Crystallization of Binary Nanocrystal Superlattices and the Relevance of Short-Range Attraction

TL;DR

This study combines experiments and simulations to understand how binary nanocrystal superlattices form, revealing that short-range attraction between particles accelerates nucleation and that their formation follows classical nucleation without intermediate phases.

Contribution

It demonstrates that BNSL formation is driven by short-range attraction and follows classical nucleation, providing a validated framework for predicting superlattice structures.

Findings

No intermediate structures before final phases

Short-range attraction accelerates nucleation

Classical nucleation observed in experiments and simulations

Abstract

The synthesis of binary nanocrystal superlattices (BNSLs) enables the targeted integration of orthogonal physical properties, like photoluminescence and magnetism, into a single superstructure, unlocking a vast design space for multifunctional materials. Yet, the formation mechanism of BNSLs remains poorly understood, restricting the use of simulation to predict the structure and properties of the superlattices. Here, we use a combination of in situ scattering and molecular simulation to elucidate the self-assembly of two common BNSLs through emulsion templating. Our self-assembly experiments reveal that no intermediate structures precede the formation of the final binary phases, indicating that their formation proceeds through classical nucleation. Using simulations, we find that, despite the formation of AlB2 and NaZn13 typically being attributed to entropy, their self-assembly is most consistent with the nanocrystals possessing short-range interparticle attraction, which we find can dramatically accelerate nucleation kinetics in BNSLs. We also find homogenous, classical nucleation in simulation, corroborating our experiments. These results establish a robust correspondence between experiment and theory, paving the way towards a priori prediction of BNSLs.