Electron transport through molecular-carbon nanotube interfaces

Investigations have focused on electron transport through metal-molecule systems. Less effort has been directed towards semiconductor-molecule systems, and the least attention has been given to electron transport through carbon nanotube-molecule systems. A specific implementation of the latter system consists of two CNTs joined by a molecule, or a CNT-molecule-CNT system. Such a system can provide the electronic functionality of a resonant tunnel diode. The molecular contacts, i.e. the CNTs, are a $\pi $-bond surface and, as such, they are both chemically and geometrically different from metal contacts or sp$^{3}$ semiconductor contacts. A model system is studied to focus solely on the interface geometry of two simple $\pi $-bond systems, CNTs and polyacetylene (CH)$_{n}$. The system is CNT-(CH)$_{n}$-CNT. At the interface, in the relaxed structure, the (CH)$_{n}$ is oriented coplanarly with the tangential plane of the CNT. The transmission, calculated with our DFT (FIREBALL)-NEGF code is, on average, 3 or more orders of magnitude larger than the transmission of an unrelaxed structure in which the (CH)$_{n}$ is perpendicular to the CNT at the point of contact. This is also true when the (CH)$_{n}$ of the relaxed structure undergoes a 180$^{o}$ twist. Interface geometry plays a crucial role in the electron transport.