Theoretical and experimental study of dielectrophoretic force controlled nanowires assembly

Because of their appealing characteristics, quasi one-dimensional nanostructures like semiconducting nanowires have drawn much attention in the past decade. They can be utilized in a variety of applications such as field-effect transistors, chemical sensors, and photodectors. These devices are expected to deliver unprecedented performance because of the quantum confinement and the large surface-to-volume ratio. To fabricate these practical devices, nanowires need to be manipulated towards pre-defined electrodes in a controllable fashion. Enlightened by Pohl´s pioneering contribution in dielectrophoresis (DEP), many researchers have utilized an electric field to align the nanowires. However, assembly of nanowires by DEP are studied mainly through experimental observations so far, very little theoretical studies have been reported, which could provide useful guidance in real application. In this paper, we aim to theoretically analyze the assembly of nanowires by DEP under real conditions. In a non-uniform electric field, the nanowire is polarized and can be treated as an effective dipole, thereby receiving dielectrophoretic (DEP) force and torque, while the motion of the nanowire is hampered by the hydrodynamic drag force and drag torque, which increases the difficulty and complexity in theoretical analysis on nanowire trajectory. In our previous work, a model involving different forces and torques is constructed to simulate the nanowire trajectory. However, the Brownian motion of nanowires, which could be significant, is ignored. In this paper, a more comprehensive model considering DEP force, DEP torque, drag force, drag torque, and Brownian motion is constructed to predict the nanowire trajectory by simulation. Depending on the attaching point of the nanowire on the electrode and the length of the nanowire, the nanowire is predicted to either align with the direction of the electric field or bridge the electrodes ultimately. We also fabricated a pair of microelec- rodes and implemented experiments to dielectrophoretically assemble nanowires. The experimental results agree with the simulation results. Such agreement validated our theoretical analysis.