Silicon Epoxide: Unexpected Intermediate during Silicon Oxide Formation

Abstract

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 $\mathrm{Si}(100)\ensuremath{-}(2\ifmmode\times\else\texttimes\fi{}1)$ surface. We find that initially there is a strong tendency for oxygen to agglomerate on single dimer units at $T\ensuremath{\sim}800\mathrm{K}$. 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.