Plasma Nitriding of TiO(2) Nanotubes: N-Doping in Situ Investigations Using XPS

[Image: see text] The nitrogen doping of titanium dioxide nanotubes (TiO(2) NTs) was investigated as a result of well-controlled plasma nitriding of TiO(2) NTs at a low temperature. This way of nitrogen doping is proposed as an alternative to chemical/electrochemical methods. The plasma nitriding process was performed in a preparation chamber connected to an X-ray photoelectron spectroscopy (XPS) spectrometer, and the nitrogen-doped TiO(2) NTs were next investigated in situ by XPS in the same ultrahigh vacuum (UHV) system. The collected high-resolution (HR) XPS spectra of N 1s, Ti 2p, O 1s, C 1s, and valence band (VB) revealed the formation of chemical bonds between titanium, nitrogen, and oxygen atoms as substitutional or interstitial species. Moreover, the results provided a characterization of the electronic states of N–TiO(2) NTs generated by various plasma nitriding and annealing treatments. The VB XPS spectrum showed a reduction in the TiO(2) band gap of about 0.6 eV for optimal nitriding and heat-treated conditions. The TiO(2) NTs annealed at 450 or 650 °C in air (ex situ) and nitrided under UHV conditions were used as reference materials to check the formation of Ti–N bonds in the TiO(2) lattice with a well-defined structure (anatase or a mixture of anatase and rutile). Scanning electron microscopy microscopic observations of the received materials were used to evaluate the morphology of the TiO(2) NTs after each step of the nitriding and annealing treatments.