1 Depth Profile with X-ray Photoelectron Spectrometry using C 60 + 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）

2 Structural Analysis of Organic Electronics Cross-sectional SEM with XEDS? - ~ μ m 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? - ~ μ m 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?

3 Principle of Depth Profile Surface Layer Sample Matrix Depth Profile Analysis Analysis Depth ( nm) Sputter Ion Beam

4 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 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

5 15 keV C 60 Sputtering with C 60 + Ions 15 keV Ga Enhancement of Sputtering Yields due to C 60 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, (2003) Microscopic insights into the sputtering of Ag{111} induced by C 60 and Ga Bombardment; Zbigniew Postawa, Bartlomiej Czerwinski, Marek Szewczyk, Edward J. Smiley, Nicholas Winograd, and Barbara J. Garrison J. Phys. Chem., 108, (2004) Enhancement of Sputtering Yields due to C 60 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, (2003) Microscopic insights into the sputtering of Ag{111} induced by C 60 and Ga Bombardment; Zbigniew Postawa, Bartlomiej Czerwinski, Marek Szewczyk, Edward J. Smiley, Nicholas Winograd, and Barbara J. Garrison J. Phys. Chem., 108, (2004) T=29ps Traditional ion sources such as Ar and Ga can impart significant damage to a samples surface C 60 ions are more efficient in removing material and leave behind a relatively thin damage layer 1nm

10 keV rel. yield (Ga=1) ‡  d (cm 2 )range (nm) * removed depth (nm) ** SF x Au 3 1,0001x C 60 2,0002x Au ,000 † 2x ‡ Adapted from Kersting, et al. Appl. Surf. Sci. (2004) and Tempez, et al. Rapid Comm. Mass Spectr. (2004). † Conservatively estimated lower limit. Values of  d are applicable to most organic systems. * Calculated using SRIM2003. ** Calculated using relative yield and  d, 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  d are applicable to most organic systems. * Calculated using SRIM2003. ** Calculated using relative yield and  d, 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 Profiling

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

8 Depth Profile of PEDOT:PSS with Ar beam voltage sputter time atomic concentration 3 kV 0.5 min88%C, 3% O, 9% S 2 kV 1 min88% C, 4% O, 8% S 1 kV 5 min85%C, 6% O, 9% S 0.5 kV 15 min85% 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 ➡ 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

9 Depth Profile of PEDOT:PSS on ITO: C Sputter Time (min) Atomic Concentration (%) O1s C1s S2p In3d5 67%C, 24%O, 9%S

Binding Energy (eV) c/s Depth Profile of PEDOT:PSS on ITO: S Peak 10kV C60 c/s 0.5kV Ar Binding Energy (eV)

11 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 (SiO 2 /PEDOT:PSS) - constant Si:PEDOT:PSS ratio through the thickness - uniform distribution of SiO 2 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 (SiO 2 /PEDOT:PSS) - constant Si:PEDOT:PSS ratio through the thickness - uniform distribution of SiO 2 nano-dots ➡ preferential sputtering and sputtering-reduction did not be observed!! XPS Depth Profiling of Organic Thin-Films using C 60 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, (2008)

12 Depth Profile with Ar + /C 60 + Co-sputtering beam voltage sputter time atomic concentration min67% C, 24% O, 9% S 0.2 kV, 75 nA 4.24 min67% C, 24% O, 9% S 0.1 kV, 300 nA 4.87 min67% C, 24% O, 9% S 0.2 kV, 300 nA 3.76 min67% C, 24% O, 9% S 0.1 kV, 600 nA 4.87 min67% C, 24% O, 9% S 0.2 kV, 600 nA 4.29 min67% C, 24% O, 9% S 0.25 kV, 600 nA 4.03 min70% C, 21% O, 9% S 0.3 kV, 600 nA 4.49 min72% C, 20% O, 8% S 0.5 kV, 600 nA 5.56 min78% 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

13 Depth Profile of OLED

14 Summary Using a combination of 10 kV, 10 nA C 60 + 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 C 60 + 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 C 60 + 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, (2008)

15 Depth Profile of Complete OLED Device

16 Al Spectrum at Al-Organic Interface O 1s indicates ionic form Al 3+ is observed Both side of the Al cathode is partially oxidized Oxygen diffuses through the Al-organic interface O 1s indicates ionic form Al 3+ is observed Both side of the Al cathode is partially oxidized Oxygen diffuses through the Al-organic interface

17 Device after Aged at 5V DC for 12 h

18 Spectrum at EL ( 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 Al 3+ is detected in EL Electron migration of Al and oxidation of Al Al and Al 3+ is detected in EL Electron migration of Al and oxidation of Al Al Ir Binding Energy (eV) c/s Binding Energy (eV) c/s Binding Energy (eV) c/s

19 Electron Transporting Layer: TPBi Binding Energy (eV) c/s

20 Progress of the Degradation of OLED

21 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 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)

22 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 C 60 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 C 60 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

23 Conclusion to avoid excessive damage to the surface while maintaining a steady sputtering rate, combination of high-energy C 60 and low-energy Ar beams are used concurrently the surface is eroded by the C 60 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 C 60 and low-energy Ar beams are used concurrently the surface is eroded by the C 60 beam and the residual carbon is removed by Ar thick organo-electronic devices can be analyzed with this technique and invaluable information is revealed