<p>This thesis reports on the development of low-temperature processes for transition metal carbide and MAX-phase thin film growth. Magnetron sputtering and evaporation, far from thermodynamical equilibrium, have been utilised to engineer the properties of the films by physical and chemical control. Deposition of W, W<sub>2</sub>C and β-WC<sub>1-x</sub> films with controlled microstructure, from nanocrystalline to epitaxial, is shown in the W-C system down to 100 <sup>o</sup>C. W films with upto 20 at% C exhibited an extreme solid-solution hardening effect, with a nanoindentation hardness maximum of 35 GPa. Furthermore, the design of epitaxial ternary carbide films is demonstrated in the Ti<sub>1-x</sub>V<sub>x</sub>C<sub>y</sub> system in the form of controlled unit-cell parameters, strain-free films with a perfect match to the substrate, and ternary epitaxial gradient films. Moreover, phase stabilisation and pseudomorphic growth can be tuned in (Nb,Mo)C and (Ti,W)C films. The results obtained can be used for example to optimise electrical contacts in SiC high-power semiconductor devices. </p><p>A large part of this thesis focuses on the deposition of MAX-phases. These compounds constitute a family of thermally stable nanolaminates with composition M<sub>n+1</sub>AX<sub>n</sub>, n=1, 2 or 3, where M is an early transition metal, A is generally a group 13-14 element, and X is C or N. They show a combination of typical ceramic and metallic properties and are also machinable by virtue of the unique deformation behaviour observed only in laminates. So far, the MAX-phases have almost exclusively been prepared by high-temperature sintering and studied in bulk form. However, this thesis establishes a patented seed layer approach for successful MAX-phase thin film depositions down to 750 <sup>o</sup>C. For the first time, single-phase and epitaxial films of Ti<sub>3</sub>SiC<sub>2</sub>, Ti<sub>3</sub>AlC<sub>2</sub> and Ti<sub>2</sub>AlC have been grown. The method has also been used to synthesise a new MAX-phase, Ti<sub>4</sub>SiC<sub>3</sub>. In addition, two previously unreported intergrown MAX-type structures are presented, Ti<sub>5</sub>Si<sub>2</sub>C<sub>3</sub> and Ti<sub>7</sub>Si<sub>2</sub>C<sub>5</sub>. Combined theoretical and experimental results show the possibility to deposit films with very low bulk resistivity and designed mechanical properties. Furthermore, the demonstration of MAX-phase and carbide multilayer films paves the way for macrostructure engineering, for example, in coatings for low-friction or wear applications.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-3972 |
| Date | January 2004 |
| Creators | Palmquist, Jens-Petter |
| Publisher | Uppsala University, Department of Materials Chemistry, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1104-232X ; 930 |
Page generated in 0.0023 seconds