RAMAN-SPECTROSCOPIC INVESTIGATION OF ION-BEAM-IRRADIATED GLASSY-CARBON

Raman spectroscopy has been used to monitor the changes induced in glassy carbon as a result of irradiation with H, He, C, N, Si, and Xe ions. The Raman spectrum of unirradiated glassy carbon consists of an intrinsic graphite peak at 1590 cm-1 (the a peak) and a disorder-induced D peak at 1350 cm -1. The G peak position and FWHM and the ratio of the D peak intensity to that of the G peak [I(D)/I(G)] are plotted as functions of the calculated damage density induced by the ion beam. The results show that at very low damage levels [< 0.008 displacements per atom (DPA)], considerable disorder is being introduced into the system, and the average crystallite size has been reduced from 35 Å for the unirradiated material to about 25 Å. At damage levels of ∼0.21 DPA, the material starts to undergo an ion-beam-induced modification which saturates at about 5 DPA. The Raman spectra for these heavily irradiated samples are very similar to those obtained from amorphous carbons. At yet higher doses there is some evidence suggesting that ion-beam-induced partial graphitization of the irradiated glassy carbon has occurred. The results are discussed in the context of previously reported Raman studies of amorphous carbons and highly oriented pyrolytic graphite.