Surface reconstructions and morphological modifications: restructuring of W(111) induced by sulfur overlayers

Abstract

The restructuring of S/W(111) surfaces has been studied using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and scanning tunneling microscopy (STM). Dosing W(111) with a saturation coverage of H 2S followed by annealing to >800 K causes a substrate reconstruction with (4×4) periodicity. After the formation of the (4×4) structure over the entire surface, and upon further annealing, the terrace–step configurations also restructure and form triangular terraces. Upon heating to T>1000 K, the triangular terraces coalesce and enlarge, in addition to forming multiple steps. A size-mismatch mechanism, based on charge transfer between S and W atoms, is proposed to explain the formation of (4×4) structures: strain introduced at the surface by adsorption of large sulfur anions is relieved by the (4×4) reconstruction. We have explored the consequences of a terrace growth mechanism for S(4×4)/W(111) that is based on local step structures, coupled with domain mismatch.