Electromigration and gold-induced step bunching on the Si(111) surface

Abstract

Step bunching instability induced by adatom electromigration is studied on the Si(111) surface at temperatures of 830–1000°C by ultrahigh vacuum reflection electron microscopy. To highlight the role of the effective charge of adatoms in step bunching, a small amount of gold atoms was deposited onto the Si(111) surface at these temperatures. It was found that in the case of sample heating by DC in the step-up direction, regular steps on the clean surface were unstable after submonolayer gold adsorption, while step bunches on the clean surface were transformed to regular steps on the gold-adsorbed surface during heating by DC in the step-down direction. We conclude that gold adsorption changes the sign of the effective charge of silicon adatoms from positive to negative. In this temperature range, the value of the adatom effective charge was estimated to be 0.004±0.001 in units of the elementary charge.