Micro‐Rotors on Frictional Solid Surfaces via Optothermally‐Invoked Chirality

Abstract

As an elementary mode of locomotion, rotation has been ubiquitously demonstrated in macroscopic dimensions, or microscopically realized in levitated systems and hydrodynamic environments. However, it has remained an untouched research topic to achieve regulated rotation on solid surfaces at microscale, wherein friction serves as the dominant yet formidable external force. Here, this gap is bridged through an all‐optical approach. By utilizing pulsed light with an elongated Gaussian profile and twisting it relative to an illuminated object, chiral vortexes are introduced in both the optothermally excited elastic waves and the as‐induced surface friction, endowing the object with a restoring torque. Self‐regulation of the rotor and refueling of the chirality synergistically modulate the rotational motion. On this basis, orientation of the rotor can be adjusted arbitrarily by any specific angle, achieving an angular resolution of rad and rotation speed up to 10 rpm. Furthermore, the composite motion is demonstrated, combining both rotational and translational modes into the light field‐rotor system. The proposed technique extends the capability of optical manipulation on frictional solid surfaces by exploring the relation between the symmetry‐breaking condition and the modes of locomotion, which provides theoretical guidance and practical opportunities for building reconfigurable devices on solid substrates.