Headgroup dimerization in methanethiol monolayers on the Au(111) surface: a density functional theory study

TL;DR

This study uses density functional theory to resolve a controversy about the dimer pattern of methanethiol on Au(111), revealing new insights into adsorption behavior and surface chemistry.

Contribution

First computational demonstration of methanethiol dimerization on Au(111), clarifying coverage-dependent dimerization and desorption mechanisms.

Findings

Methanethiol dimerizes on Au(111) at intermediate coverage.

Dimerization does not occur at high coverage for methylthiolate.

Dialkyl disulfide species form during desorption, not surface attachment.

Abstract

A long-standing controversy related to the dimer pattern formed by S atoms in methanethiol ($CH_{3}SH$) on the Au(111) surface has been resolved using density functional theory. For the first time, dimerization of methanethiol adsorbates on the Au(111) surface is established by computational modeling. For methylthiolate ($CH_{3}S$), it is shown that the S atoms do not dimerize at high coverage but reveal a dimer pattern at intermediate coverage. Molecular dynamics simulation at high coverage demonstrates that the observed dialkyl disulfide species are formed during the desorption process, and thus are not attached to the surface.