Narrowing SWNT diameter distribution using size-separated ferritin-based Fecatalysts

Abstract

Sensors and devices made from single-walled carbon nanotubes (SWNTs) are most oftenelectrically probed through metal leads contacting the semiconducting SWNTs (s-SWNTs).Contact barriers in general and Schottky barriers (SBs) in particular are usuallyobtained at a metal–semiconductor interface. The unique one-dimensional structure(1D) of SWNTs allows tailoring of the SB heights through the contact metaltype and the size of the s-SWNT bandgap. A large workfunction reduces the SBheight (e.g. using Pd as the metal contact material). The bandgap of an SWNT isinversely proportional to its diameter. Ohmic contacts—the preferable choice—areachieved for s-SWNTs with diameters greater than 2 nm on Pd metal leads. SWNTdevice reproducibility, on the other hand, requires a narrow distribution of theSWNT diameters. Here, we present a method to fabricate SWNTs with a large andadjustable mean diameter (1.9–2.4 nm) and very narrow diameter distribution (± 0.27 nm at mean diameter 1.9 nm). The results are achieved through a size separation of theferritin catalyst particles by sedimentation velocity centrifugation prior to their use in thechemical vapor deposition (CVD) formation of SWNTs.