Solution processing and properties of functional oxide thin films and nanostructures

Resume : The use of low temperature and sustainable processes based on cheap and safe chemicals and not toxic solvents is a challenging issue in modern inorganic chemistry, and the obtainment of crystalline functional nanostructures at low or even room temperature is the goal of many synthetic efforts [1]. In this framework, in these last years, in our group we have developed different low temperature (T<150°C) wet chemistry routes to prepare different inorganic functional nanomaterials, ranging from i) ferrites [2] to pure and doped ii) metal oxides [3-5], sulphides [6] and halogenides, to iii) metal/metal oxide nanocomposites [7]. The adopted wet chemistry routes ranged from 1) miniemulsions [3-4, 7] to 2) coprecipitation combined with hydrothermal route [2] to 3) more classical colloidal routes [5-6]. This contribution provides an overview of the pros and cons of the proposed routes for the obtainment of targeted inorganic systems for applications in optical bioimaging or in energetics. [1] Cushing et al. Chem. Rev. 2004, 104, 3893-3946 [2] Diodati S. Synthesis and characterization of nanostructured ferrites Ph.D. Thesis, University of Padova, Italy 2013 [3] Dolcet et al. J. Mater. Chem. 2012, 22, 1620-1626 [4] Dolcet et al. Eur. J. Inorg. Chem. 2013, 13, 2291-2300 [5] Famengo et al. Eur. J. Inorg. Chem. 2009, 5017–5028 [6] Armelao et al. J. Nanosci. Nanotechnol. 2006, 6, 401-408 [7] Heutz et al. Nanoscale 2013, 5, 10534-10541

Resume : Metal-oxides have evolved as powerful interface materials that facilitate charge injection/extraction into/out of organic devices. E.g., transition metal oxides like WO3, MoO3, V2O5 etc., with extremely deep lying electronic levels and a work function (WF) of up to 7 eV can make a favorable electronic match even to organic materials with very deep HOMO levels. Thereby, substantially enhanced device characteristics of organic light emitting diodes, organic solar cells (OSCs), and organic field-effect transistors have been achieved along with a significant improvement in lifetime. On the cathode side, metal oxides with a lower WF, like ZnO, TiOx and SnOx can be used. Some recent progress to prepare metal-oxides from solution at low temperatures will be highlighted. Aside from fundamental studies of their electronic structure, their application especially in OSCs will be presented. Furthermore, the realization of In-free transparent conductive layers based on composites of silver nanowires and solution processed conductive metal-oxides will be shown. The metal-oxide conductively joins the wires and also to ‘glues’ them to the substrate. As a result, a low sheet resistance down to 5.2 Ohm/sq. is achieved with a high average transmission of 87%. These In- and PEDOT:PSS-free hybrid layers are successfully implemented as transparent top-electrodes in efficient all-solution-processed semitransparent OSCs.

Resume : The solution processing of YBa2Cu3O7-x (YBCO) coated conductors is already extensively studied, but the critical current density Jc remains too low for applications in high magnetic fields. This can be circumvented by the incorporation of inert metal oxide nanoparticles (NPs) in the layer. However, it is very challenging to synthesize these inert metal oxides (ZrO2, HfO2, BaZrO3 …) as monocrystalline and monodisperse NPs (d < 10 nm) in a reproducible manner. We compared two different synthesis routes for ZrO2 nanocrystals for the incorporation in an YBCO coated conductor. Firstly, we make use of a microwave method using benzyl alcohol and ZrCl4, similar to the microwave-assisted synthesis of HfO2 NPs.[1] Aggregates of monoclinic ZrO2 NPs (4.5 nm) are obtained after 4 hours at 220°C. Post-modification of the NPs with dodecanoic acid and oleylamine breaks the aggregates into individual NPs, rendering them dispersible in nonpolar solvents. Secondly, we make use of a heating-up method using ZrCl4 and Zr(OiPr)4 as precursors and trioctylphosphine oxide as ligand and solvent. Here, a higher temperature (340°C) and lower reaction time (2h) are used. Cubic ZrO2 NPs (3-4 nm) are synthesized, agglomeration-free and readily dispersible in nonpolar solvents. Both methods gives rise to crystalline ZrO2 NPs, but to a different surface chemistry. This diversity allows us to adopt different strategies for the transfer to a YBCO precursor solution. [1] J. De Roo, J. Nanopart. Res. (2013)

Resume : Barium strontitum titanate BaxSr1-xTiO3 with the compositions in the paraelectric phase at the operating temperatures, but nevertheless close above the Curie temperature, exhibits high dielectric permittivity and high tunability but also low dielectric losses at microwave frequencies. Ba0.5Sr0.5TiO3 thin films were prepared from solutions based on earth-alkaline acetates and Ti-alkoxide in organic solvents. The films were deposited on alumina substrates by spin-coating and heated after each deposition at 900 °C. For investigation of dielectric properties in the kHz range, co-planar capacitors were patterned by lift-off photolithography and sputtering of Cr/Au and the split-post dielectric resonators were used for measurements in the GHz range. According to the XRD, the films with thicknesses from 90 nm to 170 nm crystallized in a randomly oriented perovskite phase. With increasing film thickness the grain size increased from ~ 40 nm to ~ 80 nm as revealed by FE-SEM and AFM. The dielectric permittivity of the films increased with increasing film thickness, from 650 to 1300 at 100 kHz for 90 nm and 170 nm thick films, respectively. The permittivity and losses of the 170 nm thick films at 15 GHz were 1200 and 0.15. In the contribution we discuss the relation between the microstructure and dielectric properties of the films. Acknowledgements: This work was supported by the Slovenian Research Agency (PR-05026 and P2-0105) and by the European Space Agency (Project FERRO-PATCH).

Resume : In recent years a wide variety of soluble precursors have been investigated as potential alternatives for the fabrication of oxide-based TFTs using large area deposition methods including spin casting, dip coating and spray pyrolysis. The ever increasing demand for high performance thin film transistors based on metal oxide channels has given a boost to the development of alternatives to SiO2 gate dielectrics with desirable characteristics in terms of thermal stability, band offset, interface quality and ability to control the FET’s gate threshold voltage. Among these, ZrO2, HfO2, Y2O3 and Al2O3 are the most studied dielectrics and are widely considered to be excellent candidates because of their high dielectric constants, good thermal stability and large band gaps. This work reports on the structure and properties of spray pyrolysis-grown HfO2 thin films and their implementation in ZnO-based TFTs. The HfO2 films were found to be of monoclinic crystal structure with a band gap of 5.7 eV, dielectric constant as high as 19, very low leakage currents and dielectric breakdown in excess of 2.7 MV/cm. The related ZnO based TFTs exhibit excellent electron transport characteristics with negligible hysteresis, operating voltages in the range between 5-6 V, high electron mobility on the order of 40 cm2 V−1 s−1 and high current on/off ratio of about 10^7.

Resume : Solution processable metal oxides come out as an enabling technology for the low-temperature preparation of high-performance layers on flexible plastic substrates. Major efforts are focused on semiconductors, where synthetic solution methods are investigated to reduce the temperature of formation of the oxide. Crystallinity improves the electric characteristics of the semiconductor oxides in comparison with amorphous ones. But, this is mandatory for the properties of some oxides. It is for inorganic ferroelectrics, where a non-centrosymetric crystal structure is responsible for the functional response. The handicap is their high crystallization temperature. However, the use of ferroelectrics in flexible devices would make real applications not possible before (e.g. smart skin, flexible sensitive displays) associated to their intrinsic multifunctionality. In this scenario, solution techniques offer the unique advantage of tailoring the solution chemistry to decrease the Gibbs free energy barrier for the formation of the oxide. Synthetic methods in solution will be shown in this talk to stabilize non-equilibrium phases at room temperature or to reduce the formation temperature of electronic oxide films (mostly ferroelectrics) directly on flexible plastic substrates. The properties of these films will be compared with those of the materials already used in flexible electronics (amorphous/nanocrystalline oxides and organic dielectrics). Financed by Spanish Project MAT2010-15365

Resume : We will present a chemical deposition method, based on aqueous polymeric/metal solutions, for the fabrication of epitaxial thin-films of different oxides. The method is able to produce ultrathin films of very high quality, with an exceptional homogeneity in their chemical composition, thickness and physical properties, over cm2 areas. The thickness can be well controlled in the range from 4 nm to 40 nm. To demonstrate the versatility of this method, we will show the results of the synthesis and characterization of different materials, such as ferromagnetic manganites and cobaltites (including misfit cobalt oxides) with different compositions, multiferroic BiFeO3, doped ZnO, etc. We will also show that epitaxial bilayers of different oxides can be fabricated with this method, introducing new functionalities due to interface coupling. All these results demonstrate that chemical deposition methods of ultrathin films are competitive for the fabrication of high quality ultrathin films and multilayer oxides, as required for fundamental studies or highly demanding applications.

