1. 1 On the relation between gas phase electron scattering and processes at the STM tip (with emphasis on vibrational excitation) Michael Allan Department of Chemistry University of Fribourg, Switzerland

2. 2 typical references H. Gawronski, M. Mehlhorn, K. Morgenstern, Science 319, 930 (2008) M. Paulsson, T. Frederiksen, H. Ueba, N. Lorente, and M. Brandbyge, Phys. Rev. Lett. 100, 226604 (2008) Peter Liljeroth, Jascha Repp, Gerhard Meyer, Science 317, 31, 1203 (2007) B. C. Stipe, M. A. Rezaei, W. Ho, Science 280, 1732 (1998) P. A. Sloan and R. E. Palmer, Nature 434, 367 (2005) G. A. Gallup and I. I. Fabrikant, Phys. Rev. A 75, 032719 (2007) O. Sueoka and S. Mori, J. Phys. B 19, 4035 (1986) G. J. Schulz, Rev. Mod. Phys. 45, 423 (1973) Isobel C. Walker, A. Stamatovic and S. F. Wong, J. Phys. Chem. 69, 5532 (1978) E. Brüche Ann. Phys. Lpz. 2, 909 (1929) Electron collisionsSTM

3. 3 phonon excitation, phonon emission, inelastic electron-phonon effect Spatial resolutionn. a. Vibrational excitation Differential tunneling conductance, action spectroscopy Cross section IETS Inelastic Electron Tunneling Spectroscopy EELS Electron energy-loss spectrum Local Density of States Resonances Terms and methods

4. 4 see: B. N. J. Persson and A. Baratoff, Phys. Rev. Lett. 59, 339 (1987) J. J. Pascual, Eur. Phys. J. D 35, 327 (2005) electron scattering vs. electron tunneling see: G. J. Schulz, Rev. Mod. Phys. 45, 423 (1973)

5. 5 SCIENCE 1998 1 st glimpse

6. 6 incident electron energy distribution

7. 7 Differential tunneling conductance Cross section

8. 8 observing resonances JASCHA REPP | GERHARD MEYER Phys. Unserer Zeit 2006

9. 9 observing vibrations

10. 10 observing vibrations G. A. Gallup and I. I. Fabrikant, PRA 1993 M. A. Gata and P. R. Antoniewicz, PRA 1993

11. 11 observing vibrations: theoretical formalism M. A. Gata and P. R. Antoniewicz, PRA 1993  A 0 +  0 ) = 0.45 eV  0 =  0.4 eV Re     =  0.2 eV Im     = 0.1 eV (other formalisms: N. Lorente etc.)

12. 12 observing vibrations : electron-phonon coupling above threshold M Allan and I I Fabrikant, J Phys B 2002 Energy-analysis of scattered electrons permits: -separation of elastic and inelastic channels -measurement of inelastic cross section (electron- phonon coupling) as a function of excess energy (EDS) -at threshold only -elastic and inelastic together 

13. 13 observing vibrations virtual state  * shape resonance Electron energy-loss (eV) Čížek, Horáček, Allan, Fabrikant, Domcke, J. Phys. B (2003) Dipole-bound states Vibrational Feshbach Resonances (VFR) Allan, Phys. Rev. Lett. (2001)

14. 14 observing vibrations

15. 15 observing vibrations (1)separately from elastic process (2)at or above threshold; E i can be chosen to ‘hit’ various resonances Energy-analysis of scattered electrons allows vibrations to be observed : Cross section can be recorded as a function of  E (ELS) → spectrum of vibrational states E i (EDS) → spectrum of resonances (1)elastic and inelastic processes measured together (except: action spectroscopy !) (2)vibrational spectra are measured at threshold No analyzer : Resonant enhancement only when there is a resonance at vibrational threshold

16. 16 shift of resonances due to substrate and tip K. J. Franke, I. Fernández-Torrente, J. I. Pascual and N. Lorente, PCCP 10, 1640 (2008) N 2 O on Cu

17. 17 peculiarities near threshold in N 2 O : VFR K. J. Franke, I. Fernández-Torrente, J. I. Pascual and N. Lorente, PCCP 10, 1640 (2008) Dissociative attachment in N 2 O Vibrational Feshbach Resonances in Excitation of high vibrational levels

18. 18 shift of resonances due to substrate and tip D. C. Marinica, D. Teillet-Billy, J. P. Gauyacq, M. Michaud and L. Sanche, Phys. Rev. B, 64, 085408 (2001) gas phase N 2 on Ar on Pt

