National Institute Of Materials Physics - Romania

Fe clusters have been synthesised in ultrahigh-vacuum chamber using a gas-stabilized cluster aggregation method that ensures good control of the cluster size and naturally oxidized in order to obtain Fe/Fe oxide core-shell nanoparticles. The morphology of an individual nanoparticle, as revealed by transmission electron microscopy, consists of a Fe core of an average diameter of 4.4 nm surrounded by an oxide shell of uniform thickness of about 1.2 nm in average. The nanoparticles may be assimilated with a ferro-/antiferromagnetic (FM/AF) system. The morpho-structural features have been correlated with magnetic measurements on the core-shell nanoparticles. A significant exchange bias effect has been measured, when the sample was field-cooled under an applied field of 3 T. As the morphology of core-shell nanoclusters is much more complicated than in FM/AF bilayers of regular thickness due to the particular geometry of the coronal AF layer, the shape and surface anisotropy have to be taken into account for a correct interpretation of the magnetic data.

The fullerenated poly vinyl chloride was synthesized by the addition reaction of azido-substituted poly vinyl chloride with C-60. Structural characterization carried out using Raman and FTIR spectroscopy confirm the presence Of C-60 chemically bound in the new compound. Also, the photoluminescence properties of fullerenated poly vinyl chloride are considerably changed from those Of C-60.

Optical properties of amorphous Strontium Barium Niobate (a-SBN) thin film are investigated using spectroscopic ellipsometry. Since the SBN can be applied to optoelectronic devices, the dispersion of refractive index is desirable. The films are obtained by Pulsed Laser Deposition (PLD) onto MgO and Si substrates by targeting a SBN:60 monocrystal: The dielectric function of a-SBN is approximated using a single Tauc-Lorentz oscillator model. Thicknesses of the films and of their rough layer are in agreement with SEM and AFM results. The dispersion of the refractive index is presented in the 1 - 5 eV range.

Design, simulation fabrication and measurement of fractal antennas for wireless communications are presented in this paper Two types of geometries, Le. Sierpinski gasket and Koch curve, were investigated The proposed antennas are compact, can operate for multiple frequency bands and exhibit small mutual coupling.

The paper presents a few examples relevant for the application of radiofrequency plasmas for processing of materials and surfaces. The examples have been chosen in order to match the trends in plasma processing science, namely processing at atmospheric pressure, growth of nanostructured materials and design of filtration systems responsive to external stimuli.

This paper deals with preparation of PEM, based on commercial block copolymer of the styrene-butadiene. The copolymer was structurally changed by sulfonation followed by cross linking, in order to design a Proton Exchange Membrane for Fuel Cells. The membranes were structural tested by FTIR Spectroscopy and Scanning Electron Microscopy. Ionic Exchange Capacity (IEC) and thermal behavior by Differential Scanning Calorimetry (DSC) were measured too.

A high quality PZT type material was designed and produced in order to be used as sensor for a high internsity siren. Two disks from this materials were assembled into a parallel bimorph type transducer with an intermediate metallic plate. This assembly behaves like an acoustic resonator in the high frequency audio range. The fundamental of the flexural mode for a free resonator is taken into account Its frequency dependence on the geometry of the system and on its material properties is computed using the results for a circular plate with clamped edges and an observation on the equivalence between the movement of a particular part of a resonator in a stationary state and the movement of that pari separated from the resonator but with the same border conditions. Acoustical and impedance measurements were made in order to appreciate the influence of the metallic plate on the frequency. In order to increase the acoustic emission a frontal cardboard horn was added to the resonator.

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.