Los puntos clave no están disponibles para este artículo en este momento.
The Raman spectra of a new type of graphite whiskers have been measured in the range of 150--7800cm^-1. The intensity of the overtone (2D) located at 2700cm^-1 is found to be about 10 times stronger than that of the C-C stretching mode (G) at 1582cm^-1. Because of the peculiar enhancement of the 2D mode, high-order Raman bands up to fifth order at 7500cm^-1 have been observed. Polarized micro-Raman spectroscopy has been performed on an individual graphite whisker, and angular-dependent intensity measurements of all Raman modes in the VV and HV geometries are in agreement with the theoretical calculated results. Laser-energy-dependent dispersion effects and the frequency discrepancy of Raman modes between their Stokes and anti-Stokes lines in graphite whiskers are also carefully investigated. The energy dispersion of the D mode and G mode is very similar to that of highly oriented pyrolytic graphite (HOPG). In contrast to the Raman spectra of HOPG and other graphite materials, two laser-energy-dependent Raman lines are revealed in the low-frequency region of the Raman spectra of graphite whiskers, which are believed to be the resonantly enhanced phonons in the transverse-acoustic and longitudinal-acoustic phonon branches. Moreover, the obvious energy dispersion of the D^' mode at 1620 cm^-1 is observed in graphite whiskers. The results clearly reveal how strongly the peak parameters of Raman modes of graphite materials are dependent on their structural geometry. The Stokes and anti-Stokes scattering experiments show that the frequency discrepancy between the Stokes and anti-Stokes sides of a Raman mode in graphite materials is equal to the frequency value covered by the one-phonon energy of this Raman mode in its frequency versus laser energy curve, which is the product of the one-phonon energy of this mode (Eₒ) and the value of its laser-energy dispersions (ₒ/₋).
Tan et al. (Mon,) studied this question.