Chemisorption of sulfur on Ge(100)

Abstract

The adsorption of elementary sulfur on Ge(100) has been studied with AES, LEED and various surface photoemission spectroscopy techniques. The adsorption of sulfur reaches saturation after a few langmuir exposure and yields an ordered (1×1) structure with one sulfur atom per surface unit cell bonded on a bulk-like bridge site. Sulfur deposition exceeding one monolayer is possible, probably due to defects. During room temperature submonolayer adsorption no sulfur islands are formed. The adsorbed single atoms are bonded in well-defined bridge sites as in the case of full monolayer coverage. The valence band structure of the Ge surface is changed under sulfur adsorption: The surface states of clean Ge(100)(2×1) disappear, for S/Ge(100)(1×1) one strongly and two weakly dispersing sulfur induced states with E B=2−4 eV, E B θ5 eV and E B θ7.5 eV, respectively, are identified. The resulting two-dimensional band structure confirms the idea of covalent SGe bonds wiht (1×1) periodicity. The system S/Ge(100)(1×1) can be regarded as an ideally terminated surface.