Soft X-ray absorption study of tantalum incorporation in titanium oxide films: Impact of flash-lamp annealing

The impact of Ta incorporation (up to ~21 at.%) in titanium dioxide (TiO2) films subjected to post-deposition millisecond-range flash-lamp annealing (FLA) is addressed. Phase formation with short-range information was established by means of soft X-ray absorption near-edge structure (XANES) in combination with standard X-ray diffraction. As-grown films are X-ray amorphous, but display a significant structural improvement upon FLA. Up to relatively large Ta concentrations (~ 12 at.%), FLA can be used to effectively incorporate Ta into a nanocrystalline anatase TiO2 phase, although its structural quality deteriorates progressively with the Ta content. For the intermediate Ta range between 12 and 17 at.%, the structure of the FLA films is highly disordered, being unable to overcome the initial distorted arrangement. In any case, rutile- or Ta2O5-like environments emerge for low and high contents, respectively. Finally, for the highest Ta content (~21 at.%), the formation of good-quality nanocrystalline Ta2O5 phase occurs after FLA. As assessed by XANES, the structural evolution upon FLA seems to be determined by the initial (amorphous) structure. Lastly, all the samples are highly transparent from the visible to the near-infrared region, and the band-gap can be tailored from ~3.2 to ~3.8 eV with increasing the amount of incorporated Ta.