www.phi.com Depth Profiling of Organic Photovoltaic and OLED Materials by Cluster Ion Beams J.S. Hammond 1 , S. N. Raman 1 , S. Alnabulsi 1 , N. C. Erickson 2 and R. J. Holmes 2 1. Physical Electronics, 18725 Lake Drive East, Chanhassen, MN. *2. University of Minnesota, Minneapolis, MN.
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Depth Profiling of Organic Photovoltaic and OLED Materials ... · OLED Materials by Cluster Ion Beams J.S. Hammond1, S. N. Raman1, S. Alnabulsi1, N. C. Erickson2 and R. J. Holmes2
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Depth Profiling of Organic Photovoltaic and
OLED Materials by Cluster Ion Beams
J.S. Hammond1, S. N. Raman1, S. Alnabulsi1, N. C. Erickson2 and R. J.
Holmes2
1. Physical Electronics, 18725 Lake Drive East, Chanhassen, MN.
*2. University of Minnesota, Minneapolis, MN.
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Challenges for Organic Electronics Research
Efficiencies are based on optimum band matching and the
physical dispersions of components
– Work functions at discrete interfaces e. g. metal electrodes
– Diffusion lengths of charge carriers
Device lifetimes influence customer acceptance and profit
Chemical and molecular specific depth profiling is desired
– Depth resolution of a few nm with high sensitivity
– Cluster ion depth profiling interleaved with XPS and TOF-SIMS may
be solution
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Why use Depth Profiling for Organic Electronics?
New “nanotechnology” products use extremely thin
organic and polymer structures
– OLEDS
– Energy conversion materials and fuel cell membranes
Fabrication process producing molecular gradients can
result in significant differences in efficiency
Product degradation can result from molecular oxidation
and molecular diffusion
Spectroscopy with a nano-scale depth of analysis (XPS
and TOF-SIMS) needed for surface and depth profiling
characterization of molecular composition and diffusion
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Comparison of XPS and TOF-SIMS
XPS TOF-SIMS
Probe Beam Photons Ions
Analysis Beam Electrons Ions
Spatial Resolution 10 µm 0.10 µm
Sampling Depth(Å) 5-75 1-10
Detection Limits 0.01atom % 1ppm
Information Content Elemental Elemental
Chemical Chemical
Molecular
Quantification Excellent Std. needed
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XPS System Schematic
Electron Source Quartz Crystal
Monochromator
Aluminum Anode Sample
Rowland
Circle
Multi-channel
Detector
Al ka x-rays
Photoelectrons
X-ray Source
Hemispherical
mirror analyzer
Energy Analyzer
15 kv electrons
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Scanning Micro Focused X-ray Source
Al X-rays
Raster Scanned
Micro-Focused
Electron Beam
Al Anode
Monochromatic
Raster Scanned
Micro-Focused
X-ray Beam
Sample
Analyzer
Input Lens
Al X-rays
Electron Gun
Analyzer
Input Lens
Quartz Crystal
Monochromator
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0 200 400 600 800 1000 Binding Energy (eV)
c/s
-O
KL
L
-O
1s
-C
1s
-O
2s
280 285 290 295 300 Binding Energy (eV)
c/s
XPS survey spectra provide
quantitative elemental
information
High resolution XPS spectra
provide quantitative chemical state
information
C 1s
CH C-O C-O=O
C C O O
O O
CH2 CH2
PET Atom %
C 70.9
O 29.1
% of C 1s
CH 62.7
C-O 20.2
O=C-O 17.1
Typical XPS Spectra Poly(ethylene terephthalate)
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PHI TRIFT V nanoTOF
8
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Unique Polymer "Fingerprint” Identification
Using TOF-SIMS Spectra XPS shows identical spectra for both polymers
0 20 40 60 80 100 0
2.0E5
4.0E5
6.0E5
8.0E5
1.0E6
To
tal C
ou
nts
101 85 29 45 117
87 109
99
57 41
59
0 20 40 60 80 100 0
2.0
4.0E4
6.0E4
8.0E4
1.0E5
To
tal C
ou
nts
29 115 41 97 87
45
71 59 85
101 75
(CH2CHO)n
CH3
Polypropylene glycol
(CH2CH)n
O-CH3
Polyvinylmethyl ether
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Damage is observed.
275 280 285 290 295 300
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Binding Energy (eV)
c/s
PET C 1s
surface
20 nm sputtered
522 524 526 528 530 532 534 536 538 540 542 544
0
500
1000
1500
2000
2500
3000
3500
Binding Energy (eV)
c/s
PET O 1s
surface
20 nm sputtered
O=C-O C-O
C-C
C-H
O=C O-C
500 eV Ar+ Sputter
Damage Accumulation Indicated by XPS
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275 280 285 290 295 300
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Binding Energy (eV)
c/s
PET C 1s
surface
20 nm sputtered
522 524 526 528 530 532 534 536 538 540 542 544
0
500
1000
1500
2000
2500
3000
3500
Binding Energy (eV)
c/s
PET O 1s
surface
20 nm sputtered
O=C-O
O=C O-C
C-O
C-C
C-H
No damage observed.
10keV C60+ Sputter
No Damage Observed by XPS
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Altered Volume & Sub-surface Damage
15 keV Ga 15 keV C60
1 nm
Graphic courtesy B. Garrison & Z. Postawa.
Non-C60 sputter sources result in the
accumulation of sub-surface damage.
Residual C60 sputter damage is mostly
removed with the next C60 impact event.
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Molecular Dynamics: Ar9000+ GCIB on PS/Ag
The permission of the pictures is by courtesy of Professor Zbigniew Postawa, Jagiellonian University (Poland); L. Rzeznik, B. Czerwinski, B.J. Garrison, N.
Winograd and Z. Postawa, "Microscopic Insights into the Sputtering of Thin Polystyrene Films on Ag{111} Induced by Large and Slow Ar Clusters", J. Phys.