Thermal Annealing Effect on Optical Properties of Binary TiO₂-SiO₂ Sol-Gel Coatings.

Xiaodong Wang,Guangming Wu,Jun Shen,Bin Zhou

doi:10.3390/ma6010076

Xiaodong Wang, Guangming Wu + Show 2 more

Open Access

https://doi.org/10.3390/ma6010076

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Journal: Materials	Publication Date: Dec 24, 2012
Citations: 66	License type: CC BY 4.0

Affiliation: Tongji University, Institute of Solid State Physics

Abstract

TiO2-SiO2 binary coatings were deposited by a sol-gel dip-coating method using tetrabutyl titanate and tetraethyl orthosilicate as precursors. The structure and chemical composition of the coatings annealed at different temperatures were analyzed by Raman spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy. The refractive indices of the coatings were calculated from the measured transmittance and reflectance spectra. An increase in refractive index with the high temperature thermal annealing process was observed. The Raman and FTIR results indicate that the refractive index variation is due to changes in the removal of the organic component, phase separation and the crystal structure of the binary coatings.

Highlights

In optical thin film application, it is important to have tunable refractive indices over a range as large as possible and continuously if feasible
We report on the synthesis and characterization of binary TiO2-SiO2 optical coatings prepared by a sol-gel method
We demonstrated that the increase in refractive index was due to the combined effects of the removal of the organic component, phase separation and the crystal structure transition of the binary coatings

Summary

Introduction

In optical thin film application, it is important to have tunable refractive indices over a range as large as possible and continuously if feasible. Due to the low cost, wide spectral region of transparency from visible to near infrared [1], as well as the high chemical and thermal stabilities, SiO2 and TiO2 are commonly used as low and high refractive index materials, respectively They have been successfully used in optical device applications, such as antireflective coatings [2], high reflecting. A recent exception in this regard is the work of Louis et al [12], which constitutes a thorough investigation of the correlations between the microstructure of SiO2/TiO2 thin films and their optical properties They investigated how the binary coating is affected by the mixing ratio of the two oxides and the thermal annealing of the samples through an in situ thermal ellipsometry analysis. We demonstrated that the increase in refractive index was due to the combined effects of the removal of the organic component, phase separation and the crystal structure transition of the binary coatings

Sol Synthesis

Coating Preparation

Characterization

Results and Discussion

Conclusions