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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

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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 collisions STM

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phonon excitation,phonon emission,inelastic electron-phonon effect

Spatial resolution

n. a.

Vibrational excitation

Differential tunneling conductance, action spectroscopy

Cross section

IETS Inelastic Electron Tunneling Spectroscopy

EELS Electron energy-loss spectrum

Local Density of StatesResonances

Terms and methods

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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)

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SCIENCE 1998

1st glimpse

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incident electron energy distribution

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Differential tunneling conductance

Cross section

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observing resonances

JASCHA REPP | GERHARD MEYERPhys. Unserer Zeit 2006

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observing vibrations

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observing vibrations

G. A. Gallup and I. I. Fabrikant, PRA 1993

M. A. Gata and P. R. Antoniewicz, PRA 1993

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observing vibrations: theoretical formalism

M. A. Gata and P. R. Antoniewicz, PRA 1993

A0 + 0) = 0.45 eV 0 = 0.4 eV

Re = 0.2 eV Im

= 0.1 eV

(other formalisms: N. Lorente etc.)

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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

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observing vibrations

virtual state * shape resonance

Electron energy-loss (eV)

Čížek, Horáček, Allan, Fabrikant, Domcke, J. Phys. B (2003)

Dipole-bound statesVibrational Feshbach Resonances (VFR)

Allan, Phys. Rev. Lett. (2001)

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observing vibrations

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observing vibrations

(1) separately from elastic process

(2)at or above threshold; Ei 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

Ei (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

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shift of resonances due to substrate and tip

K. J. Franke, I. Fernández-Torrente, J. I. Pascual and N. Lorente, PCCP 10, 1640

(2008)

N2O on Cu

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peculiarities near threshold in N2O : VFR

K. J. Franke, I. Fernández-Torrente, J. I. Pascual and N.

Lorente, PCCP 10, 1640 (2008)

Dissociative attachment in N2O

Vibrational Feshbach Resonances in Excitation of high vibrational levels

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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

N2 on Ar on Pt

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role of angular momentum

Angular distribution of scattered electrons

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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

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VE by electron collisions

1. dipole excitationforward scattering

low energies

2. resonant excitationselectivity related to temporarily occupied orbital

partial waves

3. “exotic mechanisms”dipole bound resonances – Vibrational Feshbach Resonances (VFR)

virtual states (remember CO2)

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Selectivity related to temporarily occupied orbital

Force field

b2g b2g = a1g

totally symmetric vibrations only

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Selectivity : special case 1

Force field:

u u =

g

8 u 6 g

8 g 6 gOK

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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)

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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)

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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

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Chlorobenzene

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

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Chlorobenzene

Skalický, Chollet, Pasquier, Allan, PCCP 2002

P. A. Sloan and R. E. Palmer, Nature 434, 367 (2005)

Two-electron dissociation of singlemolecules by atomic manipulation

at room temperature

Chlorobenzene on Si(111)

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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 : d2I/dV2

phonon excitation probability varies with the lateral position of the tip

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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

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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

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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 themanipulation 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)

4-dimethyl-amino-azobenzene-4-sulfonic acid (C2H6N-C6H4N=NC6H4SO3

-Na+) in trans- and cis-configuration

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Current-Induced Hydrogen Tautomerization of Naphthalocyanine

P. Liljeroth, J. Repp, G. Meyer, Science 317, 1203 (2007)

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Electron collisions with pyrrole

T. Skalický and M. Allan, J. Phys. B (2004)

Vibrational excitation Dissociative attachment

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