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

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Abstract
Measurements of the extended fine structure in the photoemission intensity from the S(1s) core level were performed for a (2×2) 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±0.05 Å above the Ge surface. The separation between the first and second Ge layers is contracted by (9±6)%, and some Ge—Ge bond lengths between the Ge bilayers are expanded by (8±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).