Detection of Microelectromechanical System Acoustics via Scanning Tunneling Microscopy

Scanning tunneling microscopy (STM) and microelectromechanical systems (MEMS) traditionally address vastly different length scales─one resolving atomic structure and the other, engineering macroscopic motion. Bridging these regimes is particularly compelling for high-Q membrane resonators operating at cryogenic temperatures, where conventional optical and electrical readout methods introduce dissipation, heating, or electromagnetic loading that perturbs temperature-dependent force measurements. Here, we unite these two fields by using an STM tip as both an actuator and a detector to perform minimally invasive measurements of high-aspect-ratio MEMS resonators. We resolve acoustic modes of millimeter-scale, high-Q membranes with picometer spatial precision, without relying on optical readout or capacitive coupling. Because the tunneling junction is intrinsically localized and dissipates negligible power, the measurement introduces minimal back-action or heating, enabling direct access to the intrinsic dynamics of microgram-mass oscillators. We implement three complementary detection modalities: phase-sensitive homodyne readout, rapid measurements compatible with the STM feedback cycle, and near-nonperturbative operation via controlled tip retraction─that together span a wide range of measurement conditions and enable force sensitivity on the order of a few piconewtons. These approaches establish STM as a broadband, surface-localized nanomechanical detector capable of operating where conventional optical access is impractical, including cryogenic and high-magnetic-field environments. This platform expands the experimental toolbox for nanomechanics, enabling precision measurements of forces, displacements, and pressures in suspended systems─including Casimir interactions and hybrid electromechanical devices─across cryogenic and high-field environments.