Local electronic properties of single-wall nanotube circuits measured by conducting-tip AFM

We use conducting-tip atomic force microscopy (AFM) to measure local electronic properties of single-wall carbon nanotube (SWNT) circuits on insulating substrates. When a voltage is applied to the tip and AFM feedback is used to position the tip, images formed from the tip-sample tunnel current have single tube resolution (near 1 nm diameter), more than an order of magnitude better than simultaneously acquired topographic AFM images. By finding points where the tip-sample current is zero, it is possible to measure the electrochemical potential within the circuit, again with nanometer resolution. Such measurements provide compelling evidence that nanotubes within a bundle have only weak electronic coupling. Finally, the AFM tip is used as a local electrostatic gate, and the gating action can be correlated with the structure of the SWNT bundle sample. This technique should be useful for a broad range of circuits containing SWNT's and other molecules.