US Patent 7719032 - MWCNT transistor

http://www.freepatentsonline.com/7719032.html

Multiwall carbon nanotubes tend to have metallic rather than semiconductor electronic properties and thus have conventionally been considered inappropriate to form transistor channels. However, this patent from Sony teaches a way to use the inner carbon shell as the electrode contact and the outer carbon shell as a semiconductor channel which may allow multiwall carbon nanotube transistors (although mass production could be problematic).
Claim 5 reads:

5. An electronic device including a multi-walled carbon nanotube having at least two layers, the electronic device comprising:

a field effect transistor comprising:

an outer carbon nanotube having semiconductivity;

an inner carbon nanotube that is partially included in the outer carbon nanotube;

a current-input terminal that inputs current to the outer carbon nanotube;

a current-output terminal that outputs current from the outer carbon nanotube; and

an electrode in contact with the inner carbon nanotube and applying voltage to the inner carbon nanotube to control operation of a conduction channel of the field effect transistor formed in the outer carbon nanotube between the current-input terminal and the current-output terminal.