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Overview of coatings research and recent results at the University of Glasgow

Overview of coatings research and recent results at the University of Glasgow.

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Overview of coatings research and recent results at the University of Glasgow

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  1. Overview of coatings research and recent results at the University of Glasgow M. Abernathy, I. Martin, R. Bassiri, E. Chalkley, R. Nawrodt, M.M. Fejer, A. Gretarsson, G. Harry, D. Heinert, J. Hough, I. MacLaren, S. Penn, S. Reid, R. Route, S. Rowan, C Schwarz, P. Seidel, J. Scott, A.L. Woodcraft University of Glasgow GWADW, Kyoto Japan, May 2010 Document #: LIGO-G1000508-x0

  2. Things You Should Already Know: • Thermal Noise • Limits Detectors • Important component comes from Ta2O5 • Doping Ta2O5 has been shown to reduce thermal noise. • Temperature Dependence of mechanical loss can tell us about loss mechanisms

  3. Things You should Know by the End of this Talk Pt. 1: Ta2O5 • Doping changes the activation energy of Tantala’s loss mechanism. • Does anything else do that? • Heat treatment also changes the activation energy • Different deposition techniques change activation energies.

  4. Things You Should Know by the End of this Talk Pt. 2: Additional Notes • Ion Beam Sputtered (IBS) Silica coatings have temperature dependant loss too • Hafnia (HfO2) is an interesting material for study

  5. Thermal Noise Coating thermal noise • Coating thermal noise will limit sensitivity of Next-generation detectors at their most sensitive frequencies Evans et al PRD 78 102003 (2008) 5 5

  6. Mechanical Loss Y,Y’ … Young’s modulus of the bulk/coating material  … mechanical loss o the coatings [Harry et al. 2002] • Thermal noise of the coatings is related to the mechanical loss of the coating material:

  7. Mechanical Loss and Measurement

  8. Mechanical loss spectroscopy electrostatic drive 34mm 50mm thick Coating applied here 500mm tantala coating coated cantilever in clamp • Single layers of coating materials appliedto silicon cantilever substrates supplied by Stanford / KNT • Cantilever clamped rigidly and bending modes excited electrostatically. Loss obtained from exponential decay of amplitude

  9. Measuring coating loss (c) (b) (a) Loss of (a) uncoated silicon cantilever with thermal oxide layer, (b) cantilever coated with 500 nm of TiO2-doped Ta2O5 (14.5 % Ti) and (c) the calculated loss of the coating layer • Mechanical loss of coating layer calculated from difference in loss of a coated and un-coated cantilever

  10. Measuring coating loss (c) (b) (a) Loss of (a) uncoated silicon cantilever with thermal oxide layer, (b) cantilever coated with 500 nm of TiO2-doped Ta2O5 (14.5 % Ti) and (c) the calculated loss of the coating layer • Mechanical loss of coating layer calculated from difference in loss of a coated and un-coated cantilever

  11. Measuring coating loss (c) (b) (a) Loss of (a) uncoated silicon cantilever with thermal oxide layer, (b) cantilever coated with 500 nm of TiO2-doped Ta2O5 (14.5 % Ti) and (c) the calculated loss of the coating layer • Mechanical loss of coating layer calculated from difference in loss of a coated and un-coated cantilever

  12. Ta2O5 and Doping G. M. Harry et al 2007 Class. Quantum Grav. 24 405.

  13. Effect of doping on loss of Ta2O5 coatings Comparison of dissipation in tantala doped with 14.5 % TiO2 and un-doped tantala for 3rd (left) and 4th (right) bending modes.

  14. Effect of doping on loss of Ta2O5 coatings • TiO2 doping reduces the height and slightly increases the width of the dissipation peak • TiO2 doping reduces the loss of Ta2O5 throughout the temperature range studied, with the exception of the wings of the peak

  15. Analysis of coating loss peak (TiO2 doped coating) Debye-like dissipation peaks Tpeak increases with mode frequency indicating a thermally activated dissipation mechanism  … relaxation strength  … relaxation time t0 = relaxation constant Ea = activation energy

  16. Analysis of coating loss peak Activation energy of dissipation process: • (40 ± 3) meV for titania doped tantala • (29 ± 2) meV for undoped tantala • Doping increases the activation energy • Transition between two stable states appears to be hindered by doping

