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Losses in silicon surfaces relevant for suspension elements in future detectors

Losses in silicon surfaces relevant for suspension elements in future detectors Ch. Schwarz 1 , R. Nawrodt 1,2 , S. Kroker 3 , D. Heinert 1 , S. Reid 2 , P. Murray 2 , I. Martin 2 , A. Tünnermann 3 , S. Rowan 2 , J. Hough 2 , P. Seidel 1

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Losses in silicon surfaces relevant for suspension elements in future detectors

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  1. Losses in silicon surfaces relevant for suspension elements in future detectors Ch. Schwarz1, R. Nawrodt1,2, S. Kroker3, D. Heinert1, S. Reid2, P. Murray2, I. Martin2, A. Tünnermann3, S. Rowan2, J. Hough2, P. Seidel1 1Friedrich-Schiller-Universität Jena, Institut für Festkörperphysik, Helmholtzweg 5, D-07743 Jena, Germany 2University of Glasgow, Institute for Gravitational Research, Kelvinbuilding, University Avenue, G12 8QQ Glasgow, Scotland 3Friedrich-Schiller-Universität Jena, Institut für Angewandte Physik, Albert-Einstein-Straße 15, D-07745 Jena, Germany DFG / SFB TR 7

  2. Overview - Introduction - surface loss - Experimental setup for general investigation of mechanical losses - Surface loss vs. sample roughness - Extraction of the surface loss from experimantal data - Conclusions

  3. Possible mechanisms causing surface related losses breaking and reordering of unterminated bonds interactions with a surface layer rearranging of defects interactions with micro- cracks near the surface (friction/ phonon scattering)

  4. How to investigatemechanicallosses? cantilever clamp for mechanical loss measurements suspension setup for bulk material measurements

  5. How to investigatemechanicallosses? Reflective readout for vibration detection Multi-channel setup for loss measurements of up to 4 cantilevers

  6. 5 1 2 3 4 How to investigatemechanicallosses? Cryostat for bulk measurements 1 probe chamber 2 experimental platform 3 LHe tank (49 l) 4 LN2 tank (62 l) 5 heat radiation shields > T = 5…325 K ΔT = ± 0.1 K > p < 3x10-6 mbar > LHe hold time of 36 h cryostat for cantilever measurements

  7. Why is it important to measure the surface related loss at low temperatures? Estimation of damping contributions of a thin silicon flexure silicon substrate Ø 3”x12 mm

  8. Why is it important to measure the surface related loss at low temperatures?

  9. How to investigatesurface related mechanicallosses? 1. change of surfacetreatmentprocedure (dry/ wet etching, lapping, polishing, …) by keeping same geometry of all samples 18.6 kHz

  10. 2. change of the surface (S) to volume (V) ratio (S/V) by changing the substrate's geometry following the same approach as Gretarsson and Harry 1999: µ …geometrical factor (depending on modeshape and geometry) ds …dissipation depth ε …displacementfield µ = 3 for the obtainedthinflexures with rectangular cross-section (bending modes)

  11. - experimental value obtained from measurements of  vs. µS/V of • oscillators with similar surface treatment (here: dry etching) • - neglecting bulk effects (possible for thin elements) • - S/V is changed by changing the thickness • of the oscillator … surface loss parameter with

  12. thickness 60 nm … 1 µm thickness 50 … 150 µm bulk samples  intinsic bulk loss becomes noticable model: as = 0.5 pm (25% error) (as = 3-6 pm for fused silica)

  13. Conclusions: - Surface loss as a limitation for the lowest achievable loss in small scale structures like suspension elements and wave guide mirrors (see talk of R. Nawrodt) - Silicon surface loss 10 times smaller than the loss of fused silica - More investigations with different surface treatment procedures needed (indication of influence of surface loss by different treatments by other groups)

  14. Änderung der Substrataufhängung

  15. Cantilever Coating Research

  16. Cantilever setup for the “large” cryostat 4 3 2 1 1 massive base plate 2 cantilever clamping blocks 3 excitation structure mount 4 cantilever

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