1. Francesco Cottone INFN & Physics Departments of Perugia, Pisa, Florence (Collaboration Work under VIRGO Project) Thermomechanical properties of silicon fibers for 3 rd GW detectors ILIAS GW Meeting – October 25 th, 2005 Palma de Mallorca, Spain

2. Francesco Cottone ILIAS GW Meeting - 25 October 2005 Outlines  Requirements for low thermal noise Suspension wire  Silicon thermo-mechanical properties  Experimental setup  Measurements of thermo-mechanical parameters at Room and low Temperature  Conclusions

3. Francesco Cottone ILIAS GW Meeting - 25 October 2005 Requirements for low thermal noise Suspension wire  Low loss angle φ  High tensile strength TB  High thermal conductivity  Low thermal expansion coefficient Horizontal displacement power spectrum Wire length Number of wires Mirror mass Tensile strength LOSS ANGLE

4. Francesco Cottone ILIAS GW Meeting - 25 October 2005 Thermo-elastic Loss Angle: Why crystalline Si for future GW detectors?

5. Francesco Cottone ILIAS GW Meeting - 25 October 2005 Thermomechanical Properties of Crystalline Silicon Low thermal expansion coefficient α That expected to vanish at about 17 K and 123 K Crystalline silicon is a good candidate thanks to its high thermal conductivity (at 300K) = 1.48 × 10^2Wm −1 K −1 ) Huge Peak between 20-30K

6. Francesco Cottone ILIAS GW Meeting - 25 October 2005 Thermomechanical Properties of Crystalline Silicon Amplitude of the linear thermoelastic loss angle Vs Temperature Expected temperature dependence of the thermoelastic peak frequency

7. Francesco Cottone ILIAS GW Meeting - 25 October 2005 Production of Silicon Fibers (Pisa group ) Crucible After heater Grown fiber RF coil Seed Crystal melt Insulating shields μ-pulling down Technique

8. Francesco Cottone ILIAS GW Meeting - 25 October 2005 Cryogenic Experimental Setup (Perugia Lab) Clamping system Fiber Copper block and conduction plate to realize thermal link steel alloy spring Shadow meter HV excitator He Laser lens

9. Francesco Cottone ILIAS GW Meeting - 25 October 2005 Experimental results at Room and Low Temperature Resonance frequencies modes The fiber has roughtly elliptical section apporximated with two circular sections with 2 diameters d1 and d2 that can be deduced from each mode Free lenght=111.5 mm diameter 242  m

10. Francesco Cottone ILIAS GW Meeting - 25 October 2005 Experimental results at Room and Low Temperature Young Modulus Vs Temperature Relative resonance frequency variation Wachtman et al., Phys. Rev. 122 (1961)

11. Francesco Cottone ILIAS GW Meeting - 25 October 2005 Experimental results at Room and Low Temperature Loss Angle at Room Temperature Vs Frequency (Firenze group) Free lenght=278 mm diameter 574  m Free lenght=111.5 mm diameter 242  m

12. Francesco Cottone ILIAS GW Meeting - 25 October 2005 Experimental results at Room and Low Temperature Loss angle vs temperatureLoss angle vs frequency Loss Angle at low Temperature (Perugia group) Excess losses?

13. Francesco Cottone ILIAS GW Meeting - 25 October 2005  The µ-pulling down technique and the etching procedure permit to realize fibers having the appropriate size  At room temperature, the fibres confirm the expected properties: the high thermal conductivity of the Silicon pushes the thermo– elastic dissipation peak at high frequency  At low temperature (about 120 K) the reduction of the thermo– elastic dissipation, due to the thermal expansion coefficient behavior, is hidden by the presence of other dissipation mechanisms, probably related to bulk and surface defects. Conclusions

14. Francesco Cottone ILIAS GW Meeting - 25 October 2005  Better control of the diameter regularity and crystal orientation must be developed  Improving of the clamping system to realize more robust blocking to reduce extra losses (in progress)  Necessity to investigate the behavior of a crystalline Silicon fibres suspension at really cryogenic temperature  At about 5–20 K the thermo–elastic dissipation will be negligible thanks both to the thermal expansion coefficient vanishing and to the direct temperature dependence of the thermo–elastic strength Δ. Next steps