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Suppression of photocatalytic efficiency in highly N-doped anatase films

2005; American Physical Society; Volume: 72; Issue: 11 Linguagem: Inglês

10.1103/physrevb.72.115124

1550-235X

Takeshi Okato, Tatsunori Sakano, Minoru Obara,

TiO2 Photocatalysis and Solar Cells

We report the role of N in epitaxial films of anatase $\mathrm{Ti}{\mathrm{O}}_{2}$. The films were artificially grown with a two-step temperature-tuned epitaxy which utilized the high-temperature cubic phase of $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ substrates. The preparation of highly crystallized anatase with various N concentrations $({C}_{\mathrm{N}}\ensuremath{\leqslant}3.85\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.2em}{0ex}}%)$ allowed us to identify the optimum dopant concentration $({C}_{\mathrm{N}}=1--2\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.2em}{0ex}}%)$. At higher doping levels, N is found to be difficult to substitute for O having been predicted to contribute to the band-gap narrowing, giving rise to the undesirable deep-level defects. In addition, a study by x-ray and Raman spectroscopy revealed that the growth of anatase became more difficult, and the stable phase was shifted to rutile at the higher N concentrations.