1. AMCF Materials Characterization School 2012 X-Ray Photoelectron Spectroscopy Tim Morgan

2. Overview What is XPS? The Physics Behind XPS Instrumentation Data Analysis – Elemental Analysis – Chemical State Identification – Quantification Capabilities

3. What is it? XPS is a technique designed to give chemical information. light electrons e-e-

4. What is on the surface? XPS is a technique designed to analyze the surface of a material Light penetrates microns Inelastic electrons only escape a few nanometers e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e-

5. EFEF E Vac 1s 2s 2p φsφs BE 2 Fingerprinting Atoms X-ray (hν) KE = hν-BE-φ s EFEF E Vac 1s 2s 2p φsφs BE 1 photoelectron KE Intensity photoelectron X-ray (hν) BE 1 BE 2

6. Photoelectron Detection EFEF E Vac 1s 2s 2p X-ray (hν) φsφs BE Excited Ion photoelectron E Vac φ an KE = hν-BE-φ s φ an -φ s ) KE = hν-BE-φ s -(φ an -φ s ) KE = hν-BE-φ an Analyzer EFEF KE = hν-BE-φ s XPS is independent of the sample’s work function.

7. Basic XPS Instrumentation MCD Quartz crystal monochromator Al Anode Electron Gun Rowland Circle Al Kα x- rays (1486eV) Lens Energy Analyzer (SCA) Photoelectrons Sample 15-20kV electrons V E0E0 UHV Chamber ΔEΔE

8. Charge Neutralization Conducting Sample +++ X-ray beam Electron neutralizer

9. Surface Charge Neutralization Insulating Sample +++ X-ray beam Electron neutralizer - - - - - - - - - - - - - - - - - - - Ion Gun

10. The Internal Workings MCD Quartz crystal monochromator Al Anode Electron Gun Rowland Circle Al Kα x- rays (1486eV) Lens Energy Analyzer (SCA) Photoelectrons Sample 15-20kV electrons Electron Neutralizer 1eV electrons Ion Gun V E0E0 UHV Chamber ΔEΔE

11. PHI VersaProbe 5000 Spherical Capacitve Analyzer C-60 Ion Gun Ar Ion Gun Entry/Exit Chamber

12. PHI VersaProbe 5000 Ar Ion Gun Lens Electron Gun Sample Stage

13. Important Operational Concerns Ultra High Vacuum: 10 -10 Torr Base Pressure Monochromated X-ray beam – Spot size ranges from 8 – 200 microns Electron Gun for Positive Ion Charge Neutralization Argon Ion Gun for Insulators 5 axis stage

14. THE EXPERIMENT

15. Vacuum Watcher Control: -Venting E/E -Pumping Down E/E -Gate Valve Operations Monitor -Pressure in E/E & Main Chamber -Gate Valve Status

16. Summit: Image Control: -Sample Stage -X-ray Setup -SXI Image Capture -Neutralizer Settings -Sputter Settings Monitor -Analysis Position -Ion Gun Pressure -SXI Image

17. Summit: Acquisition Control: -Experimental Setup -Scan Ranges -Data Save Location -Advanced Setup

18. Setting Up an Experiment Average over an area to avoid anomalies Balance is key to getting good statistics in a reasonable amount of time Always perform a survey scan before detailed scans Understand your resolution needs Is your sample an insulator?

19. DATA ANALYSIS

20. Typical Spectra Features Reverse Energy Scale Sharp Photoelectron peaks Broader Auger peaks with fine structure Background BE = hν-KE-φ an

21. Complete Chemical Analysis 1.Identify All Elements 2.Determine Chemical Environment 3.Calculate the Stoichiometry

22. Survey Scan Qualitative Data Analyis: 1.Identify All Major Peaks 2.Identify All Other Peaks 3.Look up Reference Peaks What material do you think this is?

23. Quantitative Analysis Carbon Iron Oxygen How do we prove if carbon is a surface contaminent?

24. Comparing Pre & Post Sputter Cleaning the surface removes atmospheric contamination and real analysis of the sample Postsputter Presputter

25. Peak Fitting Carbon for PET

26. ADVANCED FEATURES

27. Additional Questions How do I examine layers below the surface? How surface sensitive can I get? How can I differentiate regions with different chemical species? How can I examine polymers?

28. How to examine the orange material?

29. X-ray beam Ion Gun Detector High Energy Ions (2keV)

30. X-ray beam Ion Gun e-e- e-e- e-e- Detector

31. X-ray beam Ion Gun Detector

32. X-ray beam Ion Gun e-e- e-e- e-e- Detector

33. Depth Profiling Si/SiO 2 Si O Double Si Peak

34. Depth Profiling 1-2 nm depth resolution Variable Energy Argon Ion Gun – 5 kV to 100 V C-60 Gun for Polymers

35. Angle Resolved XPS Detector Decreasing the Take Off Angle decreases the analysis depth.

36. Elemental Mapping

37. Chemical Mapping

38. Questions?

39. X-ray Sources LineEnergy (eV)Width (eV) Y Mζ132.30.47 Mg Kα1253.60.7 Al Kα1486.60.85 Cu Kα8048.02.6 Ultraviolet (UV)10-100

40. What is on the surface? XPS is a technique designed to analyze the surface of a material light electrons e-e-

41. The Internal Workings MCD Quartz crystal monochromator Al Anode Electron Gun Rowland Circle Al Kα x- rays (1486eV) Lens Energy Analyzer (SCA) Photoelectrons Sample 15-20kV electrons Electron Neutralizer 1eV electrons Ion Gun V E0E0 UHV Chamber ΔEΔE

42. Quantitative Analysis Higher Resolution – Peak energy Accuracy – Chemical State Identification Peak Fitting – Deconvolution – Detailed Peak Information Stoichiometry Calculations