National Institute Of Materials Physics - Romania

Matrix assisted photo-amorphization effect has been observed in thin chalcogenide films of composition As40S30Se30 deposited by thermal evaporation on silicon wafer substrate covered by silver. The initial films contain Ag2S and Ag4SeS crystallites embedded in an amorphous matrix. Illumination by a cold light halogen lamp induces the disappearance of the crystalline fraction and leads to significant changes in the diffraction pattern of the amorphous films.

Electrochemical polymerization of indole in a LiClO4/CH3CN solution on a single-walled carbon nanotubes (SWNTs) film was studied by cyclic voltammetry, Raman scattering and FTIR spectroscopy. Comparing the cyclic voltammograms recorded on a blank Pt electrode with those obtained when carbon nanotubes films were previously deposited onto the Pt electrode, a down-shift of the indole reduction peak potential in the latter case was observed. Raman spectroscopy studies indicate that the electrochemical deposition of polyindole (PIN) onto the SWNT film results in a breaking of SWNT bundles into individual tubes. A covalent functionalization of SWNTs with PIN in the doped state is demonstrated by FTIR spectroscopy, when an increase in the intensity of the absorption band at 1045 cm(-1) is observed. Besides, Raman and FTIR studies performed on samples electrochemically prepared and thereafter post-chemically reacted with an NH4OH solution, indicate both a roping process of individual tubes with PIN as a binding agent and a strong steric hindrance effect. (C) 2009 Elsevier B.V. All rights reserved.

Composites based on carbon nanotubes and ZnO particles with needle shapes were prepared for applications in energy storage. Depending on the temperature (85 or 25 degrees C) at which the reaction between NaOH and ZnCl(2) was carried out, particles with two different morphologies: needle-shaped (NS) and double-pyramid-shaped (DPS), respectively, are obtained. Scanning electron microscopy, photoluminescence, UV-Vis absorption spectroscopy, x-ray diffraction and Raman light scattering studies reveal that the NS and DPS particles belong to ZnO with wurtzite (WZ) structure and epsilon-Zn(OH)(2) as precursors of ZnO, respectively. Using the ZnO/carbon nanotube composite as a negative electrode and an electrolytic solution containing LiPF(6), the charge-discharge characteristics of rechargeable lithium ions cells were determined. Additional information concerning the electrochemical reactions at the interface of the two electrodes was obtained by cyclic voltammetry.

A method for building photonic structures in As2S3 amorphous chalcogenide films has been developed. 2-D photonic configurations characterized by a regular assembly of rods (triangular lattice) or gratings with traces of micrometer period have been obtained. A femto-second laser has been used in photonic crystal registration. The simulation performed on these photonic configuration shows that the obtained chalcogenide structures could be efficient for operation in the infrared range around several micrometers wavelength.

The heterostructure Ag/As2S3 was deposited on glass substrate in two configurations: Ag/As2S3/glass and As2S3/Ag/glass. The effect of light emitted by a halogen lamp has been investigated by optical microscopy and X-ray diffraction. Particular morphological and structural aspects were revealed. Lateral diffusion rate of Ag has been determined.

In this paper, we present the anti-Stokes Raman scattering as a technique allowing investigations of materials at a nanoscale level. When the energy of the excitation light coincides with the energy of an electronic transition, a strong anti-Stokes Raman spectrum with respect to the prediction of the Maxwell-Boltzman (MB) law is regularly observed. Under a tight-focusing of the excitation light, the anti-Stokes Raman emission is reminiscent of Coherent anti-Stokes Raman Scattering (CARS). It has been detected on carbon nanotubes (CNTs), prototypes of nanometric materials, as well as on other compounds such as copper phthalocyanine (CuPc), poly(bithiophene) (PBTh), poly(3,4-ethylene dioxythiophene) (PEDOT), polyparaphenylene vinylene (PPV) layered as thin films on a metallic support in which are generated surface plasmons. We demonstrate that nanostructures by themselves can be of importance by generating non-linear phenomena that can be exploited for studying such materials and in particular carbon nanotubes. (C) 2009 Elsevier B.V. All rights reserved.

The transition from the crystalline state to amorphous state and back has been studied in the particular case of the GeSb2Te4 phase-change material by a computer simulation procedure. Modelling at the nanoscale indicates specific structural characteristics, especially the multiplicity of the amorphous phase as opposite to the uniqueness of the crystalline phase. in the particular case of the Si(12)Ge(10)AS(30)Te(48) switching glass two types of ordering have been pointed out and characterized. (C) 2009 Elsevier B.V. All rights reserved.

Transparent oxyfluoride glass-ceramic in the system SiO2-Al2O3-CaF2-EuF2 containing Eu-doped CaF2 nanocrystals were produced by using the controlled crystallization of melt-quenched glass. X-ray diffraction and transmission electron microscopy data have revealed the formation of the CaF2 nanocrystals of about 65 nm size. Photoluminescence spectra have shown an increase of the splitting of the luminescences associated to the Eu3+ ion along with annealing time which is consistent with the Eu3+ environment evolving from a glassy to a crystalline state. (C) 2009 Elsevier B.V. All rights reserved.

A new model is proposed for the structure of low atomic coordination chalcogenide glasses. The closed clusters model is based on the various types of clusters, packed by van der Waals forces in a molecular-type packing. Arguments are given to support the new model, taken as example the typical chalcogenide glass As2S3. (C) 2009 Elsevier B.V. All rights reserved.

Electrochemical deposition was performed in order to prepare CdS nanowires. The method employed for preparation of such high aspect ratio nanostructures was template replication. Ion track polycarbonate membranes were used as templates. The nanowires were studied by scanning electron microscopy (morphology characterization), energy dispersive X ray analysis (composition) and optical spectroscopy. Optical reflection spectroscopy was performed in order to determine the band gap value while photoluminescence spectroscopy was used for getting information regarding the point defects in the material.