The ion-beam-induced self-diffusion in pyrolytic graphite was investigated. In order to look for anisotropic effects two target orientations were chosen, one with the basal planes perpendicular to the surface (pyrolytic graphite edge) and a second one with the planes parallel to it (pyrolytic graphite base). Samples pre-implanted with a 13C marker were bombarded with 20keV D+ ions at different temperatures. The 13C depth profiles were analyzed by Rutherford back-scattering using 2.0- and 2.6MeV He4+ ions. Strong effects of anisotropy were found for different target orientations despite the high damage levels. A simulation of the marker diffusion was presented which was based on radiation damage and the behavior of moving defects in graphite. The theoretical description was in good agreement with the experimental results if suitable rate constants of interstitial-vacancy recombination and vacancy-vacancy annihilation were chosen. The orientational effects were explained by an interstitial diffusion which proceeds mainly parallel to the graphite planes.

Anisotropy of Ion-Beam-Induced Self-Diffusion in Pyrolytic Graphite. Söder, B., Roth, J., Möller, W.: Physical Review B, 1988, 37[2], 815-25