Reduced Density of Missing-Dimer Vacancies on Tungsten-Contaminated Si(100)-(2×n) Surface by Hydrogen Termination

A Si(100) surface with missing-dimer vacancies forming (2× n ) phase was prepared by tungsten deposition and the morphological change was observed by scanning tunneling microscopy when the surface was terminated by hydrogen. The density of dimer vacancies was significantly reduced by the hydrogen termination, suggesting that the density of subsurface W atoms decreased. We discuss the mechanism of this morphological change based on the traditional theory of chemisorption-induced surface segregation and on the energetic instability of W atoms buried in the subsurface of the hydrogen-terminated Si surface.