Dynamics of atomically thin layers-surface interactions in tip-substrate geometry

Nano-scale point-contact experiments involving the interactions of atomically-sharp tips with metallic substrates (akin to the STM and AFM configurations) have revealed that the physiosorption of an atomically-thick monolayer film on the surface of a substrate leads to the lowering of the force of adhesion between the tip and the surface. We have carried out large-scale constant-temperature molecular dynamics (MD) simulations based on the Nose-Hoover constraint formalism and using many-body inter-atomic potentials of Finnis-Sinclair type to show, at the atomistic level, the mechanisms contributing to the above phenomenon. We show that, irrespective of whether the wetting phenomenon occurs between the tip and the adsorbed monolayers, the force of adhesion is always reduced relative to the case of an atomically clean surface. The results of our computer-based simulation studies seem to be in agreement with similar point-contact experimental investigations. An analytic model, based on contact angle theories, is developed to give an inter-pretation of the simulation results.