Spectroscopic characterization of thiol-derived self-assembling monolayers

This article reviews recent progress in the spectroscopic characterization of aliphatic and aromatic thiol-derived self-assembled monolayers (SAMs) on noble metal substrates. Several complementary techniques such as near edge x-ray absorption fine structure spectroscopy, x-ray photoelectron spectroscopy, and infrared reflection absorption spectroscopy were applied to study the balance between intermolecular and adsorbate-substrate interactions, chemical identity of the headgroup, and absorption site homogeneity at the sulphur-metal interface. Whereas in the thioaliphatic SAMs the headgroup-substrate interaction was found to be a decisive factor for the structure and packing in these films, these parameters are mainly determined by the intermolecular interactions in the thioaromatic films. Only one sulphur species could be detected in the S 2p HRXPS spectra of both aliphatic and aromatic SAMs suggesting binding of individual molecules as thiolates. Conclusions on the heterogeneity of the adsorption sites are derived and evidence that the investigated films represent highly correlated molecular assemblies are presented.