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Nano-coatings the reasons and the R&D status

Nano-coatings the reasons and the R&D status. Riccardo DeSalvo I.M. Pinto, V. Pierro , V. Galdi , M. Principe, Shiuh Chao, Huang-Wei Pan, Chen-Shun Ou , V. Huang. Gravitational Wave Advanced Detector Workshop, Waikoloa Marriott Resort, Hawaii, May 14 2012. JGW-G1201029. 1. Outline.

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Nano-coatings the reasons and the R&D status

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  1. JGW-G1201029 LIGO-G1200562 Nano-coatingsthe reasons and the R&D status Riccardo DeSalvo I.M. Pinto, V. Pierro, V. Galdi, M. Principe, Shiuh Chao, Huang-Wei Pan, Chen-Shun Ou, V. Huang Gravitational Wave Advanced Detector Workshop, Waikoloa Marriott Resort, Hawaii, May 14 2012 JGW-G1201029 1

  2. JGW-G1201029 LIGO-G1200562 Outline • Reasons to study nanometer coatings • Status of R&D 14 may 2012 GWADW 2012 JGW-G1201029 2

  3. First interest for nanocoatings JGW-G1201029 LIGO-G1200562 • RDS participated to the PXRMS conference Big Sky – Montana • X-ray mirror coating community • LIGO-G080106-00-R 14 may 2012 GWADW 2012 JGW-G1201029 3

  4. Lessons from x-ray community JGW-G1201029 LIGO-G1200562 • Extremely thin layers are always glassy • More stable ! • Natural doping due to inter-diffusion may also play a relevant role • Different atomic radius and oxydation pattern assure glassy structure around the interface between different materials Sub-layer thickness 14 may 2012 GWADW 2012 JGW-G1201029 4

  5. Lessons from x-ray community, II JGW-G1201029 LIGO-G1200562 • Good glass formers remain glassy even for large thicknesses • Poor glass formers • first produce crystallites inside the glass • Invisible to x-rays • Then crystallites grow into columnar-growth poli-crystalline films • Crystallites are bad for scattering • Probably bad for mech. losses also • (Dopants induce better glass formers) N.S. Gluck et al., J. Appl. Phys., 69 (1991) 3037 Ghafor et al. Thin Solid Films, 516 (2008) 982 14 may 2012 GWADW 2012 JGW-G1201029 5

  6. Lessons from x-ray community, III JGW-G1201029 LIGO-G1200562 • Not surprising Chao first managed to reduce scattering in gyrolaser dielectric mirrors by inventing the SiO2 doped TiO2 • But the important message is that thinner coatings are more stable ! • They will probably have evenless scattering (crystallite free) • Will they also have less mechanical losses? Shiuh Chao, et al., "Low loss dielectric mirror with ion beam sputtered TiO2-SiO2 mixed films" Applied Optics. Vol.40, No.13, 2177-2182, May 1, 2001. 14 may 2012 GWADW 2012 JGW-G1201029 6

  7. Layer thickness vs. Annealing JGW-G1201029 LIGO-G1200562 • Higher T annealing reduces losses • In co-sputtering large percentages of dopant (SiO2 in TiO2) are needed • Thinner layers require less (%) SiO2 for the same anneal-ing stability W.H. Wang and S. Chao, Optics Lett., 23 (1998) 1417; S. Chao, W.H. Wang, M.-Y. Hsu and L.-C. Wang, J. Opt. Soc. Am. A16 (1999) 1477; S. Chao, W.H. Wang and C.C. Lee, Appl. Opt., 40 (2001) 2177 14 may 2012 GWADW 2012 JGW-G1201029 7

  8. Why using layered SiO2::TiO2 JGW-G1201029 LIGO-G1200562 Titania Silica TiO2 Doped Tantala • Comparing: stratified 66%TiO2 36%SiO2 with same refraction index as TiO2 doped Ta2O5 • 1) If mech. losses in TiO2::Ta2O5 are the same as in glassy TiO2 (worst case) Mech. dissipation reduction ~ 36% 14 may 2012 GWADW 2012 JGW-G1201029 8

  9. How much gain from layered TiO2::SiO2 JGW-G1201029 LIGO-G1200562 If we trust Effective Medium Theory, • Measured loss angles from TNI: • plain Ta2O5 : 4.72±0.14 10-4 TiO2 doped Ta2O5 : 3.66±0.29 10-4 • are consistent with a loss angle for glassy TiO2 : 1.2 - 1.4 10-4 • Mech. dissipation reduction ~ 65% 14 may 2012 GWADW 2012 JGW-G1201029

