Vapor Adsorption onto Metal and Modified Interfaces:  Evidence for Adsorbate Penetration of an Alkanethiol Monolayer on Gold

Abstract

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.

Onset of Crystalline Order in 1‐Nonanethiol Monolayers Deposited from Solution

“…Additional experiments carried out in a controlled atmosphere chamber indicate that full removal of the solvent molecules from the monolayer appears to be a rate‐limiting prerequisite for the onset of the ordering process. The presence of a limited number of intercalated solvent molecules in the disordered monolayer is supported by the electrochemical quartz balance and ellipsometric measurements reported by Blanchard and Karpovich 17 …”

Chemical Force Microscopy Study of Adhesion and Friction between Surfaces Functionalized with Self-Assembled Monolayers and Immersed in Solvents

“…We believe these discrepancies are related to solvent partitioning into the monolayer. It has been demonstrated that methanol and hexane measurably penetrate into even a close-packed alkanethiolate monolayer (56). SAMs of alkylsiloxanes lack the long-range order that SAMs of alkanethiolates possess (41)(42)(43)(44)(45)57), so penetration of the solvent is expected to be more significant in SAMs of alkylsiloxanes.…”

Onset of Crystalline Order in 1‐Nonanethiol Monolayers Deposited from Solution

“…A value of n close to 1 may arise in either a) a constant rate of nucleation, combined with ordered domains of homogeneous size whose number increases with time, or b) an instantaneous (delta-shaped) nucleation rate, combined with a domain growth along one dimension only. [17] Our results provide for the first time evidence of the dynamic structure of alkanethiol SAMs in contact with a liquid phase. [16] As shown in the inset of Figure 3, peak widths remain constant during the ordering process, thus providing a time-independent average mosaic size of 50 nm.…”