Theory of vacancies near a bimetallic interface

The theory of vacancies near a bimetallic interface is developed within a tight-binding model. It is shown that the local density of states is significantly influenced only in the immediate vicinity of the vacancy, and that the vacancy-formation energy is an oscillatory function of the distance of the vacancy from the interface. For the specific interface considered the vacancies tend to be attracted towards the interface. In the extreme case a vacancy can gain more than 10 percent of its formation energy by migrating from the bulk to the interface region. When two vacancies are present in the system they interact due to the polarization of the medium. This interaction is shown to have an oscillatory dependence on the intervacancy separation. The nearest-neighbor interaction of the interface considered is found to be attractive with an energy which is about $\frac{1}{3}$ of the vacancy-formation energy.