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Träfflista för sökning "WFRF:(Schneider Jochen M.) srt2:(2002-2004)"

Sökning: WFRF:(Schneider Jochen M.) > (2002-2004)

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1.
  • Palmquist, Jens-Petter, 1974- (författare)
  • Carbide and MAX-Phase Engineering by Thin Film Synthesis
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • 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, W2C and β-WC1-x films with controlled microstructure, from nanocrystalline to epitaxial, is shown in the W-C system down to 100 oC. 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 Ti1-xVxCy 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.A large part of this thesis focuses on the deposition of MAX-phases. These compounds constitute a family of thermally stable nanolaminates with composition Mn+1AXn, 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 oC. For the first time, single-phase and epitaxial films of Ti3SiC2, Ti3AlC2 and Ti2AlC have been grown. The method has also been used to synthesise a new MAX-phase, Ti4SiC3. In addition, two previously unreported intergrown MAX-type structures are presented, Ti5Si2C3 and Ti7Si2C5. 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.
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2.
  • Rosen, Johanna, et al. (författare)
  • Thin Film Growth Related Adsorption Study of Al and O Ions on an -Al2O3 Surface
  • 2004
  • Ingår i: J. Phys. Chem. B. - : American Chemical Society (ACS). ; 108, s. 19320-19324
  • Tidskriftsartikel (refereegranskat)abstract
    • The surface reactivity of -Al2O3 (0001) has been investigated theoretically using density functional theory. The adsorption process of Al+, Al2+, Al3+, and O+ were studied to identify possible preferential adsorption sites during thin film growth. Differences in near surface atomic displacements (e.g., adsorption-induced surface reconstructions), energies, and bonding character have been evaluated. The adsorption energies for the metallic ions showed a strong dependence on both initial charge and adsorption site. The O+ ions showed no site dependence, but adsorption energies similar to those calculated for Al+. The results indicate that the adsorption of O+ and Al3+ may favor the formation of an amorphous structure, which is consistent with experimental observations. The results are of fundamental importance for the understanding of thin film microstructure evolution.
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