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 Br2 molecule is inside the (10,0) carbon nanotube, a trace of electron charge transfers from the nanotube to the Br2 adsorbate, resulting in an increased Br–Br bond length. When the supercell contains two Br2 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 Br2 partial pressure could result in a strong hole-doping of the nanotube, which makes the semiconducting nanotubes nearly metallic.