Direct Measurement of the Surface Energy of Bimetallic Nanoparticles: Evidence of Vegard’s Rulelike Dependence

Adrian Chmielewski(1), Jaysen Nelayah(1), Hakim Amara(2), Jérôme Creuze(3), Damien Alloyeau(1), Guillaume Wang(1), and Christian Ricolleau(1), 2018

Image courtesy of Physical Review Letters

Abstract

We use in situ transmission electron microscopy to monitor in real time the evaporation of gold, copper, and bimetallic copper-gold nanoparticles at high temperature. Besides, we extend the Kelvin equation to two-component systems to predict the evaporation rates of spherical liquid mono- and bimetallic nanoparticles. By linking this macroscopic model to experimental TEM data, we determine the surface energies of pure gold, pure copper, Cu50Au50, and Cu25Au75 nanoparticles in the liquid state. Our model suggests that the surface energy varies linearly with the composition in the liquid Cu-Au nanoalloy; i.e., it follows a Vegard’s rulelike dependence. To get atomic-scale insights into the thermodynamic properties of Cu-Au alloys on the whole composition range, we perform Monte Carlo simulations employing N-body interatomic potentials. These simulations at a microscopic level confirm the Vegard’s rulelike behavior of the surface energy obtained from experiments combined with macroscopic modeling. 

Impact Statement

As the surface of NPs are where reactions occur (such as in catalysis) , the ability to determine surface activity is crucial. Using in situ observations and calculations the authors were able to calculate the surface energy of different ratios of Cu:Au alloyed NPs and develop a model to predict surface energy. Their results are confirmed with monte carlo simulations.