  The epitaxial growth process of a high symmetry surface occurs because
adatoms meet and nucleate new islands, that eventually coalesce and complete
atomic layers. During multilayer growth, nucleation usually takes place on top
of terraces where the geometry of the diffusion process is well defined: We
have studied in detail the spatiotemporal distribution of nucleation events and
the resulting nucleation rate, a quantity of primary importance to model
experimental results and evaluate diffusion barriers at step-edges. We provide
rigorous results for irreversible nucleation and we assess the limits of
mean-field theory (MFT): we show that MFT overestimates the correct result by a
factor proportional to the number of times an adatom diffusing on the terrace
visits an already visited lattice site. In this report we aim at giving a
simple physical account of our results.
