In situ atomic-scale observation of dislocation-mediated discrete plasticity in nanoscale crystals

Abstract

electron microscope (TEM) nanomechanical testing opens up an avenue to directly observe the atomic-scale dislocation dynamics in nanoscale metals. Here we report an in situ atomic-scale observation of dislocation-mediated discrete plasticity in gold (Au) and tungsten (W) nanowires NW. 3,4 In the tensile test of Au NW loaded along [001] under a strain rate of 10 −3 s −1 and viewed along [ 1 planes were zigzag, while the ( 1 − 10) sur faces were atomically flat. At high strain level, there exist local strain concentration at surface facets of ( 1 1 − − 1) planes, favoring surface dislocation nucleation. Similar to face-centered cubic (FCC) and body-centered cubic (BCC) nanoscale metals, surface dislocation nucleation is also dominant in other nanostructured metals, including Au NWs with nanotwins, bi- and penta-twined silver (Ag) NWs, and bicrystalline Ag NWs. 6 In summary, our work offers atomic-scale insights into surface dislocation nucleation and the related dislocation dynamics in nanoscale metals, providing guidelines to fabricate nanomaterials with high performance to achieve their potential applications in nanoscale devices. To date, the effect of chemical passivation layer on surface dislocation nucleation remains experimentally unclear, which probably attracts a great deal of interest for future research. Nanoscale metals with superior mechanical properties are promising building blocks in the next generation flexible electronics. Due to the pronounced surface effect caused by the ultrahigh surface-to-volume ratio of nanocrystals, the mechanical behaviors of nanoscale metals are quite different from their bulk counterparts. Dislocation nucleation is demonstrated to be related to the microstructural length scale of materials. With decreasing the feature size, dislocation