rate etc. will be carefully controlled. In order to change the prepared glass to glass-ceramic samples, heat treatment technique was employed. The as-received glass ceramics will be examined in terms of phase by X-ray diffraction (XRD) and microstructure by electron microscopy. After receiving the glass-ceramics embedded with desired crystals, tests on physical, magnetic properties, biocompatibility, toxicity and power loss will then be carried out for considering the possibility of using in hyperthermia applications. Finally, the knowledge base from this study will be shared with other organizations in both government and private sectors.

Resume : Calcium Copper Titanate (CCTO) is one of many rare earth oxides that displays a colossal permittivity [1], yet the mechanism behind this phenomenon is not currently fully understood [2]. As bulk CCTO is known to exhibit very low permittivity, it is currently believed that the formation of grain boundaries and their resultant properties are responsible for this high permittivity. The first step to understanding these grain boundaries is to explore the surfaces. Various CCTO slabs are modelled and their respective electronic properties calculated. These properties are calculated using first principles simulations based upon Density Functional Theory. These slabs undergo substantial surface reconstruction in the [100] plane and the properties of TiO2 overgrowth are explored. We find that the TiO rich surfaces are more favourable than CuO surfaces and that the Jahn-Teller distortion is modified. This is directly related to the occupation of the d-orbitals of the surface states. We find that the oxygen at the surface are less negatively charged than in the bulk and that the bond angles are distorted. These results shed further light on the properties of colossal permittivity materials and how growth environments control these properties, suggesting limitations on growth conditions in order to maximise the colossal permittivity. References [1] D. C. Sinclair et al., Appl. Phys. Lett. 80, 2153 (2002). [2] D. C. Sinclair et al., Nova Science Publishers (2013).

Resume : Optical filters and colored filters are widely used in photonic devices, decorative glasses, photography, and film camera production. These filters should be tailored for their transmittance, reflectance and specially absorbance in visible wavelength. As an instance, neutral density filters (NFDs) should exhibit unique color (gray) and must be transparent (with the same extinction) in whole visible wavelengths. Traditionally optical filters were produced by solving metals or metal oxides in molten glass. As an alternative for this method, INM developed three different approaches: 1) wet chemical method (sol-gel) using Mn-Cu-Cr-spinel-nanoparticles with SiO2 nanoparticles as network, 2) solvothermal method for producing of nanoparticles of Mn-Cu-Cr-spinel, and 3) physical vapor deposition (PVD) method to produce the Mn-Cu-Cr-spinel with a subsequent post thermal treatment of the deposited metal or metal-alloys. In both methods 1 and 2, the produced sol can be coated on glass substrate using dip- or spin coating method. Depending on the desired transmittance of the NDFs, The thickness of coating can be controlled about 300 nm to 800 nm. In addition, these three mentioned routes were compared and the results were discussed. Easier fabrication process of NDFs with different optical densities and cost-effectively are at least two of the advantages of our methods in comparison to the traditionally methods which make our method interesting for industrial mass-production.

Resume : The structural and magnetic properties of La0.67(PrxBa1-x)0.33MnO3 (0.05 ≤ x ≤ 0.20) perovskite prepared by the sol–gel based Pechini method at low temperatures have been studied. X-ray diffraction revealed that the compound is in the orthorhombic phase with an Pnma space group, no. 62. Upon Pr doping on the La site, the lattice parameters, the B-O1-B bond angle and the unit cell volume are reduced due to the larger ionic size difference between Pr3+ (1.179 Å) and Ba2+ (1.47 Å). Magnetization as a function of temperature under 0.05 T magnetic field showed that all our samples exhibit a paramagnetic–ferromagnetic transition. Results show that the Curie temperature TC decreases from 330 to 309 K when varies from 1.1310 to 1.1131 Å. Magnetic entropy change, relative cooling power and specific heat for magnetic field variation were predicted with the help of the phenomenological model.

