Recoverable plasticity in penta-twinned metallic nanowires governed by dislocation nucleation and retraction

Abstract

There has been relatively little study on time-dependent mechanical properties of nanowires, in spite of their importance for the design, fabrication and operation of nanoscale devices. Here we report a dislocation-mediated, time-dependent and fully reversible plastic behaviour in penta-twinned silver nanowires. In situ tensile experiments inside scanning and transmission electron microscopes show that penta-twinned silver nanowires undergo stress relaxation on loading and complete plastic strain recovery on unloading, while the same experiments on single-crystalline silver nanowires do not exhibit such a behaviour. Molecular dynamics simulations reveal that the observed behaviour in penta-twinned nanowires originates from the surface nucleation, propagation and retraction of partial dislocations. More specifically, vacancies reduce dislocation nucleation barrier, facilitating stress relaxation, while the twin boundaries and their intrinsic stress field promote retraction of partial dislocations, resulting in full strain recovery.

2D Single‐Crystalline Copper Nanoplates as a Conductive Filler for Electronic Ink Applications

“…In addition, there were no oxide‐related peaks for Cu 2 O or CuO, indicating that our Cu NPLs are mostly composed of metallic Cu. From detailed high‐resolution transmission electron microscopy (HR‐TEM) studies on the as‐grown Cu NWs, we found that the Cu NWs show a fivefold twinned structure in which the growth direction is 〈220〉, which is the well‐known crystalline structure of Cu NWs obtained from solution‐phase synthesis (Figure S4, Supporting Information) . To confirm the crystalline structure of the Cu NPLs by transmission electron microscopy (TEM) analysis, the samples were carefully prepared by dropping them on hollow carbon‐coated nickel TEM grids for top‐view imaging and on silicon oxide substrates for cross‐sectional TEM analysis after focused ion beam modification.…”

Failure criterion of silver nanowire electrodes on a polymer substrate for highly flexible devices

“…Regardless of the size, those mechanical properties are almost constant in about fracture strain and yield stress of 2% and 1.2 GPa, respectively (see the Supplementary Table S2 for more details). The constant mechanical properties are mainly attributed to the 5-fold twin boundaries along the <110> growth direction26273334, because they act as energy barriers of moving dislocations, leading to the brittle failure of Ag NWs. Unlike five-fold twinned Ag NWs, the single-crystalline FCC NWs303132 showed that as the NW size decreases, it is hard to nucleate partial dislocations on the surface and easy to propagate twin via the growth direction of the NW.…”

The Mechanical Properties of Nanowires

“…This suggests that the different deformation behaviors observed in the experimental characterization of SiC NWs might be attributed to their microstructural difference 204. Recent comparative in situ EM tensile tests demonstrated that five‐twinned silver NWs underwent stress relaxation during loading and then completed plastic strain recovery during unloading, while the other similar experiment on single‐crystalline silver NWs could not show such a behavior 117. It is presumed that vacancies can reduce dislocation nucleation barrier, facilitating stress relaxation, while twin boundaries and their intrinsic stress field may promote retraction of partial dislocations.…”

“…In fact, in situ TEM techniques have now become the most widely used method for characterizing a range of NWs, such as Si,101, 102 GaAs103, 104, 105, 106 ZnO,107, 108 VO 2 109. GaN,99, 110, 111 ZnTe,112 Ag,113, 114, 115, 116, 117 Ni118, 119 Cu,120, 121, 122 and metallic glasses 123, 124 9 shows an SEM image of the first MEMS device successfully integrated into a TEM for in situ nanoscale mechanical testing by Saif et al13 The freestanding specimen being tested was fabricated together with the MEMS structure, and is suspended at the center of the MEMS device.…”

“…Size‐dependent plastic deformations were frequently observed in various metallic NWs, such as Au,226, 256 Cu,257 Ag117 and Ni 119. Seo et al found that defect‐free Au NWs of ≈100 nm in diameter exhibited super‐plasticity induced by the formation and propagation of partial dislocations 90.…”