Spectroscopy of Hybrid Inorganic/Organic Interfaces Electron Spectroscopy

1
Spectroscopy of Hybrid Inorganic/Organic
InterfacesElectron Spectroscopy

• Dietrich RT Zahn

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Photoemission Spectroscopy UPS and
XPS

• X-Ray Source (Mg K?/ Zr M?)
• UV Lamp (He I/ He II)
• Lens System 5 operation modes
• Angular Resolved Energy Analyser
• Detector (Channeltron)
• Data acquisition system

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OMBD System and Electrical Measurements
in situ IV / CV
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Determination of Energy Diagram using
Photoemission Spectroscopy
X5

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Reduction of Inhomogeneous Fermi Level Pinning by
PTCDA Deposition

• PTCDA/Se-GaAs(100)
• Lineshape remains unchanged
• ? Negligible interaction between PTCDA and
  Se-GaAs(100).
• Gaussian broadening of Se3d core level is
  reduced
• 0.87 ? 0.78 eV by 0.09 eV.
• ? Reduction of inhomogeneous Fermi level pinning
  by preferential adsorption of PTCDA on defect
  sites.

S.Park, D.R.T. Zahn et al., APL 76 (22) (2000)
3200.
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Valence Band Offset at the PTCDA/S-GaAs Interface

• Valence band HOMO offset
• (1.1eV?0.1)eV
• No change in band bending of the substrate upon
  PTCDA deposition.

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Ionization Energy of Differently Treated
GaAs(100) Surfaces

• IE spans from 5.18 to 6.4eV.
• A wide range of IE of wet S treated surfaces
  (5.535.91eV).?Due to the degree of the surface
  dipole formation.
• Similar IE for GaAs(100)-c(4?4) and H-plasma
  treated GaAs(100).

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Valence Band Spectra of PTCDA/S-GaAs(100)

• Assignment- A ? MO in perylene- B,C,D ? MO
  in perylene and CO- E mixture of
  ? and ? states
• No change in energy position of A E upon PTCDA
  deposition.
• Shift of Ecutoff towards higher binding energy.

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Valence Band Spectra of PTCDA/GaAs(100)-c(4?4)
Change in direction of interface dipole is
observed.
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Band Diagram of PTCDA on Differently treated
GaAs(100)
IEGaAs5.75eV
IEGaAs5.23eV
IEGaAs6.40eV
S-GaAs
GaAs
Se-GaAs
PTCDA
PTCDA
PTCDA

• Possible LUMO position(Eg,o2.2eV)(Eg,t2.8eV
  from Kahn et al.)
• Correlation between interface dipole and
  relative energy position of ELUMO to ECBM. ? EA
  difference is the driving force for the formation
  of the interface dipole.

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Interface Dipole vs. Electron Affinity of
GaAs(100)

• Linear relation of interface dipole to ?GaAs.
• At interface dipole0, ?GaAs(4.12?0.1)eV?PTCD
  A
• Eg,t(PTCDA)2.442.55eV

GaAs -c(4?4)
S-GaAs -(2?1)
Se-GaAs -(2?1)
?PTCDA4.12eV
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VB Spectra of Ag on PTCDA

• At low Ag thickness, features from PTCDA are
  still seen without energy shifts.
• Very weak charge transfer between Ag atoms and
  PTCDA molecules.

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VB Spectra of Ag on DiMe-PTCDI

• Very weak charge transfer between Ag atoms and
  DiMe-PTCDI molecules.
• Slightly different Ag4d band lineshape.

DiMethyl-3,4,9,10-Perylenetetracarboxylic diimide
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Influence of Organic Substrate on Metal
Workfunction

• Ag film on PTCDA closer ? to ?Ag(111), stronger
  (111) diffraction peak
• Crystalline structure of underlying organic film
  strongly influence the crystalline structure and
  ? of metal film.

?Ag(111), ?Ag,poly Dweydari et al., Phys.
Stat. Soli. A 17 (1973) 247
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Energy band alignment DiMePTCDI / S-GaAs(2?1)
EFS

• interface dipole ?-0.68 eV
• strong surface dipole ? good interface
  properties

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Density of states for a neutral molecule of
DiMePTCDI

• valence band states corresponding
• to bonding combinations of C2s, C 2p,
• N2s, N2p or O2s, O2p

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Molecular orientation of DiMePTCDI on S-GaAs(100)

• deviation from the predicted value by 15 ?
  better estimation of V0

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Photon energy dependence spectra
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Intermolecular energy band dispersion

• the final continuum state is a parabolic
  free-electron-like band in a constant inner
  potential V0.

• Parameters
• V05.8 eV, t0.04eV, a? 4.1 Å
• ? tilt 42

D. Yoschimura at al, PRB, 60, 12, 9046-9060,
1999
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The Transport Gap from Combined PES and IPES
Measurements
EVAC
IE
EA
LUMO
EF
HOMO