Inward diffusion of oxygen on a silicon surface

Cluster computations with the density functional theory were performed to clarify the diffusion mechanism of an O atom adsorbed on a Si surface. The activation energy required for the oxygen diffusion into the Si substrate is estimated to be 1.6 eV, which is fairly small compared to oxygen diffusion within a Si crystal. The presence of a surface dangling bond is responsible for the lowering of the activation energy, assisting the generation of an intermediate which is involved in the rearrangement of the Si-O connections. Adsorption of another O atom on the Si surface appears to further enhance the inward oxygen diffusion.