Competition of Core-Shell and Janus Morphology in Alloy Nanoparticles: Insights From a Phase-Field Model

TL;DR

This paper introduces a phase-field model to study the kinetic mechanisms behind the formation of diverse morphologies in bimetallic nanoparticles, emphasizing spinodal decomposition and the influence of particle size and contact angle.

Contribution

A novel phase-field model for confined systems that elucidates the kinetic pathways and morphological outcomes of spinodal decomposition in alloy nanoparticles.

Findings

Janus structures are favored at smaller particle sizes and higher contact angles.

Metastable, kinetically trapped structures can form due to competition between capillarity and diffusion.

Surface-directed spinodal decomposition leads to core-shell or Janus morphologies.

Abstract

Bimetallic nanoparticles (BNPs) exhibit diverse morphologies such as core-shell, Janus, onion-like, quasi-Janus, and homogeneous structures. Although extensive effort has been directed towards understanding the equilibrium configurations of BNPs, kinetic mechanisms involved in their development have not been explored systematically. Since these systems often contain a miscibility gap, experimental studies have alluded to spinodal decomposition (SD) as a likely mechanism for the formation of such structures. We present a novel phase-field model for confined (embedded)systems to study SD-induced morphological evolution within a BNP. It initiates with the formation of compositionally modulated rings as a result of surface-directed SD and eventually develops into core-shell or Janus structures due to coarsening/breakdown of the rings. The final configuration depends crucially on contact angle and particle size -Janus is favored at smaller sizes and higher contact angles. Our simulations also illustrate the formation of metastable, kinetically trapped structures as a result of competition between capillarity and diffusion.