Resume : Graphene is a one-atom-thick layer of bonded-sp2 carbon atoms packed into a two-dimensional honeycomb lattice [1]. It has a high-electron mobility of up to 15,000 cm2/V•s at room temperature and 60,000 cm2/V•s at 4 K [2, 3]. Moreover, It has high optical transparency and can absorb πα ≈ 2.3% of white light, where α is the fine-structure constant. [4]. In this research, graphene oxide (GO) was deposited through the electrophoretic deposition (EPD) system to obtain lower the oxygen concentration. Moreover, the direct fabricating patterns of large-scale GO films using stamping transfer processes on a polydimethylsiloxane (PDMS) substrate. The thickness of the GO films was controlled to adjust the optical, electrical, and mechanical properties by EPD. GO was deposited by EPD system. The EPD system processed cathode (ITO), anode (highly oriented pyrolytic graphite (HOPG)), and put graphite powder (1 g) as the electrolyte (in 100 ml of water). Through the anodizing process to a direct-current (DC) voltage of 10 V was applied for 1, 3, 5, and 10 min (samples 1, 2, 3, and 4, respectively) to an electrolyte in contact with the ITO surface to generate a GO film. In addition, PDMS (evenly mixed with a hardening agent at a ratio of 10:1) was poured onto a GO/ITO substrate. The GO/ITO substrate was transferred to a furnace and heated (338K for 4 h) to solidify the PDMS. Through GO films lift-off an ITO glass substrate, leaving just the GO films on the PDMS substrate. The finished flexible substrates were samples 1~4. The GO film was characterized by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). A micro-Raman system (Renishaw, Vendor) with a wavelength is 514 nm. XPS (JEOL JAMP-9500F) system using a monochromatic Al-Kα X-ray source with photon energy is 1486.6 eV. The microstructures of the deposited materials were measured by scanning electron microscopy (SEM, Zeiss Auriga FIB-SEM system), scanning confocal microscopy (SCM, Keyence VK-X200), and transmission electron microscopy (TEM, Philips Technai G2f20). Atomic force microscopy (AFM, NT-MDT SFC050L) was used to determine the surface morphology. A nanoindentation device (Hysitron Triboscope, TI 700 Ubi) equipped with a Berkovich diamond probe with a radius of approximately 100 nm was used to measure the nanomechanical properties in the experiment. The current-voltage (I-V) characteristics of the GO films were measured using a digital sourcemeter (Keithley 2400). The absorptivity and reflectivity of the GO films were examined under various wavelengths using an ultraviolet-visible (UV-Vis) spectrophotometer (Jasco V-670). The EPD parameters for producing uniform films of GO and the average surface roughness increased as a result of oxidation [5]. AFM measurements and scanned range (area is 5×5 µm) to analyze the surface roughness of the GO films. The surface roughness values were 3.2±0.2, 3.8±0.1, 4.5±0.6, and 6.3±1.5 nm at layer thicknesses of around 150, 200, 280, and 300 nm, respectively, for samples 1~4. The SCM images, which were measured the thickness of the GO films. Resistance increased with the thickness of the deposited films because at a given voltage, the electric current decreases as the film get thicker. Raman spectra of strong peaks appear in the G band (sp3, 1336 cm-1), D band (sp2, 1590 cm-1), and 2D band (2720 cm-1). The peak frequency of the G band of single-layer graphene sheets (1585 cm-1) shifted about 5 cm-1 into higher frequencies after being stacked. The results show that high-performance GO films were fabricated. XPS spectra shows samples that the peaks for C1s are at 284.5, 285.5, 286.5, and 288.9 eV, corresponding to C–C, C–N, C–O, and O–C=O groups, respectively. The binding energy peaks at 286.5 eV (C-O) and 288.9 eV (O–C=O) indicate large numbers of oxygenated carbon structures. The sheet resistance of the GO films measured by the four-point-probe method was approximately 320~430 Ω/sq, which is comparable to previously reported values for graphene films [6, 7]. The GO films obtained using EPD had a lower sheet resistance than that of GO/r-GO films. The results show that the GO film thickness greatly affects sheet resistance. The GO films showed conductivity, with a sheet resistance of 320~430 Ω/sq with 60~72% transparency. Experiments showed that transfer processes for flexible substrates can easily produce cost-effective transparent conductive films. Keywords: Graphene oxide; electrophoretic deposition; polydimethylsiloxane (PDMS); transparent conductive films (TCFs) References 1. Geim A K and Novoselov K S 2007 Nat. Mater. 6 183. 2. Novoselov K S, Geim A K, Morozov S V, Jiang D, Zhang Y, Dubonos S V, et al. 2004 Science 306 666. 3. Zhang Y B, Tan Y W, Stormer H L and Kim P 2005 Nat. 438 201. 4. Kuzmenko A B, van Heumen E, Carbone F and van der Marel D 2008 Phys. Rev. Lett. 100 117401. 5. Zhao S, Surwade SP, Li Z, Liu H. 2012 Nanotechnology 23 355703. 6. Kim K S, Zhao Y, Jang H, Lee S Y, Kim J M, Kim K S, et al. 2009 Nature 457 706. 7. Li X, Zhu Y, Cai W, Borysiak M, Han B, Chen D, et al. 2009 Nano Lett. 9 4359.

Resume : The SiGe-based alloy is considered as one of the most promising materials for reliable and high performance microelectronic devices. The use of a lower band-gap material in the channel region of the MOSFET, such as SiGe, is a potential candidate given their compatibility with the process developed for pure Si-based devices. Moreover, the important increasing in the drain current due to the increased electrons mobility in SiGe material is expected. However, the growth of this material is not totally controlled, and the presence of defects is more than expected after a growth run of this material. Therefore, in order to obtain a global view of SiGe-based nanoscale Double Gate (DG) MOSFET performance under critical conditions, numerical modeling of nanoscale SiGe DG MOSFET including Interfacial defect effects (SiGe/SiO2) is indispensable for the comprehension of the fundamentals of such device characteristics. Based on numerical investigation of a nanoscale SiGe DG MOSFET including the defects in the interface region, in the present paper a numerical model for I-V and small signal characteristics by including the interfacial defects, after considering the uniform function approximation for the interface defects distribution at the drain said, is developed to explain the immunity behavior of the nanoscale SiGe-based transistor against the defect densities, as function of dimensional parameters and germanium mole fraction. In this context, DC and RF characteristics of the proposed design are analyzed by 2-D numerical simulation and compared with conventional Si DG MOSFET characteristics.

Resume : In this work, we present an ab initio calculation for the structural, electronic, magnetic and optical properties of the orthorhombic NdMnO3 through density-functional-theory (DFT) calculations using both generalized gradient approximation GGA and GGA+U approaches, the exchange and correlation effects are taken into account by an orbital independent modified Becke Johnson (MBJ). The predicted band gaps using the MBJ exchange approximation show a significant improvement over previous theoretical work with the common GGA and GGA+U very closer to the experimental results. Band gap dependent optical parameters like dielectric constant, index of refraction, absorption coefficient, reflectivity and conductivity are calculated and analyzed. We find that when using MBJ we have obtained better results for band gap of NdMnO3 than in the case of GGA and GGA+U. The values of band gap founded in this work by MBJ are in a very good agreement with corresponding experimental values compared to other calculations and this comprehensive theoretical study of the optoelectronic properties predicts that this material can be effectively used in optical devices. Keywords: optical properties, half-metallic ferromagnet, strong correlation, MBJ potential, Orthorhombic NdMnO3. References [1] D. Koller, F. Tram, and P. Blaha, Phys. Rev.B 85, 155109(2012). [2] B. Amin, P. Iftikhar Ahmad, M. Maqbool, S. Goumri-Said, R. Ahmad, J. Appl. Phys. 109 (2011). 023109–023105.

