Quantitative Analysis of the Interaction between an Atomic Force Microscopy Tip and a Hydrophobic Monolayer

Abstract

Atomic force microscopy has become an important technique for studying the adhesion of nanometer-sized contacts. However, there is still no good method to quantitatively characterize adhesive interactions. With a modified atomic force microscope, adhesion forces between a silicon nitride tip and a self-assembled monolayer of 1-dodecanethiol on gold(111) have been measured at different loading rates. Adhesion force-versus-loading rate curves revealed two regimes. Various interpretations of the two-regime character, like the existence of an inner transition state in the interaction potential or rebinding processes, are discussed. An explanation related to the cooperativity of individual van der Waals bonds responsible for effective adhesion is proposed. A way to extract the kinetic and interaction potential parameters for an individual van der Waals bond is demonstrated using a microscopic model to the analysis of adhesion force-versus-loading rate dependence.