LASER RAMAN MICROPROBE ANALYSIS OF THE MODIFIED SURFACE OF HE+-IRRADIATED GRAPHITE

Raman spectra of highly-oriented pyrolytic graphite irradiated with He+ are systematically investigated in terms irradiation dose and temperature. The irradiation produces a new peak at 1355 cm-1 in addition to the original peak at 1580 cm-1. The effect of irradiation on the Raman spectra becomes less appreciable with increasing irradiation temperature, probably because of dynamic annealing during irradiation. The reduction of the crystalline size, which is calculated from the intensity ratio of I1355/I1580, does not coincide with the amorphization process investigated in our previous TEM study, whereas the peakwidth, especially that of the 1355 cm-1 corresponds with amorphization. Therefore, the amorphization can not be simply attributed to the reduction of the crystalline size. The Raman spectra seem to represent some other effect, probably the change of bonding nature of the carbon atoms.