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We report the first measurements on the dynamical response of alkanethiol/gold monolayers using a depth-selective tethered probe molecule technique, where 5% of the monolayer is comprised of the probe. Our transient spectroscopic data indicate that, for the first ∼10 CH2 groups above the gold surface, the local environment is highly rigid, and from these same data, we recover an average tilt angle of 26°, in exact agreement with steady state measurements.

We have studied the adsorption of organic molecules from the vapor phase onto bare gold, n-octadecanethiol-modified, and 11-mercapto-1-undecanol-modified gold surfaces using a controlled atmosphere chamber with an ellipsometer and a quartz crystal microbalance for simultaneous in-situ determination of adsorbate thickness and mass. Our experimental data are fit by the BET adsorption isotherm, and results from these fits place limits on the ways in which the adsorbates can interact with the selected substrates. Ellipsometric data, in combination with the mass adsorption data, demonstrate that n-octadecanethiol self-assembled monolayers on gold experience penetration by adsorbates, where the 11-mercapto-1-undecanol-modified surfaces and the gold surface do not. We compare these findings to other literature reports that bear on the permeability of the alkanethiol/gold interface.

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