A New Atomistic Mechanism for Heterogeneous Nucleation in the Systems with Negative Lattice Misfit: Creating a 2D Template for Crystal Growth

Heterogeneous nucleation is a widespread phenomenon in both nature and technology. However, our current understanding is largely confined to the classical nucleation theory (CNT) postulated over a century ago, in which heterogeneous nucleation occurs stochastically to form a spherical cap facilitated by a substrate. In this paper, we show that heterogeneous nucleation in systems with negative lattice misfit completes deterministically within three atomic layers by structural templating to form a two-dimentional template from which the new phase can grow. Using molecular dynamics (MD) simulations of a generic system containing metallic liquid (Al) and a substrate of variable lattice misfit (fcc lattice with fixed Al atoms), we found that heterogeneous nucleation proceeds layer-by-layer: the first layer accommodates misfit through a partial edge dislocation network; the second layer twists an angle through a partial screw dislocation network to reduce lattice distortion; and the third layer creates a crystal plane of the solid (the 2D nucleus) that templates further growth. The twist angle of the solid relative to the substrate as a signature of heterogeneous nucleation in the systems with negative lattice misfit has been validated by high resolution transmission electron microscopic (HRTEM) examination of TiB2/Al and TiB2/alpha-Al-15(Fe, Mn)(3)Si-2 interfaces in two different Al-alloys.

Automated summary

This study reveals the deterministic heterogeneous nucleation process in systems with negative lattice misfit, where a two-dimensional template is formed within three atomic layers for new phase growth. Molecular dynamics simulations show that heterogeneous nucleation proceeds layer-by-layer, accommodating misfit through dislocation networks and creating a crystal plane as a template for further growth. High resolution transmission electron microscopy examination has validated the twist angle of the solid as a signature of heterogeneous nucleation in systems with negative lattice misfit.