Advanced oxide materials – growth, characterization and applications

Resume : TiO2 nanomaterials have over the last 30 years attracted tremendous scientific and technological interest. Main research direction using TiO2 in functional applications are s the use in photocatalysis e.g. for the direct splitting of water into H2 and O2 to generate the potential fuel of the future, hydrogen; the use in Grätzel type solar cells and in biomedical applications. Over the past decades various 1D and highly defined TiO2 morphologies were explored for the replacement of nanoparticle networks and were found in many cases far superior to nanoparticles or their assemblies. Nanotubes or wires can be grown by hydrothermal or template methods, or even more elegantly, by self-organizing anodic oxidation. The latter is not limited to TiO2 but to a full range of other functional oxide structures on various metals and alloys can be formed. These advanced and doped morphologies can be grown on conductive substrates as ordered layers and therefore can be directly used as functional electrodes (e.g. photo-anodes). The presentation will focus on these highly ordered nanotube arrays of TiO2 and discuss most recent progress in synthesis, modification and applications towards energy conversion. Literature: (reviews): 1. P. Roy, S. Berger, P. Schmuki, Angew. Chem. Int. Ed. (2011), 2904 2. K. Lee, A. Mazare, P. Schmuki, CHEMICAL REVIEWS, 114 (2014) 9385

Resume : Achieving an accurate control over the formation and manipulation of cationic and anionic defects in transition-metal oxides is a novel route to discover new functional properties. In SrTiO3 (STO), the presence of oxygen vacancies, VO, plays a very important role in the transport properties of thin films and interfaces, such as the well-studied STO/LaAlO3 [1]. Due to the donor character of VO and the large electron mobilities, even the slightest concentration of VO produces a measurable electrical conductivity. On the other hand, strontium vacancies, VSr, also play a crucial role in the structural properties of the STO thin films, influencing in the rotation pattern of the TiO6 octahedra to accommodate the epitaxial strain. We present a thermodynamic study of VO formation in e-doped STO thin films grown by Pulsed Laser Deposition. Hall effect measurements confirmed that each VO is doubly ionized and donates two electrons to the conduction band of STO. Furthermore, our results demonstrate that both, compressive and tensile strain, leads to a decrease in the VO formation enthalpy. We also determined the existence of different rotation pattern of the TiO6 octahedra of the thin films under compressive or tensile strain, which is related with the unintentional presence of the VSr in the STO thin films [2]. Additionally, we show the possibility to manipulate the VO by applying an external electric field with an Atomic Force Microscopy tip. We demonstrate a reversible change in the local surface potential of the sample associated to the accumulation/depletion of VO, and determine the strain-dependence of the oxygen diffusion coefficient in STO. [1] A. F. Santander-Syro et Al, Nature, 469(2011) 189. [2] L. Iglesias et Al, Phys. Rev. B 95(2017) 165138.

Resume : LaNiO3 is a so-called "bad metal", a conductive perovskite metal-oxide. Such materials have resistivity higher than that of conventional metals, but low enough to be studied as electrode materials.1 The mechanism responsible for the conductive properties is not fully understood, but it is thought that maintaining 3+ Ni valence in the films is key in attaining metallic-like conductivity.2 For optimum results a stoichiometric, single-crystal film is desired. This talk will describe a method to grow epitaxial LaNiO3 by atomic layer deposition (ALD), with resistivity values comparable to those produced using other deposition techniques. LaNiO3 films were prepared on SrTiO3 substrates using La(thd)3, Ni(thd)2, and O3 as precursors. Epitaxial film formation was found to be strongly thickness dependent, necessitating a two-stage deposition process. First, a seed layer (~5 nm) was grown before a 750 °C air annealing step. Further deposition (up to ~30 nm in this study) could then be performed on top of the seed layer, with additional post-deposition annealing required to produce crystalline films. The films from the two-stage process were analyzed with TOF-ERDA, STEM and HRXRD and were found to be stoichiometric, epitaxial LaNiO3 in pseudocubic crystal structure as has been produced with techniques like MBE and PLD previously. The average resistivity was found to be uniform across the film and in the order of 300±50 micro-Ohm.cm, which compares well with literature values of films deposited with PLD,3 as well as being an order of magnitude improvement on polycrystalline LaNiO3 grown by ALD. 1 Jaramillo, R., et al. Nat. Phys. 10, 304 (2014). 2 Qiao, L. & Bi, X. EPL 93, 57002 (2011). 3 Tsubouchi, K. et al. Appl. Phys. Lett. 92, 262109 (2008).

Resume : Perovskite oxides with general formula ABO3, thanks to the remarkable flexibility of their crystal structure that can host a variety of cations, present a wide range of remarkable physical properties (ferroelectricity, piezoelectricity, thermoelectricity?) that can be tailored by controlling the material structure and composition. In this context, molecular beam epitaxy appears as an unrivalled technic to design complex perovskite heterostructures and engineer their functionalities, since it provides many advantages: control of the growth down to the half-monolayer scale, flexibility for the control of the oxide composition, and control of heterogeneous interfaces that in particular allows for integrating oxide thin layers on silicon. In this communication, two recent results will be presented. We will first show that LaxSr1-xTiO3 (LSTO) epitaxial films with controlled electric/thermoelectric properties are very good candidates for on-chip thermal energy management. We have in particular explored the impact of La-doping effect on the thermoelectric and electric properties of high-quality LSTO films with low mosaicity (< 0.1°), and shown that electrical conductivity can exceed 104 S.cm-1 and thermoelectric figure of merit (ZT) can reach 0.1 at room temperature. We will then show how super-structuration of perovskite oxides in Ruddlesden Popper (RP) phases (An+1BnO3n+1) based on STO (Srn+1TinO3n+1) and BTO (Ban+1TinO3n+1) can be controlled to tune the oxide functional properties. We will also discuss the stability of the artificial phases regarding growth conditions and epitaxial strain.

Resume : The properties of crystalline oxide thin films can depend largely on the lattice strain. Today, strain engineering by selecting a particular substrate is the main methodology to improve ferroelectric and other properties of epitaxial oxides. However the magnitude of the strain and the thickness of the film are limited due to plastic relaxation, and for most of the applications the oxides have to be integrated with silicon. We present here a different methodology. Instead of varying the epitaxial strain by changing the substrate, we control the residual strain present in epitaxial oxides on a given substrate. We show that the lattice strain of ferroelectric BaTiO3 thin films grown by pulsed laser deposition can be adjusted by a suitable balance of thermodynamics/kinetics in the growth simply by selecting properly the deposition parameters. For example, in the temperature window for epitaxial growth, the polar c-axis of BaTiO3 films thicker than 100 nm can be strained ad hoc up to more than 2%, being the ferroelectric polarization proportional to the strain. This is achieved in epitaxial BaTiO3 films integrated with Si(001), and high ferroelectric polarization and low leakage are obtained at deposition temperatures as low as around 450 °C. The new strategy has permitted an unprecedented level of control in the growth of ferroelectric BaTiO3 films on Si(001), and we also show that the strategy developed can be used with other substrates, like single-crystalline perovskites.

Resume : Piezoelectronic Transistors provide a potential CMOS replacement, but necessitate finely patterned, thin piezoelectric films with excellent piezoelectric response. This paper will discuss growth and characterization of both epitaxial and highly {001}-oriented lead magnesium niobate ? lead titanate (PMN-PT) thin films for this application. It was found that both film types exhibited similar, thickness-independent high-field ?r of ~300 with highly crystalline electrode/dielectric interfaces. Irreversible domain wall motion is the major contributor to the overall dielectric response and its thickness dependence. In clamped epitaxial films the irreversible Rayleigh coefficients reduced 85% upon decreasing thickness from 350 to 100 nm. The effective interfacial layers are found to contribute to the measured thickness dependence in d33,f measured by X-ray diffraction. High field piezoelectric characterization revealed a field-induced rhombohedral to tetragonal phase transition in epitaxial films. Using optical and electron beam lithography combined with reactive ion etching, the PMN-PT films were systematically patterned down to lateral feature sizes of 200 nm in spatial scale with nearly vertical sidewalls. Upon lateral scaling, there was an increase in both small and large signal dielectric properties, including a doubling of the relative permittivity in structures with width-to-thickness aspect ratios of 0.7. The longitudinal piezoelectric coefficient, d33,f, was interrogated as a function of position across the patterned structures by finite element modeling, piezoresponse force microscopy, and nanoprobe synchrotron X-ray diffraction. It was found that d33,f increased from the clamped value of 40-50 pm/V to ~160 pm/V at the free sidewall under 200 kV/cm excitation. The sidewalls partially declamped the piezoelectric response 500-600 nm into the patterned structure, raising the piezoelectric response at the center of features with lateral dimensions less than 1 ?m (3:1 width to thickness aspect ratio). The normalized data from all three characterization techniques are in excellent agreement.

Resume : In 1971 Chua predicted existence of fourth passive electric element characterized by physical quantity called memrsitance. The memristance changes in function of a current flowing through memristor. If such the change does not exist the memristance is equal to the resistance. Strukov and colleagues were first who realized that the systems there have been investigating for years in fact were related to Chua?s idea of the memristor/memristance and show resistive switching behavior (RS). Particularly, TiO2 is considered as prototypical memristive material in which resistive switching phenomena allow for nonvolatile information storage [1,2]. In 2008 it was shown that the RS can be also observed in graphene a novel two dimensional carbon material with extraordinary electrical mobility combined with high optical transparency in visible light spectrum. Soon afterwards the RS was discovered in the graphene oxide (GO) films. Unfortunately, RS mechanism in GO is still under debate. In the presentation we will focus on models describing RS phenomena observed in TiO2 [3,4] and propose possible mechanism for RS in GO [5,6]. The experimental data obtained in nanometer scale by STM/STS and AFM/LC-AFM together with XPS/UPS results will be outlined and discussed. Finally we show possible application of GO in transparent and flexible electronics. This work is supported by the National Centre for Research and Development Poland under the project POIR.04.01.02-00-0046/16 and by the National Science Centre Poland under the project 2016/21/D/ST3/00955. [1] K. Szot, et al. Nanotechnology, 22, 254001 (2011) [2] M. Rogala, et al. Adv. Funct. Mater. 25, 6382 (2015) [3] M. Rogala, et al. Appl. Phys. Lett. 106 263104 (2015) [4] M. Rogala et al. Carbon 103, 235 (2016)

Resume : Atomic layer deposition (ALD) is a common growth method for ultrathin and dense metal oxide layers which are integrated into resistive random access memory (ReRAM) cells, as it unifies several benefits such as perfect thickness control, conformal 3D-growth and a high reproducibility of the grown layers. A major challenge remains the adjustment and control of the proper defect density of the metal oxide layers that are involved in the switching process. Especially for the realization of a moderate electroforming voltage at acceptable ON-state leakage currents of the switching devices, bilayer structures are advantageous. In this study, plasma-ALD grown HfO2 is combined with different ?qualities? of TiOx. The later ones are achieved by variation of the oxygen source, either oxygen plasma or water vapor, which were shown to affect the phase formation of the TiOx layer. The impurity contents of the films are in the 1 at% regime and thus the phase formation is addressed to growth kinetics rather than to significant differences in the impurity contents of the films. Integrated into ReRAM cells, differences of plasma-HfO2/plasma-TiO2 and plasma-HfO2/thermal-TiOx based devices with respect to electroforming voltage and resistive switching behavior will be discussed in comparison to the films? structure and chemistry.

Resume : Attention of research community in the recent years focuses more and more on oxide thin film structures with new functionalities. One of the emerging direction of research is looking for the advanced materials that could be used for manufacturing of transparent electronics devices equivalent to conventional ones, such as: transparent resistors, diodes, transistors, capacitors, and so forth. One of interesting feature that is observed in some selected oxide-based layered structures is occurrence of memory and resistive switching effects. That would open new possibilities for manufacturing of transparent memory devices. Present work consists of discussion on structure and electrical properties of multicomponent transparent oxide semiconducting thin films based on mixture of titanium-copper or titanium-cobalt oxides. The thin film structures were prepared using multitarget magnetron sputtering setup that was created by the Authors according to their own concept and allows on deposition of thin films with gradient element distribution. In the work, the results obtained for the structures with different shape of Cu or Co gradient distribution has been presented and a possible mechanism for resistive switching has been discussed.

Resume : The focus of this talk will be electron correlated mixed valence ternary vanadium oxides where closely linked lattice, orbital, and spin degrees of freedom give rise to pronounced structural and electronic instabilities. The binary vanadium oxides VO2 and V2O3 have long been canonical examples of compounds showing pronounced electronic instabilities underpinned by the interplay of electron?phonon coupling and strong electron correlation. In recent work, we have explored the intriguing electronic phase diagrams of low-dimensional ternary vanadium oxides with the formula MxV2O5 where M is an intercalating cation and x is its stoichiometry. Several of these compounds show colossal metal?insulator transitions and charge ordering phenomena. The talk will focus on mechanistic understanding of these transitions based on DFT+U calculations of electronic structure and synchrotron X-ray absorption/emission spectroscopy and imaging studies. The insulating phases of these compounds are characterized by the stabilization of small polarons, which give rise to ?mid-gap? states that reside intermediate in energy between the valence and conduction bands. The stabilization of polarons and their eventual melting to form a delocalized metallic phase has interesting implications for the design of cathode materials for intercalation batteries as well as for realizing Mott field-effect transistors. The discovery of a novel topochemical intercalation route has provided access to a wide variety of MxV2O5 phases, thereby enabling tuning of correlation strengths and allowing for the partial decoupling of the lattice and electronic facets of the transitions. Finally, dimensional reduction of layered MxV2O5 phases via ion exchange and exfoliation to few-layered nanosheets further allows for modulation of the correlation strengths and the bandgaps of these compounds as a result of the loss of 3D structural coherence. References 1) Justin L Andrews, Luis R De Jesus, Thomas M Tolhurst, Peter M Marley, Alexander Moewes, Sarbajit Banerjee, Intercalation-induced Exfoliation and Thickness-modulated Electronic Structure of a Layered Ternary Vanadium Oxide. Chemistry of Materials 2017, DOI: 10.1021/acs.chemmater.7b00597. 2) Luis R De Jesus, Gregory A Horrocks, Yufeng Liang, Abhishek Parija, Cherno Jaye, Linda Wangoh, Jian Wang, Daniel A Fischer, Louis FJ Piper, David Prendergast, Sarbajit Banerjee, Mapping Polaronic States and Lithiation Gradients in Individual V2O5 Nanowires Nature Communications 2016, 7, 12022. 3) Peter M. Marley, Gregory A. Horrocks, Kate E. Pelcher, and Sarbajit Banerjee, Transformers: The Changing Phases of Low-Dimensional Vanadium Oxide Bronzes, Chemical Communications 2015, 51, 5181-5198. 4) Peter M. Marley, Tesfaye A. Abtew, Katie E. Farley, Gregory A. Horrocks, Robert V. Dennis, Peihong Zhang, and Sarbajit Banerjee, Emptying and Filling a Tunnel Bronze, Chemical Science 2015, 6, 1712-1718. 5) Peter Marley, Adam A. Stabile, Chun Pui Kwan, Sujay Singh, G. Sambandamurthy, and Sarbajit Banerjee,* Charge Disproportionation, Charge Ordering, and Voltage-Induced Metal-Insulator Transitions Evidenced in ?-PbxV2O5 Nanowires, Advanced Functional Materials 2013, 23, 153-160.

Resume : Most current electronic and electrochemical devices are stacks of thin films and interfaces operating under electrical stress. Nanometre-thick oxide films play crucial role in performance of these devices. Injection of excess electrons and holes into oxide films and the nature of electron trapping sites are important for our understanding of the mechanisms that govern the formation of conductive filaments in resistance switching memory devices, the dielectric breakdown in microelectronic devices, and the performance of photo-electrochemical and oxide fuel cells. Our theoretical modelling combined with experimental observations demonstrates that structural disorder in amorphous SiO2, Al2O3 and HfO2 films creates precursor sites which can spontaneously trap up to two electrons or holes in deep states in the band gap. This results in weakening of Me?O bonds, which can be broken upon thermal activation, creating an O2- interstitial ion and a neutral O vacancy. O2- interstitial ions can easily diffuse through the oxide and in devices are guided to the positive electrode by the electric field. Thus electron injection can lead to the formation of new defects and significantly alter the structure of oxide films at large injection densities. The creation and field-driven movement of oxygen ions causes changes in oxide structure on a much larger scale than previously thought.I will discuss the implications of this effect for the mechanisms of electrical breakdown and resistance switching in electronic and memory devices.

Resume : TiO2 is considered as prototypical memristive material in which resistive switching phenomena allow for nonvolatile information storage [1]. Among the transition metal oxides crystalline rutile has been identified as one of the most suitable for device development and also for describing the nanoscale mechanism behind memristive switching. It is now well established that resistive switching in TiO2 crystals is not a material property by itself but is a highly localized phenomenon in the bulk material related to reduction processes and nanofilamentary structures. We describe an approach which allows for the generation of quasi-homogenous switchable regions near the surface which can be used for high density data storage by resistive switching processes. The thermal preparation method that we propose leads to the modification of extended defects in the crystal and creation of ?new? nanofilamentary structures of high density near the surface allowing for preferential and fully controllable bipolar switching. Based on experimental investigations and simulations we deeply analyze the nature of such crystal structure transformation and the mechanism responsible for the observed resistive switching processes [2]. This work is supported by the National Science Centre, Poland (project 2016/21/D/ST3/00955) and by the German Science Foundation DFG (SFB 917 ?Nanoswitches?). [1] K. Szot, et al. Nanotechnology, 22, 254001 (2011) [2] M. Rogala, et al. Adv. Funct. Mater., 25, 6382 (2015)

Resume : Oxygen defects can have a profound effect on the physical properties of transition metal oxides. Electric-?eld driven migration of oxygen vacancies provides a viable mechanism for the formation, rupture and reconstruction of conducting ?laments in insulating oxides, an effect that is used in nanoscale resistive switching devices [1,2]. In complex oxides, oxygen vacancies can radically alter a plurality of intrinsic properties via valance changes and structural phase transitions [3]. The ability to reversibly control the concentration and pro?le of oxygen vacancies in oxide nanostructures would thus open up comprehensive prospects for new functional ionic devices. Advancements in this direction require experimental techniques that allow for simultaneous measurements of oxygen vacancy dynamics, atomic-scale structural effects and macroscopic physical properties. Here, we use in situ transmission electron microscopy (TEM) to demonstrate reversible switching between three resistance states in epitaxial La2/3Sr1/3MnO3 ?lms [4]. Simultaneous high-resolution imaging and resistance probing indicate that the switching events are caused by the formation of uniform structural phases. Reversible horizontal migration of oxygen vacancies within the manganite ?lm, driven by combined effects of Joule heating and bias voltage, predominantly triggers the structural and resistive transitions. Our ?ndings open prospects based on dynamic control of physical properties in complex oxide nanostructures. [1] R. Waser and M. Aono, Nat. Mater. 6, 833 (2007). [2] J.J. Yang et al., Nat. Nanotech. 8, 13 (2013). [3] S. Kalinin and N.A. Spaldin, Science 341, 858 (2013). [4] L. Yao, S. Inkinen, and S. van Dijken, Nat. Commun. 8, 14544 (2017).

