STREGA WP1/M1 mirror substrates

GEO

LIGO

ISA

• Scientific motivation: Mechanical dissipation from dielectric mirror coatings is predicted to be a significant source of thermal noise for advanced detectors. Coatings must also be of low optical loss.

• Main workpackage outcomes/long term aim:– Measurement of the thermal expansion, thermal conduction

and mechanical losses of CaF2 (Calcium Fluorite) and Si (Silicon), varying the temperature from 300K down to 4K.

– Investigation of the alteration of thermo-mechanical properties of silicon as a function of quantity and nature of dopants

– Realisation and test of prototypes in connection with the tasks M4 and M5

Status at last meeting

To high voltage

Excitation plate(behind mass)

Silicon samples cut along different crystal axes, [111] and [100].

The [111] sample was boron-doped.

Preliminary room T measurements of mechanical dissipation of two silicon samples of identical geometry, supplied by Stanford, was measured over a range of frequencies.

Clamp

Suspension thread/wire

Schematic diagram of front view of suspended test mass.

Test mass

Status at last meeting

• Lowest loss obtained so far = (9.6±0.3)10-9

• Comparable with the lowest loss factors measured at room temperature

Sample [b] typically showed lower dissipation

Sample [a]: [100] cut, nominally undoped Sample [b]: [111] cut, boron doped

Reason for difference seen in measured loss factors (eg crystalline orientation, dopant, other?) is under investigation

Some evidence to suggest may be due to crystalline orientation

Measured loss factors fortwo samples of bulk silicon

30 40 50 600.0

2.0x10-8

4.0x10-8

6.0x10-8

8.0x10-8

1.0x10-7

1.2x10-7

1.4x10-7

Silicon (111) doped Silicon (100) undoped

[a]

[b]

Consider the [100] sample

Q of two modes of the sample studied as a function of orientation of sample in suspension loop

FE model of relative displacement of surface for 2 modes of sample

Friction at suspension points is clearly significant and dependent on position of crystalMode shapes are dependent on crystal axis

Future plans

• Constructing a prototype ‘nodal support’ system to attempt to reduce suspension losses for these samples

• Several sets of samples purchased of various aspect ratios and different crystal cuts for further study

• Measurements of bulk silicon at cryogenic temperature– Second cryostat being commissioned

in Glasgow

– Sample suspended – initial cooling taking place this week

STREGA WP1/M5 suspension substrates

• Suspension technology status:

– To achieve the desired sensitivities of future long-baseline gravitational wave detectors will require a reduction in thermal noise associated with test masses and their suspensions

– Requirement to develop ultra-low thermal noise suspensions for 3rd generation detections (cryogenic temperatures)

Currenteg. GEO600

Advancedeg. AdLIGO

Futureeg. EGO Silicon

suspension technology

Silicon cantilever fabrication

• Initial samples have been fabricated by etching from silicon wafers at Stanford (Stefan Zappe)

•First sample studied:

– P-type doping (Boron), resistivity = 10-20 Ohm-cm

– ~ 92 microns thick

– Resonant modes of samples excited using an electrostatic drive

– Sample displacement monitored using shadow sensor

– Measure rate of decay of the mode amplitudes, from which mechanical dissipation, (0) can be determined.

Set of samples fabricated with varying properties and dimensions:

1 x 10-3 Ohm-cm to >100 Ohm-cm

~40 microns to ~100’s m thick

SampleRigid clamp

5.7cm

1cm

2

0

00

t

eAA

Experimental setup

GEO

LIGO

ISA

The two cantilevers tested

GEO

LIGO

ISA

57 mm

clamping block550m thick

cantilever surface on (100) planecantilever

92m thick

width

34 mm

clamping block550m thick

cantilever surface on (100) plane cantilever92m thick

width

Identical material properties.

10 100 1000 10000 100000

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

therm

oela

stic

loss

th

erm

oe

last

ic

Frequency (Hz)

T = 293K T = 160 K T = 120 K T = 100 K

f1 f4 f6

f2f1 f3 f4 f5

f2 f3 f5

fn = room temperature bending mode resonant frequencies for cantilever of length 57mm

fn = room temperature bending mode resonant frequencies for cantilever of length 34mm

Thermoelastic curves for tested cantilevers with marked cantilever resonant frequencies

Experimental measurements

• Measured dissipation is the sum of dissipation arising from a number of sources:

calculate from siliconmaterial properties

measurements of samples of varying surface to volume ratios should allow

estimates

measurement

sin vacuum<10-5 Torr

rigid clamp holding thick

end of sample

Temperature dependence of (a) measured loss, and (b) calculated thermoelastic loss for bending mode at 670Hz (cant length 57mm)

50 100 150 200 250 300

10-8

10-7

10-6

10-5

calculated thermoelastic loss

21 Jan 05 25 Jan 05 02 Feb 05 04 Feb 05 07 Feb 05 08 Feb 05 09 Feb 05

Temperature (K)50 100 150 200 250 300

10-8

10-7

10-6

10-5

(a)

(b)

4.7x10-7

Temperature dependence of (a) measured loss, and (b) calculated thermoelastic loss for bending mode at 2185Hz. (cant length 57mm)

