Computer modeling of graphite oxidation: differences between monolayer and multilayer etching

Abstract

Highly oriented pyrolytic graphite can be etched at high temperatures in air to form both monolayer-deep and multilayer-deep etch pits with a high degree of size control, given some empirical understanding. A computer program is presented which models the oxidation of a single sheet of graphite at the atomic level, based on reaction probabilities for different types of edge carbon atoms. Edge carbons can be divided into many different types, but pit shapes were found to depend on just two types of edge carbons: zig-zag and armchair sites. Monolayer etch pits could be modeled well over a wide variety of parameter values, but the shapes of multilayer etch pits could not be modeled in a single sheet by any combination of parameters. This difference is apparently due to layer–layer interactions in multilayer pits, but investigation also revealed differences in the ways the different types of graphite edges oxidize: formation of a stable ‘armchair’ edge does not appear to be possible for any choice of reaction probabilities. This suggests that, while the shapes of monolayer etch pits are determined by the reaction rates of various carbon atoms, additional factors are involved in the formation of multilayer etch pits.