The thermal stability of amorphous hard carbon films produced by cathodic arc deposition was studied by Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, Raman spectroscopy. and nanoindentation evaluation. Pure carbon films of
The effect of postdeposition annealing to 600 °C in vacuum on the hardness, modulus, film stress, and sp3 content of nonhydrogenated amorphous carbon was studied. The films were deposited using a filtered cathodic arc source and the film properties were varied by controlling the substrate bias. In films with an initial sp3 content of greater than 80% a significant decrease (from 10.5 GPa to less than 2 GPa) in the level of compressive stress was observed without deterioration of the mechanical properties. In films with an initial sp3 content of 50%, the stress and hardness remained constant. Films with lower sp3 content showed a significant increase in the level of stresses and only a marginal decrease in hardness. The evolution of stresses and hardness with annealing is discussed in light of a proposed microstructure of these amorphous films.
The current method of analysis for hardness measurements by indentation is examined. Although the method is based on Sneddon's solution for an elastic stress field within a homogeneous half space indented by an elastically deformable indenter, it implicitly assumes a fixed indenter geometry. Therefore, if indentations are made on materials whose hardness or elastic modulus are close to those of the indenter, this method underestimates the contact area and, thus, overestimates the hardness and modulus values of the indented materials. A new method, based on the Hertz contact theory, is proposed that accounts for the elastic deformation of the indenter and provides a simple way to calculate the tip radius. The restrictions of this method are also indicated and discussed. Finally, the hardness and modulus for two recently developed films are measured by this method, and the results are compared with published finite element method (FEM) results.
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