Rutile to anatase phase transition induced by N doping in highly oriented TiO2 films

Highly oriented TiO2 thin films were deposited onto Al2O3(0001), SrTiO3(001), and LaAlO3(001) substrates by spin coating a titanium alkoxide precursor solution followed by annealing. The films were nitrogen doped by two different routes: either by adding tetramethyethylenediamine (TMEDA) to the precursor solution or alternatively by high temperature ammonolysis. Undoped TiO2 films were highly oriented and the phase was dependent on the substrate. N doping by ammonolysis led to transformation of rutile films to anatase, confirmed by XRD and by XPS valence band spectroscopy. Significant differences were observed in the spatial distribution of the nitrogen dopant depending upon which synthesis method was used. These two factors may shed light on the increased photocatalytic efficiencies reported in N doped TiO2.