The current issue of Nature Communications published online on April 23, 2013, features an experimental and computational study led by Prof. Frederic Sansoz at UVM and Prof. Scott Mao at the University of Pittsburgh entitled, “Near Ideal Theoretical Strength in Gold Nanowires containing Angstrom Scale Twins”.  The new material is shown to attain unprecedented failure strengths up to 3.12 GPa that is very close to the ideal limit predicted theoretically for gold, and about fifty times that of bulk gold used in applications. Detailed computer simulations of deformation processes at molecular scale have been performed in this research using the Bluemoon supercomputer at the Vermont Advanced Computing Center, which led to the discovery of new twin-mediated fracture mechanisms that are different from past observations.

“Gold is the most malleable of all metals and since ancient times has been used for many applications ranging from jewelry to electronics and medicine,” says Dr. Frederic Sansoz, associate professor in the School of Engineering.  “With the advent of nanotechnology, materials scientists have focused on ways to dramatically improve the failure strength of gold by either size reduction to the nanoscale or by adding special interfaces, so called twin boundaries. Yet nano-sized or nano-twinned metals generally fail well below their theoretical strength due to boundary and surface imperfections. Here, we observe strengths close to the ideal limit in ultrathin gold nanowires, where these twins have a very fine thickness, below one nanometer. This discovery is important for mechanical reliability in miniaturized devices, from gold nanoparticles used in medicine and electronics applications to foldable nanowire-based touchscreen panels and solar cells.”

Figure caption: (left) Molecular dynamics simulation of tension and fracture of an ultrathin gold nanowire containing angstrom scale twins. (right) Comparison of experimental strengths measured in present work to ultimate strengths in gold nanocrystals reported in the literature.

The article and supplementary movies are also available from:

http://www.nature.com/ncomms/journal/v4/n4/full/ncomms2768.html

Reference:

Near Ideal Theoretical Strength in Gold Nanowires containing Angstrom Scale Twins
J. Wang, F. Sansoz, J. Huang, Y. Liu, S. Sun, Z. Zhang, S. X. Mao, Nature Communications, 4 , 1742 (2013). doi:10.1038/ncomms2768.

ABSTRACT

Although nanoscale twinning is an effective means to enhance yield strength and tensile ductility in metals, nanotwinned metals generally fail well below their theoretical strength limit due to heterogeneous dislocation nucleation from boundaries or surface imperfections. Here we show that Au nanowires containing angstrom-scaled twins (0.7 nm in thickness) exhibit tensile strengths up to 3.12 GPa, near the ideal limit, with a remarkable ductile-to-brittle transition with decreasing twin size. This is opposite to the behaviour of metallic nanowires with lower-density twins reported thus far. Ultrahigh-density twins (twin thickness