T. Viseu

Optical characterisation of anatase: a comparative study of the bulk crystal and the polycrystalline thin film

The optical parameters of crystalline anatase and polycrystalline anatase films prepared by reactive magnetron sputtering were examined by spectroscopic ellipsometry and optical transmittance spectroscopy, respectively. Some films were doped with aluminium or chromium. In general, the values of the optical bandgap for the films are consistently blue-shifted as compared with the crystal. The blue shift is also found for some films doped with Al and Cr. The width of the absorption bands is considerably narrower in the films than in the crystal. These effects are interpreted as resulting from the spatial confinement of electrons and holes in the TiO2 microcrystallites. The average crystallite size determined from the shift of the optical gap was found to be in the range ∼5–8 nm, in excellent agreement with the data obtained from small-angle X-ray diffractometry.

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

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 N2:O2 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 ...

Faraday effect in ZnO:Mn thin films

Undoped and Mn‐doped ZnO transparent thin films were grown by RF magnetron co‐sputtering. The films are nanocrystalline, with wurtzite‐structure grains of a typical size of 20 nm, with a preferential orientation of the c‐axis perpendicular to the surface. Although, according to the Raman spectroscopy data, Mn mostly substitutes Zn in the lattice sites, factor that is considered favorable for ferromagnetism in this material, the ZnO:Mn films are paramagnetic at room temperature as it follows from our Faraday effect (FE) measurements. The FE spectra show a significant influence of the Mn ions for photon energies sufficiently below the ZnO:Mn band gap but not in its vicinity.

Structural and Mechanical Properties of AZOY Thin Films Deposited on Flexible Substrates

Transparent conducting Al doped ZnO films have been deposited by dc magnetron sputtering on glass and polymer substrates at room temperature. Depositions have been carried out from an AZOY (contains a small amount of Y2O3 in addition to Al2O3 and ZnO) target under different conditions such as working pressure, substrate bias voltage and oxygen flow rate. The crystallinity of the Al doped ZnO films has been improved by using low-energy-ion bombardment. Likewise, the use of either the rotation or the static mode of the substrate during deposition influences the crystallinity and therefore the optical parameters and the electrical resistance of the films. Increasing the thickness of the films reduces the threshold strain at which the films can be deformed without provoking significant changes on their electrical properties.