Resume : Lead based piezoelectric perovskite materials are well known for their excellent piezoelectric properties, which are extensively used in industrial applications. Though, considering the toxicity of lead and its compounds, there is a general awareness for the development of environmental friendly lead-free materials as evidenced from the legislation passed by the European Union in this effect. The different class of materials is now being considered as potentially attractive alternatives to lead zirconate titanate (PZT) based perovskites for various applications, as like actuators, sensors, energy harvesting. Ferroelectric BaTiO3 (BTO) thin films have received much attention for their applications. However, there are few reports on the real ferroelectric properties of BTO films, especially for samples grown on silicon substrate. In this work, 50nm-thick BTO has been deposited on silicon substrate using sputtering method, producing high homogeneous, large scale, thickness precisely controlled thin film. X-ray diffraction and transmission electron microscopy indicate that crystalline BTO is c-axis oriented with a columnar structure. Infra-red absorption characterizations performed on AILES beamline at SOLEIL allowed to study the phase transition thanks to the structural vibration properties between 5K and 385K. Low-temperature orthorhombic-rhombohedral phase transitions characteristic of bulk BaTiO3 are absent in the films.

Resume : The epsilon-polymorph of Fe(III) oxide shows very attractive properties, among them, its giant coercive field (around 2 T at room temperature), magnetoresistance or millimeter wave ferromagnetic resonance [1,2]. For these outstanding properties, epsilon-Fe2O3 nanoparticles are good candidates for the development of applications in fields as electronics as well as a new generation of hard-magnets without rare-earth compounds. We have recently discovered that the epsilon-phase is already present in sol-gel films from 350 ºC and remains stable up to 900 ºC. This is an important advance regarding its growth since the typical temperature range used in the literature for obtaining this elusive phase is comprised from 900 ºC to 1300 ºC. In the present work, we describe this novel recipe assisted by one polyalcohol (glycerol), to grow epsilon-Fe2O3 particles embedded in SiO2 films on Si(100) by an easy one-pot sol-gel method. We are able to modify the particle size as a function of the temperature. We also analyse the evolution of Raman and XAS spectra as a function of the temperature and the results are correlated with the magnetic properties as a function of the particle size. References [1] López-Sánchez, J.; Serrano, A.; Del Campo, A.; Abuín, M.; Rodríguez de la Fuente, O.; Carmona, N. Chem. Mater. 2016, 28, 511–518. [2] MacHala, L.; Tuček, J.; Zbořil, R. Chem. Mater. 2011, 23, 3255–3272.

Resume : Chemical Beam Vapour Deposition relies on thermal decomposition at the substrate surface of organometallic precursors evaporated with line of sight trajectories in high vacuum from a wall set of punctual sources. In comparison to standard CVD or ALD, precursors have to fulfill additional requirements, such as high volatility, high stability in gas phase, high residence time of a reactive species on the substrate and high decomposition probability of this intermediate, without any reactive gas. Consequently, the technique which presents a great potential to deposit in a controlled way multi-element oxides (as already demonstrated for (Nb,Si) doped TiO2, Hf doped LiNbO3, etc…) with possible 3D structuration through shadow masks is limited by the availability of well suited precursors. To enlarge the number of possible complex oxides and to improve the 3D patterning facility, new precursors are evaluated. In this work, Ti(OiPr)3(DMAP)1 is synthesized, studied and shown to be a valuable alternative to the standard Ti(OiPr)4 for Ti containing oxides, exhibiting a higher decomposition temperature and a slightly different activation energy of deposition. It is particularly demonstrated that in a mass transfer limited regime growth regime, contamination free anatase TiO2 films are deposited with a growth rate directly proportional to the precursor flow.

