The geometrical and electronic structures of open-end fully functionalized single-walled carbon nanotubes

Abstract

We have investigated the geometrical and electronic structures of open-end single-walled carbon nanotubes (SWNTs) having chemically modified tips, using semi-empirical AM1 and density functional theory methods. The hydroxyl (–OH), carboxyl (–COOH) and amide (–CONH2) functional groups were used to saturate the open-ends of nanotubes. The effects of functional groups were studied by comparison with the pristine tubes, of which the tubular lengths vary from two to ten unit-cells (40 Å). The results show that the C–C bond lengths of all model tubes are only slightly different, and the behavior of converging bond lengths in COOH– and CONH2-SWNTs is very similar to the pristine tube. Tip functionalization alters the frontier orbitals of the pristine tube, but these effects seem to rapidly decrease as the tubule becomes longer. In general, it can be concluded that the geometrical and electronic structures of pristine tubes after tube-end “full” functionalization will be preserved, hence supporting that more real-world “partially” functionalized SWNTs can be used in the same way as the pristine version in most application areas.