Charge-Induced Dynamics in Hexagonal Boron Nitride Nanoelectromechanical Resonators.

We demonstrate electrostatic actuation of insulating nanodrums made of hexagonal boron nitride (hBN), a van der Waals large bandgap dielectric. Without the explicit conductive layer, we utilize a nonuniform electric field for the electrostatic actuation. The fundamental resonance mode, observed near 26 MHz, exhibits an unconventional linear resonance frequency dispersion with applied DC bias voltage. A bias-dependent frequency drift of the nanodrums over an extended period of time suggests slow charge dynamics in the hBN drum. Band-bending analysis and wavelength-dependent optical excitation reveal deep defect states in hBN that experience bias and photoassisted ionization, resulting in asymmetric charge buildup for opposing bias polarities. Our experimental findings and theoretical analysis demonstrate that electrostatically driven hBN drums serve as a sensitive platform for investigating charge dynamics and defect physics in insulating two-dimensional materials, thereby paving the way for novel nanoelectromechanical systems-based sensors and charge-controlled mechanical devices.