MEMS-in-TEM for in-situ Nano Electromechanical Testing and High-Performance Energy Harvesters using Ionic Liquid
My research group has investigated MEMS fabrication and actuators since 1986. Recently, we inserted and operated MEMS devices in the specimen chamber of the transmission electron microscope (TEM). We conducted in situ TEM observation of the tensile and shear testing of nano junctions between two sharp tips. The tensile testing of a silicon junction of a few nm in diameter showed its extraordinary large plastic deformation. The shear deformation of a silver nano junction exhibited series of sub-nm steps correlated well with the crystalline spacing along an easy-to-slide plane; we may call those steps an atomic-scale stick-slip. Furthermore, we found the heat transfer through a short and thin, both in a few nm, silicon junction was much higher than the bulk value because of ballistic heat transfer. Also we have built a MEMS liquid cell in which the growth of a gold electrode by electroplating was observed in real time. We propose a high power-output vibrational energy harvesting based on ionic liquid. Ionic liquid enables very large capacitance (1.0-10 μF cm-2) on the electrode at bias voltage less than 1.9 V due to its extremely thin (~ 1 nm) electrical double layer. By mechanical squeezing and drawing the ionic liquid, that was solidified with a polymer additive, between a pair of electrodes at 15 Hz, we stably obtained the current output of 22 μAp-p cm-2 at 1.5 V.