Electrical contacts to carbon nanotubes down to 1nm in diameter

Rhodium (Rh) is found similar to Palladium (Pd) in making near-Ohmic electrical contacts to single-walled carbon nanotubes (SWNTs) with diameters $d>\sim 1.6\mathrm{nm}$ . Non-negligible positive Schottky barriers (SBs) exist between Rh or Pd and semiconducting SWNTs ($S$ -SWNTs) with $d<\sim 1.6\mathrm{nm}$ . With Rh and Pd contacts, the characteristics of SWNT field-effect transistors and SB heights at the contacts are largely predictable based on the SWNT diameters, without random variations among devices. Surprisingly, electrical contacts to metallic SWNTs (M-SWNTs) also appear to be diameter dependent especially for small SWNTs. Ohmic contacts are difficult for M-SWNTs with diameters $⩽\sim 1.0\mathrm{nm}$ possibly due to tunnel barriers resulted from large perturbation of contacting metal to very small diameter SWNTs due to high chemical reactivity of the latter.