Production of individual suspended single-walled carbon nanotubes using the ac electrophoresis technique

We have developed a new method for aligning individual suspended single-walled carbon nanotubes (SWNTs) using a combination of the ac electrophoresis technique and electron beam lithography. A poly(methyl methacrylate) (PMMA) "underpinning" was used in the region between the Au electrodes to prevent the carbon nanotube (CNT) from falling down on to the substrate. O₂ plasma ashing was used to control the height of the underpinning PMMA layer so that it was same as that of the pre-defined electrodes. The biggest advantage of this method is that one can easily align the suspended nanostructure in a controllable manner. This method can also be applied to making suspended structures of organic materials that are sensitive to acid treatment. We measured the temperature-dependent I-V characteristics of the suspended SWNTs and found that most of the aligned SWNTs were metallic.