Cheng Guang-Xu

Raman spectroscopic study of ceramic Sr2Bi4Ti5O18

Raman spectra of ceramic Sr2Bi4Ti5O18 (SBTi5) are reported to consist of four different Raman bands. Temperature-dependent spectra reveal the relationship between the lattice vibration and the materials structure. There appears a relatively large change in structure of the material at about 273K. The anharmonic potential the material has a great influence on its phonon mode full width at half maximum (FWHM), which can be expressed by a function of temperature. Theoretical fittings of the FWHMs for the two modes around 312 cm−1 and 464 cm−1 indicate that the latter phonon mode is more anharmonic than the former one.

Temperature of Transformation from Fullerite to Amorphous Carbon

Raman spectra during the transformation from fullerite to amorphous carbon are analyzed. The transformation temperature is obtained from intensity ratio of Stokes and anti-Stokes lines by using Placzeks formula. The temperature, less than 2.0×103 K, is in consistence with previous work.

Decomposition of C70 and C60 Under Laser Irradiation Monitored by Raman Spectroscopy

The degradation of C60 in organic solution by light has been reported by Taylor et al. [Nature, 351 (1991) 277]. The powders of the mixture of C60 and C70 prepared by arc heating of graphite electrodes in the environment of He gas was not to be stable with respect to intense irradiation of argon laser (488.0 nm), as monitored by Raman spectroscopy, C70 is found to be first decomposed into fragmentary graphite, then C60 followed suit. It is interesting to note that besides graphite, some traces of diamond-like structure are shown confirming some speculations of Mackay [Nature, 352 (1991) 762].

An Empirical Formula Approach to Total Cross Sections for Electron Scattering on Polyatomic Molecules

Considering the real experimental process of e-molecule scattering a new empirical formula has been developed to calculate the total cross sections (TCSs) for electron scattering on polyatomic molecules (CH4, C2H2, CH3OH and CH3F). The present results are compared with other available theoretical results and experimental data. The new formula incorporates an energy factor f(E) to represent the elastic and inelastic changing process during experiments. It depends on no adjustable parameters and has also extended the validity of the empirical approaches to lower energy range further.

Raman Scattering from Fine Zn Particles Coated with ZnO

Raman scattering from Zn fine spheric particles coated with ZnO of variable thickness is measured, and a broad line can be found. The Raman line shifts to lower frequency side with the increase of oxide thickness. A theoretical analysis based on the existence of surface phonon mode has been made. Agreement between experiment and theory is good.