Nano-indentation for structural analysis of hydrogen- and nitrogen-containing carbon films

It is known that films of hard carbon materials, so-called hydrogenated diamond-like carbon (DLC:H) and nitrogen-containing DLC:H (DLC:N:H), are composed of medium-range ordered clusters. In this study, the boundary structure among medium-range ordered clusters is analyzed using a nano-indentation creep technique. DLC:H and DLC:N:H films were annealed at temperatures up to 500C for 10 h. Raman spectroscopy revealed that thermal annealing promoted the increase in the boundary proportion among clusters. The strain-rate sensitivity coefficient, m, of the film also indicated that cluster flow became notable with thermal annealing. The increase in cluster flow is understood in terms of the growth in the number of boundaries. Although these phenomena were observed in both DLC:H and DLC:N:H films, the degree of flow in the DLC:N:H film was greater than that in the DLC:H film after thermal annealing. The flow characteristic was enhanced by nitrogen incorporation into the carbon cluster and/or nitrogen terminating the carbon cluster, suggesting that nitrogen incorporation promoted the formation of a thermally instable and mechanically deteriorated structure.