Effects of gas interactions on the transport properties of single-walled carbon nanotubes.

摘要

The work presented in this thesis discusses a series of in situ transport properties measurements (thermoelectric power S and electrical resistance R) on networks of randomly oriented single-walled carbon nanotube (SWNT) bundles (e.g., thin films, mats, and buckypapers), in contact with various gases and chemical vapors. Results are presented on the effects of gases that chemisorb and undergo weak charge transfer reactions with the carbon nanotubes (e.g., O2 and NH 3), gases and chemical vapors that physisorb on the tube wall (e.g., H2, alcohols, water and cyclic hydrocarbons), and gases and small molecules that undergo collisions with the carbon nanotube walls (e.g., inert gases, N2, CH4). The strong, systematic effects on the transport properties of SWNTs due to exposure to six-membered ring and polar molecules (alcohol and water) are found to increase with the quantity Ea/A, where Ea is the adsorption energy and A is the molecular projection area. The magnitudes of the remarkable effects of collisions of inert gases (He, Ne, Ar, Kr, and Xe) and small molecules (N2 and CH4) on the transport properties of SWNTs are found to be proportional to ∼ M1/3, where M is the mass of the colliding species. This is approximately the same mass dependence exhibited by the maximum deformation of the tube wall and the energy exchanged between the tube wall and the colliding atoms as a result of this collision.; A model is proposed to explain the unusual behavior of the thermoelectric power in SWNTs, wherein the metallic tubes provide the dominant contribution to this physical quantity and the observed peak at ∼ 100 K is attributed to the phonon drag effect. In addition, the details of our transport model for the behavior of the carbon nanotubes in the presence of gases and chemical vapors are presented, incorporating the effects of a new scattering channel for the charge carriers, associated with the adsorbed (or colliding) atoms and molecules. The model is found to explain qualitatively the various transport phenomena observed.