Adhesion behaviour of self-assembled alkanethiol monolayers on silver at different stages of growth

We studied the development of interfacial energy $\gamma$ of alkanethiol self-assembled monolayers on Ag/mica substrates by force-displacement spectroscopy using an atomic force microscope. Self-assembled monolayers of decanethiol $[CH_3 (CH_2)_9SH]$ and octadecanethiol $[CH_3 (CH_2)_{17}SH]$ were studied. The growth of the monolayer as a function of time was studied by an ellipsometer for three different concentrations of decanethiol and octadecanethiol. The thiols led to well-ordered self-assembled monolayer that showed atomic resolution images by lateral force microscopy mode. The behaviour of $\gamma$ showed non-monotonic variation in stages of adsorption, which was more prominent for short chain length decanethiol. The $\gamma$ reached a limiting value of $12 mJ \hspace{2mm}m^{-2}$ for decanethiol and $7 mJ \hspace{2mm}m^{-2}$ for octadecanethiol