Resume : The TiO2 has been recently used to realize high-temperature ferromagnetic semiconductors. In fact, it has been widely used for a long time as white pigment and sunscreen because of its whiteness, high refractive index, and excellent optical properties. However, its electronic structures and the related properties have not been satisfactorily understood. Here, we use Tran and Blaha’s modified Becke-Johnson (TB-mBJ) exchange potential (plus a local density approximation correlation potential) within the density functional theory to investigate electronic structures and optical properties of rutile and anatase TiO2. Our comparative calculations show that the energy gaps obtained from mBJ method agree better with the experimental results than that obtained from local density approximation (LDA) and generalized gradient approximation (GGA), in contrast with substantially overestimated values from many-body perturbation (GW) calculations. As for optical dielectric functions (both real and imaginary parts), refractive index, and extinction coefficients as functions of photon energy, our mBJ calculated results are in excellent agreement with the experimental curves. Key words: DFT / FP-LAPW / GGA / LDA / the TiO2 /the mBJ and optical properties References [1] H. K. Jang, S. W. Whangbo, H. B. Kim, Y. S. Lee, I. W. Lyo and C. N. Whang, J. Vac. Sci. Technol. A 18, 917 (2000). [2] J. D. Park and T. S. Oh, J. Korean Phys. Soc. 37, 1072 (2000).

Resume : Oxide semiconductor which has been studied extensively as a semiconductor material has a wide band gap and high mobility, capable of replacing the amorphous silicon. Recently, there have been many reports on different amorphous oxide semiconducting materials and among them, the materials that are the most extensively used currently is indium-gallium-zinc-oxide (IGZO). However, indium is not an abundant material. It is necessary to reduce indium usage for the future. Therefore, indium free materials, such as zinc-tin-oxide (ZTO) based oxide semiconductors, have been significantly studied for active channel layer of thin film transistors (TFTs). We have investigated silicon zinc tin oxide (SZTO) thin films under various silicon ratios. SZTO TFTs were fabricated by solution processing with the bottom gate structure. Furthermore, annealing process was performed in at different temperatures in various annealing conditions, such as air ambient, N2, vacuum and wet ambient. Completed fabrication of SZTO TFT, and the performance of TFT has been compared depending on the annealing conditions by measuring the bias temperature stress (BTS) and the transfer curve. In addition, chemical components in SZTO thin films has been investigated by X-ray photoemission spectroscopy (XPS). It is confirmed that the electrical performance and stability of SZTO TFTs are improved by adopting optimized annealing conditions. Optimized annealing condition has been found for obtaining high mobility and hig

Resume : Multiferroic materials have attracted great attention due to their potential applications in multifunctional devices. In this work, powders of Bi1-xNdxFeO3 (x= 0; 0.3) were successfully synthesized by a sol-gel method. X-ray diffraction patterns revealed the formation of pure BiFeO3 (BFO) and BNFO. No secondary phases were observed within the detection limit of the XRD technique. We observed that the neodymium substitution leads to the change of the BiFeO3 symmetry. The obtained samples were also characterized by Raman spectroscopy, differential scanning calorimetry (DSC) and dielectric measurements.

Resume : The increase of the accuracy of optical frequency standards by means of the development of “nuclear clocks” – a novel frequency standard based on the nuclear transition to the long-living isomer nuclear state of Th-229 with energy ~7.6 eV is of great interest. The main problem is the fact that there are no experimental data on the direct measurement of the energy of the isomeric transition in Th-229, and the above result was obtained only by indirect measurements, and has great uncertainty. Ion scattering spectroscopy (ISS) might be used for more precision investigations of the isomeric transition in Th-229. It caused by the fact that ISS spectra exhibit the fine structure determined by the target surface electronic structure. In the case of low energy nuclear transition it can give the information about the isomer nuclear state of Th-229. To proof this supposition it is necessary to prepare high quality samples with a high thorium surface coverage. An original preparation technique of the thorium films by electrochemical deposition from thorium nitrate solution on different substrate is reported. It was found that electrochemical deposition of Th on the metal surface provide formation of continuous films, while the deposition on the semiconductor substrates leads to the formation of thorium island films. The origin of the observed thorium films formation and the results on the investigation of Th films on Si(111) and polycrystalline Cu surfaces by XPS and ISS are discussed.

Resume : Lanthanide dititanate family, Ln2Ti2O7, adopts two type of structure and the stability depends of the ratio between the cations radii Ln3+ and Ti4+. For r(Ln3+)/r(Ti4+) included in the range {1.46-1.78}, the formed compound will privilege a pyrochlore-like structure for Ln = Sm to Lu. For ratio higher than 1.78, the layered perovskite type is preferred for Ln = La to Nd. Layered perovskite structure compounds are known for their ferroelectric and piezoelectric properties mainly used for the elaboration of high temperature devices. In this work, we sought to show it was possible to extend to the ranks of stability of the layered perovskite structure for smaller Ln3+ ionic radii (i.e. Sm, Eu, Gd, ...) including through epitaxial constraints. The growth of thin films has been achieved by Sol-gel method or Pulsed Laser Deposition on SrTiO3 and LaAlO3 substrates. We also present the structural characterization performed by High Resolution X-ray Diffraction on each substrate with (100) or (110) orientations. Indeed, studies performed on (110)-oriented SrTiO3 or LaAlO3 substrates, shows a growth following (00l) plans. While for the (100)-oriented SrTiO3 or LaAlO3 substrates, the growth is carried out according to the planes (012) tilted compared to the substrate plane. Finally, the ferroelectricity, in these metastable thin films, will demonstrated through measurements performed at the nanoscale level by Piezoresponse Force Microscopy (PFM).

Resume : Heterointerfaces between hematite (α-FeIII2O3, weak ferrimagnetic) and ilmenite (FeIITiO3, antiferromagnetic) are supposed to exhibit a strongly ferrimagnetic contact layer due to the formation of a mixed valence layer of Fe2+/Fe3+ (1:1 ratio) caused by compensation of charge mismatch at the chemically abrupt boundary.1 So far, it is not studied what happens when ilmenite is replaced by Ti-doped hematite Fe2-xTixO3 (x < 0.5) where Fe2+/Fe3+ < 1. We investigated thin films of α-Fe2O3/Fe2-xTixO3 (x = 0.44) on α-Al2O3 (0001) substrates which were grown by molecular beam epitaxy concerning their structural (in-situ surface X-ray diffraction, transmission electron microscopy), electronic (electron energy loss spectroscopy) and magnetic properties (superconducting quantum interference device measurements).2 We observed an increased magnetic moment and a formation of a chemically distinct interface layer, which might also be magnetically distinct as indicated by the observed magnetic enhancement in the Fe2-xTixO3/Fe2O3/Al2O3 system compared to the pure Fe2O3/Al2O3 system. The interface between this layer and the hematite layer shows an enrichment of Fe2+ which forms an uncompensated spin lattice, and might therefore be responsible for the interface magnetism. 1 P. Robinson et al., Nature 418, 517 (2002). 2 T. Dennenwaldt, M. Lübbe, M. Winklhofer, A. Müller, M. Döblinger, H. Sadat Nabi, M. Gandman, T. Cohen-Hyams, W. D. Kaplan, W. Moritz, R. Pentcheva and C. Scheu, submitted.

Resume : Development of electrode materials for lithium batteries providing high energy density and high power is a major challenge in the field of electrochemical energy storage. Nanostructuring has a profound effect on the material’s properties and is considered as one of the key routes towards the improvement of their efficiency. The performance of already known materials can be strongly enhanced by decreasing the crystal size to only a few nanometers and by judiciously designing their nanomorphology. Using a novel solvothermal tert butanol synthesis route we develop new pathways for the fabrication of different binary and ternary metal oxide nanoparticles for the application in lithium-ion batteries as well as the ways to their controlled assembly into continuous networks. The combination of extremely small crystalline nanoparticles in crystalline frameworks with extremely high surface areas is greatly beneficial in electrochemical lithium insertion reactions and leads to a drastic acceleration of the Li insertion process and a high accessible maximum capacity. We were able to obtain fully crystalline interconnected porous frameworks composed of ultrasmall titania (TiO2) and lithium titanate spinel nanocrystals, which was shown to be the fastest ever-reported titanate morphology as anode material for lithium ion insertion. Currently we work on extending our synthesis strategy to development of other nanostructured metal oxide morphologies for the use as cathode materials.

