MECHANICAL-PROPERTIES AND STRUCTURE OF DIAMOND-LIKE CARBON

A model is developed to relate mechanical properties of hard amorphous carbons to their interatomic bonding. The elasticity of amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C:H) is related to the rigidity of the CC bond and the mean CC coordination. It is shown that sp2 sites contribute no rigidity if they form graphitic clusters, as suggested by experiment and electronic structure calculations, despite them having coordinations above the critical value of 2.4. Hence both graphitic bonding and polymeric =CH2 groups severely lower the hardness of amorphous carbons. The hardness of sputtered a-C, which is mainly sp2 bonded, arises from a significant cross-linking of layers. The model is then extended to describe hardness and wear. © 1992.