A molecular dynamics study of heterogeneous nucleation in generic liquid/substrate systems with positive lattice misfit

Z Fan,H Men

doi:10.1088/2053-1591/abcc89

Abstract

Nucleation plays a critical role in many natural and technological processes, and nucleation control requires detailed understanding of nucleation process at atomic level. In this study, we investigate the atomistic mechanism of heterogeneous nucleation in generic systems of liquid/substrate with positive lattice misfit (the solid has larger atomic spacing than the substrate) using molecular dynamics (MD) simulations. We found that heterogeneous nucleation process in such systems can be best described by a 3-layer nucleation mechanism: formation of the completely ordered first layer with an epitaxial relationship with the top surface of the substrate; formation of vacancies in the second layer to accommodate lattice misfit; and creation of a nearly perfect crystal plane of the solid in the third layer that demarcates the end of nucleation and the start of crystal growth. This 3-layer nucleation process creates a 2D nucleus (a plane of the solid phase), which contrasts with the hemisphere of the solid (a 3D nucleus) in the classical nucleation theory (CNT). It is expected that this 3-layer nucleation mechanism will provide new insight for nucleation control through effective manipulation of the liquid/substrate interface.

Highlights

Introduction pteNucleation is the initial stage of any first order phase transformation and is a phenomenon widely spread in both natural and industrial processes [1,2]
While homogeneous nucleation is rarely observed in reality due to the presence of impurities in the liquid [1], so far we have little knowledge about the heterogeneous nucleation process at atomic level due to difficulties encountered by both computer simulations or direct experimental observations [9,10,11]
Atomic layering at the interface is quantified by the atomic density profile, ρ(z), where z is the distance along the z ([111]) direction of the simulation system [14]

Summary

Introduction

Introduction pteNucleation is the initial stage of any first order phase transformation and is a phenomenon widely spread in both natural and industrial processes [1,2]. The recent epitaxial nucleation model [12] represents an alternative atomistic mechanism for the heterogeneous nucleation. It proposes that heterogeneous nucleation proceeds layer-by-layer through structural templating at the liquid/substrate interface. This has been supported by the latest results from both computer simulations [13,14,15,16,17,18] and experimental observations [19,20,21,22,23,24,25,26,27]. In a recent MD study [18], we

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Conclusion