title: Orientation-dependent chemistry and band-bending of Ti on polar ZnO surfaces.
abstract: Orientation-dependent reactivity and band-bending are evidenced upon Ti deposition (1-10 Å) on polar ZnO(0001)-Zn and ZnO(0001[combining macron])-O surfaces. At the onset of the Ti deposition, a downward band-bending was observed on ZnO(0001[combining macron])-O while no change occurred on ZnO(0001)-Zn. Combining this with the photoemission analysis of the Ti 2p core level and Zn L3(L2)M45M45Auger transition, it is established that the Ti/ZnO reaction is of the form Ti + 2ZnO → TiO2+ 2Zn on ZnO(0001)-Zn and Ti + yZnO → TiZnxOy+ (y - x)Zn on ZnO(0001[combining macron])-O. Consistently, upon annealing thicker Ti adlayers, the metallic zinc is removed to leave ZnO(0001)-Zn surfaces covered with a TiO2-like phase and ZnO(0001[combining macron])-O surfaces covered with a defined (Ti, Zn, O) compound. Finally, a difference in the activation temperature between the O-terminated (500 K) and Zn-terminated (700 K) surfaces is observed, which is tentatively explained by different electric fields in the space charge layer at ZnO surfaces.
authors.affiliation: Sorbonne Universités, CNRS-UMR 7588, UPMC Univ Paris 06, Institut des NanoSciences de Paris, F-75005, Paris, France. patrizia.borghetti@insp.jussieu.fr.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Borghetti
authors.forename: Younes
authors.initials: Y
authors.lastname: Mouchaal
authors.forename: Zongbei
authors.initials: Z
authors.lastname: Dai
authors.forename: Gregory
authors.initials: G
authors.lastname: Cabailh
authors.forename: Stéphane
authors.initials: S
authors.lastname: Chenot
authors.forename: Rémi
authors.initials: R
authors.lastname: Lazzari
authors.forename: Jacques
authors.initials: J
authors.lastname: Jupille