1 / 35

On the relation between gas phase electron scattering and processes at the STM tip

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. typical references. Electron collisions. STM. H. Gawronski, M. Mehlhorn, K. Morgenstern,

selah
Download Presentation

On the relation between gas phase electron scattering and processes at the STM tip

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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. typical references Electron collisions STM H. Gawronski, M. Mehlhorn, K. Morgenstern, Science319, 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, Science317, 31, 1203 (2007) B. C. Stipe, M. A. Rezaei, W. Ho, Science 280, 1732 (1998) P. A. Sloan and R. E. Palmer, Nature434, 367 (2005) G. A. Gallup and I. I. Fabrikant, Phys. Rev. A75, 032719 (2007) O. Sueoka and S. Mori, J. Phys. B19, 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)

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

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

  5. 1st glimpse SCIENCE 1998

  6. incident electron energy distribution

  7. Differential tunneling conductance Cross section

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

  9. observing vibrations

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

  11. observing vibrations: theoretical formalism (eA0 + D0) = 0.45 eV G0 = -0.4 eV Re(cA0) = -0.2 eV Im(cA0) = 0.1 eV M. A. Gata and P. R. Antoniewicz, PRA 1993 (other formalisms: N. Lorente etc.)

  12. observing vibrations : electron-phonon coupling above threshold • at threshold only • elastic and inelastic together • 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)  M Allan and I I Fabrikant, J Phys B 2002

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

  14. observing vibrations

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

  16. shift of resonances due to substrate and tip N2O on Cu K. J. Franke, I. Fernández-Torrente, J. I. Pascual and N. Lorente, PCCP 10, 1640 (2008)

  17. peculiarities near threshold in N2O : VFR Dissociative attachment in N2O K. J. Franke, I. Fernández-Torrente, J. I. Pascual and N. Lorente, PCCP 10, 1640 (2008) Vibrational Feshbach Resonances in Excitation of high vibrational levels

  18. shift of resonances due to substrate and tip N2 on Ar on Pt gas phase D. C. Marinica, D. Teillet-Billy, J. P. Gauyacq, M. Michaud and L. Sanche, Phys. Rev. B, 64, 085408 (2001)

  19. role of angular momentum Angular distribution of scattered electrons

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

  21. VE by electron collisions • dipole excitation • forward scattering • low energies • resonant excitation • selectivity related to temporarily occupied orbital • partial waves • “exotic mechanisms” • dipole bound resonances – Vibrational Feshbach Resonances (VFR) • virtual states (remember CO2)

  22. Selectivity related to temporarily occupied orbital Force field b2g b2g = a1g totally symmetric vibrations only

  23. Selectivity : special case 1 Force field: pupu = sg n8pu n6pg 2n8sg OK 2n6sg

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

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

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

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

  28. Chlorobenzene Chlorobenzene on Si(111) Two-electron dissociation of single molecules by atomic manipulation at room temperature P. A. Sloan and R. E. Palmer, Nature434, 367 (2005) Skalický,Chollet, Pasquier, Allan, PCCP 2002

  29. the great strength of STM: spatial resolution surface phonons excited with atomic resolution spatial mapping the 2nd derivative of I : d2I/dV2 phonon excitation probability varies with the lateral position of the tip  H. Gawronski, M. Mehlhorn, K. Morgenstern, Science319, 930 (2008)

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

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

  32. The great strength of STM: product identification after chemical change 4-dimethyl-amino-azobenzene-4-sulfonic acid (C2H6N-C6H4N=NC6H4SO3-Na+) in trans- and cis-configuration 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 (Itunnel = 75 pA; Vsample = 180 mV) Karina Morgenstern, Acc. Chem. Res., 2009, 42, 213

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

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

More Related