Reflection Microscope Study of Current Effects on Si surfaces

在两年内获得的结果可以分为两个主题。(1)金属原子在Si表面的表面电迁移观察；(2)电流对干净Si表面的影响观察。(1)研究了锗平行于电流的表面电迁移和银平行于电流但优先平行于表面原子步骤的表面电迁移。对于Cu-Au共吸附结构，ROO<3>xROO<3>结构，注意到直流电流引起的相分离。研究了Ag和In在Si(III)5x5-Ge和Si(III)ROO<3>xROO<3>-Ag结构修饰表面上的表面电迁移，注意到修饰对迁移特征的强烈影响。此外，由于金属的额外沉积，迁移方向与光发射变化之间也有密切的关系。(2)众所周知，在Si(III)7x7和1x1相变以上，升压直流电流导致表面阶跃排列规则（R面），降压电流导致阶跃聚集（B面）。观察到，当表面冷却到7x7相时，这种电流效应发生了三次逆转，即在升压电流作用下，当7x7结构出现在台阶外缘时，R表面变为B表面，当7x7结构覆盖40-50%以上的梯田时，R表面又变为R表面，当7x7结构覆盖80%以上的梯田时，R表面最终变为B表面。研究还发现，这一过程与台阶的性质有轻微的关系，这与台阶的自发形状波动的相对强度密切相关。

Results obtained in two years can be classified into two topics. (1) Observations of Surface electromigration of metal atoms on Si surfaces and (2) observations of current effects on clean Si surfaces.(1) Surface electromigration of Ge parallel to the current and surface electromigration of Ag parallel to the current but preferentially parallel to surface atomic steps were studied. For co-adsorption structure of Cu-Au, ROO<3>xROO<3> structure, phase separation caused by DC current was noticed. Surface electromigration of Ag and In on modified surfaces such as Si(III)5x5-Ge and Si(III)ROO<3>xROO<3>-Ag structures was studied, and strong effect of migration features due to the modification was noticed. Also a close correlation between the migration direction and photoemission changes due to additional depositon of metals was found.(2) It was well known that above the phase transition between Si(III)7x7 and 1x1, a step-up DC current causes a regular array of surface steps (R surface) and a step-down current causes step bunching (B surface). It was observed that this current effect reverses three times when the surface was cooled to the 7x7 phase, i. e., under a step-up current, a R surface changed to a B surface when the 7x7 structure appear at outer edges of steps and returned to a R surface when the 7x7 structure cover more than 40-50% of the terraces, and finally changed into a B surface when the 7x7 structure regions covered more than 80% of the terraces. It was also found that such processes slightly depended on the character of the steps, which was closely related to relative strength of a spontaneous shape fluctuation of the steps.