Ion channeling studies of regrowth kinetics of disordered surface layers on graphite

The crystallization of disordered surface layers on highly oriented pyrolytic graphite (HOPG) has been studied by Rutherford backscattering spectrometry and channeling techniques. Disordered layers (∼1000–3000 Å thick) are produced on the surface of HOPG by the implantation of various ions. The disordered layers are regrown by thermal annealing of the samples in an inert environment. Isochronal anneals reveal two distinct regrowth processes: one, a rapid process of low activation energy (Ea∼0.15 eV) which is observed primarily in regions where the disorder is sufficient to prevent the channeling of the ions, but insufficient to totally destroy the graphitic structure. This low activation energy may indicate annealing of the damage by migration of interstitials where the interstitials are the knock-on carbon atoms produced by the primary ions. A regrowth process with higher activation energy (Ea∼1.2 eV) occurs primarily in regions where the disorder is close to the saturation disorder produced by ion implantation. Both regrowth processes are epitaxial in nature and the epitaxial nature of the process may explain the much lower activation energy for three-dimensional AB layer stacking as measured in ion-implanted graphite when compared with results on the bulk graphitization of pyrocarbons. The time dependence of the annealing process shows a depth dependence and thus the regrowth cannot be uniquely interface or diffusion limited. In the case of the damaged layer produced by As ion implantation, the ability of the lattice to retain As atoms after high-temperature anneals increases with the extent of damage in the lattice. With the advent of three-dimensional ordering, most of the As is squeezed out of the lattice.