Study the growth mechanism of AgNi nanoparticles by surface diffusion

Abstract

Quantifying the kinetic processes of the diffusion and growth of adsorbed atoms on the surface of nanoparticles at the atomic level enables the control of nanomaterial structures. To examine the diffusion and growth of adsorbed atoms on the surface of nanoparticles, this study adopts AgNi nanoparticles as an example, comprehensively explores surface diffusion, and reveals the physical causes of the growth results from the perspective of surface diffusion. Molecular dynamics, Monte Carlo, and nudged elastic band methods are utilized. Many studies have been conducted on the diffusion barriers of adsorbed atoms. On the basis of these studies, the current work classifies the diffusion paths of adsorbed atoms on the surface of nanoparticles in detail and determines the optimal surface diffusion paths. It reveals the formation mechanism of AgNi nanoparticles from the perspective of surface diffusion and the physical causes of the clustering of surface atoms into islands during growth. Among all the surface exchange diffusion paths defined in this study, the center exchange diffusion paths, especially CPDE, are the best when the system energy decreases after the substrate boundary atom is exchanged with an adatom. The relative magnitude of the exchange energy barriers between hetero adsorbed atoms and atoms on the substrate surface is a major determinant of the formation of core–shell and three-layer onion-like structures and the degree of surface alloying of the nanoparticles. In addition, the appearance of surface energy trap sites during the growth of AgShellNiCore nanoparticles leads to the diffusion of surface Ag atoms to these sites and their aggregation into Ag islands.