Surface diffusion of in on Si(111): Evidence for surface ionization effects

Second harmonic microscopy has been used to quantify the surface diffusion of In on Si(111). At temperatures near 50% of the bulk melting temperature and in the coverage range 0<θ<0.7, the activation energy E_diff and pre-exponential factor D₀ lie at 42±0.5 kcal/mol and 3 × 10^3±03 cm²/s, respectively. These parameters, which are quite large, are explained semiquantitatively by reference to an adatom-vacancy model recently developed for related systems. The present work, when compared with the results of these other systems, offers significant evidence for the effects of adatom-vacancy ionization.