1. Characterizing surface layers in Nitinol using XPS Rebecca Christopfel Western Washington University Mentor: Apurva Mehta August 15, 2007

2. outline Brief explanation of Nitinol XPS Data collection/analysis Results Conclusion

3. Nitinol is a shape memory alloy Manufactured as stents Tested –Mechanically polished –Mechanically polished in solution

4. Explanted stents –Thick oxide layer –Thin oxide layer What causes a thin layer to be more biocompatible?

5. Biocompatibility is crucial Titanium has a higher affinity for oxygen than nickel. Nickel can leak into the body--BAD NEWS!

6. titanium nickel nitinol

7. titanium oxide nickel (metallic or oxidized?)

8. x-ray photoelectron spectroscopy X-ray photons X-ray photoelectrons

9. x-ray photoelectron spectroscopy Why? –Tunability of incident energy allows us to probe certain depths. –Great for surface analysis ~ few nanometers Ti

10. probing different depths By changing detector/sample orientation we get signals from different depths detector 0 45 70 90 surface

11. getting started… Choose incident photon energy – 1100 eV

12. getting started… Choose incident photon energy – 1100 eV Perform an overview scan C O Ti Ni P

13. getting started… Choose incident photon energy – 1100 eV Perform an overview scan Choose scan ranges in a given KE range Ni O Ti C P P

14. KE (eV) Intensity

15. KE (eV) Intensity

16. KE (eV) Intensity

17. KE (eV) Intensity

18. KE (eV) Intensity

19. math…. S1 S2

20. what does it mean? Sign of slope tells us which species lies above Magnitude tells us an approximate separation between species d1>d2 d2>d1 d1=d2 (d = depth)

21. data… S1 S2S3 S3:S1 S3:S2 S2:S1 conclusion : species associated with signal three is above both two and one; species one and two appear to be coming from the same depth

22. alumina hydroxide phosphate titanium oxide partially oxidized nickel oxidized nickel metallic nickel nitinol substrate a model… mechanically polished mechanically polished in solution

23. summary… By varying angle we were able to differentiate the depths of various species Mechanically polished sample in PBS solution has a slightly thicker oxide layer Phosphorus layer near the surface suggests no nickel leaking Implies biocompatibility

24. thanks to… Apurva Mehta, SSRL/SLAC Zhi Liu, SSRL/SLAC Valeska Schroeder, NDC Alan Pelton, NDC Hirohito Ogasawara, SSRL/SLAC DOE and SLAC

25. questions?