Electromigration and phase transformation of Ag on a Cu-precovered Si(1 1 1) surface

Electromigration and phase transformation of an ultrathin-Ag film patch deposited on a Cu-precovered incommensurate “5×5” phase on Si(1 1 1) surface were investigated by in situ ultrahigh-vacuum scanning electron microscopy and microprobe reflection high-energy electron diffraction, and compared with the previous results on the clean and Au-precovered Si(1 1 1) surfaces. The film patch spread quite slowly towards the cathode by current apply (and resultant heating), at the initial stage of which the patch area showed a 3×3 phase, consisted of Ag–Cu surface alloy, with three-dimensional (3D) islands in it. Later, a phase transformation from the 3×3 into a 21×21 structure proceeded, accompanied with the 3D islands dissolving. These surface alloy formations play a key role in the migration, which is similar to the case of on Au-precovered Si(1 1 1) surfaces.