Correlated evolution of structure and mechanical loss of a sputtered silica film

Granata, M.; Coillet, Elodie; Martinez, V.; Dolique, V.; Amato, A.; Canepa, M.; Margueritat, Jérémie; Martinet, C.; Mermet, A.; Michel, C.; Pinard, L.; Sassolas, B.; Cagnoli, G.

doi:10.1103/physrevmaterials.2.053607

Cited by 25 publications

(37 citation statements)

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“…Indeed, the finding regarding the Urbach tails parallels the well-known (yet still not fully understood) doping-induced reduction of internal friction observed in these films [7]. It has been shown that there is a correlation between mechanical losses and the disordered structure of this coatings [16,25]. The results of this work offer therefore new stimuli for a more systematic investigation of the correlations between the optical properties of high quality Ti-doped tantala coatings, with particular attention to the extension of Urbach tails, and their mechanical properties.…”

Section: Resultssupporting

confidence: 74%

“…In this view, a precise determination of refractive index and thickness of coating layers is a key ingredient in the improvement of the mirrors. Adding to this, an accurate knowledge of coating thickness is important in order to evaluate the density of the materials under investigation, which is an essential parameter in the analysis of mechanical loss data providing information about the internal friction [14,16].…”

Section: Introductionmentioning

confidence: 99%

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Optical properties of high-quality oxide coating materials used in gravitational-wave advanced detectors

et al. 2019

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High-reflection interference mirrors for current gravitational wave detectors (aLIGO, Advanced Virgo, KAGRA) are made of high-quality oxide multi-layers deposited by ion beam sputtering (IBS) at the Laboratoire des Matériaux Avancés (LMA). For this task, LMA uses a large IBS custom-made machine (the grand coater GC) able to deposit very uniform coatings over very large surfaces, with diameter of some tens of cm. We report for the first time about the optical characterization by spectroscopic ellipsometry of oxide coatings deposited by the GC under strictly the same conditions used for the production of interference mirrors. We have investigated oxide materials like silica (SiO 2 ), tantala (Ta 2 O 5 ) and titania-doped tantala (Ti:Ta 2 O 5 ), providing for each material a broad-band (190-1700 nm) accurate determination of the complex index of refraction, with particular attention to wavelengths used in interferometers. Particular focus has been dedicated to the influence of Tidoping on tantala coating. The doping induces a red-shift of the optical gap and an increase of the NIR refractive index. Furthermore, doping induces a decrease of the so-called Urbach energy, consistent with the well-known reduction of the internal friction in these kind of systems.

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Section: Resultssupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Optical properties of high-quality oxide coating materials used in gravitational-wave advanced detectors

et al. 2019

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“…In order to represent the complexity of the material, different TLS having a distribution of the ADWP potential V and asymmetry Δ are considered 31 . It is possible to show that at room temperature the internal friction in a material is proportional to the density of TLS that have a barrier height of about 0.5 eV 32 . In fact, following the Arrhenius law, the TLS with lower barrier height are too fast with respect to the period of the external excitation and in this way their contribution to the energy dissipation is negligible.…”

Section: Resultsmentioning

confidence: 99%

“…These changes in the amorphous structure correlate with a reduction of mechanical losses. In another recent work, Raman spectroscopy measurements on SiO 2 coating showed that extended structures such as rings made of three tetrahedrons of SiO 2 (the PSU of SiO 2 ) are correlated to the coating loss angle 32 and have an activation energy of about 0.43 eV 42 . Furthermore, molecular dynamics of AO such as SiO 2 showed that TLS with a barrier of 0.5 eV primarily involves quasi-1D chain of Si-O-Si and rings of Si-O-Si bonds 43 .…”

Section: Discussionmentioning

confidence: 97%

Observation of a Correlation Between Internal friction and Urbach Energy in Amorphous Oxides Thin Films

