In Situ Observation on Dislocation-controlled Sublimation of Mg Nanoparticles

Yu Q, Mao MM, Li QJ, Fu XQ, Tian H, Li JX, Mao SX,3, Zhang Z, 2016

Image courtesy of Nano Lett.

Abstract

Sublimation is an important endothermic phase transition in which the atoms break away from their neighbors in the crystal lattice and are removed into the gas phase. Such debonding process may be significantly influenced by dislocations, the crystal defect that changes the bonding environment of local atoms. By performing systematic defects characterization and in situ transmission electron microscopy (TEM) tests on a core–shell MgO–Mg system, which enables us to “modulate” the internal dislocation density, we investigated the role of dislocations on materials’ sublimation with particular focus on the sublimation kinetics and mechanism. It was observed that the sublimation rate increases significantly with dislocation density. As the density of screw dislocations is high, the intersection of screw dislocation spirals creates a large number of monatomic ledges, resulting in a “liquid-like” motion of solid–gas interface, which significantly deviates from the theoretically predicted sublimation plane. Our calculation based on density functional theory demonstrated that the remarkable change of sublimation rate with dislocation density is due to the dramatic reduction in binding energy of the monatomic ledges. This study provides direct observation to improve our understanding on this fundamental phase transition as well as to shed light on tuning materials’ sublimation by “engineering” dislocation density in applications.

Impact Statement

Sublimation mechanism of MgO-Mg core-shell nanoparticles was investigated by systematic defect characterization with a focus on role of dislocations. A liquid-like motion of solid-gas interface was observed which was correlated to the remarkable change in sublimation rate.