Effects of elevated-temperature deposition on the atomic structure of amorphous Ta₂O₅ films

Creators: Prasai, K.; Lee, K.; Baloukas, B.; Cheng, H-P.; Fazio, M.; Martinu, L.; Mehta, A.; Menoni, C. S.; Schiettekatte, F.; Shink, R.; Shyam, B.; Vajente, G.¹; Fejer, M. M.; Bassiri, R.

1. California Institute of Technology

Abstract

Brownian thermal noise as a result of mechanical loss in optical coatings will become the dominant source of noise at the most sensitive frequencies of ground-based gravitational-wave detectors. Experiments found, however, that a candidate material, amorphous Ta₂O₅, is unable to form an ultrastable glass and, consequently, to yield a film with significantly reduced mechanical loss through elevated-temperature deposition alone. X-ray scattering PDF measurements are carried out on films deposited and subsequently annealed at various temperatures. Inverse atomic modeling is used to analyze the short and medium range features in the atomic structure of these films. Furthermore, in silico deposition simulations of Ta₂O₅ are carried out at various substrate temperatures and an atomic level analysis of the growth at high temperatures is presented. It is observed that upon elevated-temperature deposition, short range features remain identical, whereas medium range order increases. After annealing, however, both the short and medium range orders of films deposited at different substrate temperatures are nearly identical. A discussion on the surface diffusion and glass transition temperatures indicates that future pursuits of ultrastable low-mechanical-loss films through elevated temperature deposition should focus on materials with a high surface mobility, and/or lower glass transition temperatures in the range of achievable deposition temperatueres.

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Acknowledgement

We would like to thank Dr. Beverly Berger for helpful comments in reviewing this article. We acknowledge the support of the LSC Center for Coatings Research, jointly funded by the National Science Foundation (NSF) and the Gordon and Betty Moore Foundation (GBMF). In particular, the authors are grateful for the support through NSF under Award Nos. PHY-2011571, PHY-2011706, and PHY-2011782 and GBMF under Grant No. 6793. Partial support from the Office of Naval Research (ONR) under Grant No. N000-17-1-2536 is acknowledged. We would like to acknowledge the Sherlock Cluster at Stanford University for providing computational resources and support that contributed to these research results. This work also used the Extreme Science and Engineering Discovery Environment (XSEDE),³⁹ which is supported by the NSF under Award No. ACI-1548562. Authors from U. Montréal and Polytechnique Montréal wish to acknowledge the NSERC, the FRQNT through the RQMP, and the FCI for funding. Authors from Sungkyunkwan Univ. were supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (Grant No. 2021R1C1C1009248). This paper has LIGO document under Grant No. P2300147.

Contributions

K. Prasai: Conceptualization (lead); Data curation (lead); Formal analysis (lead); Funding acquisition (supporting); Investigation (lead); Methodology (lead); Resources (supporting); Software (lead); Validation (lead); Visualization (lead); Writing – original draft (lead); Writing – review & editing (lead). K. Lee: Investigation (supporting); Writing – review & editing (supporting). B. Baloukas: Resources (supporting); Writing – review & editing (supporting). H.-P. Cheng: Funding acquisition (equal); Methodology (supporting); Supervision (supporting); Writing – review & editing (supporting). M. Fazio: Data curation (equal); Formal analysis (supporting); Investigation (equal); Writing – review & editing (equal). L. Martinu: Resources (supporting); Writing – review & editing (supporting). A. Mehta: Conceptualization (supporting); Data curation (supporting); Formal analysis (supporting); Investigation (supporting); Methodology (equal); Resources (equal); Writing – review & editing (supporting). C. S. Menoni: Funding acquisition (equal); Resources (equal); Writing – review & editing (equal). F. Schiettekatte: Resources (equal); Writing – review & editing (equal). R. Shink: Resources (supporting); Writing – review & editing (supporting). B. Shyam: Conceptualization (supporting); Data curation (equal); Formal analysis (equal); Investigation (equal); Methodology (equal); Writing – review & editing (equal). G. Vajente: Data curation (supporting); Formal analysis (supporting); Investigation (supporting); Resources (supporting); Writing – review & editing (supporting). M. M. Fejer: Conceptualization (equal); Funding acquisition (lead); Project administration (equal); Resources (equal); Supervision (lead); Writing – review & editing (equal). R. Bassiri: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Project administration (lead); Resources (equal); Supervision (lead); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal).

Data Availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Conflict of Interest

The authors have no conflicts to disclose.

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