Ge diffusion at the Si(100) surface

Using scanning tunneling microscopy movies, we directly observe individual embedded Ge atoms to be mobile within the Si(100)-(2×1)-Ge surface at temperatures as low as 90°C. We demonstrate that Ge atoms move by exchange diffusion with (1) adsorbed monomers and (2) individual constituent atoms of adsorbed dimers. Our observations are consistent with recent density-functional theory calculations, which give the atomistic pathways and energetic barriers for both exchange mechanisms. We find that neither adsorbed monomers nor dimers can diffuse more than a few nanometers between exchange events, illustrating how Ge diffusion and intermixing are intimately coupled at the nanoscale on the Si(100) surface. © 2010 The American Physical Society.