Reflection Microscope Study of Current Effects on Si surfaces

两年内取得的成果可分为两个主题。(1)金属原子在硅表面的表面电迁移观测和(2)清洁硅表面的电流效应观测：(1)Ge的表面电迁移平行于电流，而银的表面电迁移平行于电流，但优先平行于表面原子台阶。对于铜-金的共吸附结构，Roo&lt；3&gt；xROO&lt；3&gt；结构中存在直流电流引起的相分离现象。研究了Ag和In在Si(III)5x5-Ge和Si(III)Roo&lt；3&gt；xROO&lt；3&gt；-Ag结构表面上的电迁移，发现修饰对迁移特性有很强的影响。(2)众所周知，在Si(III)7x7和1x1之间的相变上方，上升的直流电流引起规则的表面台阶排列(R表面)，而降低的电流引起台阶聚束(B表面)。观察到，当表面冷却到7×7相时，这种电流效应反转了3次，即在升压电流作用下，当7×7结构出现在台阶外缘时，R表面转变为B表面，当7×7结构覆盖超过40%-50%的阶地时，又回到R表面，当7x7结构区域覆盖超过80%的阶地时，最后变成B表面。研究还发现，这一过程与台阶的性质略有关系，而台阶的性质与台阶自发形状起伏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.