Scanned gate microscopy image of single electron charging in a nanotube quantum dot. The conductance of the dot is measured at low temperatures as an electrically biased AFM tip is scanned over it. The ridges correspond to Coulomb oscillations where the charge state of the dot changes by one electron.

M.T. Woodside and P.L. McEuen, Science 296, 1098 (2002).

Image courtesy: Dr. Paul L. McEuen, Cornell University.