Hydrogen evolution from a-C:H films

Diamond-like amorphous carbon films with high hardness, high electrical resistivity, good optical transparency into the infra-red, and good adherence to their substrates may be produced by many methods, most of which result in the incorporation of 20–40 at% hydrogen. These a-C:H films are similar to a-Si:H films and the present work contributes additional evidence for this similarity. a-C:H films were deposited on glass or NaCl-coated glass in a capacitively coupled rf discharge in CH 4. The nature of the films depends upon the specific power density (SPD): polymeric for SPD < 10W cm −2 torr −1, diamond-like for SPD between 10 and 20, and graphitic for SPD>25. The amount of chemisorbed hydrogen in the films, as determined by differential scanned calorimetry (DSC), also depends on the SPD (and concomitant negative self-bias of the substrate), decreasing by a factor of six as the SPD increases from 10 to 20 and the negative self-bias increases form 400–650V. Additionally, the exothermic DSC peak sometimes consists of two or more partially resolved overlapping peaks.