Interfacial Atomic Structure of a Self-Assembled Alkyl Thiol Monolayer/Au(111): A Sum-Frequency Generation Study

Infrared-visible sum-frequency generation (SFG) is used to spectroscopically probe the interfacial structure of a self-assembled monolayer of alkyl thiol on a Au(111) surface. The SFG spectra of the CH₃ group measured as a function of azimuthal angle indicates that sulfur atoms cannot be situated at sites of a single type, e.g., hollow or bridge, but must be in a mixed arrangement. SFG is also used to study the reconstruction of the gold substrate by alkyl thiol.