Amorphization anisotropy and the internal of amorphous layer in diamond nanoscale friction

In this work, molecular dynamic (MD) simulation is employed to investigate the formation and evolution of amorphous carbons in the surface layer of diamond crystal as the frictional sliding is performed on diamond (1 0 0) plane. Simulation results reveal that the formation of amorphous carbons at the sliding interface is inevitable due to the friction. In this case, transformation from diamond sp3 hybridized carbons to sp2 hybridization structures is dominant. More interestingly, most of the sp hybridized carbons appear on the topmost surface of the amorphous layer. Amorphization rate in sliding along the [1 0 0] direction is greater than that along the [1 1 0] direction due to the smaller resistance forces. In the light of the velocity variation of carbon atoms, the amorphous layer is divided into two layers, i.e. the coherent layer and transition layer. Moreover, a density transition region appears with the formation of amorphous carbons, and the thickness of transition region can be used to characterize the amorphization degree.