An idealized model of a carbon nanotube transistor. The metal electrode is assumed to be also a cylinder and of the same diameter as the carbon nanotube which is on the order of 1 nanometer. The cylindrical gate electrode surrounds the metal-nanotube contact.

Further reading:
S. Heinze et al., Carbon Nanotubes as Schottky Barrier Transistors, PRL 89, 106801 (2002),
S. Heinze et al., Electromigration Forces on Ions in Carbon Nanotubes, PRL 95, 186802 (2005),
N.-P. Wang et al., Random-telegraph-signal noise and device variability in nanotube transistors, Nano Lett. 7, 910 (2007).