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

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.