Nonequilibrium Green's function study of Pd4-cluster-functionalized carbon nanotubes as hydrogen sensors

Abstract

Pd-cluster-functionalized carbon nanotubes CNTs have been shown experimentally to be effective hydro- gen sensors. Semiconducting CNTs exhibit much higher sensitivity than ensemble mixed ones. Using the nonequilibrium Green?s function method combined with the density-functional theory, we simulate and con- trast 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 cause opposite effects on electron localization in the CNT backbone for the semiconducting CNT-based systems. Conse- quently Pd functionalization dramatically increases the conductance, but then it is strongly suppressed 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