1. 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 14 may 2012 GWADW 2012JGW-G12010291

2. First visit a number of reasons to study nanocoatings Then present the status of R&D 14 may 2012 GWADW 2012JGW-G12010292

3. First interest for nanocoatings RDS participated to the PXRMS conference Big Sky – Montana X-ray mirror coating community Report LIGO-G080106-00-R 14 may 2012 GWADW 2012JGW-G12010293

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 14 may 2012 GWADW 2012JGW-G12010294 Different atomic radius and oxydation pattern assure glassy structure around the interface between different materials Sub-layer thickness

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) 14 may 2012 GWADW 2012JGW-G12010295 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 SiO 2 doped TiO 2 But the important message is that thinner coatings are more stable ! They will probably have even less scattering (crystallite free) Will they also have less mechanical losses? 14 may 2012 GWADW 2012JGW-G12010296 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.

7. Layer thickness vs. Annealing Annealing temperature decreases losses In co-sputtering large percentages of dopant (SiO 2 in Ti 2 O 5 )are needed Thin layers require less % SiO 2 for the same annealing stability 14 may 2012 GWADW 2012JGW-G12010297 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

8. How much gain from layered TiO 2 Comparing: stratified 66%TiO 2 with 36%SiO 2 Equivalent refraction index to: Ta 2 O 5 doped TiO 2 First gain: If mech. losses in Ta 2 O 5 = TiO 2 => Gain in dissipation ~ 36% 14 may 2012 GWADW 2012JGW-G12010298 Doped Tantala Silica Titania

9. How much gain from layered TiO 2 Further gain: Consider now the measured loss angles: Doped Ti 2 O 5 3.66±0.29 10 -4 TiO 2 1.2 - 1.4 10 -4 Gain in dissipation = 65% 14 may 2012 GWADW 2012JGW-G12010299

10. Mixture theory: Distribution of “dopant” makes a difference in refraction index 14 may 2012 GWADW 2012JGW-G120102910 Higher refraction Index, less material, less loss

11. Titania Doped Tantala Years after Chao introduced SiO 2 -TiO 2 coatings LMA discovered that TiO 2 -Ta 2 O 5 coatings have – less mechanical noise, – better thermal noise performance Is it because TiO 2 -Ta 2 O 5 is a more stable glass? Or because of atomic level stress introduced by doping? Or both? Why stress may be important? 14 may 2012 GWADW 2012JGW-G120102911

12. Example: hydrogen dissipation a metal has P orbitals 14 may 2012 GWADW 2012JGW-G120102912

13. Example: hydrogen dissipation Proton resides in electron cloud = > Double well potential ! Flip-flops between wells Indifferent equilibrium 14 may 2012 GWADW 2012JGW-G120102913

14. In presence of acoustic wave horizontal compression: – Proton jumps down Vertical compression – Proton jumps up 14 may 2012 GWADW 2012JGW-G120102914

15. Losses in a glass Double well potential Oscillating stress Well jumping Each jump is a loss How to stop it? 14 may 2012 GWADW 2012JGW-G120102915

16. Stress the glass ! ! Static stress Biassed double well State lives always in the lower hole 14 may 2012 GWADW 2012JGW-G120102916

17. Acoustic oscillation in double well potential No stressStress Well jumpingNo well jumping DissipationNo dissipation 14 may 2012 GWADW 2012JGW-G120102917

18. Effects of Stress in Si 3 N 4 High stress Low loss x 100 14 may 2012 GWADW 2012JGW-G120102918

19. How to add Stress the coating Adding TiO 2 in Ta 2 O 5 introduce random stress – Stress from different oxidation pattern (random distribution) Observed Lower losses Alternating thin layers TiO 2 to SiO 2 introduce ordered stress – Stress from different atomic spacing (ordered) 14 may 2012 GWADW 2012JGW-G120102919

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? 14 may 2012 GWADW 2012JGW-G120102920 S.Chao, et al., Appl. Optics, 40 (2001) 2177.

