THE ENERGIES OF POINT-DEFECTS NEAR METAL-OXIDE INTERFACES

We demonstrate a simple but accurate method for the atomistic modeling of metal/oxide interfaces, even when these are complicated by charged defects and space charge in the oxide. Thus we calculate the structure and energies of Ag/MgO interfaces, in the presence of point defects in the oxide, using well-established computer simulation techniques. Our approach, which is complementary to other methods such as local density approximation calculations, requires very modest computer power. The major terms in the interaction between the oxide and the metal can be decomposed into the short-range interaction between the ions and the metal cores, the energy required to embed the ions in the jellium, and the image interactions between the ionic charges and the metal. The short-wavelength fluctuations in the induced charge distribution were eliminated in order to represent the finite Fermi wave vector of a real metal. Our predictions are in good accord with observed wetting angles; agreement with other calculations is as close as should be expected, given the somewhat different working assumptions. The energies of vacancies and interstitials in the oxide, near the interface, have also been calculated. The vacancies in the second ionic plane were found to have the lowest energies, 2 eV lower than the corresponding bulk energies. The energies of defects situated more than seven ionic planes from the interface were found to be close to the values predicted by the continuum electrostatic model. Whilst the concentration of intrinsic defects was estimated to be too small to be significant, defects introduced artificially, for example, by radiation, would increase the binding energy of the interface significantly. We therefore confirm quantitatively the explanation for adhesion in processes such as radiation-enhanced adhesion and anodic bonding, proposed by Stoneham and Tasker [A. M. Stoneham and P. W. Tasker, J. Phys. 18, L543 (1985)].