Publications

Epitaxial ferroelectric/antiferroelectric PbZr0.8Ti0.2O3/PbZrO3 multilayers were grown on SrTiO3(100) substrates, covered with a SrRuO3 (100) bottom electrode and a thin tetragonal PbZr0.2Ti0.8O3 buffer layer, using pulsed laser deposition. Polarization-field, switching current-voltage and capacitance-voltage curves show a mixed antiferroelectric-ferroelectric behavior of the multilayers with an individual layer thickness above 10 nm, but below 10 nm the multilayers show only ferroelectric behavior. Obviously the PbZrO3 layers thinner than 10 nm underwent a transition into the ferroelectric state. An X-ray diffraction -2 scan showed a corresponding orthorhombic-to-rhombohedral transition of the PbZrO3 layers. The observations are discussed in terms of a strain effect.

Piezoelectric and p type semiconductor ZnO thin films were deposited by radiofrequency beam assisted pulsed laser deposition. Optical, electrical and structural properties were found to depend on both deposition parameters and radiofrequency beam characteristics.

Electrochemical reduction of single-walled carbon nanotube (SWNT) films in the presence of Li salts dissolved ill acetonitrile (AN), as an anhydrous medium, was investigated by Raman scattering, FTIR spectroscopy and TEM studies. Differences between the in-situ and ex-situ Raman spectra recorded on the SWNT films immersed in the Li salt/AN solution consist in the fort-nation of two reaction products with different stability in air. One corresponds to SWNTs doped with Li+ ions, a compound that is instable in air. The other, stable in air, exhibits in the Raman spectrum recorded at excitation wavelengths of 676 and 1064 nm an enhanced D band, a disappearance of the Breit-Wigner-Fano component and a significant decrease in the radial breaching mode intensity. Besides, in FTIR spectra, one observes: i) a down-shift of the absorption bands from 1456 and 1540 cm(-1) to 1440 and 15 10 cm(-1), respectively accompanied by an increase of their intensities and ii) an up-shift of the IR band from 1170 to 1192 cm(-1). The influence of the applied reduction potential and cycle voltammograms number on the vibrational features of the second product is shown, too. A recovery of the initial vibrational features of SWNTs is achieved by a subsequent treatment with an aqueous HCl 1M solution. (C) 2008 Elsevier B.V. All rights reserved.

The author is presenting output performances obtained from Nd-based laser materials that were in-band pumped directly into the (4)F(3/2) emitting level. Continuous-wave (cw) laser operation at 1.06 mu m with slope efficiency of 0.79 in Nd:YAG and 0.80 in Nd:GdVO(4) and Nd:YVO(4) was realized using an end-pumping configuration and a tunable Ti:Sapphire laser around 0.88 mu m as source of excitation. These slopes are very close to the limits of the investigated laser materials. Laser operation at 0.946 mu m in Nd:YAG with slope efficiency as high as 0.68 was also demonstrated. The influence of an increased Nd concentration on the quantum efficiency of the (4)F(3/2) emitting level in Nd:YAG is discussed, and laser performances at 1.06 mu m in highly-doped Nd laser are investigated. Laser emission at 1.3 mu m was demonstrated for the first time in a highly-doped 2.5 at % Nd:YAG under pumping with diode lasers at 0.88 mu m. First diode end-pumped at 0.88 mu m Nd:GdVO(4) laser that generated 5.1 W of green at 0.53 mu m visible light by intracavity frequency doubling was realized. The pump at 0.88 mu m was also employed with active medium in thin-disk geometry. A multi-pass pumped Nd:GdVO(4) laser with cw maximum output power of 14.9 W at 1.06 mu m and that generated 9.1 W of green light at 0.53 mu m was demonstrated.

