The effect of nitrogen on the mechanical properties of tetrahedral amorphous carbon films deposited with a filtered cathodic vacuum arc

The mechanical properties of both undoped and nitrogen containing tetrahedral amorphous carbon (ta-C and ta-C:N) films, such as hardness and E-modulus, are investigated. The mechanical properties are related to the film structures. The ta-C and ta-C:N films are prepared in a filtered cathodic vacuum are process. Nanoindentation testing is used to measure the mechanical properties of these films. Since the thickness of films prepared for this study is < 100 nm, a continuous stiffness technique is therefore used to determine the mechanical properties of these films. For the lightly doped ta-C:N films, the mechanical properties are competitive with those of undoped ta-C. However, with a further increase in the nitrogen content in the films, the mechanical properties of the ta-C:N films drop. The extent of decrease of the mechanical properties of ta-C:N films shows the dependence on the N(2) partial pressure or N ion energy. The reason for this may be due to the nitrogen doping efficiency. The excess nitrogen atoms contained in the films may promote the transformation from the sp(3) bonding structure to sp(2) structure and further enlarge the size of sp(2) clusters, which causes the evident reduction of mechanical properties of the films. (C) 1999 Elsevier Science S.A. All rights reserved.