Amato

Terreni

Granata

et al. 2020

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We have investigated by spectroscopic ellipsometry (SE, 190-1700 nm) the optical properties of uniform, amorphous thin films of Ta 2 o 5 and nb 2 o 5 as deposited and after annealing, and after so-called "doping" with ti atoms which leads to mixed oxides. ta 2 o 5 and ti:ta 2 o 5 are currently used as high-index components in Bragg reflectors for Gravitational Wave Detectors. Parallel to the optical investigation, we measured the mechanical energy dissipation of the same coatings, through the so-called "loss angle" φ = Q −1 , which quantifies the energy loss in materials. By applying the well-known Cody-Lorentz model in the analysis of Se data we have been able to derive accurate information on the fundamental absorption edge through important parameters related to the electronic density of states, such as the optical gap (E g) and the energy width of the exponential Urbach tail (the Urbach energy E U). We have found that E U is neatly reduced by suitable annealing as is also perceptible from direct inspection of Se data. ti-doping also points to a minor decrease of E U. the reduction of E U parallels a lowering of the mechanical losses quantified by the loss angle φ. the correlation highlights that both the electronic states responsible of Urbach tail and the internal friction are sensitive to a self-correlation of defects on a medium-range scale, which is promoted by annealing and in our case, to a lesser extent, by doping. these observations may contribute to a better understanding of the relationship between structural and mechanical properties in amorphous oxides.

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“…In the meanwhile, structural analyses [51][52][53] and molecular dynamics simulations [54-57] might provide critical hints towards a more radical solution of the coating thermal noise issue, to benefit future GW interferometers [28,29].…”

Section: Discussionmentioning

confidence: 99%

Progress in the measurement and reduction of thermal noise in optical coatings for gravitational-wave detectors

et al. 2020

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Coating thermal noise is a fundamental limit for precision experiments based on optical and quantum transducers. In this review, after a brief overview of the techniques for coating thermal noise measurements, we present the latest world-wide research activity on low-noise coatings, with a focus on the results obtained at the Laboratoire des Matériaux Avancés. We report new updated values for the Ta 2 O 5 , Ta 2 O 5 -TiO 2 and SiO 2 coatings of the Advanced LIGO, Advanced Virgo and KAGRA detectors, and new results from sputtered Nb 2 O 5 , TiO 2 -Nb 2 O 5 , Ta 2 O 5 -ZrO 2 , MgF 2 , AlF 3 and silicon nitride coatings. Amorphous silicon, crystalline coatings, high-temperature deposition, multi-material coatings and composite layers are also briefly discussed, together with the latest developments of structural analyses and models. The issue of coating thermal noiseThe Laboratoire des Matériaux Avancés (LMA, now a division of the newly created Institut de Physique des 2 Infinis de Lyon) has provided the current high-reflection (HR) and anti-reflective (AR) coatings of the most critical optics of Advanced LIGO [1], Advanced Virgo [2] and KAGRA [3]. In these gravitational-wave (GW) interferometers, large and massive suspended mirrors (typically with ∅ = 35 cm, t = 20 cm, m = 40 kg) form the km-long resonant Fabry-Perot cavities where the astrophysical signals are embedded in the laser beam phase. Their HR coatings are Bragg reflectors of alternate layers of ion-beam-sputtered (IBS) low-and high-refractive index materials, which feature outstanding optical properties [4]. At the same time, these amorphous coatings are the source of coating thermal noise (CTN), which is a severe limitation to the detector sensitivity [1,2].In GW interferometers, thermal noise arises from fluctuations of the mirror surface under the random motion of particles in coatings and substrates [5,6]. Its power spectral density is determined by the amount of internal friction within the mirror materials, via the fluctuationdissipation theorem [7]: the higher the elastic energy loss, the higher the thermal noise level. As the coating loss is usually several orders of magnitude larger than that of the substrate [8,9], CTN is the dominant source of noise in the mirrors.More generally, CTN is a fundamental limit for precision experiments based on optical and quantum transducers, such as opto-mechanical resonators [10], frequency standards [11] and quantum computers [12]. In the last two decades, a considerable research effort has been committed to the measurement and the reduction of CTN.

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Correlated evolution of structure and mechanical loss of a sputtered silica film

Cited by 25 publications

References 37 publications

Optical properties of high-quality oxide coating materials used in gravitational-wave advanced detectors

Optical properties of high-quality oxide coating materials used in gravitational-wave advanced detectors

Observation of a Correlation Between Internal friction and Urbach Energy in Amorphous Oxides Thin Films

Progress in the measurement and reduction of thermal noise in optical coatings for gravitational-wave detectors

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