Resume : Indium-Tin-Oxide (ITO) is currently used in OLED panels for the transparent cathode and constitutes the dominant material of choice. However, indium is becoming increasingly scarce and hence an expensive resource. Also ITO itself exhibits serious technical drawbacks related to the costly deposition techniques. ITO alternatives have been investigated aiming to produce indium-reduced or indium-free oxides, conducting polymers, carbon nanotubes, graphene, nanowires and nanoparticles however they all suffer from either low optical transparency, low sheet resistivity, lower work functions than ITO, i.e. poor energetic alignment with hole transporting layer HOMO. In this work, we report the application of ambient spray pyrolysis for the deposition of highly transparent, high work function Antimony-doped Tin Oxide (ATO) thin film as OLED anodes. ATO films were studied by means of X-rays Diffraction, AFM, UV-visible absorption spectroscopy, 4-point probe, Hall Effect, Kelvin Probe and implemented in RGB OLED structures. For optimum antimony doping, the as-deposited ATO films exhibit excellent characteristics i.e. high work function (5.05 eV) wide direct band gap (4.65 eV), high transparency (90 %) in the visible spectrum, low sheet resistivity (25 Ohm/sq) and carrier mobility of 32 cm2 V-1 s-1. The antimony-doped tin oxide R,G,B, OLEDs show similar I-V and L-V characteristics to those of ITO and high external quantum efficiencies of about 12%, 0.3 % and 13% respectively.

Resume : Metal oxide semiconductors are very attractive candidates for implementation into TFTs mainly because of their high charge carrier mobility, high optical transparency and excellent chemical stability. Recent work has also been focusing on the development of variable-voltage oxide transistors using mainly high-k dielectrics i.e. ZrO2, HfO2, Y2O3 and Al2O3. Oxide transistors based on high-k dielectrics have received the most attention and variable-voltage devices have been demonstrated. Here, we report solution-processed, variable-voltage ZnO transistors based on aluminium and titanium oxide composite films as the gate dielectrics. The films were deposited on ITO-coated glass substrates from Ti and Al soluble precursors using the spray pyrolysis technique at 400 oC. The dielectric films were characterised by AFM, UV-Vis absorption spectroscopy, admittance spectroscopy, X-ray diffraction and spectroscopic ellipsometry. Data analysis showed amorphous Al2O3 and stoichiometric (in the solution) Al2O3.TiO2 films with dielectric constants in the range between 9 and 14 and optical band gaps between 6.1 eV and 4.4 eV respectively. Similarly, stoichiometric Al2O3.TiO2 showed improved leakage currents by 2 orders of magnitude (compared to Al2O3) in the order of 1 nA/cm2. BG-TC ZnO-based TFTs that also manufactured by spray pyrolysis on Al2O3.TiO2 gate dielectrics showed enhanced electron mobilities from 9 cm2 V−1 s−1 to 23 cm2 V−1 s−1 and current on/off ratios from 10^4 to 10^6.

Resume : The article examines the object - relational approach to the creation of a database, designed to provide informational support to the multiscale computational scheme of multilayer semiconductor nanostructures. The MSNS computational scheme developed earlier by our group uses hierarchic representation of computational data obtained by various computational modules. Each layer of MSNS is treated separately. In contrast to well-known materials databases, which serve for storing and retrieving of information on existing structures and its properties, the database described in this paper is the central unit of MSNS computational scheme. The database provides data interchange between various computational units. In this paper we describe the modern approach to material database design. More specifically, data storaging relational model which applies to solving resource-intensive and different-scale problems is proposed. Object-relational scheduler architecture is used in our work. It allows high-speed data exchange between various computational units of MSNS computational scheme. We introduce simple and user-friendly interface allowing criteria-based data retrieving as well as creation of input files for computational modules. These approaches can be applied in various branches of science, including the aviation and space industry, in particular in control systems of engineering (materials science) data.

Resume : Beryllium windows and lenses to control of X-Ray radiation parameters in different conditions are used in modern sources of synchrotron radiation. The disadvantage of this material is the oxidation of beryllium elements under high energy X-Ray beam. To prevent the oxidation and destruction processes of Be optical elements the nitrogen blowing is obligatory to use at the most synchrotrons at the moment. At this work we report on the passivation coatings protecting the Be windows. As beryllium lenses have typical thickness 2 μm[1], there should be an appropriate method for covering such objects with a complicated shape. Atomic layer deposition (ALD) is the most suitable method for such tasks. Al2O3 is chosen as a passivation material – that is perfect diffusion barrier for oxygen. The possibility of various sample shape using and appropriate x-ray speckle pattern image of coverage opens up the opportunities of extreme conditions experimental techniques applying. The structural properties, chemical state, interaction between thin film and substrate are investigated in both laboratory and synchrotron facilities. The set of our experimental results allow evaluating the perspectives of using protective Al2O3 coatings by ALD for additional reduction of safety requirements and the simplifying of optical experimental schemes at synchrotrons.. 1. Ali Khounsary, Eric M. Dufresne, Kristina Young, Cameron M. Kewish, conference “Advances in X-ray/EUV optics, Components and Applications”, vol. 6317, USA, 2006.

Resume : Heterointerfaces between hematite (α-FeIII2O3, weak ferrimagnetic) and ilmenite (FeIITiO3, antiferromagnetic) are supposed to exhibit a strongly ferrimagnetic contact layer due to the formation of a mixed valence layer of Fe2+/Fe3+ (1:1 ratio) caused by compensation of charge mismatch at the chemically abrupt boundary.1 So far, it is not studied what happens when ilmenite is replaced by Ti-doped hematite Fe2 xTixO3 (x < 0.5) where Fe2+/Fe3+ < 1. We investigated thin films of α-Fe2O3/Fe2-xTixO3 (x = 0.44) on α-Al2O3 (0001) substrates which were grown by molecular beam epitaxy concerning their structural (in-situ surface X-ray diffraction, transmission electron microscopy), electronic (electron energy loss spectroscopy) and magnetic properties (superconducting quantum interference device measurements).2 We observed an increased magnetic moment and a formation of a chemically distinct interface layer, which might also be magnetically distinct as indicated by the observed magnetic enhancement in the Fe2-xTixO3/Fe2O3/Al2O3 system compared to the pure Fe2O3/Al2O3 system. The interface between this layer and the hematite layer shows an enrichment of Fe2+ which forms an uncompensated spin lattice, and might therefore be responsible for the interface magnetism. 1 P. Robinson et al., Nature 418, 517 (2002). 2 T. Dennenwaldt, M. Lübbe, M. Winklhofer, A. Müller, M. Döblinger, H. Sadat Nabi, M. Gandman, T. Cohen-Hyams, W. D. Kaplan, W. Moritz, R. Pentcheva and C. Scheu, submitted.

Resume : Chemical nanotechnologies have played, in the past few decades a major role in the convergence of life, physical and engineering sciences leading not only to simple collaboration among the disciplines but to a paradigm shift based on true disciplinary integration. The successful synthesis, modification and assembly of nanobuilding units such as nanocrystals and wires of different materials have demonstrated the importance of chemical influence in materials synthesis, and have generated great expectations for the future. Implications of chemistry as an innovation motor are now visible for knowledge leap forward in various sectors such as materials engineering for energy, health and security. Inorganic nanostructures inherit promises for substantial improvements in materials engineering mainly due to improved physical and mechanical properties resulting from the reduction of microstructural features by two to three orders of magnitude, when compared to current engineering materials. This talk will present how chemically grown nanoparticles, nanowires and nanocomposites of different metal oxides open up new vistas of material properties, which can be transformed into advanced material technologies. The examples will include application of superparamagnetic iron oxide nanoparticles for magnetic resonance imaging (MRI) and drug delivery applications, vapour phase synthesis and electrospinning of nanowires for application as electrode materials and in water splitting reactions (for solar hydrogen production). Finally, the current challenges of integration of nanomaterials in existing device concepts will be discussed.

Resume : In our group, we focus on the electrochemical synthesis of metal oxides under hydrothermal conditions and utilization of these films in water splitting, solar cell and supercapacitance applications. Oxides of transition metals are very popular for such applications and research conducted in this field is directed towards improving the properties to get the highest possible performance. The electrochemical synthesis of metal oxide films, particularly Zinc, Iron and Manganese oxides under hydrothermal conditions was presented and their properties were discussed in this study. ZnO and Fe2O3 were utilized in solar energy applications. Different morphologies for doped or undoped films can be obtained by changing the synthesis conditions. Manganese oxide films are presented for their supercapacitative behavior. Manganese oxide films deposited under hydrothermal conditions demonstrated superior supercapacitative behavior to the films deposited at conventional methods.

