Thin Films of TiO<SUB>2</SUB>:N for Photo-Electrochemical Applications

Abstract

Dc-pulsed magnetron sputtering from Ti target in reactive Ar+O2+N2 atmosphere was used to grow stoichiometric TiO2:N and non-stoichiometric TiO2-x:N thin films. X-ray diffraction at glancing incidence, atomic force microscopy AFM, scanning electron microscopy SEM, X-ray photoelectron spectroscopy XPS, and optical spectrophotometry were applied for sample characterization. Measurements of photocurrent versus voltage and wavelength over the ultraviolet uv and visible vis ranges of the light spectrum were performed in order to assess the performance of nitrogen-doped titanium dioxide thin films as photoanodes for hydrogen generation in photoelectrochemical cells, PEC. Undoped TiO2 and TiO2-x films were found to be composed of anatase and rutile mixture with larger anatase crystallites (25-35 nm) while the growth of smaller rutile crystallites (6-10 nm) predominated at higher nitrogen flow rates etaN2 as measured in standard cubic centimeters, sccm. Nitrogen-to-titanium ratio increased from N/Ti = 0.05 at etaN2 = 0.8 sccm for stoichiometric TiO2:N to N/Ti = 0.11 at etaN2 = 0.8 sccm for nonstoichiometric TiO2-x:N thin films. A red-shift in the optical absorbance was observed with an increase in etaN2. Doping with nitrogen improved photoelectrochemical properties over the visible range of the light spectrum in the case of nonstoichiometric samples.

Study of N-doped TiO2 thin films for photoelectrochemical hydrogen generation from water

“…High value of I/I 0 corresponds to the fast sputtering of the metallic target surface in oxygendeficient atmosphere thus non-stoichiometric thin films are formed. Non-stoichiometric titanium dioxide, TiO 2-x :N thin films were obtained at a constant I/I 0 =0.3 while stoichiometric TiO 2 :N layers at I/I 0 =0.13 which was based on previous experience [17]. Nitrogen was introduced during deposition in a controllable way by measuring and adjusting its flow rate η N2 .…”

“…As shown by XPS spectra [17] there was no influence of increasing nitrogen flow rate on the relative content of nitrogen built in. However, in the case of non-stoichiometric TiO 2-x :N thin films an increase in N/Ti atomic ratio was accompanied by a decrease in O/Ti ratio.…”

“…In order to extend its absorption spectrum towards longer wavelengths, various modifications of TiO 2 have been proposed [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] but with a limited success.…”

“…Since the pioneering work of Asahi [13], nitrogen incorporation into the anionic sublattice of titanium dioxide has been expected to bring significant improvement in the photocatalytic and photoelectrochemical behaviour in comparison with the unmodified TiO 2 [14][15][16][17][24][25][26][27][28].…”

“…In our previous paper [17] it has been demonstrated that modification of oxygen sublattice of stoichiometric TiO 2 :N thin films by substitutional nitrogen doping is difficult. As shown by XPS spectra [17] there was no influence of increasing nitrogen flow rate on the relative content of nitrogen built in.…”