An adsorption process study on the self-assembled monolayer formation of octadecanethiol chemisorbed on gold surface

The self-assembled formation of octadecanethiol (CH3(CH2)(17)SH) on a gold substrate was studied using a quartz crystal microbalance (QCM) and a scann ing tunneling microscope (STM). From the QCM measurements at various concen trations of octadecanethiol solutions in hexane and alcohol, the adsorption process of octadecanethiol onto Au was confirmed to consist of two steps a s follows: (i) fast but disordered adsorption and (ii) a thermodynamically controlled rearrangement for uniform packing of octadecanethiol. Also, it w as revealed that the adsorption rate became faster in ethanol than in hexan e since less solubility of octadecanethiol in ethanol could help the format ion of the monolayers. At 5 x 10(-7) M solution, the monolayer formation wa s monitored by STM. The morphology of monolayer region was initially circul ar (diameter size: 7.26 +/- 2.1 nm) and gradually changed to a stripe type after several minutes. At higher concentration, the self-assembled monolaye r was formed immediately after the solution was introduced to a substrate.