Surface deformation-dependent mechanical properties of bending nanowires: an ab initio core-shell model

Ye Xiao,L Z Kou,Chun Li,J Shang

doi:10.1007/s10483-022-2814-6

Abstract

An ab initio core-shell model is proposed to evaluate the surface effect in bending nanowires, in which the elastic modulus depends on the surface relaxation and deformation induced by external loading. By using first-principles calculations based on the density functional theory (DFT), the surface and bulk properties are calculated for Ag, Pb, and Si nanowires. The obtained theoretical predictions of the effective Young’s modulus of nanowires agree well with the experimental data, which shows that the fixed-fixed nanowire is stiffened and the cantilevered nanowire is softened as the characteristic size of the cross section decreases. Furthermore, the contrastive analysis on the two kinds of nanowires demonstrates that increasing the nanowire aspect ratio would enhance the surface effect. The present results could be helpful for understanding the size effect in nanowires and designing nanobeam-based devices in nanoelectromechanical systems (NEMSs).

Highlights

As one of the most promising one-dimensional (1D) nano-sized materials, nanowires have attracted great interests due to their wide applications in miniature devices, e.g., sensors, actuators, transistors, probes, and resonators in nanoelectromechanical systems (NEMSs) andYe XIAO, J
To investigate the mechanical mechanism of surface effects on the surface and bulk elastic moduli of nanowires, we propose an ab initio core-shell model for a nanowire consisting of a surface layer with an infinitesimal thickness and a core part based on the density functional theory (DFT)
The obtained theoretical predictions of the mechanical behaviors of typical metallic and metalloid nanowires agree well with existing numerical results and experimental data. These findings provide insights into the fundamental physical mechanisms of stiffening and softening nanowires subjected to the concentrated force, and lay the ground for the optimal design in nanobeam-based devices of NEMSs

Summary

Introduction

As one of the most promising one-dimensional (1D) nano-sized materials, nanowires have attracted great interests due to their wide applications in miniature devices, e.g., sensors, actuators, transistors, probes, and resonators in nanoelectromechanical systems (NEMSs) andYe XIAO, J. The mechanical properties of nanowires exhibit significant size-dependence, owing to the surface effect induced by a large surface-tovolume ratio[8,9,10]. The surface effect has become a hotspot for nano-scaled bars and beams in NEMSs. By means of atomic force microscopy, the mechanical behaviors of nanowires with different boundary conditions have been revealed experimentally. An oppositely size-dependent behavior of the elastic modulus was found for GaN[15], Ag[16], and Si[17,18] cantilever nanowires. The classical elasticity theory is invalid to clarify the physical mechanism of the aforementioned interesting mechanical properties of nanowires. It is necessary to propose a concise theoretical model to predict the bending response of nanowires

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Conclusion