Correlation between Surface Stress and Apparent Young’s Modulus of Top-Down Silicon Nanowires

Abstract

In this work, we report experimental evidence of surface stress effects on the mechanical properties of silicon nanostructures. As-fabricated, top-down silicon nanowires (SiNWs) are bent up without any applied force. This self-buckling is related to the surface relaxation that reaches an equilibrium with bulk deformation due to the material elasticity. We measure the SiNW self-deformation by atomic force microscopy (AFM), and we apply a simple physical model in order to give an estimation of the surface stress. If the equilibrium is altered by a nanoforce, applied by an AFM tip, nanowires find a new equilibrium condition bending down (mechanical bistability). In this work, for the first time, we report a clear and quantitative relationship between the SiNWs' apparent Young's modulus, measured by force-deflection spectroscopy, and the estimated value of surface stress, obtained by self-buckling measurements taking into account the Young's modulus of bulk silicon. This is an experimental confirmation that the surface stress is fundamental in determining mechanical properties of SiNWs, and that the elastic behavior of nanostructures strongly depends on their surfaces.

Effect of surface roughness on elastic limit of silicon nanowires

“…In practice, realistic Si-NWs were usually covered by defective surfaces, surface contamination, amorphous shells or silicon oxide layers according to their synthesis methods [16][17][18]. It was reported that deformation mechanism of Si NWs under tension was largely determined by its surface effect [19]. Thus, it is expected that the role of surface or interface defects may play a key role in determining the mechanical properties of Si NWs when their sizes are reduced to several nanometers.…”

Effect of size and shape on the elastic modulus of metal nanowires

“…Over the past years, many researchers have worked on theoretical models to describe the size effects in the elastic behavior of nanowires. The sizedependent change in elasticity has been attributed to one or more of the following factors: Loss of atomic coordination [30], electron density redistribution [31], lattice contraction due to compressive strain [32], surface relaxation processes [33], and facet energy [34]. He and Lilley presented a theoretical approach analyzing the influence of surface stress on static bending [35] and in resonance vibration [36].…”

Evaluating the compressive stress generated during fabrication of Si doubly clamped nanobeams with AFM

“…In order to achieve that we compare our experimental data with models picked from present works in literature. With respect to previous works, [7][8][9][10] here we investigate silicon suspended nanostructures with rectangular sections.…”