Resume : Magnetoelectric coupling in oxide based heterostructures gives the possibility to electrically control the magnetization, with promising applications in the field of spintronics [1], [2]. Strong magnetoelectric coupling was demonstrated in magnetic thin film structures deposited on ferroelectric substrates and allowed to identify several coupling mechanisms, namely the strain transfer via converse piezoelectric and magnetostriction effects or the ferromagnetic electronic structure modification by the ferroelectric polarization. In thin film multilayer structures the piezoelectric effect is reduced by the low dimensionality, thus the interfacial charge-mediated coupling effect can predominate. We report here on the magnetoelectric properties of BiFe0.95Mn0.05O3 (BFMO) / Ni multilayer structure. BFMO displays ferroelectricity at room temperature as well as canted G-type antiferromagnetism. Therefore, a third type of coupling mechanism should be considered in such structure, due to exchange interactions between the antiferromagnetic structure of BFMO and the ferromagnetic Ni structure. The magnetoelectric coupling in the studied system manifests through the ferromagnetic coercive field modulation with the electric field. The effect is non-volatile, reversible and cyclable at room temperature. In light of our results, charge-mediated coupling mechanism seems to be the origin of the studied effect. [1] V. Garcia, M. Bibes, A. Barthélémy, C. R. Physique 16 (2015) 168?181 [2] J.-M. Hu, L.-Q. Chen, C.-W. Nan, Adv. Mater. 2016, 28, 15?39

Resume : The Neumann?s principle states that "If a system has a certain group of symmetry then any physical observable of that system must also possess the same symmetry?[1]. The application of this statement leads to new conclusions concerning alpha-Fe2O3 and Cr2O3. Both these oxides are believed to have corundum-type crystal structures described with the trigonal space group R-3c (this group posess a 3-fold rotation axis). Literature data clearly indicates that the canted magnetic orderings of both alpha-Fe2O3 [2] and Cr2O3 [3] are described with a symmetry group without 3-fold rotation axis. According to the Neumann?s principle one can expect that the symmetry of the crystal structure of alpha-Fe2O3 and Cr2O3 is not trigonal (without 3-fold rotations). Synchrotron radiation diffraction studies of alpha-Fe2O3 [4] and Cr2O3 [5] shows that their crystal structures are described by the monoclinic space group C2/c instead of R-3c. The unexpected result is that the monoclinic symmetry is observed not only below the Néel temperature, T_N=950K of alpha-Fe2O3 but also above T_N. [1] A.P. Cracknell Applied Group Theory, Pergamon Press, Oxford, 1968. [2] C.G. Shull, W.A. Strauser & E. Wollan, Phys. Rev. 83, 333 (1951). [3] P.J. Brown, J.B. Forsyth, E. Lelievre-Berna & F. Tasset, J. Phys. Condens. Matter, 14, 1957 (2002). [4] R. Przenios?o, I. Sosnowska, M. Stekiel, D. Wardecki, A. Fitch, & J.B. Jasi?ski, Physica B, 449, 72 (2014). [5] M. Stekiel, R. Przenios?o, I. Sosnowska, A. Fitch, J.B. Jasi?ski, J. A. Lussier, & M. Bieringer Acta Cryst. B71, 203 (2015). [6] P. Fabrykiewicz, M. Stekiel, I. Sosnowska & R. Przenios?o, Acta Cryst B73, 27 (2017).

Resume : Transition metal oxides having a per- ovskite structure present a wide range of functional properties ranging from insulator-to-metal, ferroelectricity, colossal magnetoresistance, high-temperature superconductivity and multiferroicity. Such systems are generally characterized by strong electronic correlations, complex phase diagrams and competing ground states. In addition, small perturbation induced by external stimuli (electric or mag- netic field, temperature, strain, pressure..) may change structure, and ultimately modify the physical properties. Here, we synthetize an orthorhombic perovskite praseodymium vanadate (PrVO3), which is grown on strontium titanate substrate. We show that the control of the content of oxygen vacancies, the so-called chem- ical strain, can indeed result in unexpected properties. We further demonstrate that the Nel temperature can be tuned using the same substrate in agreement with first-principles calculations, and 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. Funding from ANR-LABEX is acknowledged

Resume : We report the effect of doping with Y and La and hydrostatic pressure on structural, electronic, and ferroelectric properties of BiFeO3. We found that BiFeO3 undergoes a phase transition from rhombohedral (space group R3c) to orthorhombic (polar Pn21a and non-polar Pnma) structure. The phase transition caused by hydrostatic pressure appears at 5 GPa. In case of Bi1-xRExFeO3 the structural phase appears for x=0.125. The total energy difference between polar (Pn21a) and non-polar (Pnma) orthorhombic phases is less than 1 meV/f.u. This close a coexistence of these phases beyond T=0 K or under other conditions. The similarities between hydrostatic pressure and doping suggest that the latter can be regarded as a proxy for hydrostatic pressure, with an equivalence of 1% Y = 0.09 GPa and 1% La = 0.04 GPa. The experimentally obtained value was 1% La = 0.05 GPa [1]. The calculated spontaneous polarization for BiFeO3, Bi0.875La0.125FeO3, Bi0.875Y0.125FeO3 is 90 ?C/cm2, 83 ?C/cm2, 85 ?C/cm2, respectively [2, 3]. For undoped case our result is in good agreement with previous experimental and theoretical works [4]. References: [1] Ch.S. Knee, M.G. Tucker, P. Manuel, S. Cai, J. Bielecki, L. Börjesson, S.G. Eriksson, Chem. Mater. 26 (2014) 1180 [2] M. Pugaczowa-Michalska, J. Kaczkowski, J. Mater. Sci. 50 (2015) 6227 [3] J. Kaczkowski, in preparation [4] G. Catalan, J.F. Scott, Adv. Mater. 21 (2009) 2463 This work was supported by the National Science Centre, Poland through Grant No. DEC-2016/21/D/ST3/03444

Resume : Ferroelectric materials with a high piezoelectric response and flexible domain wall arrangement are essential for novel technologies as e.g. energy harvester. A possible pathway to enhance the electromechanic response is given in monoclinic phases where the electrical polarization vector is able to rotate within the mirror plane of the monoclinic unit cell. In materials with tetragonal or orthorhombic symmetry, the alignment of the domain walls is restricted to symmetry elements of the crystal yielding exclusively 45° or 90° domain wall angles. However, this restriction is released in monoclinic phases providing a new degree of freedom for domain engineering. In combination with a high piezoelectric response, such a system would be of high technological relevance. As a proof of concept, strained ferroelectric KxNa1-xNbO3 thin films were grown epitaxially on (110) NdScO3 substrates with metal-organic chemical vapor deposition. According to linear elasticity theory, the (100)pc and (001)pc crystallographic orientations concurrently occur in the films leading to the formation of a a1a2/MC multi-domain state showing up as a herringbone pattern. The domain wall angles within the herringbone can be systematically varied by changing the potassium content x, which is correlated to the monoclinic distortion angle. These results represent a first experimental verification of a flexible domain wall arrangement in monoclinic phases and agree well with values based on a domain model.

Resume : Vestigial quantities of antibiotics in wastewater are linked to the evolution of antibiotic resistant bacteria that exposes human and animal health to grave danger. Ciprofloxacin is a widely used antibiotic against gram-negative and gram-positive bacterial pathogens. This work investigated the influence of operating conditions in the removal of ciprofloxacin in suspended solution of porous ZnO/SnS2 photocatalyst under visible light irradiation. The effects of initial antibiotic concentration, catalyst dosage, and initial pH of solution were investigated. The process efficiency was evaluated in terms of antibiotic degradation. Experimental results evidenced that the highest degradation of the antibiotic occurred in the zwitterionic state at natural pH of 6.1. The ZnO/SnS2 photocatalyst exhibited stability at pH of 6.1.

Resume : Abstract Polycrystalline Hematite thin films doped by Cr were successfully deposit on glass substrate coated with fluorine-doped tin oxide (FTO) by a facile hydrothermal method. The hydrothermal bath consisted of an aqueous solution containing 25 mL capacity was filled with 20 mL aqueous solution containing 0.15 M of FeCl3.6H2O and 1 M NaNO3 at pH 1.5 (adjusted by HCl) . A piece of FTO glass slide heated at 100°C for 6 h in an oven and naturally cooled down to ambient temperature and subsequently the as-deposited samples were annealed in air at 550 °C for 4 hours. The structure and morphology of the as-synthesized products were characterized by X-ray diffraction (XRD), field-emission electron microscopy (FESEM), and High-resolution transmission electron microscopy (HRTEM). The effect of doped Cr were proven by defraction peaks (012) and (104) shifs to the lower angls. the photoelectrochemical performance of the thin films was eximined by chronoamperometry tecnique. Results of these studies showed that Cr doped films exibited higher photoelectrochemical activity over un-doped ?-Fe2O3 thin films. The highst photocurrent density of 0.015 mA cm-2 was obtaind for 16% Cr doped films in 1 M NaOH electrolyte under standerd illumination conditions ( AM 1.5 G, 100 mW cm-2). This high photoactivity can be attributed to the high active surface area and increasd doner density caused by Cr doping in the ?-Fe2O3 films. The best performing samples were 16% Cr doped which had Incident Photon Conversion Efficiencies (IPCE?s) at 400 nm, with an applied potential of 0.4V vs Ag/AgCl. These IPCE values were 22 times higher than the undoped sample for the 16% Cr sample. The increase in performance is attributed to an improvement in the charge transport properties within the films and not due to significant changes in the electrocatalytic rates due to dopants residing at the surface.

Resume : Recently, zinc oxynitride (ZnON) is attracting a significant attention as an active material of the high-mobility thin-film transistor (TFT) for next-generation high-resolution, high-frame rate, and large-size displays. In this paper, we investigate the carrier transport mechanism in a high-mobility ZnON TFT by analyzing the gate bias and temperature dependence of conductance and field-effect mobility (?FE) in the subthreshold and above-threshold regions, respectively. In the subthreshold region, the variable range hopping and trap-limited band transport are considered as dominant carrier transport mechanisms in the ZnON TFT at temperatures below ~ 207 K and above ~ 243 K, respectively. In the above-threshold region, the ?FE almost linearly depends on 1/T (T: absolute temperature) at low temperatures, however, ?FE decreases with an increase in the gate overdrive voltage and temperature at high temperatures above room temperature. It represents that the trap-limited band transport is the dominant carrier transport mechanism at low temperatures, but the phonon scattering is the dominant mechanism limiting ?FE at high temperatures in the ZnON TFT in the above-threshold region.

Resume : Composite compounds that exhibit strong magnetoelectric coupling have attracted much interest thanks to their potential room-temperature applications, e.g. low-energy-consumption storage devices. In composites with ferromagnetic and ferroelectric constituents the electric control of magnetism is, most commonly, strain-mediated by the inverse piezoelectric effect. Here we study composite samples of Fe3O4 micro/nano-particles embedded in a PZT matrix. Specifically, starting from the complete series of PZT-x%Fe3O4 with 0%?x?50% per weight prepared at T=1000 0C for 2 h in air, we focused on x=5%, e.g. PZT-5%Fe3O4, and studied the piezoelectric and magnetic properties at room temperature, in great detail. Experimentally, the strain-electric field curve, S(Eex), was recorded with a local method based on optical microscopy (OM) that enables us to monitor the dimensional changes of the sample under the variation of an external electric field, Eex. Relaxation data of the remanent magnetization were recorded with a SQUID magnetometer as host cryostat for the application of an external magnetic field, Hex, while we used a modified sample rod to apply the Eex. The combined OM and SQUID data prove that the relaxation rate (RR) of remanent magnetization presents a butterfly-like dependence on Eex, exhibiting maximum RR values at the extrema points of S(Eex). Accordingly, S(Eex) can be used as an effective variable to control the remanent magnetization (a candidate parameter for information storage in relevant devices) in the PZT-5%Fe3O4 composite compounds studied here.

Resume : In recent years, fabrication and examination of the memristor structures have become more and more popular thanks to intensive development in micro- and nanotechnology, especially semiconducting nanomaterials and nanostructures. Among various types of the RAM memories, resistive RAM memory (ReRAM) is gaining more and more interest due to high density of packaging and high speed of operation. Thanks to that, the search for the materials based on oxides, which exhibit resistive switching, including such transition metal oxides (TMO) as ZnO or TiO2 has started. Characteristic behavior of this type of memristor structures is that they exhibit change of resistance by applying electric impulses, which results in appearance of pinched hysteresis loop in the current-to-voltage plane. As a result a memristor structure has ability to remember its resistance state. This work contains a short review on the subject of thin film structures with memory effect and own original results acquired during electrical investigations of thin film of oxide compounds based on titanium and copper. The results showed dependence of observed characteristics on the construction of prepared thin films (composition, shape of element-gradient distribution) and measurement conditions (e.g. frequency, sweeping time).

Resume : In this work, we report on the growth of monoclinic ?-MoO3 nano-ribbons on varied substrates like Si (100), FTO, HOPG having almost similar morphologies keeping the substrate temperature at 350 °C by molecular beam epitaxy (MBE) technique. Scanning electron microscopy (SEM) images depict randomly oriented,out of plane nano ribbons of MoO3. For 10 nm MoO3 deposition the typical length, width, and aspect ratio (as defind by the ratio of length over width) of the nano-ribbons are 74 ± 6 nm, 12.0 ± 0.4, 6.1 ± 0.3 nm, respectively.With the increase in thickness of MoO3 at substrate temperature of 350 °C the length of the nano ribbons also increases (from 58 to 195 nm), but there is no significant change in width of the as-grown structures; hence the aspect ratio increases with increase in thickness (from 3.9 to 14). We have experimentally established the possible growth direction in [011] by thickness dependent study.Morphology of MoO3 structures found to depend on the growth temperature.

Resume : In the last years, CeO2 based materials attracted much attention for their use in many technological areas. For some devices CeO2 needs to be grown on metallic substrates, but few reports exist on CeO2 deposited on metals. Here, we studied the structural properties of ALD grown CeO2 films deposited on Si or TiN. In particular, we unveiled the differences in the film properties depending on the substrate [1]. Moreover, we studied the effects of temperature and atmosphere in post-deposition annealing on the CeO2 films, including crystalline structure, grain size and shape, and Ce chemical state. CeO2 films deposited at 250°C by ALD are polycrystalline cubic phase on both substrates, but their crystallographic preferential orientation is along < 200> direction for CeO2/Si and < 111> direction for CeO2/TiN. Further CeO2 films interface roughness and concentration of Ce3+ species depend on the substrate. We also found that 900 °C annealing enhances the diffraction signal of the < 200> crystalline orientated grains in CeO2/Si, which is explained into the frame of the Mochvan?Demchishin model. Our results help the comprehension of ceria ALD growth and add relevant findings for material design and integration. This work was partially supported by ECSEL-JU R2POWER300 project under grant agreement n.653933. [1] S. Vangelista et al., Structural, Chemical and Optical Properties of Cerium Dioxide Film Prepared by Atomic Layer Deposition on TiN and Si Substrates, Thin Solid Films (2017) accepted

Resume : The present work is focused on a plasma-assisted approach for the fabrication of Fe2O3-TiO2-Au nanosystems with tailored features. Specifically, the adopted strategy involved the initial growth of Fe2O3 nanostructures by plasma enhanced-chemical vapor deposition (PE-CVD) on fluorine-doped tin oxide (FTO) substrates, followed by the sequential functionalization with TiO2 and Au via radio frequency (RF)-sputtering, and final thermal treatment in air. The target nanosystems were characterized by a multi-technique approach, in order to investigate the interrelations between their chemico-physical properties and the processing conditions. The proposed route enabled the fabrication of pure nanocomposites, characterized by the presence of ?-Fe2O3 (hematite), an amorphous thin TiO2 overlayer, and Au nanoparticles with a controlled spatial distribution. The intimate contact between the various constituents was of considerable importance to exploit their mutual interplay in photo-activated processes. In this regard, preliminary functional tests for photoelectrochemical water splitting and self-cleaning end-uses evidenced that the control of Fe2O3-TiO2-Au interfacial interactions is a key tool to address the nanosystem potential in both renewable energy generation and pollutant decomposition. D. Barreca et al., Solar Energy Materials and Solar Cells, 2017, 159, 456.

Resume : A series of Dy3+ doped RbGd(WO4)2 (RGW) phosphors were synthesized by sol gel method using citric acid as a chelator and ethylene glycol as a binder. Powder XRD, SEM, FT-IR, Raman, photoluminescence and decay analysis were used to characterize the synthesized phosphors. Powder XRD pattern of the samples match well with the standard JCPDS card no- 45-0472, which confirms the formation of scheelite type monoclinic structure RGW compound and the particles with plate like morphology were observed from SEM image. Liberation of organic species and the tungstate ribbon formation of the sample during calcination process were analysized by FT-IR and Raman spectra. Excitation spectrum of the Dy3+:RGW phosphor shows a broader band at the lower wavelength region due to the charge transfer band of O2- ?Dy3+ and O2- ?W6+ transition and sharp excitation peaks at the higher wavelength region due to the f-f transition bands of the Dy3+ ions. In emission spectrum, strong peak at 574 nm for electric dipole 4F9/2 ? 6H15/2 transition and relatively weak peak at 487 nm for magnetic dipole 4F9/2 ? 6H13/2 transition was observed. Also, the effects of Dy3+ doping concentration on the crystal structure, luminescence properties and lifetime of the Dy3+:RGW phosphor were investigated in detail. The CIE color coordinates of the phosphor was evaluated (x=0.347, y=0.387) and the values are closer to the standard values designated for white phosphor (x=0.333, y=0.333).

