KINETICS OF SURFACE ROUGHENING VIA PIT GROWTH DURING THE OXIDATION OF THE BASAL-PLANE OF GRAPHITE .1. EXPERIMENTS

The thermal oxidation of the basal plane of highly oriented pyrolytic graphite (HOPG) has been investigated in air. Scanning tunneling microscopy (STM) was employed to determine the surface structure on the nanometer scale. In the early stages of the oxidation a number of circular pits with a depth of a monolayer are formed. Both the density of the pits and the uniformity of their diameter are sample dependent but reproducible for a given sample at given oxidation conditions. At later oxidation stages, all surfaces exhibit a number of levels of atomically flat terraces. The data are attributed to an oxidation process, which starts at intrinsic point defects and proceeds through the isotropic growth of etch pits around these defects and within the respective monolayer. At later stages, the top monolayer disappears and point defects in the underlying layer are exposed, which then cause new monolayer pits to grow. After a certain time the surface exhibits a characteristically terraced topology, which depends only on the number of the intrinsic defects. Such surfaces may become of interest for the study of the influence of surface roughness on the properties of adsorbate layers on a solid support.