Microelectromechanical Systems for Nanomechanical Testing: Electrostatic Actuation and Capacitive Sensing for High-Strain-Rate Testing

Abstract

There have been relatively few studies on mechanical properties of nanomaterials under high strain rates, mainly due to the lack of capable nanomechanical testing devices. Here we present a new on-chip microelectromechanical system (MEMS) for high strain-rate nanomechanical testing. The MEMS device consists of an electrostatic comb drive actuator, two capacitive displacement sensors and a load cell. The dynamic responses of the device in air and in vacuum are systematically modeled under both alternating and ramp forces. Two methods, capacitive readout and high-speed imaging, are used to measure the dynamic displacements, which agree well with the modeling results. While we demonstrate the maximum constant strain rate over 200 s−1 under ramp force, it is interesting to find that the capacitive readout used in this work can only measure strain rate up to 22 s−1 due to its limit in bandwidth. To demonstrate the utility of this new device, gold nanowires are tested at strain rates of 10−5 and 10 s−1 inside a scanning electron microscope. Increasing strain rate is found to yield higher yield strength and larger ductility.