Overview of coatings research and recent results at the University of Glasgow M. Abernathy, I. Martin, R. Bassiri, E. Chalkley, R. Nawrodt, M.M. Fejer,

Overview of coatings research and recent results at the University of Glasgow

M. Abernathy, I. Martin, R. Bassiri, E. Chalkley, R. Nawrodt, M.M. Fejer, A. Gretarsson, G. Harry, D. Heinert, J. Hough, I. MacLaren, S. Penn, S. Reid, R. Route, S. Rowan, C

Schwarz, P. Seidel, J. Scott, A.L. Woodcraft

University of Glasgow

GWADW, Kyoto Japan, May 2010

Document #: LIGO-G1000508-x0

22

Things You Should Already Know:

• Thermal Noise– Limits Detectors– Important component comes from Ta2O5

• Doping Ta2O5 has been shown to reduce thermal noise.

• Temperature Dependence of mechanical loss can tell us about loss mechanisms

33

Things You should Know by the End of this Talk Pt. 1: Ta2O5

• Doping changes the activation energy of Tantala’s loss mechanism.– Does anything else do that?

• Heat treatment also changes the activation energy

• Different deposition techniques change activation energies.

44

Things You Should Know by the End of this Talk Pt. 2: Additional Notes

• Ion Beam Sputtered (IBS) Silica coatings have temperature dependant loss too

• Hafnia (HfO2) is an interesting material for study

5555

Thermal NoiseThermal Noise

5

• Coating thermal noise will limit sensitivity of Next-generation detectors at their most sensitive frequencies

Coating thermal noise

Evans et al PRD 78 102003 (2008)

66

Mechanical Loss

• Thermal noise of the coatings is related to the mechanical loss of the coating material:

[Harry et al. 2002]

Y,Y’ … Young’s modulus of the bulk/coating material

… mechanical loss o the coatings

'Y

Y

Y

'Y

Yw

d

f

Tk2)T,f(S ||22

Bx

77

Mechanical Loss and Measurement

vibration

cycleperlost

E

E

2

1

0 200 400 600 800

-0.04

-0.02

0.00

0.02

0.04

Ca

nti

lev

er

dis

pla

ce

me

nt

an

gle

(ra

ds

)

Time (s)

cantilever displacement angle

exponential fit

88

Mechanical loss spectroscopy34mm

500m50m thick

Coating applied here

• Single layers of coating materials appliedto silicon cantilever substrates supplied by Stanford / KNT

• Cantilever clamped rigidly and bending modes excited electrostatically. Loss obtained from exponential decay of amplitude

coated cantilever in clamp

tantala coating

electrostaticdrive

99

Measuring coating loss

• Mechanical loss of coating layer calculated from difference in loss of a coated and un-coated cantilever

Loss of (a) uncoated silicon cantilever with thermal oxide layer, (b) cantilever coated with 500 nm of TiO2-doped Ta2O5 (14.5 % Ti) and (c) the calculated loss of the coating layer

(a)

(b)

(c)

coateduncoatedcoating

cantilever

coating

cantilever

t

t

Y

Y (3coating

1010




(a)

(b)

(c)


cantilever

coating

cantilever

t

t

Y

Y (3coating

1111




(a)

(b)

(c)


cantilever

coating

cantilever

t

t

Y

Y (3coating

1212

Ta2O5 and Doping

G. M. Harry et al 2007 Class. Quantum Grav. 24 405.

1313

Effect of doping on loss of Ta2O5 coatings

Comparison of dissipation in tantala doped with 14.5 % TiO2 and un-doped tantala for 3rd (left) and 4th (right) bending modes.

1414

• TiO2 doping reduces the height and slightly increases the width of the dissipation peak

• TiO2 doping reduces the loss of Ta2O5 throughout the temperature range studied, with the exception of the wings of the peak

Effect of doping on loss of Ta2O5 coatings

1515

Analysis of coating loss peak (TiO2 doped coating)

• Debye-like dissipation peaks

• Tpeak increases with mode frequency indicating a thermally activated dissipation mechanism

21)(

TK

E

B

a

e0

0 = relaxation constant

Ea = activation energy

… relaxation strength … relaxation time

1616

Analysis of coating loss peak

Activation energy of dissipation process:

