First-principles study on NO2-adsorbed tungsten oxide nanowires for sensing application

The effect of NO2 adsorption on the electronic structure, density of states and electron population of W18O49 nanowires were investigated by using the first principles calculation based on density functional theory (DFT). Two nanowire models, including largely cations W5+ and cations W6+ respectively, were first constructed, and then the most energetically favorable adsorption site was determined through the analysis of adsorption energy. NO2 adsorption introduced new electronic states in the valence band, and as a consequence, the Fermi level shifts toward the energy gap reducing the charge carrier concentration of electrons in adsorbed nanowire. Atomic Mulliken population analysis indicated that NO2 adsorption on W18O49 nanowire can cause more electrons transferred from nanowire to NO2 molecule compared with the case on WO3 nanowire, suggesting an even more potential of W18O49 nanowire in high sensitive NO2 gas sensor application.