  10. Dielectric Mixtures JGW-G1201029 LIGO-G1200562 Structure makes differences in refraction index 14 may 2012 GWADW 2012 JGW-G1201029 10

  11. Titania Doped Tantala JGW-G1201029 LIGO-G1200562 • Years after Chao introduced SiO2-TiO2 coatings • LMA discovered that TiO2-Ta2O5 coatings have • less mechanical noise, • better thermal noise performance • Is it because TiO2-Ta2O5is a more stable glass? • Or because of atomic level stress due to doping? • Or both? Why stress may be important? 14 may 2012 GWADW 2012 JGW-G1201029 11

  12. Example: hydrogen dissipation in metals JGW-G1201029 LIGO-G1200562 • A metal has P orbitals … 14 may 2012 GWADW 2012 JGW-G1201029 12

  13. Example: hydrogen dissipation in metals JGW-G1201029 LIGO-G1200562 • Hydrogen resides in electron cloud • = > Double well potential ! • Flip-flops between wells • Indifferent equilibrium 14 may 2012 GWADW 2012 JGW-G1201029

  14. …In the presence of an acoustic wave JGW-G1201029 LIGO-G1200562 • horizontal compression: • Proton jumps down • Vertical compression • Proton jumps up 14 may 2012 GWADW 2012 JGW-G1201029 14

  15. Losses in a glass JGW-G1201029 LIGO-G1200562 • Double well potential • Oscillating stress • Well to well jumping • Each jump gives loss • How to stop it? 14 may 2012 GWADW 2012 JGW-G1201029 15

  16. Stress the glass ! JGW-G1201029 LIGO-G1200562 • Static stress • Asymmetric double well • State lives always in the lower hole 14 may 2012 GWADW 2012 JGW-G1201029 16

  17. Acoustic oscillations in double well potential JGW-G1201029 LIGO-G1200562 • No stress Stress • Well to-well jumping ●No jumping • Dissipation ●No dissipation 14 may 2012 GWADW 2012 JGW-G1201029 17

  18. JGW-G1201029 LIGO-G1200562 Effects of Stress in Si3N4 • High stress • Low loss x 100 J.S. Wu and C.C. Yu, “How stress can reducedissipation in glasses,” Phys. Rev. B84 (2011) 174109. 14 may 2012 GWADW 2012 JGW-G1201029 18

  19. How to add Stress to the coating JGW-G1201029 LIGO-G1200562 • Adding TiO2 in Ta2O5 introduce random stress • Stress from different oxidation pattern(random distribution) • Observed Lower losses • Alternating thin layers TiO2 to SiO2 introduce ordered stress • Stress from different atomic spacing (ordered) 14 may 2012 GWADW 2012 JGW-G1201029 19

  20. How to add Stress to the coating JGW-G1201029 LIGO-G1200562 • How thick an optimal layer? • 1 interlayer diffusion length thick ? • Uniformly graded concentration => uniform stress ? • Will it lead to Lower mechanical losses? S.Chao, et al., Appl. Optics, 40 (2001) 2177. 14 may 2012 GWADW 2012 JGW-G1201029

  21. JGW-G1201029 LIGO-G1200562 • So far for the reasons to try nm layered coatings • Now let’s look at the experimental activity on nm coatings at Chao’s Lab in the National Tsing Hua University in Taiwan 14 may 2012 GWADW 2012 JGW-G1201029 21

  22. Refurbished ion-beam-sputterer JGW-G1201029 LIGO-G1200562 • Fast cycling Coater for SiO2, TiO2, Ta2O5 • For multi-layers and mixtures 14 may 2012 GWADW 2012 JGW-G1201029 22

  23. Refurbished ion-beam-sputterer JGW-G1201029 LIGO-G1200562 Exchangeable twin target holder Sputter target and rotator Kaufman-type ion beam sputter system in a class 100 clean compartment within a class 10,000 clean room Previously used to develop low-loss mirror coatings for ring-laser gyroscope Kaufman ion gun and neutralizer 14 may 2012 GWADW 2012 JGW-G1201029

