Real-Time KMC Simulation of Vacancy-Mediated Intermixing in Au@Ag Octahedral Core–Cubic Shell Nanocrystals with Ab Initio-Guided Kinetics

• Published in: ACS nano Vol. 18; no. 36; pp. 25036 - 25045
• Main Authors: Han, Yong, Evans, James W.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 10.09.2024; American Chemical Society (ACS)
• Subjects: Au@Ag core−shell nanocrystal; defects in solids; diffusion; energy; gold; interfaces; intermixing; KMC simulation; realistic vacancy-mediated diffusion kinetics; stochastic modeling; stochastic modeling; intermixing; KMC simulation; Au@Ag core−shell nanocrystal; realistic vacancy-mediated diffusion kinetics
• ISSN: 1936-0851; 1936-086X; 1936-086X
• DOI: 10.1021/acsnano.4c06435

Utilization of core–shell rather than monometallic nanocrystals (NCs) facilitates fine-tuning of NC properties for applications. However, compositional evolution via intermixing can degrade these properties prompting recent experimental studies. We develop an atomistic-level stochastic model for vacancy-mediated intermixing exploiting a formalism which allows incorporation at an ab initio density functional theory level of not just the thermodynamics of vacancy formation, but also relevant diffusion barriers for a vast number of possible local environments (in the core and in the shell, at the interface, and in the intermixed phase). This facilitates a predictive treatment and comprehensive understanding of intermixing on the relevant time scale (e.g., 101–103 s). In contrast, previous modeling at the atomistic level utilized only unrealistic generic prescriptions of barriers or employed simplified continuum treatments. For Au@Ag octahedral core–cubic shell NCs, our modeling not only captures the experimentally observed rate or time scale for intermixing of ∼100 s at 450 °C for 60 nm NCs, but also elucidates the underlying rate controlling processes and the effective intermixing barrier.