Flanged nanotube–electrode junctions

A thiol linkage designed to act as a 'conducting flange' between a carbon nanotube and a gold(111) surface is investigated computationally. Such a flange could be used to anchor long nanotubes in nanotube-based devices or, using short nanotubes, to build controlled interfaces between electrodes and molecular electronic devices for use in electronic circuits on the 1 nm scale. Density-functional calculations indicate that, even though the nanotube considered is of the 'metallic type', a Schottky barrier forms at the interface which restricts charge flow to and from short-length nanotubes. In fact, at realistic applied field strengths, sufficient charge cannot be forced onto short nanotubes for them to be useful as part of a gate electrode in a 1 nm sized field-effect device. However, the electronic density of states of short flanged nanotubes is calculated to be significant at the metal Fermi energy. Hence, adequate electrical conductivity is expected through the flange under a conductance tunnelling scenario, making the junction useful in purely nanotube-based devices. Principles of mechanically sound flange design are also considered through high-temperature molecular dynamics studies. The need to establish proper gold–sulfur binding is stressed, with strained junctions involving five thiol linkages shown to lead to lower barriers to translation than one single, fully relaxed, junction.