Optical properties and structure of the TiN–nitrogen-doped TiO₂ nanocomposite

Highlights: • Excessive N doping of TiO₂ produces TiN–N-doped TiO₂ nanocomposite. • Metal TiN-semiconductor TiO₂ interfaces may aid separation of photogenerated charge carriers. • Excessive N doping adds high density of new electronic states at the top of TiO₂ valence band. - Abstract: As one of the most versatile photocatalysts, TiO₂ is suitable for numerous environmental and energy-related applications, however its efficiency is limited by its wide band gap. Doping with anions such as nitrogen has been successful in extending the TiO₂ solar absorption into the visible spectrum, although the exact nature and optimal level of N doping are still debated. Present study shows that excessive and mostly substitutional N doping can result in an in situ formation of nanocomposite structure consisting of TiN nano-crystals embedded in the N-doped anatase TiO₂, in addition to effectively doping TiO₂ by adding electronic states at the valence band edge thereby narrowing its band gap, as reported before. The metal-semiconductor interfaces in the thin film induce local band bending in the N-doped TiO₂ phase and this may assist in separating the photogenerated charge carriers. The possible interplay between the two phases is discussed. Very low levels of N doping were found not to have any impact on the band gap of TiO₂