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 14 may 2012 GWADW 2012JGW-G120102921

22. Refurbished ion-beam-sputterer Fast cycling Coater for SiO 2, TiO 2, Ta 2 O 5 For multi-layers and mixtures 14 may 2012 GWADW 2012JGW-G120102922

23. Refurbished ion-beam-sputterer 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 Sputter target and rotator Exchangeable twin target holder Kaufman ion gun and neutralizer 14 may 2012 GWADW 2012JGW-G120102923

24. Nano-layer coating preparations Calibrating deposition rate for TiO 2 and SiO 2 SiO 2 first SiO 2 second Time(min) TiO 2 Fitting curve SiO 2 Fitting curve Thickness (nm) 8.6% 6.7% -1.2% -1.8% 2.7% -5% -10% -0.3% -1.4% 0.6% 0.2% Deposition rate : 3.40 nm/minDeposition rate : 7.62 nm/min QW :115nmQW :183nm V B =1000V V A =-200V I B =50mA±2% Ar-Gun : 10 -4 mbar Ar-PBN : 10 -4 mbar O 2 -Chamber: 5*59*10 -4 mbar ±5% V B =1000V V A =-200V I B =50±2%mA Ar-Gun : 10 -4 mbar Ar-PBN : 1.5*10 -4 mbar O 2 -Chamber: 3.27*10 -4 ±5.5% mbar 14 may 2012 GWADW 2012JGW-G120102924

25. Nano-layer coating preparations Uniformity distribution for TiO 2 and SiO 2 SiO 2 first SiO 2 second Position(cm) 1%, 3.16cm 3.6%, 5cm TiO 2 first TiO 2 second Position(cm) 4.1%, 5cm 1%, 2.66cm % % 14 may 2012 GWADW 2012JGW-G120102925

26. Q experimental setup Chamber Cold cathode ion gauge Pirani gauge Gate valve Valve Turbo vacuum pump Scroll pump Concrete block Laser QPD Detector electrode Clam p Sample Window 14 may 2012 GWADW 2012JGW-G120102926

27. Loss hunting O-ring Tight screws Frequency(Hz) Amplitude τ = 156.91926 φ = 3.75*10 -5 τ = 287.14776 φ = 2.05*10 -5 Support losses 14 may 2012 GWADW 2012JGW-G120102927

28. Neutralizing clamp losses oxy-acetylene welding 14 may 2012 GWADW 2012JGW-G120102928 Fused Silica cantilever Fused Silica bulk 2 mm 110 μ m τ = 1726(s) φ = 3.01E-06 Frequency = 61.3(Hz)

29. Neutralizing Residual gas effects Frequency = 54 Hz 14 may 2012 GWADW 2012JGW-G120102929

30. Neutralizing pump vibrations Frequency(Hz) Amplitude Frequency(Hz) Amplitude Pump on 10 -6 torr Pump off 10 -4 torr Pump on 10 -6 torr Added flexible tube sank in lead pellets – Allow continuous pumping 14 may 2012 GWADW 2012JGW-G120102930 Frequency(Hz)

31. Preparing Silicon cantilevers For cryogenic measurements 14 may 2012 GWADW 2012JGW-G120102931

32. KOH wet etching 150ml KOH DI water Ultrasonic cleaner heater Top view Si (s) + 2(OH) - + 2H 2 O → Si(OH) 2 O 2 2- +2H 2(g) 14 may 2012 GWADW 2012JGW-G120102932

33. Silicon cantilevers Etch sideProtected side 5.5mm 500 92 μm 44.35 mm 10 mm 34 mm 0.35mm 500 μm 54.74 ° 14 may 2012 GWADW 2012JGW-G120102933

34. Time(min)Ra(nm)error 00.48- 1204.296 0.36882 2407.376 1.51907 3608.782 0.34932 4693.539 0.16881 Roughness of cantilever 14 may 2012 GWADW 2012JGW-G120102934

35. Incidentally... 14 may 2012 GWADW 2012JGW-G120102935

36. Silicon cliff We live here ! That’s Scary ! ! ! Is this the reason why cryogenic mirrors do not improve? 14 may 2012 GWADW 2012JGW-G120102936

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 Al 2 O 3 instead ? ? ? More work to do 14 may 2012 GWADW 2012JGW-G120102937