Transcript No Slide Title

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
1
typical references
Electron collisions
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)
STM
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)
2
Terms and methods
n. a.
Spatial resolution
Cross section
Differential tunneling conductance,
action spectroscopy
Vibrational
excitation
phonon excitation,
phonon emission,
inelastic electron-phonon effect
EELS Electron
energy-loss
spectrum
IETS Inelastic Electron
Tunneling Spectroscopy
Resonances
Local Density of States
3
electron scattering vs. electron tunneling
see:
G. J. Schulz, Rev. Mod. Phys. 45, 423 (1973)
see:
B. N. J. Persson and A. Baratoff,
Phys. Rev. Lett. 59, 339 (1987)
J. J. Pascual, Eur. Phys. J. D 35, 327 (2005)
4
1st glimpse
SCIENCE 1998
5
incident electron energy
distribution
6
Cross section
Differential tunneling
conductance
7
observing resonances
JASCHA REPP | GERHARD MEYER
Phys. Unserer Zeit 2006
8
observing vibrations
9
observing vibrations
G. A. Gallup and I. I. Fabrikant, PRA 1993
M. A. Gata and P. R. Antoniewicz, PRA 1993
10
observing vibrations: theoretical formalism
(eA0 + D0) = 0.45 eV
Re(cA0) = -0.2 eV
G0 = -0.4 eV
Im(cA0) = 0.1 eV
M. A. Gata and P. R. Antoniewicz, PRA 1993
11
(other formalisms: N. Lorente etc.)
observing vibrations : electron-phonon coupling above
threshold
Energy-analysis of scattered electrons permits:
- at threshold only
- separation of elastic and inelastic channels
- elastic and
inelastic together
- measurement of inelastic cross section (electronphonon coupling) as a function of excess energy (EDS)
M Allan and I I Fabrikant, J Phys B 2002

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observing vibrations
Electron energy-loss (eV)
Allan, Phys. Rev. Lett. (2001)
virtual state
p* shape resonance
Dipole-bound states
Vibrational Feshbach
Resonances (VFR)
Čížek, Horáček, Allan, Fabrikant, Domcke, J. Phys. B (2003)
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observing vibrations
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observing vibrations
Energy-analysis of scattered
electrons allows vibrations to
be observed :
(1) separately from elastic
process
(2) 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
No analyzer :
(1) elastic and inelastic
processes measured
together (except: action
spectroscopy !)
(2) vibrational spectra are
measured at threshold
Resonant enhancement only
when there is a resonance at
vibrational threshold
Ei (EDS) → spectrum of
resonances
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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)
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peculiarities near threshold in N2O : VFR
Dissociative
attachment in N2O
Vibrational Feshbach Resonances in
Excitation of high vibrational levels
K. J. Franke, I. Fernández-Torrente,
J. I. Pascual and N. Lorente,
PCCP 10, 1640 (2008)
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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)
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role of angular momentum
Angular distribution of scattered electrons
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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,
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Phys. Rev. Lett. 86, 1050 (2001)
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 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:
pu  pu = sg
n8
2n8
pu
sg
n6
OK
2n6
pg
sg
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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
s
p
s
p
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)
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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
ring breathing
C-Cl stretch
- 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
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Chlorobenzene
Skalický, Chollet, Pasquier, Allan, Phys. Chem. Chem. Phys. 2002
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Chlorobenzene
Chlorobenzene
on Si(111)
Two-electron dissociation of single
molecules by atomic manipulation
at room temperature
Skalický, Chollet, Pasquier, Allan,
PCCP 2002
P. A. Sloan and R. E. Palmer, Nature 434, 367 (2005)
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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, Science 319, 930 (2008)
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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)
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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)
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The great strength of STM: product identification after chemical change
4-dimethyl-amino-azobenzene-4-sulfonic acid (C2H6NC6H4N=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
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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
Vibrational excitation
Dissociative attachment
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T. Skalický and M. Allan, J. Phys. B (2004)
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