The Case of the Disappearing Monolayer: Alkylsilane Monolayer Formation, Oxidation, and Subsequent Transparency to Scanning Tunneling Microscopy

Oxidation of a chemisorbed alkylsilane monolayer on gold spontaneously regenerates the 23 × √3 surface reconstruction typical for clean gold surfaces. A protective alkylsiloxane layer remains on the surface, preventing further reactions with alkylsilane. The resulting alkylsiloxane monolayer is transparent to typical STM imaging conditions; however, STS can detect the presence of the layer. These observations indicate that STM studies of noble metal surfaces, performed in oxidizing environments such as ambient atmosphere must be interpreted with caution. Chemisorbed species can oxidize, interact with the underlying metal surface as physisorbed layers, and give rise to STM images that would typically be interpreted as clean metal surfaces.