Double-slip mechanism in atomic-scale friction: Tomlinson model at finite temperatures

We studied the atomic scale friction mechanism of a friction force microscope (FFM) by means of the dynamical simulation in the Tomlinson model at a finite temperature. Stick-slip motion of a tip atom is the intrinsic energy dissipation mechanism at low scanning velocities of a support point of FFM and the frictional behavior is classified into three modes. The single slips occur in a high friction mode but double slips occur in a low friction mode, while mixed slips of single and double occur in an intermediate friction mode. In the intermediate friction mode, the friction force shows irregular sawtooth behavior as the support point is moved. We clarify the appearance condition of these three friction modes and each dependence of the average friction force on both temperatures and the sliding velocities.