Extension of Kinetic Monte Carlo Simulation Framework to Multilayer Graphene and Graphite Oxidation

An existing Kinetic Monte Carlo (KMC) framework for simulating carbon oxidation on graphene surfaces is extended to multilayer graphene and graphite. The phenomenology of multi-dimensional effects, both physical and chemical, are discussed based on existing experimental findings. The physical blockage of oxygen adsorption on subsurface carbon layers through the upper surface layers is identified as the key process causing three-dimensional pitting of carbon surfaces due to oxidation. We provide some of the details for the implementation of this process to extend our KMC framework. After that, oxidation of multilayer graphene with aligned monovacancy defects across layers is simulated, showing pitting of the carbon material not only across the top carbon surface layer, but also in depth into the bulk carbon material. For validation purposes, simulated pits are compared to experimental electron microscopic images of oxidized graphite surfaces, and in-depth pitting rates in the surface normal direction are evaluated. We observe both deep and shallow pit topologies based on reaction conditions. This shows the capability of the new KMC framework to simulate oxidation of complex three dimensional carbon surfaces from first principles, which is important for modelling carbon oxidation in ablative thermal protection systems.