Effect of localized oxygen functionalization on the conductance of metallic carbon nanotubes

A comprehensive study of the effect of covalent oxygen attachment on the transmission and conductance of armchair and metallic zigzag carbon nanotubes (CNTs) is presented. In both armchair and zigzag CNTs covalent oxygen attachment favors an ether-type bond in which the C-C bond breaks. Oxygen atoms attached on the CNT surface within the same carbon ring on parallel bonds are energetically more stable than well-separated attachments. In an armchair CNT, oxygen attachment favors the C-C bonds orthogonal to the CNT axis. Cooperative addition propagates axially along parallel orthogonal bonds. In a zigzag CNT, oxygen attachment prefers the slanted bond, and cooperative addition propagates spirally along parallel slanted bonds. Closely spaced oxygen attachment on the armchair and zigzag CNT surfaces causes a dip in transmission symmetrically away from the Fermi level at the turn-on of the first excited modes. For both armchair and zigzag CNTs, as more oxygen atoms are placed in close proximity, their levels interact and split and move closer to the Fermi level which results in broader dips in transmission closer to the Fermi level. The transmission of armchair CNTs near the charge-neutral Fermi level is relatively insensitive to a group of localized oxygen atoms compared to that of metallic zigzag CNTs. A clustered group of oxygen atoms covalently attached to a single-walled metallic zigzag CNT can result in a 1 order of magnitude drop in transmission that is asymmetric with respect to the Fermi energy resulting in a qualitative resemblance to conductance versus gate voltage curves observed experimentally. The covalent attachment of a single oxygen atom in any configuration, on either, an armchair, or zigzag metallic CNT does not give rise to a large change in conductance. Calculations use density-functional theory combined with nonequilibrium Green's functions.