  Rotation in micro/nanoscale provides extensive applications in mechanical
actuation$^{1, 2}$, cargo delivery$^{3, 4}$, and biomolecule manipulation$^{5,
6}$. Light can be used to induce a mechanical rotation remotely, instantly and
precisely$^{7-13}$, 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 value$^{14, 15}$ (nN -
{\mu}N) which is several orders of magnitude higher than both its gravity (~
pN) and typical value of optical force (~ pN) in experiments$^{16}$. 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{\deg} 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.
