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Thermal annealing of birefringent TiO2thin films formed by oblique-angle deposition
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.
Thermal annealing of birefringent TiO2thin films formed by oblique-angle deposition
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.
Thermal annealing of birefringent TiO2thin films formed by oblique-angle deposition
van Popta, Andy C. (author) / Cheng, June (author) / Sit, Jeremy C. (author) / Brett, Michael J. (author)
Nanocoatings ; 2007 ; San Diego,California,United States
Proc. SPIE ; 6647
2007-09-06
Conference paper
Electronic Resource
English
Thermal annealing of birefringent TiO~2 thin films formed by oblique-angle deposition [6647-13]
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