Electronic structure theory of organicinorganic interfaces

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Electronic structure theory of organic/inorganic
interfaces
Leeor Kronik Dept. of Materials and
Interfaces Weizmann Institute of
Science Rehovoth, Israel
Minerva School on Unique Molecular Effects in
Electronic Materials and Devices Safed,
Israel, 2007
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Organized organic layers controlling and
tuning surface/interface properties
More than sophisticated Lego, even without
strong bonding?
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Outline
Monolayer ? many molecules importance of
long range effects in polar organic monolayers
Monolayer many molecules
Solid monolayer ? bands molecular orbitals
Interface-induced gap states
Solid monolayer bands molecular orbitals
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THANKS
Lior Segev
Amir Natan
Dudi Deutsch
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Tuning the surface dipole
Bruening et al., J. Am. Chem. Soc. 1994, 1997
Cohen et al. J. Am. Chem. Soc. 1999
Kronik Shapira, Surf. Sci. Reports, 1999.
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Does it make sense?
Ordered polar array ? High energy penalty Is the
formation of the layer obvious? How much of the
dipole actually survives? Mechanism for
depolarization? Implications? Collective effects?
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Total dipole calculation
Supercell approach
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Partial dipole calculation
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Benzene derivatives on Si(111) monolayer
Significant, coverage-dependent, but
substrate-independent depolarization
Natan et al., Phys. Rev. B 73, 193310 (2006).
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Benzene derivatives on Si(111) cluster
Slop gt 1
Significant, enhanced polarization!
Deutsch et al., J. Am. Chem. Soc., 129, 2989
(2007)
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Rectangular array of polarizable dipoles
Macdonald and Barlow, 1963Taylor and Bayes,
1994
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Single dipole substrate polarization
Induced dipole due to pulling of density
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Suppression of substrate effects
Isolated molecule ? field 1/z3 Monolayer ?
negligible effective field exp(-2pz/L),
Natan et al., Appl. Surf. Sci., 2006 Deutsch et
al., J. Am. Chem. Soc., 2007
?

• Some disorder essential for molecular field
  effect sensors!
• Double trouble with cluster models - miss
  depolarization and introduce spurious field
  effects!

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Alkyl chains on Si(111) Deciphering the
electronic structure
Salomon et al., PRL, 2005
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Alkyl chains on Si(111) Theory and experiment
Shifting, stretching (15), broadening
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Alkyls on Si Theory and experiment
Irradiation-induced formation of defects! Amy et
al.,J. Phys. Chem. B 110, 21826 (2006).
H1sC2p
C2s
Segev et al., Phys. Rev. B 73, 165323 (2006).
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Spectra as a function of UV exposure
Amy et al., J. Phys. Chem. B 110, 21826 (2006).
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Interface induced gap states!
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Understanding PES and IPES interface induced
gap states
Experiment
Theory
Re-interpretation of transport data Salomon et
al., Adv. Mater. 19, 455 (2007).
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Conclusions

• Electronic structure of ordered organic
  monolayers interplay of localized and
  delocalized orbitals, short-range and long-range
  phenomena. More than the sum of its components!

• UPS and IPES of alkyl chains on Si explained and
  rationalized by interface-induced gap states.
  Contribution of molecular and substrate levels
  clarified.
• Dipolar effects in semiconductor-adsorbed
  self-assembled monolayers explained via
  long-range electrostatic interaction driven by
  molecular polarizability.

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Thank you!
, Antoine Kahn (Princeton), Nobuo Ueno (Chiba),
Eberhard Umbach (Würzburg)
Here David Cahen (Weizmann) Ron Naaman
(Weizmann) Eberhard Umbach (Wuerzburg)
Was Here Abraham Nitzan (Tel Aviv)
Not here Antoine Kahn (Princeton) Nobuo Ueno
(Chiba)