N doping of Ti O 2 ( 110 ) : Photoemission and density-functional studies

• Published in: The Journal of chemical physics 2006-09, Vol.125 (9), p.094706-094706-8
• Main Authors: Nambu, A., Graciani, J., Rodriguez, J. A., Wu, Q., Fujita, E., Fdez Sanz, J.
• Format: Article
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.2345062

The electronic properties of N-doped rutile Ti O 2 ( 110 ) have been investigated using synchrotron-based photoemission and density-functional calculations. The doping via N 2 + ion bombardment leads to the implantation of N atoms ( ∼ 5 % saturation concentration) that coexist with O vacancies. Ti 2 p core level spectra show the formation of Ti 3 + and a second partially reduced Ti species with oxidation states between + 4 and + 3 . The valence region of the Ti O 2 − x N y ( 110 ) systems exhibits a broad peak for Ti 3 + near the Fermi level and N-induced features above the O 2 p valence band that shift the edge up by ∼ 0.5 eV . The magnitude of this shift is consistent with the "redshift" observed in the ultraviolet spectrum of N-doped Ti O 2 . 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 N 2 ( g ) formation. When oxygen vacancies and N impurities are together there is an electron transfer from the higher energy 3 d band of Ti 3 + to the lower energy 2 p band of the N 2 − impurities.