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Nano-coatings the thought and the actions

Nano-coatings the thought and the actions. Riccardo DeSalvo, Shiuh Chao, Innocenzo Pinto, Vincenzo Pierro , Vincenzo Galdi , Maria Principe, Huang-Wei Pan, Chen-Shun Ou , Vincent Huang. First visit a number of reasons to study nanocoatings Then present the status of R&D.

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Nano-coatings the thought and the actions

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  1. Nano-coatingsthe thought and the actions Riccardo DeSalvo, Shiuh Chao, Innocenzo Pinto, Vincenzo Pierro, Vincenzo Galdi, Maria Principe, Huang-Wei Pan, Chen-Shun Ou, Vincent Huang JGW-G1201029

  2. First visit a number of reasons to study nanocoatings • Then present the status of R&D JGW-G1201029

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

  4. Lessons from x-ray community • 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 JGW-G1201029

  5. Lessons from x-ray community • 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) JGW-G1201029 N.S. Gluck et al., J. Appl. Phys., 69 (1991) 3037 Ghafor et al. Thin Solid Films, 516 (2008) 982

  6. Lessons from x-ray community • Not surprising that 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. JGW-G1201029

  7. Layer thickness vs. Annealing • Annealing temperature decreases losses • In co-sputtering large percentages of dopant (SiO2 in Ti2O5)are needed • Thin layers require less % SiO2 for the same annealing 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 JGW-G1201029

  8. How much gain from layered TiO2 • Comparing: • stratified 66%TiO2 with 36%SiO2 • Equivalent refraction index to: • Ta2O5 doped TiO2 • First gain: • If mech. losses in Ta2O5 = TiO2 => Gain in dissipation ~ 36% Titania Silica Doped Tantala JGW-G1201029

  9. How much gain from layered TiO2 • Further gain: Consider now the measured loss angles: • Doped Ti2O5 3.66±0.29 10-4 • TiO2 1.2 - 1.4 10-4 • Gain in dissipation = 65% JGW-G1201029

  10. Mixture theory: Distribution of “dopant” makes a difference in refraction index Higher refraction Index, less material, less loss JGW-G1201029

  11. Titania Doped Tantala • 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 introduced by doping? • Or both? • Why stress may be important? JGW-G1201029

  12. Example: hydrogen dissipation • a metal has P orbitals JGW-G1201029

  13. Example: hydrogen dissipation • Proton resides in electron cloud • = > Double well potential ! • Flip-flops between wells • Indifferent equilibrium JGW-G1201029

  14. In presence of acoustic wave • horizontal compression: • Proton jumps down • Vertical compression • Proton jumps up JGW-G1201029

  15. Losses in a glass • Double well potential • Oscillating stress • Well jumping • Each jump is a loss • How to stop it? JGW-G1201029

  16. Stress the glass ! ! • Static stress • Biassed double well • State lives always in the lower hole JGW-G1201029

  17. Acoustic oscillation in double well potential • No stress Stress • Well jumping No well jumping • Dissipation No dissipation JGW-G1201029

  18. Effects of Stress in Si3N4 • High stress • Low loss x 100 JGW-G1201029

  19. How to add Stress the coating • 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) JGW-G1201029

  20. How to add Stress the coating • 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. JGW-G1201029

  21. We have seen the reasons to try nanolayered coatings • Now let’s look at the experimental activity at National Tsing Hua University in Taiwan JGW-G1201029

  22. Refurbished ion-beam-sputterer • Fast cycling Coater for SiO2, TiO2, Ta2O5 • For multi-layers and mixtures JGW-G1201029

  23. Refurbished ion-beam-sputterer 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 JGW-G1201029 Kaufman ion gun and neutralizer

  24. Nano-layer coating preparations 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 • Calibrating deposition rate for TiO2 and SiO2 2.7% Thickness (nm) Thickness (nm) 0.2% -1.8% 0.6% -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 SiO2 first SiO2 second JGW-G1201029

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

  26. electrode Q experimental setup Pirani gauge Chamber Laser Clamp QPD Detector Cold cathode ion gauge Window Sample Gate valve Turbo vacuum pump Concrete block Scroll pump Valve JGW-G1201029

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

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

  29. Neutralizing Residual gas effects Frequency = 54 Hz JGW-G1201029

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

  31. Preparing Silicon cantilevers • For cryogenic measurements JGW-G1201029

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

  33. Silicon cantilevers Etch side Protected side 10 mm 54.74 ° 0.35mm 34 mm 5.5mm 500 μm 500 92 μm 44.35 mm JGW-G1201029

  34. Roughness of cantilever JGW-G1201029

  35. Incidentally . . . JGW-G1201029

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

  37. 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 JGW-G1201029

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