Research On The Electronic Structure Of Tungsten Oxide Nanowires And Its Gas Adsorption Properties

WO₃is a wide band gap semiconductor material, which has good applicationprospect and widely use in the field of the sensor, field emission, the light emittingdevices, etc. Especially, the one-dimensional WO₃nanowires are sensitive materialwith excellent performance, which can be used to dangerous and toxic high-sensitivitygas detection. In this thesis, the electronic structure of WO₃nanowires with differentsurfaces, directions and diameters are investigated by using the first principlescalculation based on density functional theory （DFT）.The terminated-surface structure of WO₃nanowires can affect the electronic bandstructure, band gap and density of states significantly. The band gap of WO₃nanowires with hydrogenated oxygen monolayer is wider0.257eV than bulk WO₃due to quantum confinement effect; The WO₃nanowires terminated-surface with bareoxygen has a lot of electrons in the fermi level for the structure of O=O, WhileWO2-terminated WO₃nanowire show metallic property. As the size of the nanowiredecreases, the calculated band gap increases along with the stronger quantumconfinement effect in thinner wires. The electrons are rearranged for the nanowiresorientations. The quantum confinement effect and periodical long and short O-O caneffect the band gap of [001]-oriented WO₃nanowires. The band gap’s change of the[001]-oriented WO₃nanowires are not always obey to quantum confinement effect.When the dangling bonds are saturated, the WO₃nanowires are in a stable statewith low surface state. Then NO2is adsorbed on WO₃nanowires with hydrogenatedoxygen monolayer, only0.04e transfers from NO2to WO₃nanowires, which isdifficult for the sensors to get high sensitivity. High sensitivity needs high surfacestates. When the O-terminated WO₃nanowires adsorbs oxygen ions in the surface,there are not only NO2transfers electrons but also more electrons transfer to surfaceoxygen. The additional electrons transfer account for NO2high sensitivity, whichexplains the gas sensitive mechanism in microscopic view.