Topographical changes induced by high dose carbon-bombardment of graphite

Abstract

Highly oriented pyrolytic graphite has been implanted at room temperature with 165 keV C+-ions at doses from 6 × 1017 to 3 × 1019 ions/m2. Implantation-induced topographical changes of differing size scales were studied by optical, scanning electron, scanning tunneling, and atomic force microscopies. Defects with atomic resolution are seen for the lower dose implants. The formation of a vacancy line is revealed for the first time. At the higher doses a dendrite-like system of deep surface cracks is observed. This cracking develops as a result of the large basal plane contraction produced by irradiation which generates high shearing stresses between the implanted, damaged surface layer and the underlying material. Two independent systems of ridges have been characterized. One appears to follow a crystallographic direction while the other appears as a dense, intricate, generally curvilinear network with short ramifications. Additional experiments in which both the ion energy and dose rate have been varied indicate that ridge evolution progresses with increased energy and fluence, but is independent of dose rate. It is suggested that the ridge networks may form as a result of C transport by diffusion from the heavily damaged near-surface region or of a tectonic-plate-like motion or both. The geometric features of the ridge networks are related to the subsurface radiation damage as well.