National Institute Of Materials Physics - Romania

Using surface-enhanced Raman scattering (SERS) and Fourier transform infrared (FTIR) spectroscopy, we show that composites based on polyaniline (PANI) and single-walled carbon nanotubes (SWNTs) are different when they are prepared by two different methods: (1) by adding dispersed SWNTs to the polymer solutions and (2) by chemical polymerization of aniline in the presence of SWNTs. The difference originates from the irreversible chemical transformation of SWNTs in the polymerization medium. The synthesis medium used for the preparation of PANI transforms SWNTs into fragments of shorter length like closed-shell fullerenes. This explains the similarity of SERS and FTIR spectra of the composites PANI/SWNTs and PANI/C-60 chemically prepared. All compounds exhibit an absorption band at 1144 cm(-1) in their FTIR spectra, increasing with the carbon nanoparticules content, as a signature of a charge transfer between the constituents. Besides, the FTIR spectrum of the compounds obtained by adding SWNTs to the polymer solution display an intense absorption band with two components at 773 and 755 cm(-1), which are associated with the vibration of deformation of the benzene and the quinoid ring, respectively. This indicates a strong hindrance effect produced by the binding on the polymer chain of voluminous carbon particles as nanotubes and large fragments of nanotubes.

We present results obtained on carbon nanotube systems by means of Raman scattering and surface enhanced Raman scattering (SERS). Such systems consist of single-walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs), or polymer/nanotubes composites. In particular, we have focused our studies on the interactions taking place in these compounds which lead to an upshift of the radial breathing mode (RBM) in the case of SWNTs, either when they are arranged in bundles or embedded in polymers. Similar calculations has allowed us to interpret the low frequency Raman modes observed in purified MWNTs. We show that they come from the RBM of individual tubes. From intensity calculations performed to simulate Raman spectra, we demonstrate the importance of two experimental parameters, namely the diameter of internal tubes and the number of shells which constitute the MWNTs, such parameters being extracted experimentally from high resolution transmission electron microscopy images. (C) 2003 Elsevier Science B.V. All rights reserved.

The glassy composition As25Te35Si40 was investigated by microhardness, differential scanning calorimetry, X-ray diffraction, electrical conductivity and Raman spectroscopy measurements. A continuous random network model of the glass structure has been developed. (C) 2003 Elsevier B.V. All rights reserved.

Electron spin resonance investigations on polyethyleneterephtalate irradiated with a YAG-Nd laser are reported. The dependence of electron spin resonance spectra on the incident laser beam intensity (power) is studied. It is noticed that the concentration of free radicals has a sigmoidal dependence on the crystal current, presenting saturation at high incident powers. The nature of free radicals induced by laser irradiation is discussed. (C) 2003 Elsevier B.V. All rights reserved.

Electron spin resonance investigations on collagen irradiated with protons are reported. The resonance spectra were assigned to a convolution of lines due to similar toCH(2)-CH2. residues and peroxy radicals. Raising the temperature of the sample (in air), the concentration of similar toCH(2)-CH2. residues decreases while, the concentration of peroxy radicals increases due to the denaturation induced enhancement of the oxidation process. An increase in the apparent intensity of the recorded spectrum has been observed around 100 degreesC and ascribed to the release of adsorbed water molecules. (C) 2003 Elsevier Science Ltd. All rights reserved.

Thin organic films based on poly-methyl-methacrylate (PMMA) polymer have been obtained by pulsed laser deposition (PLD) on silicon substrates. The films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Raman spectroscopy (RS). We observed that the film composition and structure depend on the laser fluence and on the temperature of the substrate during deposition. (C) 2002 Elsevier Science B.V. All rights reserved.

The simulation of interstitial void evolution in a model of crystalline silicon subjected to topological disordering revealed that the void size distribution broadens and shifts towards smaller mean diameter size, when the lattice disordering increases. The size distribution is not gaussian and the mean diameter of the voids is lower than the crystalline value. The calculation of the structure factor corresponding to void configuration evidences the absence of the short and long range order and point out to the presence of the medium range order.

Hybrid polymer based on selenium-sulphur doped by paraffins has been deposited by pulsed laser deposition. The properties of the thin films were investigated. Sample stabilization was carried out by annealing. A nano-crystalline fraction was obtained in the films annealed at 100degreesC. The structure of the nanocrystals corresponds to the Se3S5 crystallographic form. The films exhibit optical memory properties and are suggested for use in optical phase change memories.

Homogeneous thin films have been obtained by UV-excimer pulsed laser deposition from a PMMA bulk material. The structure of films is at variance with the structure of the bulk polymer. The size of the ordered domains, as well as the structural features, evidenced by X-ray diffraction in the deposited films, depend on the fluence of the ultraviolet laser pulse used in the ablation process and on the temperature of the substrate. The radial distribution functions of the bulk PMMA material and thin films show differences in the short range order ascribed to the breaking of the polymer chains and monomer dissociation during deposition process.

Thin films of langasite (La3Ga5SiO14) have been prepared from langasite crystal targets by pulsed laser deposition. The films deposited at room temperature on silicon wafers are amorphous. After annealing at 700 degreesC, in normal atmosphere, the films crystallize as polycrystalline langasite oriented with the plane (001) parallel to the surface of the silicon substrate.