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M. Prato, M. Canepa, A. Chincarini, G. Gemme

Multitechnique investigation of Ta 2 O 5 films and bulk samples: comparison of optical, chemical and morphological properties. M. Prato, M. Canepa, A. Chincarini, G. Gemme Dipartimento di Fisica, Univ. di Genova and INFN Genova G. Cagnoli, E. Cesarini, F. Vetrano

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M. Prato, M. Canepa, A. Chincarini, G. Gemme

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  1. Multitechnique investigation of Ta2O5 films and bulk samples: comparison of optical, chemical and morphological properties M. Prato, M. Canepa, A. Chincarini, G. Gemme Dipartimento di Fisica, Univ. di Genova and INFN Genova G. Cagnoli, E. Cesarini, F. Vetrano Istituto di Fisica, Univ. di Urbino and INFN Firenze

  2. The scientific case... • Mechanical dissipation from dielectric mirror coatings is predicted to be a significant source of thermal noise for advanced detectors. • Experiments suggest • Ta2O5 is the dominant source of dissipation in current SiO2/Ta2O5 coatings • D.R.M. Crooks et al, Class.Q.Gravity, 21, 1059 (2004) • K.Numata et al., Phys.Rev.Letters, 91,260602 (2003) • S.Penn et al, Class.Q.Gravity, 20, 2917 (2003) • D.R.M. Crooks et al, Class.Q.Gravity, 23, 4953 (2006) • G.Harry et al, Class.Q.Gravity, 24, 405 (2007) • Doping the Ta2O5 with TiO2 can reduce the mechanical dissipation • Mechanism responsible for the observed mechanical loss in Ta2O5 not yet clearly identified 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  3. Viable strategy: focusing on a single SiO2 (Corning)/Ta2O5 repeat unit (Ta2O5 200nm double ion sputtering, ATFilms) • Surface Properties: • AFM (morphology) • rms roughness • XPS Chemical analysis • stoichiometry • contaminations • Film and interface properties • Spectroscopic Ellipsometry • optical properties (refractive index) • thickness • surface roughness • interface mixing • Comparison with bulk properties • Correlation with mechanical properties E. Cesarini , Poster #111 this conference 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  4. Rotating Compensator Spectroscopic Ellipsometer WoollamM-2000X • Variableangle of incidence (40°÷90°) • Parallelacquisition of 680 wls • -range (245÷1700) nm • Fast acquisition (dynamics) • Generalized ellipsometry (non diagonal Jones Matrix anisotropic samples) • Mueller Matrix depolarization 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  5. Comparison with simulations needs a model of the optical system Ta2O5 200nm The Cody-Lorentz Oscillator 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  6. Ta2O5 refractive index n = 2.088 @ 1064 nm k = 1.3  10-3@ 1064 nm 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  7. 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  8. Cantilever The optical model needs more information on the surface layer… AFM Atomic Force Microscope VEECO Dimension 3100 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  9. Tapping mode 30  30 mm 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  10. The opticalmodelneedsmore information on the surfacelayer… XPS Multitechnique System Physical Electronics 5600ci 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  11. Ta2O5 200nm film Ta 4f peak Sub-oxides? Ta? 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  12. Ta2O5 99.99% powder Ta 4f peak 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  13. Ta2O5 200nm film O 1s peak Ta2O5 • Dissipation peak observed at ~ 20 K in both pure Ta2O5 and in Ta2O5 doped with 14.5 % TiO2 • Activation energy of dissipation process calculated to be: • 42 ± 2 meV for doped coating • 24 ± 2 meV for undoped coating • Possible dissipation mechanism is thermally activated transitions of the oxygen atoms, similar to that in fused silica • S. Reid et al, LIGO-G080048-00-R ? Some evidence that TiO2 doping reduces the height of the dissipation peak in Ta2O5, in addition to reducing the loss at room temperature. A full understanding of the dissipation mechanism may allow mechanical loss at room temperature to be further reduced 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  14. Correlation with mechanical properties E. Cesarini et al, REVIEW OF SCIENTIFIC INSTRUMENTS 80, 053904 (2009) E. Cesarini et al, Poster #111, this conference 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

  15. Future work • Wide scale alterations • Annealing in vacuum or controlled atmosphere • Small scale alterations • Doping ( ion implantation, e.g. Ti+) • Laser heating/damaging • Photon irradiation (X-rays, UV) • Ion beams • Tests withothershigh index materials : Nb2O5, HfO2…… Is there a correlationbetweenoptical and mechanicalproperties? Is there a balance betweenoptical and mechanicalproperties? O. Stenzel et al, J Phys D: ApplPhys 42, (2009) 055312 O. Stenzel et al, ThinSolid Films, (2009) prepress 8th Amaldi Conference on Gravitational Waves, Columbia University, New York

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