ECAMP 15

Highly oriented pyrolytic graphite (HOPG) structural changes caused by gallium (Ga) implantation at room temperature were investigated. Raman spectroscopy was used to investigate the structural changes in HOPG after Ga implantation at different energies (i.e., 10, 20 and 30 keV) and fluences (i.e., 2×1015, 5×1015, 1×1016, 2×1016, 4×1016, 5×1016 cm-2). SRIM (Stopping and Range of Ions in Matter 2013) software was used to determine the depth profiles of Ga ions and the degree of damage to HOPG (in dpa - displacement per atom) after implantation. The implantation was done at room temperature. SRIM predicted that implanting Ga into HOPG at 30 keV and at a fluence of 5×1016 cm-2 created 100 dpa at a depth 15 nm below the surface. This indicates that HOPG structure becomes amorphous under this implantation detail. This also agrees with the Raman results, where HOPG characteristics D and G peaks at 1359 cm −1 and 1582 cm −1 , respectively, have merged into a broad peak indicating the amorphisation of HOPG after implantation with 30 keV Ga ions at 5×1016 cm-2. On the other hand, comparing the dpa obtained from SRIM results with the Raman results, it is clear that the HOPG sample requires a dpa above 26 dpa to become amorphous, which is much higher than previously reported (0.20 dpa). This could be due to the significant proportion of perfectly formed graphite crystallites in our HOPG samples (as seen from Raman results of virgin HOPG), which require higher fluences to be fully damaged (i.e., to become amorphized).