Depth Profile with X-ray Photoelectron
+
+
Spectrometry using C60 and Ar Beams
Research Assistant: Wei-Chun Lin
Advisor: Jing-Jong Shyue, Ph.D. （薛景中）
Research Center for Applied Sciences,
Academia Sinica （中央研究院）
1
Structural Analysis of Organic Electronics
•
Cross-sectional SEM with XEDS?
•
•
~μm excitation volume ➡ bad resolution
Cross-sectional TEM?
-
difficulty in preparing composites materials of hard
(inorganic electrode) and soft (organic thin-film)
-
diffraction-based technique
· no contrast for amorphous organic materials
-
Analytical TEM (STEM-EELS/XEDS, EFTEM)?
· 106t H-bomb at 30m range
· e-beam induced damage to the sample
Depth profile in surface analysis techniques?
2
Principle of Depth Profile
Sputter Ion Beam
Analysis Depth (0.5-10 nm)
Depth Profile Analysis
Surface Layer
Sample Matrix
3
XPS Depth Profiling
•
composition as a function of depth t in thin films
•
XPS signal is generated near the surface (~3nm)
•
sputtering provides layer sectioning
•
depth profiles are usually shown as signal intensity
versus sputter time (not depth)
•
further calibrations required
-
•
convert sputter time to depth
signal intensity to atomic concentration
however, ion sputtering can causes change in the
composition of the surface layers
-
surface segregation
preferential sputtering
4
Sputtering with C60+ Ions
Traditional ion sources such as Ar and Ga can impart significant
damage to a samples surface
C60 ions are more efficient in removing material and leave behind a
relatively thin damage layer
1nm
T=29ps
15 keV C60
15 keV Ga
Enhancement of Sputtering Yields due to C60 vs. Ga Bombardment of Ag{111} as Explored by Molecular Dynamics Simulations; Z. Postawa, B.
Czerwinski, M. Szewczyk, E. J. Smiley, N. Winograd and B. J. Garrison, Anal. Chem., 75, 4402-4407 (2003)
Microscopic insights into the sputtering of Ag{111} induced by C60 and Ga Bombardment; Zbigniew Postawa, Bartlomiej Czerwinski, Marek Szewczyk,
Edward J. Smiley, Nicholas Winograd, and Barbara J. Garrison J. Phys. Chem., 108, 7831-7838 (2004)
5
Requisites for Molecular Depth Profiling
Condition for molecular depth profiling…
➱ damage must be removed as fast, or faster, than created
 sputtered depth > range
10 keV
rel. yield
(Ga=1)‡
SF5
100
5x10-13
9.8
0.06
Au3
1,000
1x10-12
19
0.3
C60
2,000
2x10-13
2.6
3.3
Au400
20,000
†2x10-13
6.6
3.4
‡Adapted
d
(cm2)
range
(nm)*
removed depth
(nm)**
from Kersting, et al. Appl. Surf. Sci. (2004) and Tempez, et al. Rapid Comm. Mass Spectr. (2004).
†Conservatively estimated lower limit. Values of  are applicable to most organic systems.
d
*Calculated using SRIM2003.
**Calculated using relative yield and  , in good agreement with Delcorte, et al. NIMB (2000) and Postawa, et al. J. Phys. Chem. B (2004).
d
PHI 5000 VersaProbe SXM at Sinica
7
(2007/6/18)
Depth Profile of PEDOT:PSS with Ar
beam voltage
sputter time
atomic concentration
3 kV
0.5 min
88%C, 3% O, 9% S
2 kV
1 min
88% C, 4% O, 8% S
1 kV
5 min
85%C, 6% O, 9% S
0.5 kV
15 min
85% C, 8% O, 7% S
expected
----
67% C, 24% O, 9% S
•
sputter time extended with lowering the beam
energy
•
significant lost of O even at low beam energy
8
Depth Profile of PEDOT:PSS on ITO: C60
100
O
O1s
O
C1s
90
S2p
S
SO3H
80
PEDOT
In3d5
PSS
67%C, 24%O, 9%S
Atomic Concentration (%)
70
60
50
40
30
20
10
0
0
1
2
3
4
Sputter Time (min)
9
5
6
7
Depth Profile of PEDOT:PSS on ITO: S Peak
0.5kV Ar
10kV C60
4500
4000
3500
3000
O
2500
c/s
2500
S
10
2000
2000
O
PEDOT
8 1500
c/s
1500
O
1000
6 1000
O
S
500
PSS
PSS
PEDOT
0
2
175
170
SO3H
4 500
SO3H
165
Binding Energy (eV)
160
155
10
0
175
170
165
Binding Energy (eV)
160
155
Analysis of Organic Thin-Films with C60
•
chemical composition is preserved through the
thickness
•
chemical state of S is preserved and the PEDOT:PSS
ratio does not change with sputtering
•
it is also possible to analyze organic/inorganic hybrid
thin film (SiO2/PEDOT:PSS)
-
constant Si:PEDOT:PSS ratio through the thickness
uniform distribution of SiO2 nano-dots
➡preferential sputtering and sputtering-reduction did
not be observed!!
