Anisotropic Diffusion Evolution of Vacancies Created by Oxygen Etching on a Si Surface

We report the diffusion behavior of dimer vacancies on a Si(100)-(2×1) surface by using ultrahigh−vacuum scanning tunneling microscopy. The dimer vacancies are created by oxygen etching of Si atoms at elevated temperatures. By annealing the sample at 600–750°C, the dimer vacancies uniformly distribute on the terrace nucleate to form larger elongated voids of one atomic layer deep. The long axis of these voids is parallel to the Si dimer rows. During annealing, the surface morphology evolves in a way dominantly caused by the anisotropic diffusion of the dimer vacancies. A difference of diffusion barriers of 0.17±0.09 eV is obtained between the 110 and 110 directions.