Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 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 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 Jena, Germany DFG / SFB TR 7

Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 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

Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 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

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

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

Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 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 cryostat for cantilever measurements

Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 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

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

Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 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

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

Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 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

Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 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)

Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz19 th May 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)

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

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

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

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

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