Distinct melting behaviour of partially oxidized Cu nanoparticles and nanowires

TL;DR

This study uses molecular dynamics simulations to reveal that partially oxidized copper nanostructures exhibit unique melting behaviors, including inward oxygen diffusion and core phase transitions, differing from traditional surface melting models.

Contribution

It provides the first detailed theoretical analysis of melting in partially oxidized copper nanosolids, highlighting behaviors not explained by existing models.

Findings

Inward diffusion of oxygen into the metallic core at room temperature.

Observation of a solid-state phase transition in the Cu core with oxide shell.

Oxide shell shrinks before and after melting, forming particulate oxide.

Abstract

While most of the experimental studies are dealing with partially oxidized metallic nanosolids, their behaviour is not well understood theoretically. To this end we utilized molecular dynamics simulation and charge-optimized many-body potential to probe melting of Cu nanoparticles and nanowires with and without a monolayer of Cu$_2$O as a shell. It is shown that partially oxidized nanosolids present a different melting behaviour than the widely accepted picture of melting, and especially different than surface melting. (i) For both types of nanosolids we observed inward diffusion of $\sim$40\% of atomic oxygen into the metallic core at room temperature. (ii) For the nanowire with oxide shell we observed a solid state phase transition in the Cu core that is not present for the case without the oxide. (iii) Prior to melting, the oxide shell shrinks, and this process continues after melting, to form a particulate oxide, for both types of nanosolids.