Publications

We apply the Keldysh formalism in order to derive a current formula easy to use for a system with many sites, one of which is interacting. The main technical challenge is to deal with the lesser Green's function. It turns out that, in the case of the left-right symmetry, the knowledge of the lesser Green's function is not necessary and an exact current formula can be expressed in terms of retarded Green's functions only. The application is done for a triangular interferometer which gives a good account of the Fano-Kondo effect. It is found that the interference effects, in the context of Kondo correlations, give rise to a point in the parameter space where the conductance is temperature independent. We include a comparison with the results from Ng's ansatz [Phys. Rev. Lett. 70, 3635 (1993)], which are less accurate, but can be used also in the absence of the above mentioned symmetry.

The present paper deals with the preparation and study of optical properties of ZnO nanowires. Nanoporous ion track polycarbonate foils were used as templates for ZnO nanowires growth by electrochemical deposition. The growth was performed using an aqueous electrochemical bath at a temperature of 70 degrees C. SEM and TEM were employed to study the morphological properties of the nanowires. Electron diffraction was employed for structural characterization. Reflection and photoluminescence spectroscopy were used for optical characterization. A comparison between the properties of electrodeposited thin films and nanowires of ZnO was made from the point of view of photoluminescence properties. (c) 2007 Elsevier B.V. All rights reserved.

Electrolytic coloration has been made for KCl crystals doped with Tl+ ions and doped with Tl+ and Ca2+ ions. Intensity decrease of the Tl+ absorption bands is observed in the two colored crystals, while several new absorption and emission bands are observed. They are attributed to Tl- ions which were converted from Tl+ ions by electron injection during electrolytic coloration. Different absorption and emission bands are observed for KCI:TI and KCI:T1 + Ca crystals. Sharp absorption band appears at 285 nm in the colored KCl:Tl and at 400 and 503 nm in the colored KCLTl + Ca. Infrared emission bands are observed at 1470, 1600 and 2185 nm in colored KCI:Tl, while at 1630 and 1900 nm in colored KCl:Tl + Ca. It is suggested that the absorption and emission bands in KCl:Tl + Ca are due to Tl- ions perturbed by Ca2+ or vacancy at the nearest neighbor. (c) 2006 Elsevier B.V. All rights reserved.

The X-ray, HRTEM, electrical resistivities, magnetic and Mossbauer effect studies were performed on Sr2FeMoO6 samples. It was shown that the nonuniform composition inside the grains and that at grain boundaries influence the magnetoresistive properties. (c) 2007 Elsevier B.V. All rights reserved.

Pb(Zr1-xTix)O-3 (PZT) thin films were prepared by sol-gel method on stainless steel (SS) and on platinum-coated silicon substrate (Pt/Si). The structure revealed by X-ray diffraction shows strong crystallographic orientation: (110) and (100), respectively. A small amount of pyrochlore phases (Pb-2(Zr,Ti)(2)O6-delta is formed in the films deposited on SS substrate. The crystallite size shows significant differences: d((00l))((SS)) = 27.1 nm, d((h00))((Pt)) = 88 nm. The tetragonal splitting is (Delta c/c)((SS)) = 3.55 % and (Delta c/c)((Pt)) = 3.32 %.

The Fe-57 Mossbauer spectra of NdFe1 (-x) GaxO3 ( x = 0, 0.1, 0.2, 0.25, 0.5 and 0.7) have been measured at room temperature (RT). For x < 0.5 the spectra have been fitted with magnetic sextets with their areas following a binomial distribution of Fe surroundings with Ga neighbours. The spectra for x = 0.5 and 0.7 show paramagnetic doublets, which account for the percolation effect induced by the non-magnetic Ga substitution for Fe, which has been estimated to be x = 0.43 at RT. The analysis of the hyperfine field values as a function of the Ga concentration shows the effect of the variations of the antiferromagnetic sublattice magnetization. Moreover, the dependence of this field with the number of susbstituted neighbours suggests an increase of the average Fe-O-Fe exchange interaction as a consequence of the lattice contraction when Ga susbtitutes for Fe. (c) 2007 Elsevier B.V. All rights reserved.

In order to prepare poly(N-vinyl carbazole) (PVK) and carbon nanotube (CNs) based composites, electrochemical polymerization of N-vinyl carbazole (NVK) was studied by cyclic voltammetry (CV) in LiClO4/acetonitrile solutions. Cyclic voltammograms recorded on a blank Pt electrode and those obtained when single or multi-walled carbon nanotubes (SWNTs or MWNTs) films were previously deposited onto the Pt electrode show a down-shift of the VK reduction peak potential in the latter case. The influence of monomer concentration and supporting electrolyte on the polymerization conditions and electrochemical properties of these composite materials were also investigated. Morphologic aspects as well as the photoluminescence properties of the PVK/CNs composite were also investigated. A covalent functionalization of carbon nanotubes with PVK is suggested on the basis of infrared (IR) spectroscopic studies. Using the PVK/CN composite as a positive electrode and an electrolytic solution containing LiPF6, a higher specific discharge capacity of the rechargeable lithium cells, similar to 45 and 115 mA h g(-1), are reported for PVK functionalized SWNTs and MWNTs, respectively. (c) 2007 Elsevier Ltd. All rights reserved.

The Fe-Pt-rich alloys has recently attracted a lot of interest for their potential development of the hard magnetic L1(0) (also denoted gamma(1)) FePt phase with high magnetocrystalline anisotropy. An alloy with the nominal composition Fe65Pt25Nb2B8 has been synthesised by rapid quenching of the melt. The phase evolution in the as-cast ribbons was monitored by energy dispersive X-ray diffraction of the synchrotron radiation. It is shown that the Fe65Pt25Nb2B8 alloy is completely crystallized in the as-cast state. With increasing temperature a partial disorder-order phase transformation with occurrence of hard magnetic L1(0) phase is observed. This transformation is directly related to thermal and pressure effects in the sample. With applying pressure, the phase transformation between cubic and tetragonal FePt symmetry is more pronounced and is accompanied by a strong uniaxial lattice expansion. The results are extremely promising for the direct formation from the melt of an exchange coupled hard-soft magnetic alloy with initial formation of the tetragonal hard magnetic L1(0) FePt phase. (C) 2006 Elsevier B.V. All rights reserved.

Skutterudite (Co0.92Ni0.08)(4) Sb11.88Te0.12 powder has been consolidated under an applied electrical field using a field-assisted sintering technique (FAST). The low FAST sintering temperature and relatively high heating rate considerably reduce grain growth during sintering. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Exchange coupling between alternatively dispersed hard and soft magnetic phases, gives rise to exchange spring magnets with enhanced energy product (BH)(max) that are believed to represent a novel class of permanent magnets with improved properties. The synthesis of a hybrid nanocomposite system made of soft magnetic Fe3B melt spun ribbon and hard magnetic Fe-Pt thin film, obtained by e-beam co-deposition in ultrahigh vacuum onto the ribbons, is reported. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction are used for structural characterization of these hybrid samples. Magnetic measurements provide observation of a drastic decrease of the saturation magnetization, compatible with the exchange coupling between hard and soft magnetic phases in the melt spun/thin film samples.