Influence of hydrogen on the structure of amorphous carbon

We have studied the influence of hydrogen on the structure of a-C:H films (produced by sputtering) by measuring the stress, hardness, and Raman spectrum as a function of the hydrogen concentration ${\mathit{C}}_{\mathrm{H}}$. Addition of hydrogen, on the one hand, reduces the stress and hardness, and on the other hand, reduces the intensity ratio (${\mathit{I}}_{\mathit{D}}$/${\mathit{I}}_{\mathit{G}}$) of the Raman D to G line. Discontinuous change of both stress and ${\mathit{I}}_{\mathit{D}}$/${\mathit{I}}_{\mathit{G}}$, and a minimum of the G-line full width at half maximum have been observed at ${\mathit{C}}_{\mathrm{H}}$≊32.5 at. %. Scanning-electron-microscopy analysis has been used to verify the stress transition. The role of hydrogen is discussed.