Evolution of surface morphology of Si(100)-(2×1) during oxygen adsorption at elevated temperatures

We used scanning tunneling microscopy and low-energy electron microscopy to study the etching of the Si(100)-(2×{}1) surface by oxygen at low pressures and elevated temperatures. At 5×{}10^-8 torr partial pressure of oxygen, the transition from random etching of terraces to step etching occurs at {~}580 ^∘{}C, while at the higher partial pressure of 5×{}10^-7 torr, the transition temperature is {~}625 ^∘{}C. The diffusing species is a dimer vacancy, formed by the desorption of two SiO molecules. Anisotropic diffusion of the vacancies is observed, with a preferred direction along the dimer rows. The reaction probability, defined as the number of desorbed SiO molecules to the number of incident O₂ molecules, is estimated to be 0.010±{}0.005.