Low‐Temperature In Situ Large‐Strain Plasticity of Silicon Nanowires

Abstract

Elastic-plastic and fracture properties are key issues in characterizing materials' mechanical behavior, and they have been extensively studied for over a century for bulk structured materials. [1][2][3] Silicon is one of the most important and representative materials for these studies owing to its extremely important applications. [4,5] Silicon nanowires (NWs) are one of the most important nanostructures used for fabricating various electronic and optoelectronic nanodevices, [6,7] and they could be a building block for the construction and assembly of functional nanometer-scale systems. Although the electrical and optical properties of Si NWs have been extensively studied, only limited information is available about the structure-mechanical property correlations of Si NWs. This is likely due to the difficulty of carrying out in situ tensile or bending measurements on individual NWs. The elastic-plastic strains retained in NWs can significantly affect their electronic properties by perturbing the band structure or changing the Fermi energy of the nanostructures. [8] For example, the applied strains of continuous torsion on carbon NTs could result in chirality variation and therefore introduce a distinct conductance oscillation from metallic to semiconductor.[9] A straininduced giant piezoresistance effect has also been observed for Si NWs.[10]Results of studies of the elastic-plastic behavior of Si NWs are of technological importance. Silicon NWs are a potential candidate for building devices that are to be integrated with microelectronics and microelectromechanical systems (MEMS). They are also an outstanding candidate for constructing devices for flexible electronics. Several approaches have been developed to study the mechanical properties of NWs and nanotubes (NTs) based on atomic force microscopy (AFM) at nanometer-scale spatial resolution. [11,12] The major limitation of AFM measurements is that they are unable to reveal the atomic-scale structural evolution process during the in situ elastic-plastic-fracture process. Transmission electron microscopy (TEM) has been one of the most important and effective tools with a capability of atomic level imaging for investigating the in situ mechanical properties of single NWs and NTs, [13,14] although ex situ studies have to be carried out. [15,16] Direct and in situ atomic level imaging during tensile testing is fundamentally important to view and provide true physical insight into the elastic-plastic and fracture processes, [12,13] but this type of study is challenging experimentally.In this report, we present in situ TEM observation of the elastic-plastic-fracture processes of a single Si NW recorded at atomic resolution. The study directly shows the strain-induced structural evolution process of Si NWs and its largestrain plasticity (LSP). Our results indicate that the LSP of Si NWs via a brittle-ductile transition originates from a dislocation-initiated amorphization. This behavior is in contrast to the mechanical behavior of bulk Si. Our observation reveals a ...

Mechanical Properties of Vapor−Liquid−Solid Synthesized Silicon Nanowires

“…The brittle facture observed in all our experiments is in contrary to a recent report by Han et al, 2 where large-strain plasticity was observed for Si NWs with diameters smaller than 60 nm under tension in TEM. The authors found that the tensile plasticity was initiated by the emergence of a high density of dislocations followed by the development of a continuous disordered lattice by the emission of dislocations.…”

“…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.…”

“…Several major mechanisms have been proposed including (1) surface effects (surface stress and surface elasticity), 30,33,[40][41][42] (2) nonlinear elastic response of the NW core, 43 and (3) specifically for NWs with an oxide layer such as Si NWs, increasing importance of the oxide shell following the simple core-shell model. 19,21,44 In view that the modulus of silicon oxide is smaller than that of Si, Si NWs with reducing NW diameter but constant oxide layer possess smaller Young's modulus.…”

Atomic-scale microstructure underneath nanoindentation in Al-Cr-N ceramic films

“…In general, dislocations are easily generated on close-packed planes where dislocations slip with low resistance. [34][35][36][37] So we examined the dislocations on close-packed planes along several directions in the obtained TEM micrographs. Away from the zone of indentation impression, there are not so many dislocations comparing with the obvious pile-up of dislocations around grain boundaries underneath indenter impressions.…”

Magnetic Force Driven Nanogenerators as a Noncontact Energy Harvester and Sensor

“…At the same time, nanowires have good mechanical performance, such as flexibility, fatigue durability, and so forth. 30 So PZT nanowires should be a good candidate for the high output ICLNG. Here, we use the electrospinning method to make well aligned PZT nanowires as shown in Figure 3a.…”