Mechanism of H$_2$O Induced Conductance Changes in AuCl$_4$ Functionalized CNTs

Functionalized carbon nanotubes (CNTs) are promising candidates for nanoscale sensors due to their high surface-to-volume ratio and the fact that their properties are very sensitive to perturbations. We employ \textit{ab-initio} self-interaction corrected density functional theory combined with the non-equilibrium Green's function method to study the electronic and quantum transport properties of CNTs functionalized with AuCl$_4$ molecules. In particular, we investigate the electronic structure and characterize the conductance for different concentrations and configurations of randomly distributed AuCl$_4$ with and without the adsorption of H$_2$O molecules, and propose a mechanism that explains the origin of the recently observed resistivity changes of AuCl$_4$ functionalized CNTs upon H$_2$O adsorption. We find that the adsorption of H$_2$O shifts the highest occupied Cl and Au states down in energy and thereby reduces the scattering of the electrons around the Fermi level, hence enhancing the conductivity. Our results help facilitate the development of highly sensitive nanoscale H$_2$O vapor sensors based on AuCl$_4$ functionalized CNTs.