| Hydrogenated amorphous carbon(a-C H) films prepared by plasma-assisted chemical vapor deposition of C₃H_8-Ar are studied by thermal analysis by using gas chromatography (GC) and differential scanning calorimetry(DSC) at constant heating rate and Ar atmosphere. Hydrogen evolution is detected by GC above 380℃ and the evolution rate increases with temperature up to 700 ℃. Corresponding to the hydrogen evolution exothermic reaction appears in the DSC curve followed by a sudden conversion into endothermic reaction at higher temperature. The starting points of endothermic reactions on the DSC curves are raised by the temperature and time of the prior heat treatments. It Is considered that during heating the overall structural changes, including C-H bond breaking, H₂formation, C = C double bond formation and network distortion etc., occur consecutively, irreversibly and endothermically and the initial exothermic reaction is due to the evolution of hydrogen weakly bound during cooling or the structural relaxation. |
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