First Principle Studies On Inorganic Semiconductor Nanotubes And The Support Of Gold Clusters

One-dimension nanotubes own a series of distinctive physical and chemical properties,which are different from their bulk.Therefore,there is broad application as electronic devices,gas sensors,photovoltaic materials and so on.Now the preparation of nanotubes can be achieved through different methods,however,we know little about the geometry structures and chemical reactions on the nanotube surfaces.Theoretical methods is very helpful for us to make further studies on the nanotubes.In this article,based on first principle calculation we have reported the adsorption mechanism of small gold clusters on the anatase nanotube surface;the geometry structures and electronic properties of AlAs nanotubes;the characteristics of CeO2 nanotubes and the Au atom adsorption on the surface.The main results are as follows:(1)We have discussed the geometric structures,interaction mechanism and electronic properties when small gold clusters Aux(x=1-4)absorbed onto the nanotube surface.The gold clusters prefer to stand on the nanotube surface because the reactive orbitals are in the periphery of the clusters.The average adsorption energy,the Au-O2c bond length and the Au-Tisc bond length perform odd-even oscillations with the size of Aux clusters increasing.Not only gold clusters interact with O anions,the Ti5c cations also play an important role in the bonding between gold clusters and surface.It also has been found that impurity states are introduced into the band gap of TiO2NT,which makes the visible light absorption efficiency improved.Moreover,the Fermi levels of Aux/TiO2NT have shifted toward the bottom of conduction band and Schottky barriers exist which benefits the electron-hole pairs separation.(2)The electronic structures of cubic aluminum arsenide(111)nanotubes associate closely with the chirality.The strain energies of the zigzag and armchair nanotubes are negative,which mean the AlAs nanotubes can be synthesized under certain conditions.Due to the different chiralities,the distribution patterns of Al-As bonds in the tube walls are different.The Al-Al distances of small-radius zigzag nanotubes in the same circumference are small enough leading to strong interaction between the unoccupied 3p orbitals of A1 atoms.Then the circular ?-orbitals have formed which makes the band gaps of zigzag nanotubes increase at first and then decrease,while the behavior is not exist for armchair nanotubes.(3)The strain energies are negative when the diameters of CeO2(111)nanotubes increase up to about 12 A,which means that the CeO2(111)nanotubes can exist.The Ce-O bonds perpendicular to the tube axis play an important role in the stabilization.When single Au atom is absorbed onto the outer surface we have found that the absorption energies were not big.The most stable position is not at the O top site due the curvature.We also have discussed the Au atom adsorption on the Oin vacancy.The absorption energy is as big as 2.90 eV when the Au atom is on the top site of O vacancy.Moreover,some negative charge has been partly transferred to the Au atom from the Ce3+ beside the vacancy.The Au atom bonding to the vacancy is mainly ascribed to the electrostatic interaction between Au anion and the Ce cations.