Publications

In this paper, dispersion/attenuation diagrams are investigated for purely left-handed (PLH) and for composite right/left handed (CRLH) transmission lines. The magnitude and phase of the S parameters of these structures are analyzed in a broadband (1-7 GHz) range. The investigations on microstrip CRLH lines demonstrate the presence of the left-handed range, the stop-band (only for the unbalanced lines) and the right-handed range. By edge-coupling two such CRLH lines, devices with new properties, different from conventional microstrip devices were obtained. Symmetric and asymmetric 0 dB backward couplers working in the stop-band of the CRLH line were achieved. Very short 3 dB couplers (with only 2 or 3 unit cells) were also investigated.

In this paper a band-pass filter in microstrip technology, with cross couplings and with a pair of attenuation poles, is investigated. The equi-ripple in-band response and the location of the poles on the frequency axis can be precisely controlled through a new technique which combines accurate electromagnetic-field simulation and fast linear circuit optimization, allowing this way the design of band-pass filters with improved performances. To illustrate the procedure, a microstrip band-pass filter was designed, verified by em-field simulation, fabricated and tested. The response of the designed filter is in good agreement with the specification, confirming the possibilities of realizing microwave band-pass filters with rigorously controlled characteristics, with reduced design time and non-prohibitive computational effort.

Electrochemical deposition in nanoporous ion track membranes is used for the preparation of multisegment CdTe-homojunction diode nanowires. Our study is based on the fact that the deposition overpotential strongly influences the composition of the compound semiconductor nanowires. Therefore, the transport behavior of the nanowire devices can be tailored by appropriately choosing a certain sequence of electrodeposition potentials. The wires were characterized using scanning electron microscopy, energy dispersive x-ray analysis, optical spectroscopy and x-ray diffraction. The current-voltage characteristics measured prove that, by appropriately choosing the voltage pulse pattern, one can fabricate nanowires with ohmic or rectifying behavior. The semiconducting nanowires are sensitive to light, their spectral sensitivity being characteristic of CdTe. The preparation of functional nanostructures in such a simple approach provides, as a major advantage, an increase in the process reproducibility and opens a wide field of potential optoelectronic applications.

This paper presents a study of some thin monomer films deposited by MAPLE. These monomers have been synthesised from maleic anhydride and aniline derivatives and are characterized by a molecular structure adequate for the generation of optical non-linear phenomena. UV-VIS, FTIR, Raman and Photoluminescence spectroscopy have been used to investigate the influence of the experimental conditions on the properties of the films. X-Ray Diffraction has evidenced a certain degree of disorder in the thin films, which is correlated with the randomly orientated molecules and AFM images have revealed different roughness for different monomer layers and different substrates. Second harmonic measurements have shown a strong signal emitted by the thin film prepared from the monomer with one [-NH-NH-] donor and two [-NO(2)] acceptor groups. This thin film is characterized by good transparency and low photoluminescence emission at excitation with the wavelength of the second harmonic (lambda-400 nm).

Silicon wafers have been submitted to hydrogen RF-plasma treatment in various experimental conditions. Hydrogen RF-plasma treatment induced two kinds of effects on Si wafers, depending on the treatment conditions: surface corrugation and formation of structural defects below the free surface. Atomic force microscopy (AFM) investigations showed that the surface roughness significantly increased with the treatment duration, leading to the formation of pyramidal humps on the surface. The structural defects resulting after the plasma treatments were investigated by conventional and high-resolution transmission electron microscopy (CTEM and HRTEM) techniques. The specificity of the induced extended defects due to hydrogen decoration was emphasized. Three types of extended defects were identified and characterized: planar defects in the {111} and {100} planes and nanometric voids. Point defects related to the hydrogenation process were investigated by electron paramagnetic resonance (EPR) in correlation with the electron microscopy results.

A multifrequency Electron Paramagnetic Resonance (EPR) investigation of Ce3+ impurities in PbWO4 single-crystals at the conventional microwave frequency (CMF) (X-band: 9.43 GHz) and at the high frequencies/fields (HF) 95, 190 and 285 GHz was carried out. The resulting spectra are well described at all frequencies by an axial spin-Hamiltonian corresponding to an effective spin one-half system in a tetragonal site symmetry. The diagonal values of the effective g matrix of the lowest doublet of the ground multiplet, g(parallel to) and g_, are frequency dependent at high fields. For the magnetic field perpendicular to the tetragonal axis, the g_-parameter exhibits also a small azimuthal angular dependence, which is frequency dependent, corresponding to the tetragonal S-4 symmetry. These HF effects are associated with the mixing by the large Zeeman interaction of some of the upper-lying doublets of the ground multiplet into the lowest-lying doublet states. The CMF and multifrequency HF-EPR analysis gives a good description of the magnetic properties and allows an estimation of the crystal field splitting of the ground multiplet of Ce3+ ions with tetragonal symmetry S-4 in the PbWO4 scintillator. (c) 2009 Elsevier BM. All rights reserved.

Nanoparticles of iron oxide embedded in C(60) matrices are synthesized by co-evaporation of iron and C(60)-fullerene, and analyzed using X-ray photoelectron spectroscopy, X-ray absorption near-edge structure spectroscopy and MOKE magnetometry. C(60) molecules in the neighborhood of the iron oxide nanoclusters transfer charge to the oxide, and the charge deficit fully delocalizes onto the fullerene molecules. The composition of the nanoclusters of iron oxide is similar to both hematite and magnetite, in comparable proportions. One analyzes the amplitude of the pre-edge XANES peak, yielding the average ionization state of absorbing Fe atoms, which is confirmed by the simulations of XANES spectra.

Nanoxide based composites are suitable materials for advanced medical application. Fe(3)O(4), CoFe(2)O(4), and MnO(2) nanoparticles, synthesized by different soft chemistry routes (precipitation in the presence of soft template and solution combustion) were coated by a biocompatible polymer, sodium alginate. The oxides and corresponding composites were structural and morphological characterized. The saturation magnetization for Fe(3)O(4)-based composite is 10.1 emu.g(-1), resulting magnetic domains of 5.2 nm that suggests a superparamagnetic property. Radical scavenging capability of the composites was investigated by two different methods, Trolox Equivalent Antioxidant Capacity (TEAC) and peroxide-chronoamperometry.

Amorphous thin films of SnSe2 and Ge2Sb2Te5 doped by different amount of silver (0.1, 0.2, 0.5 and 1 Ag atoms per formula unit) have been prepared by pulsed laser deposition (PLD) starting from solid polycrystalline targets. The films were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The good gas sensing properties for CO, as well as the sensitivity for CH4 and NO of the Ag; doped SnSe2 films have been demonstrated in the composition SnSe2Ag0.2. The structural effect of silver introduced in Ge2Sb2Te5 matrix has been investigated. The freshly deposited thin films doped by various amount of Ag develop three phases: an amorphous one, and two crystalline phases consisting of a major fcc cubic phase of AgSbTe2 and a minor cubic phase of composition Ag2Te. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim