In-situ measurement of Poisson's ratio for germanium nano-bridge in TEM

In the work a microelectromechanical systems (MEMS) based in-situ tensile test for germanium nano-bridge in transmission electron microscope is presented. With a carefully designed electrostatic actuator, germanium nano-bridge can be stretched stably at a speed rate less than 0.05% per step in strain. Assisted with the selected area electron diffraction (SAED) images, Poisson's ratios measured from a local area whose diameter is less than 20 nm can be obtained. Three different sized samples (marked as a, b, c) were tested and the Poisson's ratios were measured to be 0.18, 0.25, 0.27, respectively, comparing to 0.28 for the bulk germanium. The smallest scaled sample (a) presents a remarkable lower Poisson's ratio than bulk germanium, which may result from the increasing radial stress caused by the decreasing dimension of the nano-bridge.