Adsorbed Si on the Si(111)-(7×7) surface studied by scanning tunneling microscopic and molecular-orbital approaches: Stationary and diffusing Si adsorbates

In experiments of Si deposition onto the Si(111)7×7 surface using scanning tunneling microscopy, we observe “diffusing” Si adsorbates detected as a noise-shaped pattern in addition to the previously reported “stationary” ones that remain at the same positions. The stable positions and diffusion energy barriers of Si atoms on the surface are obtained using molecular-orbital calculations. For one Si atom, the diffusion barrier is only several tenths of eV, while it exceeds 1 eV for two Si atoms. We propose some assignments: the “stationary” adsorbate for the two Si atoms and “diffusing” one for the single Si atom.