Department of Chemistry and Biochemistry
University of Notre Dame
Notre Dame, Indiana 46556

Using Molecular Dynamics simulations, we have simulated the rapid cooling experienced by bimetallic nanoparticles following laser excitation at the plasmon resonance and find evidence that glassy beads, specifically Ag-Cu bimetallic particles at the eutectic composition (60% Ag, 40% Cu), can be formed during these experiments. The bimetallic nanoparticles are embedded in an implicit solvent with a viscosity tuned to yield cooling curves that match the experimental cooling behavior as closely as possible. Since the nanoparticles have a large surface-to-volume ratio, experimentally realistic cooling rates are accessible via relatively short simulations. The presence of glassy structural features was verified using bond orientational order parameters which are sensitive to the formation of local icosahedral ordering in condensed phases. As the particles cool from the liquid droplet state into glassy beads, a silver-rich monolayer develops on the outer surface, and local icosahedra can develop around the silver atoms in this monolayer. However, we observe a strong preference for the local icosahedral ordering around the copper atoms in the particles. As the particles cool, these local icosahedral structures grow to include a larger fraction of the atoms in the nanoparticle, eventually leading to a glassy nanosphere.