Polarization properties, high-order Raman spectra, and frequency asymmetrybetween Stokes and anti-Stokes scattering of Raman modes in a graphite whisker - art. no. 214301
Ph. Tan et al., Polarization properties, high-order Raman spectra, and frequency asymmetrybetween Stokes and anti-Stokes scattering of Raman modes in a graphite whisker - art. no. 214301, PHYS REV B, 6421(21), 2001, pp. 4301
The Raman spectra of a new type of graphite whiskers have been measured in
the range of 150-7800 cm(-1). The intensity of the over-tone (2D) located a
t similar to 2700 cm(-1) is found to be about 10 times stronger than that o
f the C-C stretching mode (G) at 1582 cm(-1). Because of the peculiar enhan
cement of the 2D mode, high-order Raman bands up to fifth order at similar
to 7500 cm(-1) have been observed. Polarized micro-Raman spectroscopy has b
een per-formed on an individual graphite whisker, and angular-dependent int
ensity measurements of all Raman modes in the VV and HV geometries are in a
greement with the theoretical calculated results. Laser-energy-dependent di
spersion effects and the frequency discrepancy of Raman modes between their
Stokes and anti-Stokes lines in graphite whiskers are also carefully inves
tigated. 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 R
aman lines are revealed in the low-frequency region of the Raman spectra of
graphite whiskers. which are believed to be the resonantly enhanced phonon
s in the transverse-acoustic and longitudinal-acoustic phonon branches. Mor
eover, the obvious energy dispersion of the D' mode at similar to 1620 cm(-
1) is observed in graphite whiskers. The results clearly reveal how strongl
y the peak parameters of Raman modes of graphite materials are dependent on
their structural geometry. The Stokes and anti-Stokes scattering experimen
ts show that the frequency discrepancy between the Stokes and anti-Stokes s
ides 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 (E omega (s)) and the value of its laser-energy dispersions (partial d
erivativeE omega (s)/partial derivative epsilon (L)).