Light-Controlled Oscillation of Microplates Leveraging Contact Adhesion.

Abstract

Miniaturized mechanical oscillation is mostly realized in microelectromechanical systems (MEMS). Its routine implementation involves carefully configuring a driving force, such as electrostatic force, while concurrently mitigating contact adhesion that tends to anchor moving parts. Though often undesirable, contact adhesion plays a significant role at micronano scales and may be harnessed as a driving force for miniaturized oscillators. This potential remains largely unexplored owing to the complex nature of adhesion force and, more importantly, the paradox of using an anchoring force for actuation. In this article, we explore this possibility in an optical system that consists of a suspended microplate adhered to a cylindrical microfiber. The combination of these two elements with contrasting surface curvatures constitutes a light-controlled cantilever. A theory is developed to elucidate the adhesion-induced deformation of this cantilever, and how it can be photothermally modulated by light. Experimentally, oscillation of the microplate is measured in response to square-wave light signals. At low modulation frequencies, the "smoking-gun" signature─a downward deflection with a linear spatial profile─is measured, evidencing that the short-range adhesion acts as the driving force. In the high-frequency regime, we demonstrate control of oscillations by exciting resonance modes, attaining frequencies up to the submegahertz range. These findings facilitate the development of micromechanical applications in challenging adhesive environments.