XPS Depth Profiling of Organic Thin-Films using C60 Sputtering; Ying-Yu Chen, Bang-Ying Yu, Mao-Feng Hsu, Wei-Ben Wang, Wei-Chun Lin, YuChin Lin, Jwo-Huei Jou and Jing-Jong Shyue, Anal. Chem. 80, 501-501 (2008)
11
Depth Profile with Ar+/C60+ Co-sputtering
beam voltage
sputter time
atomic concentration
0
5.42 min
67% C, 24% O, 9% S
0.2 kV, 75 nA
4.24 min
67% C, 24% O, 9% S
0.1 kV, 300 nA
4.87 min
67% C, 24% O, 9% S
0.2 kV, 300 nA
3.76 min
67% C, 24% O, 9% S
0.1 kV, 600 nA
4.87 min
67% C, 24% O, 9% S
0.2 kV, 600 nA
4.29 min
67% C, 24% O, 9% S
0.25 kV, 600 nA
4.03 min
70% C, 21% O, 9% S
0.3 kV, 600 nA
4.49 min
72% C, 20% O, 8% S
0.5 kV, 600 nA
5.56 min
78% C, 14% O, 8% S
•
sputter time decreased with high dose and low dose Ar
•
lost of O at >0.25 kV Ar
➡dose of Ar is optimized with minimize damage and enhance
sputtering rate
12
Summary
•
Using a combination of 10 kV, 10 nA C60+ and 0.2 kV, 300 nA
Ar+ ion beams, steady sputtering rate is achieved and the
damage to the chemical structure is minimized
•
Thick organic films can be profiled
Depth Profiling of Organic Films with X-ray Photoelectron Spectroscopy using C60+ and Ar+ Co-Sputtering; Bang-Ying Yu, Ying-Yu Chen, Wei-Ben Wang,
Mao-Feng Hsu, Shu-Ping Tsai, Wei-Chun Lin, Yu-Chin Lin, Jwo-Huei Jou, Chih-Wei Chu and Jing-Jong Shyue, Anal. Chem. 80, 3412-3415 (2008)
14
Depth Profile of Complete OLED Device
15
Al Spectrum at Al-Organic Interface
•
O 1s indicates ionic form
•
Al3+ is observed
•
Both side of the Al cathode is partially oxidized
•
Oxygen diffuses through the Al-organic interface
16
Device after Aged at 5V DC for 12 h
17
Spectrum at EL (350-500 min)
500
2500
500
400
2000
400
300
Ir
300
-0.56
Al
1500
c/s
c/s
c/s
-0.67
200
200
1000
100
100
500
0
-100
0
•
•
0
-100
410 410 408
400
406 405
404
402
400
398
Binding
Energy
(eV)
Binding
Energy
(eV)
395
396
394
N 1s doublet indicates TPBi
presents in EL
392390
90
85
80
75
70
65
60
Binding Energy (eV)
•
Al and Al3+ is detected in EL
•
Electron migration of Al and
oxidation of Al
Electron migration of small
molecule
18
55
Progress of the Degradation of OLED
20
Summary
•
Both side of the Al cathode on OLED is oxidized
indicating the diffusion of oxygen through interface
•
Upon exposure to the bias, small TPBi molecule
migrated toward the ITO anode
-
Bulky molecules might be at advantage in terms of
device life time
•
Al cathode migrated into the organic layers under the
current
•
oxygen diffusion through the interface is faster than
that through Al cathode
Migration of Small Molecules during the Degradation of Organic Light-Emitting Diodes; Wei-Chun Lin, Wei-Ben Wang, Yu-Chin Lin, Bang-Ying Yu,
Ying-Yu Chen, Mao-Feng Hsu, Jwo-Huei Jou and Jing-Jong Shyue, Organic Electronics (under review)
21
Conclusion
•
XPS is widely used to study the surface chemical
composition of materials
•
to probe below the surface, Ar ion sputtering is
typically used to remove material but it is generally not
possible to apply to organic materials because of the
high level of damage
•
C60 ion sputtering has been demonstrated to remove
organic materials while causing minimal damage to the
surface
•
however, the sputtering rate decreased with sputtering
time due to the C deposition
22
Conclusion
•
to avoid excessive damage to the surface while
maintaining a steady sputtering rate, combination of
high-energy C60 and low-energy Ar beams are used
concurrently
•
the surface is eroded by the C60 beam and the residual
carbon is removed by Ar
•
thick organo-electronic devices can be analyzed with
this technique and invaluable information is revealed
23