Work functions of pristine and alkali-metal intercalated carbon nanotubes and bundles

The work functions (WF's) of single-walled carbon nanotubes and bundles are studied using first-principles methods. For individual metallic tubes, the WF is independent of the chirality and increase slightly with tube diameter. For semiconducting tubes, the WF (as defined by the HOMO energy) decreases rapidly. The WF of nanotube bundles (similar to5 eV) shows no clear dependence on the tube size and chirality, slightly higher than individual tubes. For both metallic and semiconducting nanotubes, the WF decreases dramatically upon alkali-metal intercalation. The electronic states near the Fermi level are significantly modified and the metallic and semiconducting tube bundles become indistinguishable.