11

Depth Profile with X-ray Photoelectron Spectrometry using C60

+ and Ar+ Beams

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）

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）

22

Structural Analysis of Organic ElectronicsStructural 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?

• 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?

33

Principle of Depth ProfilePrinciple of Depth Profile

Surface LayerSurface Layer

Sample MatrixSample Matrix

Depth Profile AnalysisDepth Profile Analysis

Analysis Depth (0.5-10 nm)Analysis Depth (0.5-10 nm)

Sputter Ion BeamSputter Ion Beam

44

XPS Depth ProfilingXPS 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

• 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

55

15 keV C6015 keV C60

Sputtering with C60+ IonsSputtering with C60+ Ions

15 keV Ga15 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)

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)

T=29psT=29ps

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

10 keVrel. yield(Ga=1)‡

σd (cm2) range (nm)* removed depth (nm)**

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 from Kersting, et al. Appl. Surf. Sci. (2004) and Tempez, et al. Rapid Comm. Mass Spectr. (2004). †Conservatively estimated lower limit. Values of σd are applicable to most organic systems. *Calculated using SRIM2003. **Calculated using relative yield and σd, in good agreement with Delcorte, et al. NIMB (2000) and Postawa, et al. J. Phys. Chem. B (2004).

‡Adapted from Kersting, et al. Appl. Surf. Sci. (2004) and Tempez, et al. Rapid Comm. Mass Spectr. (2004). †Conservatively estimated lower limit. Values of σd are applicable to most organic systems. *Calculated using SRIM2003. **Calculated using relative yield and σd, in good agreement with Delcorte, et al. NIMB (2000) and Postawa, et al. J. Phys. Chem. B (2004).

Condition for molecular depth profiling…➱ damage must be removed as fast, or faster, than created

∴ sputtered depth > range

Condition for molecular depth profiling…➱ damage must be removed as fast, or faster, than created

∴ sputtered depth > range

Requisites for Molecular Depth ProfilingRequisites for Molecular Depth Profiling

77

PHI 5000 VersaProbe SXM at Sinica (2007/6/18)PHI 5000 VersaProbe SXM at Sinica (2007/6/18)

88

Depth Profile of PEDOT:PSS with ArDepth Profile of PEDOT:PSS with Ar

beam voltagebeam voltage sputter timesputter time atomic concentrationatomic concentration

3 kV3 kV 0.5 min 88%C, 3% O, 9% S

2 kV2 kV 1 min 88% C, 4% O, 8% S

1 kV1 kV 5 min 85%C, 6% O, 9% S

0.5 kV0.5 kV 15 min 85% C, 8% O, 7% S

expectedexpected ---- 67% C, 24% O, 9% S

• sputter time extended with lowering the beam energy

• significant lost of O even at low beam energy

➡Ar is not suitable for analyzing organic films

• sputter time extended with lowering the beam energy

• significant lost of O even at low beam energy

➡Ar is not suitable for analyzing organic films

99

Depth Profile of PEDOT:PSS on ITO: C60Depth Profile of PEDOT:PSS on ITO: C60

0 1 2 3 4 5 6 70

10

20

30

40

50

60

70

80

90

100

Sputter Time (min)

Ato

mic

Con

cent

ratio

n (%

)

O1s

C1s

S2p

In3d5

O O

SSO3H

PEDOT PSS

67%C, 24%O, 9%S67%C, 24%O, 9%S

1010

1551601651701750

500

1000

1500

2000

2500

3000

3500

4000

4500

Binding Energy (eV)

c/s

Depth Profile of PEDOT:PSS on ITO: S PeakDepth Profile of PEDOT:PSS on ITO: S Peak

10kV C6010kV C60

c/s

SO3H

PSS

O O

S

PEDOT

0.5kV Ar0.5kV Ar

155160165170175

2

4

6

8

10

0

500

1000

1500

2000

2500

Binding Energy (eV)

SO3H

PSS

O O

S

PEDOT

1111

Analysis of Organic Thin-Films with C60Analysis 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!!

• 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, Yu-

Chin Lin, Jwo-Huei Jou and Jing-Jong Shyue, Anal. Chem. 80, 501-501 (2008)

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, Yu-

Chin Lin, Jwo-Huei Jou and Jing-Jong Shyue, Anal. Chem. 80, 501-501 (2008)

1212

Depth Profile with Ar+/C60+ Co-sputteringDepth Profile with Ar+/C60+ Co-sputtering

beam voltagebeam voltage sputter timesputter time atomic concentrationatomic concentration

00 5.42 min 67% C, 24% O, 9% S

0.2 kV, 75 nA0.2 kV, 75 nA 4.24 min 67% C, 24% O, 9% S

0.1 kV, 300 nA0.1 kV, 300 nA 4.87 min 67% C, 24% O, 9% S

0.2 kV, 300 nA0.2 kV, 300 nA 3.76 min67% C, 24% O, 9%

S

0.1 kV, 600 nA0.1 kV, 600 nA 4.87 min 67% C, 24% O, 9% S

0.2 kV, 600 nA0.2 kV, 600 nA 4.29 min 67% C, 24% O, 9% S

0.25 kV, 600 nA0.25 kV, 600 nA 4.03 min 70% C, 21% O, 9% S

0.3 kV, 600 nA0.3 kV, 600 nA 4.49 min 72% C, 20% O, 8% S

0.5 kV, 600 nA0.5 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

• 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

1414

SummarySummary

• 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

• 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)

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)

1515

Depth Profile of Complete OLED DeviceDepth Profile of Complete OLED Device

1616

Al Spectrum at Al-Organic InterfaceAl 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

• O 1s indicates ionic form

• Al3+ is observed

• Both side of the Al cathode is partially oxidized

• Oxygen diffuses through the Al-organic interface

1717

Device after Aged at 5V DC for 12 hDevice after Aged at 5V DC for 12 h

1818

Spectrum at EL (350-500 min)Spectrum at EL (350-500 min)

• N 1s doublet indicates TPBi presents in EL

• Electron migration of small molecule

• N 1s doublet indicates TPBi presents in EL

• Electron migration of small molecule

• Al and Al3+ is detected in EL

• Electron migration of Al and oxidation of Al

• Al and Al3+ is detected in EL

• Electron migration of Al and oxidation of Al

AlAl

IrIr

390395400405410-100

0

100

200

300

400

500

Binding Energy (eV)

c/s

5560657075808590-100

0

100

200

300

400

500

Binding Energy (eV)c/

s

3923943963984004024044064084100

500

1000

1500

2000

2500

Binding Energy (eV)

c/s

-0.67-0.67

-0.56-0.56

2020

Progress of the Degradation of OLEDProgress of the Degradation of OLED

2121

SummarySummary

• 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

• 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)

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)

2222

ConclusionConclusion

• 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

• 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

2323

ConclusionConclusion

• 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

• 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