Resume : Pr2NiO4 shows large anisotropy in oxide ion and hole conductivity. In this study, change in oxide ion and hole conductivity in Pr2NiO4 doped with Cu and Ga by dispersion of Au was studied by using ion blocking techniques and Hall effects measurement. Dispersion of Au nano particles was performed by impregnation of Au source in liquid followed by sintering. Because of difference in thermal expansion of Au and Pr2NiO4, tensile strain was formed after sintering and cooled to low temperature. Tensile strain was estimated with line broadening method by XRD measurement and it was found that oxide ion conductivity was increased by formation of Au dispersion. Increase in oxide ion conductivity became more significant with decreasing temperature, however, hole conductivity was also increased by dispersion of Au nano particle because of increased amount of hole which is charge compensate of interstitial oxygen. In contrast, mobility of hole was decreased because of distorted lattice by tensile strain. Oxygen diffusivity was further studied with 18O diffusion. In reply to the increased oxide ion conductivity, diffusion constant of oxygen was confirmed. Increase in surface exchange coefficient of oxygen was also observed by dispersion of Au nano particles in bulk of Pr2NiO4. Surface composition was analyzed with low energy ion scattering spectroscopy and oxygen vacancy was concentrated at surface by Au dispersion resulting in the increased surface exchange coefficient of oxygen.

Resume : Lithium-ion (Li-ion) batteries are promising candidates to tackle the challenging energy storage problem due to their high power and energy density. However, contemporary Li-ion batteries suffer from limited lifetime and safety hazards because of the liquid electrolyte used. Introduction of a solid electrolyte such as LLT, which is known for its high Li+ conductivity [1], could circumvent these issues. Although solid electrolyte thin films are crucial to form an all-solid-state Li-ion battery, little is known about synthesis of LLT thin films. In this study thin films of LLT have been deposited on TiO2 as an anode material; via spin-, spray- and dip coating an aqueous citrate and non-aqueous ethanol based precursor solution. Thermal analysis of the solution gels showed that the organic matrix of both precursors is decomposed at 600°C in air. The crystallization of the obtained LLT thin films was investigated by in-situ XRD. A prolonged heating at 700 °C in air was required to obtain tetragonal perovskite LLT on TiO2. SEM and GATR-FTIR showed that dense thin films with a thickness between 50 and 400 nm have formed without significant precursor residues. The results, presented in the current study, significantly contribute to the detailed understanding of the solution deposition process and phase formation in towards dense, crystalline thin films of LLT as a possible candidate material for all-solid-state Li-ion batteries. [1] Inaguma et al.; Solid State Comm. 86, 1993, 689

Resume : In Li-ion batteries, high rate electrochemical performance is enhanced by using nanostructured electrodes with shorter diffusion paths and higher surface area in contact with the electrolyte. In particular, mesoporous thin films (MTFs) offer 3D interconnection of the inorganic network at the nanoscale and favor good electrical contact and efficient charge transport inside the pore walls. In the present work, V2O5 and LiV2O5 MTFs were prepared by soft-templating methods combining sol-gel chemistry and block copolymer structuring agents. Wormlike vanadium oxide and lithium vanadium oxide MTFs were obtained on silicon by Evaporation Induced Micelles Packing using a polystyrene-block-poly(ethylene oxide) structuring agent. Optimized heat treatments lead to the crystallization of gamma-LiV2O5 or alpha-V2O5. These calcination conditions ensure the degradation of the structuring agent while preventing the collapse of the mesostructure, yielding MTFs with 30-35 nm pore size diameter. Using the same sets of synthesis conditions, films were coated on conductive glass to compare the electrochemical performance of chemically lithiated films (LiV2O5 films) with post-synthesis electrochemical lithium intercalation in V2O5 films: V2O5 films have better specific capacities; cyclability is good for both compositions, even at relatively high current density (30 C).

Resume : The ability to control structure and functionality at all length scale has developed tremendously in the last decades. It is clear that optimal design of nanostructured materials require integration of various approaches to synthesize, functionalize, characterize and process the nanosized species for various applications. Here, we will give an overview of recent research on the bio-inspired fabrication of multifunctional materials based on nanocellulose and inorganic nanoparticles. We will demonstrate how the microstructure and magnetic, mechanical, and optical properties of various inorganic-nanocellulose hybrids can be tailored by controlling the foaming and helical assembly of nanocellulose and how the properties can be tailored by nucleation and growth of inorganic nanoparticles onto the nanocellulose surfaces. Examples include hybrids based on nanocellulose crystals and amorphous calcium carbonate results in transparent and hard hybrid coatings and hybrids of cellulose nanofibrils and titania nanoparticles that result in transparent and flexible free-standing films with a hardness comparable to concrete. We will also describe recent work on the preparation of thermally insulating and flame retardant nanocellulose hybrid foams. References: 1. D. Gebauer, V. Olinyk, M. Salajkova, J. Sort, Q. Zhou, L. Bergström, and G. Salazar-Alvarez, Nanoscale, 3, 3563-3566, 2011 2. C. Schütz et al., PLoS ONE 2012, 01/2012 7(10):e45828 3. N. T. Cervin, L. Andersson, J. Ng Boon Sing, P. Olin, L. Bergström and L. Wågberg, Biomacromolecules, 14, 503-511 2013. 4. J. P. F. Lagerwall, C. Schütz, M. Salajkova, J. Noh, J. Hyun Park, G. Scalia, and L. Bergström, NPG Asia materials 2014.

Resume : A variety of layered metal oxides have been successfully exfoliated into molecularly thin two-dimensional crystals via reaction with an aqueous solution containing quaternary ammonium ions. The resulting oxide nanosheets are monodisperse polyanions and they can be assembled layer-by-layer into various nanostructures through solution-based processes such as electrostatic self-assembly and Langmuir-Blodgett deposition. Assembly under optimized conditions can lead to multilayer and even superlattice films with precisely controlled nanostructures. Based on this what we call 2D nanoarchitectonics, we have artificially designed various nanostructures, which show attractive functionalities. For example, multilayer films of Ti0.87O20.52- and Ca2Nb3O10- nanosheets exhibit superior dielectric properties even at a nanometer scale thickness. In addition, superlattice assembly of LaNb2O7-/Ca2Nb3O10- develops ferroelectric properties. Function design via this strategy like these examples will be presented.

Resume : Both ferroic and redox-active oxides are ubiquitous in today's society and have been studied for decades. They are constantly undergoing changes to adapt to modern device requirements, and in recent years particularly, nanostructures of these materials are in the focus of interest. This is due, in part, to the fact that many such materials have been shown to be able to outperform their bulk counterparts. Advances in polymer templating over the past years have enabled the fabrication of a myriad of nanocrystalline (non-silicate) oxides with different pore structures and ordering lengths. Their formation essentially relies on the coassembly of inorganic sol-gel precursors with an organic structure-directing agent (SDA). Despite the simplicity of this solution processing route, the difficulty of controlling the crystallization process has limited the preparation of multimetallic oxides with a well-defined pore-solid architecture so far. In this talk, I will specifically focus on the evaporation-induced self-assembly synthesis of ternary (and even more complex) metal oxide thin films having both a cubic mesoporous morphology and highly crystalline walls by using tailor-made polymer SDAs with improved templating properties. Overall, I will show that the integration of mesoporosity with texture-specific properties might pave the way to broaden the scope of application of these oxide materials, particularly when considering the wealth of opportunities for novel device design.

Resume : Although the solution processing of YBa2Cu3O7-x (YBCO) coated conductors is extensively optimized, the critical current density remains too low for high field applications. A possible solution is the introduction of nanocrystals (NCs) of inert metal oxides in the YBCO layer. For this, the NCs are to be stabilized in the YBCO precursor solution, which requires an in depth knowledge of their surface chemistry. In this contribution, we focus on HfO2 NCs as a model system. NCs of 5 nm are solvothermally synthesized in benzyl alcohol using microwave heating. The surface of the charge-stabilized NCs thus obtained can be subsequently modified with fatty acids and oleylamine to disperse them in nonpolar solvents. Concomitantly, aggregates are broken up into the constituting NCs. We present a detailed study of the fundamental (acid/base) processes during the surface modification using 2D NMR techniques like NOESY and DOSY . We also demonstrate that there is no difference in steric stabilization between our system and a surfactant-based synthesis. Importantly, identical results were obtained for ZrO2 NCs. Using these insights, it proved possible to transfer the hafnia NCs to the YBCO precursor solution. The resulting ink was processed via ink-jet printing and after deposition and epitaxial film growth, the superconducting nanocomposite was retrieved. This demonstrates how fundamental insights can have a direct impact on applications.

