Orientation and size dependence of the elastic properties of zinc oxide nanobelts

Abstract

Molecular dynamics simulations are performed to characterize the response of zinc oxide(ZnO) nanobelts to tensile loading. The ultimate tensile strength (UTS) and Young’smodulus are obtained as functions of size and growth orientation. Nanobelts in threegrowth orientations are generated by assembling the unit wurtzite cell along the [0001],, and crystalline axes. Following the geometric construction, dynamic relaxation is carried outto yield free-standing nanobelts at 300 K. Two distinct configurations are observed in the[0001] and orientations. When the lateral dimensions are above 10 Å, nanobelts with rectangularcross-sections are seen. Below this critical size, tubular structures involving two concentricshells similar to double-walled carbon nanotubes are obtained. Quasi-static deformations ofbelts with and orientations consist of three stages, including initial elastic stretching, wurtzite-ZnO tographitic-ZnO structural transformation, and cleavage fracture. On the other hand, [0001]belts do not undergo any structural transformation and fail through cleavage along (0001)planes. Calculations show that the UTS and Young’s modulus of the belts are sizedependent and are higher than the corresponding values for bulk ZnO. Specifically, as thelateral dimensions increase from 10 to 40 Å, decreases between 38–76% and 24–63% areobserved for the UTS and Young’s modulus, respectively. This effect is attributed to thesize-dependent compressive stress induced by tensile surface stress in the nanobelts. and nanobelts with multi-walled tubular structures are seen to have higher values of elastic moduli(∼340 GPa)and UTS (∼36 GPa) compared to their wurtzite counterparts, echoing a similar trend in multi-walledcarbon nanotubes.