Thermal stretching of defective nanowires: the coupled effects of vacancy cluster defects, operating temperature, and wire cross-sectional area

Abstract

Extensive atomistic simulations of the thermal stretching of defective nanowires (NWs) were performed using the embedded-atom molecular dynamics modeling approach. The nucleation and propagation of dislocations are described via quantitative dislocation-based analyses. The investigation focuses on the coupled effects of various vacancy cluster (VC) defects, operating temperature, and wire cross-sectional area on the mechanical properties and plastic deformations of defective NWs. With increasing internal stress of a stretched wire, a rapidly moving dislocation loop that transferred atoms to fill up the original vacancy cluster before the wire yielded was found (i.e. it carried the vacancies away from the inside of the wire and formed a notch at the wire edge). The heterogeneous nucleation of dislocations from the notch site propagated along the {111}〈112〉 partial dislocations and formed stacking faults or perfect dislocations on the {111} activated planes. Simulation results show a decreasing yield strength with increasing VC size for a given wire sectional area and temperature. Quasi-linear decreasing Young’s moduli were observed with increasing operation temperature. For a given operation temperature, NW Young’s modulus increased with increasing NW size. Two typical deformation regimes under various operation temperatures were found: (i) a high-temperature-induced pre-melting phenomenon and a thermal softening effect caused low-stress plastic flow and rapid pillar-necking deformation, and (ii) step-wise glides, slip bands, and cross-slips proceeded along the activated glide planes in the low-temperature hard-brittle structure. These two regimes were thoroughly characterized via the evolutions of microscopic dislocations and the changes of true stress. For operation at high temperatures, the ultra-thin 1/5-type pentagonal ring chains exhibit a relatively robust structure, which can potentially be used as building blocks and components for high-temperature nanoelectromechanical systems (NEMS) devices in the future.