| Metal-oxide interfaces play a major role in a variety of applications, such as packaging for electronic devices, oxide-dispersion-strengthening of alloys, and thermal barrier coatings. For many of these applications, it would be a great advantage if it was possible to engineer the mechanical properties of metal-oxide interfaces.; The present thesis describes experiments I have carried out on a model metal-oxide interface to understand diffusion reactions and the effect of an external electric field across the interface. I have focused on investigating the formation of a reaction phase, morphological changes, and redistribution of ions at the interface. These features are believed to impact the mechanical properties of a metal-oxide interface.; A planar Al-MgAl2O4 interface was considered as a suitable model system due to the small lattice mismatch between aluminum and MgAl2O4 and its coherent interface. Thin film of aluminum on a planar MgAl2O4(001) substrate was prepared by molecular beam epitaxy (MBE), electron beam evaporation, and thermal evaporation. After annealing of different polarity at 620--630°C for 5--40 h with and without an applied voltage, the interface was investigated using conventional transmission electron microscopy (CTEM), high-resolution TEM (HRTEM), X-ray energy-dispersive spectroscopy (XEDS), electron spectroscopic imaging (ESI), and electron energy-loss spectroscopy (EELS).; When Al-MgAl2O4 interfaces were annealed without an applied electric field, a {lcub}111{rcub}- and {lcub}100{rcub}-faceted phase formed at the interface toward the aluminum film. The reaction phase is believed to be gamma-Al 2O3, which is formed by oxidation of aluminum at the interface and diffusion of oxygen into the aluminum film. It was also observed that magnesium ions at the interface were replaced by aluminum ions which diffused from the aluminum film.; When Al-MgAl2O4 interfaces were annealed with an applied electric field, the results were different depending on the polarity of the applied voltage. When a positive voltage (Ua > 0V) was applied to the aluminum film, magnesium ions migrate into the MgAl2O4 substrate from the interface, which results in a Mg-deficient layer close to the interface. In the case of (U a < 0V), pyramidal islands of {lcub}111{rcub}-faceted MgAl 2O4 form in the presence of trapped or dissolved oxygen in the aluminum film. (Abstract shortened by UMI.)... |
