AVS 58th Annual International Symposium and Exhibition
    Energy Frontiers Focus Topic Wednesday Sessions
       Session EN2+TF-WeA

Paper EN2+TF-WeA7
N-doped SrTiO3(100) Epitaxial Films for Fundamental Studies of Visible Light Active Photocatalysts

Wednesday, November 2, 2011, 4:00 pm, Room 106

Session: Thin Films for Solar Fuels
Presenter: Tim Luttrell, University of South Florida
Authors: T. Luttrell, University of South Florida
M. Batzill, University of South Florida
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N-doping of photocatalysts, in particular TiO2, has been extensively studied for its ability to increase visible light activity. However, the solubility of N in TiO2 is limited to ~ 2% and thus limits the visible light absorption. One reason for the low solubility of nitrogen is the different preferred charge state of nitrogen (3-) compared to the substituted oxygen (2-) anions. Here, we investigate the less studied perovskite SrTiO3, which has similar photocatalytic activity to TiO2. Because a wide range of oxides crystallize in the perovskite structure, we anticipate that charge compensating co-doping in N:SrTiO3 can be more easily accomplished than in TiO2. Such co-doping may result in a higher achievable N-concentration. In our studies, the stability of N-doping in SrTiO3 and the effect of co-doping have been investigated in thin films. High quality pure and N-doped epitaxial films of SrTiO3 have been grown on LaAlO3(100) substrates by pulsed laser deposition (PLD). The structural and electronic properties have been investigated, by x-ray and UV photoemission spectroscopy (XPS and UPS) and ex-situ atomic force microscopy (AFM). N-doping was accomplished by deposition in an ammonia atmosphere. N3- ions are substituting for O2- ions in the SrTiO3 matrix and thus cause a charge imbalance that is compensated for in pure films by formation of oxygen vacancies. To avoid this defect formation, substitution of the quadrivalent cations in SrTiO3 by co-doping with La5+ is investigated. La co-doping allows a higher nitrogen solubility in SrTiO3. Nitrogen doping causes a band gap narrowing due to formation of filled N-2p states at the top of the valence band and thus an increase in visible light adsorption. The UV and visible light photocatalytic activity is assessed by decomposition of methyl orange.