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

HART, M. J., Bassiri, R., Borisenko, K. B., Véron, M., Rauch, E. F., Martin, I. W. , Rowan, S., Fejer, M. M. and MacLaren, I. (2016) Medium range structural order in amorphous tantala spatially resolved with changes to atomic structure by thermal annealing. Journal of Non-Crystalline Solids, 438, pp. 10-17. (doi:10.1016/j.jnoncrysol.2016.02.005)

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Abstract

Amorphous 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.

Item Type:Articles
Additional Information:MJH, IM, IWM and SR gratefully acknowledge the support of the STFC (ST/L000946/1 'Investigations in Gravitational Research'), for this work. MJH is grateful to the EPSRC for a PhD studentship. IWM is supported by a Royal Society Research Fellowship. The authors would like to thank Dr. Stavros Nicolopoulos of NanoMegas SPRL for his support for the work in Grenoble, without which this work would not have been possible. RB and MMF gratefully acknowledge the support of the NSF, under award number PHY-1404430.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Rowan, Professor Sheila and Martin, Dr Iain and MacLaren, Dr Ian and Bassiri, Mr Riccardo and HART, Martin
Authors: HART, M. J., Bassiri, R., Borisenko, K. B., Véron, M., Rauch, E. F., Martin, I. W., Rowan, S., Fejer, M. M., and MacLaren, I.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Journal of Non-Crystalline Solids
Publisher:Elsevier B.V.
ISSN:0022-3093
ISSN (Online):1873-4812
Copyright Holders:Copyright © 2016 The Authors
First Published:First published in Journal of Non-Crystalline Solids
Publisher Policy:Reproduced under a Creative Commons License
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
624341Investigations in Gravitational Radiation / Particle Astrophysics Capital equipmentSheila RowanScience & Technologies Facilities Council (STFC)ST/L000946/1S&E P&A - PHYSICS & ASTRONOMY
608951Engineering and Physical Sciences Doctoral Training Grant 2012-16Mary Beth KneafseyEngineering & Physical Sciences Research Council (EPSRC)EP/K503058/1VICE PRINCIPAL RESEARCH & ENTERPRISE