Scanning electrochemical microscopy of individual single-walled carbon nanotubes

Here we report on the novel application of scanning electrochemical microscopy (SECM) to enable spatially resolved electrochemical characterization of individual single-walled carbon nanotubes (SWNTs). The feedback imaging mode of SECM was employed to detect a pristine SWNT (∼1.6 nm in diameter and ∼2 mm in length) grown horizontally on a SiO₂ surface by chemical vapor deposition. The resulting image demonstrates that the individual nanotube under an unbiased condition is highly active for the redox reaction of ferrocenylmethyltrimethylammonium used as a mediator. Micrometerscale resolution of the image is determined by the diameter of a disk-shaped SECM probe rather than by the nanotube diameter as assessed using 1.5 and 10 μm diameter probes. Interestingly, the long SWNT is readily detectable using the larger probe although the active SWNT covers only ∼0.05% of the insulating surface just under the tip. This high sensitivity of the SECM feedback method is ascribed to efficient mass transport and facile electron transfer at the individual SWNT.