  Controlled plastic forming of nanoscale metallic objects by applying
mechanical load is a challenge, since defect-free nanocrystals usually yield at
near theoretical shear strength, followed by an uncontrolled catastrophic
failure. Herein, instead of mechanical load, we utilize chemical stress from
imbalanced interdiffusion to manipulate the shape of nanowhiskers. Bimetallic
Au-Fe nanowhiskers with an ultra-high bending strength were synthesized
employing the molecular beam epitaxy technique. The one-sided Fe coating on the
defect-free, single-crystalline Au nanowhisker exhibited both single- and
poly-crystalline regions. Annealing the bimetallic nanowhiskers at elevated
temperatures led to gradual change of curvature and irreversible bending, which
is attributed to the grain boundary Kirkendall effect during the diffusion of
Au along the grain boundaries in the Fe layer. The results of this study
demonstrate a high potential of chemical interdiffusion in the controlled
plastic forming of ultra-strong metal nanostructures.
