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The research on amorphous coatings for future GW detectors Francesco Piergiovanni University of Urbino - INFN Firenze on behalf of the Virgo Collaboration Thermal Noise It characterizes each dissipative mechanical system at thermal

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The research on amorphous coatings for future GW detectors

Francesco Piergiovanni

University of Urbino - INFN Firenze

  • n behalf of the Virgo Collaboration
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Thermal Noise

  • It characterizes each dissipative mechanical system at thermal equilibrium
  • It’s produced by irreversible processes with typical time constants and activation energies
  • Same mechanism produces energy dissipation and thermal fluctuation

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Mechanical dissipation is quantified by the loss angle 𝜚 πœ• =

πΉπ‘šπ‘π‘‘π‘’ π‘žπ‘“π‘  π‘‘π‘§π‘‘π‘šπ‘“ 2πœŒπΉπ‘‘π‘’π‘π‘ π‘“π‘’

𝜚 πœ• = 1/𝑅 @ resonances Thermal noise can be reduced:

  • low temperature
  • low dissipation material

𝑇𝑦 πœ• = 4π‘™πΆπ‘ˆ πœ•2 𝑆𝑓[𝑍 πœ• ] Fluctuation-Dissipation Theorem

(Callen, Welton 1951)

Fluctuation Dissipation

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The origin of the TN amorphous materials

  • In Two Level System (TLS): metastable states are separated

by an energy barrier

  • Transitions between the two levels explain the anelastic

behavior of amorphous materials 𝜐 ∝ 𝜐0 Ξ” exp π‘Š/ π‘™π‘π‘ˆ π‘Š: barrier high Too fast relaxation Too slow relaxation Relaxation producing losses 𝜐 𝜐 𝜐

  • Only transitions with a relaxation time of the same order of

the period of the strain wave propagating in the material produce mechanical losses. At room temperature (300 𝐿)

  • nly TLS with π‘Š β‰ˆ 0.5π‘“π‘Š are relevant

Dove et al. Mineralogical Magazine (2000) Gilroy & Phillips Philosophical Magazine B (1981)

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  • Alternate layers of transparent materials with different

index of refraction (Bragg reflection).

  • Impedance mismatch and interference produce high

coefficient of reflectivity.

  • Its structure is not compact as the substrate.
  • 5 πœˆπ‘› of coating produces more thermal noise than

20 𝑑𝑛 of substrate.

𝑆 = 𝑠2 = π‘œπΌ π‘œπ‘€

2𝑂

βˆ’ 1 π‘œπΌ π‘œπ‘€

2𝑂

+ 1

2

Coating In GW detectors

Aasi J et al. 2015 Classical and Quantum Gravity 32 Acernese F et al. 2015 Classical and Quantum Gravity 32

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35 cm 20 cm 40 kg

Ta2O5-TiO2 thicker layer SiO2 layer Ta2O5-TiO2 layer N doublets SiO2 thinner layer (cap)

~6 Β΅m

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Coating thermal noise

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Coating Thermal Noise (CTN) limits the detection band in the Β« bucket Β» (middle frequencies) which is the most sensitive region of the Advanced and the future Advanced+ GW detectors

Advanced Virgo

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Coating thermal noise (CTN)

𝑇𝑦 πœ• ∝ π‘ˆ 𝑒 π‘₯2 𝜚𝐷

Coating thermal noise (CTN) contribution goes like: Research to reduce CTN involves:

  • enlarging the laser beam size π‘₯;
  • minimizing the overall coating thickness (𝑒) increasing the contrast between the high and the low refractive index

materials in Bragg reflector;

  • finding new materials-techniques for reducing the coating loss angle 𝜚𝐷.
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Sysnthesis:

βœ“ Coating deposition βœ“ Heat treatments

Modeling:

βœ“ Structure βœ“ TLS relaxations

Macroscopic characterization:

βœ“ Loss angle measurements βœ“ Optical characterization βœ“ Dielectric response βœ“ Elastic constants βœ“ Density

The Virgo Coating R&D activities

Microscopic characterization:

