Publications

The growth of La5Ca9Cu24O41 thin films on SrLaAlO4 (1 0 0) and Gd3Ga5O12 (1 0 0) substrates by pulsed laser deposition is reported in this paper. The influence of deposition process parameters, such as oxygen pressure, substrate temperature, and laser repetition rate, on the crystallinity, orientation and microstructure of the films has been investigated. X-ray diffraction and atomic force microscopy studies showed a clear dependence of the film crystallographic orientation and morphology (grain size) on the substrate temperature and the oxygen pressure used in the deposition process. (c) 2012 Elsevier B.V. All rights reserved.

Intermetallic Fe-Sn and nanocrystalline metallic Sn nanoparticles have been successfully synthesized from organic precursors using the laser pyrolysis technique with ethylene as sensitizer. Nano-structured Sn (single phase) was prepared by the pyrolysis of Sn(CH3)(4) (TMT) vapors. Controlled Fe/Sn atomic ratios, ranging from 0.69 to 1.64 were obtained for the prepared Fe-Sn nanopowders by the control of Fe(CO)(5) and TMT flows, respectively. XRD studies evidence three main phases: the tetragonal metallic Sn phase and the intermetallic FeSn2 phase and, to a much lesser extent, the cubic ternary carbide Fe3SnC. Complex core-shell structural characteristics were found by HRTEM analysis. More complete information about the Fe phase distributions in the new intermetallic Fe-Sn nanomaterial is provided by temperature dependent Fe-57 Mossbauer spectroscopy. (c) 2012 Elsevier B.V. All rights reserved.

The hysteretic behavior of the epitaxial Pb(Zr,Ti)O-3 thin films with different top metal electrodes is studied, with emphasis on the influence of the leakage current and trap generation current on the shape of the loop as well as on the magnitude of the measured polarization. Cu, Pt, and SrRuO3 were used as top contacts and important differences were observed for measurements performed in both dynamic and static modes, although the contacts were deposited on the same epitaxial Pb(Zr,Ti)O-3 film grown on SrRuO3/SrTiO3 substrate. A peculiar behavior was observed especially for the static hysteresis loops where, depending of the top contact, the loop is influenced mainly by the leakage current (Pt) or by the trap generation current (Cu and SrRuO3). The last one can contribute with an additive charge, having a linear dependence on the applied voltage, as suggested by the simple model developed to explain the abnormally high values of the dielectric constant extracted from the linear part of the static hysteresis loop. It is concluded that the properties of the top electrode interface can significantly impact the hysteretic behavior of the ferroelectric films. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754318]

We synthesized by wet chemical route a novel europium-potassium phthalate complex Eu3+K+[(COO)(2)(C6H4)](2). The compound is a white powder insoluble in water. X-ray diffraction evaluation shows that we obtained a new crystalline compound with no traces of the starting materials (potassium hydrogen phthalate and europium chloride). Scanning electron microscopy reveals that the powder consists of fiber-shaped structures with sizes larger than 250 nm in diameter. Energy dispersive X-ray analysis proves that the compound has a 1:1 europium-potassium ratio. Fourier transform infrared spectroscopy confirms the presence of the phthalate in the new compound. Photoluminescence and cathodoluminescence measurements show that the fiber-shaped structures are intensely luminescent with emission bands corresponding to the D-5(0) -> F-7(J) (J = 1-4) Eu (III) ion's transitions in the region between 580 nm and 700 nm, the most intense maximum being observed around 615 nm. Up-converted luminescence with a maximum at 315 nm was recorded. (c) 2012 Elsevier B.V. All rights reserved.

Acid-base interactions between amino-silica and carboxyl-gold protected nanoparticles, functionalized or not with free stable radicals or fluorescent moieties, were studied by ESR, fluorescence, and TEM. While those nanoparticles are stable in solution, mixing them induces aggregation, due to acid-base interactions; addition of a base or an acid redissolves them. By ESR, strong spin-spin interactions were noticed; by fluorescence, only small differences may be observed, while by TEM, it was noticed that gold nanoparticles are distributed evenly on the surface of the silica nanoparticles. (C) 2012 Elsevier B.V. All rights reserved.

Transparent ZnO films are synthesized by RF-magnetron sputtering (1.78 MHz) onto glass substrates, using a mild-pressed ZnO powder target. The depositions were carried at three inert argon pressures (0.25 Pa, 0.30 Pa, and 0.45 Pa) at two substrate temperatures (100 degrees C and 400 degrees C). The role of the sputtering conditions on ZnO thin films nanostructuring, optical properties and morphology is investigated by Xray diffraction (XRD), X-ray reflectometry (XRR) and Spectroscopic ellipsometry (SE). XRD investigations revealed that ZnO films show a (0 0 l) texture with nanosized crystallites. Right-angle asymmetry of the (0 0 2) diffraction peak is observed. The peak profile analysis using pseudo-Voigt functions unveils a double overlapped peak structure with different coherent zone size values. A double layer structure is evidenced by analyzing the XRR data. Samples prepared at 0.3 Pa at a temperature of 400 degrees C have a similar to 4 nm bottom layer consisting of highly depleted in oxygen ZnO1-x structure, continued by a 53 nm top layer of textured ZnO. Electrical measurements show that the temperature dependence of the conductivity is well described by the Mott variable range hopping (VRH) law. The samples obtained at 400 degrees C have a significantly lower resistivity. (C) 2012 Elsevier B. V. All rights reserved.

Indium zinc oxide (IZO) thin films were obtained using pulsed laser deposition. The samples were prepared by ablation of targets with In concentrations, In/(In + Zn), of 80 at.%, at low substrate temperatures under reactive atmosphere. IZO films were used as transparent electrodes in polymer-based -poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 1:1 blend - photovoltaic cells. The action spectra measurements revealed that IZO-based photovoltaic structures have performances comparable with those using indium-tin-oxide as transparent electrode. (C) 2012 Elsevier B.V. All rights reserved.

The present paper presents the effects of a nanostructured, ferromagnetic La1-xSrxMnO3(LSMO) thin film on the pinning characteristics of an epitaxial YBa2Cu3O7(YBCO) thin film deposited on top. Ordered arrays of LSMO grains were obtained upon growing the film on a terraced (001) SrTiO3 substrate. The analyses of magnetic measurements revealed the presence of a complex vortex pinning mechanism within the YBCO film. With respect to a reference single YBCO layer, an additional pinning potential was observed. Its temperature evolution suggests that a magnetic pinning mechanism is responsible for improved pinning characteristics in the high temperature and field region. Based on the morphology of the underlying LSMO buffer, a strong pinning force is expected to arise due to the anti-dot formations, where a high magnetization gradient exists. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4748049]

Styrene, methyl methacrylate and glycidyl methacrylate vinyl monomers were grafted onto chitosan by surfactant-free emulsion copolymerization using potassium persulfate as initiator. The grafted compounds were characterized by X-ray diffraction, FTIR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and zeta potential measurements. X-ray diffraction showed changes in the crystallinity pattern of chitosan after the copolymerization reaction. Evidence of grafting was confirmed by FTIR spectroscopy. From zeta potential measurements it is found that the surfaces of graft copolymers latex particles have positive charges resulting from the cationic chitosan molecules. The morphology evaluated by SEM, TEM and AFM proves that in the absence of chitosan, latexes of vinyl homopolymers contain quasi-monodispersed spheres with average diameter of about 400 nm or 250 nm while the graft copolymers latexes are formed by clustered irregular beads with average diameter around 100 nm.