Inelastic Electron Tunneling Spectroscopy

1
Inelastic Electron Tunneling Spectroscopy
E
I
EF
Elastic
Tip
V
Inelastic
EF - eV
Sample
dI/dV
V
A molecular vibration can be stimulated when V

d2I/dV2
V
2
Acetylene on Cu(100)
Vibrational Imaging
Vibrational Spectroscopy
A Topography B d2I/dV2 _at_ V 358 mV C
d2I/dV2 _at_ V 266 mV D d2I/dV2 _at_ V 311 mV
C2H2 C2D2 Difference
B. C. Stipe, M. A. Rezaei, W. Ho, Science 280
(1998) 1732-1735.
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Benzene on Pt(111)
Clean Pt(111) 30Å x 15Å Vs 100mV I 6nA T4K
Benzene on Pt(111) 30Å x 30Å Vs 200mV I
550pA T 4K
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I-V of Benzene on Pt(111)
Current (nA)
Voltage (mV)
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Vibrational Spectroscopy of Benzene on Pt(111)
Conductivity of the tunnel junction decreases by
18 at threshold for C-H out of plane bending
mode.
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Theoretical Predictions

• Conductivity increase of 1 for dipole coupling.
  (Binnig et al. Persson and Demuth)
• Conductivity increase (Gata and Antoniewicz) or
  decrease (Persson and Baratoff) of 10 or more
  for resonant coupling.

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Electronic States Far Away in Energy Contribute
to the Tunneling Current
Adsorbed Xe electrons at position of tip electron
overlap
6s
EFermi
5p
?6
?4
2
0
?2
4
Voltage (V)
N. D. Lang, IBM Yorktown
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Future IETS Studies

• Switch to Ni(110) substrate.
• Confirm decrease in conductivity (negative peak
  in d2I/dV2) for benzene C-H bending mode.
• Look for inequivalent C-H stretching modes and
  S-Ni stretch for thiophene.