Effect of gas on individual single walled carbon nanotube bundles

SWNTs devices were prepared on silicon substrate using two different methods. The first method is to have SWNT bundles on the gold electrodes and the second method was to have gold electrodes on the SWNT bundles. For the first method the steps for sample preparation were photolithography, sputtering, liftoff, dicing. The nanotubes solution drops were put on the gold - chromium electrodes. For the second method the sample preparation were photolithography, sputtering, liftoff, dicing, e-beam lithography and evaporation. Drops of SWNT solution were put on the sample or the SWNT were grown using CVD process. AFM pictures were taken to locate the tubes along the grid pattern and then gold-titanium contact pads were put. Both the samples were wire bonded and initial testing using probe station was done. Samples were annealed in vacuum at 300°C for 3 hrs, using an annealing system.; Initial 2-probe resistance was found to be ∼300 KO. The resistance of the SWNT devices was then monitored in a sealed chamber under various gas environments. We observe a two order of magnitude increase in the resistance of a SWNT device following degassing of the sample. Theoretical analysis suggests that the O2 molecules provide acceptor impurity states to the nanotubes, which shift the Fermi energy towards the valence band. The resulting increase in positive charge carriers leads to an increase in conductance.