Titanium dioxide thin films were obtained by RF magnetron sputtering system with different Ar and O atmospheres. Chemical bonding structures of the thin films were investigated using the Fourier transform infrared spectroscopy (FTIR) in the range of 400-7500 cm(-1) for as-deposited and conventionally thermal annealed films at different temperature in air. These structural characterizations of the films were carried out by describing the low-frequency fluctuations of the FTIR spectra using the noninvasive (i.e. error controllable) procedure of the optimal linear smoothing. This approach is based on the criterion of the minimal relative error in selection of the proper smoothing window. It allows the receiving an optimal separation of a possible trend from the high-frequency fluctuations, defined as a random sequence of the relative fluctuations possessing zero trends. Thus, the noise can be read and extra information about the structures was then obtained by comparing with the experimental results. In the film annealed at 900 degrees C, the rutile phase was the dominant crystalline phase as revealed by infrared spectroscopy. At the annealing temperatures lower than 900 degrees C, both the anatase and the rutile phases were coexisting. In addition, symmetric and asymmetric Si-O-Si vibrations modes were observed at around 1000 cm(-1) and 800 cm(-1), respectively. These peaks suggest that a thin SiO2 film was formed at the TiO2/Si interface during the growth and the annealing of the TiO2 films. It was also observed that the reactivity between TiO2 film and Si substrate is increased with the increasing annealing temperature. (C) 2011 Elsevier B.V. All rights reserved.