Publications

Epitaxial antiferroelectric/ferroelectric PbZrO3/PbZr0.8Ti0.2O3 multilayers were grown on SrRuO3-electroded SrTiO3(100) substrates by pulsed laser deposition. Polarization-field and switching current-voltage curves show a mixed antiferroelectric-ferroelectric behavior of the multilayers with an individual layer thickness above 10 nm, whereas below 10 nm the multilayers show only ferroelectric behavior. Clearly the PbZrO3 layers thinner than 10 nm experienced a transition into the ferroelectric state. X-ray diffraction reciprocal space mapping showed a corresponding orthorhombic-to-rhombohedral transition of the PbZrO3 layers. The observations are discussed in terms of the influence of strain.

The Bloch T-3/2 law is obtained for three-dimensional magnons at low temperatures. When decreasing the dimensionality of the magnetic system, the 3/2 exponent is expected to be equal to one for two-dimensional (2D) systems. I present a theoretical sketch of 2D spin wave theory, in which a long magnon wavelength cutoff is introduced, connected to the lateral size of the 2D system investigated. I report a study by X-ray magnetic circular dichroism at the Ni L-edges on the onset of ferromagnetic, order on 1.5 atomic Ni layers deposited on Cu(1 0 0), with spin and orbital moments' dependence with temperature. A linear dependence is found for both spin and orbital moments with the same initial slope. This temperature dependence can be used to probe the size of the 2D magnetic islands, which is particularly useful for embedded 2D objects. (C) 2007 Elsevier B.V. All rights reserved.

Nitrogen doping was proposed recently as a low-cost means to shift the absorption edge of titania towards 450-500 run. Results are reported here on the preparation of nitrogen-doped 250 nm thick TiO2 films on glass substrates by RF magnetron sputtering. The nitrogen content in the films was modified by changing the N-2 partial pressure in the discharge from 0.00 to 0.27 Pa. An additional amount of oxygen was added in the deposition chamber (Po-2 = 0.11 Pa) to compensate for oxygen depletion in the films. Surface composition and structure were derived from XPS and XRD data, respectively. XRD data revealed a mixture of amorphous phase and rutile polymorph in the as-deposited films, while an anatase-rich phase occurs in the samples deposited under N2 pressure of 0.05 and 0.16 Pa. Above 0.16 Pa, a rutile-rich phase is present. Surface wettability was investigated from contact angle data of de-ionized water with solid surface. The films deposited under mid-range N2 pressure in the discharge are super-hydrophilic. The photo-induced super-hydrophilicity decays after 36 h. Film wettability is discussed in terms of the synergic effects of surface roughness (measured by AFM) and rutile-anatase TiO2 phase transition, induced by doping. The TiO2 surface super-hydrophilicity (and catalytic efficiency) are related to beneficial properties of anatase phase (E-g = 3.2 eV), associated with a low recombination rate of charge carriers in the surface. (C) 2007 Elsevier B.V. All rights reserved.

The reactive sputtering technique was used to obtain undoped and Fe-doped TiO2 thin films deposited on glass substrates. At 250 degrees C substrate temperature, undoped TiO2 films crystallize in a mixed rutile/anatase phase, while Fe-doped films exhibit the rutile phase only. Presence of Fe3+ ions into the TiO2 lattice is suggested by the intensity variation of forbidden 1s -> 3d transitions between the Ti and Fe K-edges. Ti K-edge EXAFS data are assessed to a mixture of the two kinds of surroundings, a rutile-like crystalline phase, identified also by X-ray diffraction, and a nanosized or amorphous anatase-like surrounding. The local atomic order about Fe atoms is quite different and could be related also to an amorphous phase. The Swanepoel method is used to obtain the dispersion of the refractive index below the interband absorption edge. The dispersion energy, the single-oscillator energy and the coordination number of the Ti atoms are evaluated using the single-oscillator model (Wemple-DiDomenico). (C) 2007 Elsevier B.V. All rights reserved.

