Papers by Keyword: Micro Raman

Abstract: Silver telluride (Ag2Te), I-VI semiconductor compound with potential applications in various advanced fields. Ag2Te nano films of thickness between 16 nm and 145 nm prepared by thermal evaporation technique at high vacuum better than 2x105 mbar. These films are found to exhibit polycrystalline nature with monoclinic structure from their XRD studies. The average particle size of these films are found to be around 24 nm using the Debye-Scherrer’s formula From AFM measurements, the average particle size is around 24 nm. The emission spectra of these films were recorded and analysed to determine its optical band gap. Optical band gap of Ag2Te varies from 1.6 eV to 1.8 eV with respect to their corresponding thicknesses of films.

Abstract: To improve the quality of AlN layer deposit on SiC/Si, different Ge amounts (0.25, 0.5, 1, 2ML) were deposited before the carbonization process at the silicon substrate in order to reduce the lattice parameters mismatch between Si and SiC grown layers. The residual stress of the hexagonal AlN layers derives from the phonon frequency shifts of the E1(TO) phonon mode. The crystalline quality of the AlN layer is correlated to and investigated by the full width of the half maximum (FWHM) and the intensity of E1(TO) mode of the 2H-AlN. Best crystalline quality and lower stress value are found in the case where 1ML of Ge amount is predeposited. The E1(TO) mode phonon frequency shifts-down by 3 cm-1/GPa with respect to an unstrained layer.

Abstract: We report the synthesis of single-crystalline α-Fe2O3 nanoflakes by the oxidation reaction of water vapor through a gas-solid method. The samples are characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), micro-Raman spectrometer, and transmission electron microscopy (TEM). As-synthesized nanoflakes have a pseudotriangle morphology: 20-50 nm in thickness, 0.5-1.5 μm in length and base-width. It is observed that vertically aligned arrays of leaf-like α-Fe2O3 grow at the verges of the iron foils. The possible mechanism is discussed to elucidate the formation of α-Fe2O3 nanostructures. The experimental results indicate that water vapor plays an important role in controlling the morphology of the final products.

Abstract: Bioglass films were prepared by reactive magnetron sputtering from a 45S5 target and than annealed in air up to 550 oC in order to relax the mechanical stresses. The mixtures (0, 7 and 15%) of oxygen and argon were used in order to modify the films stoichiometry. Morphological and compositional studies were performed by SEM coupled with an EDAX system. FTIR and micro Raman measurements were performed in order to investigate the molecular vibrations of the BG structure. A modified composition respect to the target one was found for all the films, with lower silicon dioxide concentrations. The films displayed rough surfaces with spherical particles of 10-20 μm diameter embedded in the surfaces. The Raman results evidenced important carbonate lines besides the silica-phosphate bands.

Abstract: We report the results of a SIMS and micro-Raman investigation performed on cubic (3C) SiC crystals grown on hexagonal SiC seeds using a Ge-Si bath and the so-called Vapor Liquid Solid growth technique. From SIMS measurements, we find a Ge concentration which, roughly, scales like the Ge concentration in the melt and, in term of micro-Raman measurements, explains the presence of weak but discernable Ge-Ge peaks around 300 cm-1. Since no similar Si-Si vibrations are found, this discard the possibility of having at the same time both Ge and Si constitutional super-cooling with two separate Ge and Si phases.

Abstract: Three types of defects, namely defect I, defect II, defect III, in the 4H-SiC homoepilayer were investigated by micro-raman scattering measurement. These defects all originate from a certain core and are composed of (I) a wavy tail region, (II) two long tails, the so called comet and (III) three plaits. It was found that there are 3C-SiC inclusions in the cores of defect II and defect III and the shape of inclusion determines the type of defect II or defect III. If the core contains a triangle-shaped inclusion, the defect III would be formed; otherwise, the defect II was formed. No inclusion was observed in the core of the defect I. The mechanisms of these defects are discussed.

Abstract: In this work we present an equipotential surface map with a resolution higher than 100 nm, resulting from conductive atomic force microscopy (AFM). The images, obtained in polycrystalline MPCVD (Microwave Plasma Assisted Chemical Vapor Deposition) diamond devices, are clearly structure dependent. Diamond and non-diamond phases were identified by micro-Raman spectroscopy and correlated with the electrical conduction map. The application of the non-homogeneous contact theory lead to the extraction of two Schottky Barrier Heights (SBH), one close to 0.6 V with dispersion ~ 0.1 V, attributed to the diamond / metal interface, and the other close to 0.4 V with dispersion ~ 0.04 V, due to the non-diamond phases / metal interface. The diamond / non-diamond phase ratio is about 85:15, taken from the micro-Raman spectra. Combining these results with the electrical conduction map, a general model to predict the macroscopic electrical behavior of polycrystalline diamond based devices is proposed.