Interpretation of ac dielectrophoretic behavior of tin oxide nanobelts using Maxwell stress tensor approach modeling

In order to explain the dielectrophoretic behavior of ethanol suspended tin oxide (SnO2) nanobelts observed experimentally, modeling of the ac dielectrophoresis (DEP) phenomenon is carried out. Nanobelts are a type of ribbon like semiconducting oxide nanowire with rectangular cross-sections. To calculate the DEP induced forces and torques the Maxwell stress tensor (MST) approach is used. DEP experiments have indicated negative DEP (repulsion) in the low frequency range (<100 kHz) and positive DEP (attraction) in the high frequency range (∼1–10 MHz) of the applied ac electric field. The experimentally observed DEP characteristic is unusual if the nanobelt is treated as possessing uniform bulk material electrical properties of tin oxide. Several different nanobelt models are studied using simulations to explain the unusual behavior. The model providing the best explanation is the one where the nanobelt has an electrically conductive interior and a non-conductive outer layer, depleted of charge carriers. This is consistent with the surface depletion phenomenon commonly observed in SnO2 and other semiconducting metal oxide materials. This work demonstrates the importance of surface dominant properties of nanostructures in DEP manipulation and assembly.