Comparative study of surface disorder in gold and silver nanoparticles obtained by molecular dynamics in cooling processes

Abstract

This work presents structural analyses of gold and silver nanoparticles with a surface-to-volume aspect ratio of about 50%. The simulations were performed by molecular dynamics using the Sutton–Chen potential. The atoms were randomly placed in a box with periodic boundary conditions to realize a cooling process under the consideration of a canonical ensemble. The results of the potential energy as a function of temperature are presented, showing the transitions to the solidification phase. At low temperatures, the radial distribution for all nanoparticles follows patterns similar to those reported for metals with FCC structure. Coordination number and interatomic distance were established as parameters to analyze surface particularities. In general, a decrease in the inter-atomic distance was observed with respect to the bulk. In gold nanoparticles, the formation of surface planes is favored and the interatomic distances increase with the coordination number under a well-defined tendency. Interior atoms have an interatomic distances closer to the expected value. In silver nanoparticles, atoms with a coordination number equal 9, located in surface, are at distances closer to the expected value than the internal atoms, at the scale considered. However, the trend with the increments of particle size shows go to a similar gold tendency. Silver led to a more disordered surface with respect to Gold. Therefore, the properties that depend on the surface ordering will exhibit more abrupt transitions with particle size in Silver at the treated scale.