Estimation of frequency-dependent electrokinetic forces on tin oxide nanobelts in lowfrequency electric fields

Abstract

A novel experimental approach is used for studying the response of ethanol-suspendedSnO2 nanobelts under the influence of low frequency ac electric fields. The electrically generated forcesare estimated by analyzing the angular motion of the nanobelt, induced by repulsive forcesoriginating predominantly from negative dielectrophoresis (DEP) on planar microelectrodes.The nanobelt motion is experimentally recorded in real time in the low frequency range (<100 kHz) and the angular velocities are calculated. A simple analytical model of force balancebetween the electrical forces and fluidic drag for long nano-objects is developed and used todeduce estimates of the frequency-dependent DEP force and torque magnitudes from theangular velocity data. Additional experiments, performed in a parallel plate electrodeconfiguration in a fluidic channel to investigate the effect of dc and very low frequency ac (∼Hz) electric fields, indicate the presence of electrophoresis in the ethanol-suspendedSnO2 nanobelts. The experimentally observed nanobelt motion is analyzed using the equation ofmotion, and an order-of-magnitude estimate of the nanobelt surface charge density isobtained.