In situ tensile testing of nanoscale freestanding thin films inside a transmission electron microscope

The unique capability of rendering opaque specimens transparent with atomic resolution makes transmission electron microscopy (TEM) an indispensable tool for microstructural and crystallographic analysis of materials. Conventional TEM specimens are placed on grids about 3 mm in diameter and 10-100 μm thick. Such stringent size restriction has precluded mechanical testing inside the TEM chamber. So far, in situ testing of nanoscale thin foils has been mostly qualitative. Micro-electro-mechanical systems (MEMS) offer an unprecedented level of miniaturization to realize sensors and actuators that can add TEM visualization to nano-mechanical characterization. We present a MEMS-based uniaxial tensile experiment setup that integrates nanoscale freestanding specimens with force and displacement sensors, which can be accommodated by a conventional TEM straining stage. In situ TEM testing on 100-nm-thick freestanding aluminum specimens (with simultaneous stress measurement) show limited dislocation activity in the grain interior and consequent brittle mode of fracture. Plasticity at this size scale is contributed by grain boundary dislocations and partial dislocations.