Effects of annealing temperature on the mechanical, optical, and electrical properties of hydrogenated, nitrogen-doped diamond-like carbon films

We have deposited nitrogen-doped diamond-like carbon (N-DLC) films by plasma-enhanced chemical vapor deposition using H2 as a dilution gas and investigated the effects of post-deposition annealing in a vacuum on the film properties. It was found that the optical bandgap slightly increased after annealing at 235 °C, whereas it substantially decreased after annealing at 420 and 490 °C. At these temperatures, the critical load increased primarily due to a decrease in internal stress. Simultaneously, the amount of bound hydrogen in the films decreased, whereas sp2 C=C increased and its clustering was accelerated. On the other hand, both friction coefficient and specific wear rate became lowest at 347 °C. We found that the N-DLC/p-type silicon heterojunction annealed at 347 °C exhibited the highest rectification ratio. These results were discussed based on the structure and chemical bonding states of the annealed films.