Surface conductance induced dielectrophoresis of semiconducting single-walled carbon nanotubes

Dielectrophoresis on surfactant-stabilized single-walled carbon nanotube (SWNT) suspensions has been demonstrated to separate metallic from semiconducting tubes by their different electric field-induced polarizabilities. Here we report that the interaction between SWNTs and the surfactant induces a nanotube surface conductance which gives rise to a unique electric field frequency dependence of the nanotube dielectrophoresis. We observe a surfactant concentration dependent crossover frequency enabling separation of metallic from semiconducting SWNTs at high frequency and deposition of metallic and semiconducting SWNTs at low frequency - both being important aspects for building nanotube-based electronics. Moreover, the data demonstrate that the theoretical description of dielectrophoretic forces is valid beyond the dimensions of cells or viruses.