Resume : Metallic oxides are known for their use as electrodes in electronic devices. SrRuO3 (SRO) is a typical conductive ferromagnetic (Tc=160K) perovskite oxide material, which has been extensively studied because it’sintriguing physical properties due to the coupling of charge, spin, and orbital orders. SRO has been used as electrodes for example in magnetic tunnel junctions and resistive switching devices [1-3].Bulk SRO exhibits orthorhombic symmetry at room temperature (space group Pnma) with a pseudo cubic lattice constant a= 3:93 Å. This material presents a good electrical conductivity, high chemical stability and good lattice mismatch with various perovskite oxides which makes it an ideal candidate as bottom electrode (or buffer layer) in epitaxial perovskite heterostructures.The structural and electrical/electronic or magnetic properties of SRO thin films are very sensitive to the lattice strain and thickness effects. For example Shen et al. reported an evolution from a metallic to an insulating behavior as the film thickness decreases from 20 to 4 unit cells [4].A metal-insulator transition was observed below a critical thickness of 4–5u.c. Liu et al. studied the electronic properties of SrRuO3/LaAlO3 superlattices(SLs) by varying the interlayer thicknesses of SRO layers [5].The authors reported that the SLs exhibit a metal-insulator transition when the thickness of SRO layers is reduced implying transformation into a more localized state from its original bulk metallic state. In our work, we present thickness-dependent structural, electronic and magnetic investigations on Nx[(BiFeO3)xuc/(SrRuO3)xuc] SLs. The samples have been grown using pulsed laser deposition on SrTiO3 substrate and studied by x-ray diffraction (Ɵ/2Ɵ, reciprocal space maps and phi scan), transmission electron microscopy (TEM), and electrical/magnetic measurements. We have varied the number of modulation period 10 ≤N≤ 60 and the number of unit cell of each layer 2≤x≤ 18 in order to tune the structural, electronic and magnetic properties in these systems.The SLs exhibit a temperature-driven metal-insulator transition when we reduce the thickness of the layers and the temperature of transition is very sensitive to the thickness of SRO. A critical thickness of SRO for which the SL becomes insulator was determined. [1] Z. Q. Liu et al. Phys. Rev. B 84, 165106 (2011). [2] L. Antognazza, K. Char, T. H. Geballe, L. L. H. King, and A. W. Sleight, Appl. Phys. Lett. 63, 1005 (1993). [3]M. Minohara, I. Ohkubo, H. Kumigashira, and M. Oshima, Appl. Phys. Lett. 90, 132123 (2007). [4] XuanShen, XiangbiaoQiu, Dong Su, Shengqiang Zhou, Aidong Li, and Di Wu, JAP, 117, 015307 (2015). [5] Z. Q. Liu et al. Applied Physics Letters, 101, 223105 (2012).

Resume : In organic-inorganic lamellar hybrid materials, a wide variety of organic chains can be inserted within the host architecture, i.e., between the transition metal ion-based oxide layers [1]. This allows for a fine-tuning of the physical and chemical properties of the resulting system, mainly because of the flexibility and the chemical nature of the organic chains. The use of an external macroscopic quantity, such as pressure, or playing on the organic-inorganic interfacial chemistry (i.e., introducing different organic moieties) is a practical tool to tune the properties of these materials and, ultimately, control their magnetic character. The aim of this work is to present state-of-the-art achievements concerning the applications of first-principles molecular dynamics combined with density functional theory to the field of nanostructured hybrid materials. Herein, we will elucidate the complex interplay between structural properties of such, nanoscale structured, materials and their magnetic character, both at the local (atomic) and bulk level. Spanning through different organic components (such as acetate and fluorene phosphonate), we show how external stimuli (pressure) or different interfacial chemistry can be used to tune the magnetic properties for the case of copper hydroxide-based hybrid materials [2]. [1] G. Rogez, C. Massobrio, P. Rabu, and M Drillon Chem. Soc. Rev. 40 1031, 2011. [2] F. Yang, C. Massobrio, and M. Boero J. Phys. Chem. C 118 18700, 2014.

Resume : Ferroelectric perovskites based on NBT are considered the most promising lead-free candidate materials to substitute Pb(Zr1-xTix)O3 (PZT) in devices designed to respect standards and environmental laws. Nonetheless, to transpose bulk properties to NBT-BT thin films is a major challenge. The goal of this study was to investigate the optical, structural, dielectric and ferroelectric properties of NBT-BT thin films obtained by pulsed laser deposition as a function of composition, from pure NBT across and beyond morphotropic phase boundary (MPB) (x=0, 0.04, 0.06, 0.08). Dielectric and ferroelectric measurements were performed using an impedance analyzer HP 4294A and RT 66A Ferroelectric Test System. XRD, SEM, HR-TEM and AFM techniques have been used for morphologic and structural characterizations of NBT-BT films. Pyroelectric properties were investigated with a Woollam Variable Angle Spectroscopic Ellipsometer (VASE) system under different temperature conditions.This work has been financed by the National Authority for Research and Innovation in the frame of the project PED 2017(PROFILE).

