Low mechanical loss and high refractive index in amorphous Ta₂O₅ films grown by magnetron sputtering
Creators
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1.
California Institute of Technology
Abstract
The ability to observe astronomical events through the detection of gravitational waves relies on the quality of multilayer coatings used on the optical mirrors of interferometers. Amorphous Ta₂O₅ (including TiO₂:Ta₂O₅) currently limits detector sensitivity due to high mechanical loss. In this paper, mechanical loss measured at both cryogenic and room temperatures of amorphous Ta₂O₅ films grown by magnetron sputtering and annealed in air at 500 ∘C is shown to decrease for elevated growth temperature. Films grown at 310 °C and annealed yield a mechanical loss of 3.1×10⁻⁴ at room temperature, the lowest value reported for pure amorphous Ta₂O₅ grown by magnetron sputtering to date, and comparable to the lowest values obtained for films grown by ion beam sputtering. Additionally, the refractive index n increases 6% for elevated growth temperature, which could lead to improved sensitivity of gravitational-wave detectors by allowing a thickness reduction in the mirrors' coatings. Structural characterization suggests that the observed mechanical loss reduction in amorphous Ta₂O₅ films with increasing growth temperature correlates with a reduction in the coordination number between oxygen and tantalum atoms, consistent with TaOₓ polyhedra with increased corner-sharing and reduced edge- and face-sharing structures.
Copyright and License
© 2024 American Physical Society.
Acknowledgement
The authors thank P. Ci and J. Wu for assistance with Raman measurements. We gratefully acknowledge support of the LIGO Scientific Collaboration (LSC) Center for Coatings Research (CCR), jointly funded by the United States National Science Foundation (NSF) through Grants No. PHY-2011719, No. 2011571, No. 2011706, No. 1708010, No. 1710957, No. 0823459, and No. 0757058 to each institution, and the Gordon and Betty Moore Foundation through Grant No. 6793. This work was also partially supported by the Office of Naval Research at NRL.
Data Availability
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PhysRevMaterials.8.035603.pdf
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Additional details
Funding
- National Science Foundation
- PHY-2011719
- National Science Foundation
- PHY-2011571
- National Science Foundation
- PHY-2011706
- National Science Foundation
- PHY-1708010
- National Science Foundation
- PHY-1710957
- National Science Foundation
- PHY-0823459
- National Science Foundation
- PHY-0757058
- Gordon and Betty Moore Foundation
- 6793
- Office of Naval Research