ARSENIC TERMINATION OF THE SI(110) SURFACE

Si(100) and Si(111) surfaces both have singly occupied dangling bonds in their lowest-energy configurations. A single Monolayer of arsenic has been shown to passivate the surfaces and lead to simple, nearly ideal (2 X 1) and (I X 1) reconstructions, respectively. The bare Si(110) surface also has a complex reconstruction and high surface free energy. As presented here it can be shown theoretically that termination of Si(110) with a monolayer of As lowers the free energy of the ideal surface by 1.1 eV/(As atom). We would therefore expect that As adsorption would again lead to a topographically simple passivated structure. Using x-ray-photoemission spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy we show here that, to the contrary the Si(110):As surface, in fact consists of 2/3 monolayer of As in a two-dimensional corrupted unit cell with real-space unit vectors 5alpha and 3alpha + 3beta, where alpha = [001] and beta = 1/2[1-10]. We propose a model for the surface which consists only of fourfold-coordinated Si atoms and threefold-coordinated As atoms.