The document discusses fragmentation of organic molecules during desorption from a surface using secondary ion mass spectrometry (SIMS). There are three types of fragmentation: 1) direct desorption without fragmentation, 2) desorption followed by fragmentation of the molecule, and 3) ion beam-induced fragmentation where the beam directly breaks bonds. The study uses a model system of CD3SH molecules adsorbed on a Cu(100) surface to investigate the fragmentation patterns and mechanisms using an ARTOF-SIMS machine. Primary ion interactions can create metastable fragments like CuM+ and CD3+ ions, while high energy cascades can further fragment desorbed species.

1. Fragmentation of Organic Molecules Desorbed from a Surface Alger Pike Nicholas Winograd

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)

5. The ARTOF-SIMS Machine

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.

7. Ion Trajectories

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.

14. Direct Desorption Fragmentation

15. Fragmentation after Desorption High energy cascades lead to desorbed species which has enough energy to further fragment.

16. Fragmentation after Desorption

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

22. Further Evidence for CD 3 + Formation XSCD 3 +  XS + CD 3 +

23. Image Potential