Melting of Ni nanowires with and without oxide capping

The effects of wire diameter and grain size on the melting point of Ni nanowires with and without oxide capping were systematically examined. It was found that, for uncapped Ni nanowires, the melting point drops monotonically with grain size and also with the nanowire diameter; for oxide-capped Ni nanowires, the melting point rises when the nanowire diameter is decreased. Findings indicate that: (i) the reduced cohesive energy of under-coordinated atoms at the surface skin or grain boundaries and the fraction of such under-coordinated atoms dominate the undercooling of pure Ni nanowires; (ii) bond nature alteration by oxidation strengthens the surface bonds and hence results in the observed overheating; (iii) the bonds in the core interior retain their bulk nature, making contribution to neither the observed undercooling nor overheating. All these findings are very consistent with the bond-order-length-strength theoretical predictions.