Nanomechanical modeling of the bending response of silicon nanowires

Abstract

Understanding the mechanical behavior of silicon nanowiresis essentialfor the implementation of advanced nanoscale devices. Although bendingtests are predominantly used for this purpose, their findings shouldbe properly interpreted through modeling. Various modeling approachestend to ignore parts of the effective parameter set involved in therather complex bending response. This oversimplification is the mainreason behind the spread of the modulus of elasticity and strengthdata in the literature. Addressing this challenge, a surface-basednanomechanical model is introduced in this study. The proposed modelconsiders two important factors that have so far remained neglecteddespite their significance: (i) intrinsic stresses composed of theinitial residual stress and surface-induced residual stress and (ii)anisotropic implementation of surface stress and elasticity. The modelingstudy is consolidated with molecular dynamics-based study of the nativeoxide surface through reactive force fields and a series of nanoscalecharacterization work through in situ three-pointbending test and Raman spectroscopy. The treatment of the test datathrough a series of models with increasing complexity demonstratesa spread of 85 GPa for the modulus of elasticity and points to theorigins of ambiguity regarding silicon nanowire properties, whichare some of the most commonly employed nanoscale building blocks.A similar conclusion is reached for strength with variations of upto 3 GPa estimated by the aforementioned nanomechanical models. Preciseconsideration of the nanowire surface state is thus critical to comprehendingthe mechanical behavior of silicon nanowires accurately. Overall,this study highlights the need for a multiscale theoretical frameworkto fully understand the size-dependent mechanical behavior of siliconnanowires, with fortifying effects on the design and reliability assessmentof future nanoelectromechanical systems.