Microstructure aspects of transition metal carbide thin films

Sammanfattning: Transition metal carbides are important refractory materials used in many thin film applications. In this thesis, several transition metal carbides have been deposited using different chemical vapour deposition (CVD) and evaporation processes. In particular, the phase composition and microstructure of these carbide films have been studied. Several molybdenum carbides have been synthesised by thermal CVD using gas mixtures of MoCl5/H2/C2H4 and MoCl5/H2/CH2I2. Theoretical calculations have been carried out to compare the stabilities of these carbides. The calculations, as well as the experimental studies, suggest that the γ'-MoC1-x phase is a true binary carbide which can be synthesised without stabilisation of oxygen. Nanocrystalline δ- MoC1-x was deposited using both C2H4 and CH2I2 as carbon precursors. A study of general growth trends suggests that the nanocrystalline growth can be explained by a low surface mobility, caused by strongly adsorbed carbon-containing species.Films of hexagonal WC have been deposited from a gas mixture of WF6/H2/C3H8 using very low pressures and high gas flows. The influence of substrate material on the film microstructures was studied using two model substrates, Ta and Ni. It was found that factors such as etching and carburisation of the substrate played an important role in the microstructure development. The final microstructure could also be influenced by formation and decomposition of more complex carbide phases.Epitaxial films of TiC have been deposited by co-evaporation of C60 and Ti at temperatures as low as 250 °C on MgO(100) and 6H-SiC(0001). The technique has also been used to synthesise superlattices of transition metal carbides Tic/VC. The epitaxial growth temperature is much lower than expected, and can be explained by a high surface mobility of C60 and/or fragments of this molecule.