Si ejection and regrowth during the initial stages of Si(001) oxidation

The initial stages of oxidation of the Si(001)-2×1 surface have been studied using scanning tunneling microscopy and spectroscopy. Among the new sites generated by the exposure of this surface to O2 are 1.4 Å high bumps on top of the surface. Upon annealing the O2-exposed surface, or upon O2 exposure at an elevated temperature, these bumps form highly anisotropic islands. Evidence is presented that these bumps and islands are made up of silicon ejected from the surface by the oxidation reaction.