Simulation and Experimental Study of Nanowire Assembly by Dielectrophoresis

Although dielectrophoretic (DEP) assembly has been demonstrated to be an efficient way to align nanowires or nanotubes for making nanodevices based on one-dimensional nanostructures, misalignment is often observed in experimental implementation. This unfavorable observation discourages researchers´ enthusiasm in making devices by DEP. To make DEP assembly in a controllable fashion, theoretical and simulation studies are indispensable. However, traditional analysis on DEP is based on a zero-dimensional model derived from the interaction between a nonuniform electric field and dielectric particles, which might not be directly applicable to nanowires or nanotubes. In this paper, we propose an approach similar to finite element method to calculate the total DEP force and torque on the one-dimensional nanostructure by considering the dimensional effect. It is shown from the simulation that the magnitude of DEP force is related to the conductivity of the nanostructure and the frequency of the electric field, which provides feasibility on controllable and selective assembly of the nanowires or nanotubes. To study the trajectory of single nanowire or nanotube assembled by DEP, a comprehensive model involving DEP force, DEP torque, drag force, drag torque, and Brownian motion is proposed. The one-dimensional nanostructure is predicted from the simulation to either attach one electrode and align at certain direction or bridge the electrodes. The theoretical and simulation study indicate that the alignment of one-dimensional nanostructure is mainly related to its length, the gap size of the electrodes as well as the initial contact position of the nanowire or nanotube onto the electrode. The predication from the simulation has been confirmed by assembled zinc oxide nanowires and carbon nanotubes using DEP.