Adsorption of Oxygen Molecules on Individual Carbon Single-walled   Nanotubes
  Our study of the adsorption of oxygen molecules on individual semiconductiong single-walled carbon nanotubes at ambient conditions reveals that the adsorption is physisorption, that the resistance without O2 increases by ~two orders of magnitude as compared to that with O2, and that the sensitive response is due to the pinning of the Fermi level near the top of the valence band of the tube resulting from impurity states of O2 appearing above the valence band. 
A. Tchernatinsky, B. Nagabhirava, S. Desai, G. Sumanasekera, B.   Alphenaar, C.S. Jayanthi, and S.Y. Wu