Impacts of terminal molecules on metal-atom diffusion into alkane self-assembled-monolayer films: first-principles study

Abstract

The effects of terminal molecules on metal-atom diffusion into alkane self-assembled-monolayer (SAM) films were studied using first-principles calculations. It was shown that the diffusion of Al and Au atoms easily occurs when the alkane molecules have a CH3 termination, while the diffusion is suppressed by COOK terminal molecules for Au atom and by COOH and COOK molecules for Al atom. This is in good agreement with experiments. We showed that such suppression is caused by the orbital-hybridization-induced interaction between a metal atom and terminal molecules: the ionic bonding between negatively charged Au and surrounding positively charged K atoms, and the covalent-like bonding between Al and neighboring O atoms. We also showed that, once the metal atoms form films on the SAM surface, the metal atoms bond to each other and stabilize, thus also suppressing the diffusion into the SAM substrate.