Resume : Thermal detector test vehicles were fabricated from semiconducting YBa2Cu3O6+x (x < 0.5) films in amorphous form (a-YBCO) and characterized. Both planar (a-YBCO film connected to two metal pads) and trilayer (a-YBCO film sandwiched between two metal pads) structures were investigated. Sensing characteristics could be discussed in both the electrically biased bolometric low-pass mode (resistive current probing) and the unbiased pyroelectric high-pass mode (capacitive current probing). The pyroelectric mode appears to be the most promising because: i) operation is performed without DC bias, with very low noise level; ii) capacitive sensing exhibits fast response (microsecond range). At present, very competitive sensitivity has been achieved in the near-IR with noise equivalent power below 10 pW/rootHz at modulation frequencies in the 1 kHz to 100 kHz range. To migrate from IR to far infrared, the main issue to be overcome is a proper knowledge of a-YBCO absorption at THz frequencies. We have undertaken reflection / transmission / absorption spectrometric studies in both continuous wave mode (regular and Fourier transform) and pulsed mode. From the former techniques, the moderate a-YBCO THz absorption was evidenced, suggesting the use of micro-antenna coupling. The time resolved pulsed spectroscopy technique allowed to have access to the THz electrical conductivity, so allowing to optimize the antenna structure for optimal matching with both planar and trilayer structures.

Resume : A new concept that does not require magnetic ordering would extend the current scope of spintronics allowing for example the transmission of electrical signals through paramagnetic insulators (PMI) mediated by some form of magnetic fluctuations [1]. With this in mind we propose the study of ferromagnetic/paramagnetic interfaces in MnGeSb2.2 : (Fe, Co) / PMI and Co2MnSi/PMI. The PMI is Dy-doped P2O5-Al2O3-BaO-Li2O glass, MnGeSb2.2 : (Fe, Co) is a diluted magnetic semiconductor (DMS) and Co2MnSi ia a Heusler alloy (HA) with demonstrated spin polarization. The structures were fabricated by pulsed laser deposition (PLD) using in-house prepared targets whose properties have been previously determined showing Curie points above 600K for both DMS and HA. The good compositional uniformity of the films, their morphology and reduced surface roughness were checked by EDX-mapping, SEM and AFM. The bonding features at the interfaces were studied by micro-Raman spectroscopy. Impedance measurements at room temperature were performed to understand the electrical properties. The optical conductivity was derived from spectroscopic ellipsometry investigations showing intraband transitions. Attempts have been made to measure T2 using a variation of the simple method published by Johnson and Silsbee [2]. Acknowledgements: PN-5N 2016 Romania & M-ERANET 35 2016 [1] Satoshi Okamoto, PhysRev B 93, 064421 (2016) [2] Mark Johnson and R. H. Silsbee http://dx.doi.org/10.1063/1.340611

Resume : Hybrid energy harvesters have been drawing increasing interest in recent years. Harvesters scavenging solar and mechanical energy have been demonstrated, however the structures remain complicated. Here, a simple structure based on a p-n junction-based ZnO nanorod piezoelectric energy harvester was designed. This was adapted to either form a ZnO nanorod-based dye-sensitised solar cell (DSSC), or ZnO nanorod - perovskite solar cell (PSC). The two photovoltaic systems required different adaptations, with long nanorods, CuSCN and traditional water-based PEDOT:PSS being used in the DSSC and short nanorods and a non-aqueous PEDOT:PSS used in the PSC. To allow high processing temperatures while maintaining mechanical flexibility, ‘Corning Willow glass’ was used as a substrate, which can be annealed up to 800 °C, and was compared to the more common PET/ITO. This resulted in lower internal resistance as shown by impedance analysis, and a related increase in efficiency. Mechanical and solar testing indicated that the devices operated both as mechanical and solar energy harvesters separately, with the current generated by the photovoltaic around two times greater than from mechanical excitation. In addition, by simultaneously stimulating with simulated sunlight and mechanical bending a combined output from the solar cell and piezoelectric was observed, indicating the device could also perform as a hybrid nanogenerator and photovoltaic simultaneously with enhanced output.

Resume : Ferroelectric materials are receiving a renewed attention owing to their great application potential in non-volatile memories, optoelectronics, energy harvesting[1], photocatalysis[2], etc. For optoelectronic applications it is important to know how the ferroelectric properties are modified by the effect of light. In particular, it has been reported that the remnant polarization can be largely reduced by the application of light in the range of the UV, see f.i. ref. [3,4]. To elucidate the key factor that dominates the light-induced screening in BaTiO3 thin films and to be able to modify it, a series of BaTiO3 thin films were grown using the same growth parameters but on different substrates imposing different epitaxial strain and with different thicknesses. Dramatic variation of the reduction of polarization by light (at 405 nm) has been observed among the studied films. X-ray photoelectron spectroscopy (XPS) shows a clear correlation between the content of OH- and H2O on the surface of the films and light-induced polarization reduction and both effects appear to be related to the strain state of the films. Trying to disclose the effect of H2O on the surface states different room-temperature treatments with continuous flux of water steam have been performed. The results show that chemically adsorbed OH- largely enhances the light-induced polarization reduction. These results illustrate a simple and convenient way of tuning surface states in ferroelectrics and this may be important for applications. Reference [1] K. T. Butler et al., Energ. Environ. Sci. 8, 838 (2015). [2] X. Bai et al., J. Phys. Chem. C 120, 3595 (2016). [3] D. Dimos et al., J. Appl. Phys. 76, 4305 (1994). [4] F. Liu et al., Adv. Electron. Mater. 1, 1500171 (2015).

