National Institute Of Materials Physics - Romania

The atomic ordering of the amorphous diamond-like carbon at the scale larger than short-range order is directly related to the characteristics of the array of interstitial voids. The large interstitial voids are responsible for the first diffraction peak, while the smaller ones (second and third order size of the voids) are responsible especially for the intensity and position of the second peaks in the interference function (structure factor).

A binary telluride (CdTe) as well as a ternary telluride (PbSeTe) were electrodeposited in the pores of a track-etched polycarbonate membrane, resulting nanowires and nanotubes. Either acid or alkaline solutions were used for preparing CdTe compound, whereas the ternary PbSe1-xTex compound was deposited from an acid solution, only. The investigation of electrode mechanisms was performed by cyclic voltammetry. The nanostructures were visualized using scanning electron microscopy (SEM).

Modelling of several large molecular clusters possible to be formed in non-crystalline arsenic chalcogenides (As2S3, As2Se3 or mixed compositions) during cooling down of the melts has been performed. The structure of minimum free energy was calculated in the frame of valence force field theory using a Monte-Carlo-Metropolis method. The structural characteristics of the clusters were computed after energy relaxation. There was demonstrated that specific cluster configurations of the type nano-hat, nano-pie and nanotube are crystallo-chemically compatible with the non-crystalline structure of the arsenic chalcogenides.

Selenium-sulphur layers prepared by warm pressing or deposited by pulsed laser deposition (PLD) on silicon wafers were subjected to laser pulses in order to test the possibility of recording the optical information in these glassy materials. There was demonstrated that the contrast of reflectivity between the irradiated places and the amorphous matrix could be used for storage of information at a reasonable density.

Surface-enhanced Raman scattering (SERS) and cyclic voltammetry (CV) were used to investigate oxidation-reduction processes of single-wall carbon nanotube (SWNT) films deposited on Au supports in 0.5 M H2SO4 solutions. In the potential range (0; +1000) and (0; +1500)mV versus saturated calomel electrode (SCE), the oxidation-reduction reactions of SWNT films are quasi-reversible and irreversible, respectively. Anodic polarization of SWNT films until +1000 mV versus SCE produced compounds similar to the bisulfate intercalated graphite. Regardless of excitation wavelength, i.e. 1064 or 676.4 nm, variation in the Raman spectra exhibited a decrease in the intensity of the bands associated with the radial breathing mode (RBM) situated in the 120-240 cm(-1) spectral range. Also an increase in the intensity of the D band is accompanied an up-shift of this band. A gradual decrease of the Breit-Wigner-Fano component was observed at lambda(exc) = 676.4 mn. Partial restoration of the Raman spectra was achieved by a subsequent alkaline solution treatment. Potentials higher than +1000 mV versus SCE resulted in SWNTs breakage and fragments of different length were formed such as closed-shell fullerene. This was observed in the SERS spectrum by: (i) the disappearance of the RBM band, (ii) the increased D-band shifted to ca. 1330 cm(-1) and (iii) the appearance of a new band at 1494 cm(-1), frequently observed also in the Raman spectrum of fullerenes on the type C-70, C-84, C-119, as well as in its derivative compounds (e.g. C60O, clathrates, etc.). Appearance and increase in the intensity of the Raman band at 1494 cm(-1) as result of an anodic polarization of the SWNT film in solution of H2SO4 0.5 M in 1-butanol is a further evidence of the nanotubes breakage. (C) 2004 Elsevier B.V. All rights reserved.

Modeling of nano-tube clusters based on As,S(Se)(3) has been performed. The structural data were calculated on a single nano-tube model of As2S3. For the first time electron microscope images of nanometer size objects in As2Se3 and AS(5.5)Se(4.5) glass have been observed and discussed.

Scanning electron microscopy, Raman scattering, UV-VIS absorption spectroscopy and low temperature photoluminescence (PL) were used to examine small particles produced by the chemical reaction between Pb(NO3)(2) and KI in different liquid media: water, methanol, ethanol and acetonitrile. By stoichiometric changes in the synthesis reaction, platelets of PbI2 and rods probably of KPbI3 are produced. Regardless of shape and size, these particles exhibit almost the same PL, which consists of two intense bands centred around the 2.5 (E band) and 2.0 eV (G band), in turn similar to that of a crystalline slide or a micrometric powder, both prepared from a PbI2 single-crystal grown from the melt. Crystalline PbI2 platelets exhibit an E band with two components, at 2.49 (E-F band) and 2.47 eV (E-T band), originating in the recombination of the free and trapped excitons produced by inter-band irradiation. A close relation between the enhancement of the E-T and G band reveals that they are linked to the surface defects. For the rod-like particles, the PL spectrum is somewhat similar to that of a Pb2+ ion introduced into an alkaline halide lattice, which as for any ns(2) ion displays two emission bands, A(T) and A(X), whose correspondents are E and G bands.

Hydrogenated and nitrogenated carbon films were obtained by PECVD with carbon species supplied by acetylene gas injected into an argon or argon/nitrogen remote plasma generated by an expanding radiofrequency discharge. The properties of carbon material like the nature of bonds, morphology, surface topography, crystallinity are presented. The reaction pathways linking the precursors with the depositing species, as revealed by emission spectroscopy, are discussed. (C) 2003 Elsevier B.V. All rights reserved.

A chalcogenide material of composition Se42S58, doped by 10 wt.% paraffins has been prepared as thin films by pulsed laser deposition. The structural properties of the films have been investigated by X-ray diffraction. Sample stabilization was carried out by annealing at temperatures around 100degreesC.

Structural and electrical properties of polycrystalline CdSe thin films irradiated with high-energy electrons are analyzed. The samples were prepared by vacuum deposition onto optical glass substrate. Their structure and the temperature dependence of the electrical resistance were determined, both before and after irradiation with 6 MeV electrons and fluencies up to 10(16) electronS/cm(2). There were no measurable changes in the crystalline structure of the films after irradiation. Electrical properties are controlled by a defect level of donor type, possibly a selenium vacancy, with two charge states having ionization energies of about 0.40 eV, respectively 0.22 eV. Irradiation increases significantly the concentration of those defects.