Muraoka Mikio, Tobe Ryohei
Department of Mechanical Engineering, Akita University, Akita 010-8502, Japan.
J Nanosci Nanotechnol. 2009 Aug;9(8):4566-74. doi: 10.1166/jnn.2009.1079.
A mechanical characterization technique for nanowires (NWs) longer than approximately 10 microm is proposed, based on optical microscopic observations under bending test. Low flexural rigidity of NWs often results in large deflection, which rules out the use of linear beam theory; however, the largely bent shape is optically visible as a diffraction image under transmitted illumination. The NW standing on a rod-like substrate was deflected by means of a micro-cantilever, where interactive forces, such as van der Waals forces, provide sufficient adhesion for fixing the free end of the NW. The reactive force was measured from the cantilever deflection and detected by a laser interferometer. The luminance profile of the diffraction image provided a good measure of the NW diameter. Inverse analysis using geometrically nonlinear mechanics for the bent shape enabled successful evaluation of the Young's modulus. In addition, a fracture test was conducted by manipulating the cantilever for intense deformation of the NW, such as buckling. The maximum curvature was observed at the freely suspended part of the bent NW where fracture was assured. The bending strength was determined from observation of the curvature at the fracture. Examples for CuO NWs of 40 nm to 190 nm in diameter indicated dependence of the Young's modulus and strength on the NW diameter.
基于弯曲试验下的光学显微镜观察，提出了一种针对长度大于约10微米的纳米线（NWs）的力学表征技术。纳米线的低弯曲刚度常常导致大挠度，这排除了线性梁理论的应用；然而，在透射照明下，大幅弯曲的形状作为衍射图像在光学上是可见的。置于棒状基底上的纳米线通过微悬臂梁发生偏转，其中诸如范德华力等相互作用力为固定纳米线的自由端提供了足够的附着力。从悬臂梁的偏转测量反作用力，并通过激光干涉仪进行检测。衍射图像的亮度分布提供了纳米线直径的良好测量方法。对弯曲形状使用几何非线性力学进行反分析能够成功评估杨氏模量。此外，通过操纵悬臂梁使纳米线发生诸如屈曲等剧烈变形来进行断裂试验。在弯曲纳米线的自由悬垂部分观察到最大曲率，此处可确定会发生断裂。根据对断裂处曲率的观察来确定弯曲强度。直径为40纳米至190纳米的氧化铜纳米线的示例表明杨氏模量和强度与纳米线直径有关。
