In situ microtensile stage for electromechanical characterization of nanoscale freestanding films

This article presents the second generation of a microtensile stage that allows mechanical and electrical characterizations of nanoscale freestanding material samples in situ in analytical chambers such as scanning electron microscopy and transmission electron microscopy. The first generation [M. A. Haque and M. T. A. Saif, Proc. Natl. Acad. Sci. U.S.A. 101, 6335 (2004)] had the limitation of mechanical characterization only. Furthermore, it had a high probability of sample failure during fabrication and the force sensor could only be calibrated by cleaving the stage after sample testing. The new stage prevents sample failure (100% yield) and allows (1) calibration prior to testing without cleaving and (2) resistivity measurement of the sample at different temperatures, in addition to stress-strain measurements under uniaxial tension. A new fabrication process is also presented, which involves only two lithographic steps and a single Si etching step to fabricate the testing stage and the sample together with necessary electrical isolations for resistivity measurement. Testing stages are fabricated using the new process and are applied to test a 100-nm -thick freestanding Al sample with 65 nm grain size. The stress-strain response of the sample shows an elastic modulus of 61 GPa. The room temperature resistivity of this nanograined specimen is almost 20 times higher than the bulk value. The resistivity decreases irreversibly with increasing temperature (tested up to 98 °C) and time without any significant grain growth. Upon cooling from 98 °C, the resistivity increases with the decreasing temperature, contrary to bulk metallic behavior.