  Rhodium (Rh) is found similar to Palladium (Pd) in making near-ohmic
electrical contacts to single-walled carbon nanotubes (SWNTs) with diameters d
> ~ 1.6 nm. Non-negligible positive Schottky barriers (SBs) exist between Rh or
Pd and semiconducting SWNTs (S-SWNTs) with d < ~ 1.6 nm. With Rh and Pd
contacts, the characteristics of SWNT field-effect transistors (FETs) 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 < ~ 1.0 nm
possibly due to tunnel barriers.
