Infrared response of vitreous titanium dioxide films with anatase short-range order

Abstract

The polarization-dependent optical response of vitreous titanium dioxide films was determined by infrared reflection–absorption spectroscopy (IRAS). The predominant nearest-neighbor coordination (short-range order) in the films was characteristic of crystalline anatase. A dielectric function ε(ν) was constructed, based on random orientational disorder of anataselike, octahedral TiO6 units relative to the substrate. This dielectric function, which is the directional average of the dielectric function for an anatase crystal in the E⊥c and E∥c orientations, was used to calculate energy loss functions from which theoretical IRAS spectra were obtained. Experimental absorption band frequencies are in good agreement with peaks in the calculated transverse optic loss function, Im[ε(ν)], at 261 and 436 cm−1, and in the calculated longitudinal optic loss function, Im[−1/ε(ν)], at 840 cm−1. Agreement (i.e., polarization-dependent behavior, band frequency, and relative intensity) between the experimental and theoretical IRAS spectra indicates that orientational disorder of TiO6 units is the important factor governing infrared reflection–absorption behavior of the films.