Enhancement in the photocatalytic nature of nitrogen-doped PVD-grown titanium dioxide thin films

• Published in: Journal of applied physics 2009-12, Vol.106 (11), p.113535-113535-8
• Main Authors: Tavares, C. J., Marques, S. M., Viseu, T., Teixeira, V., Carneiro, J. O., Alves, E., Barradas, N. P., Munnik, F., Girardeau, T., Rivière, J.-P.
• Format: Article
• Language: English
• Subjects: ANIONS; ANNEALING; CATALYSIS; CATIONS; CHALCOGENIDES; CHARGED PARTICLES; CHEMISTRY; COATINGS; DEPOSITION; DOPED MATERIALS; ELECTRON SPECTROSCOPY; ELEMENTS; ELLIPSOMETRY; HEAT TREATMENTS; HEAVY IONS; IONS; MATERIALS; MATERIALS SCIENCE; MEASURING METHODS; METALS; MINERALS; NITROGEN; NONMETALS; OPTICAL PROPERTIES; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; PHOTOCATALYSIS; PHOTOCHEMISTRY; PHOTOELECTRON SPECTROSCOPY; PHYSICAL PROPERTIES; PHYSICAL VAPOR DEPOSITION; RADIOACTIVE MATERIALS; RADIOACTIVE MINERALS; REFRACTIVE INDEX; RUTHERFORD BACKSCATTERING SPECTROSCOPY; RUTILE; SEMICONDUCTOR MATERIALS; SPECTROSCOPY; SPUTTERING; SURFACE COATING; THIN FILMS; TITANIUM; TITANIUM COMPOUNDS; TITANIUM OXIDES; TRANSITION ELEMENT COMPOUNDS; TRANSITION ELEMENTS; X-RAY PHOTOELECTRON SPECTROSCOPY
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.3269702

Nitrogen-doped titanium dioxide semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron physical vapor deposition on glass substrates for self-cleaning applications. In order to increase the photocatalytic efficiency of the titania coatings, it is important to enhance the catalysts absorption of light from the solar spectra. Bearing this fact in mind, a reduction in the titania semiconductor band-gap has been attempted by using nitrogen doping from a coreactive gas mixture of N 2 : O 2 during the titanium sputtering process. Rutherford backscattering spectroscopy was used in order to assess the composition of the titania thin films, whereas heavy-ion elastic recoil detection analysis granted the evaluation of the doping level of nitrogen. X-ray photoelectron spectroscopy provided valuable information about the cation-anion binding within the semiconductor lattice. The as-deposited thin films were mostly amorphous, however, after a thermal annealing in vacuum at 500 ° C the crystalline polymorph anatase and rutile phases have been developed, yielding an enhancement in the crystallinity. Spectroscopic ellipsometry experiments enabled the determination the refractive index of the thin films as a function of the wavelength, while from the optical transmittance it was possible to estimate the semiconductor indirect band-gap of these coatings, which has been proven to decrease as the N-doping increases. The photocatalytic performance of the titania films has been characterized by the degradation rate of an organic reactive dye under UV/visible irradiation. It has been found that for a certain critical limit of 1.19 at.% of nitrogen doping in the titania anatase crystalline lattice enhances the photocatalytic behavior of the thin films and it is in accordance with the observed semiconductor band-gap narrowing to 3.18 eV. By doping the titania lattice with nitrogen, the photocatalytic activity is enhanced under both UV and visible light.