Surajit Kumar

Ac Dielectrophoresis of Tin Oxide Nanobelts Suspended in Ethanol: Manipulation and Visualization

This article presents results of detailed and direct real-time observations of the wide variety of SnO(2) nanobelt motions induced by ac dielectrophoresis (DEP) in an innovative microfluidic setup. High ac electric fields were generated on a gold microelectrode (approximately 20 microm electrode gap) array, patterned on a glass substrate and covered by a approximately 10 microm tall polydimethylsiloxane (PDMS) microchannel. Ethanol suspended SnO(2) nanobelts were introduced into the microchannel, and the DEP experiments were performed. Negative DEP (repulsion) of the nanobelts was observed in the low-frequency range (<100 kHz) of the applied electric field, which caused rigid body motion as well as deformation of the nanobelts. The negative DEP effect observed in ethanol is unusual and contrary to what is predicted by the Clausius-Mossotti factor (using bulk SnO(2) conductivity and permittivity values) of the dipole approximation theory. In the high-frequency range (approximately 1-10 MHz), positive DEP (attraction) of the nanobelts was observed. Pearl chain formation involving short nanobelts and particles was also observed in the two DEP regimes.

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.

Visible light response of tin oxide nanobelts

In the present work we report the effect of visible (VIS) light on the conductivity of SnO2 nanobelts. The existence of visible light effect is unusual, since bulk SnO2 is a wide band gap semiconductor. Two types of nanobelt alignment/trapping methods were used in fabricating devices for study of the visible light effect. Fluid flow alignment was used for making individual nanobelt devices, while AC dielectrophoresis was used to trap multiple nanobelts. DC current passing through the SnO2 nanobelt devices was monitored under VIS and UV light illumination. Visible photoluminescence was also observed in the nanobelt samples.

Dielectrophoretic Characterization of SnO2 Nanobelts

In the present work we report the results of AC dielectrophoresis experiments on ethanol suspended SnO2 nanobelts. AC field (frequency ~ 5 Hz - 10 MHz) was applied between microelectrodes, and detailed and direct observations of the nanobelt motion were performed. It revealed a wide variety of nanobelt motions induced by the dielectrophoretic forces, which include attraction and repulsion depending on the signal frequency range. These forces caused rigid body motion and deformation in long nanobelts, and pearl chain formation in short nanobelts and particles. The presence of negative (repulsion) dielectrophoresis is unusual in SnO2, since bulk material properties dictate positive dielectrophoresis in the frequency range studied.