Thin film growth and characterization of Ti-(Si,Ge)-C compounds

Sammanfattning: This thesis describes growth by de magnetron sputtering of thin film Ti-Si-C and Ti-Ge-C materials, with an emphasis on the deposition conditions for nanocomposite and epitaxial growth at low and high temperature processing, respectively. In the Ti-Si-C materials system, I have synthesized nanocomposite thin films from a Ti3SiC2 compound target in an Ar discharge on Si(100), Al2O3(0001), and Al substrates at low substrate temperature (300 oC and below). The films consisted ofnanocrystalline (nc-) TiC and amorphous (a-) SiC, with possible presence of a small amount of non-carbidic C. Mechanically, the films exhibited a remarkable ductile behavior. Their nanoindentation hardness and E-modulus values were 20 GPa and 290 GPa, respectively. The electrical resistivity was 330 μΩcm for optimal Ar pressure (4 mTorr) and substrate temperature (300 °C). The resulting nc-TiC/a-SiC films performed well as electrical contact material, exhibiting contact resistances against Ag as low as 6μΩ at a contact force of 800 N compared to 3.2 μΩ for Ag against Ag. The chemical stability of the nc-TiC/a-SiC films was excellent, as shown by a Battelle flowing mixed corrosive gas test, with no N, Cl, or S contaminants entering the bulk of the films. Furthermore, the thesis describes epitaxial growth on Al2O3(0001) substrates of single- crystal thin films of the Mn+1AXn phases Ti2GeC and Ti3GeC2, and a new phase Ti4GeC3 as well as two new intergrown MAX structures, Ti5Ge2C3 and Ti7Ge2C5. X-ray diffraction shows that Ti-Ge-C MAX-phases require somewhat higher deposition temperatures (1000 oC) in a narrower window than their Ti-Si-C correspondences do, while there are similarities in phase distribution. Nanoindentation reveals a Young's modulus of 300 GPa, lower than that of Ti3SiC2, 320 GPa. Four point probe measurements yield resistivity values of 50-200 μΩcm. The lowest value is obtained for phase-pure Ti3GeC2(0001) films.