Oxidation of Silicon Carbide by O2 and H2O: A ReaxFF Reactive Molecular Dynamics Study, Part I

Simulations of the initial oxidation process of a SiC surface exposed to O-2 and H2O molecules was studied with ReaxFF, an atomically detailed reactive molecular dynamics method that naturally models the breaking and forming of bonds. In this work, the ReaxFF forcefield was first expanded by training it with new quantum mechanics data of the binding energy, equation of state, and heat of formation of the SiC crystal, along with data from earlier studies that describes Si - Si, Si - O, and Si - H interactions. This expanded ReaxFF forcefield is capable of simultaneously describing both Si-C-O and Si-O-H bonding interactions. Using the forcefield, oxidation simulations were performed at various temperatures (in the range of 500 to 5000 K), and the trajectories were analyzed. The analyses showed that SiC gradually transforms into the oxides of silicon with simultaneous formation of a graphite-like layer. In presence of excess O-2, the graphite-like layer was further oxidized to CO and CO2. We also analyzed the trajectories with two-atom and three-atom clusters to quantitatively track the oxidation progress. This analysis clearly showed Si-O and C-C bond formation at the expense of O-O and Si-C bond consumption indicating SiC oxidation with simultaneous formation for carbon-like structure. Consumption of SiC with O-2 was found to be faster than that with H2O. We have also reported the oxidation simulation of SiC with a mixture of H2O and O-2. Oxidation proceeded effectively as a two-part sequence, with O-2 first oxidizing the SiC, followed then by H2O.