title: N doping of TiO2(110): photoemission and density-functional studies.
abstract: The electronic properties of N-doped rutile TiO2(110) have been investigated using synchrotron-based photoemission and density-functional calculations. The doping via N2+ ion bombardment leads to the implantation of N atoms (approximately 5% saturation concentration) that coexist with O vacancies. Ti 2p core level spectra show the formation of Ti3+ and a second partially reduced Ti species with oxidation states between +4 and +3. The valence region of the TiO(2-x)N(y)(110) systems exhibits a broad peak for Ti3+ near the Fermi level and N-induced features above the O 2p valence band that shift the edge up by approximately 0.5 eV. The magnitude of this shift is consistent with the "redshift" observed in the ultraviolet spectrum of N-doped TiO2. The experimental and theoretical results show the existence of attractive interactions between the dopant and O vacancies. First, the presence of N embedded in the surface layer reduces the formation energy of O vacancies. Second, the existence of O vacancies stabilizes the N impurities with respect to N2(g) formation. When oxygen vacancies and N impurities are together there is an electron transfer from the higher energy 3d band of Ti3+ to the lower energy 2p band of the N(2-) impurities.
authors.affiliation: Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: A
authors.initials: A
authors.lastname: Nambu
authors.forename: J
authors.initials: J
authors.lastname: Graciani
authors.forename: J A
authors.initials: JA
authors.lastname: Rodriguez
authors.forename: Q
authors.initials: Q
authors.lastname: Wu
authors.forename: E
authors.initials: E
authors.lastname: Fujita
authors.forename: J Fdez
authors.initials: JF
authors.lastname: Sanz