In Situ TEM Observation of the Coalescence between Immiscible Au and Rh Nanoparticles to Form AuRh Heterostructures

Abstract

The performance of heterostructured nanoparticles across diverse applications is closely related to the structure of their interfaces, yet how lattice mismatch and thermodynamic miscibility dictate the assembly of monometallic nanoparticle to form bimetallic interfaces is not well understood. In this study, we combined in situ transmission electron microscopy and molecular dynamics simulations to investigate the collision dynamics of immiscible Au and Rh nanoparticles. It is found that the interfacial structure between Au and Rh is highly sensitive to the local environment of nanoparticle collision. The collision between individual Au and Rh nanoparticles favors the formation of lattice-coherent and defect-free interfaces through rotational alignment of the nanoparticles. This oriented attachment, observed along (111), (100), or (110) facets, is thermodynamically driven by the minimization of the interfacial energy. In particular, the coherent Au–Rh interfaces show significantly lower energy and strain compared with that of noncoherent Au–Rh interfaces, as confirmed by molecular dynamics simulations. In contrast, multinanoparticle collisions introduce spatial constraints that suppress rotational freedom of the monometallic nanoparticles, creating kinetically trapped noncoherent heterostructures with strains and rich defects at the interfaces. The results unravel the thermodynamic and kinetic factors that dictate the growth pathways of bimetallic heterostructures, providing guidance for the construction of nanoparticles with controlled phase boundaries.