Resume : A large-scale use of nanotechnology for photocatalysis-based water purification requires to identify simple, reliable and low cost processes for the production of the photocatalytic materials. To this aim we have investigated the possibility to deposit, by electrophoresis, composite layers formed by multi-walled carbon nanotubes (MWCNTs) and titanium dioxide nanoparticles (np-TiO2), with different weight ratios. This method allows one to obtain photocatalytic layers, on any conductive substrates, that in principle can be re-used several times. The photocatalytic efficiency for each MWCNT/np-TiO2 composite layer is evaluated by measuring the degradation of methylene blue (MB) dye induced by UV-Vis light irradiation. The composite layers were characterized by scanning electron microscopy (SEM), Energy Dispersive X-ray analysis (EDX), and photoluminescence (PL) measurements in order to explain the different photocatalytic behaviours observed for each material.

Resume : ZnO has attracted considerable attention for its potential applications, such as ultraviolet light-emitting diodes, laser diodes, solar cells and thin film transistors, because of its wide direct band gap of 3.37 eV and large exciton binding energy of 60 meV at room temperature. The band gap energy of MgZnO can be tuned from 3.37 eV to 7.8 eV by incorporating Mg into ZnO. For the study of the doping effects of MgZnO films, Ga and Al were used to obtained n-MgZnO. For the study of p-type dopant of MgZnO, Cu and N have been discussed. In this study, we are interested in the discussion of the microstructural and optical characteristics of the N doped MgZnO films. The nitrogen-doped MgZnO thin films were prepared on Si substrate by sol-gel spin coating process. The undoped Mg0.1Zn0.9O thin film shows high quality crystallinity after RTA annealing at 800C for 45 sec. It is found that the crystallinity of the Mg0.1Zn0.9O thin film and the preferred c-axis orientation was enhanced through the incorporation of nitrogen doping and heat treatment. The surface morphology of the nitrogen doped Mg0.1Zn0.9O thin film was observed by SEM and showed obviously change after various temperature annealing. The incorporation of nitrogen doping also causes the blue shift of optical band gap energy and the enhancement of transparency of the Mg0.1Zn0.9O thin film.

Resume : Rare-earth doped TiO2 nanoparticles via colloidal so-gel route have been the focus of intense research due to their potential optical application in filters, solar cells and light emitters. These applications require the preparation of good quality thin films from the colloids. Therefore different procedures have been used ranging from simple dipping, and spin coating to electrophoretic deposition. However, these techniques do not allow a precise, nanometric control of the thickness of the deposited layers required for the targeted applications. In this work we report the successful production of optically active thin films using a non-conventional laser based method, called matrix assisted pulsed laser evaporation (MAPLE). TiO2 nanoparticles doped with Eu have been produced using a colloidal sol gel route [1]. The obtained solutions were frozen in liquid nitrogen to form a solid target further used in the MAPLE experiments. The thin film deposition was performed in vacuum or controlled oxygen atmosphere. The films have been characterized by X-ray photoelectron spectroscopy and X-ray diffraction to determine their chemical composition and crystalline structure. Optical properties have been determined by UV-visible spectroscopy and photoluminescence in the visible region. The as-grown films show good uniformity, and efficient Eu light emission in the 600-700 nm range. The enhancement of the films light emission and improvement of the optical response as a function of the post-deposition thermal annealing treatments will be discussed. [1] M. Borlaf, M.T. Colomer, F. Cabello, R. Serna, R. Moreno, J. Phys.Chem C. B 117, 1556 (2013).

Resume : We present our results in nano- and microstructural design of oxide materials by synthesis strategies based on phase separation in sol-gel system. Condensation of hydrolyzed silicon or metal alkoxides progressively decreases the solubility between the gel-forming component and a polar solvent, leading to the formation of spatially separated phase domains. This mechanism has been used for preparing oxide films with continuous pore network [1]. We have applied similar approach to develop high-performance electro-optical hybrids in which LC droplets are encapsulated in gel matrix [2]. Possible applications include privacy glass, optical sensors, light modulators and angular discriminating filters. We have also used the same phase separation principles in a novel method for patterning substrates with round silica features with diameters tunable from nano to micro scale [3]. In addition to non-wetting properties of such surfaces, optical functionality is also achieved as each surface feature acts as a lens. These patterned surfaces can thus be used as structured diffusive, light trapping or anti-glare coatings. References: [1] Nakanishi K., Tanaka N., Accounts of Chemical Research 40 (2007) 863. [2] Timusk M., Järvekülg M., Salundi A., Lõhmus R., Kink I., Saal K., J. Mater. Res. 27 (2012) 1257. [3] Kangur T., Nurmis, L., Järvekülg M., IOP Conf. Ser.: Mater. Sci. Eng, 49 (2013) 012035.

Resume : The p-n junctions, consisting of p-type Pr0.7Sr0.3MnO3 (PSMO) and n-type ZnO layers, have been fabricated on Al2O3 (012) substrates by using pulsed laser deposition. The x-ray diffraction pattern of PSMO/ZnO/sapphire heterostructure implies high degree of epitaxy and good crystallinity. No secondary phase could be found. Such junctions also exhibited excellent and reproducible rectifying behaviors over the temperature range 180K-300K. By applying different magnetic fields, the junction properties can be modified significantly. The influences of optical and strain fields on the junction behaviors were also investigated. Moreover, from the photoluminescence spectra of these heterojunctions, the wavelengths were observed to shift considerably at the magnetic field of H=1T. These phenomena can be attributed to the high magnetic sensibility of PSMO, which causes the dependence of photoluminescence of the junctions on external magnetic fields.

Resume : The sol-gel chemical spray pyrolysis method was used to deposit TiO2 films with gold nanoparticles. The TiO2 spray solution was composed of titanium(IV) isopropoxide (0.2 mol/L) and acetylacetone in a molar ratio of 1:2 in ethanol. HAuCl4∙3H2O (0, 2.6 or 5.4 mol%) was added into the spray solution for incorporation of Au-nanoparticles into TiO2 films. TiO2 and Au:TiO2 layers were deposited onto glass substrates at substrate temperatures in the range of 260-400 °C using pulsed spray solution feed followed by the annealing at 400°C in air. The effect of the deposition and annealing temperature on the plasmonic effect in the Au:TiO2 layers with various Au concentrations was characterized. According to XRD, TiO2 films are amorphous at temperatures below 400 °C; metallic Au was observed in Au:TiO2 layers deposited in the temperature range of 260-300 °C. The mean crystallite size of the Au-nanoparticles remained between 10 and 20 nm. Au:TiO2 layers deposited in the temperature range of 260-300 °C show plasmonic light extinction in the spectral range of 570- 580 nm, which shifts to 620 nm after annealing at 400°C in air. It is planned to adapt TiO2 layers with gold-nanoparticles for thin plasmonic coatings for photovoltaic applications.

Resume : Undoped ZnO and Nd-F codoped ZnO (NFZO) thin films were synthesized at 350 °C on glass substrates by chemical spray pyrolysis method. The effects of cationic and anionic atoms (Nd and F) on the structural, optical and electrical properties were studied. X-ray diffraction analysis indicates that all the films have polycrystalline nature and exhibit hexagonal wurtzite crystal structure. The surface morphology was investigated using atomic force microscopy. The addition of fluorine induced an increase in the optical band gap of the films. Photoluminescence measurements showed that all the films have a strong emission band at around 380 nm. In addition some lines are also observed around 900 nm that are characteristics of Nd3+. This is an experimental evidence of an electronic transfer between ZnO and Nd3+. Finally, a minimum electrical resistivity value, of about 4.0×10-2 Ω.cm was obtained after the insertion of F in the ZnO matrix.

Resume : The insulator–to–metal transition (IMT) in VO2 is accompanied by dramatic increases in electrical conductivity, magnetic susceptibility and infrared reflectivity. It is also accompanied by structural transformation from monoclinic (M1) to rutile (R) structure. The transition is reversible and can be induced in a variety of ways including thermal heating, electrical pumping, or pulsed-laser excitation. In pure VO2 the IMT occurs at about 67C during thermal heating. Due to these features, VO2 is a promising material for optical switching. Incorporation of optically active impurities such as Er3+ into VO2 is of interest for possible integration of optical switching and amplification at telecommunication wavelengths in a single device. We have studied incorporation of Er into VO2 films. Films were formed by pulsed laser deposition. Er incorporation was achieved by ion implantation and thermal annealing. Er photoluminescence (PL) was measured for various Er fluences and annealing treatments. The effects of implantation on the IMT and VO2 structural properties were characterised by Raman spectroscopy and infrared reflectometry. We have found that Er can be incorporated in its optically active state in VO2 for anneals above 800C. The IMT in the Er-doped films occurs at slightly increased critical temperature and the width of the transition is somewhat broadened. We present results of our studies and discuss the implications for incorporation of optically active Er into VO2.

