Wavelength-Dependent Light-Driven Nanomotor

Abstract

Nano/micro-motor shows various promising applications in the areas of biomedicine, catalysis, environmental remediation.[1-4] The precise controlling of the speed and direction are the most important issues that must be solved for the real application. Light controlling is a newly proposed hot topic in this area[5,6]. Here we report a visible-light-driven silicon nanomotor based on core-shell p-n junction, which shows size and wavelength dependent motion behavior. Under light illumination, photoexcited carriers decompose hydrogen peroxide on p-Si and n+-Si surface and generate H+ and OH- respectively. The localized electrophoretic field generated by unbalanced ions propels the motion of the nanomotor. The proposed self-electrophoretic mechanism was demonstrated by real-time individual motor motion and ionic strength measurement. The as-prepared motor shows instant “ON-OFF” response through switching the “ON-OFF” of PEC reaction by light illumination. The morphology of fracture surface shows crucial effect on the motion trajectory, which proves that the chemical energy to the mechanical energy is sufficient and fast even in the nanoscale level. The silicon nanomotor shows wavelength and diameter dependent motion speed, which originates from the different absorption, in line with the results of finite-difference time domain (FDTD) simulations. These results imply a promising prospect for novel design of individually light-controlled nano/micro machines.