Band Gap Tailoring of TiO2 Nanowires by Nitrogen Doping Under N2/Ar Plasma Environment

Glancing angle deposited TiO2 nanowires (NWs) were doped with nitrogen (N) using plasma-enhanced chemical vapour deposition technique, under the treatment of N-2/Ar plasma. A red shift (similar to 0.51 eV) in the main band transition and oxygen defect related transition (similar to 2.1 eV) was observed for the N doped TiO2 nanowires. The interstitial nitrogen introduces mid-gap levels N (2P) above the O (2P) in the TiO2 forbidden gap. The photoluminescence measurement revealed a small red shift of similar to 7 nm of anatase band gap from N doped TiO2 nanowires due to radiative recombination of carriers from conduction band to the N (2P) trap state. The low frequency Raman peaks at 304 cm(-1) (acoustical phonons with LA mode), 618 cm(-1) (optical phonons with LO modes) and the high frequency peak at 832 cm(-1) was observed from Ti-O-N due to the partial replacement of oxygen molecules by nitrogen into TiO2, during the doping process.