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SPECIAL SECTION ON NANOMATERIALS AND NANOMECHANICS

Tetragonal Phase Transformation in Gold Nanowires

[+] Author and Article Information
Ken Gall, Jiankuai Diao, Martin L. Dunn

Department of Mechanical Engineering,  University of Colorado at Boulder, Boulder, CO 80309

Michael Haftel, Noam Bernstein, Michael J. Mehl

Center for Computational Materials Science,  Naval Research Laboratory, Washington, DC 20375-5345

J. Eng. Mater. Technol 127(4), 417-422 (Dec 28, 2004) (6 pages) doi:10.1115/1.1924558 History: Received September 21, 2004; Revised December 28, 2004

First principle, tight binding, and semi-empirical embedded atom calculations are used to investigate a tetragonal phase transformation in gold nanowires. As wire diameter is decreased, tight binding and modified embedded atom simulations predict a surface-stress-induced phase transformation from a face-centered-cubic (fcc) ⟨100⟩ nanowire into a body-centered-tetragonal (bct) nanowire. In bulk gold, all theoretical approaches predict a local energy minimum at the bct phase, but tight binding and first principle calculations predict elastic instability of the bulk bct phase. The predicted existence of the stable bct phase in the nanowires is thus attributed to constraint from surface stresses. The results demonstrate that surface stresses are theoretically capable of inducing phase transformation and subsequent phase stability in nanometer scale metallic wires under appropriate conditions.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Schematic of three different freestanding nanometer scale materials. Tensile surface stresses result in unique intrinsic compressive stress states in the material cores. The nanofilm experiences an in-plane biaxial stress, the nanowire experiences a triaxial stress state, with a larger component along the wire axis, and the nanoparticle experiences a hydrostatic stress state.

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Figure 2

Energy as a function of lattice spacing for various simulation methods. The curves were generated by displacement-controlled expansion and contraction of bulk periodic Au along the [100] fcc axis. The [010] and [001] axes were allowed to adjust freely. Energy minimums exist for fcc and bct phases.

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Figure 3

Three-dimensional image of a nanowire (a) before (fcc) and (b) after (bct) transformation predicted by static TB energy minimization simulations

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Figure 4

Cross-section view of two parallel atomic planes from a bct nanowire predicted by (a) TB simulations and (b) MEAM simulations. Both wires began as ⟨100⟩ fcc wires with a size of 1.63 by 1.63nm and were relaxed to the lower energy bct state. The orientation of the bct wire is [100] with [011] and [0-11] side surfaces.

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