Accelerating the Kinetics of Thiol Self-Assembly on GoldA Spatial Confinement Effect

Abstract

The adsorption of alkanethiols onto gold surfaces to form self-assembled monolayers (SAMs) occurs more than 10 times faster in a spatially confined environment than on unconfined bare substrates, and the adsorbed layers exhibit higher coverage and two-dimensional crystallinity. The spatially constrained reaction environment is prepared with use of an atomic force microscope tip to displace thiols within a previously formed SAM. During the displacement, the thiol molecules present in the solution above the SAM rapidly assemble onto the exposed nanometer-size gold area that is confined by the scanning tip and surrounding SAM. The accelerated rate is attributed to a change in the pathway for the self-assembly process as the spatial confinement makes it geometrically more probable and energetically more favorable for the initially adsorbed thiols to adopt a standing-up configuration directly in this microenvironment. In contrast, thiols that self-assemble onto gold surfaces in an unconstrained environment ini...