Combined atomistic simulations to explore metastability and substrate effects in Ag-Co nanoalloy systems

The Ag/Co nanoalloy system is a model system situated energetically at the limit of stability of the core-shell chemical ordering with respect to a simple phase separation behavior. This makes the system highly susceptible to effects of the environment, such as interaction with a substrate. However, kinetic effects may also be exploited by careful atom-by-atom particle growth that allows to lock in certain out-of-equilibrium configurations, such as off-center, quasi-Janus and even Janus type particles. In this contribution, we explore to what extent out-of-equilibrium structures are due to kinetic effects and the influence of the interaction of the particles with an amorphous carbon substrate by a joint experimental and molecular dynamics study. The simulation set up performed at 300 K and 600 K mimicks the experimental growth process. The substrate deforms the particles, but has also an ordering effect on particle orientation and particle structure. In the case of growth of Ag on Co seeds, particles assume close to equilibrium quasi-Janus structures, while for the deposition of Co on Ag seeds, highly out-of-equilibrium structures with several subsurface Co clusters are obtained.

Automated summary

The Ag/Co nanoalloy system is energetically located at the limit of stability of the core-shell chemical ordering and phase separation behavior, making it highly susceptible to environmental effects. By carefully controlling atom-by-atom particle growth, out-of-equilibrium configurations can be locked in. Through experimental and molecular dynamics studies, we investigate the extent to which out-of-equilibrium structures are due to kinetic effects and the influence of particle-substrate interaction. Both experimental and simulation results demonstrate the significant impact of the substrate on particle morphology and structure.