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

Structural modifications of polymeric amorphous hydrogenated carbon (a-C:H) films by 2 MeV He+ irradiation and by thermal annealing up to 400 degrees C have been made. After irradiation with a dose of 1.2 x 10(15) cm(-2), the him 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 f rom 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 degrees C for 30 min, the varia tions in the refractive index and film hardness were not detectable. The st ructural modifications of the carbon network in the a-C:H films by the ion irradiation and thermal anneal are discussed. (C) 2000 Published by Elsevie r Science S.A. All rights reserved.