Resume : Zinc oxide is very attractive material for optoelectronics. As for many of its applications control of electrical properties is crucial, a lot of reports deal with the possible reasons of high n-type conductivity of this material. Noteworthy, the electron density reported for ZnO grown by different methods is 10?15 orders of magnitude higher than its intrinsic value, derived from the energy gap. The current work presents possible contributions to the n?type behavior of ZnO films grown by Atomic Layer Deposition. The room?temperature photoluminescence (RTPL) and Secondary Ion Mass Spectroscopy (SIMS) investigations suggest important role played by the zinc?related defects in their electrical response. This is supported by increasing n value (from 1.7×10^(17) cm^(-3) to 8.6×10^(19) cm^(-3)) with increasing ZnO growth temperature. We show that the RTP process results in changes in the defect?related RTPL, suggesting the contributions of defects of miscellaneous origin in different spectral range, i.e., RTP in N_(2) enhances the emission at 2.23?2.38 eV (ascribed to the oxygen vacancies), whereas RTP in O_(2) activates the PL nearby 1.70 ? 1.90 eV (where V_(Zn) defects are dominating). The work was supported by the Polish National Centre for Research and Development (NCBiR) through the project PBS2/A5/34/2013 and by the EU 7th FP REGPOT project INERA (GA 316309) of ISSP-BAS.

Resume : The aluminum oxides thin films are electrical insulators with high temperature resistance and high hardness. Thanks to physical properties, the Al2O3 thin films are applied as mechanically and chemically protective layers, heat resistance components and electric insulators in optoelectronic and electronic devices. The aluminum oxide is a high band gap material (?9 eV), with a high breakdown electric field (5?10M Vcm-1), a high permittivity (8.6?10), high thermal stability up to at least 1000 °C and remains amorphous under typical processing conditions [1]. Amorphous Al2O3 layers are found to significantly improve physical and electrical characteristics in GaAs MOS capacitors. They enhance thermal stability by blocking the diffusion process of oxidizing species upon annealing [2]. The Al2O3 thin films are applied as a high-k dielectrics in MOSFETs and DRAMs to replace silicon dioxide as the gate dielectric [3-7]. A dual-gated graphene FETs are produced with 2 nm Al2O3 top layer deposited on graphene [8]. Thermal properties of thin films are very important due to their applications. Nowadays, the progressive miniaturization and increasing integration of electronic devices causes problems with efficient heat dissipation from devices. Heat management is the key factor to improve functionality and reliability of the structure. The aim of this work was characterization of thermal properties of thin oxides films deposited on various substrates and correlation with morphology to study the influence of technological parameters on heat transport properties. Samples were produced using the magnetron sputtering method, well known technique used for deposition of thin metallic films as well as their oxides and nitrides. In this process atoms were released from a target in a strong magnetic field and condensed on a substrate in a high vacuum environment. In case of compound deposition the atoms react with ionized gases before condensation, e.g. oxygen, nitrogen. Determination of the thermal conductivity of Al2O3 samples was realized by the use of scanning thermal microscopy (SThM). This nondestructive method allowed for quantitative measurements of thermal properties with high spatial resolution. Determination of thermal conductivity was based on calibration curve build on SThM signal measured for reference samples of known thermal conductivity. The calibration procedure enabled the objective characterization of thermal properties of thin films and allowed to study the influence of substrate on thermal properties of the layer. References [1] H. C. Lin, P. D. Ye, G. D. Wilk, Appl. Phys. Lett. 87 (2005) 182904. [2] D. C. Suh, Y. D. Cho, S. W. Kim, D.-H. Ko, Y. Lee, M.-H. Cho, J. Oh, Appl. Phys. Lett. 96 (2010) 142112. [3] Frank M. M. et al, Appl. Phys. Lett. 83 (2003) 740. [4] Kim S. K. and Hwang C. S., J. Appl. Phys. 96 (2004) 2323. [5] Huang M. L. et al, Appl. Phys. Lett. 87 (2005) 252104. [6] Duenas S. et al, J. Appl. Phys. 99 (2006) 054902. [8] Xu M. et al, J. Appl. Phys. 99 (2006) 074109 [9] B. Fallahazad, K. Lee, G. Lian, S. Kim, C. M. Corbet, D. A. Ferrer, L. Colombo and E. Tutuc, Applied Physics Letters 100 (2012) 093112.

Resume : We present the synthesis of ZnO/ZnMgO heterostructures on r- and c- plane Al2O3 by MBE and investigation of their structural and optical properties. The structures were grown at oxygen-rich conditions at temperature of 550°C. We demonstrate that it is possible to grow a good quality nanocolumns on c- plane Al2O3 substrate without employing a catalyst such as Au or Ag. We have studied also shift between polar- and nonpolar- ZnO/ZnMgO quantum wells. The non-polar (a-plane) ZnO/ZnMgO nanocolumns were achieved on semi-polar (r-plane) sapphire substrate while on polar c-plane substrate was used to obtain a polar c-orientation of the nanostructures. We present the research of ZnMgO nanocolumns with ZnO QWs located in single nanocolumns. The studied samples consist of two ZnO/ZnMgO quantum wells with the wells widths of 1.5 and 4 nm. The quantum wells were separated with 15 nm ZnMgO barrier. All samples were characterized with XRD, PL at different temperatures, TEM and SEM. We measured also the effects of a piezoelectric field on the spectroscopic properties ZnO/ZnMgO QWs in the strained ZnMgO self-assembled nanocolumns. We compared the luminescence spectra of ZnO/ZnMgO structures grown on the semi-polar substrate with r orientation and on polar c-oriented substrate. It is probably the first experiment comparing the quantum confined Stark effect for structures of different polarities, grown on Al2O3 substrates of different crystallographic orientations.

Resume : Ion implantation effects in semiconductor compounds have been widely studied in the last decade by many groups. However, a lack of complete understanding remains on the mechanism of damage buildup of compound crystal. The RBS/c technique is typically used for the analysis of structural properties of ion implanted single crystals by many authors. Unfortunately, oversimplified methods of spectral analysis have been typically applied, which may produce misleading results. ZnO is a very promising material for semiconductor device applications. In order to tune the optical emission from ZnO into the visible spectral range the optically active centers have to be formed. Recently, the studies on REs (rare earth) doped materials have received considerable interest for their possible applications in the light emitters. ZnO commercial single crystals (MaTecK) and epitaxial ZnO thin films, grown by atomic layer deposition (ALD) were implanted with 300 keV Er ions to fluencies ranging from 1e14 to 5e16 at/cm2. Quantitative analysis of the damage has been carried out using Monte Carlo simulation code McChasy, which allows to differentiate between type of defects. Model of structural transformation has been conceived based on their evolution as a function of ion fluence. Obtained differences between two investigated materials are presented and discussed in details.

Resume : In the paper we address the problem of a stable p-type conductivity of zinc oxide, which is the main obstacle in a wide application of this material in optoelectronics. Polycrystalline ZnO and ZnO:N films were grown at low temperature (100oC) by thermal Atomic Layer Deposition (ALD) under oxygen rich conditions. Low temperature photoluminescence (PL) spectra reveal emission at 3.36 eV as well as acceptor-related emissions at 3.302 and 3.318 eV. Annealing at 800oC leads to a considerable enhancement of PL at 3.302 eV in the ZnO:N. Based on temperature dependent photoluminescence spectra we calculated activation energies of acceptors related to the 3.302 eV and 3.315 eV PL peaks. The calculated activation energies suggest that low temperature deposition and oxygen-rich conditions provide a ZnO material with relatively shallow acceptor levels. We tentatively ascribe this levels to the nitrogen-hydrogen complexes. Acknowledgements. The work was supported by the Polish National Centre for Research and Development (NCBiR) through the project PBS2/A5/34/2013. + Author for correspondence: guzel@ifpan.edu.pl

Resume : Zinc oxide (ZnO) is a promising candidate for many opto-electronic applications as UV LEDs and photodetectors. ZnO has recently received a lot of attention due to its high radiation hardness and thus possible application in space. The ZnO:Sb layers with different Sb concentration (from 0.77% to 1.73%) were grown by MBE on a- and r- plane Al2O3 substrates in polar and no polar directions. Raman spectroscopy, photoluminescence, X-ray, SIMS and XPS measurements provided information about composition and strain in the material. The binding energy shift of the Sb3d peak observed in the XPS data has been correlated with XRD results. Additionally, the Raman spectra, besides typical sapphire and zinc oxide modes, include also additional modes at 511 and 531 cm-1 associated with the presence of Sb dopant. The differences between layer growth on polar and nonpolar direction was observed both in optical and structural characterizations. The research was supported by the NCN project DEC-2013/09/D/ST3/03750 and partially by the statutory grant Wroclaw University of Technology S50013.

Resume : The influence of substrate temperature and postdeposition annealing condition on structural, optical, and electrical properties of p-type semiconductor CuAlO2 thin films prepared by rf-magnetron sputtering has been investigated. The CuAlO2 thin films were deposited using oxygen gas as the sputtering gas and employing synthesized CuAlO2 target. The depositions were carried out at 2.66 Pa of sputtering pressure with rf-power of 100W. The substrate temperatures were 20°C (RT) - 600°C, and the postdeposition annealing temperatures were 700°C - 1000°C in nitrogen, respectively. The as?grown films deposited on quartz substrates were amorphous and brown colored. These films show X-ray diffractions of CuAlO2 after a postdeposition annealing at higher temperature than 700°C. Colours of the films become thin brown at annealing temperature at 700°C, and opaque white or transparent at higher temperature than 800°C. Transparency of the films showed dependency not only on the annealing temperature but also on substrate temperature in film depositions. At substrate temperature of 200 or 300°C, and annealing temperature of 800°C transparency of the films become most preferable. Resistivity of the films also becomes the lowest, less than 100 ohm-cm, at substrate temperature of 200 or 300°C, and annealing temperature of 800°C.

Resume : Chemical processing of graphene via reduction of graphene oxide has been regarded as a scalable and an economical method for most graphene-based applications. Recently graphene oxide itself has attracted significant attention due to its solution dispersibility and for its oxygen functionalities. As a result graphene oxide has become the primary raw material in developing new technologically advanced materials specifically in the areas of nanocomposites, functional coatings, paints and electrode material for chemical and biological sensing. However, one of the biggest challenges in the use of chemically processed graphene oxide or graphene in the above applications is the randomness of its oxygen functionalities and their inhomogeneous spatial distribution. Therefore, as part of controlling the process, one needs to understand the mechanism and the kinetics of the process that forms graphene oxide, and its subsequent reduction to graphene. In this study we look at graphene oxide and reduced graphene oxide synthesized from high purity vein type crystalline graphite under varying oxidation and reduction conditions. These samples were then characterized by a combination of spectroscopic and microscopic techniques that include infrared reflection absorbance spectroscopy, x-ray diffraction, x-ray photoemission spectroscopy, thermo gravimetric analysis, Raman spectroscopy, ultraviolet?visible spectroscopy, scanning electron microscopy and atomic force microscopy. The results were analyzed to identify the structural variations that occur during the oxidation and reduction processes respectively. The results obtained during oxidation indicate a rapid incorporation of oxygen functionalities and a complete interlayer expansion from that of graphite. Continued oxidation resulted in an increase in interlayer spacing and a complex interlayer strain relationship. These observations can be related to the attachment and subsequent prorogation of oxygen functionalities within the graphitic layers. It was also observed that exfoliation ability of expanded graphite oxide into single layer grapehen oxide in aqueous solutions is preceded by an abrupt change in the material structure and oxygen functionalities. Further the observed exfoliation of graphene oxide in aqueous solutions occurred at a much lower reaction time period than reported in literature for similar chemical treatment processes to obtain graphene oxide from graphite. The resulting graphene oxide obtained show large lateral dimensions in the range 5 to 10 micron with minimal morphological defects to the basal plane structure. The thermal reduction of synthesized graphene oxide was carried out under varying temperatures and the data indicate a significant level of reduction at temperatures as low as 200 degree Celsius. The reduction data also indicate a modulation in the optical band gap corresponding to the reduction temperature. Keywords: Graphene Oxide, Vein Graphite, Oxidation, Reduction Acknowledgment: This publication has emanated from research conducted with the financial support of University of Colombo under the grant AP/3/2/2016/CG/29 and of the National Science Foundation Sri Lanka under the OSTP grant OSTP/2016/46.

Resume : VO2 was synthesized on Si, SiO2, MgO and Al2O3 substrates by microwave-assisted physical vapor deposition. The morphology of the surface were observed via SEM and AFM. On Si and SiO2 random smooth-edged and bacilli-shaped structures were the dominant feature. On MgO, the film had sharp and smooth-edged irregular grains. Patterned triangular parallelepipeds and ball-like structures grew on the Al2O3. The presence of VO2 was confirmed by XRD. At room temperature, Raman spectroscopy showed that Si, SiO2 and MgO-grown vanadium dioxide exhibited a shift signature similar to the M1 phase while the Al2O3-deposited VO2 had the signature shift of the M2 phase. The difference in the growth formation will be discussed in regards to the substrate surface energy and thermal conductivity.

Resume : Electrochemical treatment was used to modify properties of ZnO films deposited by RF magnetron sputtering. Constant current was applied between the ZnO film and Pt electrode in the electrolyte solution containing phosphoric acid (4.9×10?5 M), potassium chloride (5.6×10?3 M), and deionized water (150 ml). When the ZnO film was used as a cathode, the sheet resistance of the ZnO film was decreased. However, the optical transparency decreased with increasing treatment time. Thus, the direction of the current flow was changed every 60 s (repetitive electrochemical treatment). The O/Zn ratio and transparency of the ZnO film were kept by the repetitive electrochemical treatment. The sheet resistance depended on the direction of the current flow. When the ZnO film was used as a cathode, the sheet resistance decreased. On the other hand, when the ZnO film was used as an anode, the sheet resistance increased. The sheet resistance of the ZnO films annealed in H2 showed large changes for the repetitive treatment. Defects formed during the H2-annealing possibly caused the enhancement. The optical bandgap of the H2-annealed ZnO films also depended on the direction of the current flow. These results indicate that electrical and optical properties of ZnO films can be modified by the electrochemical treatment.

Resume : High-performance solution-processed oxide thin-film transistors (TFTs) for large-area display backplane have superior performance, including low cost, high mobility, good environmental stability, and low temperature process ability. We investigated the electrical performance of the IZO TFTs as a function of the spin coating speed. The effect of the spin casting speed on the electrical characteristics as a function of time of the thin-film and oxide IZO TFTs was observed. The structural properties of the IZO thin films are investigated by atomic force microscopy (AFM). An AFM image reveals that the IZO thin-film with a thickness of 1000 rpm and 3000 rpm has an uneven distribution of grains, which deformed the thin film and affects the performance of the IZO TFT. And the IZO thin-film with a thickness of 2000 rpm has a homogeneous and smooth surface with a low RMS roughness of 1.88 nm. In particular, the IZO TFTs exhibit an excellent result, show a field-effect mobility of 3.0(±0.2) cm2/Vs, a high Ion/Ioff ratio of 1.1×10^7, a threshold voltage of 0.4(±0.1) V, and a subthreshold swing of 0.7(±0.01) V/dec.

Resume : Electrochromic properties of c-axis oriented monoclinic tungsten trioxide (m-WO3) epitaxial films were studied by fabricating an electrochromic device operated in a 10 mM aqueous solution of sulfuric acid. The WO3 films were grown on r-plane sapphire substrates by molecular beam epitaxy as described elsewhere [1]. We measured optical transmittance of the WO3 films at the as-grown state, at the protonated state after 4V biasing for 25 min in the solution, and at the deprotonated state after ?4V biasing for 25 min in the solution. At the protonated state, broad and intense transmittance decreases in visible (VIS) and near-infrared (NIR) regions appeared. The decrease in VIS region disappeared at the deprotonated state, however, the decrease in NIR region remained. To disappear the decrease in NIR region, annealing the sample in air at 100 °C for 20 min was effective. When we used amorphous WO3 films for the electrochromic device, on the other hand, both decreases in VIS and NIR regions easily disappeared at the deprotonated state. Therefore, the remaining of the NIR decrease at the deprotonated state might be a characteristic of the epitaxial WO3 films. To analyze the structural change of the epitaxial WO3 films during operation, we measured x-ray diffraction at respective states, and related the protonated and deprotonated states to the formation of hexagonal (h-) HxWO3 tungsten bronze and orthorhombic (o-) WO3·0.33H2O hydrate, respectively. It was also found that both transitions from the m-WO3 to h-HxWO3 and from the h-HxWO3 to m-WO3 were conducted by passing through the formation of o-WO3·0.33H2O. This work was supported in part by JSPS KAKENHI Grant Numbers 16K04936 and 17K06472. [1] M. Yano et al., Appl. Surf. Sci. 381, 2016, pp. 32-35.

Resume : Indium zinc tin oxide (IZTO) thin films with composition corresponding to In:Zn:Sn = 40:50:10 at.% were fabricated on n++ heavily-doped Si wafer using radio frequency magnetron sputering at room temperature under 5% O2/(Ar+O2) ambient. In order to study the application of oxide semiconductor for thin film transistor (TFT) devices, the IZTO thin films were utilized as active channel layer. Bilayer Cu/Ti metal was deposited on the top surface as source/drain electrode. The annealing temperature and IZTO film thickness were varied as an effort to enhance the electrical properties of the TFTs. Annealing treatment for as-deposited IZTO films showed the best TFT device performance at 350°C in air atmosphere as the interface defect concentration was reduced with higher annealing temperature. All IZTO thin films remained amorphous regardless the annealing temperature. The deposition of IZTO thin films were also carried out with thickness varied from 15 nm ~ 150 nm and the films were then annealed at 350°C. The thickness of active channel layer greatly influences the characteristics of the TFTs, and the best characteristics were observed in the transistor device having the channel thickness of 30 nm. It was found that the intrinsic field-effect mobility was independent of the channel thickness and the mobility and subthreshold swing values were sensitive to the channel defects present at the interface between active channel and gate dielectric. The 30 nm-thick annealed IZTO TFT achieved the best device characteristics with a high on/off current ratio of about 2.5×108, a high field effect mobility of 25 cm2/Vs, a low threshold voltage -0.1 V and a very small subthreshold swing of 0.14 V/dec.

