Semiconductor–metal transition induced by nanoscale stabilization

Abstract

The structure of tin (Sn) nanoparticles as function of size and temperature has been studied using density functional theory and thermodynamic considerations. It is known that bulk Sn undergoes a transition from the semiconducting α-phase to the metallic β-phase at temperatures higher than 13.2 °C under atmospheric pressure. Here we show that, independent of temperature, Sn nanoparticles smaller than 8 nm diameter always crystallize in the β-phase structure in thermodynamic equilibrium, and up to a size of 40 nm of the Sn nanoparticles this metallic phase is stable at all reasonable ambient temperatures (≳−40 °C). The transition to the metallic phase is caused by nanoscale stabilization due to the lower surface energies of the β phase. This study suggests that the atomic structure and conductivity of nanostructured Sn anodes can change dramatically with size and temperature. This finding has implication for understanding the performance of future Li-based batteries since Sn nanostructures are considered as one of the most promising anode materials, but the mechanism of nanoscale stabilization might be used as a design strategy for other materials.