This image shows a bimetallic Au-core Ag-shell nanoparticle that has an interface that is "dirty". 5% of the interfacial atoms are missing from the lattice and these built-in vacancies greatly increase (by 8 orders of magnitude) the alloying rates for the two metals. The vacancy sites are shown as pink "ghost" atoms, and the diffusion of the vacancies through the metallic lattice does a great job of mixing the two metals.

Research: Chuck Vardeman, Image rendered by Matthew A. Meineke.