Influences of ac electric field on the spatial distribution of carbon nanotubes formed between electrodes

Influences of ac electric field on the spatial distribution of single wall carbon nanotubes (SWCNTs) between two adjacent electrodes have been studied. The SWCNTs are found to be well aligned with the electric field direction and the number density of the SWCNTs attached to the electrodes is increased with the magnitude of the electric field. Induced ac dielectrophoresis force and torque on the SWCNTs are analyzed. It is suggested that the SWCNTs rotate to align with the external field direction almost instantaneously once the electric field is applied. In contrast, the translational motion along the field gradient takes a much longer time. Our results show that it is possible to separate metallic and semiconducting SWCNTs by frequency tuning. Taking the influences of frequency and viscosity into consideration, we simulate the distributions of SWCNTs between different electrode structures. Both theoretical and experimental results show that perpendicular electrodes have better control over the SWCNT's location and direction than parallel electrodes.