Velocity-dependent phononic friction in commensurate and incommensurate states

Abstract

We investigate that multiple friction peaks occur with an increase in velocity in commensurate and incommensurate states between graphene layers. Fast Fourier transform analysis of instantaneous friction force confirms that frictional spectrum mainly distributes at washboard frequency of tip and its harmonics. When washboard frequency approaches natural frequency of tip and its fractional frequencies, resonance will occur in both contact cases, resulting in friction peaks. Further observations indicate that phonon spectra of tip and substrate match in commensurate state, thereby establishing effective energy dissipation channels; however, phonon spectra do not match in incommensurate state. Finally, we deduce a theoretical model for calculating number of excited phonons and quantitatively explain friction discrepancy in different contact states and velocities.