Molecular dynamics investigation on the atomic-scale indentation and friction behaviors between diamond tips and copper substrate

Classical molecular dynamic (MD) simulations are used to investigate the atomic-scale indentation and friction behaviors of the spherical diamond(111) or diamond(001) tip in contact with a flat copper(001) substrate. In the indentation simulations, six radii ranging from 5 to 30 nm are adopted for each tip and the contact radius is examined as a function of normal load. The results demonstrate that the contact radii calculated from the MD simulation always deviate from the continuum theory predictions and the deviation varies with the tip surface atomic structure, tip radius, and normal load. Furthermore, the atomic-scale friction behaviors are investigated using 10 nm and 30 nm diamond(111) tips sliding over the copper(001) surface with a variety of loads. Apparent atomic stick–slip behavior is observed on such ordered but incommensurate contact interface; moreover, it does not disappear with increasing tip radius. It is also revealed that the friction versus load relationship is approximately linear, which is not in agreement with the continuum theory predictions and many reported atomic force microscope (AFM) experiments.