Conductance of a conjugated molecule with carbon nanotube contacts

The conductance of an experimentally measured metallic carbon nanotube (CNT)-molecule-CNT structure is calculated. The features in the predicted transmission correspond directly to the features of the isolated molecular orbitals and surface states of the cut ends of the CNTs. The highest occupied molecular orbital (HOMO) provides a weakly coupled conductive channel with transmission features that are qualitatively insensitive to the chemical end groups of the cut CNTs, the cut angle, the CNT chirality, and the number of molecular bridges. Quantitatively, however, these factors can modify the resonance width by an order of magnitude giving rise to corresponding changes in the resistance. Furthermore, the cut ends of a zigzag CNT can have surface states which hybridize with the molecular HOMO state giving a large transmission peak at the Fermi level. To understand the molecular energy-level alignment with the CNT Fermi level, a quantum chemical calculation of the ionization potential and electron affinity and a density-functional theory calculation of the CNT image potential are performed. A twist on molecular conformation-change switching is also suggested.