THEORETICAL STUDY ON DYNAMICS OF ATOMIC ARRANGEMENT AT STEPS

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We have studied behavior of steps and effect of steps in growth and decay of islands on a surface using a kinetic Monte Carlo simulation. We have also developed a reflection high energy electron diffraction (RHEED) code which calculates a wave function in a crystal in order to analyze atomic structures around steps.Our prime results are summarized as follows.1)We reveal that surface diffusion is not a simple process. When an island on a terrace decays, an atom at a step of the island moves out of it, but it is quite rare for the atom to move directly to a step away from the island. An atom hopping from the terrace and the resulting atomic vacancy play an important role ; once it hops out of the terrace, there is no distinction between a diffusing atom from the island and the hop-up atom.2)We reveal a change in a role of step during formation of an island on Si(100)-2 x1 terrace. A so-called Sb-type step acts as a drain of diffusing atoms before formation of an island but it acts as a source after starting the formation. The change of role promotes the island formation.3)Decay of an island is interpreted as a process of decreasing the step length and total hopping rate of atoms. As the hopping rate of atom at step is higher than that on terrace, a step atom moves more frequently to reduce the number of step atoms.4)We have shown that under surface resonance condition, a RHEED wave function is quite localized at the surface. The localization occurs as a result of multiple scattering of surface waves which propagate nearly parallel to the surface.