Diameter dependence of modulus in zinc oxide nanowires and the effect of loading mode: In situ experiments and universal core-shell approach

Abstract

Effect of surface stress on the stiffness of micro/nanocantilevers: Nanowire elastic modulus measured by nano-scale tensile and vibrational techniques

Quantifying the defect-dominated size effect of fracture strain in single crystalline ZnO nanowires

“…1(c)]. We hereinafter focused on e FS instead of on the conventionally discussed r FS , seeing that the measurement error in the strain is smaller than that in the stress; 15 moreover, the ideal strain (e th , i.e., the e FS in defect-free ZnO NWs) is more insensitive to D than is the ideal strength (r th ), which means that the size effect of r FS is partly contributed by the surface-dominated diameter dependence of YM, 13 whereas that of e FS is mostly defect-dominated. 15 The remarkable scattering of e FS can thus be attributed to the size distribution of critical defects, and their size effect results from the reduction of critical defects with decreasing D, which is in accordance with previous qualitative reports.…”

“…The experimental details can be found elsewhere; 13 in short, each individual NW was axially aligned with the tensile direction and was loaded by deflecting a cantilever [see Fig. 1(a)].…”

“…5 However, the quantitative mechanisms for the size effect (i.e., how the scattered r FS are related to the NW diameters and, especially, how they are determined by the real microstructural defects in NWs) have not been theoretically clarified yet, but they are of basic importance for the potential application of NWs in nanoelectromechanical devices with predictable and reproducible responses. 12 In our previous experiments, 13 methodologies were developed for in situ uniaxial tensile testing using a scanning electron microscope (SEM). The diameter dependence of r FS has also been revealed in a concise form.…”

Mechanical properties of ZnO nanowires under different loading modes

“…Recent MD simulations showed that a core and a shell with different Young's moduli exist in ZnO NWs; the Young's moduli of the core and of the shell are lower and higher than the bulk value, respectively [12]. The elastic modulus varies continuously from the core to the surface as a result of energy minimization [12,24]. Both models used in our work are first-order approximations (assuming step-like modulus distribution in the core and the shell) that at the least explain our experimental results reasonably well.…”

“…The objectives are twofold: (1) to explain the large discrepancy in experimental results in the literature, and (2) to elucidate the underlying mechanism(s) of the size effects, i.e., the relative importance of the surface and the core of NWs, especially when integrated with computational studies. So far only one study compared the Young's moduli of ZnO NWs under tension and resonance and found considerable difference in the size effects, albeit with very different setups/conditions in the two experimental methods [24].…”