Influence of hydrogen on the structure and properties of tetrahedral amorphous carbon films obtained by the filtered cathodic vacuum arc technique

Hydrogenated tetrahedral amorphous carbon (ta-C:H) films prepared by filtered cathodic vacuum are at different hydrogen partial pressures (0.0008-0.5 mTorr) were studied in terms of their structure and properties. It is shown that a single Breit-Wigner-Fano (BWF) line shape is appropriate to fit the Raman spectra acquired from the ta-C:H films deposited at a hydrogen partial pressure of 0.0008-0.08 mTorr. However, the: single BWF fit shows a residual near 1350 cm(-1) for the film deposited at a higher hydrogen partial pressure. This indicates the presence of graphitic clusters in the corresponding film. The data from infrared spectroscopy show that the hydrogen in the ta-C:H films is associated with triply bonded spl, CHn sp(2) and CHn sp(3) bonding. The absorption for the CHn sp(3) is maximum for ta-C:H at a hydrogen partial pressure of 0.008 mTorr. It was observed that the film hardness and:compressive stress are about 70 GPa and 12 GPa respectively cor responding to the hydrogen partial pressure from 0.0008 to 0.02 mTorr. When I:he hydrogen partial pressure further increases from 0.02 to 0.5 mTorr, the hardness and compressive stress decrease to about 50 GPa and 8 GPa respectively. The optical bandgap is about 3.0 eV for the ta-C:H film deposited at hydrogen partial pressure of 0.008 mTorr compared with 2.7 eV for the hydrogen free ta-C films. A lower intraband absorption coefficient of the-ta-C:H sample (hydrogen partial pressure, 0.008 mTorr) indicates that the defect states are lower in this sample.