Friction and Wear of Amorphous Hydrogenated Carbon

ABSTRACTUniform amorphous hydrogenated carbon (a-C:H) films with surface roughnesses ranging between 1 nm and 4 nm were produced by radio frequency self biased plasma enhanced chemical vapor deposition (rf PECVD) on > Silicon substrates using 100% methane precursor gas mixture, rf power densities ranging between 0.11 W/cm2 and 1.07 W/cm2, and pressures ranging between 0.67 Pa and 40 Pa. Reciprocating sliding friction experiments were conducted on the a-C:H films with hemispherical, silicon nitride pins in dry nitrogen and in 60% relative humidity. The coefficients of friction and the wear rates of the a-C:H were very low in dry nitrogen, ranging from 0.03 to 0.05, and from 1.1 × 108 mm3/Nm to 2.3 × 10−6 mm3/Nm, respectively. In 60% relative humidity, the initial coefficients of friction were approximately 0.30. However, the steady state coefficients of friction of the a-C:H films ranged from 0.10 and 0.30, depending on the deposition conditions. The wear rates ranged from 2.0 × 10−9 mm3/Nm to 8.9 x 10−8 mm3/Nm in 60% relative humidity. Raman microprobe spectroscopy and Auger electron spectroscopy (AES) revealed that sliding friction was transforming the a-C:H films into a material primarily composed of sp2 bonded carbon with increasing short range order. Qualitatively, the amount of wear which occurred corresponded to the extent that the structural changes progressed. The a-C:H films were further characterized by scanning electron microscopy (SEM) and surface profilometry.