Effects of implantation conditions on retention behavior of deuterrium in highly oriented pyrolytic graphite

Implantation temperature dependence on chemical behavior of energetic deuterium (D) implanted into highly oriented pyrolytic graphite (HOPG) was investigated by thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS) in the temperature range 323-873 K. The experimental results showed that the D retention decreased with the increase of the implantation temperature. The pi-pi* transition peak of HOPG, which suggests the existence of sp(2)-pi bonding of graphite structure, disappeared after D-2(+) implantation at 323 K, while the peak recovered when isochronal heating above 773 K was performed, which corresponded to the beginning temperature of the D desorption in the TDS spectrum. Therefore, this suggests that the D desorption could correlate with the recovery of graphite structure disordered by the D-2(+) implantation. In addition, the implanted D was found to be trapped in two different chemical states that desorbed at 900 K and 1050 K, namely Peak I and Peak 2, respectively: the former is a trapping state of D with forming sp(3) hybrid orbital type C-D bond and the latter with forming sigma type C-D bond of sp(2) hybrid carbon. (c) 2007 Elsevier B.V. All rights reserved.