TiO<sub>2</sub> films with thicknesses (<i>d</i>) above 15 nm were grown on optically polished surfaces of MgO (001) substrates held at 400 °C by sputtering a Ti target with an argon-ion beam when the partial pressure of O<sub>2</sub> was kept at 1.1 × 10<sup>−2</sup> Pa. X-ray diffraction patterns show that TiO<sub>2</sub> films with <i>d</i> < 56 nm are composed of an <i>a</i>-axis anatase-type structure, whereas those with <i>d</i> > 56 nm are composed of a mixture of phases with the <i>c</i>-axis parallel to the film surface. The thickness dependence of the infrared reflection-absorption spectra shows that TiO<sub>2</sub> films with <i>d</i> < 56 nm are composed of both anatase and amorphous phases, whereas those with <i>d</i> > 56 nm are composed of anatase, rutile, and amorphous phases. The crystallinity in TiO<sub>2</sub> films is also evaluated from the infrared reflection-absorption spectra by comparison of the observed and the calculated results determined from the dielectric function of anisotropic TiO<sub>2</sub> bulk single crystal.
© 2001 Optical Society of America
(240.0310) Optics at surfaces : Thin films
(300.6340) Spectroscopy : Spectroscopy, infrared
(310.6860) Thin films : Thin films, optical properties
(310.6870) Thin films : Thin films, other properties
Dai Osabe, Hideo Seyama, and Kunisuke Maki, "Evaluation of Crystallinity in TiO2 Films with Mixed Structures Grown on MgO (001) Substrates by argon-ion Beam Sputtering Based on Infrared Reflection–Absorption Spectra," Appl. Opt. 41, 739-746 (2002)