A detailed analysis of the C 1s photoemission of n-alkanethiolate films on noble metal substrates

High-resolution C 1s X-ray photoemission spectra for the series of n-alkanethiolate (AT) self-assembled monolayers (SAMs) with different lengths of the alkyl chain have been acquired and analyzed in terms of initial and final state effects and fine structure of the C 1s emission. Independent of the alkyl chain length, the binding energy position of this emission was found to be higher by ≈0.35 eV for AT SAMs on Ag substrate as compared to Au, which was attributed to the differences in the final state screening mediated by the intermolecular charge transfer. It was assumed that the extent of this effect is a function of the detailed molecular arrangement in the alkyl matrix and demonstrated that the difference in the C 1s peak position disappears as soon as this arrangement is distorted by the incorporation of sulfone moiety in the alkyl chain. In addition, a change of the C 1s peak shape from a symmetric to asymmetric line with increasing alkyl chain length has been observed. This development could be described assuming the existence of a fine structure in the C 1s emission, with two low-intensity components at the higher and lower BE sides of the main emission peak. An assignment of these components has been considered.