Sulfur-induced mobilization of Au surface atoms on Au(111) studied by real-time STM

The interaction of sulfur with gold surfaces has attracted considerable interest due to numerous technological applications such as the formation of self-assembled monolayers and as a chemical sensor. Here, we report on the interaction of sulfur with Au(1 1 1) at two different temperatures (300 K and 420 K) studied by real-time scanning tunnelling microscopy, low energy electron diffraction and Auger electron spectroscopy. In the low coverage regime (< 0.1 ML), S adsorption lifts the herringbone reconstruction of the clean Au(1 1 1) surface indicating a lateral expansion of the surface layer. An ordered (root 3 x root 3)R30 degrees sulfur adlayer develops as the coverage reaches similar to 0.3 ML. At higher S coverages (> 0.3 ML) gold surface atoms are removed from regular terrace sites and incorporated into a growing gold sulfide phase. At 300 K this process leads to the formation of a rough pit and mound surface morphology. This gold sulfide exhibits short-range order and an incommensurate, long-range ordered AuS phase develops upon annealing at 450-525 K. In contrast, formation of an ordered AuS phase via rapid step-retraction rather than etch pit formation is observed during S-interaction with Au(1 1 1) surfaces at 420 K. Our results shed new light on the S-Au(1 1 1) interaction. (c) 2007 Elsevier B.V. All rights reserved.