Resume : Utilization of thin film oxides for Solid Oxide Fuel Cells (SOFC) applications is among the modern solution considered for decreasing the operation temperature of such systems. Heterostructures based on La0.5Sr0.5Co0.8Fe0.2O3-δ (LSCF)/ Yttria stabilized zirconia (8%-YSZ) thin films were grown by Pulsed Laser Deposition onto NiO/ Ce0.85-xPr0.10Er0.05SrxO2 (x= 0.02 and 0.05) anodes in order to obtain typical SOFC systems. An ArF laser working in oxygen atmosphere (8 x 10-2 mbar) at a fluence of 3 J/cm2 and 30Hz repetition rate was used. High number of pulses (160000 -400000) were used in order to obtain thicknesses above 500 nm for each layer. The obtained thin film heterostructures were investigated as regarding morphology and structure, evidencing a crystalline and columnar growth. The surface chemistry was studied by X-ray photoelectron spectroscopy. Thus, Ni2p, Ce3d, Er4d and Sr2p prominent XPS transitions display typically 2 , 4 and 3 valence states, respectively. A close inspection of Pr3d photoelectron spectra highlighted the presence of the mixture Pr3 /4 valence states. Electrochemical impedance spectroscopy and E-I measurements were performed at 700°C, 750°C and 800°C on single cell fueled with H2/Ar mixture on anode side and with synthetic air on cathode side. A decrease in cell electrochemical performance with time was evidenced.

Resume : Energy harvesting is the process of capturing and converting ambient waste energy into useable electricity. Energy harvesters not only solve the concerns related to energy crises, but also endeavour a step towards wireless communication. Energy can be harnessed sufficiently using a variety of ambient sources like solar, mechanical etc. for the development of self powered devices. The mechanical and electromagnetic (EM) energies have been considered in the present work as they are independent of climatic conditions. For scavenging EM energy, magnetoelectric (ME) system is the promising one where magnetic energy can be easily converted into electrical energy. For realization of such system, Lead Zirconium Titanate (PZT) has been chosen as the most suitable candidate having high piezoelectric coefficient which is integrated with the magnetostrictive nickel. The same ME system can be utilized for harvesting mechanical energy through cantilevers and hence multifunctional energy harvester has been developed. For the fabrication of multifunctional energy harvester, functional layer of PZT was deposited on Ni cantilever using Pulsed Laser Deposition under the optimized parameters. The cantilever studies were performed for PZT/Ni bimorph thin film system as a function of acceleration. A high output power across the load was obtained which increases efficiently in presence of magnetic field due to the combination of piezoelectric and ME effect.

Resume : Lead-based ceramics are the most efficient piezoelectric in electronic devices. A well-known compound is lead zirconate titanate (PZT). An important issue which concerns manufacturing is the toxicity of Pb element for the environment and human health. Therefore, worldwide researchers do efforts to develop new environment-friendly materials with high-performance as piezoelectric transducer. Usually, single-crystals present enhanced properties than their respective ceramics. Among the most promising lead-free materials, sodium potassium niobate (KNN) is considered a potential candidate to replace the PZT compounds because of its good piezoelectric and ferroelectric properties. A systematic investigation to find the appropriate composition combining the properties and application must be carried out. Micro-pulling-down technique (µ-PD) rises as a useful tool to grow single crystals in a short period of time by using a reduced amount of raw materials. We pulled undoped, Cu-doped and Li-doped KNN crystal fibers with compositions near the morphotropic phase boundary. Experimental parameters as crucible features, nozzle geometry, initial stoichiometry, temperature gradient close to solid-liquid interface and pulling rate played an import role in the crystal quality. Despite the challenges, the electrical properties of the samples were investigated. Our results demonstrated that the µ-PD method is suitable for growing KNN crystals for technological applications.

