Structural modification of polymeric amorphous hydrogenated carbon films induced by high energetic He+ irradiation and thermal annealing

Abstract Structural modifications of polymeric amorphous hydrogenated carbon (a-C:H) films by 2 MeV He + irradiation and by thermal annealing up to 400°C have been made. After irradiation with a dose of 1.2×10 15 cm −2 , the film hardness was increased by a factor of 3. Correspondingly, the optical band gap shrank from 3.0 to 2.5 eV and the refractive index was increased from 1.5 to 1.6. In contrast, although the optical band gap was found to be decreased to a similar small value of 2.0 eV after the films were thermally annealed in a vacuum of 10 −6 torr at 400°C for 30 min, the variations in the refractive index and film hardness were not detectable. The structural modifications of the carbon network in the a-C:H films by the ion irradiation and thermal anneal are discussed.