Simulated surface diffusion in nanoporous gold and its dependence on surface curvature

TL;DR

This study uses molecular dynamics simulations to investigate how surface curvature influences surface diffusion in nanoporous gold, revealing that mass transport rates are nearly curvature-independent but with subtle curvature effects on activation energies.

Contribution

It isolates the dependence of surface diffusivity on curvature by simulating surfaces of constant mean curvature, providing new insights into surface diffusion mechanisms.

Findings

Surface diffusivity has an activation energy of ~0.74 eV with weak curvature dependence.

The apparent concentration of mobile surface atoms varies with temperature and curvature.

Mass transport rate by surface diffusion is nearly independent of curvature, with an activation energy of ~1.01 eV.

Abstract

The morphological evolution of nanoporous gold is generally believed to be governed by surface diffusion. This work specifically explores the dependence of mass transport by surface diffusion on the curvature of a gold surface. The surface diffusivity is estimated by molecular dynamics simulations for a variety of surfaces of constant mean curvature, eliminating any chemical potential gradients and allowing the possible dependence of the surface diffusivity on mean curvature to be isolated. The apparent surface diffusivity is found to have an activation energy of ~0.74 eV with a weak dependence on curvature, but is consistent with the values reported in the literature. The apparent concentration of mobile surface atoms is found to be highly variable, having an Arrhenius dependence on temperature with an activation energy that also has a weak curvature dependence. These activation energies depend on curvature in such a way that the rate of mass transport by surface diffusion is nearly independent of curvature, but with a higher activation energy of ~1.01 eV. The curvature dependencies of the apparent surface diffusivity and concentration of mobile surface atoms is believed to be related to the expected lifetime of a mobile surface atom, and has the practical consequence that a simulation study that does not account for this finite lifetime could underestimate the activation energy for mass transport via surface diffusion by ~0.27 eV.