Resume : Thin films on SrTiO_3 substrates and substrate-free networks of superconducting Bi_2Sr_2CaCu_2O_8 (Bi-2212) were fabricated using sol-gel processing and the electrospinning technique. All samples were thoroughly characterized by SEM, TEM and EBSD. The resulting nanowire networks are formed of individual nanowires with a diameter of the order of 150-200 nm and lengths up to the micrometer range. This non-woven, fabric-like network shows a porosity of 0.9928, and contains numerous interconnects enabling a current flow between the individual nanowires. The nanowires are polycrystalline, consisting of elongated grains with dimensions of ~ 80 × 40 × 40 nm3 (SEM). For comparison of the microstructures, we fabricated thin films on SrTiO_3 substrates employing the same precursors and the same preparation temperatures. The resulting thin films are polycrystalline and exhibit a coarse-grained structure with much larger grains in the 100 µm-range. Magnetization data [M(T) and M(H)] were recorded by SQUID magnetometry, and magneto-transport measurements [R(T,B) and I/V-characteristics] were performed in an Oxford Instruments Teslatron system in fields up to 10 T. Due to the high number of interconnects between the nanowires, the nanowire networks may carry a current of 10^5 A/cm2 at T = 5 K, which is comparable to that of the thin films.

Resume : This presentation gives a short review on what can be learned about interfaces of functional oxides using X-ray photoelectron spectroscopy (XPS). XPS is sensitive to the chemical composition but also to the electronic structure of a material. The latter enables the determination of energy band alignment, which is closely related to materials properties such as the electrical conductivity. The talk covers results on conducting but also on electrically insulating oxides. Specific experi¬mental conditions to study insulating oxides using nanometer scale thin films or top electric contacts are outlined. As an example it is shown how the influence of dopants and substrates on the Fermi level positions in CeO2 can be determined. The Fermi energy is closely related to defect concen-trations, which can be responsible for material destabilization and a modification of energy band alignment. Measuring and understanding the Fermi level position is a key to unravel these relationships.

Resume : Nanostructured transparent conducting oxide (TCO) layers gain increasing importance as high surface area electrodes enabling incorporation of functional redox species with high loading. We will present different strategies towards the facile fabrication of TCO electrodes with different types of porous structures and pore dimensions based on the assembly of dispersible TCO nanoparticles [1-3]. The crystallinity of the nanoparticles serving as building blocks enables the formation of fully crystalline porous transparent scaffolds with high electric conductivity. The nanostructure can be controlled using suitable templates such as amphiphilic polymers or latex beads, giving access to a broad range of TCO electrodes with pore sizes between 3 nm and 300 nm. While commercial templates like Pluronic polymer or latex beads result in predetermined pore sizes, we could show that the novel amphiphilic PEO-b-PHA polymer enables the fabrication of remarkably tunable TCO morphologies with nominal pore sizes from 10 nm mesopores to 80 nm macropores. The combination of porous architecture with a large conducting interface makes the obtained layers versatile current collectors with adjustable performance. [1] K. Peters et al. Adv. Funct. Mater. 2016, 26, 6682. [2] K. Peters et al. Chem. Mater. 2015, 27, 1090. [3] Y. Liu et al. Electrochim. Acta 2014, 140, 108.

Resume : Hydrogen doped Indium Oxide (In2O3:H) is a promising material for a wide field of applications due to its low optical absorption and high electron mobility of up to 130 cm2/Vs. The introduction of water vapor during an RF sputtering process causes an amorphous growth of the In2O3:H film [1]. During a post deposition thermal treatment, usually done in vacuum, the film crystallizes leading to the good optical properties and resistivity as low as 250 µOhm*cm. Despite the great potential, the films are still only produced on a laboratory scale. In this work we investigated an inline DC sputtering process with a deposition area of 60x30 cm2. We show that this process in combination with a post thermal treatment in atmospheric air can also yield high mobility In2O3:H films. Critical factors are the water and oxygen partial pressure during the sputter process as well as annealing temperature and duration. Due to diffusion processes during the crystallization in air the carrier density is lower than in films annealed in vacuum. We introduce a bi-layered In2O3:H stack to avoid the diffusion induced lower carrier density while keeping the mobility high and thus lowering the resistivity of the films from about 400 µOhm*cm to 300 µOhm*cm. [1] T. Koida, H. Fujiwara und M. Kondo, „Hydrogen-doped In2O3 as High-mobility Transparent Conductive Oxide“, Japanese Journal of Applied Physics Vol. 46 No. 28, pp. 685-687, 2007

