Reflection Microscope Study of Current Effects on Si surfaces

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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.