Berreman effect applied to phase characterization of thin films supported on metallic substrates: The case ofTiO2

Abstract

Infrared reflection-absorption spectra of TiO 2 thin films deposited by plasma-enhanced chemical vapor deposition onto aluminum and by a sol-gel process onto platinum were obtained using s-and p-polarized light and oblique incidence angles. Prominent bands with variable reflection minima position and line shapes, which were shown to be phase dependent, were observed for all samples in the 800Ϫ900 cm Ϫ1 wave number range when p-polarized light and oblique incidence were used. Such bands were attributed to an LO mode of TiO 2 and their enhancement with the incidence angle is a good example of Berreman effect. Such spectra were analyzed by means of spectral simulation based on the Fresnel equation for a three-layered system. The films' optical constants used in the simulations were obtained through the Kramers-Krönig analysis ͑KKA͒ of the reflectance spectra of pellets of powdered amorphous TiO 2 , anatase and rutile. Optical constants for hypothetical polycrystalline TiO 2 systems were also calculated from the dielectric functions of single crystals by means of effective medium theories ͑EMTs͒, such as those of Bruggeman, Maxwell-Garnett, and Hunderi. These optical constants were used both for spectral simulation and for understanding the bands observed. However, the optical constants for the powdered standards determined through KKA reproduced experimental results more accurately than those determined through the EMTs. In both experimental and simulated spectra, Berreman effect was very clear-cut and a reliable phase characterization could be carried out.

Tailoring the surface properties of Ti6Al4V by controlled chemical oxidation

“…The coupling of IR analysis with ellipsometric measurements demonstrated experimentally the growth of intensity in the IR band at 400e1000 cm À1 with increasing thickness of the TiO 2 layer, previously simulated by Trasferetti et al [63]. Moreover, such an increase in the thickness of the oxide layer can be deduced from the failure to detect the XPS Ti Metallic peak after 15 min of etching.…”

“…9b), which shows a close relation between the integrated area of IR peaks related to TieO bonds and the thickness of the oxide layer as estimated by ellipsometry. Such correlations between absorbance and oxide thickness were previously hypothesized by Trasferetti et al [63] based on theoretical simulations. In agreement with these simulations, the oxide thickness measured by ellipsometry was about 5 nm in untreated samples, and it did not change significantly up to 15 min of etching (Fig.…”

Application of the Berreman Effect to the Characterization of TiO2 Thin Layers Formed onto Titanium Substrates

“…The bands occur only when the incident radiation beam is not normal to the surface and only in the (2011) 000 000 p-polarized component of the radiation. The Berreman effect can be employed to obtain information on the crystalline structure of the film, and in the next paragraphs we will summarize the main consequences of the Berreman effect for TiO 2 thin films [Trasferetti et al 2001].…”

“…Simulated reflection-absorption spectra (p-polarization and an incidence angle of 70°) for a TiO2/Pt system and four different film thickness. Taken from Trasferetti et al 2001. effect, and several important conclusions can be drawn. Firstly, the film thickness must be less than 1000 nm for this effect to be observed.…”

“…From materials characterization point of view, the results presented by Trasferetti et al 2001 extracted from simulated and experimental spectra of TiO 2 thin films when p-polarized radiation is employed at a relative high incidence angle (typically 70º), can be summarized as follows:…”