Resume : Zinc oxide (ZnO) is an often employed semiconductor with wide prospects in optoelectronic, catalysis and lasing applications [1]. Also, ZnO has attracted considerable interest in fundamental studies considering magnetism and regarding the instability of polar {0001} surfaces. According to the classification of Tasker ZnO{0001} corresponds to the type III ionic surfaces which are inherently unstable owing to the divergence of the electrostatic potential [2]. Possible stabilization mechanisms have been discussed based on theoretical and experimental studies involving complex structural rearrangements, charge transfer, and adsorption of foreign species (see e.g. Ref.[3]). We have carried out a combined experimental (surface x-ray diffraction) and theoretical study which provides evidence that in the film thickness regime of a few ZnO layers, where the h-BN structure is expected to be stable [4], the ZnO film adopts the bulklike WZ-type structure rather than the h-BN-type structure [5]. This is a consequence of the anisotropic charge redistribution within the ZnO film induced by the presence of interface oxygen. Although the WZ structure is polar, its metallic surface renders its stability. Its formation is related to oxygen impurities in Fe(110) hollow sites inducing an anisotropic charge redistribution within the film. Our results provide a deeper understanding of depolarization mechanisms in ultrathin polar films at the atomic scale. [1] M. Bäumer and H.-J. Freund, Prog. Surf. Sci. 61, 127 (1999). [2] P. W. Tasker, J. Phys. C 12, 4977 (1979). [3] J. Goniakowski, F. Finocchi, and C. Noguera, Rep. Prog. Phys. 71, 016501 (2008) [4] C. Tusche, H. L. Meyerheim, and J. Kirschner, Phys. Rev. Lett. 99, 026102 (2007). [5] H. L. Meyerheim, A. Ernst, K. Mohseni, et al., Phys. Rev. B 90, 085423 (2014)

Resume : Making transparent and conductive interconnects on surfaces is a must for a large number of applications including solar cells, low-emissivity, architectural and automotive windows, liquid crystal displays and light emitting diodes. Due to high cost of indium tin oxide an extensive research is ongoing to develop transparent conductive oxides based on abundant materials. This work presents low resistivity aluminum doped zinc oxide (AZO) films deposited by RF magnetron sputtering (2 inch target, 2% Al, Kurt Lesker) without additional substrate heating except for plasma exposure. The films are deposited in a vacuum chamber that can accommodate 8 soda lime glass samples (1x5 cm) on a rotating stage. Discharge pressure, target to substrate distance and RF power have been investigated as discharge parameters with the aim of obtaining a resistivity below 5x10-4 ohms cm over the whole length of the sample. The resistivity, transmittance and film thickness were measured with a spatial resolution of 1 mm. XPS, XRD, TOF-SIMS and SEM were used for surface characterization. Besides the well-known non uniformity correlated with the erosion tracks on the target surface (attributed to film growth assisted by energetic negative ions or oxygen inhomogeneity), uniform resistivity and transmittance values were also obtained for certain discharge parameters. Spatial profiles of plasma density have been measured by electrical probes while optical emission spectroscopy was used to investigate some of the main species relevant to film properties. The authors acknowledge financial support under the SmartCoating project (6151-00011B) financed by the Innovation Fund Denmark.

Resume : We have previously demonstrated that reduction of screening of the polarisation is important to increase power output from ZnO nanorod-based piezoelectric energy harvesters, including through surface passivation and use of non-ohmic top contacts. However, the influence of the ZnO seed layer (commonly deposited by sputtering) on device performance has not previously been considered. Here we investigate the effect of the composition of this seed layer and the addition of insulating interlayers on the performance of the devices. A ~100 nm film of ZnO was sputtered from either a ceramic ZnO source in Ar, or a Zn source using reactive sputtering in Ar+O2. The ceramic source produced an O-poor ZnO film, which led to high conductivity due to intrinsic doping. This produced very low peak voltage output of 20-50 mV, and power output less than 1 uW on a load. Reactive sputtering produced films with low conductivity and significantly enhanced nanogenerator performance of 400-500 mV with 10-20 uW on a load. We relate this behaviour to the change in impedance properties, and reduction in screening from the ZnO seed layer. Furthermore, we investigated the addition of a thin Al2O3 interlayer between the contact and ZnO seed layer. This led to further enhanced peak voltage output of 0.9-1 V, with a power of 50 uW on a load. This demonstrates the importance of considering the interface between ZnO nanorods and the substrate when attempting to enhance power output from such devices.

