Surface modifications in diamond-like carbon films submitted to low-energy nitrogen ion bombardment

Abstract

Amorphous hydrogenated carbon films (a-C:H) films deposited by plasma enhanced chemical vapor deposition in CH 4 atmosphere were submitted to nitrogen r.f.-plasma treatment. The influence of several parameters was investigated: the chamber pressure, ranging from 0.5 to 10 Pa, the self-bias voltage in the range between −50 and −500 V and the exposure time. The erosion rate was determined by profilometry. It increases as the self-bias increases and tends to saturate for higher pressures. The nitrogen incorporated in the films was measured by nuclear reaction analysis. The results indicate a decrease in the N content as the pressure or the self-bias increase. The chemical bonds were probed by XPS and two chemical environments can be identified, one with N atoms surrounded by C atoms and the other one with N atoms binding to H. Surface roughness and friction coefficient modifications were followed by atomic force and lateral force microscopies. The surface roughness is independent on the value of the self-bias voltage, while the friction coefficient decreases.