Chemical doping of individual semiconducting carbon-nanotube ropes

We report the effects of potassium doping on the conductance of individual semiconducting single-walled carbon nanotube ropes. We are able to control the level of doping by reversibly intercalating and deintercalating potassium. Potassium doping changes the carriers in the ropes from holes to electrons. Typical values for the carrier density are found to be ;100–1000 electrons/mm. The effective mobility for the electrons is meff;20–60 cm 2 V s, a value similar to that reported for the hole effective mobility in nanotubes @R. Martel et al., Appl. Phys. Lett. 73, 2447 ~1998!#.