The dependence of specific interface energy on the size of contact area between a nucleus and a substrate: cause and effect

Abstract

The optimum geometry of contact and the energy of binding between a finite rigid nucleus and a substrate have been determined by computer experiments for various values of their crystallographic parameters. The interaction of atoms is described by a model non-spherical four-parametric potential, their number varying from 2 to 20 000. The strong dependence of the specific interface energy σ ns on the nucleus base size (in some cases up to 500 Å), neglected in theories of heterogeneous nucleation, has been studied. This effect results from a weakening interface interaction at the nucleus periphery followed by misfit dislocations. In the other extreme case - a non-rigid crystal monolayer - the nucleus energy has been minimized taking into account the fitting of its structure to the substrate surface. Formulae have been derived to describe the equilibrium shape of a nucleus with σ ns varying in the process of crystal growth. The Wulf law proves to be a particular case for σ ns = constant. An estimation of these effects on the nucleation rate is made.