Alkanethiol/Au(111) Self-Assembled Monolayers Contain Gold Adatoms: Scanning Tunneling Microscopy before and after Reaction with Atomic Hydrogen

Alkanethiol self-assembled monolayers on Au(111) are widely studied, yet the exact nature of the sulfur−gold bond is still debated. Recent studies suggest that Au(111) is significantly reconstructed, with alkanethiol molecules binding to gold adatoms on the surface. These adatoms are observed using scanning tunneling microscopy before and after removing the organic monolayer with an atomic hydrogen beam. Upon monolayer removal, changes in the gold substrate are seen in the formation of bright, triangularly shaped islands, decreasing size of surface vacancy islands, and faceting of terrace edges. A 0.143 ± 0.033 increase in gold coverage after monolayer removal shows that there is one additional gold adatom for every two octanethiol molecules on the surface.