• (40 ± 3) meV for titania doped tantala

• (29 ± 2) meV for undoped tantala

• Doping increases the activation energy

• Transition between two stable states appears to be hindered by doping

1717

Distribution of parameters

• Amorphous structure results in a distribution of potential barrier heights g(V)

• Activation energy calculated from Arrhenius law corresponds to the average barrier height in this distribution

• The barrier height distribution function g(V) can be calculated from temperature dependent loss data

• Doping shifts distribution of barrierheights to higher energy, thusreducing loss

)(02

VTgkC

fB

ii

1 Gilroy, Phillips, Phil. Mag. B 43 (1981) 735

2 Topp, Cahill, Z. Phys. B: Condens. Matter 101 (1996) 235

1818

Distribution of parameters

• Amorphous structure results in a distribution of potential barrier heights g(V)

• Activation energy calculated from Arrhenius law corresponds to the average barrier height in this distribution

• The barrier height distribution function g(V) can be calculated from temperature dependent loss data

• Doping shifts distribution of barrierheights to higher energy, thusreducing loss

)(02

VTgkC

fB

ii

1 Gilroy, Phillips, Phil. Mag. B 43 (1981) 735

2 Topp, Cahill, Z. Phys. B: Condens. Matter 101 (1996) 235

1919

Heat Treatment

2020

Effect of heat treatment temperature on Ta2O5 loss

• 35 K peak– Observed in Ta2O5 heat treated at 300, 400 C. Evidence suggests may

also be present in Ta2O5 heat treated at 600 C– Activation energy 54 meV– Postulate that this may be analogous to dissipation peak in fused silica ,

involving thermally activated transitions of oxygen atoms

Above: Electron diffraction pattern of Ta2O5 heat treated at 300 C

Left: Loss at 1.9 kHz of 0.5 m Ta2O5 coatings annealed at 300, 400, 600 and 800 C.

300C

600 C

800 C

400C

(i)

300 C

800 C800 C

600 C

800 C

600 C

800 C

600 C

800 C

400C

600 C

800 C

400C

600 C

800 C

300C400C

600 C

800 C

300C400C

600 C

800 C

2121


• 18 K peak– Observed in Ta2O5 heat treated at 600 C and 800 C– Dissipation mechanism may be related to structural changes brought on by heat

treatment close to re-crystallisation temperature– Perhaps some pre-crystallisation ordering (but still appears amorphous on

electron diffraction measurements)



300C

600 C

800 C

400C

(i)

600 C

800 C800 C

600 C

800 C

600 C

800 C

600 C

800 C

400C

600 C

800 C

400C

600 C

800 C

300C400C

600 C

800 C

300C400C

600 C

800 C

600 C

2222


• 90 K peak– Observed in coating heat treated at 800 C– Large, broad loss peak likely to be related to (expected) onset of

polycrystalline structure due to high temperature heat treatment– Dissipation mechanism could be e.g. phonon scattering at grain boundaries

– more analysis required



300C

600 C

800 C

400C

(i)

800 C800 C

600 C

800 C

600 C

800 C

600 C

800 C

400C

600 C

800 C

400C

600 C

800 C

300C400C

600 C

800 C

300C400C

600 C

800 C

800 C

800 C

2323


• 90 K peak– Observed in coating heat treated at 800 C– Large, broad loss peak likely to be related to (expected) onset of

polycrystalline structure due to high temperature heat treatment– Dissipation mechanism could be e.g. phonon scattering at grain boundaries

– more analysis required



300C

600 C

800 C

400C

(i)

800 C800 C

600 C

800 C

600 C

800 C

600 C

800 C

400C

600 C

800 C

400C

600 C

800 C

300C400C

600 C

800 C

300C400C

600 C

800 C

800 C

800 C

2424

Deposition Effects

2525

Silica - comparison of deposition methods

• Bulk silica (a) & thermal oxide (b)grown on silicon have a dissipationpeak at ~ 35 K1,2

• e-beam SiO2 (5.5 kHz)1 (c)

– 109 nm thick e-beam film showsno peak at 35 K

– Higher loss than bulk and thermaloxide above 40 k

• Ion beam sputtered silica (d)– Broad loss peak at ~ 23 K

– Significantly lower loss than similar thickness of e-beam and thermal SiO2

• Deposition method can have a significant effect on loss – studies of coatings deposited by different methods planned

1White and Pohl, Phys. Rev. Lett. 75 (1995) 4437, 2Cahill and Van Cleve Rev. Sci. Inst. 60 (1989) 2706.

