The effect of substrate inhomogeneity on the kinetics of heterogeneous nucleation from vapours

Abstract

An equation expressing the time dependence of the number of nuclei is derived on the basis of the following supposition. The substrate is considered as a system of active centres stimulating the nucleation process and prossessing varied potency with respect to nucleus formation. A nucleation exclusion zone with reduced adatom concentration is formed around every growing nucleus, within which the probability of new nucleus formation is practically zero. As they spread with time the nucleation exclusion zones may overlap adjacent active centres on which nuclei have not yet formed. In this way a part of the active centres can be deactivated and will not participate in the nucleation process. As a consequence, the saturation nucleus density is determined by the combined influence of both the finite number of centres active at the given super-saturation and the nucleation exclusion zones. It is shown that the nucleation rate, the spreading rate of the nucleation exclusion zones, as well as the centre activity distribution, introduced as parameters in the theory, can be evaluated if experimental data for the variation of nucleus density with time are available. The effect of coalescence on the saturation nucleus density derived according to the present model is discussed.