Two-dimensional ordering of octadecanethiol molecules on graphite observed by scanning tunneling microscope

Molecular-resolution images of n-octadecanethiol monolayer molecules on a graphite substrate are successfully observed with a scanning tunneling microscope (STM) in air. The images reveal that the molecules arrange in a hexagonal p(3 × 3) structure with a periodicity of 7.5 Å, a feature associated with the graphite substrate. X-ray photoelectron spectroscopy studies suggest that the methyl terminal group is adsorbed on the graphite. A model for the possible arrangement of the molecules on graphite surfaces is proposed.