Publications

The energy band alignment at interfaces between different materials is a key factor, which determines the function of electronic devices. While the energy band alignment of conventional semiconductors is quite well understood, systematic experimental studies on oxides are still missing. This work presents an extensive study on the intrinsic energy band alignment of a wide range of functional oxides using photoelectron spectroscopy with in-situ sample preparation. The studied materials have particular technological importance in diverse fields as solar cells, piezotronics, multiferroics, photoelectrochemistry and oxide electronics. Particular efforts have been made to verify the validity of transitivity, in order to confirm the intrinsic nature of the obtained band alignment and to understand the underlying principles. Valence band offsets up to 1.6 eV are observed. The large variation of valence band maximum energy can be explained by the different orbital contributions to the density of states in the valence band. The framework provided by this work enables the general understanding and prediction of energy band alignment at oxide interfaces, and furthermore the tailoring of energy level matching for charge transfer in functional oxides. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We report on the changes on the microstructural, hardness, and corrosion properties induced by carbo-chromization of 316L stainless steel prepared by Spark Plasma Sintering technique. The thermo-chemical treatments have been performed using pack cementation. The carburizing and chromization were carried out between 1153 K (880 A degrees C)/4 h to 1253 K (980 A degrees C)/12 h and 1223 K (950 A degrees C)/6 h to 1273 K (1000 A degrees C)/12 h in a solid powder mixture of charcoal/BaCO3 and ferrochromium/alumina/NH4Cl, respectively. The obtained layers were investigated using X-ray and electron diffraction, optical and scanning electron microscopies, Vickers micro-hardness, and potentiodynamic measurements. The thickness of the carbo-chromized layer ranges between 300 and 500 mu m. Besides the host gamma-phase, the layers are mainly constituted of carbides (Fe7C3, Cr23C6, Cr7C3, and Fe3C) and traces of alpha'-martensite. The average hardness values decrease smoothly from 650 HV at the sample surface down to 200 HV at the center of the sample. The potentiodynamic tests revealed that the carbo-chromized samples have smaller corrosion resistance with respect to the untreated material. For strong chromization regimes, the corrosion rate is increased by a factor of four with respect to that of the untreated material, while the micro-hardness of the layer is three times larger. Such materials are suited to be used in environments where good corrosion resistance and wear properties are required.

A new noniterative method, for determining the dielectric, piezoelectric and elastic constants, in complex form, for piezoceramic materials, in the thickness extensional mode, was proposed. This method is very flexible, as it is based on the standard approach to determine the elastic stiffness, followed by the measurement of the impedance at two frequencies to calculate the dielectric and piezoelectric constants, by solving a system of two equations. The new method was tested on materials with various thickness coupling factors (k(t) = 4.5-60%) and mechanical quality factors (Q(m) = 20-1600), proving very good accuracy for all of them. The accuracy of standard method was also evaluated for the same materials. (C) 2014 Elsevier Ltd. All rights reserved.

Organic heterostructures were fabricated by matrix assisted pulsed laser evaporation (MAPLE) method using arylenevinylene oligomers based on triphenylamine (P78)/carbazole (P13) group and tris(8-hydroxyquinolinato)aluminum salt (Alq3). Optical properties of the organic multilayer structures were characterized by spectroscopic techniques: FTIR, UV-vis and photoluminescence (PL). A good transparency (over 60%) was remarked for the structures with two organic layers in the 550-800 nm range. Photoluminescence (PL) spectra proved that the emission characteristics of the materials have been preserved. I-V characteristics of (ITO/oligomer/Alq3/Al and ITO/Alq3/Al) heterostructures were symmetrically while rectifying properties of these heterostructures have not been observed. A comparison between the heterostructures made of layers with different thickness reveals that the higher current (8 x 10(-6) A at 1 V) was obtained for the ITO/P78/Alq3/Al heterostructure, which is characterized by a larger thickness of the double organic layer. AFM measurements revealed a similar topography while RMS values of the reported structures depend on the organic material. (C) 2013 Elsevier B.V. All rights reserved.

