| Summary: | Our current understanding of heterogeneous nucleation has been largely confined to the classical nucleation theory (CNT) that was postulated over 100 years ago based on a thermodynamic approach. Further advances in heterogeneous nucleation research requires detailed knowledge of atomistic activities at the liquid/substrate interface. In this work, using a classical molecular dynamics (MD) simulation, we investigated the atomistic mechanisms of heterogeneous nucleation in systems with a large lattice misfit (|<i>f</i>| > 12.5%) demonstrated by the liquid Pb and solid Cu system (denoted as the Pb(<i>l</i>)/Cu(<i>s</i>) system) with a misfit of 27.3%. We found that heterogeneous nucleation in systems with a large misfit takes place in two distinctive steps: (1) Prenucleation creates a coincidence site lattice (CSL) on the substrate surface to accommodate the majority (<i>f</i><sub>csl</sub>) of the initial misfit (<i>f</i>) and (2) Heterogeneous nucleation accommodates the residual misfit <i>f</i><sub>r</sub> (<i>f</i><sub>r</sub> = misfit − <i>f</i><sub>csl</sub>) at the nucleation temperature to create a plane of the new solid phase (a two-dimensional (2D) nucleus) through either a three-layer dislocation mechanism if <i>f</i><sub>r</sub> < 0 or a three-layer vacancy mechanism if <i>f</i><sub>r</sub> > 0, such as in the case of the Pb(<i>l</i>)/Cu(<i>s</i>) system.
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