| Many recent technological materials advances result from novel structures rather than optimized bulk materials. Accurate characterization of these complex structures is challenging; often, a detailed understanding of even fundamental features remains elusive. Specifically, in the case of heterogeneous interfaces, the primary attractive contribution to interface adhesion continues to be an issue of debate, with van der Waals, electrostatic, and chemical forces each playing a role of greater or lesser importance in the observed interface stabilization. Current theoretical assumptions regarding "nonreactive" interfaces tend to focus on either van der Waals or electrostatic contributions as the strong attractive term.; We present evidence, based on first principles density functional calculations, that chemical interactions can contribute significant attractive forces even in systems typically considered "non-reactive." First, we display how atomic-level properties obtained from density functional calculations can provide insight into macroscopic failure mechanisms of bulk crystalline materials. Next, we describe how the presence of defects such as surfaces and surface reconstructions can alter the electronic states, resulting in unique local features that may be beneficial or highly detrimental depending on the intended practical application. Armed with this background, we discuss our detailed characterization of a clean, ideal Al2O3/Ni interface and display how local chemical effects may influence the macroscopic failure at this interface in extreme environments. We then describe how chemical interactions at heterogeneous interfaces may be exploited to dramatically enhance interface strengths. We explore the effects of introducing open-shell electronic structure at the interface by doping with early transition metals and by employing a more covalently bonded oxide. A particular goal of our work is improving performance of thermal barrier coatings for jet engine turbines; however, the insights obtained in these studies may be extrapolated to diverse applications ranging from heterogeneous catalysts to biomedical applications to electronics. |