  17. Distribution of parameters • Amorphous structure results in a distribution of potential barrier heights g(V) • Activation energy calculated from Arrhenius law corresponds to the average barrier height in this distribution • The barrier height distribution function g(V) can be calculated from temperature dependent loss data • Doping shifts distribution of barrierheights to higher energy, thusreducing loss • 1 Gilroy, Phillips, Phil. Mag. B 43 (1981) 735 • 2 Topp, Cahill, Z. Phys. B: Condens. Matter 101 (1996) 235

  18. Distribution of parameters • Amorphous structure results in a distribution of potential barrier heights g(V) • Activation energy calculated from Arrhenius law corresponds to the average barrier height in this distribution • The barrier height distribution function g(V) can be calculated from temperature dependent loss data • Doping shifts distribution of barrierheights to higher energy, thusreducing loss Doping Affects Activation Energy • 1 Gilroy, Phillips, Phil. Mag. B 43 (1981) 735 • 2 Topp, Cahill, Z. Phys. B: Condens. Matter 101 (1996) 235

  19. Heat Treatment

  20. Effect of heat treatment temperature on Ta2O5 loss 300 C 800 C 600 C 400C 300C • 35 K peak • Observed in Ta2O5 heat treated at 300, 400 C. Evidence suggests may also be present in Ta2O5 heat treated at 600 C • Activation energy 54 meV • Postulate that this may be analogous to dissipation peak in fused silica , involving thermally activated transitions of oxygen atoms 800 C 800 C 800 C 800 C 800 C 800 C 800 C 800 C 800 C Above: Electron diffraction pattern of Ta2O5 heat treated at 300 C Left: Loss at 1.9 kHz of 0.5 mm Ta2O5 coatings annealed at 300,400, 600 and 800 C. (i) 600 C 600 C 600 C 600 C 600 C 600 C 600 C 400C 400C 400C 400C 300C 300C

  21. Effect of heat treatment temperature on Ta2O5 loss 600 C 800 C 600 C 400C 300C 600 C • 18 K peak • Observed in Ta2O5 heat treated at 600 C and 800 C • Dissipation mechanism may be related to structural changes brought on by heat treatment close to re-crystallisation temperature • Perhaps some pre-crystallisation ordering (but still appears amorphous on electron diffraction measurements) 800 C 800 C 800 C 800 C 800 C 800 C 800 C 800 C 800 C Above: Electron diffraction pattern of Ta2O5 heat treated at 600 C Left: Loss at 1.9 kHz of 0.5 mm Ta2O5 coatings annealed at 300,400, 600 and 800 C. (i) 600 C 600 C 600 C 600 C 600 C 600 C 600 C 400C 400C 400C 400C 300C 300C

  22. Effect of heat treatment temperature on Ta2O5 loss 800 C 800 C 600 C 400C 300C 800 C • 90 K peak • Observed in coating heat treated at 800 C • Large, broad loss peak likely to be related to (expected) onset of polycrystalline structure due to high temperature heat treatment • Dissipation mechanism could be e.g. phonon scattering at grain boundaries – more analysis required 800 C 800 C 800 C 800 C 800 C 800 C 800 C 800 C 800 C Above: Electron diffraction pattern of Ta2O5 heat treated at 800 C Left: Loss at 1.9 kHz of 0.5 mm Ta2O5 coatings annealed at 300,400, 600 and 800 C. (i) 600 C 600 C 600 C 600 C 600 C 600 C 600 C 400C 400C 400C 400C 300C 300C

  23. Effect of heat treatment temperature on Ta2O5 loss 800 C 800 C 600 C 400C 300C 800 C • 90 K peak • Observed in coating heat treated at 800 C • Large, broad loss peak likely to be related to (expected) onset of polycrystalline structure due to high temperature heat treatment • Dissipation mechanism could be e.g. phonon scattering at grain boundaries – more analysis required 800 C 800 C 800 C 800 C 800 C 800 C 800 C 800 C 800 C Above: Electron diffraction pattern of Ta2O5 heat treated at 800 C Left: Loss at 1.9 kHz of 0.5 mm Ta2O5 coatings annealed at 300,400, 600 and 800 C. Heat Treatment Affects Activation Energy (i) 600 C 600 C 600 C 600 C 600 C 600 C 600 C 400C 400C 400C 400C 300C 300C

