1. Cryogenic Si-Si Bond Strength Testing
2nd ET Annual Workshop October 2009
Cryogenic Si-Si Bond Strength Testing
Nicola Beveridge1, Mariëlle van Veggel1, Jim Hough1, Sheila Rowan1, Ronny Nawrodt1, Stuart Reid1, Bostjan Besentzek1, John Davidson2, Donald Nicholson3
1 Institute for Gravitational Research, University of Glasgow
2 Faculty of Mechanical Engineering, University of Glasgow
3 Faculty of Electrical Engineering, University of Glasgow

2. Introduction to Silicate Bonding
Originally developed for NASA’s Gravity Probe B mission, launched April (Gwo et al., patent)
Construction of the ultra-rigid, ultra-stable optical benches for the LISA Pathfinder mission.
GEO600 currently operates with quasi monolithic fused silica suspensions and mirrors.
Advanced LIGO upgrades include silica suspensions similar to that used in GEO600
High bond strength and ability to withstand the forces and thermal cycling associated with space launches and conditions
J R Smith, G Cagnoli, D R M Crooks - Class. Quantum Grav. 21 (2004) S1091–S1098

3. Hydroxy-Catalysis Bonding
Step 1 of 3 – Hydration
The surface of silica is hydrophilic and will attract OH− ions to fill any open bonds from the silica (hydration).
During the bonding process, cleaning the bonding surface with cerium oxide makes the surface hydrophillic.

4. Hydroxy-Catalysis Bonding
Step 2 of 3 – Etching
Placing a solution with a high concentration of OH− ions on the surface of silica causes etching to take place.

5. Hydroxy-Catalysis Bonding
Step 3 of 3 – Polymerisation
When the concentration of Si(OH)4 molecules reaches ~2%, the solution polymerises and becomes “rigid”.
pH < 11:
the silicate ion hydrolyses to soluble Si(OH)4 and OH− when the pH is below 11
Si(OH)4 is a monomer which likes to form a polymer arrangement
Bonding requires a silica bulk to bond to
R.K. Iler, 1979, The Chemistry of Silica

6. Reducing Thermal Noise
A fundamental noise source caused by thermally driven fluctuations in the interferometer optics and their suspensions
Intent is to reduce thermal noise
[Punturo, ET talk at the LSC meeting, Amsterdam 2008]

7. Reducing Thermal Noise
Cryogenic operating temperatures
Monolithic Suspension
Low thermal noise
Low loss in pendulum modes
Matched thermal expansion
High thermal conductivity
Silicon suspension
technology (E.T.)
GEO600
Advanced LIGO
Cryo temp necessitates a change in material – high dissipation peak in silica
Mono sus has low loss in pendulum modes in operational frequency band.

8. 3rd Generation Detectors
Schematic of a 3rd gen monolithic suspension
Use silicate bonding to joint the Si suspensions to the Si mass

9. Research Aims
Strength testing of silicate bonding for use in 3rd generation detectors
Strength of silicon-silicon silicate bonds at cryogenic temperature
To determine if bonding silicon to silicon is strong enough to bear the weight of the mass.
Zwick-Rowell 250 machine

10. Sample Preparation Silicon pieces oxidised in wet N2 environment
In order to bond,

11. Testing Set-up
ASTM C c four point ¼ point flexural strength test P L
Silicon piece size: 5 x 10 x 20 mm
(b x d x l)
Bonding surface has PV flatness < 60 nm

12. Previous Research Presented in Erice, October 2009
Average silica-silica bond strength
Presented in Erice, October 2009

13. Previous Research
Average strength of silicate bonds between samples of oxidised silicon higher than silicate bonds between pieces of silica
Strength of bond is not significantly changed by cooling to cryogenic temperatures
No apparent correlation between oxide layer thickness and bond strength
70 Silicon samples oxidised at reduced times
10 samples left with native oxide (<10nm)
40 Pairs bonded – 6 failed prior to testing

14. Results

15. Conclusions
Combined oxide layer minimum of ~80 nm

16. Future Work Add control samples Shear and tensile strength tests
Alternative oxidation techniques
Thermal conductivity
Bond loss measurements