Resume : There have been many researches on the instability of the SnO phase in p-type SnO TFTs. The p-type transport in tin monoxide occurs only in a very narrow window of deposition process condition. In this study, we tried to widen the process window and enhance the p-type performance by doping aluminum. Al-doping in SnO TFTs could improve the electrical properties such as field effect mobility, subthreshold swing, and threshold voltage.

Resume : Functional oxides such as lead-free piezoelectrics and ferroelectrics attract an increasing attention in the field of energy correlated with eco-responsible label. In this context, our work was focused on the growth of new environmentally friendly ferroelectric oxides such as Ln2WO6 (Ln = lanthanide). In particular, La2WO6 thin films have been grown on (001)-oriented SrTiO3 substrates by pulsed laser deposition. The structural properties were systematically studied by High Resolution X-ray Diffraction and Transmission Electron Microscopy (TEM). The epitaxial strain stabilization of the high temperature allotropic variety of the material was successfully achieved. Nanoscale piezoelectric and ferroelectric properties were detected into the La2WO6 layer by Piezo-Force Microscopy.[1, 2] As-grown ferroelectric domain patterns were imaged, while domain manipulations and remnant piezoelectric loops measurements have revealed local switching behavior and electromechanical activity. In addition, piezo-/ferroelectric responses were locally detected by an original in situ combination of TEM and Scanning Tunneling Microscopy techniques. These findings pave the way to new eco-responsible multifunctional oxide thin-films dedicated to advanced electronic devices. [1] T. Carlier, M.-H. Chambrier, A. Ferri, S. Estrade?, J.-F. Blach, G. Martín, B. Meziane, F. Peiro?, P. Roussel, F. Ponchel, D. Re?miens, A. Cornet, R. Desfeux. ACS Applied Materials & Interfaces 7, 24409 (2015). [2] T. Carlier, M.-H. Chambrier, A. Ferri, A. Bayart, P. Roussel, S. Saitzek, R. Desfeux. Thin Solid Films 76, 617 (2016).

Resume : We determine the density of interface and bulk trap states in the amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) by using a simple extraction method. The current-voltage curve is measured to determine the bulk trap density, between the source and drain electrodes of the TFT at room temperature under the flat-band condition. In the high voltage region, the carrier transport is well described by the space charge limited current controlled by the bulk trap states that are exponentially distributed in energy with a trap density at the conduction band edge of 6.27 e17 cm-3eV-1 and an inverse slope for the trap distribution of 0.12 eV. The density of traps at the a-IGZO/gate dielectric interface is calculated by subtracting the bulk trap components from the density of total subgap trap states extracted from the subthreshold slope in the transfer curve and the frequency-independent capacitance-voltage characteristics. The experimental results show that the contribution of the interface trap is more significant compared to that of the bulk trap in the subgap density of states of the fabricated a-IGZO TFTs.

Resume : Recently, many research groups have investigated zinc oxide (ZnO) for wide range of applications such as light-emitting diodes, solar cell, UV photodetectors, chemical sensors and transparent electronics. Especially, ZnO nanorod is an excellent UV-sensing material because it has wide band gap (3.34 eV) and prominent photoconductivity when exposed to UV. There are many methods to synthesize ZnO nanorod such as chemical vapour deposition (CVD), hydrothermal synthesis, and solution-processing technique. In this study, we synthesized ZnO nanorods successfully by solution-processing method and controlled the lengths of nanorods by varying the precursor concentration of solutions between 0.5M and 3M in growth step. The morphologies of the nanorods were characterized using scanning electron microscopy (SEM). The crystal structures of the ZnO nanorods were confirmed by X-ray diffractometer (XRD). We fabricated solution-processed ZnO nanorod based UV photodetectors and characterized the sensitivity of the devices with different lengths of ZnO nanorod. The devices showed better UV sensing properties when the lengths of ZnO nanorod are increased.

Resume : The effects of semiconductor thickness variations on the current-voltage characteristics of indium-gallium-zinc-oxide (IGZO) Schottky diodes are investigated. Oxide-semiconductors ? particularly IGZO ? have emerged as both an attractive alternative to amorphous-Si for many current applications and as vehicles for the realisation of entirely novel applications, including large area transparent and flexible electronics. Recently, oxide-semiconductor TFTs and Schottky diodes have demonstrated GHz operation ? further confirming their suitability for future electronics. The scalability of TFTs has been well documented ? particularly the short-channel effect ? but there has been very little discussion of the effects of device scalability in Schottky diodes. In published literature on IGZO thin-film Schottky diodes there is a noticeable dependence of the current on the thickness of the semiconductor layer. This phenomenon remains largely undiscussed even though it can cause the reverse current to vary over orders of magnitude. A combination of simulations and experiments has been carried out to demonstrate such an effect and elucidate its origins. Our work indicates that the diodes are diffusion-limited and that that non-uniform Schottky interface properties play an important role in the thickness dependence. These findings may have implications for other device structures employed in large scale thin-film electronics such as Schottky barrier transistors and MESFETs.

Resume : Because of its promising potential for applications ZnO has been widely studied recently by many authors. It is expected that implantation of different RE ions can be used for fabrication of white light emitters. In this, the epitaxial thin ZnO films grown by Atomic Layer Deposition were implanted with Er, Pr, Tb, Dy, Eu and Yb to fluence of 5E14 /cm2 and subsequently annealed by RTA. The optical and structural studies were performed by PL and RBS/c, respectively. Our results have shown that two groups of defects are present in our samples: post-implanted defects and native defects. Both play an important role for the luminescence in the visible region. The latter's are present before implantation and after annealing the optical activation of them occurs. RTA leads also to the removal of the defects formed in ZnO during ion implantation along with optical activation of REs. As noted, presence of REs in the structure is influencing the shape of the PL spectrum, unexpected. It means, that we are observing not only sharp lines related to RE emission with characteristic color and broad peaks from native defects, but also peaks originated from complexes related to RE and annealing atmosphere. Interestingly, the different RE implanted ions in a different manner are modeling the shape of the PL emission. Because of applications reasons the color temperature seems most important and we decided to use NBE blue emission with green light originated from native defects combined with the other emissions related with RE for the fabrication of the white light source. This work was supported by the Polish National Centre for Research and Development (NCBiR) through the project PBS2/A5/34/2013 and project by Helmholtz Zentrum Dresden-Rossendorf (HZDR) in the frame of the program: Access to Infrastructure (16000696-ST)

Resume : The paper presents illumination intensity spectra measured for the selected semiconductors photojunctions based on Si(p/n), GaAs, CdTe, ZnTe and ZnO. The illumination intensity spectra were measured with application of lasers sources of selected wave length and intensity to generate carriers in selected crystal components of junction. The used model predicts smooth continuous scan of quasi Fermi level energy in the related band gap region. The ?defect states? located in the forbidden gap within the junction region disturb this continuous scan. Comparison of the spectra measured and proposed by a model allows to determine values of parameters describing distinguished elements of a structure of photovoltaic open circuit intensity spectra. The one kind of differences illustrates the influence of light scattered on introduced crystalline and surface defects. The second difference shows the characteristic decrease of VOC value. This can be caused by electronic defects causing the decrease of minority carriers density of steady states concentration and lowering the energy distance of quasi Fermi level energy from the thermal equilibrium Fermi level. This effect of electrons interaction lowers the minority carriers density and corresponding to it VOC. The used method allows to estimate the binding energy position of the defect levels. [1] H.Y. Fan, Phys.Rev.75, 1631 (1949). [2] B.A. Orlowski at.al Acta Phys.Pol, 129, (2016) A-100.

Resume : Surface enhanced Raman spectroscopy (SERS) has been attracted much attention within the scientific community as a powerful analytical method in detection ultra-low concentration of chemical and biological species. Although it is an important technique, there are still many limitations to the commercialization of this technique like being disposable in especial SERS substrates made of noble metals. For this reason, there is a need to develop SERS surfaces with high sensitivity, uniformity, reproducibility, stability and low cost for practical applications and research. In recent years, there have been many research to improve the properties of SERS substrate. In particular, due to the high charge transfer rates, the investigation of using various semiconductors (ZnO, TiO2, Fe2O3, CuO, etc.) as the SERS surface have increased inevitably. Among these semiconductors, zinc oxide (ZnO) with controllable morphology and adjustable the band gap has been considered as promising SERS material. However, it is clear that there is a need for extending the knowledge about usage these materials in SERS application. The studies showed that nano-metric roughness of these noble metals significantly affected the intensity of SERS signal. The aim of this study, investigating the SERS properties of silver (Ag) coated ZnO nanostructured surfaces fabricated on ITO glass. For this purpose, 3D nanostructured ZnO films were synthesized in three different morphology nanorods, nanoplates and nanoflowers by electrochemically. Subsequently, Ag nanoparticles was deposited onto ZnO surfaces to increase the detection sensitivity. The surface morphology and crystallographic properties of prepared ZnO nanostructures films in 3 morphologies were characterized by FE-SEM and XRD analysis. The SERS performance and properties of this Ag coated ZnO nanostructured films were evaluated with using methylene blue (MB) as test molecule. The sample solutions containing MB were added dropwise onto newly fabricated in three different morphologies for the detection. The SERS measurements were performed in Alpha 300 Raman microscope using a laser source at 532 nm and with an excitation power of 100 µW. The angle of the light is 900. All Raman spectra were measured at 20 scans with integration time of 0.1 second over a range from 0 to 3500 cm-1. These hierarchically nanostructured hybrid surfaces exhibited SERS signals of MB demonstrates that Ag coated ZnO nanostructures on ITO can be used as an active SERS surface with high sensitivity and reusability in practical applications.

Resume : Surface Enhancement Raman Spectroscopy (SERS) has growing interest in scientific researches for the detection of trace molecules. Basically, the noble metals such as gold, silver and others were used to obtain the SERS signal. The aim of the study the rough silver metal based shell over the monodisperse-porous poly(mono-2-(methacryloyloxy) ethyl succinate-co-glycerol dimethacrylate) (poly(MMES-co-GDMA)) microparticles 5 mm in size was constructed by seed-mediated growth technique. Monodisperse-porous poly(MMES-co-GDMA) microbeads were synthesized using a modified staged shape template polymerization. The magnetization of the microbeads was achieved by the generation of magnetic hematite nanoparticles within the polymer microbeads using their carboxyl functionality. Magnetic particles were then refluxed with 3-aminopropyl) triethoxysilane (APTES) in toluene for the attachment of primary amine functionality onto the magnetic polymer microbeads. The gold seed decoration was carried out via amino group of the magnetic microbeads. Gold seed decorated particles is used for growing a rough silver shell around the magnetic polymer core. The morphology and crystalline form of the SERS substrate were characterized by SEM, XRD. Magnetic behavior of the material was determined by VSM. The surface morphology of this newly synthesized material gives an opportunity to detect just 1 µl of any SERS active sample at sub-micro molar concentrations. The stability, reproducibility and high detection limits by using limited sample creates the idea of detecting drugs at very low concentrations particularly important for forensic science or environmental health. The successful results were obtained for 10-8M antibiotic detection and its commercial product also the quantitative calibration curve showed the strength of this technique.

Resume : The stabilization of non-centrosymmetric orthorhombic HfO2 with space group Pbc21 is related to the ferroelectricity of this material [1]. However, this stabilization requires a strict process control [2,3] and/or the application of an encapsulation layer [1]. In ZrO2, the stabilization of this phase has so far only been reported in magnesium stabilized alloys after thermal shocking [4]. Here, we report on the formation of orthorhombic ZrO2 (that can be described with the space group Pbc21) in thin Zr-Ta-O films. Thin Zr-Ta-O films with different tantalum concentrations and a thickness of 500 nm were deposited on silicon wafers by co-sputtering a ZrO2 and a mixed ZrO2/Ta2O5 target. In the as-deposited state, all films were amorphous. After annealing, formation of tetragonal (Zr,Ta)O2 was observed for [Ta]/([Ta] [Zr]) ? 0.19, that of orthorhombic (Zr,Ta)O2 for [Ta]/([Ta] [Zr]) > 0.19. Thin films containing at least as much tantalum as zirconium ([Ta]/([Ta] [Zr]) ? 0.50) decomposed in two orthorhombic phases upon crystallization: (Zr,Ta)O2 and tantalum-rich (Ta,Zr)2O5. The Rietveld analysis of X-ray diffraction patterns revealed that the crystal structure of (Zr,Ta)O2 can be described with the non-centrosymmetric space group Pbc21. The broad range of tantalum concentrations in which orthorhombic (Zr,Ta)O2 is formed as a single crystalline phase, is promising for the use of this compound in ferroelectric field effect transistors. [1] T. S. Böscke et al., Appl. Phys. Lett. 99, 102903 (2011). [2] T. Olsen et al., Appl. Phys. Lett. 101, 82905 (2012). [3] M. Hoffmann et al., J. Appl. Phys. 118, 72006 (2015). [4] E. H. Kisi, C. J. Howard, and R. J. Hill, J. Am. Ceram. Soc. 72, 1757 (1989).

Resume : Nonstoichiometric phases of the WO3 compound, i. e. in the form of WO3-x, attracted a lot of interest due to their well-defined phases and distinctive morphological structure. For x=0.1 (WO2.9 or W20O58), this compound undergoes metal-insulator transition in bulk. For x>0.1, (WO2.72 or W18O49, WO2.8 or W5O14, WO2.83 or W24O68), the electrical and optical properties are dominated by free electrons in bulk. At the nanoscale, these suboxides can be found as nanoplates, nanowires1 and nanoparticles. We report on suboxide nanotiles produced with high yield. Their width ranges from couple of hundreds of nm to 2 µm, while the lenght spans from a 1 to several µm. WO3-x nanotiles have been characterized with electron microscopy (SEM and TEM) and various spectroscopic methods, such as XRD, XPS, Raman and UV-Vis spectroscopy, in order to determine their phase and structure.

Resume : Tungsten trioxide (WO3) is an n-type semiconductor (Egap = 2.6 eV) presenting great potential for applications in gas sensors, solar cells, photocatalysis and transistors. WO3 films were shown to be electrochemically active on aqueous (acidic) and non-aqueous (LiClO4 dissolved in propylene carbonate) solutions with reversible oxidation/reduction behaviour on voltammetric measurements, enabling them to be used as electrolyte gated transistors (based on the use of electrolytes as the gating medium). Three different types of WO3, fabricated using different synthesis procedures, were considered as transistor channel materials in this work. Granular hexagonal WO3 films were prepared by sol-gel method, and WO3 hexagonal nanofibers were synthetized in-situ on substrates with pre-deposited granular WO3 films (seed layer) using a hydrothermal procedure. WO3 monoclinic nanoplates, in powder form, were obtained by microwave-assisted hydrothermal method, and the powder was film deposited by spin coating, followed by heat treatment at 400 oC for 2 hours for organic removal. Electrolyte-gating was performed using an ion-gel composed of triblock copolymers (poly (styrene-ethyleneoxide-styrene)) and ionic liquids (such as [EMIM][TFSI]) and a high surface area carbon top-gate electrode. Different values of the charge doping density and charge carrier mobility were expected for the three types of transistor channels and results were discussed in function of material morphology and film density.

Resume : SnO2 is a well-consolidated industrial sensor material used to detect a wide range of flammable and toxic gases. However, recent results show that one-dimensional (1D) Sn3O4 structures emerge as unusual alternative building blocks for the fabrication of next-generation sensor devices composed of a single structure or to create p-n junctions with other oxides. In this work, the gas sensor properties of pristine and metal-decorated Sn3O4 nanobelts are presented. Sn3O4 nanobelts were synthesized by carbothermal reduction method and catalyst metal nanoparticles (Pt, Pd and Ag) were prepared by Polyol method. Surface functionalization of the nanobelts was achieved by coating the structures with 1wt% of metallic nanoparticles. Differences in the gas sensing features of the multiple samples were observed after exposures to different concentrations of NO2, H2, CO and CH4 (1-1000 ppm) and their properties (sensitivity and selectivity) were altered by the surface modification. This effect can be attributed to the role of metal nanoparticles which act as catalysts in the interaction of the oxide with reducing gases and as deactivators in the interaction with oxidizing gases, suggesting that chemical or electrical sensitization took place. Furthermore, the sensitivity of materials was found to be highly dependent on the operating temperature of sensors. Impedance Spectroscopy was used to further investigate those processes and a model for the effects of metal catalysts could be proposed.

Resume : Several approaches have been used to optimize and improve the gas detection properties in metal oxide semiconductors, either by chemical or morphological modifications or by optimization of operating conditions. Studies have pointed out that the formation of p-n junction can significantly improve the sensing performance due to the increase of defect sites at the interface region. In this work, we present the effects of p-n junctions on the gas sensor response of SnO2-CuO nanofibers in comparison to the pristine SnO2, both prepared by the electrospinning method. XRD and TGA showed that after annealing at 500 °C, crystalline and free of impurities materials were obtained. FE-SEM and TEM were used to analyze the crystallinity and the morphological characteristics of the fibers after the annealing. EDS and XPS techniques confirmed the chemical composition of the grown structures as well as the distribution of the chemical elements in the structures. AFM and specific surface area measured by the BET method revealed that the surface roughness and surface area of the fibers depending on their chemical composition. From the gas sensor characterizations, it was found that the sensor responses of both materials are highly dependent on the concentration of NO2, H2, CO and CH4 and the operating temperature. SnO2 fibers exhibited higher sensing response to NO2, while the SnO2-CuO fibers presented higher sensitivity to H2, showing the importance of junctions for the sensor properties.

Resume : In this work dielectric and electrical properties of Al2?3/HfO2 multilayer stacks obtained by atomic layer deposition in dependence on the thickness of Al2?3 and HfO2 layers and the post-deposition annealing (PDA) in different ambient (O2, N2, air) have been investigated in terms of their application as trapping layers in emerging charge-trapping non-volatile flash memories. It is found that O2 and N2 PDA have distinctly different influence on electrically active defects in the stacks - N2 introduces negative charges whereas O2 ? positive ones. Three different processes give rise to hysteresis effects: 1) trapping of electrons under positive gate bias; 2) trapping of holes under negative gate bias. These are the useful processes which define the memory window. The third process is the generation of positive charge under high electric field stress which degrades the stacks and results ultimately in breakdown. The results unambiguously show that PDA in O2 enhances the charge storage ability of the stacks and anneals defects in HfO2 which are precursors of stress-induced positive charge. Negligible memory window is observed for samples annealed in N2 or air. The as-deposited stacks are more susceptible to stress-induced positive charge generation. The results imply that the charge storage ability of Al2?3/HfO2 stacks could be tailored by optimization of stack parameters as well as annealing processes. Acknowledgements: The work was financially supported by EC in the frame of project INERA REGPOT 316309.

