NUS Nanoscience & Nanotechnology Initiative, National University of Singapore, Singapore.
Langmuir. 2010 Jan 19;26(2):1165-71. doi: 10.1021/la9022739.
Molecular dynamics simulations of ZnO nanowires under tensile loading were performed and compared with simulations of TiO(2) wires to present size-dependent mechanical properties and super ductility of metal oxide wires. It is shown that while large surface-to-volume ratio is responsible for their size effects, ZnO and TiO(2) wires displayed opposite trends. Although the stiffness of both wires converged monotonically to their bulk stiffness values as diameter increases, bulk stiffness represented the upper bound for ZnO nanowires as opposed to the lower bound for TiO(2) wires. ZnO nanowires relaxed to either completely amorphous or completely crystalline states depending on wire thickness, whereas a thin amorphous shell is always present in TiO(2) nanowires. It was also found that when crystalline ZnO nanowires are stretched, necking initiated at localized amorphous regions to eventually form single-atom chains which can sustain strains above 100%. Such large elongations are not observed in TiO(2) nanowires. Using the analogy of a clothesline, an explanation is offered for the necessary conditions leading to super ductility.
对拉伸载荷下的 ZnO 纳米线进行了分子动力学模拟，并与 TiO(2) 纳米线的模拟进行了比较，以呈现出金属氧化物纳米线的尺寸相关力学性能和超延展性。结果表明，尽管大的表面积与体积比是导致其尺寸效应的原因，但 ZnO 和 TiO(2) 纳米线表现出相反的趋势。尽管随着直径的增加，两种纳米线的刚度都单调收敛到其体相刚度值，但体相刚度是 ZnO 纳米线的上限，而不是 TiO(2) 纳米线的下限。 ZnO 纳米线根据线厚可以松弛到完全非晶态或完全晶态，而在 TiO(2)纳米线中总是存在一个薄的非晶壳。还发现，当晶态 ZnO 纳米线被拉伸时，颈缩首先发生在局部非晶区，最终形成单原子链，其可以承受超过 100%的应变。在 TiO(2)纳米线中没有观察到这种大的伸长。通过类比晾衣绳，给出了导致超延展性的必要条件的解释。
