Friction reduction mechanism of hydrogen- and fluorine-terminated diamond-like carbon films investigated by molecular dynamics and quantum chemical calculation

The friction reduction mechanisms of diamond-like carbon (DLC) and H- or F-terminated DLC films were investigated using molecular dynamics (MD) and tight-binding quantum chemistry (TBQC) calculations. Atomistic-scale friction dynamics of both DLC and the surface-terminated DLC model in which the unsaturated bonds on their surface were terminated with H or F atoms were investigated by MD. The F-terminated DLC model showed lower friction than that of the H-terminated DLC model because of the stronger repulsive Coulombic force between F atoms at the surfaces. On the other hand, strong van der Waals interaction acting on the interface was observed for the H-terminated DLC model compared to that for the F-terminated DLC models. TBQC calculation indicates a bonding interaction between the surfaces of DLC, while the antibonding interaction was observed for the surface-terminated DLC model. Those interactions would make the difference in the friction properties among the studied models.