Resonant Raman scattering ͑RRS͒ measurements made with a tunable laser provide a highly reliable technique to study the shape of the joint density of electronic states ͑JDOS͒ of isolated single-wall carbon nanotubes ͑SWNTs͒. RRS can be used to determine the energy value for the one-dimensional ͑1D͒ van Hove singularities of a SWNT with a precision better than 5 meV, thereby providing important information that could be used for subsequent measurements on this same SWNT. With RRS, the measured width of the JDOS is on the order of ϳ0.1Ϫ1.0 meV, further demonstrating that SWNTs really provide a remarkably good model for 1D mesoscopic systems.

In this work, we investigated structural, morphological, electrical, and optical properties from a set of Cu 2 ZnSnS 4 thin films grown by sulfurization of metallic precursors deposited on soda lime glass substrates coated with or without molybdenum. X-ray diffraction and Raman spectroscopy measurements revealed the formation of single-phase Cu 2 ZnSnS 4 thin films. A good crystallinity and grain compactness of the film was found by scanning electron microscopy. The grown films are poor in copper and rich in zinc, which is a composition close to that of the Cu 2 ZnSnS 4 solar cells with best reported efficiency. Electrical conductivity and Hall effect measurements showed a high doping level and a strong compensation. The temperature dependence of the free hole concentration showed that the films are nondegenerate. Photoluminescence spectroscopy showed an asymmetric broadband emission. The experimental behavior with increasing excitation power or temperature cannot be explained by donor-acceptor pair transitions. A model of radiative recombination of an electron with a hole bound to an acceptor level, broadened by potential fluctuations of the valence-band edge, was proposed. An ionization energy for the acceptor level in the range 29-40 meV was estimated, and a value of 172 ± 2 meV was obtained for the potential fluctuation in the valence-band edge.

Ordered Ba(B1/3′B2/3″)O3 ceramics are currently used as dielectric resonators for microwave and millimeter wave technologies. The degree of ordering is generally determined by x-ray techniques. In this work, we demonstrate that Raman spectroscopy can be used to evaluate the degree of long-range order of these materials. We also show how varying the degree of order of samples allows partial assignment of the optical vibrational modes.

Sr 1-3x/2 Ce x TiO 3 dielectric ceramics (with x varying from 0.133 to 0.400) were investigated by Raman and infrared spectroscopies. The observed features could be related to SrTiO 3 phonon modes. The Raman spectra show first-order modes-which are modes either activated by polar defects or due to local symmetry lowering-together with classical second-order modes of SrTiO 3 . The infrared spectra are dominated by the three predicted polar phonons of SrTiO 3 , although a faint tetragonal distortion confirmed by lowtemperature measurements was observed for all compositions. For increasing Ce content, the infrared spectra show a continuous hardening of the TO modes and the softening of the highest frequency LO mode. Together with the broadening of the TO phonon lines, these phonon energy evolutions explain the observed dielectric behavior of the material: namely, the decreasing of the dielectric constant and temperature coefficient of the resonance frequency (τ f ) with x. The quality factor is maximized for x ) 0.25. Compared to pure SrTiO 3 , chemically substituted Sr 1-3x/2 Ce x TiO 3 ceramics present more adequate dielectric properties at microwave frequencies for technological applications.