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AMCF Materials Characterization School 2012

AMCF Materials Characterization School 2012. X-Ray Photoelectron Spectroscopy. Tim Morgan. Overview. What is XPS? The Physics Behind XPS Instrumentation Data Analysis Elemental Analysis Chemical State Identification Quantification Capabilities. What is it?. light. electrons. e -.

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AMCF Materials Characterization School 2012

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

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

  5. Fingerprinting Atoms KE = hν-BE-φs EVac EVac φs φs EF photoelectron EF photoelectron 2p BE2 2s 2p BE1 2s X-ray (hν) X-ray (hν) 1s 1s BE2 BE1 Intensity KE

  6. Photoelectron Detection KE = hν-BE-φs EVac EVac φan φs EF EF photoelectron Analyzer 2p BE 2s X-ray (hν) 1s KE = hν-BE-φs-(φan-φs) Excited Ion KE = hν-BE-φan XPS is independent of the sample’s work function.

  7. V MCD Basic XPS Instrumentation UHV Chamber Quartz crystal monochromator Energy Analyzer (SCA) Electron Gun Rowland Circle Al Kα x-rays (1486eV) 15-20kV electrons Photoelectrons ΔE Lens E0 Al Anode Sample

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

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

  10. V MCD The Internal Workings UHV Chamber Quartz crystal monochromator Energy Analyzer (SCA) Electron Gun Rowland Circle Al Kα x-rays (1486eV) 15-20kV electrons Photoelectrons ΔE Lens E0 Electron Neutralizer Al Anode Ion Gun 1eV electrons Sample

  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: 10-10Torr 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-φan

  21. Complete Chemical Analysis • Identify All Elements • Determine Chemical Environment • Calculate the Stoichiometry

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

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

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

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

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

  31. Ion Gun Detector X-ray beam

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

  33. Depth Profiling Si/SiO2 Double Si Peak O Si

  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

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

  41. V MCD The Internal Workings UHV Chamber Quartz crystal monochromator Energy Analyzer (SCA) Electron Gun Rowland Circle Al Kα x-rays (1486eV) 15-20kV electrons Photoelectrons ΔE Lens E0 Electron Neutralizer Al Anode Ion Gun 1eV electrons Sample

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

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