MODIFICATION OF SELF-ASSEMBLED MONOLAYERS OF ALKANETHIOLS ON GOLD BY IONIZING-RADIATION

Self-assembled films of octadecanethiols on polycrystalline Au have be en studied with monochromated X-ray photoelectron spectroscopy (XPS). The focus has been on the S-Au interface. It is demonstrated that ioni zing radiation causes breaking of S-Au bonds and formation of disulfid es. The modification of the alkane chains and the S headgroups has bee n investigated as a function of X-ray exposure. Long time X-ray expose d films have also been characterized by polarized reflection infrared spectroscopy, single-wavelength ellipsometry and water and hexadecane contact angle measurements. All these data show that in addition to th e disulfide formation at the gold interface, the originally well order ed hydrophobic film is strongly modified by the ionizing radiation, in volving C-H and C-C bond breaking, interchain cross linking and a gene ral disordering of the film. (C) 1997 Elsevier Science B.V.