Haque M A, Saif M T A
Department of Mechanical and Nuclear Engineering, Pennsylvania State University, 317A Leonhard Building, University Park, PA 16802, USA.
Proc Natl Acad Sci U S A. 2004 Apr 27;101(17):6335-40. doi: 10.1073/pnas.0400066101. Epub 2004 Apr 14.
We have added force and displacement measurement capabilities in the transmission electron microscope (TEM) for in situ quantitative tensile experimentation on nanoscale specimens. Employing the technique, we measured the stress-strain response of several nanoscale free-standing aluminum and gold films subjected to several loading and unloading cycles. We observed low elastic modulus, nonlinear elasticity, lack of work hardening, and macroscopically brittle nature in these metals when their average grain size is 50 nm or less. Direct in situ TEM observation of the absence of dislocations in these films even at high stresses points to a grain-boundary-based mechanism as a dominant contributing factor in nanoscale metal deformation. When grain size is larger, the same metals regain their macroscopic behavior. Addition of quantitative capability makes the TEM a versatile tool for new fundamental investigations on materials and structures at the nanoscale.
我们已在透射电子显微镜（TEM）中增加了力和位移测量功能，用于对纳米级试样进行原位定量拉伸实验。利用该技术，我们测量了几种纳米级自支撑铝膜和金膜在多个加载和卸载循环下的应力-应变响应。我们观察到，当这些金属的平均晶粒尺寸为50纳米或更小时，它们具有低弹性模量、非线性弹性、缺乏加工硬化以及宏观脆性。即使在高应力下，通过原位TEM直接观察到这些薄膜中不存在位错，这表明基于晶界的机制是纳米级金属变形的主要贡献因素。当晶粒尺寸较大时，相同的金属恢复其宏观行为。增加定量功能使TEM成为用于对纳米级材料和结构进行新的基础研究的多功能工具。
