Low temperature internal friction of diamond-like carbon films

We have studied the internal friction of amorphous diamond-like carbon films prepared by pulsed-laser deposition from 0.4 to 300K. The low temperature internal friction below 10K is dominated by the atomic tunnelling states for amorphous solids, which is a measure of structure disorder. We have tried to vary the content of sp carbon atoms versus sp ones by changing laser fleunce, by doping with N and Ar, and by annnealing at 500◦C for 20 minutes. Our results show that the internal friction varies about one order of magnitude from 2×10−5 to 2×10−4, and its value is higher with higher sp content when the film quality is generally considered superior. However, it is known that as-deposited diamond-like carbon films with high sp content are heavily stressed. Annealing and doping are used to release the stress. We conclude that in addition to tetrahedral bonding, low stress is also important in reducing struture disorder associated with the low energy tunnelling states in amorphous solids.