  To develop active nanomaterials that can instantly respond to external
stimuli with designed mechanical motions is an important step towards the
realization of nanomachines and nanorobots. Herein, we present our finding of a
versatile working mechanism that allows instantaneous change of alignment
direction and speed of semiconductor nanowires in an external electric field
with simple visible-light exposure. The light induced alignment switch can be
cycled over hundreds of times and programmed to express words in Morse code.
With theoretical analysis and numerical simulation, the working principle can
be attributed to the optically tuned real-part (in-phase) electrical
polarization of a semiconductor nanowire in an aqueous suspension. The
manipulation principle is exploited to create a new type of microscale stepper
motor that can readily switch between in-phase and out-phase modes, and agilely
operate independent of neighboring motors with patterned light. This work could
inspire the development of a new type of micro/nanomachines with individual and
reconfigurable maneuverability for many applications.