Resume : The preparation and properties of novel ZnO nanostructures - nanorods, nanoneedles, hierarchical nanorods and scrolled nanobelts made by simple, robust and low cost chemical spray pyrolysis method will be introduced. ZnO nanostructures are grown on glass and/or polymeric substrates using aqueous or alcohol based solutions of zinc salts. Solution is pulverised in form of fine droplets onto a preheated substrate. The morphology of ZnO nanorod layers, dimensions and orientation of ZnO crystals are controlled by the growth temperature, precursor concentration and additives in the spray solution which could retard the crystal lateral growth. The density of nanorods is controlled by the substrate type and number of the nucleation centers. The growth and nucleation mechanisms of ZnO nanorods and scrolled nanobelts, and formation of hierarchical nanostructures will be discussed. Examples on growth of metal oxide or sulfide shells by solution methods on ZnO nanorod core will be presented. ZnO nanorod based structures with different morphology are proposed as efficient building blocks for dye, organic and inorganic absorber sensitized solar cells.

Resume : Hexagonal ZnO plates dominated by their highly chemically active polar surfaces were grown in a rapid process in a domestic microwave oven. The aspect ratio of the grown crystals was controlled by adding different concentrations of KCl to an aqueous solution of Zn(NO3)2 and HMTA. A uniform growth product consisting of only ZnO platelets was achieved by tuning the growth solution composition. The chemical composition and the crystal structure of the grown ZnO platelets were characterized using Auger electron spectroscopy and HR-TEM respectively. The surface morphology and electronic structure were studied using AFM and STM. It was found that the nanoplates are terminated by their polar (0001) surfaces. The AFM investigation was performed in ambient conditions with the nanoplates “as grown”. The AFM images of the top surfaces revealed an interesting triangular reconstruction, which was earlier observed only after cycles of sputtering and annealing of the ZnO(0001) surface in Ultra High Vacuum (UHV) systems. The surface atomic and electronic structures of these nanoplates were further studied using STM and Scanning Tunneling Spectroscopy (STS) in UHV. The STM images, captured after a few sputtering and annealing cycles, also showed a triangular structure with single atomic steps and, in addition, a 2x2 surface reconstruction. This reconstruction agrees well with a recently proposed model that involves the removal of 1/4 of the topmost Zn atoms from the ZnO(0001) surface.

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

Resume : ZnO exhibits a wurtzite hexagonal structure and a direct optical bandgap and has been studied for use in many attractive applications such as gas sensors, transport electrodes, piezoelectric devices, varistors and surface acoustic wave devices. Its direct optical bandgap of 3.4 eV at RT is wide enough to transmit most of the useful solar radiation in ZnO/CuInSe2 based solar cells. Furthermore, doped ZnO such as AZO (Al-doped ZnO) is a good candidate to substitute for ITO (Sn-doped In2O3) and FTO (F-doped SnO2) in transparent conductive electrodes. Low-temperature growth method for ZnO is important for compatibility with photovoltaic device fabrication processes. However, it is known that low-temperature growth is difficult in non-vacuum processes. There are few reports on low-temperature growth, less than 200 ˚C under non-vacuum condition. Recently, Blumstengel et al. reported that a low-temperature growth of ZnO epitaxil film on ZnMgO/sapphire (11-20) by plasma-assisted MBE at 50 °C [1]. Furthermore, Nishinaka et al reported low temperature growth of ZnO at 180 ˚C by an ultrasonic-spray assisted mist CVD using zinc acetate dehydrate in a mixture of methanol and water [2]. They indicated that the deposition at low-temperature was attributed to water-activated precursor reactions. In our previous work [3], non-doped ZnO films were successfully grown on a polyethylene terephthalate film by a conventional spray pyrolysis at 150 ˚C using a diethylzinc (DEZ)-based solution under an air atmosphere. The samples average optical transmittance had more than 80%, flat surfaces and a predominately a-axis orientation determined from optical transmittance, scanning electron microscopy (SEM) and x-ray diffraction (XRD) measurements, respectively. It is well known that the DEZ reacts with water and/or oxygen at low temperature, and ZnO can be generated [4, 5]. However, the DEZ reacts violently with water and easily ignites upon contact with air. Therefore, in its pure state, it should be handled using inert atmosphere techniques. In this work, the DEZ solution was diluted by diisopropyl ether in order to control its reactivity towards an air and water. The diisopropyl ether is a secondary ether that is used as a solvent. The solution is a colorless liquid that is slightly soluble in water, but miscible with most organic solvents. Non-doped ZnO films were grown on a glass substrate by a spray pyrolysis under an air atmosphere. The conventional spray pyrolysis system described in previous work [3] was used. The substrate temperature was between RT and 300 ˚C and the DEZ, in solution form, was used as the Zn source material. The thickness of the samples was approximately 0.6 m. The growth rate was approximately 50 nm/min in this study. The samples were examined by XRD and SEM for structural characterization. Optical transmittance was measured at room temperature (RT) for wavelengths between 300 and 2000 nm. Furthermore, Hall measurements were carried out at RT using Van der Pauw method. Indium was used as an ohmic contact. It is clearly observed that peaks of (10-10) at 31.75˚ which represents a-axis orientation, (0002) at 34.39˚ which represents c-axis orientation and (10-11) at 36.19˚ are dominant in the XRD spectrum of the ZnO. Their peak positions correspond to those of the JCPDS ZnO reference. This indicates that the non-doped ZnO film, with a hexagonal wurtzite structure was successfully grown on a glass substrate at low temperature using DEZ-based solution under an air atmosphere. The lattice constants of both a- and c-axes are calculated from the three peaks in the XRD spectrum. It is clear that the lattice constants of both a- and c-axes correspond to those of the JCPDS ZnO reference. The average optical transmittance is clearly above 80% in both samples. The transmittance in the IR region is also above 80%. This indicates poor absorption due to free carriers in the IR region. The carrier concentration of is 2 × 1018 cm-3 obtained by Hall measurement. A fundamental absorption is clearly observed approximately at 350 - 370 nm. This value is similar to that reported Gao et al., indicating that the sample has a high level crystallinity [6]. An interference wave can be observed, which means that the sample grown at 150 ˚C has a smoother and more homogenous surface. The ZnO films are nearly uniform over the entire substrate surface area. ZnO films have been grown using a non-vacuum process at low temperature. It is known that growth using DEZ solution at low temperature (150 ˚C) is attributed to atmospheric oxygen and/or steam [4, 5]. In the sample grown at 150 ˚C, however, it is assumed that atmospheric steam plays dominant role in comparison to the atmospheric oxygen because DEZ reacts violently with water and easily ignites upon contact with air at low temperature [3]. It is well known that ZnO films can be obtained at low temperature by the reaction of water and DEZ: (C2H5)2Zn + 2H2O = Zn(OH) 2 + 2C2H6. Zn(OH) 2 = ZnO + H2O However, from the quantum chemical method as well as from the experiments [7], it is suggested that ZnO film can be obtained by the reaction of water and DEZ, which, when driven to completion, is given by: (C2H5)2Zn + H2O = (C2H5)Zn(OH) + C2H6 (C2H5)Zn(OH) + H2O = Zn(OH)2 + C2H6 Zn(OH) 2 = ZnO + H2O In this chemical reaction, the DEZ reacts violently and exothermically with water at low temperature. [1] S. Blumstengel, S. Sadofev, H. Kirmse, and F. Henneberger, Appl. Phys. Lett. 98 (2011) 031907. [2] H. Nishinaka, Y. Kamada, N. Kameyama and S. Fujita, Jpn. J. Appl. Phys. 48 (2009) 121103. [3] K. Yoshino, Y. Takemoto, M. Oshima, K. Toyota, K. Inaba, K. Haga, and K. Tokudome, Jpn. J. Appl. Phys. 50 (2011) 040207 [4] C. K. Lau, S. K. Tiku, and K. M. Lakin, J. Electrochem. Soc. 127 (1890) 1843. [5] S. K. Ghandhi, R. J. Field, and J. R. Shealy, Appl. Phys. Lett. 37 (1980) 449. [6] X. D. Gao, X. M. Li, W. D. Yu, L. Lei, J. J. Qiu, and F. Peng, Sol. Energy Sol.cells 91 (2007) 467. [7] K. Maejima, H. Kawabata, and S. Fujita, Jpn. J. Appl. Phys. 46 (2011) 7885.

