| The phenomenology of gas and molecular adsorption in single wall carbon nanotubes (SWNTs) is of strong interest yet highly controversial. It is now known that the electrical transport properties of SWNTs change dramatically upon exposure to various gaseous molecules such as O2, NH 3, NO2 and chemicals such as alcohols and hydrocarbon ring molecules. However, the role of O2 in the dramatic changes in the transport properties in SWNTs is not well understood and still discussed controversially. Several microscopic processes such as charge transfer due to chemical doping of the SWNTs and modification of SWNT-metal contact have been proposed to be responsible for the changes. To address this problem we performed a detailed study of the kinetics of O2 adsorption/desorption in SWNTs by measuring the thermoelectric power of commercially available bucky paper consisting of entangled bundles of SWNTs at various temperatures. Our study reveals evidence for the existence of at least 2 adsorption sites or processes. We further observed the difference in the kinetics in as prepared bucky papers and after being subjected to high temperature annealing at 1200 C. We attribute the difference to surfactant mediated charge transfer in un-annealed bucky papers. |
