Engineering carbon nanotubes and nanotube circuits using electrical breakdown

Carbon nanotubes display either metallic or semiconducting properties. Both Large, multiwalled nanotubes (MWNTs), with many concentric carbon shells, and bundles or "ropes" of aligned single-walled nanotubes (SWNTs), are comp lex composite conductors that incorporate many weakly coupled nanotubes tha t each have a different electronic structure. Here we demonstrate a simple and reliable method for selectively removing single carbon shells from MWNT s and SWNT ropes to tailor the properties of these composite nanotubes. We can remove shells of MWNTs stepwise and individually characterize the diffe rent shells. By choosing among the shells, we can convert a MWNT into eithe r a metallic or a semiconducting conductor, as well as directly address the issue of multiple-shell transport. With SWNT ropes, similar selectivity al lows us to generate entire arrays of nanoscale field-effect transistors bas ed solely on the fraction of semiconducting SWNTs.