We report the continuous, single step synthesis of titania/iron-based magnetic nanocomposites in a single step using gas-phase laser pyrolysis technique by separately and simultaneously introducing the precursors (together with C2H4 sensitizer) in the reaction zone: Fe(CO)(5) on the central flow and, using air as carrier, TiCl4 on the annular coflow. The laser power and, for the last experiment, the injection geometry were modified in order to change the Fe/Ti ratio in the resulted nanopowders. Due to the specific geometry, the reaction zone (visible as a flame) have a reductive inner central zone surrounded by and oxidative environment, allowing the formation of the metallic-carbidic iron and/or iron-doped titania and iron oxide nanophases. The raw Fe-containing nanopowders have a ferromagnetic behavior, those synthesized at higher laser power and gas velocities show significant saturation magnetization M-s values (10-12 emu/g), whereas those obtained (with higher yield and carbon content) at lower laser power and gas velocities (using wider central nozzle cross-section) have a very weak magnetization (M-s similar to 0.05 emu/g) in spite of the higher ethylene carried Fe(CO)(5) flow. The powders were annealed in air at 400 degrees C show lower carbon content and, for those highly Fe-doped, the hematite phase formation. Preliminary tests using UV light confirm the photocatalytic action of the annealed nanopowders in salicylic acid degradation process in solution. (C) 2013 Elsevier B.V. All rights reserved.

This paper presents some studies about the bi-layer organic heterostructures realized with zinc phthalocyanine (ZnPc) as donor layer and 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) as acceptor layer, on substrate of glass covered by Al doped ZnO (AZO) layer. These heterostructures have been prepared using laser techniques: pulsed laser deposition (PLD) in an atmosphere of oxygen for AZO films deposition and matrix assisted pulsed laser evaporation (MAPLE) for organic films deposition. The influence of the deposition conditions on the transmission of the organic films has been analysed. The effect of the oxygen plasma treatment, with duration of 5 min and 10 min, on the surface topography, structural and optical properties of AZO layers deposited by PLD and, as consequence, on the optical and electrical properties of the single layer (ZnPc) and bi-layer (ZnPc/NTCDA) organic heterostructure, deposited by MAPLE, was investigated. (C) 2014 Elsevier B.V. All rights reserved.

Vortex excitations and creep regimes in YBa2Cu3O7 (YBCO) films with nonsuperconducting nanorods (columnar defects) and/or nanoparticles in a low external magnetic field H oriented perpendicular to the film surface have been identified using standard DC magnetization relaxation measurements. It was found that by increasing the pinning energy dispersion through nanoparticle addition the relevant changes in the temperature T variation of the normalized magnetization relaxation rate S appear at relatively high temperatures (T similar to 65K for H = 2 kOe), owing to the inhibition of double vortex- kink formation. This indicates that the often observed S(T) maximum at low T (around 30 K) is not related to the excitation of double vortex kinks and super-kinks in specimens with columnar defects, as previously believed. The low-T S(T) maximum is present in the case of strongly pinned specimens without nanorods, as well, and depends on the film thickness, which definitely shows that it is caused by thermo-magnetic instabilities, as recently suggested. (C) 2014 Elsevier B.V.All rights reserved.

Multivalence Ce and Sn oxide doped materials are of critical importance in many renewable energy applications, especially in a porous form. Of special interest is the understanding of the basic properties of Ce-Sn-O nanoparticles and the effect of doping with different trivalent (Fe3+, Yb3+, Gd3+) elements, as well as developing Ce-Sn-O materials in the form of homogeneous and heterogeneous multilayers with unique properties at high temperature. We discuss various applications of nanosize metal-oxide sensors and energy conservation through improved energy efficiency such as renewable sources and fuel cells. In addition, ceria and ceria-based materials are studied for their electronic, magnetic, optical, and catalytic properties, which are important in applications such as gas sensors, heterogeneous catalysis, solid electrolyte fuel cells (SOFC), and UV-shielding application. Additionally, at the nanoscale, the surface area of metal oxide particles is dramatically increased, which not only increases oxygen exchange but also makes it easy for redox reactions.

In this work we have investigated the electrochemical processes by which Pt nanoparticles were included in (Bi,Sb)(2)Te-3 films and submicrometer wires. Solutions containing ions of Bi3+, HTeO2+ and Sb3+ as well as Pt nanoparticles or [PtCl6](2-) ions were used for this study. For comparison, a solution with the same composition in Bi3+, HTeO2+ and Sb3+ ions was used to study the electrodeposition process of (Bi,Sb)(2)Te-3 films and submicrometer wires. Linear and cyclic voltammetry was employed in experiments to find the influences of addition to electrodeposition bath of Pt nanoparticles or [PtCl6](2-) ions on deposition process of (Bi,Sb)(2)Te-3 film. Pt-(Bi,Sb)(2)Te-3 nanocomposites has been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectrometry (EDX) to determine structural, morphological and compositional properties. Two mechanisms for Pt nanoparticles embedding in (Bi,Sb)(2)Te-3 films and wires have been proposed. (c) 2014 Elsevier Ltd. All rights reserved.