  The oxidation of SiC and Si provide a unique opportunity for studying
oxidation mechanisms because the product is the same, SiO2. Silicon oxidation
follows a linear-parabolic law, with molecular oxygen identified as the
oxidant. SiC oxidation obeys the same linear-parabolic law but has different
rates and activation energies and exhibits much stronger face-dependence. Using
results from first-principles calculations, we show that atomic and molecular
oxygen are the oxidant for Si- and C-face SiC respectively. Comparing SiC with
Si, we elucidate how the interface controls the competition between atomic and
molecular mechanisms.
