in situ Nano-Fatigue Study of 1-D Nanostructures

In the past decade, tremendous efforts have been made in the study of fatigue behavior of nanostructured materials, in particular nanocrystalline metals. Recently, with the rapid development of nanowire/nanotube-based devices, structure stability of such 1-D building blocks has emerged as a critical issue for many novel nano-applications that involved with cyclic loading, such as flexible nanoelectronics/NEMS and bio-nano interfaces. Under such circumstances, quantitative understanding of the fatigue behavior of 1-D nanostructures becomes crucial, despite that limited experimental data were reported so far. In this work, we demonstrated the in situ nano-fatigue characterizations of a few metallic and semiconductor nanowires by using a piezo-driven Pico-indenter inside SEM assisted by a push-to-pull (PTP) micro-mechanical device, with the cyclic frequency up to 10 Hz. We observed that both single crystalline nickel (Ni) and silicon (Si) nanowires could fracture after tens to hundreds of thousands cycles of loading-unloading straining, depending on the amplitudes of stresses (but generally much lower than their yielding stresses), indicating that low-cycle fatigue for such defect-free 1-D nanostructures could indeed occur. In addition, the dependency of fatigue life on the applied stress magnitude has been investigated and discussed with the assistance of TEM-analysis for samples before and after fatigue failures. Lastly, polycrystalline nanowire samples with similar dimensions will be investigated and compared with the results from their single crystalline counterparts.