MECHANICAL AND TRIBOLOGICAL PROPERTIES OF DUAL-FREQUENCY PLASMA-DEPOSITED DIAMOND-LIKE CARBON

Hydrogenated amorphous carbon (a-C:H) films with ''diamond-like'' properties have been deposited in dual-mode microwave-radio frequency discharges in CH4, CH4 + Ar or CH4 + H2 Mixtures. Properties, such as the microhardness, density, friction coefficient, stress and adhesion, have been studied and correlated with the films' microstructure. It is shown that the mechanical and tribological properties strongly depend on the amount of unbonded hydrogen in the films. They have been shown to belong to one of the following three microstructural categories. (a) Films deposited under high ion energy bombardment (more than 200 eV). They possess high fracture strength and are resistant to severe conditions of humidity, load and sliding speed. This film type is a hard, brittle hydrocarbon, with a high compressive stress (about 8-12 GPa) and high content of unbonded hydrogen (about 80% of the total hydrogen content c(H)). (b) Films deposited under high ion flux and intermediate ion energy (about 100 eV). These are characterized by moderate fracture strength and they resist moderately severe sliding at a load of 0.5 GPa and a speed of 50 mm s-1. This film type is a hard hydrocarbon with a low compressive stress (about 1-3 GPa) and high content of bonded hydrogen (about 40%-60% of c(H)). (c) The final category results from a high ion flux and low ion energy (20 eV or less). The films are soft, polymer-like and possess low fracture resistance.