Effects of surface defects on the mechanical properties of ZnO nanowires

Abstract

The elastic modulus of ZnO nanowires was measured using a resonance method based on laser Doppler effect and their fracture strains were determined via two-point bending with the aid of optical nanomanipulation. The elastic moduli of ZnO nanowires with diameters of 78 to 310 nm vary from 123 to 154 GPa, which are close to the bulk value of 140 GPa and independent of the diameters and surface defects. However, the fracture strains of the ZnO nanowires depend significantly on their diameters, increasing from 2.1% to 6.0% with the decrease in diameter from 316 to 114 nm. Post-mortem TEM analysis of the ends of the fractured nanowires revealed that fracture initiated at surface defects. The Weibull statistical analysis demonstrated that a greater defect depth led to a smaller fracture strain. The surface-defect dominated fracture should be an important consideration for the design and application of nanowire-based nanoelectromechanical systems.

The kinetic frictional shear stress of ZnO nanowires on graphite and mica substrates

“…Adjacent surfaces of tip and NW, and substrate and NW were modelled as Herztian contact pairs. During FEM simulation, a vertical load was applied by the tip, with a magnitude corresponding to a maximum contact pressure of 10 GPa, equal to the fracture strength of the NW[29]. As expected, the normal compressive stress experienced at the NW-substrate interface reached a maximum of 70 MPa at the NW's midpoint, and fell abruptly below 1 MPa at distance of just 1 µm from the midpoint.…”

“…According to the elastic beam theory, can be estimated by [19], where , , , and are the elastic modulus, area moment of inertia, half length, and deflection of the NW, respectively. For the ZnO NWs being tested, GPa and were used [29], while the diameter, , and length, of the NW were measured by SEM. The frictional shear stress, , i.e.…”

“…A 2 µm long segment of the NW was modelled on each side of its midpoint, and the NW-substrate interface was6 perfectly smooth. The elastic moduli for the substrate, NW and tip were 24.1GPa[34], 140 GPa[29], and 410 GPa[35] respectively, and Poisson's ratios were all 0.3. All three components were meshed with SOLID 185 elements.…”

ZnS coating for enhanced environmental stability and improved properties of ZnO thin films

“…The thin ZnS layer enhances ZnO hardness and elastic modulus due to improving quality of ZnO surface. 38,39 The passivation process of ZnO remove surface defects and signicantly improved its mechanical properties, for example, elastic moduli in case of ZnO nanowires. 38 The previous optical studies of the ZnO/ZnS nanolms showed that suldation process removed ZnO surface defects.…”

“…38,39 The passivation process of ZnO remove surface defects and signicantly improved its mechanical properties, for example, elastic moduli in case of ZnO nanowires. 38 The previous optical studies of the ZnO/ZnS nanolms showed that suldation process removed ZnO surface defects. 24 The cathodoluminescence (CL) intensity of the band-to-band emission for ZnO/ZnS nanolayer was one order of magnitude higher than that of ZnO.…”