Size Effects in Mechanical Deformation and Fracture of Cantilevered Silicon Nanowires

Abstract

Elastic modulus and fracture strength of vertically aligned Si [111] nanowires (ø = 100-700 nm) in an as-grown state have been measured using a new, multipoint bending protocol in an atomic force microscope. All wires showed linear elastic behavior, spring constants which scale with (length)(3), and brittle failure at the wire-substrate junction. The "effective" Young's modulus increased slightly (100 --> 160-180 GPa) as wire diameter decreased, but fracture strength increased by 2-3 orders of magnitude (MPa --> GPa). These results indicate that vapor-liquid-solid grown wires are relatively free of extended volume defects and that fracture strength is likely controlled by twinning and interfacial effects at the wire foot. Small wires (100 nm) grown with a colloidal catalyst were the best performers with high modulus ( approximately 180 GPa) and fracture stress >1 GPa.

Deflection induced cellular focal adhesion and anisotropic growth on vertically aligned silicon nanowires with differing elasticity

“…In agreement with a previous study, 39 the deflection degree of nanowires increased depending on their length. Consistent with this, increasing the length of SiNWs leads to a greater deflection of the SiNWs-10 substrate ( Figure 5 and Supplementary Figure 8).…”

Mechanical Properties of Vapor−Liquid−Solid Synthesized Silicon Nanowires

“…The Si NWs tested in our experiments possess much larger fracture strength than Si thin films (1-4 GPa) 46 and NWs with larger diameters (0.03-4 GPa). 21,28 A similar fracture strength of 12 GPa in VLS-grown Si NWs have been reported recently using the AFM bending technique, but their NW diameters ranged between 100 and 200 nm. 3 The size effects on the fracture strain and strength are assumed to be related to the defects presented in the NWs.…”

“…34 It is believed that using H 2 as the carrier gas passivates the surface. Our Si NWs are different from many other Si NWs reported in the literature using either the CVD-VLS method 21 or other methods such as thermal evaporation, 2,35 where the Si NW surfaces are either covered with an at least 1-3 nm thick amorphous oxide or treated to be hydrogen terminated. The surface condition might play an important role in the mechanical property of Si NWs as will be discussed later.…”

“…27 Available experimental results on Si NWs exhibit significant scatter including the following: (1) some reported a decrease in Young's modulus with decreasing size, 2,9,24,28 while others showed an opposite trend; 20,21 (2) the reported strength values of vapor-liquid-solid (VLS) grown Si NWs ranged from 500 MPa to 12 GPa; 3,28 (3) Han et al 2 observed pronounced plastic deformation of Si NWs by in situ TEM tensile tests at room temperature, while Gordon et al 21 reported linear elastic behavior followed by brittle fracture using AFM bending tests.…”

The Mechanical Properties of Nanowires

“…MD simulations based on different interatomic potential models showed that the elastic stain of Si NWs was greater than 15% 185. Experimental measurements showed different elastic strains for Si NWs, such as 16% from the in situ TEM tensile test,217 12% from the in situ SEM tensile test,86 1.5% from the in situ SEM bending test,231 ≈5% from the nanoindentation31 and AFM bending tests,22, 31 and 4.6% and 14.7% from the respective in situ TEM tensile and bending tests 101. For SiC NWs, a maximum elastic stain of 10% was observed in an early AFM‐bending test 15.…”