50 100 150 200 250 300

10-8

10-7

10-6

10-5

10-4

calculated thermoelastic loss

10 Jan 05 12 Jan 05 14 Feb 05 28 Feb 05 30 Feb 05 01 Feb 05

Temperature (K)50 100 150 200 250 300

10-8

10-7

10-6

10-5

10-4

(a)

(b)

Temperature dependence of (a) measured loss, and (b) calculated thermoelastic loss for bending mode at 1935Hz. (cant length 34mm)

50 100 150 200 250 300

10-8

10-7

10-6

10-5

calculated thermoelastic loss

15 Apr 05 19 Apr 05 20 Apr 05

Temperature (K)50 100 150 200 250 300

10-8

10-7

10-6

10-5

(a)

(b)

Temperature dependence of (a) measured loss, and (b) calculated thermoelastic loss for bending modes at 3785 Hz and 6265 Hz. (cant l = 34mm)

50 100 150 200 250 300

10-7

10-6

10-5

10-4

calculated thermoelastic loss

18 Apr 05 21 Apr 05

Temperature (K)50 100 150 200 250 300

10-7

10-6

10-5

10-4

(a)

(b)

50 100 150 200 250 300

10-7

10-6

10-5

10-4

calculated thermoelastic loss

18 Apr 05 21 Apr 05

Temperature (K)50 100 150 200 250 300

10-7

10-6

10-5

10-4

(a)

(b)

Results and interpretation

• The intermittent dissipation peaks observed appear related to changes in temperature distribution in system

• Suggests they are due to energy coupling to resonances in the clamping structure

• Also need to consider surface effects (sample is 92 microns thick)

Surface losses

• Yasumura et al. measured the loss factors of single-crystal cantilevers with thickness 0.06 0.24 m and found they could be represented by:

• surface is the limit to the measurable loss of a cantilever of thickness t and Young’s modulus E1 set by the presence of a surface layer of:

• Surface layer thickness ,

• Young’s modulus E1S, and

• loss s

• For simplicity assume, E1 E1S

• Can use the above to estimate limit to measurable loss for our sample set by surface loss

S1

1surface

6 E

E

t

S

50 100 150 200 250 300

10-7

10-6

10-5

measured

surface thermoleastic

Temperature (K)

(a)

(b)

Surface effects are significant but do not account for total loss measured - next source to investigate is

‘stick-slip’ damping of end of sample in clamp

(a) Ave. loss of third bending mode (670Hz) compared to

(b) sum of scaled surface loss + calculated th-elas loss.

Results and interpretation

• Studies have been carried out to investigate energy coupling to the clamping structure

Normalised piezo response showing energy coupling from resonating cantilever into steel clamp at 1.3, 2.2 and 3.1 kHz

160 180 200 220 240 260 2803x10-6

4x10-6

5x10-6

6x10-6

7x10-6

8x10-6

9x10-6

1x10-51.3kHz bending mode

measured

-thermoelastic

Piezo response

Temperature (K)

mea

sure

d-

th

erm

oela

stic

2x10-5

3x10-5

4x10-5

5x10-5

6x10-5

7x10-5

Norm

alised piezores

160 180 200 220 240 260 2800

1x10-5

2x10-5

3x10-5

4x10-5

5x10-5

6x10-5

2.2kHz bending mode

measured-

thermoelastic

Piezo response

Temperature (K)

mea

sure

d-

th

erm

oela

stic

1x10-4

2x10-4

3x10-4

4x10-4

5x10-4

6x10-4

Norm

alised piezores

160 180 200 220 240 260 2800

2x10-6

4x10-6

6x10-6

8x10-6

1x10-5

3.1kHz bending mode

measured-

thermoelastic

Piezo response

Temperature (K)

mea

sure

d-

th

erm

oela

stic

0

2x10-4

4x10-4

6x10-4

8x10-4

1x10-3

Norm

alised piezoresponse

(arb. units)

silicon cantilever

macor spacer

piezo

40g mass

electrostatic pusher

Response of the clamping structure to a constant driving signal from 2-3 kHz at 240, 270 and 285 K from 2–3 kHz.

The measured dissipation Q-1 in silicon oscillators (kHz frequency band)

1 10 100

Tem perature (K )

1e-010

1e-009

1e-008

1e-007

1e-006

1e-005

0.0001

Q-1

1

2

3

45

1 – Calculated from “phonon-phonon” mechanism(f = 10 kHz)

2 – MSU – 1980, unpublished (t 10 cm, f = 10 kHz)

3 – D.F. McGuigan et al., J.Low Temp.Phys. 30 (1978), 621 (t 10 cm, f = 19.5 kHz)

4 – B.H.Houston et al., Appl.Phys.Lett. 80 (2002), 1300 (t 100 m, f = 5.5 kHz)

5 – U.Gysin et al., Phys.Rev. B69 (2004), 045403(t 2 m, f = 10.8 kHz)

Slide courtesy of V. Mitrofanov, Moscow State University

Summarise

• So far we do not see evidence of dissipation peaks intrinsic to our sample

• Evidence of coupling to resonances of clamping structure under investigation

In short term:

• We will study both thinner and thicker samples to further quantify surface loss effects

• Reduce surface loss effects to allow studies of other dissipation mechanisms presents

In medium term:

• Continue studies of effects of doping on intrinsic dissipation and thermoelastic loss