Characteristics of a direct negative carbon ion beam source and AFM observations of DLC film

The properties of a direct negative carbon ion beam source were characterized to optimize the conditions for deposition of diamond-like carbon films on Si substrates at room temperature. The effect of secondary negative carbon ion beam energy on deposition rate, surface roughness and tribological properties of the DLC films were studied. During deposition, approximately 30% of the all sputtered carbon atom is negatively ionized at the target surface, with a surface ionization and carbon ion yield strongly dependent on the primary Cs+ ion dose and bombarding energy. Also, Cs sputter generated carbon ion has a narrow ion beam energy spread. The measured results of atomic force microscopy (AFM) showed that surface roughness decreased with increasing ion beam energy due to increased adatom mobility and resputtering of weekly bonded carbon atom. However, beyond 200 eV, surface roughness increased steeply. It is considered that the kinetic energy of carbon ions contributes to form the very flat surface but that the excessive energy results in damage to the DLC films. The friction coefficient of the DLC films was evaluated using a ball on disk tribotester. It was found that the surface roughness has an effect on the friction coefficient.