The laser pyrolysis is a powerful and a versatile tool for the gas-phase synthesis of nanoparticles. In this paper, some fundamental and applicative characteristics of this technique are outlined and recent results obtained in the preparation of gamma iron oxide (gamma-Fe2O3) and titania (TiO2) semiconductor nanostructures are illustrated. Nanosized iron oxide particles (4 to 9 nm diameter values) have been directly synthesized by the laser-induced pyrolysis of a mixture containing iron pentacarbonyl/air (as oxidizer)/ethylene (as sensitizer). Temperature-dependent Mossbauer spectroscopy shows that mainly maghemite is present in the sample obtained at higher laser power. The use of selected Fe2O3 samples for the preparation of water-dispersed magnetic nanofluids is also discussed. TiO2 nanoparticles comprising a mixture of anatase and rutile phases were synthesized via the laser pyrolysis of TiCl4- (vapors) based gas-phase mixtures. High precursor concentration of the oxidizer was found to favor the prevalent anatase phase (about 90%) in the titania nanopowders. Copyright (C) 2008 R. Alexandrescu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Co-MgO granular films presenting TMR effects were prepared by thermo-ionic vacuum arc (TVA) method with the simultaneous ignition of plasma in Co and MgO vapors, respectively. The processing method is suitable for the simultaneous preparation of films of different relative content of Co in the MgO insulating matrix. Morphologic, structural and magnetic behaviors were analyzed in as prepared and annealed samples. The influence of the Co content on the magnetic properties of the prepared films was analyzed, in correlation with tunneling magneto-resistance effects. The tunneling magneto-resistance effect is maximal for certain Co content. This behavior was interpreted by the contrary effects of decreasing the average size of the magnetic grains, and hence the average inter-grains distance at higher Co relative content, and the enhanced magnetic disorder in very fine grains dispersed in the insulating matrix. This mechanism was suggested by the comportment of as prepared and thermally annealed samples.

Ba(Zn1/3Ta2/3)O-3 (BZT) ceramics were prepared by solid-state reaction and sintered in air at temperatures in the range 1550-1650 degrees C, for 2 hours. In order to improve the microwave and millimeter wave properties, annealing treatment at 1400 degrees C for 10 hours was applied. The long-range order with a 2:1 ratio of Ta and Zn ions on the octahedral positions of the perovskite structure and the vibrational modes were investigated by using XRD and Raman spectroscopy as function of sintering temperature. Presence of small amount of secondary phase, Ba8ZnTa6O24, affects Q factor even in the dense, highly ordered samples. The dielectric parameters were measured in the microwave range by Hakki-Coleman method and were correlated with structural and optical properties. Sintering temperature higher than 1600 degrees C are required for BZT ceramics in order to obtain low microwave loss (Q x f similar to 100 THz).

Defects in silicon are studied as function of the dimensionality of the investigated structures. Defects produced by strong irradiation in bulk crystals, like vacancies or interstitial defects, induce other defects, so that the irradiated devices are irreversibly damaged. Defects in nanostructures are shown to be produced mainly by surface/interface states and strains, and are therefore specific to the investigated structure. The modeling of the experimental methods allows the determination of defect parameters that are not directly measurable. The carriers capture on quantum confinement levels in OD systems has a similar behavior with the trapping phenomena.

Electrical properties of new Polymer-Iron nanocomposite materials obtained by laser pyrolysis were investigated, in order to find applications for the detection of reducing gases. The aim of this paper was to prove the necessity of complex experimental investigation in order to point out the contribution of different types of adsorption. Usually resistance measurement cannot fully describe the surface interactions. The electronaffinity changes are of real interest for in-field conditions which always involve humidity of surrounding gas atmosphere. On the other hand, the nanocomposite materials can be a solution for specific gas-sensing properties.

This paper is dedicated mainly to the study of couplings between planar resonators in multilayer structures with modified (defected) ground plane. Couplings between two miniaturized resonators are investigated, by full electromagnetic field simulation. Based on the results of this study, several models of planar microwave bandpass filters, with a single or with two apertures, are designed, verified by simulation, fabricated and measured. Compared to the classical filters, these novel structures show a good compactness and can offer some technological advantages.