  24. Deposition Effects

  25. Silica - comparison of deposition methods (c) (a) (b) (d) • Bulk silica (a) & thermal oxide (b)grown on siliconhave a dissipationpeak at ~ 35 K1,2 • e-beam SiO2 (5.5 kHz)1(c) • 109 nm thick e-beam film showsno peak at 35 K • Higher loss than bulk and thermaloxide above 40 k • Ion beam sputtered silica (d) • Broad loss peak at ~ 23 K • Significantly lower loss than similar thickness of e-beam and thermal SiO2 • Deposition method can have a significant effect on loss – studies of coatings deposited by different methods planned 1White and Pohl, Phys. Rev. Lett. 75 (1995) 4437, 2Cahill and Van Cleve Rev. Sci. Inst. 60 (1989) 2706.

  26. ‘Low water content’ Ta2O5 from ATF • ATF Ta2O5 heat treated at the same temperatures as CSIRO / LMA Ta2O5 has loss peaks at significantly higher temperatures. Full analysis underway • Suggests details of coating deposition procedure may have significant impact on the temperature dependence of the mechanical loss – further study of great interest Left: CSIRO / ATF comparison, heat treated at 600 C post-deposition. Right: CSIRO / ATF comparison, heat treated at 300 C post-deposition.

  27. ‘Low water content’ Ta2O5 from ATF • ATF Ta2O5 heat treated at the same temperatures as CSIRO / LMA Ta2O5 has loss peaks at significantly higher temperatures. Full analysis underway • Suggests details of coating deposition procedure may have significant impact on the temperature dependence of the mechanical loss – further study of great interest Deposition Affects Activation Energy Left: CSIRO / ATF comparison, heat treated at 600 C post-deposition. Right: CSIRO / ATF comparison, heat treated at 300 C post-deposition.

  28. Additional Notes

  29. Comparison of SiO2 and Ta2O5 • Ta2O5 has higher loss throughout temperature range, but loss of SiO2 will also be significant below 100 K Scatter at higher temperatures, possibly due to loss into clamp.

  30. Temperature dependence of coating thermal noise at 100 Hz Using measuredcoating loss • If coating loss was constant with temperature, could gain factor of ~ 4 in coating thermal displacement noise of a mirror at 18 K • Measured coating losses imply a gain of a factor of ~ 1.7 in coating TN by cooling to 18 K Optimistic estimate – constantcoating loss at all temperatures

  31. Temperature dependence of coating thermal noise at 100 Hz Using measuredcoating loss • If coating loss was constant with temperature, could gain factor of ~ 4 in coating thermal displacement noise of a mirror at 18 K • Measured coating losses imply a gain of a factor of ~ 1.7 in coating TN by cooling to 18 K IBS Silica Coating Loss is Temperature Dependant Optimistic estimate – constantcoating loss at all temperatures

  32. Alternative high index materials - hafnia loss peak/plateau around 200 K • Hafnia studied – allow comparisonof loss in another high-index oxide • Different atom weight / size • Differences in dynamics arisingfrom atom weight expected • Loss significantly lower thantantala below 125 K • Peak position and width shiftedcompared to tantala • High optical absorption (60 ppm)measured at Stanford loss peak around 50 K Coating loss at ~ 1kHz for HfO2 and Ta2O5 heat treated at 300ºC. (E. Chalkley)

  33. Effect of heat treatment on loss of hafnia • As-deposited (100 C) shows no clear loss peaks • Peak at ~50 K observedin coatings heat treatedat 300 and 400 K • Electron diffractionmeasurements show evidenceof both crystalline and amorphous structure in all thehafnia coatings • Silica-doped hafnia remains amorphous when annealed up to 500 C, and presence of silica appears to only slightly increase loss at room temperature

  34. Effect of heat treatment on loss of hafnia • As-deposited (100 C) shows no clear loss peaks • Peak at ~50 K observedin coatings heat treatedat 300 and 400 K • Electron diffractionmeasurements show evidenceof both crystalline and amorphous structure in all thehafnia coatings • Silica-doped hafnia remains amorphous when annealed up to 500 C, and presence of silica appears to only slightly increase loss at room temperature Hafnia Is Interesting

  35. Things You should Now Know • Doping changes the activation energy of Tantala’s loss mechanism. • Heat treatment also changes the activation energy • Different deposition techniques change activation energies. • IBS silica coating has temperature related loss • Hafnia (HfO2) is an interesting material for study

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