THEORETICAL STUDY ON DYNAMICS OF ATOMIC ARRANGEMENT AT STEPS

本文用动力学蒙特卡罗模拟方法研究了台阶在表面岛生长和衰变中的行为和作用。我们还开发了一个反射高能电子衍射（RHEED）程序，通过计算晶体中的波函数来分析台阶周围的原子结构，主要结果如下：1）我们揭示了表面扩散不是一个简单的过程。当阶地上的一个岛衰变时，岛的一个台阶上的原子会移出岛，但原子直接移出岛的一个台阶是相当罕见的。从平台上跳下的原子和由此产生的原子空位起着重要的作用;一旦跳下平台，从岛上扩散的原子和跳上的原子之间没有区别。2）我们揭示了台阶在Si（100）-2x1平台上形成岛的过程中的作用的变化。所谓的Sb型台阶在形成岛之前用作扩散原子的漏极，但在开始形成之后用作源极。3）岛的衰变被解释为原子的总跳跃率和步长减小的过程。由于台阶处原子的跳跃速率高于平台处原子的跳跃速率，台阶原子的运动频率增加，从而减少了台阶原子的数目。4）我们证明了在表面共振条件下，RHEED波函数在表面的局域性。局部化是由于表面波的多次散射而发生的，表面波几乎平行于表面传播。

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.