Resume : InGaAs is one of the III-V active materials of modern high-electron-mobility transistors or high-speed electronics. The Fermi level pinning at the Metal/Semiconductor (InGaAs) junction is an issue that can be solved by inserting an ultra thin (1 nm) tunneling insulator layer (such as ZnO) in between the metal and semiconductor, in fine leading to a decrease of contact resistivity. We have studied the incipient Atomic Layer Deposition (ALD) of ultra-thin ZnO layers on In0.53Ga0.47As substrates by in situ synchrotron X-ray characterization. We will report on a) total X-ray fluorescence (TXRF) measurements performed at 20keV during ZnO ALD at different deposition temperatures and as a function of the incident angle b) in-plane reciprocal space maps as a function of the ZnO layer thickness. We will point out to the existence of an amorphous to crystalline transition when the ZnO layer thickness is increased. The Zn fluorescence yield measured upon the number of cycles during ZnO ALD clearly show that a substrate-inhibited ZnO growth of type II takes place on InGaAs terraces. The corresponding growth per cycle (GPC) curves demonstrate islands growth at the early stage. X-ray absorption spectra (XAFS) show ZnO wurtzite above 25 cycles, whereas X-ray Diffraction reveals an amorphous ZnO layer. All the synchrotron experiments were carried out at ESRF (ID3) and SOLEIL (SIRIUS) with a custom built ALD reactor. R. Boichot et al., J. Chem. Mater. (2016) 28, 592 M.H. Chu at al., Cryst. Growth Des. (2016) 16 (9), 5339

Resume : Nanolaminates are a promising method of improving upon the optoelectronic properties of Transparent Conducting Oxide (TCO) structures. The invariability of the refractive index of TCO materials leads to reflection losses at the surface and internal interfaces of transparent devices such as solar cells or displays. The development of a transparent material or structure of tuneable refractive index would allow for the integration of anti-reflective coatings which would reduce such losses significantly, thus improving device efficiency. Previous attempts to modify the refractive index have been marred by the degradation of the electrical or optical properties of the tuned material. We demonstrate the use of a TCO/dielectric nanolaminate structures, with individual layer thicknesses far below the wavelength of visible range light, to achieve a superstructure of altered refractive index, while maintaining high values of transparency, conductivity and mobility. We demonstrate the efficacy of these nanolaminate structures on both amorphous InGaZnO4 and ZnO:Al via SiO2 and TiO2 based nanolaminates. The refractive indices of the a-InGaZnO4 nanolaminates were successfully tuned over a range of Δn≈0.6 (1.8 [SiO2] to 2.4 [TiO2]) while maintaining the high quality of the electrical properties. We also illustrate how the electrical conductivity and mobility of such superstructures can be optimised by careful selection of materials to minimise band offsets.

Resume : This work focuses on ZnO and Yb doped ZnO thin films elaborated on Si substrates by magnetron sputtering. ZnO is a well-known transparent conducting oxide with a wide bandgap (3.34eV), while Yb is a rare earth characterized by a light emission at 980 nm. This latter is linked to the radiative de-excitation of an electron between the 2F5/2 and 2F7/2 electronic levels. Many works have already been realized on ZnO:Yb films but only a few of them report results on the thermal behavior of this material. This study deals with the structural and photoluminescence evolution of thin films annealed with different temperatures from 873K to 1173K for 1h under N2. For temperatures higher than 973K, the dopant segregation towards the film-substrate interface as well as the Si diffusion towards the bottom of the film is observed, resulting in the emergence of an amorphous phase. Measurements by X-ray diffraction show that annealing is effective to improve the structural properties of the upper part of the film with the formation of nanoscale ZnO grains close to the ZnO bulk structure. Moreover, photoluminescence measurements show the activation of the rare earth by optical excitation from a 325 nm source. The emission intensity behavior with temperature is discussed. At last, electrical measurements at room temperature have been carried out indicating an improvement of the conductivity with temperature. The obtained values suggest that electroluminescence applications are achievable.