Resume : Hexagonal ZnO nanorods were grown on P-Si (100) substrates by simple chemical method by using precursors as ammonium persulphate (NH4)2S2O8, sodium hydroxide NaOH and zinc metal powder (Merck chemicals). X-ray diffraction, field emission scanning electron microscope, high resolution transmission electron microscope and photoluminescence have been used to characterize the structural and optical properties of the grown ZnO nanorods. Structural and photoluminescence properties of ZnO nanorods were investigated as a function of growth temperatures. X-ray diffraction patterns of ZnO nanorods reveal the formation of hexagonal wurtzite structures. Room temperature photoluminescence spectrum of ZnO nanorods showed the emission peak at 3.254 eV, originate from the recombination of free excitons. Origin of green emission at 2.470 eV has been explained in light of oxygen vacancy mediated deep donor levels transition to valence band edge. Reference 1. Z. L. Wang, J. Phys. Condens. Matter. 2004,16, 829-858 2. U. Ozgur, Y. I. Alivov, C. L. A. Teke, M. A.Reshchikov, S Dogan, V Arutin, S. J Cho, H. Morkoc, J. Appl. Phys., 2005, 98, 41301 3. H. Yu, E. A. Azhar, T. Belagudu, S Lim, and S. Dey, 2012, 111, 102806 4. R. Viswanatha, H. Amenitsch, and D. D. Sarma, J. Am, Chem. Soc., 2007, 129, 4470-4475

Resume : Photocatalytic materials' latest challenge nowadays is the fine tuning of their activity, selectivity towards a given pollutant. To achieve this scope there are several ways. One of them is the shape tailoring of the semiconductor oxides. In the present work TiO2 and WO3 nanocrystals shape was varied using different hydrothermal synthesis approaches. The obtained differently shaped (nanoeggs, nanostars, nanorods) semiconductor oxides were characterized by XRD, TEM, SEM, XPS and DRS. The obtained nanomaterials photocatalytic activity was evaluated for phenol and oxalic acid removal. Their degradation intermediates profile was registered and structural entities-degradation intermediates relation was successfully explored. This latter process makes possible the safe application of these photocatalytic materials. Acknowledgements: The following projects are acknowledged: PN-II-ID-PCE-2011-3-0442, financed by Romanian National Authority for Scientific Research, CNCS-UEFISCDI and the Romanian-Hungarian bilateral project nr.661/2013/K-TÉT_12_RO-1-2013-0109966. Also the research grant nr. GTC 34027 is thanked, which was provided by the Babes-Bolyai University for young researchers

Resume : For efficient silicon solar cells fabrication, anti-reflective coating facilitates transmission of majority of the light and less scattering. One dimensional Nanostructures and Nanoporous material play vital role to improve anti-reflection properties due to their wave guiding and/or grade refractive index nature. In this connection, TiO2 nanotubes (TiNT) were synthesized by alkaline hydrothermal method at 130C for 20 h using commercial TiO2 bulk particles as precursor. In the following, TiNT films were deposited on polished as well as textured silicon substrates using electrophoretic deposition. The films showed a minimum reflectance of ~ 6% at the wavelength of 600 nm. Quasi-steady state photoconductivity measurements on the TiNT coated samples showed a considerable improvement of minority carrier lifetime in n-type silicon is considerable after a short annealing in forming gas at 400oC for 30 min. Capacitance ? Voltage measurements suggested that the TiNT layers contain negative fixed charge, which led to passivate n-type silicon. The dual property of TiNT layers such as anti-reflection as well as passivation is promising for the enhancement of the photovoltaic conversion efficiency of silicon solar cells.

Resume : Recent reports on the influence of performance of perovskite-type materials on photovoltaics have led to increased interest. The photovoltaic (PV) effect of ferroelectric materials like perovskite BaTiO3 was studied in the 1970s. One particular multiferroic material, coupling both ferroelectric and magnetic properties, is perovskite bismuth ferrite (BiFeO3, BFO). Interest in BFO has gathered pace due to inherent properties and recently reported anomalous photovoltage. A ZnO:sensitiser photovoltaic device without BFO (ZnO/N719/CuSCN) produced a Jsc of 0.64 mA/cm2, Voc of 0.38 V giving an overall efficiency of 0.1% giving equivalent results to that reported previously. For ZnO/BFO/N719/CuSCN structures with partial BFO coverage (50-60% of ZnO exposed), the Jsc and Voc increased to 0.79 mA/cm2 and 0.47 V, and efficiency to 0.2%. The efficiency increased to 0.38 % with conformally covered BFO at 2.5 nm average thickness, but dropped with a thicker BFO coating that averaged 7 nm. The Voc increased to 510 mV when the surface of the ZnO was conformally coated. In contrast, Jsc increased with BFO coverage up to a maximum of 1.38 mA/cm2 2.5 nm thick BFO. It then decreased for the thicker BFO coating. In all cases fill factors (FF) were around 0.55. We describe the evaluation of device enhancement and conclude that for our structures we have produced an effective BFO solid-state electron blocking layer that is responsible for a ca 400% enhancement in performance.

Resume : In this work, we report the application of a sol-gel derived ZnO thin film as a buffer layer for high efficiency inverted polymer solar cells (PSC). ZnO films are widely used in inverted devices because they have a relatively high electron mobility, high transparency and environmental stability. The ZnO precursor was prepared by dissolving zinc acetate and ethanolamine in the 2-methoxyethanol. ZnO thin films were then deposited on ITO/glass substrates by spin casting the above solution. Different annealing temperature were at relatively low annealing temperatures (<200°C). Inverted polymer solar cells whit the configuration ITO/ZnO/PBDTTT-C:[70]PCBM/MoO3/Ag were realized in order to test the performance of ZnO thin film. We made a comparative study of the electrical behaviour of different devices in order to investigate the influence of different annealing temperature of the ZnO layer on the solar cells performances. All the devices were characterized by UV-VIS spectroscopy, IV light, IV dark and quantum efficiency measurements. The best device reached a power conversion efficiency of 7%.

Resume : Compact thin films of TiO2 are required for recombination blocking in DSSCs. They are grown on FTO by electrochemical deposition from solutions of TiCl3 or by sol-gel dip-coating from solutions containing poly(hexafluorobutyl methacrylate) as the structure-directing agent. The films are quasi-amorphous, but crystallize partly to anatase upon heat treatment. Cyclic voltammetry using ferri/ferrocyanide or spiro-OMeTAD as the model redox probes indicates selectively the pinholes, if any, in the layer. The pinhole-free films on FTO represent excellent rectifying interface, at which no anodic Faradaic reactions occur in the depletion state. The flatband potentials of the electrodeposited films, determined from Mott-Schottky plots, are comparable to those of anatase single crystal. The values of sol-gel films are upshifted by ca. 0.2-0.4 V, yet still follow the Nernstian pH dependence. The optimized buffer layer embodies interplay of quasi-amorphous morphology, responsible for the electrochemical blocking function, and the calcination-induced crystallinity, responsible for the fast electron injection and transport in the conduction band. The latter manifests itself by reversible charging of chemical capacitance and band-gap trap states of TiO2 in its accumulation state. The solution-processed layers are outperforming those made by standard methods, i.e. spray pyrolysis and ALD. This work was supported by the Czech National Foundation, contract No. 13-07724S.

Resume : Breakthroughs in the field of solar-to-electricity conversion are intimately related to the progress in materials research and development. In particular, materials obtained using the potential of nanotechnologies should give rise to new advances. The photoactive properties of transition metal oxides are very attractive allowing many applications in the environmental domains (photocatalysis, photovoltaics…). Their integration in hybrid solar cells requires the elaboration of films to optimize collection and transport of the photogenerated charge carriers. We develop solvothermal syntheses of nanostructured transition metal oxides leading to stable colloidal solutions. In order to remain compatible with low temperature processes on plastic substrates, the solvent is selected to monitor the physico-chemical properties of the obtained solutions. They can be deposited as thin films by printing processes or by electrodeposition [1], without annealing at high temperature. Some examples of oxide layers processed from solutions will illustrate the potentials of our approach in the field of organic bulk heterojunction solar cells. [2] [1] Jouenne, V.; Duvail, J.-L.; Brohan, L.; Richard-Plouet, M., MRS Online Proceedings Library, 1578, 2013 [2] Karpinski, A.; Berson, S.; Terrisse, H.; Mancini-Le Granvalet, M.; Guillerez, S,; Brohan, L.; Richard-Plouet, M. Solar Energy Mater. & Solar Cells 116, 27-33, 2013