Formation of stable ultra-thin pentagon Cu nanowires under high strain rate loading

Molecular dynamics (MD) simulations of $<100>/\{100\}$ Cu nanowires at 10 K with varying cross-sectional areas ranging from $0.3615\times0.3615 nm^2$ to $2.169\times2.169 nm^2$ have been performed using the embedded atom method (EAM) to investigate their structural behaviors and properties at high strain rate. Our studies reported in this paper show the reorientation of $<100>/\{100\}$ square cross-sectional Cu nanowires into a series of stable ultra-thin pentagon Cu nanobridge structures with diameter of $\sim 1$ nm under a high strain rate tensile loading. The strain rates used for the present studies range from $1 \times 10^9$ to $0.5 \times 107 s^{-1}$. The pentagonal multi-shell nanobridge structure is observed for cross-sectional dimensions < 1.5 nm. From these results we anticipate the application of pentagonal Cu nanowires even with diameters of $\sim 1$ nm in nano-electronic devices. A much larger plastic deformation is observed in the pentagonal multi-shell nanobridge structure as compared to structures that do not form such a nanobridge. It indicates that the pentagonal nanobridge is stable. The effect of strain rate on the mechanical properties of Cu nanowires is also analyzed and shows a decreasing yield stress and yield strain with decreasing strain rate for a given cross-section. Also, a decreasing yield stress and decreasing yield strain are observed for a given strain rate with increasing cross-sectional area. The elastic modulus is found to be $\sim 100$ GPa and is independent of strain rate effect and independent of size effect for a given temperature