Order within disorder: The atomic structure of ion-beam sputtered amorphous tantala (a-Ta2O5)

Bassiri, R.; Liou, Franklin; Abernathy, M. R.; Lin, A. C.; Kim, Namjun; Mehta, Apurva; Shyam, Badri; Byer, Robert L.; Gustafson, E. K.; Hart, M. J.; MacLaren, Ian; Martin, I. W.; Route, R.; Rowan, S.; Stebbins, Jonathan F.; Fejer, M. M.

doi:10.1063/1.4913586

Cited by 21 publications

(18 citation statements)

References 37 publications

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“…Extended X-ray Absorption Fine Structure (EXAFS) shows more extensive order to perhaps the 3rd or 4th nearest neighbour and is chemically sensitive to the ordering about specific atoms, although this still does not reveal any order beyond 1 nm. Our recent work has shown that this provides further insights into the behaviour on annealing [15]. The previous electron diffraction studies have shown the atomic structure to be homogeneous at volumes probed with electron beams of 50 nm in lateral extent up to a 600°C heat treatment, whereas in the present study the atomic structure is shown to be heterogeneous over volumes probed with an electron beam of 2 nm in lateral extent.…”

Section: Introductionsupporting

confidence: 53%

Medium range structural order in amorphous tantala spatially resolved with changes to atomic structure by thermal annealing

Hart

Bassiri

Borisenko

et al. 2016

Journal of Non-Crystalline Solids

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International audienceAmorphous tantala (a-Ta2O5) is an important technological material that has wide ranging applications in electronics, optics and the biomedical industry. It is used as the high refractive index layers in the multi-layer dielectric mirror coatings in the latest generation of gravitational wave interferometers, as well as other precision interferometers. One of the current limitations in sensitivity of gravitational wave detectors is Brownian thermal noise that arises from the tantala mirror coatings. Measurements have shown differences in mechanical loss of the mirror coatings, which is directly related to Brownian thermal noise, in response to thermal annealing. We utilise scanning electron diffraction to perform a modified version of Fluctuation Electron Microscopy (FEM) on Ion Beam Sputtered (IBS) amorphous tantala coatings, definitively showing an increase in the medium range order (MRO), as determined from the variance between the diffraction patterns in the scan, due to thermal annealing at increasing temperatures. Moreover, we employ Virtual Dark-Field Imaging (VDFi) to spatially resolve the FEM signal, enabling investigation of the persistence of the fragments responsible for the medium range order, as well as the extent of the ordering over nm length scales, and show ordered patches larger than 5 nm in the highest temperature annealed sample. These structural changes directly correlate with the observed changes in mechanical loss. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

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Section: Introductionsupporting

confidence: 53%

Medium range structural order in amorphous tantala spatially resolved with changes to atomic structure by thermal annealing

Hart

Bassiri

Borisenko

et al. 2016

Journal of Non-Crystalline Solids

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“…Recently published Ta-centered local structure from Ta L 3 edge EXAFS data3031 indicate that the Ta ions are surrounded by between 5 and 6 oxygens. There are different ways in which these Ta centered polyhedra connect to each other to give rise to different polymorphs.…”

Section: Resultsmentioning

confidence: 99%

“…Extracting the bond distances and average coordination number constrains (shown in Fig. 2b), from Ta-centered information from Ta L 3 edge EXAFS data3031 and O-centered information from NMR spectroscopy32, we construct the backbone of the topological PSU as a kinked Ta-O-Ta chain, with a Ta-O bond of ca. 2.05 Å and a Ta-O-Ta angle of approximately 135–150 degrees.…”

Section: Resultsmentioning

confidence: 99%

Measurement and Modeling of Short and Medium Range Order in Amorphous Ta2O5 Thin Films

Shyam

Stone

Bassiri

et al. 2016

Sci Rep

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Amorphous films and coatings are rapidly growing in importance. Yet, there is a dearth of high-quality structural data on sub-micron films. Not understanding how these materials assemble at atomic scale limits fundamental insights needed to improve their performance. Here, we use grazing-incidence x-ray total scattering measurements to examine the atomic structure of the top 50–100 nm of Ta2O5 films; mirror coatings that show high promise to significantly improve the sensitivity of the next generation of gravitational-wave detectors. Our measurements show noticeable changes well into medium range, not only between crystalline and amorphous, but also between as-deposited, annealed and doped amorphous films. It is a further challenge to quickly translate the structural information into insights into mechanisms of packing and disorder. Here, we illustrate a modeling approach that allows translation of observed structural features to a physically intuitive packing of a primary structural unit based on a kinked Ta-O-Ta backbone. Our modeling illustrates how Ta-O-Ta units link to form longer 1D chains and even 2D ribbons, and how doping and annealing influences formation of 2D order. We also find that all the amorphousTa2O5 films studied in here are not just poorly crystalline but appear to lack true 3D order.

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“…Techniques such as Extended X-ray Absorption Fine Structure (EXAFS) and Fluctuation Electron Microscopy (FEM) have recently been used to explore the atomic structure of tantala and Ti-doped tantala [97,98]. Theoretical modeling by using density functional theory molecular dynamic simulation with reverse Monte Carlo refinements [99,100] in conjunction with the experimental probing techniques will be useful to gain insight for the mechanical loss of the amorphous coating materials and will lead to feedbacks for material tailoring for improving coatings of the laser interference gravitational wave detector.…”

Section: Correlations Between Atomic Structure and Mechanical Lossmentioning

confidence: 99%

Technology for the next gravitational wave detectors

Mitrofanov

Chao

Pan

et al. 2015

Sci. China Phys. Mech. Astron.

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This paper reviews some of the key enabling technologies for advanced and future laser interferometer gravitational wave detectors, which must combine test masses with the lowest possible optical and acoustic losses, with high stability lasers and various techniques for suppressing noise. Sect. 1 of this paper presents a review of the acoustic properties of test masses. Sect. 2 reviews the technology of the amorphous dielectric coatings which are currently universally used for the mirrors in advanced laser interferometers, but for which lower acoustic loss would be very advantageous. In sect. 3 a new generation of crystalline optical coatings that offer a substantial reduction in thermal noise is reviewed. The optical properties of test masses are reviewed in sect. 4, with special focus on the properties of silicon, an important candidate material for future detectors. Sect. 5 of this paper presents the very low noise, high stability laser technology that underpins all advanced and next generation laser interferometers

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Order within disorder: The atomic structure of ion-beam sputtered amorphous tantala (a-Ta2O5)

Cited by 21 publications

References 37 publications

Medium range structural order in amorphous tantala spatially resolved with changes to atomic structure by thermal annealing

Medium range structural order in amorphous tantala spatially resolved with changes to atomic structure by thermal annealing

Measurement and Modeling of Short and Medium Range Order in Amorphous Ta2O5 Thin Films

Technology for the next gravitational wave detectors

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