Atomistic modeling and thermodynamic interpretation of the bridging phenomenon observed in the Co-Au system

Abstract

For the Co-Au system, a $n$-body potential is derived by fitting to the properties acquired by ab initio calculations for a few possible metastable Co-Au compounds and proven to be realistic. Based on the derived potential, molecular dynamics simulations are performed, using the $\mathrm{Au}∕\mathrm{Co}∕\mathrm{Au}$ sandwich models, to investigate the bridging phenomenon ever observed in experiments. The simulations reveal that bridging is dependent on the temperature as well as on the thickness of the Co interlayer. A thermodynamic model is proposed and accordingly, it is the energy difference between the interface of $\mathrm{Au}∕\mathrm{Co}$ and the interface of $\mathrm{Au}∕\mathrm{Co}\text{\ensuremath{-}}\mathrm{Au}$ mixture that overcomes an intrinsic repulsion between Co and Au originated from a large positive heat of formation of the Co-Au system and drives the atomic movement as well as accounts for the thickness and temperature dependences in the bridging phenomenon.