Pulsed laser deposition of hydrogenated amorphous diamond-like carbon films from a polymer target

Abstract

Hydrogenated amorphous diamond-like carbon (a-DLC:H) films have been prepared by pulsed laser ablation of a polymer target in the presence of hydrogen (H2) gas. The growth rate of these films was found to be highly dependent on the deposition temperature and the amount of H2 gas used during the deposition process. The optical band gap of these a-DLC:H films changed in a wide range (0.25–2.5 eV) with substrate temperature and H2 pressure, and was found to be highly correlated to the ratio of sp3/sp2 in the film. The gap reached a maximum in a temperature range between 100 and 200 °C and had small values at either lower or higher temperatures. With increasing H2 pressure, the band gap increased monotonically and saturated around 0.5 mbar. It was found that the refractive index and the imaginary part of dielectric constant of these a-DLC:H films monotonically increased with decreases in the wavelength of the probing beam. It was also found that these laser derived a-DLC:H films could be made either completely insulating [∼10−11 (Ω cm)−1] or conducting [∼1 (Ω cm)−1] by simply varying the deposition temperature and H2 pressure. Very little photoconduction has been observed in these a-DLC:H films.