Electromigration and phase transformation of Ag on a Cu-precovered Si(111)surface

Electromigration and phase transformation of an ultrathin-Ag film patch dep osited on a Cu-precovered incommensurate "5 x 5" phase on Si(111) surface w ere investigated by in situ ultrahigh-vacuum scanning electron microscopy a nd microprobe reflection high-energy electron diffraction, and compared wit h the previous results on the clean and Au-precovered Si(111) surfaces. The film patch spread quite slowly towards the cathode by current apply (and r esultant heating), at the initial stage of which the patch area showed a ro ot3 x root3 phase, consisted of Ag-Cu surface alloy, with three-dimensional (3D) islands in it. Later, a phase transformation from the root3 x root3 i nto a root 21 x root 21 structure proceeded, accompanied with the 3D island s dissolving. These surface alloy formations play a key role in the migrati on, which is similar to the case of on Au-precovered Si(111) surfaces. (C) 2001 Elsevier Science B.V. All rights reserved.