Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics...

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



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



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



cantilever clampfor mechanical lossmeasurements

suspension setupfor bulk material measurements

How to investigate mechanical losses?



Reflective readout for vibration detection

Multi-channel setup for lossmeasurements of up to 4 cantilevers





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

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2

3

4

5

cryostat for cantilevermeasurements



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



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]


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



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)



- 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


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)



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)



Änderung der Substrataufhängung

10 40 100 400105

106

107

108

experimantal data @ 61kHz

mec

hani

cal Q

-fac

tor

temperature [K]



Cantilever Coating Research



Cantilever setup for the “large” cryostat

1 massive base plate2 cantilever clamping blocks3 excitation structure mount4 cantilever

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2

3

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Friedrich-Schiller-Universität Jena Institute of Solid State Physics – Low Temperature Physics...

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