Abstract
Pd-cluster-functionalized carbon nanotubes (CNTs) have been shown experimentally to be effective hydrogen sensors. Semiconducting CNTs exhibit much higher sensitivity than ensemble (mixed) ones. Using the non-equilibrium Green's function method combined with the density functional theory, we simulate and contrast the (8,0) semiconducting and the (5,5) metallic CNT model systems. We find that the electron localization effect plays a crucial role in determining electron transport. Pd clusters and hydrogen adsorption causes opposite effects on electron localization in the CNT backbone for the semiconducting CNT based systems. Consequently Pd-functionalization dramatically increases the conductance but then it is strongly supressed by hydrogen absorption. For the
metallic CNT based systems, there is a tiny shift of the transmission peak near the Fermi energy. These results offer a consistent explanation for the experiments.