The future micro/nanorobots require high degrees of freedom in motion control to perform complex tasks by individuals or by a swarm. It remains a great challenge to control the motions of an individual nanomachine amidst many, to switch the operation modes facilely, and it is even more difficult to actuate several components of a nanomachine coordinately for purposed actions. This high degree of versatility is essential for the future micro/nanorobots and requires investigation of innovative actuation mechanisms. In this dissertation, we report our recent finding about a new approach combining two types of stimulation to achieve such goal. The micromotors being studied are made of semiconductor silicon nanowires. Mechanical motion of the motors is driven by several types of AC electric field. Meanwhile, the electrical property of the nanowires can be locally and instantaneously modulated by visible light illumination in a reversible manner. We demonstrate that visible light is able to change the electric polarization of semiconductor nanowires under AC electric field, and reflected by the dramatic change of mechanical motions with very rich configurations. Under a rotating electric field, the rotation speed of semiconductor Si nanowires in electric fields can instantly increase, decrease, and even reverse the orientation by light illumination in the visible to infrared regime at various AC E-field frequencies. Under a linear AC electric field, instantaneous change of alignment direction and speed of semiconductor nanowires is observed under visible-light exposure. With theoretical analysis and simulation, the working principle can be attributed to the optically tuned imaginary-part (out-phase) and real-part (in-phase) electrical polarization of a semiconductor nanowire in aqueous suspension. Based on the understanding of this system, we further propose a new approach to control the semiconductor micromotor via light tunable dielectrophoresis. Localized control of collective behavior in a highly density silicon nanowire suspension is also investigated. Finally, we demonstrated how to utilize the mechanical motion at microscale for practical application of biosensing.Materials Science and Engineerin
