Adhesion-assisted nanoscale rotary locomotor in non-liquid environments
Abstract
Rotation in micro/nanoscale provides extensive applications in mechanical actuation1, 2, cargo delivery3, 4, and biomolecule manipulation5, 6. Light can be used to induce a mechanical rotation remotely, instantly and precisely7-13, where liquid throughout serves as a must-have enabler to suspend objects and remove impact of adhesion. Achieving light-driven motion in non-liquid environments faces formidable challenges, since micro-sized objects experience strong adhesion and intend to be stuck to contact surfaces. Adhesion force for a usual micron-sized object could reach a high value14, 15 (nN - μN) which is several orders of magnitude higher than both its gravity (~ pN) and typical value of optical force (~ pN) in experiments16. Here, in air and vacuum, we show counter-intuitive adhesion-assisted rotary locomotion of a micron-sized metal nanoplate with ~30 nm-thickness, revolving around a microfiber. This locomotor is powered by pulsed light guided into the fiber, as a coordinated consequence of photothermally induced surface acoustic wave on the nanoplate and favorable configuration of plate-fiber geometry. The locomotor crawls stepwise with sub-nanometer locomotion resolution actuated by designed light pulses. Furthermore, we can control the rotation velocity and step resolution by varying the repetition rate and pulse power, respectively. A light-actuated micromirror scanning with 0.001 resolution is then demonstrated based on this rotary locomotor. It unfolds unprecedented application potential for integrated micro-opto-electromechanical systems, outer-space all-optical precision mechanics and controls, laser scanning for miniature lidar systems, etc.