Abstract
In this paper, the dependence of the differential Raman cross section of the , , , and bands of nanographites on the excitation laser energy and also on the crystallite size is reported. We show that is proportional to the fourth power of the excitation laser energy , as predicted by the Raman scattering theory. For the bands which arise from the double-resonance mechanism (, , and ), the differential cross section does not depend on , explaining the strong dependence of the ratio on the excitation laser energy used in the Raman experiment. The dependence of and band differential cross sections is measured, confirming that the proportionality originates from the strong dependence of on the inverse of the crystallite size. In the band case, the data show that its differential cross section increases with the increasing crystallite size , following an opposite behavior when compared with the disorder induced and bands. An analysis on the dependence of the full width at half maximum of the , , , and bands on the crystallite size of nanographites is performed, showing that the phonon lifetime is proportional to the crystallite size.
- Received 2 April 2007
DOI:https://doi.org/10.1103/PhysRevB.76.064304
©2007 American Physical Society