Sims Workshop 2000
- 1. Fragmentation of Organic Molecules Desorbed from a Surface Alger Pike Nicholas Winograd
- 2. Why Study Fragmentation? To learn what factors contribute to and cause fragmentation patterns seen in SIMS spectra Knowing how to control these can lead to easier to interpret spectra and complex organic mixture analysis Wide ranging implications for imaging SIMS of organic molecules – i.e. cells
- 3. Types of Fragmentation 1) Direct Desorption 2) Desorb then Fragment 3) Ion Beam Induced
- 4. CD 3 S-Cu (100): The Model System 1) Chemisorption to a four-fold hollow 3) No domains 2) No tilt angle due to short R group 4) Simplifed mass spectra Imanishi, S. Takenaka, T. Yokoyama, Y. Kitajima and T.Ohta J. PHYS. IV FRANCE 7 (1997)
- 6. ARTOF-SIMS Sample Manipulator a) Azimuthal Rotation: Sample rotates like the hands of a clock, around the center of the crystal. b) Polar Rotation: Sample rotates like a revolving door, around the axis perpendicular to the azimuthal axis.
- 8. FCC (100) Surface 1) Red atom is an ejecting atom 2) Blue atoms are blocking atoms 3) SIMS yield decreases with blocking
- 9. Azimuthal Distribution of Cu(100) 50 0
- 10. 1200 L CD 3 SH on Cu(100) High Mass
- 11. 1200 L CD 3 SH on Cu (100) Low Mass
- 12. Overall Fragmentation of CD 3 SH
- 13. Direct Desorption Fragmentation Low energy cascade that desorbs an ion which does not have enough energy to fragment.
- 15. Fragmentation after Desorption High energy cascades lead to desorbed species which has enough energy to further fragment.
- 17. Ion Beam Induced Fragmentation The ion beam directly breaks a bond which causes desorption of the fragment into vacuum.
- 18. Ion Beam Induced Fragmentation
- 19. Summary Fragmentation shows orientation effects CuM + yield is higher with normal primary ions Primary ion interactions create fragmentation Three distinct fragmentation mechanisms Direct desorption of CuM + CD 3 + metastable decay of high energy M + C + and D + fragments created by primary ions
- 20. Acknowledgements People Nick Winograd Barbara Garrison Winograd and Garrison Groups Money ONR, NIH, NSF
- 21. Further Evidence for Cu 2 SCD 3 + Ejection No SCD 3 + ions seen in SIMS Small amounts of CuSCD 3 + are seen Cu 2 + itself is formed by recombination i.e. there are no ejected Cu dimers Peak width of Cu 2 SCD 3 + is consistent with dimer formation not trimer
- 22. Further Evidence for CD 3 + Formation XSCD 3 + XS + CD 3 +
- 23. Image Potential