Download - Spectroscopy of Hybrid Inorganic/Organic Interfaces Electron Spectroscopy Dietrich RT Zahn
Spectroscopy of Hybrid Inorganic/Organic Interfaces
Electron Spectroscopy
Dietrich RT Zahn
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
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
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
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.
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
• 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
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.
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.
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.
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
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.
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
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.
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
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
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
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
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
The Transport Gap from Combined PES and IPES Measurements
HOMO
LUMO
EF
EVAC
IE EA