19. 19 role of angular momentum Angular distribution of scattered electrons

20. 20 role of angular momentum J. I. Pascual, J. J. Jackiw, Z. Song, P. S. Weiss, H. Conrad, and H.-P. Rust, Phys. Rev. Lett. 86, 1050 (2001) Benzene on Cu external vibrations: - frustrated translation - frustrated rotations

21. 21 VE by electron collisions 1.dipole excitation forward scattering low energies 2.resonant excitation selectivity related to temporarily occupied orbital partial waves 3. “exotic mechanisms” dipole bound resonances – Vibrational Feshbach Resonances (VFR) virtual states (remember CO 2 )

22. 22 Selectivity related to temporarily occupied orbital Force field b 2g  b 2g = a 1g totally symmetric vibrations only

23. 23 Selectivity : special case 1 Force field:  u   u =  g 8  u 6  g  8  g  6  g OK

24. 24 Selectivity : special case 2 S. F. Wong and G. J. Schulz, Phys. Rev. Lett. 35, 1429 (1975) “Vibrational excitation in benzene by electron impact via resonances: Selection rules” Observation: in-plane modes, but also out-of-plane modes Proposition: incoming d  outgoing d  wave :  u   u =  g incoming d  outgoing s  wave :  u   g =  u       M. Paulsson, T. Frederiksen, H. Ueba, N. Lorente, and M. Brandbyge, Phys. Rev. Lett. 100, 226604 (2008)

25. 25 Selectivity : special case 2 S. F. Wong and G. J. Schulz, Phys. Rev. Lett. 35, 1429 (1975) M. Paulsson, T. Frederiksen, H. Ueba, N. Lorente, and M. Brandbyge, Phys. Rev. Lett. 100, 226604 (2008)

26. 26 Chlorobenzene - the  * resonances act as doorway states into the  * resonance - no activation barrier ← symmetry lowering ← vibronic coupling Skalický, Chollet, Pasquier, Allan, Phys. Chem. Chem. Phys. 2002 ring breathing C-Cl stretch

27. 27 Chlorobenzene Skalický, Chollet, Pasquier, Allan, Phys. Chem. Chem. Phys. 2002

28. 28 Chlorobenzene Skalický, Chollet, Pasquier, Allan, PCCP 2002 P. A. Sloan and R. E. Palmer, Nature 434, 367 (2005) Two-electron dissociation of single molecules by atomic manipulation at room temperature Chlorobenzene on Si(111)

29. 29 the great strength of STM: spatial resolution H. Gawronski, M. Mehlhorn, K. Morgenstern, Science 319, 930 (2008)  surface phonons excited with atomic resolution spatial mapping the 2nd derivative of I : d 2 I/dV 2 phonon excitation probability varies with the lateral position of the tip

30. 30 the great strength of STM: spatial resolution B. C. Stipe, M. A. Rezaei, W. Ho, Phys. Rev. Lett. 82, 1724 (1999) acetylene chemisorbed on Cu(100) : C-D stretch excited with atomic resolution normal constant current image image of the 266 mV inelastic signal

31. 31 the great strength of STM: action spectroscopy Yasuyuki Sainoo, Yousoo Kim, Toshiro Okawa, Tadahiro Komeda, Hidemi Shigekawa, and Maki Kawai1, Phys. Rev. Lett. 95, 246102 (2005) cis-2-butene on Pd(110) : vibration induced motion

32. 32 The great strength of STM: product identification after chemical change Karina Morgenstern, Acc. Chem. Res., 2009, 42, 213 IET manipulation of a single 4-dimethyl-amino-azobenzene-4-sulfonic acid molecule: (a) molecule in trans-configuration before manipulation; the STM tip is positioned above the N=N group of the molecule (position marked by cross), while the manipulation voltage is increased within 1 s from 100 mV to 1 V; (b) after manipulation the molecule is found in cis-configuration (I tunnel = 75 pA; V sample = 180 mV) 4-dimethyl-amino-azobenzene-4-sulfonic acid (C 2 H 6 N- C 6 H 4 N=NC 6 H 4 SO 3 - Na + ) in trans- and cis-configuration

33. 33 Current-Induced Hydrogen Tautomerization of Naphthalocyanine P. Liljeroth, J. Repp, G. Meyer, Science 317, 1203 (2007)

34. 34 Electron collisions with pyrrole T. Skalický and M. Allan, J. Phys. B (2004) Vibrational excitationDissociative attachment

35. 35