(a)(c)

(d)

(b)

2626

‘Low water content’ Ta2O5 from ATF

• ATF Ta2O5 heat treated at the same temperatures as CSIRO / LMA Ta2O5 has loss peaks at significantly higher temperatures. Full analysis underway

• Suggests details of coating deposition procedure may have significant impact on the temperature dependence of the mechanical loss – further study of great interest

Left: CSIRO / ATF comparison, heat treated at 600 C post-deposition. Right: CSIRO / ATF comparison, heat treated at 300 C post-deposition.

2727

‘Low water content’ Ta2O5 from ATF

• ATF Ta2O5 heat treated at the same temperatures as CSIRO / LMA Ta2O5 has loss peaks at significantly higher temperatures. Full analysis underway

• Suggests details of coating deposition procedure may have significant impact on the temperature dependence of the mechanical loss – further study of great interest

Left: CSIRO / ATF comparison, heat treated at 600 C post-deposition. Right: CSIRO / ATF comparison, heat treated at 300 C post-deposition.

2828

Additional Notes

2929

Comparison of SiO2 and Ta2O5

0 50 100 150 200 250 300

2.0x10-4

4.0x10-4

6.0x10-4

8.0x10-4

1.0x10-3

Tantala coating 350 Hz Silica coating 350 Hz

Mec

han

ical

dis

sipa

tion

Temperature (K)

• Ta2O5 has higher loss throughout temperature range, but loss of SiO2 will also be significant below 100 K

Scatter at higher temperatures, possibly due to loss into clamp.

3030

Temperature dependence of coating thermal noise at 100 Hz

• If coating loss was constant with temperature, could gain factor of ~ 4 in coating thermal displacement noise of a mirror at 18 K

• Measured coating losses imply a gain of a factor of ~ 1.7 in coating TN by cooling to 18 K

Optimistic estimate – constantcoating loss at all temperatures

Using measuredcoating loss

3131

Temperature dependence of coating thermal noise at 100 Hz

• If coating loss was constant with temperature, could gain factor of ~ 4 in coating thermal displacement noise of a mirror at 18 K

• Measured coating losses imply a gain of a factor of ~ 1.7 in coating TN by cooling to 18 K

Optimistic estimate – constantcoating loss at all temperatures

Using measuredcoating loss

3232

Alternative high index materials - hafnia

• Hafnia studied – allow comparisonof loss in another high-index oxide

• Different atom weight / size– Differences in dynamics arising

from atom weight expected

• Loss significantly lower thantantala below 125 K

• Peak position and width shiftedcompared to tantala

• High optical absorption (60 ppm)measured at Stanford

Coating loss at ~ 1kHz for HfO2 and Ta2O5 heat treated at 300ºC. (E. Chalkley)

loss peak around 50 K

loss peak/plateau around 200 K

3333

Effect of heat treatment on loss of hafnia

• As-deposited (100 C) shows no clear loss peaks

• Peak at ~50 K observedin coatings heat treatedat 300 and 400 K

• Electron diffractionmeasurements show evidenceof both crystalline and amorphous structure in all thehafnia coatings

• Silica-doped hafnia remains amorphous when annealed up to 500 C, and presence of silica appears to only slightly increase loss at room temperature

3434

Effect of heat treatment on loss of hafnia

• As-deposited (100 C) shows no clear loss peaks

• Peak at ~50 K observedin coatings heat treatedat 300 and 400 K

• Electron diffractionmeasurements show evidenceof both crystalline and amorphous structure in all thehafnia coatings

• Silica-doped hafnia remains amorphous when annealed up to 500 C, and presence of silica appears to only slightly increase loss at room temperature

3535

Things You should Now Know

• Doping changes the activation energy of Tantala’s loss mechanism.

• Heat treatment also changes the activation energy

• Different deposition techniques change activation energies.

• IBS silica coating has temperature related loss• Hafnia (HfO2) is an interesting material for study

Documents

Overview of coatings research and recent results at the University of Glasgow M. Abernathy, I. Martin, R. Bassiri, E. Chalkley, R. Nawrodt, M.M. Fejer,