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 Raman spectroscopy. It has been found that a film of 70-nm thickness remains structurally stable after annealing in air at up to 300°C for 4 h. Although some degree of graphitization was observed on a film annealed at 400°C, the film begins to oxidize and lose thickness only after annealing at 500°C for more than 2 h. This reflects the high thermal stability of the films. In general, annealing results in a narrowing and an upshifting of the G-band together with an increase in the ID/IG ratio. Most of these changes were observed during the first 2 h of annealing, after which the structure of the film appears to stabilize, with the exception at 500°C in which the film deteriorates further as oxidation occurs. It was also observed that thin film has better thermal stability against graphitization than thick film.