Silicon Epoxide: Unexpected Intermediate during Silicon Oxide Formation

Infrared absorption spectroscopy and density functional cluster calculations are used to identify the intermediate oxide structures formed by high temperature annealing of the water-exposed $\mathrm{Si}\left(100\right)-(2\times 1)$ surface. We find that initially there is a strong tendency for oxygen to agglomerate on single dimer units at $T\sim 800\mathrm{K}$. Upon dehydrogenation, a remarkable structural transition is observed, wherein the dangling bonds recombine to form silicon epoxides (three-membered $\mathrm{Si}—\mathrm{O}—\mathrm{Si}$ rings). We demonstrate that these epoxides are the thermodynamically favored product in such constrained systems and, consequently, should be preferentially formed at silica interfaces.