Microstructure of plasma-deposited SiO2/TiO2 optical films

Abstract

SiO 2 and TiO2, with their high refractive index contrast, are interesting candidates for the fabrication of graded-index optical filters. In this work, SiO2/TiO2 mixtures were prepared by plasma-enhanced chemical vapor deposition from SiCl4 and TiCl4. By controlling the gas flow ratio, it is possible to obtain coatings with refractive index values between 1.48, for SiO2, and 2.35, for TiO2, and with an extinction coefficient below 10−4 in the visible and near-infrared regions. The optical properties of the mixtures do not respect the Bruggeman effective medium approximation that supposes two separate phases. Using a combination of x-ray photoelectron spectroscopy, Fourier transform infrared spectrometry, and elastic recoil detection, we demonstrate that SiO2/TiO2 is a single-phase material. Two separate phases can develop at certain compositions by annealing-induced precipitation.

Correlation between optical properties and electronic parameters for mixed oxide thin films

“…10 The existence of this kind of mixed structures, where silicon and titanium ions are linked by oxide ions with different electronic characteristics than in the bulk oxides, has been previously evidenced by FTIR. 10,12 Here, the appearance of an extra shoulder in the O 1s spectra of the samples with intermediate compositions confirms the existence of these singular oxide ions (cf. Fig.…”

Refractive index profile modelling of dielectric inhomogeneous coatings using effective medium theories

“…Finally, depending on the level at which materials are mixed, one effective medium theory will be more appropriate than the other and will give more accurate prediction of the optical properties of the mixture. For example, in the case of SiO 2 -TiO 2 amorphous mixture it has been shown experimentally [13,14] that LL model is more appropriate than BG, although not all the studies are in accordance [15]. (1)…”

Photo-induced properties of thin TiO2 films deposited using the radio frequency plasma enhanced chemical vapor deposition method

“…Enhancement of chemical reactions by means of low temperature plasma has been known and practiced for many years. Effective use of radio frequency (RF) glow discharges to deposit insulating, semiconducting, and conducting thin films has promoted substantial progress in the field of electrical and optical devices, such as optical filter systems [31][32][33][34], and in the area of property-altering surface coatings [34][35][36]. It was exactly the optical filter application of titanium dioxide films, which stimulated a development of their synthesis with the help of the PECVD technique [31].…”