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

• Published in: Thin solid films Vol. 401; no. 1; pp. 216 - 224
• Main Authors: Viseu, T.M.R., Almeida, B., Stchakovsky, M., Drevillon, B., Ferreira, M.I.C., Sousa, J.B.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 17.12.2001; Elsevier Science
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Optical properties; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Other semiconductors; Physics; Quantum effects; Structural properties; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; Titanium oxide; Quantum effects; Titanium oxide; Optical properties; Structural properties; Grain size; Confinement; Inorganic compounds; Anatase; Spectroscopic ellipsometry; Transition element compounds; Doped materials; Polycrystals; Chromium additions; Experimental study; Thin films; Titanium oxides; Energy gap; Monocrystals; Optical transmission; Aluminium additions; Reactive sputtering; Microstructure; Optical constants
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/S0040-6090(01)01479-1

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 TiO 2 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.