Resume : In recent years, there has been an extensive attention towards the development of enzymless amperometric glucose sensors due to its high stability and repeatability compared to enzyme-based glucose biosensors. CuO has been investigated as an enzymeless glucose sensor due to its high chemical activity, nontoxic nature and outstanding redox behavior. On the other hand ZnO is also a good functional material in glucose sensing area as it possesses nice biocompatibility and fast electron transfer ability between the active sites and the electrodes. We have synthesized Zn(Cu)O composite structures through electrodeposition technique. The structure and morphology of the samples were characterized using XRD & FESEM . XPS and Raman studies confirm the presence of specific copper related phase. These composite structures display glucose sensing . The optical properties of these structures have also been investigated. Results show band gap tailoring of these structures.

Resume : Metal oxide semiconductor nanowires (NWs) such as SnO2, In2O3 etc have been investigated extensively in the past for the fabrication of nanoscale devices. These are n-type wide band gap semiconductors and have relatively low carrier densities of the order of 1016 cm-3 as we have shown previously for SnO2 NWs grown by the vapor liquid solid mechanism [1]. Consequently they require doping to increase their conductivity and improve the performance of devices. In the past Sb doped SnO2 NWs with metallic conductivity have been obtained but recently Ma et al [2]. showed that a substantial band-gap tuning and a strain-controlled, semiconductor to gapless semimetal transition, is possible via the incorporation of Pb in SnO2. However no one has investigated Pb doping of SnO2 NWs. In contrast PbO2 is a narrow energy band semiconductor with metallic like conductivity due to oxygen vacancies, which form a donor state, resonant in the conduction band but more importantly PbO2 has a tetragonal rutile crystal structure with a = 0.491 nm and c = 0.3385 nm which are close to the lattice constants of tetragonal rutile SnO2 i.e. a = 0.4737 nm and c = 0.318 nm, so they differ only by 3%. This means that PbO2 could be grown on SnO2 or form the ternary oxide PbxSn1-xO2. Recently Ganose et al [3] carried out detailed theoretical calculations and found that the energy band gap and work function of SnO2 may be tailored by alloying it with PbO2 in order to improve its transparency and conductivity. Here we describe our latest work on (a) Pb doping of SnO2 NWs as well as the growth of PbxSn1-xO2 NWs and (b) the growth of PbO2/SnO2 core-shell NWs. A high yield uniform distribution of SnO2 NWs with diameters of 10 to 100 nm's and lengths up to 100 um can be readily obtained by the VLS mechanism at 800C and 0.1 mBar on Si, metal foils such as Ni and Mo but also C fibers using Au as a catalyst. The SnO2 NWs have a tetragonal rutile crystal structure and an n-type carrier density of 1016 cm-3 due to donor like states related to oxygen vacancies. We show that Pb doping of SnO2 NWs is not possible via the VLS mechanism at 800C. In other words the Pb can not be incorporated into the SnO2 probably due to the large difference in the radii of Sn and Pb but we observe a complete suppression of the one dimensional growth of the SnO2 NWs due to the small surface tension of Au:Sn:Pb nanoparticles for high contents of Pb. It is not surprising then that PbSnO2 NWs can not be obtained at 800C since its binary consistuent components i.e. SnO2 and PbO2 can not be grown under identical conditions, primarily due to the fact that PbO2 has a low melting point of 300C. To the best of our knowledge only Pan et al [4] has obtained PbO2 nanobelts at low temperatures that were not explicitly specified and by using PbO at 900 C . Here we show that PbO2 NWs may be obtained without a catalyst by the reaction of Pb and O2 between 100C to 300C and 0.1 mBar which allows the formation of droplets that are necessary for one dimensional growth and the incorporation of Sn. Another way of improving the conductivity of SnO2 NWs is the growth of a SnO2/PbO2 core-shell NWs in view of the fact that their lattice constants differ only by 3%. We show that this is feasible only via the deposition of PbO2 from solution at room temperature and describe the structural, optical and electronic properties such as the charge distribution and potential profile of both SnO2/PbO2 and SnO2/PbO core-shell NWs in the context of energy conversion and storage. [1] Tsokkou D, Othonos, A and Zervos M 2012 Carrier Dynamics and Conductivity of SnO2 Nanowires Investigated by THz Conductivity Spectroscopy Appl. Phys. Lett. 100,133101-1. [2] F.Ma, Y.Jiao, G.Gao, Y.Gu, A.Bilic, S.Sanvito and A.Du, Substantial Band-Gap Tuning and a Strain-Controlled Semiconductor to Gapless/Band-Inverted Semimetal Transition in Rutile Lead/ Stannic Dioxide, ACS Appl. Mater. Interfaces, 2016, 8, 25667?25673. [3] A.M.Ganose and D.O.Scanlon, Band gap and work function tailoring of SnO2 for improved transparent conducting ability in photovoltaics, J. Mater. Chem. C, 2016, 4, 1467. [4] Z.W.Pan, Z. R.Dai, and Z. L.Wang, Lead oxide nanobelts and phase transformation induced by electron beam irradiation, Appl.Phys.Lett., 2002, 80, 309.

Resume : ?-Al2O3 specimens (144 ?m thick) by the heat treatment at 1400 °C of free-standing sulfuric acid anodic alumina were obtained. Scanning electron microscopy analysis shows that the as-anodized anodic alumina films possess well-ordered porous structure with the pore diameter of about 10.2 nm. After heat treatment at 1400 °C the samples lose their porous structure and certain crystallites with average size of 2?6 ?m can be observed. These crystallites can be visualized by fluorescence imaging. According to differential scanning calorimetry data accomplished by X-ray analysis, the first step of crystallization occurs at around 967 °C, producing ?-Al2O3. The second one takes place at around 1194 °C, which corresponds to the formation of ?-Al2O3. Both the as-anodized and 1400 °C-treated anodic alumina samples possess the fluorescence in the wavelength range 400 700 nm with maximum at around 450 nm.

Resume : The coupling of TiO2 with graphene can lead to enhanced electronic and photocatalytic properties of TiO2 because the graphene can lower the recombination of electron-hole pairs, enhancing the charge transfer rate of electrons and surface adsorption of target gaseous or organic pollutants. In this study, anatase TiO2-graphene oxide (GO) nanocomposites with different GO loadings were prepared by a solvothermal method. The prepared photocatalyst were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infra-red spectroscopy (FTIR), and photoluminescence spectroscopy (PL). The XRD results confirmed the anatase phase of TiO2 in the composites and Raman analysis revealed the presence of GO in the nanocomposites. TEM studies indicated the uniform dispersion of TiO2 NPs on the GO surface with slight aggregation. The photocatalytic performance of the prepared nanocomposites was evaluated by the degradation of gaseous benzene under UV light irradiation. Anatase TiO2-GO nanocomposites exhibits better photocatalytic performance than pure TiO2 nanoparticles (NPs). The apparent photocatalytic reaction rate constant of 0.25wt% GO-loaded TiO2 nanocomposites(GOT-0.25) is about 3 times higher than that of pure anatase TiO2 NPs. Especially, the GOT-0.25 exhibit high photocatalytic activity compared to anatase TiO2 under UV light, likely due to the effective separation of photogenerated charges. The anatase TiO2-GO nanocomposites facilitate the separation of photogenerated charge carriers along with high stability, which ultimately enhance the photocatalytic activity under ultraviolet irradiation.

Resume : Titanium dioxide is still a promising wide bandgap material for optical coating, gas sensors, optoelectronic and photo-electrochemical applications. TiO2-based photocatalysts have been interesting for their high solar-energy conversion efficiency. Higher efficiency of photo-activated processes is observed for crystalline TiO2 in the anatase phase, which is characterized by a wider band gap and reveals semiconducting properties. We present results for TiO2 films deposited on a (0001) sapphire substrate by reactive magnetron sputtering and atomic layer deposition (ALD). The films were doped with Nb or N to increase electrical conductivity. Pulse dc reactive co-sputtering was performed from Ti and Nb target in a O-Ar or O-N-Ar gas mixture, at total pressure of 0.004 mbar and at substrate temperature up to 600 C deg. ALD films were formed with TiCl4 and H2O precursors at 220 C deg. Highly oriented anatase (112) nanocrystalline TiO2 films were received by the sputtering method at temperature in range of 400 ? 600 C deg., while the ALD films apart from the anatase contain admixture of the rutile phase. Undoped and Nb doped TiO2 films are highly transparent (70-80 %). The bandgap of 3.79 eV for the sputtered TiO2 film increases to 3.87 eV for the TiO2?x:Nb film with a 19% at. Nb content, while the bandgap of 3.7 eV was observed for the ALD TiO2 film. Photoluminescence spectra of the TiO/2?x/:Nb films measured at 5K reveal UV emission peaks and a broad peak in range of 440 - 740 nm. The lowest resistivity of 70 m-ohm-cm was recorded for the TiO/2?x/ ALD film doped with 2 at.% of Nb. The work was partially supported by the European Regional Development Fund, through the Innovative Economy grant "MIME" (POIG.01.01.02-00-108/09).

Resume : ZnO doped with Rare Earth (RE) have been widely investigated because of possible application in optoelectronics. Ion implantation is a convenient technique for introducing RE ions into the material, because dopant concentration and its depth profile can be easily controlled. However, the ballistic nature of the implantation process leads to the damage of a crystal lattice, so a high temperature post-growth annealing is required for crystal structure recovery and activation of optical emission. Unfortunately, the side effect of a high-temperature annealing is displacement of RE ions from substitutional to interstitial sites and out-diffusion of RE to the surface, where they are no longer optically active. In the paper we present an attempt to overcome this problem by placing an additional ZnO cap layer at the top of implanted ZnO:Yb films. Epitaxial ZnO/GaN films were implanted with Yb ions to a fluence of 1x1015 and 3x1015 at/cm2. After implantation, a 30 nm thick cap ZnO films was grown by ALD prior to post-growth Rapid Thermal Annealing, which was performed at temperature 900 and 1000oC. We found out that for lower fluence an additional cap ZnO layer considerably enhances the photoluminescence intensity, especially in the visible spectral region. The work was supported by the Polish National Centre for Research and Development (NCBiR) through the project PBS2/A5/34/2013 and by the Helmholtz Zentrum Dresden-Rossendorf (HZDR) program Access to Infrastructure (15000594-ST).

Resume : The proton conducting membranes fuel cells for various applications, which employ polymer Nafion membranes, yield the best performance around 80oC. The operation of fuel cells at this temperature has a number of shortcomings which can be avoided by raising the temperature to 120°C and even higher. However, Nafion membranes experience a rapid drop in conductivity as temperature increases to above 100°C, and not suitable for high-temperature operation. There is, therefore, a demand for membranes which can operate in the temperature range up to 200°C. In this context, the improvement of the existing membranes are pursued, namely composite membranes consisting from Nafion, and inorganic nanoparticles are considered. In this study, we specifically focus on the effect of careful doped TiO2 nanoparticles on the performance of the Nafion/TiO2 composite membranes in high temperature. In the framework of the research by XPS, SEM, XRD, TPD-MS, optical and vibrational spectroscopy is investigated the properties of modified titanium oxide and composite polymer membranes. Effect of concentration of proton generation additions on the total and specific proton conductivity of composite polymer membranes depending on the concentration of proton-generating additives and relative humidity had been estimated. Established, that modified titanium oxide nanostructures have an enhanced capacity for coordination of water molecules on the surface, causing the formation of the grid of hydrated structures with labile protons that maintenance of structures percolation cluster hydrophilic channels in membranes. The conductivity of the Nafion/TiO2 composite ?an is a consequence the formation of a percolation cluster, as result of mesoscopic ordering and polarization of water molecules on the strong acid groups of doped titanium dioxide species to form hydrated. Preliminary tests of proton conductivity (the direct injection of protons) that was carried out on the composite membrane, has highlighted the benefit of doped titania nanocomposites introduction on the conductivity in the temperature range up to 240° C, that maintained at (10-3-10-5 S), compared to the commercial Nafion membrane.The above may be a prerequisite for effective function of composite polymer membrane in conditions close to the operating conditions of fuel cells.

Resume : Facile growth of ZnO films: the effect of La doping S.Aydogan1* and M. Yilmaz1,2, 1Advanced Materials Research Laboratory, Department of Nanoscience and Nanoengineering, Graduate School of Natural and Applied Sciences, Ataturk University, 25240, Erzurum, Turkey 2 Department of Science Teaching, Faculty of K.K. Education, Atatürk University, 25240 Erzurum, Turkey *Physics Department, Science Faculty, Ataturk University, 25240, Erzurum, Turkey *Environment Department, Engineering Faculty, Ardahan University, 75000, Ardahan, Turkey *saydogan@atauni.edu.tr Generally, indium (In) doped tin oxide (ITO) is widely used in optoelectronic applications where a transparent conductor is required. Due to the fact that the main constituent of ITO is In, which has been listed among the critical raw materials by the EU, it has been become compulsory to search for alternative materials instead of ITO. However, some problems such as poor stability, difficulty of preparation and limited natural reserves of In, restrict its utilization for device applications. At present, metallic films and metallic oxide films are mainly used as transparent conductive oxides (TCO). Among them, ZnO takes an important role as TCO because of its excellent photoelectric, piezoelectric, dielectric properties and easy dope characteristic. In this context, we can say that characteristic properties of ZnO can be easily changed by using different dopant. The difference between ionic radius of zinc or oxygen and dopant materials affects the characteristics of ZnO. In this study, La-doped ZnO films were prepared via chemical spray pyrolysis technique and its device performances were investigated as a function of La content.

Resume : Anodic aluminum oxide (AAO) template has gained increasing importance in recent years due to its potential industrial and technological applications for nanometric device fabrication incorporating electrodeposition, such as nanorods, nanotubes and nanowires [1]. In this study AAO membrane on the surface of aluminum alloy (AA 1050) sheet was fabricated in sulfuric acid solution using a two-step anodization process [2]. Cross-sectional and top-view SEM images showed that obtained pores are straight and extend throughout the entire thickness of the oxide (~ 6 µm). The diameter of the nanowires was measured to be about 25 nm and the porosity of self-ordered anodic alumina - around 20 %. The porous alumina is separated from the Al alloy by thick nonoporous barrier layer (~ 26 nm). In order to improve the conductivity for electrodeposition process, barrier oxide layer has been thinned up to ~ 10 nm after the treatment in the same solution as for anodization at 30 °C under potentiostatic conditions (E = -1 V). Electrodeposition of Co-7 at.% W nanowires has been carried out with a pulse mode in a solution of 120 g/l CoSO4, 60 g/l CoCl2, 30 g/l boric acid and 2 g/l polyethylene glycol 600 (pH 5, 22°C). The pulse mode consisted of a constant current pulses of - 60 mA/cm2 and 0.3 mA/cm2 for 1 ms and 4 ms, respectively. Fabricated nanowires were uniform, independent, parallel to each other and their density was close to the pores density of the original AAO. Heat treatment has been used to obtain highly active cobalt oxide catalysts (CoO and Co3O4) and catalytic performance of fabricated nanowires into AAO has been performed. [1] N. Tsyntsaru et al., Electrochimica Acta 188 (2016) 589?601.

Resume : Titanium dioxide is one of the metal oxides used in gas sensors because of significant changes in the electrical properties of TiO2 as a result of interaction with both reducing and oxidizing gases. PVD methods are most widespread in the thin films preparing, however Langmuir ? Blodgett (LB) is emerging technique [1] which allows to obtain TiO2 ultra-thin films at room temperature. This method is successfully used for the preparation of organic monolayers [2], as well as for other metal oxides, e.g. SnO2 [3]. TiO2 thin films were obtained using Langmuir KSV NIMA trough. TiO2 solutions were prepared using powders (rutile, anatase) and liquid precursor TTIP (titanium tetraisopropoxide). A mixture of chloroform and ethanol was used as a solvent for TiO2 powders (suspension with concentration c = 0.5 mg/ml) and chloroform for TTIP (clear solution, c = 0.48 mg/ml). TiO2 thin films were deposed on amorphous silica - SiO2, Al2O3 ? ceramic, specially dedicated to sensor measurements BVT substrates. UV-VIS spectroscopy, XPS and XRD methods showed the presence of TiO2 on the coated surface. Optical profilometry revealed the thickness of TiO2 films was equal to about 60 nm. Moreover, for powder sources local grain deposition was found. A homogeneous monolayer was observed for the TTIP precursor, however the films might be discontinuous. Sample response to NO2 and H2S gases at 50°C revealed acceptable sensitivity and reproducibility. This work was supported by AGH University of Science and Technology Dean?s Grant no. 15.11.230.334. [1] K. Choudhary et al., Langmuir, 31, 1385-1392, (2015) [2] A. Tepore et al., Langmuir, 17, 8139-8144, (2001) [3] S. Choudhary et al., Applied Physics Letters, 89, 071914 (2006)

Resume : Graphene-based materials (GRMs) possess a range of different chemical, electronic and electrical behaviors [1, 2, 3]. The control and tuning of their chemical composition is one of the keys for the success of such materials in industrial applications. Despite X-ray Photoemission Spectroscopy (XPS) being one of the most powerful and commonly used techniques to study the chemical analysis of surfaces [4] a quantitative and reliable approach to study GRM is still lacking. For example, there is no standard method for estimating the degree of oxidation of GRM (O/C or C/O ratios). The ratio of the number of carbon and oxygen atoms in bulk materials is often simply given by the intensity ratio of the O 1s and C 1s XPS peaks. This approach can be applied to thin films (< 5 nm thick), with single- or several- layers deposited on oxygen-free substrates, in order to prevent any overestimation of the oxygen present in the sample. Moreover, there are various approaches used for deconvoluting the complex structure of the C 1s spectrum leading to large variations in the estimation of the various carbon oxidation states present in the sample even by factors of 2 or 3 times the measured value [5]. Here, we propose a more reliable protocol to obtain the O/C ratio to determine the chemical functionalization of GRMs using a quantitative line-shape analysis of the C 1s peak based on the Doniach?Sunjic equation and XPS measurements on freshly cleaved Highly Oriented Pyrolitic Graphite. In this way, we can attempt to distinguish the various contributions from: graphitic carbon (sp2), defects (mainly sp3), hydroxyl-, epoxy-, carbonyl- and carboxyl- groups [4]. The proposed protocol was applied to several GRMs with different O/C ratios (between 0.02 and 0.45) and different thicknesses (from 1 to 30 nm) in order to avoid substrate contributions and to check the results with measurements on the corresponding bulk systems. In particular, we have developed a simple method for comparing the results obtained using different models which can discriminate between both under- and over-estimations of the degree of oxidation of GRMs. This approach holds promise for developing a simple general protocol to analyse GRMs on various substrates. [1] William S. Hummers and Richard E. Offeman, JACS 80, 1339 (1958) [2] M. Batzill, Surface Science Reports 67, 83 (2012) [3] Z.Y. Xia et al., Chempluschem 79, 439 (2014) [4] F. Perrozzi et al., Journal of Physical Chemistry C 117, 620 (2013) [5] J.A. Leiroet al., Journal of Electron Spectroscopy and Related Phenomena 128, 205 (2003)

Resume : In recent years, molybdenum oxide (MoOx) thin ?lms are of considerable interest in variety of technological applications as solar cell, gas and chemical sensors. Depending on the oxygen contribution, there are two main principal oxide phases in MoOx structure as to be molybdenum dioxide (MoO2) and molybdenum trioxide (MoO3). Additional phases can also be formed according to the Mo-O phase diagram, however they are expected to be in non-stoichiometric and more complex structural characteristics. In the case of MoO3, it has been reported in a transparent and insulating, layered material with an orthorhombic structure and the electrical resistivities of MoO3 is predicted to be in the interval of 1010 to 1011 ?.cm. Among the MoO3 integrated devices, a complete understanding of the material characterization of MoOx ?lms and its correlation to the tuning electronic and opto-electronic properties have been point of interest for improving their use in device applications. Therefore, in this work, transparent and conductive MoO3 thin film samples were deposited on the ultrasonically cleaned soda lime glass substrates by dc sputtering technique. The effect of sputtering power on their structural, electrical, and optical properties was systematically analyzed. The structure of the films was investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) detector facility. The optical properties of the ?lms are assessed through optical transition and band gap analyses. Moreover, the complementary characterization of the films was concentrated on temperature dependent conductivity for electrical analyses.

