Photoemission surface core-level study of sulfur adsorption on Ge(100)

The interaction of elementary sulfur with Ge(100)(2\ifmmode\times\else\texttimes\fi{}1) surfaces was investigated using low-energy electron diffraction, Auger-electron spectroscopy, and photoemission core-level spectroscopy. Chemisorption of sulfur results in a binding-energy shift of the Ge 3d core-level electrons of \ensuremath{\Delta}E=0.33\ifmmode\pm\else\textpm\fi{}0.01 eV per S\char22{}Ge bond. The adsorbed sulfur dissociates and leads to an ordered (1\ifmmode\times\else\texttimes\fi{}1) reconstruction with one S atom per surface unit cell. The adsorbed sulfur atoms are bonded on bridge sites. Sulfur deposition exceeding one monolayer is possible, probably due to defects; the excess can be selectively thermodesorbed. During room-temperature adsorption, no S islands are formed. Thermodesorption is destructive, possibly etching.