Thermal annealing of birefringent TiO2 thin films formed by oblique-angle deposition

Andy C. van Popta; June Cheng; Jeremy C. Sit; Michael J. Brett

doi:10.1117/12.735425

10 September 2007 Thermal annealing of birefringent TiO₂ thin films formed by oblique-angle deposition

Andy C. van Popta, June Cheng, Jeremy C. Sit, Michael J. Brett

Proceedings Volume 6647, Nanocoatings; 66470C (2007) https://doi.org/10.1117/12.735425
Event: NanoScience + Engineering, 2007, San Diego, California, United States

Abstract

Titanium dioxide thin films were formed by electron-beam evaporation onto fused silica substrates using serial bideposition (SBD). The SBD technique combines rapid substrate rotation and oblique-angle physical vapor deposition (PVD) to create optical coatings that are composed of nanostructured columns which exhibit large birefringence values in the plane of the substrate. In this study, post-deposition annealing was used to crystallize amorphous TiO₂ thin films formed by SBD to improve birefringence without significantly increasing optical absorption or scattering. Birefringent thin films were fabricated at deposition angles ranging from 60° to 75° and annealed in air at temperatures ranging from 200°C to 900°C to form anatase and rutile TiO₂. Changes in the optical properties, crystallinity, and nanostructure were characterized by ellipsometry, x-ray diffraction, atomic force microscopy, and scanning electron microscopy. It was found that optical anisotropy increases strongly upon formation of anatase, yielding in-plane birefringence values that doubled from 0.11 to 0.22 in the case of TiO₂ thin films deposited at 60° and annealed at 400°C. Raising the annealing temperature to 900°C to form rutile thin films increased the thin film birefringence further but also led to low optical transparency due to increased absorption and diffuse scattering.

Citation Download Citation

Andy C. van Popta, June Cheng, Jeremy C. Sit, and Michael J. Brett "Thermal annealing of birefringent TiO₂ thin films formed by oblique-angle deposition", Proc. SPIE 6647, Nanocoatings, 66470C (10 September 2007); https://doi.org/10.1117/12.735425

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