Effects of air exposure and Cs deposition on the electronic structure of multiwalled carbon nanotubes

Electronic structural changes in multiwalled carbon nanotubes caused by adsorbates and Cs deposition were studied by photoemission spectroscopy. The adsorbates formed by air exposure slightly increased the work function. The increased work function is considered to be due to the surface dipole moment induced by the negatively charged adsorbates. On the other hand, the Cs deposition followed by the intercalation drastically decreased the work function. The results suggest that field emission current enhancement induced by adsorbates and by Cs deposition are based on essentially different mechanisms; that is, the former is associated with the formation of localized electronic states and the latter is mainly due to the work function decrease.