HIGH RESOLUTION X-RAY PHOTOELECTRON-SPECTROSCOPY MEASUREMENTS OF OCTADECANETHIOL SELF-ASSEMBLED MONOLAYERS ON AU(111)

We have measured high-resolution X-ray photoelectron spectroscopy (XPS ) spectra of 1-octadecanethiol (ODT) self-assembled monolayers (SAMs) on a Au(111) surface in order to investigate the Au-S binding properti es at the initial stage of SAM growth and after the desorption of the ODT from the Au surface. For the SAM prepared by the 1 min immersion i nto the ODT solution, we found new sulfur species around 161 eV and as signed it to isolated sulfur without C-S cleavage. We also confirmed t he presence of a similar 161 eV peak in the S(2p) spectra after desorp tion of the ODT molecules. Furthermore, we observed a peak shift in th e carbon 1s (C(1s)) peak, depending on the surface coverage of the ODT . In addition to the C(1s) peak of 285.1 eV which might correspond to alkyl chains of densely packed ODT molecules, another lower binding en ergy peak at 284.3 eV appeared after annealing. This lower C(1s) bindi ng energy peak formation suggested that some of the alkyl chains for t he remaining ODT molecules might be oriented parallel to the Au surfac e after annealing.