Effect of nitrogen content at coating film and film thickness on nanohardness and Young's modulus of hydrogenated carbon films

In the present study, hydrogenated amorphous carbon (a-C:H) films with different nitrogen content and thickness were prepared by differing both the ratio of volume of nitrogen in the gas mixture of (N₂+C₂H₂) and the deposition time. The results of specimen hardness and Young's modulus were obtained from the nanoindentation tests done at different indentation depths. The effects of the nitrogen content on the coating film and the effect of the film thickness on both the specimen's hardness and Young's modulus were evaluated as a function of the indentation depth. The increase in the film thickness is proportional to increase of the specimen hardness; however, we found that an increase in the nitrogen content of the coating film reduces the hardness. The specimen hardness and Young's modulus of a specimen is thus factored by a combination of the film thickness, the nitrogen content and the indentation depth. The bulge, which is apt to appear in graphs of the specimen hardness curves for the specimens, which has a high volume ratio of nitrogen is discussed from the viewpoint of the plastic deformation energy change due to the occurrence film delamination from the substrate.