The aim of the present work is the investigation of the core-shell Fe@Au nanoparticles obtained by the inverse micelles method. Also hybrid structures between Fe@Au nanoparticles and the well-known conducting polymer polypyrrole (PPY) were obtained and investigated. The properties of the composites were investigated by TEM, HRTEM, X-ray diffraction (XRD), X-ray Photoelectron spectroscopy (XPS) and magnetization measurements. The TEM, HRTEM measurements show that two categories of core-shell nanoparticles with mean diameters of 5 nm and 25 nm, respectively, are formed. The XPS investigations of the core-shell Fe@Au nanoparticles indicate that besides Fe-0 inside the cores, small amounts of Fen,111, located onto the gold surface were also formed during the samples preparation. The magnetization of the investigated nanocomposites measured versus increasing and decreasing magnetic field shows no hysteresis loop, this behavior being consistent with a superparamagnetic behavior. The behavior of the SQUID magnetization vs. temperature under field cooled (FC) and zero field cooled (ZFC) at 0.1 T magnetic field for Fe@Au nanoparticles confirmed the existence of superparamagnetism. The superparamagnetic model was used to fit the experimental magnetization vs. applied magnetic field as it was measured by SQUID up to 5 T. (C) 2007 Elsevier B.V. All rights reserved.

The relaxation of the remnant magnetisation in optimally doped disk-shaped YBa2Cu3O7-delta films with the initially applied magnetic field H oriented along the c axis was measured using dc SQUID magnetometry. The temperature (7) dependence of the experimentally observed normalised magnetisation relaxation rate S exhibits three distinct regions. At high T, S(7) increases with increasing T, which can be explained in terms of plastic vortex creep. The well known plateau in the S(7) variation at intermediate T appears to be caused by collective (elastic) creep in a dynamically ordered vortex system. At low T, where S increases again with increasing T, the magnetisation relaxation is not in a pure thermally activated flux-creep regime, due to the occurrence of micro-flux jumps. This seems to be the origin of the recently proposed exponential current density dependence of the effective vortex pinning potential. (c) 2007 Elsevier B.V. All rights reserved.

Critical temperature T-c of the Li-2(Pd1-xPtx)(3) B was reported to be 7-8 K for x = 0 and 2.2-2.8 K for x = 1. In this article we present our preliminary results on behavior of magnetization-temperature curves with starting composition of Pd-B precursor, y-Li concentration in LiyPd3B and post-annealing of the Pd-end compound. Results suggest that to maximize T-c ratio Pd: B should be close to 3: 1, while y-Li has to be optimum. The lowest T-c for LiyPd3B was 4.4-4.6 K, while post-annealings at 560 degrees C allowed enhancement of T-c up to 8.2-8.4 K. Compositions Li(2)Z(3)B with Z = Ni, Ru, Rh, Re, Ag are not superconducting down to 1.8 K. Exception is composition with Re showing superconductivity due to Re3B compound. All samples were prepared by arc melting. (c) 2007 Elsevier B.V. All rights reserved.

Zero-field-cooling dc magnetisation relaxation measurements performed on optimally doped epitaxial YBa2Cu3O7-delta films with the external magnetic field H oriented parallel to the c-axis reveal the ordering of the creeping vortex-system in the low temperature T domain, due to the macroscopic currents induced in the sample. This dynamic ordering manifests itself through the appearance of a maximum in the T variation of the normalised vortex-creep activation energy. The location of this maximum in the H-T plane describes a well-defined current induced order-disorder line. Our results suggest the absence of a static elastic vortex glass in disordered high-temperature superconductors at high H, and the current induced ordering of the vortex-system as a possible origin for the current-voltage characteristic scaling in terms of an elastic vortex glass-vortex liquid transition. (c) 2007 Elsevier B.V. All rights reserved.

X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) have been used to investigate the elemental composition, chemical and electronic state of elements that exist within the Herastrau Lake (Bucharest, Romania) sediments. XPS spectra were obtained by irradiating the sediment samples with an Al source of X-rays (1486.6 eV). C, N, O, F, Na, Mg, Al, Si, S, Cl, K, Ca, V, Mn, Fe, Co, Ni, Cu, Zn, and Pb have been determined by XPS and AES techniques. The analysis of Electron Paramagnetic Resonance (EPR) spectra revealed an additional free radical peak in the center of Mn2+ sextet, at a g = 2.0038, attributed to SO3- species as well a very intense and broad signal due to Fe3+ ions.

A compact microstrip dual-mode resonator with slots in the ground plane is presented in this paper. Several methods for coupling between the dual modes are investigated. One of the methods involves using slots in the ground plane in order to enhance the external coupling and to introduce the necessary perturbation to the initially symmetrical structure. The proposed device requires a surface area about 6 tunes smaller than the area needed for a conventional patch dual-mode resonator. (C) 2007 Wiley Periodicals, Inc.