Diffusion anisotropy of Ag and In on Si(111) surface studied by UHV-SEM

Anisotropic features of Ag and In electromigration on clean and Au-precover ed Si(111) surfaces were studied by in situ scanning electron microscopy in ultrahigh vacuum. It was noted that the migration direction of Ag was dete rmined by both applied direct-current direction and step orientation on the substrate surface; on an Si(111) surface with steps inclined with respect to the current direction, the electromigration direction shows an apparent deviation from the accurate current direction. On clean and Au-precovered S i(111) surfaces with various coverages of Au(within submonolayer range), th e migration behaviors of Ag and In drastically changed with Au coverages an d showed different diffusion anisotropy (either thermal diffusion and elect romigration) depending on the adsorbate surface structures. Particularly, o n a beta-root 3 x root 3-Au surface of one monolayer Au coverage, In migrat ed with the highest mobility across the step bands, whereas In showed only a slow movement on the 7x7 clean surface due to a migration barrier at step edges. This result implied that the beta-root 3 x root 3-Au surface phase served as an intermediate layer for In adatoms migration. On the contrary, Ag showed negligible migration on the beta-root 3 x root 3-Au surface, whil e the 7x7 surface was the substrate for appreciable migration of Ag atoms. The results are discussed in terms of step-edge barriers in migration and o n-terrace migration. (C) 2000 Elsevier Science B.V. All rights reserved.