Magnetron sputtering of thin nitride films

The objective in this investigation was to design and commission a magnetron sputter deposition system and investigate the properties of hard coatings for mechanical and biomedical applications. The deposition of titanium (Ti) and titanium nitride (TiN) was undertaken as part of the commissioning tests and further work was conducted on the effect of the deposition parameters on the properties of TiN, specifically for biocompatible applications. A thorough understanding of the deposition process, film microstructure and sample preparation was achieved, and several measurement techniques utilised in the characterisation of the films. The nature of TiN as a biocompatible coating, and the effect of the deposition parameters on the hermeticity of the film was investigated by using electrographic printing as a technique for observing the pinhole defects on the film surface. It was found however, that the fluid used in the printing method caused corrosion of the substrate material and hence may have caused increased pinhole size. The second topic of investigation was the novel film caibon nitride (CNX), a new and promising coating in the area of tribological coatings. Investigations were undertaken to deposit the theoretical coating P-C3N4, a material harder than diamond. The understoichiometric CNX form was deposited successfully, and the films characterised optically, structurally, compositionally and topographically. An investigation of the effect of the deposition parameters - magnetron current, substrate bias, system pressure and nitrogen partial pressure on film properties revealed that the films were amorphous in nature with nitrogen incorporation of upto 18.5 % atomic. The films showed evidence of carbon bonding ,as detected by infra-red spectroscopy. It was also found that increased graphitic bonding occurred during nitrogen partial pressure increase but that a reduction in the graphitic nature was seen for films deposited at high magnetron current, low system pressure and high negative substrate bias, all of which affect the ion bombardment of the film. The film surface was smooth and featureless and brown in colour. Tribological evaluation was undertaken of caibon nitride films deposited onto tool steel and surgical steel. It was found that the films possessed low coefficients of friction and good wear resistance, but these properties were dependent on the substrate material due to the thinness of the films. An investigation of adhesion promoted by interiayer growth was also conducted, and it was found for carbon nitride coatings on steel substrates, that Ti and TiN interlayers promoted adhesion, but there was no advantage in a TiC interiayer. Carbon nitride has good tribological properties, and could possibly be used in both mechanical and biomedical applications