Observation of discrete quantum levels in multi-wall carbon nanotube quantum dots

Quantum dots with a size less than 100 nm have been fabricated in multi-wall carbon nanotubes (MWNTs) by using the local Ar beam irradiation technique for tunnel barrier formation. The electrical transport measurement has been carried out at liquid helium temperatures, and the typical Coulomb blockade characteristics have been observed. The most striking observation is the clear indication of excited states, which is not usual for MWNTs with diffusive nature. The present result originates from the shorter dot size than the mean free path in the MWNT.