Spectroscopy of Hybrid Inorganic/Organic Interfaces Electron Spectroscopy Dietrich RT Zahn.
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Transcript of Spectroscopy of Hybrid Inorganic/Organic Interfaces Electron Spectroscopy Dietrich RT Zahn.
![Page 1: Spectroscopy of Hybrid Inorganic/Organic Interfaces Electron Spectroscopy Dietrich RT Zahn.](https://reader037.fdocuments.in/reader037/viewer/2022102906/56649c755503460f949285f4/html5/thumbnails/1.jpg)
Spectroscopy of Hybrid Inorganic/Organic Interfaces
Electron Spectroscopy
Dietrich RT Zahn
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Photoemission Spectroscopy: UPS and XPS
X-Ray Source (Mg KX-Ray Source (Mg K/ Zr M/ Zr M))
UV Lamp (He I/ He II) UV Lamp (He I/ He II)
Lens System: 5 operation modesLens System: 5 operation modes
Angular Resolved Energy AnalyserAngular Resolved Energy Analyser
Detector (Channeltron)Detector (Channeltron)
Data acquisition system Data acquisition system
VGX900IC data system
Ah
,
Ratemeter and
Channeltron supply
Lense Supply
SPECTROMETER
CONTROL UNIT
Lens
System
Retard
ChanneltronElectrons
path
Pre Amp
Lens Voltages
Fermi analyserHVKE = +R +WF
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OMBD SystemOMBD Systemand Electrical Measurementsand Electrical Measurements
O M BD &M etalliza tion
C ham ber
In s itu IV /C V
K nudsence lls
P lasm aC ell
LE E D
X P S U P S
K e lv inP r o b e
R A SS tage
II-V I M B EC ham ber
R H E E DG un
AnalysisC ham ber
(AR U PS10)
E lectronA nalyzer
S pectroscopicE llipsom etry
in situIV / CV
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X5
EF
cutoffE
h
HOMO
VBM
IES-GaAs
S -GaAs
CBM
LUMO
IEPTCDA
PTCDA 1PTCDA 0 nm
×S -GaAs(10 ) : (20 1)
h
K inetic energy Binding Energy
(Vacuum Level shift)
Interface dipole
1PTCDA 0 nm×S -GaAs(10 ) : (20 1)
Determination of Determination of Energy Diagram using Photoemission Spectroscopyusing Photoemission Spectroscopy
E = - h E - K IN B
,g tE
gE
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Reduction of Reduction of IInhomogeneous nhomogeneous FFermi ermi LLevel evel PPinning by inning by PTCDAPTCDA DDepositioneposition
S.Park, D.R.T. Zahn et al., APL 76 (22) (2000) 3200.
• 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.
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Valence Band Offset at thePTCDA/S-GaAs Interface
• Valence band – HOMO offset : (1.1eV0.1)eV
• No change in band bending of the substrate upon PTCDA deposition.
10 8 6 4 2 0 -2
1.97eV
S-GaAs(100) PTCDA(6nm)
0.89eV
Inte
nsi
ty /
a.u.
Binding energy / eV
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• IE spans from 5.18 to 6.4eV. • A wide range of IE of wet S treated surfaces (5.53~5.91eV).Due to the degree of the surface dipole formation.
• Similar IE for GaAs(100)-c(44) and H-plasma treated GaAs(100).
Ionization Energy of Differently Ionization Energy of Differently Treated Treated GaAs(100) SurfacesGaAs(100) Surfaces
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Valence Band Spectra of Valence Band Spectra of PTCDAPTCDA//SS-GaAs(100)-GaAs(100)
• Assignment- A: MO in perylene- B,C,D: MO in perylene and C=O- 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 Valence Band Spectra of PTCDAPTCDA//GaAs(100)-c(4GaAs(100)-c(44)4)
Change in direction of interface dipole is observed.
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Band Diagram of Band Diagram of PTCDAPTCDA on on Differently treated Differently treated GaAs(100)GaAs(100)
IEGaAs=6.40eVSe-GaAs PTCDA
IEGaAs=5.75eVS-GaAs PTCDAGaAs PTCDA
IEGaAs=5.23eV
• Possible LUMO position:(Eg,o=2.2eV)–(Eg,t=2.8eV 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 Interface Dipole vs. Electron Affinity of Affinity of GaAs(100)GaAs(100)
3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2
-0.8
-0.6
-0.4
-0.2
0.0
0.2
PTCDA
=4.12eV
Interface dipole Linear fit
Inte
rfac
e d
ipol
e / e
V
Electron affinity of GaAs / eV
Se-GaAs-(21)
S-GaAs-(21)
GaAs-c(44)
• Linear relation of interface dipole to GaAs.
• At interface dipole=0, GaAs=(4.120.1)eV=PTCDA
• Eg,t(PTCDA)=2.44–2.55eVPTCDA=4.12eV
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VB Spectra of Ag on VB Spectra of Ag on PTCDAPTCDA
• 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 VB Spectra of Ag on DiMe-DiMe-PTCDIPTCDI
• 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 Influence of Organic SubstrateOrganic Substrate on Metal Workfunctionon Metal Workfunction
IH P R esea rch Tra in ing N e tw orkAg(111), Ag,poly :Dweydari et al., Phys. Stat. Soli. A 17 (1973) 247
• 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.
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interface dipole =-0.68 eV
strong surface dipole good interface properties
Energy band alignment DiMePTCDI / S-GaAs(21)
EFS
1.18eV2.04eV
6.28eV
6.46eV
=-0.68eV
EVBM
EHOMO
Gianina Gavrila 26.06.03
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Gianina Gavrila 26.06.03
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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Gianina Gavrila 26.06.03
Molecular orientation of DiMePTCDI on S-GaAs(100)
56°
deviation from the predicted value by ~ 15 ° better estimation of V0
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Photon energy dependence spectra
16 15 14 13 12 11 10 9 8 7 6 5 4
90 eV 85 eV 80 eV 75 eV 70 eV 65 eV 60 eV 55 eV 50 eV 45 eV 42 eV 40 eV 37 eV 35 eV
Inte
ns
ity
/a
.u.
EB-E
VAC /eV
HOMO
Gianina Gavrila 26.06.03
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Intermolecular energy band dispersion
2
01/ 2
0*
/ 2 , ( / )2 ( - - ) /
/ 1B
E k m V k n ak m h E V
m m
the final continuum state is a parabolic free-electron-like band in a
constant inner potential V0.*
0( ) 2 cos( * )B BE k E t a k
Parameters:Parameters: V0=5.8 eV, t=0.04eV, 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
HOMO
LUMO
EF
EVAC
IE EA