Coatings and surface treatments for enhanced performance suspensions for future gravitational wave detectors

Birney, R and Cumming, A V and Campsie, P and Gibson, D and Hammond, G D and Hough, J and Martin, I W and Reid, S and Rowan, S and Song, S and Talbot, C and Vine, D and Wallace, G (2017) Coatings and surface treatments for enhanced performance suspensions for future gravitational wave detectors. Classical and Quantum Gravity, 34 (23). 235012. ISSN 1361-6382 (https://doi.org/10.1088/1361-6382/aa9354)

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Abstract

Further improvements in the low frequency sensitivity of gravitational wave detectors are important for increasing the observable population of astrophysical sources, such as intermediate mass compact black hole binary systems. Improvements in the lower stage mirror and suspension systems will set challenging targets for the required thermal noise performance of the cantilever blade springs, which provide vertical softness and, thus, isolation to the mirror suspension stack. This is required due to the coupling between the vertical and horizontal axes due to the curvature of the Earth. This can be achieved through use of high mechanical Q materials, which are compatible with cryogenic cooling, such as crystalline silicon. However, such materials are brittle, posing further challenges for assembly/jointing and, more generally, for long-term robustness. Here, we report on experimental studies of the breaking strength of silicon at room temperature, via both tensile and 4-point flexural testing; and on the effects of various surface treatments and coatings on durability and strength. Single- and multi-layer DLC (diamond-like carbon) coatings, together with magnetron-sputtered silica and thermally-grown silica, are investigated, as are the effects of substrate preparation and argon plasma pre-treatment. Application of single- or multi-layer DLC coatings can significantly improve the failure stress of silicon flexures, in addition to improved robustness for handling (assessed through abrasion tests). Improvements of up to 80% in tensile strength, a twofold increase in flexural strength, in addition to a 6.4 times reduction in the vertical thermal noise contribution of the suspension stack at 10 Hz are reported (compared to current Advanced LIGO design). The use of silicon blade springs would also significantly reduce potential 'crackling noise' associated with the underlying discrete events associated with plastic deformation in loaded flexures.

ORCID iDs

Birney, R, Cumming, A V, Campsie, P ORCID logoORCID: https://orcid.org/0000-0003-4570-7133, Gibson, D, Hammond, G D, Hough, J, Martin, I W, Reid, S, Rowan, S, Song, S, Talbot, C, Vine, D and Wallace, G;
  • Item type:Article
    ID code:62899
    Dates:
    Date
    Event
    15 November 2017
    Published
    13 October 2017
    Accepted
    Notes:This is an author-created, un-copyedited version of an article published in Classical and Quantum Gravity. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-6382/aa9354.
    Subjects:Science > Physics
    Department:Faculty of Engineering > Biomedical Engineering
    Depositing user: Pure Administrator
    Date deposited:16 Jan 2018 14:39
    Last modified:11 Nov 2024 11:51
    Related URLs:
    URI:https://strathprints.strath.ac.uk/id/eprint/62899
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