Anisotropic diffusion of Si adsorbates on a Si(001) surface

The behavior of Si adsorbates evaporated on a Si(001) surface is studied by tracing their diffusion caused by radiative heating. A reflection electron microscope (REM) is used to observe denuded zones that are created at the terrace edge and grow with heating time. Diffusion constants of Si adsorbates are determined using the denuded zone widths on a Si(001) surface. The diffusion constants on the 2×1 terrace have directions parallel to a surface dimer connected to two nearest-neighbor atoms on the surface. Similarly, the diffusion constants on the 1×2 terrace have directions perpendicular to the dimer. Diffusion constants in the opposite directions are the same on both structures, so the isotropic diffusions in the opposite directions are observed on a Si(001) surface: u D 2×1 = d D 2×1 = D 2×1 and u D 1×2 = d D 1×2 = D 1×2 . The index u indicates diffusion from the down-side to the up-side and d vice versa. However, a difference in diffusion constants between D 2×1 and D 1×2 is observed. It is concluded that D 1×2 is about 5-6 times as large as D 2×1 on the Si(001) surface.