Frictional Behavior of Nano-undulated Surface of Diamond-like Carbon Films

Frictional behavior of nano-undulated diamond-like carbon (DLC) films deposited by plasma assisted chemical vapor deposition (PACVD) process was investigated. In order to prepare the nano-undulated DLC film, a Si wafer with nano-sized Ni dots was prepared by rapid thermal annealing of Ni thin films. Since the structure of DLC film deposited by PACVD was independent of the substrate materials and that the size of Ni nano dots could be controlled in a systematic way by changing the thickness of the Ni film, we could investigated the effect of nanoscale surface roughness on the tribological behavior of DLC films. The friction coefficient between steel ball and undulated DLC films of the roughness varying from 0.6 to 13.7 nm was measured by using a ball-on-disk type wear rig in ambient environment. The friction coefficients were in the range from 0.15 to 0.2, independent of the surface roughness. Wear of the steel ball was much enhanced with higher content of Fe in the debris as the roughness increased. However, the size of the debris decreased with increasing roughness. Raman spectrum analysis revealed that the chemical bond structure of the debris is significantly dependent on the surface roughness. The friction behavior was discussed in terms of the chemical compositions and the agglomeration behavior of debris.