Lack of Pinning for Rigid Sliding Monolayers in Microbalance Experiments

TL;DR

This paper investigates why monolayers on metallic substrates in microbalance experiments often slide despite theoretical expectations of pinning, proposing that defect potential ranges cause force cancellations leading to unpinned motion.

Contribution

It introduces a hypothesis that defect potential ranges larger than atomic spacing reduce net pinning forces, explaining observed sliding behavior.

Findings

Defect potential range affects pinning strength.

Force cancellations occur with slightly extended defect potentials.

Monolayer sliding can happen without pinning despite substrate imperfections.

Abstract

Recent work on the dynamics of monolayers on a metallic substrate attached to a quartz oscillator has provided interesting data on kinetic friction at the microscopic level. Sliding of the film relative to the substrate is often observed even in situations in which theory seems to predict that the film should be pinned by substrate imperfections. In this letter we propose, in order to attempt to resolve this issue, that if the defect potentials have a range of a little more than an atomic spacing, the net forces on the film due to the defects are likely to be quite small due to cancellations.