The preparation and evaluation of graded multilayer ta-C films deposited by FCVA method

In this study, a series of graded multilayer ta-C films were investigated by varying their sublayer thickness ratios, in which each film sublayer was prepared at different substrate bias by filtered cathode vacuum arc (FCVA) method. The experimental results show that the graded multilayer film structure can effectively decrease the internal stress level of deposited ta-C film, and meanwhile the graded multilayer ta-C films still have high sp3 fractions. The applied substrate bias voltage and sublayer thickness ratio can apparently influence the microstructure characteristics and internal stress of the graded multilayer ta-C films. The graded multilayer ta-C film has larger sp3 fraction when applying a larger negative substrate bias voltage and having a thicker outer sublayer during the film deposition process. However, the internal stress in the as-deposited film also increases with larger thickness of the outer sublayer, and the optimal ratio of sublayer thicknesses is 1:1:1:1 for graded ta-C film with four sublayers.

Research highlights▶ The graded multilayer tetrahedral amorphous carbon film has low internal stress. ▶ The film has more sp3 bonds when applying a larger negative substrate bias voltage. ▶ The sp3 fraction of ta-C film is increasing with larger thickness of outer sublayer. ▶ However, its internal stress also increases with thicker outer sublayer. ▶ The optimal sublayer thickness ratio is 1:1:1:1 for four-sublayer graded ta-C film.