DIRECT OBSERVATION OF SUBSTRATE INFLUENCE ON CHEMISORPTION OF METHANETHIOL ADSORBED FROM THE GAS-PHASE ONTO THE RECONSTRUCTED AU(111) SURFACE

Methanethiol adsorption onto Au(111) was studied in situ by scanning t unneling microscopy in air at room temperature. By maintaining registr y on the surface during adsorption, it was demonstrated that gold vaca ncy islands (i.e., ''etch pits''), which are created by the chemisorpt ion of methanethiol, exist in rows that exactly follow the (22 x root 3) gold reconstruction. Ostwald ripening produces larger gold vacancy islands that are no longer coincident with the original Au(111) recons truction. Further annealing produces well-ordered domains of methaneth iol that have the same surface structures observed for other alkanethi ol-based self-assembled monolayers on Au(111). The results demonstrate for the first time that at high rates of dosing, the structure of a f ully-formed thiol monolayer on Au(111) is influenced by the original ( 22 x root 3) reconstruction of the underlying gold surface. These data strongly suggest that the gold vacancy islands observed in methanethi ol, thiophene, and other alkanethiol-based monolayers are not the resu lt of chemical etching.