Two-dimensional simulation of superlubricity on NaCl and highly oriented pyrolytic graphite

The friction between an atomically sharp tip and a solid surface (NaCl and highly oriented pyrolytic graphite) is analyzed theoretically in the framework of a modified Tomlinson model in two dimensions. Lateral forces are studied as a function of temperature, load, and magnitude of actuation. The actuation leads to a reduction in friction and allows one to enter a dynamic superlubricity regime. In addition, our model is able to describe other ultralow friction states as static superlubricity and thermolubricity. We find a good agreement between the calculations and the experimental results.