Hydrogen free tetrahedral carbon film preparation and tribological characterisation

Abstract

Amorphous carbon containing very little hydrogen and having a highly tetrahedral structure was deposited by the filtered cathodic vacuum arc technique. The tribological properties of the films produced were determined by an ultralow load depth sensing nanoindenter to examine their dependence on the carbon ion energy. An optimum ion energy of around 80 to 90 eV has been found, which coincides with the energy at which the Sp3 content and film density reach maximum values. At this ion energy, the hardness, modulus, and critical load of a 60 nm film on sapphire exhibit maximum values of 60 GPa, 580 GPa, and 7 mN, respectively. The frictional coefficient shows a minimum of 0·16. The use of a continuous stiffness technique with sapphire substrates registered improvements of 43 and 68% in hardness and modulus over the same film on silicon using a normal loading and unloading indentation technique. The modulus to hardness ratio of close to 10 for these samples confirms that there is a great improvement in modulus.