Resume : With the age of fossil fuels moving towards its brink of exhaustion, the ever-rising global energy demand will be turning towards renewable resources. For the successful development of solar energy production, discovery and utilization of semiconductor materials with advantageous chemical and physical properties is crucial. Photoelectrochemical water splitting devices have been envisioned as a significant part of sustainable energy sources since the process was demonstrated for the first time1. Metal oxide semiconductors are seen as potential candidates for the role of photoanodes due to their stability during the application in oxidative environments. Binary metal oxides such as TiO2, ZnO, and WO3 suffer from high bandgap that lowers their photoconversion ability. Hence, the scientific community is focusing on developing complex metal oxides, which might exhibit lower band gaps and desirable band alignment for the water splitting reaction. One of the very recently suggested candidates for this application is the class of copper vanadates2. The seeded growth approach to produce complex metal oxide (Sb-BiVo4) thin films, starting from monodisperse metal seeds, has been successfully applied earlier in our group3 . In the current work, we synthesise monodisperse copper nanoparticles of 6, 15 and 40 nm using the colloidal synthesis approach. Vanadium acetylacetonate is used as a precursor for the second cation, which during the annealing process reacts with the nanoparticles to form copper vanadate. This approach has the advantage of growing the crystals at much lower temperatures (350℃, 2h) in comparison to the conventional methods (550 ℃, 10h)2. At such low temperatures the reaction becomes kinetically controlled, and allows one to overcome the thermodynamic limitations. Thus, by varying the time of annealing, quenching the oxygen supply for the reaction and controlling the seed size, it is possible to selectively grow Cu3VO4, Cu2V2O7 and Cu3V2O8 phases. From literature, it is known that Cu3VO4 is a p type semiconductor4, whereas Cu2V2O7 is a n type semiconductor5. We have shown that, when exposed to the same annealing process, 6 nm Cu seeds form Cu2V2O7 (n type) while, 40 nm Cu seeds form Cu3VO4 (p type). We hypothesise that this result is due to the different reactivity of copper for different seed sizes and further research is underway to support this claim. This result illustrates the unique ability to target the final crystalline phase of materials with complex phase diagrams by fine-tuning the seed size through colloidal synthesis, an approach not explored before. (1) Fujishima, A.; Honda, K. Nature 1972, 238 (5385), 37–38. (2) Zhou, L.; Yan, Q.; Shinde, A.; Guevarra, D.; Newhouse, P. F.; Becerra-Stasiewicz, N.; Chatman, S. M.; Haber, J. A.; Neaton, J. B.; Gregoire, J. M. Adv. Energy Mater. 2015, 5 (22), 1500968. (3) Loiudice, A.; Ma, J.; Drisdell, W. S.; Mattox, T. M.; Cooper, J. K.; Thao, T.; Giannini, C.; Yano, J.; Wang, L.-W.; Sharp, I. D.; Buonsanti, R. Adv. Mater. 2015, 27 (42), 6733–6740. (4) Sahoo, P. P.; Zoellner, B.; Maggard, P. A. J. Mater. Chem. A 2015, 3 (8), 4501–4509. (5) Guo, W.; Chemelewski, W. D.; Mabayoje, O.; Xiao, P.; Zhang, Y.; Mullins, C. B. J. Phys. Chem. C 2015, 119 (49), 27220–27227.

Resume : Chromia, α - Cr2O3, is a corundum-type crystal (crystalline form of α - Al2O3) with alternating oxygen layers and chromium bilayers along the c-axis of the hexagonal lattice. Bulk Cr2O3 present antiferromagnetic properties (TN = 307 K), exhibiting uniaxial magnetic anisotropy along [111]. These magnetic properties make Cr2O3 suitable for spintronic applications. However, complex oxides grown as thin film can result in a modification of their intrinsic properties, and therefore, it is crucial to fully understand structural, magnetic or electronic modifications of the thin films in comparison with the bulk. We have grown, for the first time, crystalline α-Cr2O3 thin films onto SrTiO3(111) substrates by PLD, as well as satisfactory, on Al2O3, due to their similar lattice parameters. The crystallographic properties of the grown films have been studied using synchrotron based GIXRD and XRR. A novel study of the coupling of the Cr2O3 lattice in both substrates has been fulfilled, revealing, for the Cr2O3/SrTiO3(111) thin films, an in-plane rotation of 30° of the layer respect to the underlying substrate. However, Cr2O3/Al2O3 are epitactical. These different orientations could result in divergent magnetic properties. Both samples present a sharp buried interface, with layers 16 nm thick. The film surfaces, investigated by AFM, show good homogeneity and low roughness. EXAFS and XANES measurements have been also performed to study the local coordination environment of Cr and O atoms.

Resume : Recently, dopant free silicon solar cells (Si SCs) based on metal oxide hole and electron transport heterocontacts have demonstrated itself as an alternative cost effective approach to the state-of-the-art high efficiency Si SCs. In contrast to the standard Si heterojunction design, rather than n- and p-type doped a-Si:H thin layers, carrier selective metal oxide materials with extreme work function (?) values are chosen to achieve carrier selectivity in dopant-free cell design. When a material with a very high ? is brought in contact to a lightly-doped Si, accumulation of holes (and repulsion of electrons) occurs near the surface. The corollary holds for electrons when a very low work function material is in touch with Si. In this manner, by placing materials with an extreme ? difference on either side of a Si, efficient separation of photogenerated carriers can be achieved. Therefore, ? and resulting band alignment of the carrier-selective materials play a crucial role in achieving high efficiency dopant free Si SCs. In this work, we measured ?, valance band maximum value (VBM) and band gap (Eg) of molybdenum oxide (MoOx), zinc oxide (ZnOx) and Si, and constructed the band alignment of MoOx/Si and ZnO/Si interfaces. While XPS was employed to measure the stoichiometry of materials, UPS measurements were carried to determine ? and VBM values. The band gap of the materials were calculated using Tauc plot constructed using the optical transmission and reflection spectra. A monochromatic Al K? line at 1486.6 eV and He-I line at 21.22 eV were used as light sources in XPS and UPS, respectively. MoOx (200 nm) and ZnOx (150 nm) films were deposited on cleaned Si wafers by thermal evaporation using MoO3 powders and by RF magnetron sputtering using a power of 300 W and an Ar flow rate of 20 sccm, respectively. XPS and UPS measurements were performed following a low energy (100 eV) Ar ion treatment for 5 min. To achieve high efficient dopant free Si SCs, on one hand, we need near-stoichiometric compositions to effectively passivate the defects on Si surface. On the other hand, sub-stoichiometric oxides allows higher conductivity required to transport charge carriers. In this study, stoichiometry values of ZnO0.96 and MoO2.56 were determined by XPS analysis. The measured band gap values (E_(g,?ZnO?_0.96 )=3.2 eV, E_(g,?MoO?_2.56 )=3.3 eV) are consistent with the measured stoichiometry values and the literature. Based on UPS analysis, we found that ?_(ZnO_0.96 ) and ?_(MoO_2.56 ) are equal to 3.99 eV and 4.92 eV, respectively. Additionally, we obtained the electron affinity values of both materials as ?_(?ZnO?_0.96 ) =3.77 eV and ?_(?MoO?_2.56 )=4.92 eV. It is obvious from the values that both ZnO0.96 and MoO2.56 are degenerately-doped n-type materials. Superior alignment of ZnO0.96 and Si conduction bands and that of MoO2.56 conduction band with Si valence band reveal that ZnO0.96 and MoO2.56 can be used in dopant free Si SCs. Further optimization of band alignment of electron and hole transport layers with Si will allow high efficient dopant free Si SCs.

Resume : Solar energy technologies represent a unique opportunity to overcome issues related to the use of fossil fuels and the corresponding environmental pollution. In this regard, great efforts are being devoted to the study of sustainable energy alternatives with reduced ecological footprint. In particular, solar-driven hydrogen generation from water solutions by photo-activated processes has received a great attention as an amenable route to convert sunlight into storable chemical energy. In this scenario, the design of suitable supported photocatalysts with tailored structure, morphology and composition, is of key importance for H2 production. Fe2O3 represents an interesting option as photocatalyst thanks to its favourable chemico-physical properties. In particular, Fe2O3 nanosystems are very promising for the possibility of obtaining a minimized carrier-transport distance and a high surface area resulting in a recombination losses decrease. This contribution will provide a survey of our recent research activities on photo-activated H2 production promoted by supported Fe2O3-based nanosystems: i) anion-doped alpha-Fe2O3, the most thermodynamically stable polymorph; ii) beta- and epsilon-Fe2O3, two scarcely investigated phases, adopted for the first time in the target application; iii) Fe2O3/TiO2 nano-heterostructures, eventually functionalized with Au nanoparticles. The role of the interplay between synthesis parameters and the resulting systems functional properties will be also analyzed.

Resume : Advances in science and technology have had a strong impact on the development of modern society. Among others, issues of high societal relevance are renewable ?green? energy conversion, energy storage, health/medicine, and information and communication technology, where ever-growing demands for improving efficiency, lowering power consumption, saving costs by avoiding precious/expensive materials, and making systems/devices smaller and smarter need to be met. New materials and devices are constantly being developed to meet these challenges. At the root of these material and device developments, across disciplines in physics, chemistry and engineering, are effects strongly related to and based on electrochemical fundamentals and processes. In the meantime, the advances in nanoscale materials and devices, along with new measurement and characterization techniques, have significantly advanced our understanding of electrochemical processes. Nanoscale materials with a broad variety of forms and properties have been developed ? nanoparticles, nm thick films or film stacks, nanotubes, embedded (nano)structured materials, etc. Some of them are reaching even atomic dimensions, in the case of 2D materials and atomic switches. At such scales the properties of matter can significantly deviate from those of their macroscopic descriptions. In addition to well-known size effects such as energy quantization, conductance quantization and Coulomb blockades, additional phenomena arise from the different thermodynamic and kinetic factors of nanosized systems. For example, for nanoscale systems space-charge regions can become larger than the electrolyte thickness, inducing fully depleted or fully enriched regions. Additionally, lattice misfit and specific surface termination occurring at interfaces can induce 2D electron gas phenomena. These material and technology advances in turn pose opportunities and challenges for the understanding and control of the physical and physicochemical processes of matter at the atomic and mesoscopic levels. In this contribution, the fundamentals of nanoscale electrochemistry with insulators will be discussed. Experimental results and discussion on interface interactions, charge transfer processes and ion transport in nano-scaled electrochemical systems using SiO2 and Ta2O5 as ion transporting solid (solid electrolyte) will be shown. The structure and reactivity of the interfaces appear to be of crucial importance for reproducible and reliable experiments. We demonstrate that both potentiodynamic and steady state measurements can be used to determine reaction kinetics parameters. The influence of the counter charge/electrode reaction and its influence on the overall cell behavior will be emphasized as well as the role of the electrocatalytic activity of the electrodes. The dynamics of electrochemical processes in/within insulators will be shown and the activity and mobility of different cations such as Ag, Cu, Ta, Ti etc. as well as noble metals e.g. Pt and Pd will be demonstrated. Our results highlight electrochemical systems in a qualitatively different way, showing deviations in thermodynamics and kinetics at the nanoscale.

Resume : One-dimensional TiO2 nanotubes (NTs) by electrochemical anodization are currently used in a wide range of energy-related and bio-applications. 1D TiO2 NTs are typically grown on a Ti foil and, if separated from the metallic substrate, can form both-side-open NT membranes that provide an ideal geometric arrangement for e.g. flow-through applications. However, NT membranes usually suffer from poor mechanical stability and, when annealed, feature voids or other morphological defects that have so far hindered any potential development of functional NT membrane devices. We report the fabrication of robust, free-standing and crystalline TiO2 NT membranes, achieved by producing nanotube layers in the presence of lactic acid electrolyte, followed by chemical etching for tube detachment from the Ti substrate. This type of NT membrane features no morphological damage over their entire surface area and thickness, and withstands annealing treatment up to ~ 1000°C without curling or cracking and, most remarkably, maintaining a full anatase phase composition. We demonstrate that the high crystallinity and pure anatase phase composition of these layers, combined with their robustness, are keys for their use in a flow-through photoreactor for the degradation of Acid Orange 7 (AO7). By combining the permeability characteristics of a defect-free tube membrane with the desired photocatalytic activity of crystalline TiO2, we could achieve and control AO7 diffusion through the tubes along with its photocatalytic degradation.

Resume : ‘Black’ TiO2 – in the widest sense TiO2 reduced by various treatments – has gained in recent years tremendous scientific interest because of some outstanding properties; including a strong visible light absorption (the blacker, the better). We show that high pressure hydrogenated TiO2 in the form of nanotubes and powder shows another key feature, that is, a strongly enhanced photocatalytic activity for hydrogen production in absence of any noble metal cocatalyst. The work shows that the proper high pressure hydrogenation on TiO2 can provide a cocatalytic center, similar in its effect to noble metal decoration. This catalytic center is proposed to involve an unusually stable Ti3+ species with characteristic EPR and PL features. The intrinsic activity for photocatalytic hydrogen evolution is not coupled with the visible light absorption behavior, but it rather must be ascribed to an optimized and specific defect-center. It is found that a highest photocatalytic activity from an optimized hydrogen treatment that leads to ‘grey’ anatase; we discuss structure, morphology, composition, and defect structure of this noble metal free modification of a H2 evolution TiO2-photocatalyst.

Resume : Thin films of MgO are of interest for both spin-electronics and CMOS type of devices, due to its spin-filtering property, high dielectric constant and large band gap. This work demonstrates feasibility of single crystal growth of polar MgO(111) at low temperatures on 6h-SiC, despite a lattice mismatch of 3 %. The films have been analysed using in situ electron diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and electrical measurements. From these experimental techniques, we have observed epitaxial growth of MgO on Si- and C- terminated 6h-SiC surfaces and determined the valence and conduction band offsets for the MgO/6H-SiC hetero-interface. In addition we demonstrate the film surface morphology control between faceted (100) and atomically flat (111) type of surfaces as a function of oxygen plasma pressure and film deposition rate.

Resume : Solid solutions of ZnO with MgO for Mg content above 45% have a tendency to segregate to hexagonal and cubic crystal phases. In ZnO/MgO superlattices (SL) it is possible to manipulate with layer thicknesses to avoid metastability and to get the whole superlattice in the wurtzite structure while preserving the wide band gap of alloy. Short period ZnO/MgO SLs with pair thicknesses on the order of few lattice constants can also be treated as ordered alloys. In this work we attempt to realize ZnO/MgO superlattices with the thickness of ZnO and MgO layers on the order of 0.5-2 nm. The number of ZnO/MgO pairs was 50-80. SLs were deposited on c- and a-oriented bulk ZnO substrates. The existence of local SLs and their thicknesses have been confirmed by Transmission Electron Microscope imaging. Two dominant emission bands were observed in photoluminescence (PL) of all the SLs which behaved differently with temperature. In the PL spectra of SLs deposited on c-ZnO we observed a PL band typical for random ZnMgO alloys and also a lower energy band revealing anomalously large red-shift of 160 meV between 10K and 180K. In the case of SLs grown on m-ZnO polarization studies of the PL were also performed. It was found that the degree of polarization of these two PL bands differs. We interpret the PL spectra of the SLs in terms of recombination of excitons in ordered and disordered regions of ZnO/MgO structures. The research was supported by the NCN project DEC-2014/15/B/ST3/04105.

Resume : The field of electronic unipolar devices, including THz QCLs and HEMTs, remains wide open for ZnO/MgxZn1-xO heterostructures. However, they require a high control of the heterointerfaces as well as an accurate knowledge of their electrical and transport characteristics. Depending on the application, large Mg contents as well as high n-type dopings have to be achieved, which will directly impact some of the key material parameters, such as effective mass (meff), carrier concentration or mobility. We combine IR reflectance spectroscopy, UV absorption spectroscopy, Hall Effect, and Capacitance-Voltage profiling, to fully characterize a series of non-polar m-plane MgxZn1-xO layers grown by MBE on m-sapphire with varying Mg concentrations (0 % to 50 %) and Ga dopings (undoped to above 10E19 cm-3). We obtain the plasma frequency from fitting the reflectance spectra with a dielectric function model built with a Drude term for free electrons and Gervais oscillators for the phonon modes. The plasma frequency, along with the electron density and mobility extracted from Hall effect, are used to deduce meff. The incorporation of Mg in the structure is assessed by measuring the optical absorption band edge of the structures. Thus, we establish a correlation between Mg/Ga incorporation, meff and measured electron density and mobility for the same doping level. This project has received funding from EU Horizon 2020 research and innovation programme under grant No 665107 (project ZOTERAC).