βœ“ TEM, SEM βœ“ Raman, Brillouin βœ“ XRD, XPS, XAS βœ“ AFM

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Credits: G. Cagnoli

The Virgo Coatings R&D Collaboration

GENOVA

  • GENOVA

♦ Ellipsometry ♦ Optical properties ♦ AFM, XPS ♦ Raman

  • SALERNO/SANNIO

♦ IAD ♦ SEM,TEM,AFM and XRD ♦ nanolayered composites and Mie-metamaterials

URBINO

  • URBINO

♦ GeNS Cryo ♦ FEA

SALERNO SANNIO

  • PERUGIA-CAMERINO

♦ Cantilevers & GeNS Cryo ♦ Physics of Glasses ♦ Brillouin, Raman ♦ SEM, XRD, XAS

VIRGO

LMA

  • LMA

♦ IBS HighT, IAD ♦ GeNS [300-10] K ♦ FEA ♦ Optical metrology

♦ Sample production ♦ Characterization ROMA 1 PISA

  • PISA

♦ Study of the crystallization processes ♦ Physics of deposition and ultrastable glasses ♦ Molecular Dynamics and Modelling ♦ Calorimetry and Dielectric response

  • ROMA 1

♦ Structural characterization ♦ Thermobalance

  • ROMA 2

♦ Laser Polishing ♦ GeNS 300K 1’’ ♦ FEA and AFM ♦ XPS ♦ Ellipsometry

ROMA 2 PERUGIA PADOVA

  • PADOVA

♦ Mag. Sputtering ♦ XRD High T

  • g-MAG

♦ Pulsed Laser Dep. ♦ Rapid Th. Annealing ♦ Raman, Brillouin ♦ Physics of Glasses ♦ Molecular Dynamics

g-MAG

Formed on January 2017

Other groups (from KAGRA and Belgium) are interested to join

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The Virgo Coating R&D research lines

BETTER COATING Materials Deposition Post-deposition treatments Absorption and Metrology Oxides ● Mixing ● High Index ● Silica Glasses Nitrides ● Fluorides ● High Coordination ● Number Glasses SiN, GaN, SiC, etc Origin of absorption ● Loss measurement ● protocol Thermo-elastic ● effect

  • Annealing
  • Outgassing and

chemical status

  • Controlled

crystallization

  • High Temperature
  • Nano-layering

β€’ High index β€’ Low index β€’ HR stack O5 horizon, CRD project accepted by funding agencies Beyond O5

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Updated measurement of current coatings

Refractive index: α‰Šπ‘œπΌ = 2.09 π‘œπ‘€ = 1.45 Extinction coeff.: 𝑙 β‰ˆ 10βˆ’7 π‘ˆπ‘2𝑃5 π‘ˆπ‘—π‘ƒ2: π‘ˆπ‘2𝑃5 𝑇𝑗𝑃2 πœšπ‘‘(𝑔) = 𝑏 𝑔𝑐 πœšπ‘‘ 𝑔 = 𝑏 𝑔𝑐 + πœ— 𝑒 πœšπ‘“ πœšπ‘‘ = 𝑏 𝑔𝑐

  • M. Granata, OIC 2019

Cagnoli et al. PLA (2018),

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Oxide mixtures recap

𝑂𝑐2𝑃5 500Β°C π‘ˆπ‘—π‘ƒ2: π‘ˆ

𝑏2𝑃5 500Β°C

π‘ˆπ‘2𝑃5 500°𝐷 π‘ˆπ‘—π‘ƒ2: π‘ˆπ‘2𝑃5400 Β°C π‘Žπ‘ π‘ƒ2: π‘ˆπ‘2𝑃5 700 Β°C 𝑇𝑗𝑃2 500°𝐷 𝑇𝑗𝑃2 900°𝐷

Granata et al. Optical Interference Coatings Conference (OIC) 2019 Post-deposition annealing temperature are reported

High refractive index Low refractive index

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Annealing

𝑇𝑗𝑃2

Amato et al. J. Phys Conf. Ser. 957 (2018) Granata et al Phys. Rev. Mater. 2 (2018)

