Time and temperature-dependent changes in the structural properties of tetrahedral amorphous carbon films

The time and temperature-dependent changes in the structural properties of tetrahedral amorphous carbon (ta-C) films were accessed continuously by Ram an spectroscopy. It has been found that a film of 70-nm thickness remains s tructurally stable after annealing in air at up to 300 degrees C for 4 h. A lthough some degree of graphitization was observed on a film annealed at 40 0 degrees C, the film begins to oxidize and lose thickness only after annea ling at 500 degrees C for more than 2 h. This reflects the high thermal sta bility of the films. In general, annealing results in a narrowing and an up shifting of the G-band together with an increase in the I-D/I-G ratio. Most of these changes were observed during the first 2 h of annealing, after wh ich the structure of the film appears to stabilize, with the exception at 5 00 degrees C in which the film deteriorates further as oxidation occurs. It was also observed that thin film has better thermal stability against grap hitization than thick film. (C) 2000 Elsevier Science S.A. All rights reser ved.