Resume : Multiferroic magnetoelectric heterostructures are an intriguing candidate for the next generation data storage devices, where their unique properties can be utilized to control a single magnetic bit using electric fields. The understanding of the coupling between the magnetic and electric properties in these materials is paramount. We report here on one of the highest values of the magnetoelectric voltage coefficient published so far. It reaches its maximum of 60.2 V / (cm Oe) at 300 K, for a BaTiO3 ? BiFeO3 superlattice with a BaTiO3 thickness of 10 nm and a BiFeO3 thickness of 5 nm. We have studied the origin of the increased magnetoelectric coupling in BaTiO3 ? BiFeO3 superlattices, using SQUID magnetometry, conversion electron Mößbauer spectroscopy and magnetoelectric voltage measurements and found that the magnetoelectric coupling can be tuned by varying the BiFeO3 layer thickness. The temperature dependencies of the magnetoelectric voltage coefficient lead us to the conclusion that the main mechanism responsible for the magnetoelectric coupling at 300 K is dominated by charge transfer for the sample with a BiFeO3 layer thickness of 50 nm. With decreasing BiFeO3 thickness the main coupling mechanism is dominated more and more by strain. Furthermore we established a correlation between the hyperfine field, magnetoelectric voltage coefficient and the magnetization.

Resume : p-CuSCN/n-Fe2O3 heterojunctions were electrochemically prepared by sequentially depositing ?-Fe2O3 and CuSCN films on FTO substrates. ?-Fe2O3 and CuSCN films and ?-Fe2O3/CuSCN heterojunctions were characterized by Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDX), and X-Ray Diffraction (XRD) measurements. Pure crystalline CuSCN films were electrochemically deposited on ?-Fe2O3 films by fixing the SCN/Cu molar ratio in the electrolytic bath to 1:1.5 at 60 °C and a potential of -0.4 V. The photocurrent measurements showed an increase of the intrinsic surface states or defects at the ?-Fe2O3/CuSCN interface. The photoelectrochemical performance of the ?-Fe2O3/CuSCN heterojunction was examined by chronoamperometry and linear sweep voltammetry techniques. It was found that the ?-Fe2O3/CuSCN structure exhibits a higher photoelectrochemical activity when compared to ?-Fe2O3 thin films. The highest photocurrent density was obtained for ?-Fe2O3/CuSCN films in 1 M NaOH electrolyte. This high photoactivity was attributed to the high active surface area and to the external applied bias favoring the transfer and separation of photogenerated charge carriers in ?-Fe2O3/CuSCN heterojunction devices. The flat band potential and the donor density were found to be maximal for heterojunction sample. These results suggest a substantial potential for applying heterojunction thin films in photoelectrochemical water splitting applications.

Resume : Spintronic offers a new range of possibilities for new semiconductor-based data processing and memory applications. The successful application of this technology relies on the efficiency injection of spin-polarized electrons into a semiconductor host material, which is directly related with the quality of the engineered heterostructures. The presence of non-stoichiometry phases and the formation of structural defects, especially at the interfaces can be detrimental for the functional properties of the system. Within this context, we have successfully prepared epitaxial Fe3O4/SrTiO3/Si heterostructures. SrTiO3 ultrathin films were evaporated on Si (001) by MBE while Fe3O4 films were subsequently deposited by PLD. Both layers shows fully relaxed character. The SrTiO3 films grow with its axis rotated 45 degrees respect to those of the Si meanwhile Fe3O4 films grow with a (100) orientation on SrTiO3 axis. A complete structural and electronic characterization of the SrTiO3 tunnel barrier and Fe3O4 electrode was performed by Reflected High-Energy Electron Diffraction (RHEED), X-Ray photoelectron spectroscopy (XPS) and Synchrotron Radiation X-Ray Diffraction and Reflectivity (SR-XRD/XRR). A discussion of the tunnel barrier stability versus Fe3O4 film quality as a function of the evaporation conditions will be presented.

Resume : The work presents both review and original data about modern state of art concerning structure, physical properties, applications and prospects of some polymer based composites incorporated with micro/nanosized particles of various oxide compounds. The results of synthesis, structure, morphology and spectroscopic study of the luminescent oxides like to doped with RE ions simple MI/MII oxides and complex oxide containing various metal cations (MI ? MIV; Na, Ca, Bi, Zr, e.g.) and molecular anions (B = phosphate, molybdate, tungstate, etc) were described. These materials can be useful in creation of new optoelectronics devices (WLED, phosphor converting layeres for solar elements covering, biomarkers, etc). Great attention was paid to the study of composite materials where micro/nanocellulse is a matrix or alternatively component of the composites. Cellulose comprising composites have strong promise due to their light weight, high tensile strength and modulus, and comparably low cost. Microcrystalline cellulose is pure partially depolymerized cellulose synthesized from ?-cellulose precursor Three sets of the samples, that are ?MNC-oxides?, ?polyethylene-oxides? and ?polyethylene-MNC? micro/nanocomposites were prepared and studied. There mechanical and thermal properties, (humidity and humidity sorption capacity, porosity, density, compressibility index, particles size, crystallinity index) were measured as they are important to qualify the suitability of such materials as valuable additives in pharmaceutical, food, cosmetic, etc. Dielectric and optical characteristics, and luminescence is among them, were studied as well as they show perceptiveness of such materials to be used in hi-tech devices. Obtained results were analyzed and discussed.

Resume : The scientific community accepted 2015 as the International Year of Light and Light-based Technologies due to the thrust of luminescent materials in every part of the human expansion. The light-based technologies have transformed into various sectors of science and technology to a larger size. Notable research activities have been targeted to find cost-effective, environment-friendly, better performance, and energy-efficient phosphor materials for the application in the solid-state lighting devices. The urge of luminescent materials with better optical and photoluminescence characteristics in a large number of areas has shared the research endeavors in this field intended to improve the material properties. In the past decades, much research interest has been focused on phosphors based on various inorganic and organic materials owing to their extensive applications in light-emitting diodes, cathode ray tubes, scintillation detectors and biological technologies. The phosphors based on various inorganic and organic materials are highly conductive to release electric charges stored on the surface and as a result, they have emerged as potential candidates for use in field emission display and plasma display panel devices. It is well known that rare earth (RE) ions doped phosphor materials have been treated as efficient candidates for generating various emission wavelengths which have many applications in solid state lighting, display devices etc. The emission of RE-doped phosphor at the particular wavelength range is because of the superb luminescence characteristics of the RE ions. This talk will cover the broad aspects of RE-doped oxide materials for tunable color emissions. Much of the material is drawn from the personal experience in synthesizing, characterizing and applying them for solid state lighting.

Resume : Processing and characterization of lead-free ceramics on the base of sodium-bismuth titanate and sodium-potassium niobate E.D. Politova1, D.A. Belkova2, D.A. Strebkov2, N.V. Golubko1, A.V. Mosunov1, N.V. Sadovskaya1, G.M. Kaleva1, S. Yu. Stefanovich1,2, P.K. Panda3 1L.Ya.Karpov Institute of Physical Chemistry; Vorontsovo pole, 10, Moscow, Russia, 105064 2Lomonosov Moscow State University; Leninskie gory, 1, Moscow, Russia, 119992 3National Aerospace Laboratories, Kodihalli, Bangalore-560017 India E-mail: politova@cc.nifhi.ac.ru Lead-free piezoelectric materials are among the most intensively studied in order to replace widely used Pb-based ones. In this work, effects of modification of compositions by various donor and acceptor dopants in the A- and B-sites of perovskite lattice and influence of nonstoichiometry on structure, dielectric and ferroelectric properties of ceramics from Morphotropic Phase Boundaries (MPB) in the (K0.5Na0.5)NbO3 (KNN), (Na0.5Bi0.5)TiO3 (NBT) and (Na1/2Bi1/2)TiO3 - BaTiO3 (NBT-BT) systems have been studied. Ceramic samples were prepared by the two-step solid-state reaction method at high temperatures of 970 ? 1470 K. The samples were characterized using the X-ray Diffraction, Differential Thermal Analysis, Scanning Electron Microscopy, Second Harmonic Generation (SHG), and Dielectric Spectroscopy methods. Depending on the cation ionic radii changes in the unit cell volume of the KNN- and NBT-based ceramics were observed. Ferroelectric phase transitions marked by steps at ~ 350 - 400 K (NBT) and by peaks at ~ 550 K (NBT) and at ~700 K (KNN) were revealed in the dielectric permittivity versus temperature curves of the compositions studied. Ferroelectric phase transitions near 350-400 K revealed typical relaxor-type behavior attributed to the presence of polar nanoregions in a nonpolar matrix. Increase in the spontaneous polarization value was proved for modified ceramics using the SHG method. At the room temperature, non monotonous changes of the dielectric parameters ?rt and tan?rt were observed in modified BNT- and KNN-based compositions, thus confirming prospects of new lead-free materials development. Acknowledgment. The work was supported by the Russian Foundation for Basic Research (Project 16-16-53-48009).

Resume : Transition-metal oxides exhibit a wide range of technically important electronic properties which include magnetic, dielectric, ferroelectric, catalytic, superconductive, redox, thermoelectric, and multiferroic properties, insulator?metal transitions, and mixed electronic/oxide ion conduction. [1] The list of properties is valid also for late transition metals of the 1st row (Fe, Co, Ni, Cu) and these interesting properties can be utilized in many micro- and nanodevices. The catalytic properties of the metal oxides have recently been widely studied in visible light photo- or electrocatalysis to destroy organic pollutants or water splitting. Common feature of transition metals is their ability to exist on different oxidation states and the properties of the oxides may accordingly vary significantly. The electronic properties (band gap) of transition metal oxides can be controlled by the size and dimension making the nanostructures very interesting. [2] In many of the applications the oxides are employed as thin films or nanoparticles. Often also ultrathin or conformal films are looked for and then ALD deposition technology is desired. ALD processes for iron, cobalt, nickel and iron are presented. Volatile metal compounds are typically cyclopentadienyls, ?-diketonates, carboxlates or aminoalkoxides. Oxygen precursor is very important in controlling the stoichiometry. Typically ozone is producing the higher oxidation state oxide while in water processes the low oxidation state or mixed oxidation state oxides are formed. Temperature is another important parameter in oxidation state control and at higher temperatures the oxygen metal ratio tends to decrease. In the presentation besides the ALD processes selected properties of the transition metal oxides will be discussed. Special attention will be given for the photocatalytic properties. [1] J.B. Goodenough, Chem. Mater 26 (2014) 820. [2] T. Guo, M.-S. Yao, Y.-H. Lin, C.-W. Nan, CrystEngComm 17 (2015) 3551.

Resume : Highly Ga-doped ZnO (GaZnO) nanoneedles (NNs) are formed based on the vapor-liquid-solid (VLS) growth mode by using Ag nanoparticles (NPs) as growth catalyst. During the growth of such NNs, a GaZnO thin film is simultaneously deposited through the vapor-solid (VS) growth mode, i.e., without using a catalyst. The polarities of such GaZnO thin films and NNs are analyzed with the annular bright field imaging technique in aberration corrected STEM observation. It is found that the polarity of a GaZnO thin film depends on that of the growth template. More specifically, the growth of a GaZnO thin film on Ga-face GaN or Si-face SiC (N-face GaN or C-face SiC) leads to a Zn-polar (O-polar) structure. However, the polarities of all the GaZnO NNs grown on Ga-face GaN, N-face GaN, Si-face SiC, and C-face SiC templates are Zn-polar. In other words, the VLS growth always results in Zn-polar GaZnO and the VS growth leads to the GaZnO polarity the same as that of the template. These different polarity results are caused by the different channels of metal and oxygen incorporations in the VLS process. From our EDX analysis, we can observe residual Ga and Zn atoms in the top Ag NP of a GaZnO NN, confirming that the metal atoms are adsorbed by the catalytic Ag NP during the VLS process. However, the oxygen atoms can incorporate from the VLS three-phase junction into the liquid-solid interface. Therefore, the first atomic layer in the precipitated GaZnO is oxygen, leading to Zn-polar polarity.

Resume : ZnO, a wide bandgap II-VI semiconductor (Eg = 3.4 eV) with a large exciton binding energy (60 meV), is widely studied for optical and electronic applications. ZnO can be grown from solutions by several techniques such as hydrothermal deposition, chemical bath deposition and electrochemical deposition (ECD). Electrochemical deposition is of utmost interest for integration of the films in optoelectronic devices since they are low-temperature and low-cost methods which can be scaled-up for film preparation on large surface area substrates. Moreover, due to the electron exchange process at the origin of the oxide deposition, a good electrical continuity is insured between the substrate and the oxide layer.[1] We will describe the technique of electrochemical deposition of ZnO nanowires with a high structural quality. The growth of nanocolumn and nanowire arrays can be achieved by the method with controlled aspect ratio, density and optical properties.[2-4] The final structure can be finely tuned by adjusting the precursor concentration in the bath, the deposition time, the substrate and so on. We have also shown that doping with various transition metals such as Cu, Cd, Ag, Pd with a controlled concentration can be easily achieved by the technique.[5] These nanowires have been used as single functional nanosensors with significantly changed detection properties and improved selectivity with different dopant concentrations. All these aspects will be described in detail in the talk. References 1. H. Elbelghiti, Pauporté, D. Lincot, Phys. Stat. Sol. (a) 205, 2360 (2008). 2. T. Pauporté, D. Lincot, B. Viana, F. Pellé , Appl. Phys. Lett., 89, 233112 (2006). 3. O. Lupan, T. Pauporté, T. Le Bahers, B. Viana, I. Ciofini, Adv. Funct. Mater., 21 3564 (2011). 4. O. Lupan, L. Chow, T. Pauporté, L.K. Ono, B. Roldan Cuenya, G. Chai, Sensors and Actuators B, 173 772 (2012). 5. O. Lupan, V. Cretu, V. Postica, M. Ahmadi, B. Roldan Cuenya,L. Chow, I. Tiginyanu, B. Viana, Th. Pauporté, R. Adelung, Sensors Actuators B, 223, 893 (2016).

Resume : Complex hierarchical nano structures can be achieved when combining chemical advanced bottom-up strategies, such as self-assembly and sol-gel chemistry, together with high throughput liquid solution processing. Amongst them, dip-coating is an extremely versatile tool to prepare thin nanostructured (hybrid), mesoporous metal oxide films from liquid solutions and has been used for many decades without taking advantage of its whole potentiality. [1,2] This communication reports on the recent progresses performed in nanostructing sol-gel coatings through a perfect control of the chemical and processing conditions, and the exiting possibilities associated to its combination with conventional “top-down” micro(nano) fabrication technologies such as Soft-NIL, RIE, optical lithography or FIB, to construct even more complex morphologies with multi scales features and motifs. [3] Interests of such complex patterned coatings will be illustrated with recent implementations for application in various domains such as for nano actuation, [4] photonics [5], gas sensing, [6] nanofluidic, [7] and surface wetting. [8] [1] D. Ceratti et al. A New Dip Coating Method to Obtain Large‐Surface Coatings with a Minimum of Solution. Adv. Mater. 2015, 27, 4958-4962. [2] Faustini M., et al. Engineering Functionality Gradients by Dip Coating Process in Acceleration Mode, ACS Appl. Mater. & Interf. 2014, 6, 17102–17110. [3] M. Faustini, et al. Self-assembled inorganic nanopatterns (INPs) made by sol-gel dip-coating: Applications in nanotechnology and nanofabrication. (Invitation) CRASS, 2016, 19, 248-265. [4] M. Boudot, et al. Converting Water Adsorption and Capillary Condensation in Useable Forces with Simple Porous Inorganic Thin Films. ACS Nano 2016, 10 (11), 10031–10040. [5] T. Bottein, et al. "Black" Titania coatings composed of sol-gel Imprinted Mie resonators arrays. Adv. Funct. Mater. 2016 (DOI: 10.1002/adfm.201604924). [6] M. Boudot, et al. Ethanol–water co-condensation into hydrophobic mesoporous thin films: example of a photonic ethanol vapor sensor in humid environment. J. Sol-Gel Sc. Technol. 2016 DOI 10.1007/s10971-016-4084-2. [7] D. R. Ceratti, et al. Ionic diffusion, nanoparticle formation and trapping within sol-gel made Pillar Planar Nanochannels in a simple microfluidic devices. Submitted. [8] M. Faustini, et al. Dynamic Shaping and Manipulation of Femtoliter Dew Droplets on Nanoimprinted TiO2 Hydrophilic Surfaces. Submitted.

