Suitability of Kapton for use in Low Temperature Measurements

1. Suitability of Kapton for use in Low Temperature Measurements Jacob Grimes and David Siegel With the direction of Dr. Eric Palm and Mr. Tim Murphy. With additional help from Dr. Henri Radovan. Funding provided by NSF-REU Program. Special thanks to NHMFL-CIRL

2. Team Projects (Proofs of principle) • Testing polyimide “Kapton®” film • As a patternable cantilever device • For Co-Axial Melting Curve Thermometer • Both are based on capacitance measurements

3. A Little Theory

4. Reasons for using Polyimide Film • Other materials for cantilevers exist, such as BeCu and Silicon, but they have various traits that make them undesirable. • Kapton is a material that is durable, patternable and flexible at extremely low temperatures.

5. From Magnetic Field to Capacitance Magnetic Field Force and Torque V C Displacement

6. Spring Constant of Cantilevers(for testing with a gravitational field)

7. Measuring mK Temperatures • Tube is pressurized to 38.4 atm with 3He. • As temperature is reduced a plug of liquid helium forms. • Changes in temperature cause changes in the pressure of the 3He in the tube. • The shape of the tube is distorted causing changes in capacitance. • Change in temperature is related to change in capacitance.

8. Temperature from Change in Voltage T P Expansion in Tube C dP . dCdT dP dC dT V

9. Equations for finding change in capacitance of Co-Axial tube

10. Device Construction

11. Sketch of Cantilever/Capacitor Little Boy (Los Alamos, circa 1942)

12. Sketch of mK Thermometer Fat Man (Los Alamos, circa 1942)

13. Gold Plating Kapton • A thin layer of gold provides the conductive surface for the capacitor. • Gold is applied through sputtering. • Three factors effect choice of thickness: resistivity, flexibility, and adhesion.

14. Preliminary Testing

15. Test Measurement of Cantilever to Find Spring Constant Capacitance measurements under action of a known force (gravity) to determine the spring constant. A Keithley LCZ meter used to take capacitance data

16. High Pressure Test of Kapton Tube • The Kapton tube must be able to handle high pressures. • Kapton tube is epoxied at one end to high pressure stainless steel tube, and plugged at the other end. • This assembly is attached via regulator to a high pressure helium gas bottle. • The pressure is steadily increased, 50 psi at a time, until the required pressure is reached. • This test is performed first at room temperature then at liquid nitrogen temperatures.

17. Blast Box < A blast box was constructed to contain shrapnel in the event of a rupture Kapton tube holding under a pressure of 550 psi. >

18. RESULTS (Or what you will)

19. What we were looking for when testing cantilevers: • The ability to resolve transitions to superconductivity • Material responses that deviate significantly from linearity • Which thickness/type of Kapton was more appropriate for use

20. Resolving the Transition to Superconductivity Measurement showing 2nd order transition of CeCoIn5. Low temperature measurement Showing 1st order transition.

21. Angular Dependence of Critical Field

22. Example of Cantilever Clicking(nonlinear behavior)

23. Effects of Kapton Thickness on Data Interpretation (scaling issues)

24. 3He dripping and changing levels Small signal to noise ratio Re-condense 3He Increase sample size, decrease temperature, and/or decrease spacing between capacitor plates Problems Solutions

25. Conclusions About Cantilevers • Kapton film is flexible and durable at low temperatures. • Kapton is inherently non-magnetic. • It can be easily patterned with gold to make the miniature circuitry necessary for more complex measurements. • Of the two films tested in these experiments 300HN proved to be MUCH more suitable than 200HA for use as a cantilever device.

26. Conclusions about Co-Axial Melting Curve Thermometer • Kapton tubing easily handles required pressures. • The tubing remains flexible at mK temperatures. • A co-axial device can be constructed using gold plated tubing as the central component.