Molecular dynamics studies on the growth and structural properties of hydrogenated DLC films

The novel frictional properties of hydrogenated DLC (Diamond-like Carbon) films have been reported for nearly ten years. But up to now, researchers still haven't known the exact mechanism resulting in the super-low frictional performance of hydrogenated DLC films. Especially they have little knowledge on the molecular configuration and structural properties of these kinds of films. In this paper, CH3 radicals with different impact energies are selected as source species to deposit DLC films on diamond (100) by molecular dynamics simulation. Results show hydrogenated DLC films can be successfully obtained when impact energy is in an appropriate scope that is no less than 20eV. The depositing processes involve impinging diamond surface and bonding procedure. Some atoms, instead of bonding with substrate atoms, fly away from the diamond surface. Only suitable impact energy can improve the growth of the film. Within 30eV to 60eV, the maximum deposition ratio is attained. In addition, when carbon atoms act as the deposition sources, the deposition ratio is relatively higher. Furthermore, the authors find that species with higher concentration of carbon atoms in deposition sources lead to a better deposition rate. Carbon atoms are more reactive than hydrogen atoms. Then the relative densities of DLC films are calculated. The density curves indicate that the structures of the films vary obviously as the impact energy augments. The average relative density is generally monotone increase with the increment of impact energy. The hybridization of carbon atoms greatly affects the properties of hydrogenated DLC films. The transition between sp² and sp³ will result in the graphitization and reduce the frictional coefficient when DLC films are used as tribo-pair in friction.