Metallization of the semiconducting carbon nanotube by encapsulated bromine molecules

We use ab initio density-functional calculations to investigate the electronic structure of the bromine-adsorbed carbon nanotubes. When a Br-2 molecule is inside the (10,0) carbon nanotube, a trace of electron charge transfers from the nanotube to the Br-2 adsorbate, resulting in an increased Br-Br bond length. When the supercell contains two Br-2 molecules, total energy calculations reveal the formation of a linear chain of bromine atoms inside the carbon nanotube. Electron transfer from the nanotube to the atomic chains of the bromine adsorbates is much enhanced even in large-diameter nanotubes. We suggest that an exposure of the tip-opened carbon nanotube samples to a modest Br-2 partial pressure could result in a strong hole-doping of the nanotube, which makes the semiconducting nanotubes nearly metallic. (c) 2005 Elsevier B.V. All rights reserved.