Raman spectra of undoped and uranium doped CaF2 single crystals

Raman scattering experiments for nominally pure and uranium doped CaF2 single crystals were presented. In all crystals, the Raman active T_(2g) vibration mode of CaF2 was observed, whose frequency shift and full-width at half-maximum (FWHM) broadening correspond well with defects and impurities in CaF2 lattice. Additional Raman peaks develop in nominally pure CaF2 with high etch pits density and U^(6+):CaF2 crystals. Part of additional Raman peaks in the experimental results, which are assumed due to vibration modes from F- interstitials and vacancies, are in well agreement with the theoretical predications by employing the Green-function formulation.

Study on Raman spectra of GaMnAs

Raman spectra of diluted magnetic semiconductor GaMnAs alloy were reported. The coupled plamon-LO-phonon ( CPLP) mode has LO-like polarization properties. With increasing Mn concentration, the CPLP mode shifts to low frequency. The hole density in the alloy was determined from the ratio of the intensity of the CPLP mode to that of the unscreened LO mode in the depletion layer. The hole density increases with the increase of the Mn composition. The Raman spectra of GaMnAs alloy were measured at different temperature. It is confirmed that the hole density in the alloy increases with the increase of the temperature.

Study on the Raman spectra of GaP nanorods synthesized within carbon nanotube templates

The Raman spectra of GaP nanorods grown in carbon nanotube templates have been reported. The red shifts of the TO and LO modes were observed due to phonon confinement effect in GaP nanorods. The measured red shifts range from 2 to 10cm(-1) depending on the size of the measured nanorods. It has been found that the polarization properties, which cannot be well explained by the selection rules of single nanorod, result from the direction disorder of nanorods in the measured area. The more the disorder is, the weaker the directionality of polarization properties is. The decrease of the Raman frequency of the TO and LO mode of the nanorods with the increasing power of the exciting laser suggests that the heating effect of the nanorods is far stronger than the bulk material. In addition, the saturation and then decrease of the Raman intensity with the increasing laser power indicate the rapid increase of the defects in the nanorods exposed to a strong exciting laser.

Raman spectra of SiC nanorods with different excitation wavelengths

With increasing excitation wavelength from 514 to 782 mn, a significant difference in the Raman spectra of SIC nanorods was observed as compared to bulk material. The intensity ratio of the LO mode to that of the IF mode increases with the excitation wavelength increasing. This has been identified as resonant Raman scattering caused by Frohlich interaction.

Effect of defects on optical phonon Raman spectra in SiC nanorods

Fabricated one-dimensional (1D) materials often have abundant structural defects. Experimental observation and numerical calculation indicate that the broken translation symmetry due to structural defects may play a more important role than the quantum confinement effect in the Raman features of optical phonons in polar semiconductor quantum wires such as SiC nanorods, (C) 1999 Elsevier Science Ltd. All rights reserved.

The intrinsic temperature effect of the Raman spectra of graphite

The Raman spectra of ion-implanted highly oriented pyrolytic graphite (HOPG) are reported, in which an additional mode at 1083 cm(-1) and three doublet structures in the positions of similar to 1350, similar to 2450, and similar to 2710 cm(-1) are revealed. Noticeable frequency shifts are observed for all the Raman bands between the spectra excited with different laser powers, which are interpreted as the pure temperature effect and a downshift in the C-C stretching frequency induced by the thermal expansion. Moreover, the pure temperature effect (d omega/dT)(V) without anharmonic contribution is achieved in pristine HOPG. The results suggest that the pure temperature effect without anharmonic contribution plays an important role in the frequency shifts with temperature. (C) 1999 American Institute of Physics. [S0003-6951(99)01313-3].

STUDY OF RAMAN-SPECTRA OF ZNSE-ZNTE STRAINED LAYER SUPERLATTICES

The Raman spectra of the II-VI wide band-gap compound ZnSe-ZnTe semiconductor strained-layer superlattices have been studied. The relations between the Raman shifts of the longitudinal optical phonon modes and the superlattice-structure parameters have been determined. When the layer thickness exceeds 40 angstrom, the change of the LO phonon-mode frequency shifts with the layer thickness is minimal, whereas when the layer thickness is smaller than 40 angstrom, great shifts have been observed. We estimate that the critical thickness of ZnSe-ZnTe SLS is about 40 angstrom. We have also found that the shifts induced by strain are much larger than the red shifts due to confinement.

Absorption and Raman spectra of Se-8-ring clusters in zeolite 5A

Samples with different weight ratio of Se to zeolite 5A (Se composition) have been prepared by loading Se into the cages of zeolite 5A and the measurements of the absorption and Raman spectra have been carried out for the prepared samples. The measured absorption edges of the samples close and blue shifted to the value for monoclinic Se containing Se-8-ring, suggesting the formation of Se-8-ring clusters dagger in the cages. The continuous and broadening features of the absorption spectra are interpreted by the strong electron-phonon coupling in Se-8-ring clusters. The sample with high Se composition has a red shift of the absorption band edge relative to the samples with less Se composition. It is tentatively attributed to the reason that with different Se composition, single Se-8-ring clusters and double Se-8-ring clusters are formed in the cages of zeolite 5A. A single broad band at about 262 cm(-1) is observed in the Raman spectra, that gives the further support of the formation of Se-8-ring clusters. Copyright (C) 1996 Elsevier Science Ltd

STUDY ON LOW-FREQUENCY RAMAN SPECTRA OF n-DECYLAMMONIUM CHLORIDE

The low-frequency Raman spectrum of n-decylammonium chloride was measured as a function of temperature in the temperature range from 290 to 340K, and the longitudinal acoustical mode vibration band was assigned. The results showed that there are two phase transitions at 313K and 321K, respectively. The phase transition at 313K is mainly induced by change of hydrocarbon chain conformations, while that at 321K is mainly induced by change of order degree of molecular packing. The results suggest low-frequency Raman spectroscopy is a useful probe of structural phase transition for long-chain compounds.

IR AND RAMAN-SPECTRA STUDIES OF THE RARE EARCH COMPLEXES WITH GLUTATHIONE

The complexes of rare earth ions with glutathione were prepared and charactrized by IR and Raman spectroscopy in the solid state. Based on the spectral results, the structure and coordination sites of the ligand in these complexes were determined.