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

Ross Birney, Alan Vernal Cumming, Paul Campsie, Desmond Gibson, Giles D. Hammond, Jim Hough, Iain W. Martin, Stuart Reid, Sheila Rowan, Shigeng Song, Curtis Talbot, David Vine, Gavin Wallace

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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.
Original languageEnglish
Article number235012
JournalClassical and Quantum Gravity
Volume34
Early online date15 Nov 2017
DOIs
Publication statusE-pub ahead of print - 15 Nov 2017

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surface treatment
gravitational waves
coatings
flexing
detectors
thermal noise
silicon
blades
diamonds
cryogenic cooling
mirrors
silicon dioxide
brittle materials
LIGO (observatory)
softness
abrasion
carbon
flexural strength
argon plasma
durability

Cite this

Birney, Ross ; Cumming, Alan Vernal ; Campsie, Paul ; Gibson, Desmond ; Hammond, Giles D. ; Hough, Jim ; Martin, Iain W. ; Reid, Stuart ; Rowan, Sheila ; Song, Shigeng ; Talbot, Curtis ; Vine, David ; Wallace, Gavin. / Coatings and surface treatments for enhanced performance suspensions for future gravitational wave detectors. In: Classical and Quantum Gravity. 2017 ; Vol. 34.
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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.",
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Birney, R, Cumming, AV, Campsie, P, Gibson, D, Hammond, GD, Hough, J, Martin, IW, Reid, S, Rowan, S, Song, S, Talbot, C, Vine, D & Wallace, G 2017, 'Coatings and surface treatments for enhanced performance suspensions for future gravitational wave detectors' Classical and Quantum Gravity, vol. 34, 235012. https://doi.org/10.1088/1361-6382/aa9354

Coatings and surface treatments for enhanced performance suspensions for future gravitational wave detectors. / Birney, Ross; Cumming, Alan Vernal ; Campsie, Paul; Gibson, Desmond; Hammond, Giles D. ; Hough, Jim ; Martin, Iain W.; Reid, Stuart; Rowan, Sheila; Song, Shigeng; Talbot, Curtis; Vine, David; Wallace, Gavin.

In: Classical and Quantum Gravity, Vol. 34, 235012, 15.11.2017.

Research output: Contribution to journalArticle

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AU - Birney, Ross

AU - Cumming, Alan Vernal

AU - Campsie, Paul

AU - Gibson, Desmond

AU - Hammond, Giles D.

AU - Hough, Jim

AU - Martin, Iain W.

AU - Reid, Stuart

AU - Rowan, Sheila

AU - Song, Shigeng

AU - Talbot, Curtis

AU - Vine, David

AU - Wallace, Gavin

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AB - 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.

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