Defect nucleation and mobility in gold nanowires

Christian Brandl

IAM-WBM, Karlsruher Institute of Technology (KIT)

Wednesday, 25.01.2017, 17:00
WW8, Room 2.018-2, Dr.-Mack-Str. 77, Fürth

With decreasing dimensions of metals, the strength is increasing with decreasing dimensions can approach the theoretical strength limit – even down to a regime, where the strength is theoretically predicted to be flaw insensitive.
Using atomic simulation, we investigate the effect of predefined flaws, i.e. notches, in intrinsic brittle Si nanowires and intrinsic ductile Au nanowires. The defect evolution, flow stresses and the strain hardening in the MD simulations of single crystal Au nanowires is compared to experimental studies, where gold nanowires were structured by He-ion beams with sub-50 nm diameter well-defined holes. The experimental microstructure after deformation – as seen by (high-resolution) transmission electron microscopy – suggests the formation of a nano-grained substructure at the failure location, which is also consistently observed in our MD simulation. The striking similarities between MD simulations and the experimental data are critically discussed and explained by strain hardening in a strength regime of theoretical shear strength in Au. More generally, the quantitative assessment of different models for dislocation nucleation at free surfaces points to contradicting predictions. Together with the observed flaw insensitivity the later analysis is discussed in context of thermally activated dislocation nucleation and grain boundary motion at high stresses to challenge our conventional notion of defect nucleation and mobility.