In this study, three-dimensional MD simulations are carried out to study the nanometric scratching process. The ploughing friction coefficient and the adhesion friction coefficient are distinguished for the first time using MD simulations. The contribution of chip to friction coefficient is also evaluated. The simulation results show that the macroscale theory can qualitatively evaluate the ploughing friction coefficient, but it slightly overestimates the ploughing friction coefficient on the nanoscale for the scratching depths studied. It is found that the adhesion friction coefficient is independent of the scratching depth as predicted by macroscale theory. It is also found that the contribution of chip to friction coefficient is independent of the scratching depth and cannot be neglected on the nanoscale.

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Three-dimensional molecular dynamics simulations using the Tersoff potential are conducted to investigate the nanoindentation process of monocrystalline germanium (Ge). It is found that a phase transformation from fourfold-coordinated diamond cubic phase (Ge-I) to sixfold-coordinated β-tin phase (Ge-II) occurs during the nanoindentation process. The simulation results suggest that a pressure-induced phase transformation instead of dislocation-assisted plasticity is the dominant deformation mechanism of monocrystalline Ge thin films during the nanoindentation process.

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