ION-ASSISTED COATINGS FOR TRIBOLOGICAL AND ELECTRICAL APPLICATIONS

Group IVB nitrides such as TiN are metallic conductors widely used as coatings for tribological applications. Ion-assisted coating provides a low temperature route for their deposition (below 150-degrees-C) with excellent adhesion to the substrate. The grain size is low, being of the order 1-3 nm. Mechanical and electrical properties are, however, strongly dependent on stoichiometry, the presence of oxygen contamination and in turn the ratio between arrival rates of metal atoms and bombarding ions. We have compared two different ion energies (250 and 500 eV) and varied other parameters in the preparation of titanium nitride films on semi-insulating substrates. The film composition and thickness were established by Rutherford backscattering and nuclear reaction analysis against suitable standards and correlated with the room temperature electrical resistivity and temperature coefficient of resistance determined by a four-point probe measurement using semi-insulating substrates. It has been shown that the temperature coefficient of resistance for these coatings provides a convenient and reliable figure of merit that is well correlated with their purity and stoichiometry. It is already known that these factors control the tribological properties and to a large extent their colour.