Effects of adsorption of alcohol and water on the electrical transport of carbon nanotubebundles

Abstract

In situ studies on the effects of physisorption of various alcohol molecules(CnH2n+1OH;n = 1–4) on the transport properties of thin films of bundled single-walled carbonnanotubes reveal large increases in the thermoelectric power (TEP)S () and four-probe resistance R () at 40 °C. Interestingly, exposure to water causes virtually no change in the TEP, although theelectrical resistance shows a change of , typical for the alcohols. We observe a simple exponential response ofS(t) and R(t) to a sudden change in the molecular pressure. The characteristic time constants ( min) for S and R are found to be essentially the same for a given molecule, indicating thatthe changes in these transport properties track each other. In fact, plots ofS versus ΔR are linear, the slopes depending on the specific molecule. The transportresults are interpreted in terms of a Boltzmann model and the introductionof a new scattering channel for charge carriers in metallic tubes due toweak interactions with physisorbed molecules. The trends in the changes inS and R with adsorption of these polar molecules can be explained on the basis of the interplaybetween the adsorption energy and the molecular coverage on the nanotube surfaces.