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Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th May 2010 - GWADW Kyoto 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
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th 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
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th May 2010 - GWADW Kyoto 3
rearrangingof defects
breaking and reordering of unterminated bonds
interactions witha 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 Schwarz 19th May 2010 - GWADW Kyoto 4
cantilever clampfor mechanical lossmeasurements
suspension setupfor bulk material measurements
How to investigate mechanical losses?
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th May 2010 - GWADW Kyoto 5
Reflective readout for vibration detection
Multi-channel setup for lossmeasurements of up to 4 cantilevers
How to investigate mechanical losses?
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th May 2010 - GWADW Kyoto 6
How to investigate mechanical losses?
Cryostat for bulkmeasurements
1 probe chamber2 experimental platform3 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 cantilevermeasurements
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th May 2010 - GWADW Kyoto 7
Why is it important to measure the surface related loss at low temperatures?
Estimation of damping contributionsof a thin silicon flexure
silicon substrate Ø 3”x12 mm
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th May 2010 - GWADW Kyoto 8
Why is it important to measure the surface related loss at low temperatures?
10 30 100 30010-8
10-7
10-6
10-5
10-4
experimental data (@ 18kHz) calculated thermo-elastic loss
mec
hani
cal l
oss
temperature [K]
4 10 40 100 400107
108
109
mec
hani
cal Q
-fac
tor
temperature [K]
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th 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
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th 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:
V
Sµd1 sbulk
µ …geometrical factor (depending on modeshape and geometry)ds …dissipation depth
V
S
rdr
rdr
S
Vµ
32
22
)(
)(
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 Schwarz 19th 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
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th May 2010 - GWADW Kyoto
thickness 60 nm … 1 µm
thickness 50 … 150 µm
bulk samples intinsic bulk loss becomes noticable
V
Sµ
V
Sµd ssbulk 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 Schwarz 19th 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)
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th May 2010 - GWADW Kyoto 14
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th May 2010 - GWADW Kyoto 15
Änderung der Substrataufhängung
10 40 100 400105
106
107
108
experimantal data @ 61kHz
mec
hani
cal Q
-fac
tor
temperature [K]
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th May 2010 - GWADW Kyoto 16
Cantilever Coating Research
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th May 2010 - GWADW Kyoto 17
Cantilever setup for the “large” cryostat
1 massive base plate2 cantilever clamping blocks3 excitation structure mount4 cantilever
1
2
3
4
Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics
Christian Schwarz 19th May 2010 - GWADW Kyoto 18