Unraveling the Radiation Damage of n-Dodecanethiol Self-Assembled Monolayers on Au(100) and Au(111): A Prerequisite to Understand the Oriented Attachment of Au Nanoparticles

We present a quantitative X-ray photoelectron spectroscopy study on the electron-induced degradation of self-assembled monolayers of n-dodecanethiol on Au(100) and Au(111). This study is motivated by the lack of mechanistic explanations of the oriented attachment of n-dodecanethiolate-protected nanoparticles exposed to irradiation during imaging by transmission electron microscopy. The coalescence of these nanoparticles preferentially occurs through the encounter of the (100) faces. It could be hypothesized that thiolate desorption from the Au(100) faces is faster than that on Au(111), which would overcome the steric hindrance for the encounter of the (100) metallic surfaces. Nevertheless, we found that the organic material desorbs at comparable rates and extension from both single-crystalline surfaces, despite the fact that the most abundant damaging products are different on these surfaces. Furthermore, although RS–R′ prevails on Au(111) while RS–SR is formed on Au(100), complete moieties derived from dodecanethiolate are the main desorption products from both SAMs. In addition, we provided arguments based on the reaction mechanism to describe the cross-linking of hydrocarbon chains and to explain why sulfur-containing species desorbs at the same rate from both single-crystalline surfaces.