IBS SPECTOR – annealed – IBS GC – not annealed – fused silica – bulk –

SiO2

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Deposition parameters (IBS coating)

π‘ˆπ‘2𝑃5

π»π‘ π‘π‘œπ‘π‘’π‘ 𝑓𝑒 π‘π‘š, π‘—π‘œ π‘žπ‘ π‘“π‘žπ‘π‘ π‘π‘’π‘—π‘π‘œ 𝐡𝑛𝑏𝑒𝑝 𝑓𝑒 π‘π‘š, 𝐾. π‘„β„Žπ‘§π‘‘. π·π‘π‘œπ‘”. 𝑇𝑓𝑠. 957 (2018)

βœ“ Films deposited with different coaters (at different rates) show different loss angles βœ“ Slower is the deposition, lower the dissipation

as deposited annealed

SPECTOR DIBS GC

structural limit? erasing effect

𝑇𝑗𝑃2

as deposited annealed

SPECTOR GC

βœ“ A sort of erasing effect of the annealing is visible, which is more evident for the tantala coating

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Absorption vs mechanical losses

Urbach tail: broadening in the band-gap absorption edge especially visible in poor crystallin and amorphous material, related to thermal and structural disorder 𝛽 𝐹 ∝ 𝑓𝐹/𝐹𝑉 Urbach energy Absorption coefficient

Photon energy (eV)

Ellipsometry

βœ“ A strong correlation between 𝐹𝑉 and mechanical losses has been found βœ“ Different materials show the same behavior

βœ“ Rapid estimation of mechanical losses βœ“ Extend the range of structural analysis

Amato et al. arXiv:1903.06094

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π‘ˆπ‘2𝑃5

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Modelling: Molecular Dynamics

MD-DMS: Molecular Dynamics simulation of Dynamical Mechanical Spectroscopy

  • A theory-independent method: the only ingredient is the interatomic potential of the

specific glassy system (π‘ˆπ‘2𝑃5, 𝑇𝑗𝐷 in progress)

  • Mechanical losses are computed by the dephasing btw applied oscillating strain and the

resulting stress

  • Simulation frequency range is GHz to

THz , but the frequency power law is compatible with what has been experimentally found in acoustic band

  • MD-DMS and experimental results,

are in good agreement

Puosi et al. in preparation Puosi 10th Einstein Telescope Symposium 2019

MD-DMS makes possible a rapid evaluation of mechanical properties

  • f new materials
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New materials

π‘ˆπ‘2𝑃5 𝑇𝑗𝑂𝑦 Nitrides: 𝑇𝑗𝑂𝑦 is a promising high index material

  • Mechanical losses about 3x

better than π‘ˆπ‘2𝑃5 issues

  • Refractive index slightly lower

than π‘ˆπ‘2𝑃5

  • Extinction coefficient more

than 10x larger!!! Fluorides: 𝑁𝑕𝐺

2and π΅π‘šπΊ 3

  • lower refractive index than silica

issues

  • Higher mechanical losses than silica

(at least at room T) 𝑇𝑗𝑃2 500°𝐷 𝑇𝑗𝑃2 900°𝐷 𝑁𝑕𝐺

2 as deposited

𝑁𝑕𝐺

2 400Β°C

IBS coatings

Bischi et al. poster GWADW 2019 Granata et al. Optical Interference Coatings Conference (OIC) 2019 Amato et al. Journal of Physics: Conf. Series 957 (2018)

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Nano-layered coating deposition

  • Post-deposition annealing largely improves coating mechanical characteristics.
  • Maximum annealing temperature is limited by the beginning of the film crystallization (i.e. Tmax β‰ˆ 300 °𝐷 for π‘ˆπ‘—π‘ƒ2)
  • In nano-layered films crystallization is frustrated by the size of the layers, higher annealing temperature is allowed

