Surface structure of (22) S/Ge(111) determined by angle-resolved photoemission fine structure.

Abstract

Measurements of the extended fine structure in the photoemission intensity from the S(1s) core level were performed for a (2\ifmmode\times\else\texttimes\fi{}2) overlayer of S on Ge(111). This is the first application of angle-resolved photoemission fine structure (ARPEFS) to study an adsorbate on a semiconductor substrate to our knowledge. The adsorption site and local geometry were determined from the ARPEFS with use of comparisons to multiple-scattering calculations. The results of this analysis indicate adsorption in a twofold bridge site 1.03\ifmmode\pm\else\textpm\fi{}0.05 A\r{} above the Ge surface. The separation between the first and second Ge layers is contracted by (9\ifmmode\pm\else\textpm\fi{}6)%, and some Ge---Ge bond lengths between the Ge bilayers are expanded by (8\ifmmode\pm\else\textpm\fi{}3)%. This adsorption site is different from that determined for another chalcogenide, Te, on the Ge(111) surface on the basis of surface extended x-ray-absorption fine-structure measurements, but it is the same as those found for Te/Si(111) and Se/Si(111).