Alkyl chain length effect on growth kinetics of n-alkanethiol self-assembled monolayers on gold studied by x-ray photoelectron spectroscopy

Growth kinetics of self-assembled monolayers (SAMs) of n-alkanethiols on gold substrates was studied by X-ray photoelectron spectroscopy (XPS). We compared adsorption kinetics for three alkanethiol homologues: butanethiol (C4SH), dodecanethiol (C12SH), and octadecanethiol (C18SH). Results of quantitative analysis by XPS suggested that the adsorption rate of short alkyl chain thiols is higher than that of long ones on gold substrates at the initial growth stage, in contrast to previous reports. For C4SH SAM formation, we have also confirmed the occurrence of a replacement effect from contamination to SAM on gold, based on our observation of a decrease in the amount of carbon and an increase in the amount of gold where as determined from XPS spectra.