Formation of polybromine anions and concurrent heavy hole doping in carbon nanotubes

Abstract

Using density-functional theory calculations, we investigate the atomic and electronic structure of the bromine species encapsulated in carbon nanotubes. We find that the odd-membered molecular structures (Br-3 and Br-5) are energetically favored than the common Br-2 molecule. The transformation from bromine molecules (Br-2) into Br-3 or Br-5 is found to be almost barrierless. A strong electron transfer from the nanotube to the adsorbates, which has been doubtful in previous studies, is accompanied by the formation of such odd-membered polybromine anions. We suggest that the tip-opened carbon nanotube samples can be heavily hole-doped after exposure to Br-2 gas.