Influence of Nitrogen Doping on the Defect Formation and Surface Properties ofTiO2Rutile and Anatase

Abstract

Nitrogen doping-induced changes in the electronic properties, defect formation, and surface structure of TiO2 rutile(110) and anatase(101) single crystals were investigated. No band gap narrowing is observed, but N doping induces localized N 2p states within the band gap just above the valence band. N is present in a N(III) valence state, which facilitates the formation of oxygen vacancies and Ti 3d band gap states at elevated temperatures. The increased O vacancy formation triggers the 1 x 2 reconstruction of the rutile (110) surface. This thermal instability may degrade the catalyst during applications.

Synergistic Effects on Band Gap-Narrowing in Titania by Codoping from First-Principles Calculations

“…The environment acts as a reservoir, which can give or take any amount of oxygen without changing its temperature and pressure [26]. [29], and N ions [30], it configuration of N 2 to calculate nitrogen's chemical potential by many authors [25,31]. Furthermore, this avoids the introduction of any other impurity atoms into the TiO 2 lattice besides the dopant sources themselves.…”

Comment on “Enhancement of room temperature ferromagnetism in N-doped TiO2−x rutile: Correlation with the local electronic properties” [Appl. Phys. Lett. 97, 012506 (2010)]

“…4,5 This prediction has been further confirmed by the photoemission spectroscopic and scanning tunnelling microscopic ͑STM͒ results with appearance of the Ti 3+ 2p should peak in the core level spectrum, Ti 3d emission line in the valence band spectrum both for the rutile and anantase TiO 2 , and increase of the surface vacancies in the STM images at a N-doping rate of 3%. 3 Actually, increase of oxygen vacancy concentration in TiO 2 could also be found for Fe-, Co-doped TiO 2 in order to compensate for the Fe or Co charge. [6][7][8] These oxygen vacancies are believed to play an important role in explaining the coupling of the magnetic moments in the dilute ferromagnetic oxides.…”

“…This assignment can also be proved by the previous literature. 2,3 The BE of N 1s is even lower than that of titanium nitride, suggesting more charge transfer to the N ions and further oxidizing the Ti ions ͑e.g., from Ti 3+ to Ti 4+ ͒. This will break the charge balance in the TiO 2 system.…”

Response to “Comment on ‘Enhancement of room temperature ferromagnetism in N-doped TiO2−x rutile: Correlation with the local electronic properties’ ” [Appl. Phys. Lett. 97, 186101(2010)]

“…2͔, is therefore ascribed to CT of excess electrons to N, rather than to molecules adsorbed on the surface. As reported in literature, 8 the Ti 3d in-gap states are restored upon annealing in vacuum, a treatment that produces V O s. We avoided this treatment, as the increase of the V O density is known to change the saturation magnetization of ferromagnetic TiO 2−x samples ͑see, e.g., Ref. 9͒.…”