  24. Nano-layer coating preparations JGW-G1201029 LIGO-G1200562 SiO2 TiO2 VB=1000V V A =-200V IB=50±2%mA Ar-Gun :10-4 mbar Ar-PBN : 1.5*10-4 mbar O2-Chamber: 3.27*10-4 ±5.5% mbar Fitting curve VB=1000V V A =-200V IB=50mA±2% Ar-Gun :10-4 mbar Ar-PBN : 10-4 mbar O2-Chamber: 5*59*10-4 mbar ±5% Fitting curve 2.7% 0.2% -1.8% 0.6% Thickness (nm) Thickness (nm) -1.4% -1.2% -0.3% Deposition rate : 3.40 nm/min Deposition rate : 7.62 nm/min 6.7% -10% 8.6% -5% Time(min) QW :115nm Time(min) QW :183nm • Calibrating deposition rate for TiO2 and SiO2 SiO2 first SiO2 second 14 may 2012 GWADW 2012 JGW-G1201029 24

  25. JGW-G1201029 LIGO-G1200562 1% , 2.66cm 1% , 3.16cm TiO2 first SiO2 first TiO2 second SiO2 second 4.1% , 5cm 3.6% , 5cm % % Position(cm) Position(cm) Nano-layer coating preparations • Uniformity distribution for TiO2 and SiO2 14 may 2012 GWADW 2012 JGW-G1201029 25

  26. Q Measurement setup JGW-G1201029 LIGO-G1200562 electrode Pirani gauge Chamber Laser Clamp QPD Detector Cold cathode ion gauge Window Sample Gate valve Turbo vacuum pump Concrete block Scroll pump Valve 14 may 2012 GWADW 2012 JGW-G1201029 26

  27. JGW-G1201029 LIGO-G1200562 Tight screws O-ring τ = 287.14776 φ = 2.05*10-5 τ = 156.91926 φ = 3.75*10-5 Frequency(Hz) Frequency(Hz) Loss hunting • Support losses 14 may 2012 GWADW 2012 JGW-G1201029 27

  28. JGW-G1201029 LIGO-G1200562 110 μ m 2 mm Fused Silica cantilever Fused Silica bulk Frequency = 61.3(Hz) τ = 1726(s) φ = 3.01E-06 Neutralizing clamp losses • oxy-acetylene welding 14 may 2012 GWADW 2012 JGW-G1201029 28

  29. JGW-G1201029 LIGO-G1200562 Neutralizing Residual gas effects Frequency = 54 Hz 14 may 2012 GWADW 2012 JGW-G1201029 29

  30. Neutralizing pump vibrations JGW-G1201029 LIGO-G1200562 Pump on 10-6torr Pump on 10-6torr Pump off 10-4torr Frequency(Hz) Frequency(Hz) • Added flexible tube sank in lead pellets • Allow continuous pumping Frequency(Hz) 14 may 2012 GWADW 2012 JGW-G1201029 30

  31. JGW-G1201029 LIGO-G1200562 Preparing Silicon cantilevers • For cryogenic measurements ??? 14 may 2012 GWADW 2012 JGW-G1201029 31

  32. JGW-G1201029 LIGO-G1200562 Top view KOH heater DI water 150ml Ultrasonic cleaner KOH wet etching Si(s)+2(OH)-+2H2O → Si(OH)2O22- +2H2(g) 32 14 may 2012 GWADW 2012 JGW-G1201029

  33. Silicon cantilevers JGW-G1201029 LIGO-G1200562 Etch side Protected side 10 mm 54.74 ° 0.35mm 34 mm 5.5mm 500 μm 500 92 μm 44.35 mm 14 may 2012 GWADW 2012 JGW-G1201029 33

  34. Roughness of cantilever JGW-G1201029 LIGO-G1200562 14 may 2012 GWADW 2012 JGW-G1201029 34

  35. JGW-G1201029 LIGO-G1200562 Incidentally . . . 14 may 2012 GWADW 2012 JGW-G1201029 35

  36. Silicon cliff JGW-G1201029 LIGO-G1200562 • We live here ! • That’s Scary ! ! ! • Is this the reason why cryogenic mirrors do not improve? 14 may 2012 GWADW 2012 JGW-G1201029 36

  37. JGW-G1201029 LIGO-G1200562 Better cryo coatings? • What can we do to get better cryo coatings ? ? • Is getting away from silica a simple answer??? • Should we switch to Al2O3 instead ? ? ? • More work to do 14 may 2012 GWADW 2012 JGW-G1201029 37

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