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

A novel experimental approach is used for studying the response of ethanol-suspended SnO(2) nanobelts under the influence of low frequency ac electric fields. The electrically generated forces are estimated by analyzing the angular motion of the nanobelt, induced by repulsive forces originating 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 balance between the electrical forces and fluidic drag for long nano-objects is developed and used to deduce estimates of the frequency-dependent DEP force and torque magnitudes from the angular velocity data. Additional experiments, performed in a parallel plate electrode configuration in a fluidic channel to investigate the effect of dc and very low frequency ac (approximately Hz) electric fields, indicate the presence of electrophoresis in the ethanol-suspended SnO(2) nanobelts. The experimentally observed nanobelt motion is analyzed using the equation of motion, and an order-of-magnitude estimate of the nanobelt surface charge density is obtained.