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

It is known that films of hard carbon materials; so-called hydrogenated dia mond-like carbon (DLC:H) and nitrogen-containing DLC:H (DLC:N:H), are compo sed of medium-range ordered dusters. In this study, the boundary structure among medium-range ordered clusters is analyzed using a nano-indentation cr eep technique. DLC:H and DLC:N:H films were annealed at temperatures up to 500 degreesC for 10 h. Raman spectroscopy revealed that thermal annealing p romoted the increase in the boundary proportion among clusters. The strain- rate sensitivity coefficient, m, of the film also indicated that cluster fl ow became notable with thermal annealing. The increase in cluster flow is u nderstood in terms of the growth in the number of boundaries. Although thes e phenomena were observed in both DLC:H and DLC:N:H films, the degree of fl ow in the DLC:N:H film was greater than that in the DLC:H film after therma l annealing. The flow characteristic was enhanced by nitrogen incorporation into the carbon cluster and/or nitrogen terminating the carbon cluster, su ggesting that nitrogen incorporation promoted the formation of a thermally instable and mechanically deteriorated structure.