Molecular dynamics simulations of friction between an ordered organic monolayer and a rigid slider with an atomic-scale protuberance

The atomic-scale friction between an ordered organic monolayer and a rigid probing slider with an atomic-scale protuberance was investigated using a molecular dynamics method. The slider was used to model the tip apex used in atomic force microscopy. In order to control the normal load, three orthogonal springs and a feedback regulation unit were introduced. The protuberance, composed of a small number of atoms, brought about local and collective deformation of the monolayer and generated a friction force. Various frictional properties were investigated in terms of the size of the protuberance, the length of molecules in the monolayer, and the conditions, such as temperature, applied normal load, and some parameters of the external observation system. Lattice-resolved friction signals were obtained when the size of the protuberance was comparable to the cross-sectional area of the molecule.