Micro- and nanoelectromechanical systems (MEMS/NEMS) lie at the heart of technologies ranging from precision sensors to signal processing. Their performance often depends on non-linear effects, ranging from amplitude-dependent frequency shifts, bistability, mode coupling and symmetry-breaking bifurcations such as period doubling. Understanding these dynamics at the nanoscale is essential for both fundamental physics and future device design. Yet conventional readout methods, whether electrical or optical, only indirectly capture the local structural motion underlying these phenomena.
In our laboratory, we address this gap with a new approach: event-based, time-resolved convergent-beam electron diffraction (CBED) in an ultrafast transmission electron microscope (UTEM). By focusing a continuous electron beam onto a vibrating, high-quality-factor sample and recording diffraction patterns with an event-based detector, we can reconstruct its motion with nanometre spatial precision and nanosecond time resolution, directly from the local Bragg-line dynamics. As our first sample system, we use a tensile-strained, single-crystalline silicon membrane resonator.
Using this method, we have observed the complete progression from Duffing-type nonlinear resonance to vibrational high-harmonic generation and, at the highest drive amplitudes, clear period doubling. This establishes electron diffraction as a powerful new tool for probing nonlinear nanomechanics, with the potential to extend down to atomically thin resonators.
To extend our measurement capabilities, we are also building a Laser Doppler Vibrometer (LDV), which will complement our electron diffraction approach with independent, high-precision optical vibration readout, thereby further broadening the range of nonlinear nanomechanical phenomena we can explore.