Kinetics of nucleation on non-homogeneous surfaces

Abstract

The analysis of nucleation kinetics has been carried out taking into account the inhomogeneous structure of real substrates. Kinetic equations for homogeneous nucleation are modified to take into account surface defects which serve as sinks or traps for adatom. Approximate analytical solutions of these equations describe the time dependence of nucleus density on an inhomogeneous surface under different condensation conditions. Special terms are introduced into equations that take into account the effect of growth coalescence and possible mobility of nuclei. The conditions under which a homogeneous or a heterogeneous nucleation mechanism prevails are established by comparing the relative contribution of these two mechanisms (“normal” nucleatin and nucleation on defects, respectively) to the total nucleus density. Circumstances exist under which similar kinetic curves describe nucleation occuring by different mechanisms, due to the influence of some other effects; for example, the mobility of nuclei. Such “degenerate” curves may, for example, be curves arising from early and prolonged saturation and differing only in quantitative parameters. At the present time no independent data on the numerical values of the parameters involved in the theory are available, therefore often the same experimental data on the kinetics of thin film nucleation may be equally well interpreted in terms of homogeneous or heterogeneous nucleation.