1. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 1 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 1 Friedrich-Schiller-Universität Jena, Institut für Festkörperphysik, Helmholtzweg 5, D-07743 Jena, Germany 2 University of Glasgow, Institute for Gravitational Research, Kelvinbuilding, University Avenue, G12 8QQ Glasgow, Scotland 3 Friedrich-Schiller-Universität Jena, Institut für Angewandte Physik, Albert-Einstein-Straße 15, D-07745 Jena, Germany DFG / SFB TR 7

2. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 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. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 3 rearranging of defects breaking and reordering of unterminated bonds interactions with a surface layer interactions with micro- cracks near the surface (friction/ phonon scattering) Possible mechanisms causing surface related losses

4. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 4 cantilever clamp for mechanical loss measurements suspension setup for bulk material measurements How to investigate mechanical losses?

5. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 5 Reflective readout for vibration detection Multi-channel setup for loss measurements of up to 4 cantilevers How to investigate mechanical losses?

6. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 6 How to investigate mechanical losses? 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 1 2 3 4 5 cryostat for cantilever measurements

7. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 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. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 8 Why is it important to measure the surface related loss at low temperatures?

9. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 18.6 kHz How to investigate surface related mechanical losses? 1. change of surface treatment procedure (dry/ wet etching, lapping, polishing, …) by keeping same geometry of all samples

10. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 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) d s …dissipation depth ε …displacement field µ = 3 for the obtained thin flexures with rectangular cross-section (bending modes)

11. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 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 with … surface loss parameter

12. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto thickness 60 nm … 1 µm thickness 50 … 150 µm bulk samples  intinsic bulk loss becomes noticable model:  s = 0.5 pm (25% error) (  s = 3-6 pm for fused silica)

13. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 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. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 14

15. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 15 Änderung der Substrataufhängung

16. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 16 Cantilever Coating Research

17. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 17 Cantilever setup for the “large” cryostat 1 massive base plate 2 cantilever clamping blocks 3 excitation structure mount 4 cantilever 1 2 3 4

18. Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 2010 - GWADW Kyoto 18