Resume : The conventional method to prepare functional oxides is ceramic-powder-based processing, i.e., through solid-state reaction at high temperatures. This process has several disadvantages, such as high-temperature reaction, limited degree of chemical homogeneity, and low sintering ability. Therefore, during past years, several chemical-based processing routes, including freeze-drying, spray-pyrolysis, sol? gel, spray-drying, and pyrolysis of complex compounds, have been developed to prepare powders with more homogeneous composition, improved reactivity, and sintering ability at low temperatures. Recently, non-conventional processing methods such as mechanical alloying and mechano-chemical approaches have been used to create reactions between species. However in this method the reaction kinetics is very slow and processing time long. Here we report application of an Electric Discharge Assisted Mechanical Milling (EDAMM)[1] technique to synthesize various functional oxides. By using EDAMM, high purity single phase multi-element oxides can be formed in as little as 0.1% of the processing time required in conventional solid-state techniques. An even more important feature of EDAMM is that the crystallite size of the synthesized compound is able to be reduced to nanometer size , by careful selection of electrical (voltage, current, total power) and mechanical (vibration frequency and amplitude) experimental parameters. We use EDAMM for (i) synthesis of oxides from elemental powders by oxidation in oxygen plasma and for (ii) synthesis of single phase multi element oxides from pre-mixed oxides as starting materials. In the former case we investigated the effect of oxygen, argon, helium, nitrogen, AC and DC plasmas on phase formation, rate of synthesis and powder morphology. This presentation provides an overview of recent development of Electric Discharge Assisted Mechanical Milling and its application in rapid complex oxides processing and synthesis. In particular: i) detailed analysis of the method will be presented, ii) the effect of AC and DC discharges on phase transformations in solid will be discussed, iii) characteristic of power supplies, construction of reaction chambers unusual effects of electrode coatings will be presented and discussed. Example applications of this method: The following compounds: MgAl2O4, LiFePO4, CaCu3Ti4O12, BaLa2Ti4O12, Nd2Ba2CaZn2Ti3O14 and many others were synthesized within minutes. We found that using EDAMM method, non-stoichiometric oxides, can be synthesized with compositions not achievable by conventional methods. Samples were characterized using x-ray analysis, SEM, TEM and capacitance measurement. The EDAMM technique offers an exciting opportunity to synthesize a range of new and existing materials to be used in a variety of energy storage applications that include rechargeable lithium batteries, hydrogen fuel cells, and super-capacitors. [1] A.Calka and D.Wexler, Nature, 419,(2002)147-151

Resume : Gypsum is one of three main phases of calcium sulfate [1] and is the most abundant evaporitic mineral on the Earth?s and Mars? surfaces. In industry, the main constituent in plaster products for casting and construction applications, it is widely used as a fertilizer and as an additive in concrete. On the other hand, the unwanted precipitation of gypsum constitutes one of the main hurdles in making sea water desalination plants. Hence, comprehending the fundamental mechanisms driving the formation of gypsum from dissolved ions is of paramount importance. Here we present data from the development and testing of a custom-made cell flow reactor coupled to a Raman microscope stage that allowed us to follow the time-dependent changes in the Raman spectra during the formation of gypsum from mixed aqueous solutions of sodium sulfate and calcium chloride [1]. The Raman spectra show a concurrent decrease of the Raman band intensity of the S-O stretching mode of the aqueous sulfate at 980 cm?¹ and an increase of the corresponding band of crystalline gypsum at 1007 cm?¹. We found that the band intensities were linearly proportional to the actual concentrations of the corresponding phases. Based on this, the apparent rate of disappearance of the aqueous sulfate was faster than the appearance of gypsum, which could indicate the formation of a new precursor phase preceding the crystalline gypsum. These results nicely complement our previous in situ gypsum formation studies using scattering [1], but importantly demonstrate the feasibility of a new cell system to perform real in situ Raman studies of phase formation in liquid environments. [1]. M. Stawski, A. E. S. van Driessche, M. Ossorio, J. D. Rodriguez-Blanco, R. Besselink and L. G. Benning, Nat. Commun., 2016, 7, 11177, DOI: 10.1038/ncomms11177.

Resume : Metal oxides are known electrocatalyst in water oxidation reaction. Due to the fact that it is desirable for efficient oxygen evolution catalyst to contain numerous redox-active metal ions to guard four electron water oxidation reaction, mixed metal oxides exhibit enhanced catalytic activity towards oxygen evolution reaction compared to single metal oxide systems. On the surface of fluorine doped tin oxide coated glass slide (FTO) deposited (doctor blade technique) mixed metal oxide layer composed of nickel, iron and chromium. Oxide coating was acquired by heat treatment of the aqueous precursors solutions of the corresponding salts. As-prepared electrodes were photosensitive and acted as an efficient oxygen evolution catalyst. Our results showed that obtained by this method electrodes can be activated which leads to achieving of higher current densities. The recorded current and photocurrent associated with oxygen evolution process were at least two orders of magnitude higher in the presence of oxide layer compared to bare FTO electrode. The overpotential of the process is low (ca. 0,2 V). We have also checked the activity of the catalyst at different known photoanodes used in sun-driven water splitting. Herein, we demonstrate that we were able to achieve efficient oxygen evolution catalysts using relatively cheap precursor consisting of earth abundant metals and simple method of preparation.

Resume : Charge compensation in zinc oxide has been discussed for many years. However, there still a lot of questions in detail, although many experimental and theoretical studies were conducted. At this situation, we realize that every experimental study were conducted with every different samples. Namely, there are a lot of reports with missing information: such as reports on transport property measurements without analyses of hydrogen concentration, mass transport study without minor impurity analysis. In order to reveal real nature of zinc oxide, it is necessary to characterize all possible parameters relating to charge compensation. To this context, we have performed analyses of impurity concentration and transport properties measurements on ZnO single crystals with different quality. In addition, to reveal the hydrogen related phenomena, annealing in ultra-high-vacuum and hydrogen ion implantation was also performed. The electric properties of ZnO in terms of defect formation and charge compensation will be discussed based on all those experimental results.

Resume : Ion beam induced defect processes in wide bandgap compound semiconductors are rather complex because of the formation of different types of defects and their transformations. In this paper we report results of the study on the mechanism of defect formation, migration and agglomeration in 300 keV Ar-ion bombarded ZnO single crystals. RBS/c analysis performed with the use of the unique McChasy code allowed determination of depth distributions for different defect types separately. Complementary HRXRD analysis was applied to study lattice deformation due to ion bombardment. It has been observed that migration of simple defects and their agglomeration lead to the formation of two types of dislocation loops: basal loops located at the depth corresponding to the range of incident Ar ions and pyramidal loops located beyond the ion range. The stress induced by defects in the bombarded layer has been identified as the driving force for defect migration and loop formation. As soon as the critical stress is attained bombarded layer undergoes plastic deformation resulting in the formation of a dense dislocation tangle.

Resume : Transparent conductive oxides (TCOs) are essential components of numerous optoelectronic devices such as light emitting diodes and solar cells. Historically, indium-based materials have dominated the TCO market due to their good optoelectronic properties and their compatibility with a wide range of substrates. Nonetheless, alternatives must be developed as indium is a scarce element. Amorphous zinc tin oxide (ZTO) is a wide band gap alloy that has proven to be a promising alternative to replace In-based materials from various devices.[1,2] However, its optoelectronic properties must be further improved to expand its applicability. In this work, experimental and computational techniques are used to understand the defects limiting electron transport in ZTO. ZTO films were annealed systematically in oxidizing and reducing atmospheres and their optoelectronic and structural properties were characterized. Using density functional theory, it was found that oxygen vacancies (Vo) and hydrogen play a crucial role in the resulting properties of ZTO. While Vo are the main intrinsic dopant in ZTO, their presence limits the electron mobility and creates absorption centers in the visible range of the spectrum [3]. We demonstrate that these defects can be suppressed by either a thermal treatment > 400 °C in oxygen-rich atmospheres3 or at low-temperatures (< 200 °C) by co-sputtering4 ZTO with SiO2. Interestingly, co-sputtering with SiO2 decreases the subgap absorption without detrimental effects on the electrical properties. Motivated by the versatility of co-sputtering, ZTO-SiO2 is furthermore co-deposited Zr-doped In2O3, to create a reduced In-content film with excellent optoelectronic properties, hence with a broad application range.

Resume : Transparent Conducting Oxides have gained large interest because of the peculiar combination of high transparency and low electric resistivity, with applications in optoelectronic and plasmonic devices.[1] Their properties can be largely modified by inclusion of dopants in wide-band gap semiconductors over a large range of concentration (like in Al-doped ZnO). However, the presence of structural defects results in an unpredictable complexity that prevents a clear identification of chemical and structural properties of the films, thus their identification and control is highly desirable. We have exploited the chemical sensitivity of Hard X-ray Photoelectron Spectra and Near Edge X-ray Absorption Fine Structure in combination with DFT to determine the spectroscopic response of defects in Al:ZnO films. Modifications in O1s and O K-edge have allowed to determine the concentration of embedded H, Zn vacancies and O interstitials in undoped ZnO. Contributions coming from substitutional and interstitial Al atoms have been identified and related to changes in the oxide stoichiometry and an increased oxygen coordination, together with small lattice distortions.[2] Consequences on the optical response in the UV-VIS and IR and band populations are discussed. This provides a tool to control defects and doping and improve the performance of TCO films. [1] K. Ellmer, Nature Photonics 6, 809 (2012). [2] I. Valenti et al., J. Appl. Phys. 118, 165304 (2015); S. Benedetti et al., submitted.

Resume : The origin of conductivity in intrinsically conductive atomic layer deposited (ALD) ZnO is still a subject of controversial discussion. To solve this problem, the three candidates for providing shallow donor states are investigated: intrinsic point defects, elemental impurities and hydrogen. Impurities other than hydrogen are ruled out due to their ultra-low concentrations in the ppm range. Intrinsic point defects are also considered unlikely since the evolution of conductivity with deposition temperature is not reproduced in the Zn/O ratio as measured by Rutherford backscattering spectrometry. Hence, the most promising candidate is hydrogen with a concentration of 1 at%, which is more than sufficient to account for the free electron density (up to 5x10^19 1/cm³). The formation energy of the conductive, hydrogen-related state is determined to be 40 meV. Hall measurements down to liquid helium temperatures revealed that the electron densities are constant over the whole temperature range. This constitutes a quasi-metallic behavior of ALD-ZnO for deposition temperatures of ? 150 °C. Ref.: Beh et al., J. Appl. Phys (under review)

Resume : Ga-doped ZnO (GaZnO) nanoneedles (NNs) are grown with the vapor-liquid-solid mode of molecular beam epitaxy by using Ag nanoparticles as growth catalyst. Based on the effective refractive-index effect, such GaZnO NNs can produce the function of anti-reflection for solar cell application. However, such a function relies on the orientation distribution of the NNs. In this paper, we first demonstrate the dependencies of light reflection and transmission on the orientation distribution of GaZnO NNs. Parallel and vertical GaZnO NNs on a device surface can lead to a stronger anti-reflection effect. Then, we disclose the mechanism of controlling the growth direction of a GaZnO NN. In particular, we show the relation between the crystalline structures of GaZnO and catalytic Ag. It is found that ZnO (002) plane always coincides with Ag (111) plane. The Ag crystalline orientation is controlled by the used substrate. For Si solar cell application, GaZnO NNs are randomly oriented on Si (100). To improve the orientation uniformity of GaZnO NNs for enhancing the anti-reflection effect, GaZnO NNs are grown after a GaZnO thin film is first deposited on Si (100). On this partly c-plane-oriented thin film, GaZnO NNs become more parallel and vertical, leading to a stronger anti-reflection effect. Based on the solar cell fabrication results, such a GaZnO NN structure can enhance the energy conversion efficiency of a Si solar cell by 33 %.

Resume : Materials that change colour with light carry large potential for technological applications. For example, in 1727 H. J. Schulze discovered that silver salts change colour when exposed to sun light, the starting point for the invention of photography. Recently, we discovered that polycrystalline samples of Nd2Ti2O7 show an instantaneous and totally reversible change of colour when exposed to different sources of light. In particular, Nd2Ti2O7 powders appear purple under visible light but rapidly switches to green if exposed to fluorescent light. This effect may be related to the ?Alexandrite effect? found first in the mineral Alexandrite, BeAl2O4, doped with a small amount of Cr3+, but was also observed in Nd3Li5Ta2O12, in Nd3+ containing minerals, such as Monazite, and even in Nd2O3. It can be therefore assumed that the dichroism shown by Nd2Ti2O7 is due to the presence of Nd. We have discovered that the colour can be tuned and the phenomenon of colour switching can be suppressed via chemical substitution on the Nd3+ and the O2? sites. We also studied alternative synthesis methods to the conventional solid-state approach to prepare single-phase samples, yet using lower temperatures and obtaining a homogeneous distribution of the particle size. UV-vis spectra are discussed. We believe that this optical phenomenon of color changing coupled with the well-documented ferroelectric and piezoelectric properties of Nd2Ti2O7 and similar titanates can lead to interesting applications.

Resume : In this work, pure samarium metal thin film was sputtered on silicon substrates followed by thermal oxidation in oxygen (samarium oxide) and thermal oxynitridation in nitrous oxide (samarium oxynitride), respectively. Various characterization techniques such as X-ray diffraction, Fourier transformed infrared spectroscopy analysis, Raman analysis, high resolution transmission electron microscopy, capacitance-voltage measurements, leakage current density-electric field measurements, and trap-assisted tunneling analysis were carried out to evaluate and compare the structural, chemical, and electrical properties of the both films. It proved that the incorporation of nitrogen improved and enhanced the electrical properties by the passivation of silicon bond and stabilization of oxygen ions.

Resume : In recent years, the great interest of nano- and micro-particle studies has given an opportunity to make further researches on material science with their advance physical, chemical, optical and biological properties potentially used in biomedicine, drug delivery, catalysis, sensor technology, and energy unit cells. Particularly, noble metal based nanoparticles have superior characteristics for many chemical reactions utilized as catalysts with high surface to volume ratio. As an important family of catalysts, gold nanoparticles (AuNPs) are attractive because high surface energy gives an efficient catalytic reaction in different particle size whereas bulk gold is often a passive catalyst. Besides all beneficial features, working with NPs is really difficult because the tendency to aggregation damages the shape and the surface states of AuNPs and undesirably decreases the catalytic activity. The objective of this study was to fabricate multifunctional microbeads to use for removal of environmental pollutants. By this aim, carboxyl carrier polymeric microbeads poly(mono-2-(methacryloyloxy) ethyl succinate -co- glycerol dimethacrylate) ?poly MMES-co-GDMA)? were synthesized monosized in 5µm diameter. Then iron oxide nanoparticles were attached on polymeric microbeads to obtain superparamagnetic properties to collect microbeads from removal media. At the last step, magnetic polymeric microbeads were decorated with AuNPs produced approximately 15nm in size. The obtained monodisperse gold catalyst with magnetic properties and polymeric template gave several advantages in catalytic system such as easy handling comparing with nanoparticle (no aggregation problem), separation from media with natural magnets and reuse of catalyst without leaching metals. The fabricated gold catalyst was characterized with scanning electron microscope (SEM), vibrating sample magnetometer (VSM), XRD and EDAX. As we know, environmental safety has a vital importance in human life and one of the important issue for world heritage. There are many regulation authorities around the world to keep environment in safe positon such as Environmental Protection Agency (EPA). This organization choose 4-nitrophenol (4-NP) one of the organic contaminants listed as priority pollutant because of highly soluble and having good stability in water. The newly fabricated gold catalyst was used to remove this organic substance from water medium. The degradation process of 4-NP to 4-aminophenol (4-AP) was monitored by UV-visible spectrometer. The parameters of the removal system were determined as concentration of catalyst, concentration of 4-NP and temperature of the media. The gold catalyst was collected by a powerful natural magnet for each experimental design. The reusability was test for fabricated material. The results were successful with high catalytic activity for several time the degradation of 4-NP to 4-aminophenol form in few seconds by using fabricated microbeads.

Resume : In the field of carbon dioxide capture and storage, two well-researched approaches are the reaction of alkali earth metal oxides, CaO to form metal carbonates and, the physisorption of CO2 in the channels of zeolites. We investigate a new approach that merges these strategies and aims to the preparation of novel carbonate-based materials. Oxides of the general formula A2CuO3 (A = Ca, Sr, Ba) contain alkali metals, which tend to react readily with CO2 to form stable carbonates and, also show a crystal structure with anion vacancies, which can mimic the cavities in zeolites and be host sites for CO2. We exploit the simultaneous presence of vacant sites and alkaline earth metals to form oxide-carbonates via reaction with CO2. A2CuO3 (A=Sr, Ca) compounds were reported to ?host? F? anion via fluorination, leading to A2CuO2F2 ?, (0???0.35), with A2CuO2F2 ? showing High Tc superconductivity. Sr2CuO3 can form the oxide carbonate Sr2CuO2(CO3) as a result of Sr-O groups reacting with CO2 to form metal carbonates. We were able to prepare Sr2CuO2(CO3), Sr1.8Ba0.2CuO2(CO3) and Sr1.5Ca0.5CuO2(CO3) via the direct reaction of Sr2CuO3 with CO2. We also studied the reaction of compounds isostructural to A2CuO3, A2PdO3 (A = Ba, Sr) and Ce2MnN3. We have monitored the incorporation of CO2 using a combination of Thermo Gravimetric Analysis, Powder X-Ray Diffraction and studied the reaction via DFT. The removal of CO2 to reform Sr2CuO3 was also carried out under O2, over multiple cycles.

Resume : Fragility of inorganic materials is a fundamental problem and considered disadvantage in various applications where physical integrity must take crucial role in processing versatility, efficiency and recoverability. In this present research, we successfully fabricate stable metal oxide photocatalytic nanofibrous membrane as a representative physical integrity solution. Experimentally, we formulate a stable multicomponent metal complex solution for electrospinning followed a specific two-step thermal treatment. During calcination process, we investigate the duration, heating rate and temperature under structural confinement in order to obtain the stable metal oxide nanofibrous membrane. We discover the unfamiliar phenomena of metal oxide?s phase separation after calcination at more than 600 °C with ZnWO4 nanorods stemming out of the TiO2-ZnWO4 nanofiber?s surface. Furthermore, we successfully fabricate as-designed and stable metal oxide nanofibrous membrane through a continuous two-step calcination under unique environment provided by fiber glass confinement technique. It is observed that crosslinking among calcined nanofibers under different confinement conditions represents a physical origin of the membrane?s dimensional stability. We also show that the resulted metal oxide nanofibers could be decorated with Pd and Pt nanoparticles via facile and solution-based photoreduction. Both types of nanofibers, ZnWO4-TiO2 and Pd/Pt- ZnWO4-TiO2, show exceptional MB degradation efficiency within 15 minutes of the reaction under natural sunlight irradiation. In addition, ZnWO4-TiO2 nanofibers show promising benzene decomposition efficiency under visible light irradiation at room temperature.

Resume : Complex oxides are fascinating materials, in which the manipulation of charge, orbital and lattice degrees of freedom leads to numerous exciting phenomena. We report here the use of He ion irradiation to control the out-of-plane lattice constant of epitaxial LaNiO3 (LNO) thin films independently without a change of the in-plane lattice constant. All the LNO films with the fluence less than 1×1015 He/cm2 exhibit metallic behaviors along with a slight resistivity upturn at low temperature, whereas the film with 2.5×1015 He/cm2 shows metallicity at high temperature and insulator-like behavior at low temperature. Further, the fitting for the temperature dependent resistance indicates that electrical-conductivity carriers are mainly scattered by electron-boson interactions rather than electron-electron interactions. These results suggest that He ion irradiation can be an alternative route to tune the functionality of complex oxides.