3D Monolayers of 1,4-Benzenedimethanethiol on Au and Ag Clusters: Distinct Difference in Adsorption Geometry with the Corresponding 2D Monolayers.

Au and Ag clusters of 3-nm mean diameter were prepared with 1,4-benzenedimethanethiol (BDMT) as the capping molecule. In both the monolayer-capped clusters, BDMT adsorbs in the dithiolate form in contrast to in the 2D monolayers, where the dithiolate form exists only in the case of Ag. As a result, the molecule lies flat on the cluster surface in both Au and Ag, whereas the molecular plane is perpendicular to the surface in the 2D monolayer of Au. This difference in adsorbate structure is attributed to the evolution in the cluster surface as adsorption occurs. Transmission electron microscopy and X-ray powder diffraction suggest that no superlattice of the clusters exists. Mass spectrometry suggests the presence of the phase transfer reagent at the surface. X-ray photoelectron spectroscopy confirms the chemical similarity of the two surfaces and suggests that the thiolate at the surface is susceptible to X-ray beam induced damage. Copyright 1999 Academic Press.