The surface-conditioning effect of gold substrates on n-octadecanethiol (ODT) self-assembled monolayer (SAM) growth was studied by X-ray photoelectron spectroscopy (XPS). The gold substrates were immersed in an ethanol solution containing 1 mM ODT for 1 h. The C/Au ratios of the ODT SAMs estimated by XPS formed on gold substrates depended on the amount of contamination on the gold surface. A full-coverage ODT SAM was successfully obtained on the gold substrate after ultraviolet light (UV)/ozone treatment for 1 h and rinsing with pure ethanol for 1 h. XPS measurements indicated that low contamination levels and a sulfur-free gold surface were obtained using this pretreatment and, hence, the adsorption of ODT molecules on gold proceeded efficiently. On the other hand, the C/Au ratio of an ODT SAM on a contaminated gold substrate was less following immersion in an ODT solution for 1 h, because surface contamination may reduce the adsorption rate of ODT molecules on the gold surface. When the gold substrate was rinsed with a chloroform solution for 1 h before SAM formation, the lowest C/Au ratio was obtained. XPS results showed that sulfur atoms quickly adsorbed onto the gold surface after chloroform rinsing and prevented the adsorption of ODT molecules onto the gold surface.
ASJC Scopus subject areas