Displacement field of a screw dislocation in a〈011〉Cu nanowire: An atomistic study

Abstract

By performing atomistic calculations with a tight-binding potential, we study the displacement field induced by a screw dislocation lying along a free 011 Cu cylindrical nanowire. For this anisotropic orientation that is often encountered experimentally, we show that the displacement field u z along the nanowire can be seen as the superposition of three different fields: the screw dislocation field in an infinite medium, the warping displacement field caused by the so-called Eshelby twist, and an additional image field induced by the free surfaces. A Fourier series analysis of this latter image displacement and stress fields is given. For a circular cross section of the wire, this image field corresponds mainly to an additional warping displacement u z ∝ xy. The dissociation mechanism of the dislocation into partials and the surface stress effects being also captured in our simulations, the present study enables one to quantify the various contributions to the formation of the x-ray diffractograms.

Diffraction from twisted nanowires: helicity revealed by anisotropy

“…As also shown in previous work [ Fig. 9b of Gailhanou & Roussel (2013)], both the prediction of the elasticity theory given by equation 2and the atomistic simulations converge to the same warping displacement induced by the torsion.…”

“…Interactions between copper atoms are modelled using a tight binding potential. Details of the simulations are given by Gailhanou & Roussel (2013). Fig.…”

Stability of a Screw Dislocation in a⟨011⟩Copper Nanowire

“…This so-called Eshelby twist that was observed afterwards in whiskers [7] reappears today more dramatically in nanowires [8][9][10], a smaller radius producing a larger twist [11]. To leave its metastable state and reach the lateral surface of the wire, the screw dislocation (parallel to the cylindrical wire axis) must overcome an energy barrier whose maximum is located roughly halfway and whose height does not depend on the radius of the wire in the isotropic theory.…”

“…To study this influence of the dissociation mechanism one needs to estimate the different forces acting on each partial dislocation. Only dislocation Volterra fields are considered [12] and surface stress effects are neglected [11]. To simplify further we assume that the only effect of anisotropy is contained in E d and we use the isotropic elasticity theory of dislocations.…”

“…Details on the simulations are given in Ref. [11] and in the Supplemental Material [12]. In the present work, the molecular statics (MS) calculations are 0031-9007=15=115 (7)=075503 (5) 075503-1 © 2015 American Physical Society performed to simulate an infinite twisted copper nanowire containing a perfect screw dislocation that is located at different ξ=R positions from the center.…”