Atomic and electronic structures of fluorinated single-walled carbon nanotubes

We have investigated stable adsorption geometries of fluorine atoms on a single-walled carbon nanotube (SWNT) using density-functional calculations. Chemisorption of fluorine atoms induces heavy strain on the tube wall, giving rise to one of the C-C back bonds of 1.54 Angstrom, single bonded similar to that of diamond. We find that at coverage of 0.5, the most stable isomer is a ladder-type on an armchair nanotube, whereas it is a helical-type on a zigzag tube, both revealing a semiconducting behavior. This is in good agreement with the experimental observations that the fluorinated SWNT's increase the resistivity by decreasing the electronic density of states near the Fermi level. We also demonstrate that the electron-beam-induced structural deformation of the fluorinated SWNT's could be explained by a selective desorption of fluorine atoms. Various types of isomers, relative stability, and electronic properties at different coverages will be further discussed.