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Published May 20, 2014 | Published + Submitted
Journal Article Open

Investigation of the Young's modulus and thermal expansion of amorphous titania-doped tantala films


The current generation of advanced gravitational wave detectors utilize titania-doped tantala/silica multilayer stacks for their mirror coatings. The properties of the low-refractive-index silica are well known; however, in the absence of detailed direct measurements, the material parameters of Young's modulus and coefficient of thermal expansion (CTE) of the high refractive index material, titania-doped tantala, have been assumed to be equal to values measured for pure tantala coatings. In order to ascertain the true values necessary for thermal noise calculations, we have undertaken measurements of Young's modulus and CTE through the use of nanoindentation and thermal-bending measurements. The measurements were designed to assess the effects of titania-doping concentration and post-deposition heat-treatment on the measured values in order to evaluate the possibility of optimizing material parameters to further improve thermal noise in the detector. Young's modulus measurements on pure tantala and 25% and 55% titania-doped tantala show a wide range of values, from 132 to 177 GPa, which are dependent on both titania concentration and heat-treatment. Measurements of CTE give values of (3.9±0.1)×10^(−6)  K^(−1) and (4.9±0.3)×10^(−6)  K^(−1) for 25% and 55% titania-doped tantala, respectively, without dependence on post-deposition heat-treatment.

Additional Information

© 2014 Optical Society of America. Received 16 January 2014; accepted 2 April 2014; posted 17 April 2014 (Doc. ID 204591); published 14 May 2014. The authors would like to acknowledge the contributions of the Oyen Group from the Cambridge University Department of Engineering, especially Oliver Hudson, Tamaryn Shean, and Daniel Strange for their aid in obtaining the nanoindentation data. IWM holds a Royal Society University Research Fellowship, and SR is a Royal Society-Wolfson Research Merit Award holder. The authors would like to thank the UK Science and Technology Facilities Council, the University of Glasgow, the Scottish Universities Physics Alliance, and the Scottish Founding Council for financial support through RCUK grants ST/J000361/1 and CG ST/L000946/1. We also wish to thank our colleagues in the GEO600 and LIGO Scientific Collaboration for their interest in this work. The LIGO Observatories were constructed by the California Institute of Technology and Massachusetts Institute of Technology with funding from the National Science Foundation under cooperative agreement PHY-9210038. The LIGO Laboratory operates under cooperative agreement PHY-0107417. This paper has been assigned LIGO Document Number LIGO-P1300107.

Attached Files

Submitted - 1401.7061v1.pdf

Published - ao-53-15-3196.pdf


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August 20, 2023
August 20, 2023