Simulations of Laser-Induced Glass Formation in Ag−Cu Nanoparticles

Abstract

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. Because 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 that 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.

Optical Studies of Dynamics in Noble Metal Nanostructures

“…The lines represent half-times versus radius calculated for different values of the interface conductance parameter. Comparison to the experimental data implies a value of G = 110 ± 20 MW m −2 K −1 . This is consistent with the value of G = 105 ± 15 MW m −2 K −1 measured by Plech and co-workers for gold nanoparticles in water …”

“…This is important, as electron microscopy measurements can damage the particles (if done first), and are difficult to do in combination with liquids (if done second). Transient absorption studies of single metal nanoparticles is also a relatively unexplored area of research at present, , and can potentially provide interesting information about particle cooling and the dephasing of the acoustic vibrational modes. , As the laser sources for these measurements improve, it will become possible to study smaller particles, and possibly get to the size range that is accessible to molecular dynamics simulations. ,− This would yield a molecular-level understanding of the important factors that control energy transfer to the surroundings. Having a quantitative theory for energy transfer would allow single particle transient absorption experiments to be used as a probe of the microenvironment of thin films, for example.…”

Interfacial thermal conductance of thiolate-protected gold nanospheres

“…To remove the dependence on the laboratory coordinate frame, the third order rotationally invariant combination ofQ ℓm ,ŵ ℓ , is utilized here. 40,41 For ℓ = 4, the ideal face-centered cubic (fcc), body-centered cubic (bcc), hexagonally close- The fraction of fcc-ordered gold atoms at a given radius in the nanoparticle,…”

“…To remove the dependence on the laboratory coordinate frame, the third order rotationally invariant combination of Qℓm , ŵℓ , is utilized here. 40,41 For ℓ = 4, the ideal face-centered cubic (fcc), body-centered cubic (bcc), hexagonally closepacked (hcp), and simple cubic (sc) local structures exhibit ŵ4 values of -0.159, 0.134, 0.159, and 0.159, respectively. Because ŵ4 exhibits an extreme value for fcc structures, it is ideal for measuring local fcc ordering.…”

Au-Ag-Cu nano-alloys: tailoring of permittivity

“…The Drude-Lorenz model was fitted to the experimental data using least-squares method 36 . The free and bound electron derived permittivity is defined in the following form 37 :…”