Thermal stability and relaxation in diamond-like-carbon. A Raman study of films with different sp(3) fractions (ta-C to a-C)

The thermal stability and relaxation processes in hydrogen free diamond-lik e-carbon films with different sp(3) fractions (40%, 60%, and 80%) are compa ratively studied for the first time by visible Raman spectroscopy. The 80% sp(3) film is very stable under annealing in the entire temperature region investigated (300-1270 K) and shows only a minor change of the optical tran smission, most likely due to a mild sp(2) clustering, but no graphitization . This is very important for practical applications requiring a high therma l stability. The films with lower sp(3) fraction show a thermal stability w hich decreases with the decreasing sp(3). Graphitization starts at 700 K fo r the 40% sp(3) film. (C) 1999 American Institute of Physics. [S0003-6951(9 9)00520-3].