Development of an energy barrier at the metal-chain-metallic-carbon-nanotube nanocontact

We perform ab initio pseudopotential calculations for a nanocontact between a metallic carbon nanotube and a copper chain. We find that the on-top pos ition is the most stable geometry of the copper chain on the nanotube and a local energy gap of less than or similar to 0.1 eV opens as the mirror sym metry of the nanotube is broken by the presence of copper. A weak ionic bon ding is formed between the tube and the copper chain and the charge density in the conducting channel around the Fermi level is reduced at the contact region. Therefore, the electronic transport across the contact occurs esse ntially through the tunneling process. Appearance of such a locally semicon ducting property in the intrinsically metallic carbon nanotube may explain the unusual low-temperature current-voltage characteristics exhibiting a hu ge contact resistance or a quantum dot behavior. [S0163-1829(99)05831-2].