Direct fabrication of carbon nanotube circuits by selective area chemical vapour deposition on pre-patterned structures

We report on a method for self-assembly of integrated carbon nanotube circuits using selective area chemical vapour deposition on pre-patterned catalyst electrodes. The circuits consist of a multi-wall carbon nanotube bridging a pair of electrodes, forming a metal/carbon nanotube/metal structure. Electron-beam lithography was used to define electrode sets separated by a desired distance on a 500 nm thick SiO₂ film on Si substrates. Following metal evaporation and lift-off, chemical vapour deposition was used for selective growth of carbon nanotubes on the catalyst electrodes. The carbon nanotubes eventually form a bridge between nearby electrodes consisting of one, or in some cases more than one, multi-wall nanotube. The resistance of the carbon nanotube circuits at room temperature is typically less than 100 kΩ. For a few high-resistance samples (≫100 kΩ) transport properties were studied in a temperature range from room temperature to 2 K. At room temperature the I-V is linear. The resistance increases with decreasing temperature, and the I-V gradually becomes nonlinear. At low temperatures a gap appears around V = 0 suggesting semiconducting behaviour.