Nanocrystalline anatase thin films prepared by dip-coating from titania sols have been examined by electron microscopy, X-ray diffraction, Raman spectroscopy, UV-vis spectroscopy, and grazing incidence XANES and EXAFS. The original 10 nm particles in the as-prepared films retain their morphology on firing at up to 800 degreesC. X-ray diffraction and Raman spectroscopy show that the crystallinity of the films increases with firing, but the anatase is not converted to rutile at 800 degreesC. Ti K-edge XANES show the presence of high concentrations of five-coordinate titanium in the as-prepared films; this falls on firing but remains significant even after high-temperature treatment. Ti K-edge EXAFS reveals a local anatase structure around titanium in the as-prepared films which becomes more ordered with increasing firing temperature. The anomalous optical properties of the films are attributed to the presence of high defect concentrations rather than quantum size effects.
- NANOCRYSTALLINE TIO2 FILMS
- SIZE QUANTIZATION