TiO2 = 7.36 π‘œπ‘› 𝑦 10 SiO2 = 4.32 π‘œπ‘› 𝑦 9

TiO2/SiO2stack

TiO2 = 1.8 π‘œπ‘› 𝑦 38 SiO2 = 3.6 π‘œπ‘› 𝑦 37 Kuo et al., Opt. Lett.44, 247-250 (2019); Chao et al., 41st PIERS 2019; Principe, Opt. Express 23, 10938-10956 (2015)

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Coater @UniSannio

Credit: M. Principe

Good quality nano-layered multi-stack coating produced, surface roughness RMS < 1π‘œπ‘› AFM analysis

Nano-layered coating deposition

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Metrology

Coating mechanical losses are computed by difference between the 𝜚 measurement after and before the coating process

  • High accuracy and repeatability of the measurements are needed: the Gentle Nodal Suspension (GeNS) is the best

mechanical losses measurement techniques for this purposes (Cesarini et al. 2009 Rev. Sci. Instrum. 80)

  • 𝜚 measurement protocol must be established and shared among all the laboratories
  • For thermo-elastic losses dominated samples (silicon or sapphire thin disks), an experimental technique to estimate

the thermo-elastic dissipation peak shift due to the coating film deposition, is needed. It is currently under study, first results: Cesarini et al. poster GWADW 2019

  • In many cases thin disk-shaped samples are not polished in their barrels. The effect of this extra loss has been

effectively modeled. A laser-polishing of this sample edges has been performed and a reduction of the extra losses measured (Cagnoli et al. Phys. Lett. A 382 (33), 2018)

  • Stability of substrate is mandatory: aging effects are deeply under investigation (Lumaca et al. 2019 Amaldi 13)
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Conclusions

  • To improve the sensitivity of the future gravitational wave detector, coating thermal noise must be reduced
  • Inside the VCR&D Collaboration a set of research lines are pursued in parallel by groups of labs, to optimize the

likelihood of getting to a breakthrough. Research lines exploit both experimental characterizations and theoretical and computational modelling of the coating thermal noise sources.

  • Many interesting results are coming out from the various research lines:

βœ“ New/reviewed measurement of the current GW detector coatings βœ“ New mixtures, post deposition treatments and nano layered coatings are under study βœ“ Non oxides materials: promising measurements from SiNx βœ“ A correlation between absorption and mechanical losses has been found βœ“ Encouraging results on structural modelling are coming out: a tool for a fast mechanical properties evaluation βœ“ Some metrology problems (aging, thermoelastic shifts, edge effect) are under investigation

  • VCR&D works in coordination with LSC Optics group, facilitating information exchange and avoiding research lines

superposition

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Thank you!

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Spare slides

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Thermal noise in a GW detector

Thermal fluctuation is a source of displacement noise of the GW detector test masses Mirror thermal noise: mirror bulk, lower clamps and HCB, mirror coating Suspension thermal noise: fibers (pendulum, violin), upper clamps and hydroxide catalysis bonding(HCB)

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Mirror coating is responsible for most

  • f the mirror thermal noise in current

GW detector

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Tetrahedrons is the basic block of silica molecular structure The disordered distribution in amorphous silica hides local structural units Anelastic level transition Elastic fluctuations 𝜐

The silica example

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Oxide mixtures, π‘ˆπ‘—π‘ƒ2: π‘ˆ

𝑏2𝑃5optimization

KAGRA AdV+, aLIGO About 25% loss reduction for π‘ˆπ‘—π‘ƒ2: π‘ˆ

𝑏2𝑃5 with concentration π‘ˆπ‘— Ta = 0.27

Granata et al. in preparation Amato et al J. Phys Conf. Ser. 957 (2018)

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  • Post-deposition annealing largely improves coating mechanical characteristics.
  • Maximum annealing temperature is limited by the beginning of the film crystallization (i.e. Tmax β‰ˆ 300 °𝐷 for Ta2O5)
  • In nano-layered films crystallization is frustrated by the size of the layers, higher annealing temperature is allowed

Kuo et al., Opt. Lett.44, 247-250 (2019) Chao et al., 41st PIERS 2019 Principe, Opt. Express 23, 10938-10956 (2015)

Nano-layered coating deposition