Ge 116 Module 1: Scanning Electron Microscopy

1. Ge 116 Module 1: Scanning Electron Microscopy Part 2: EDS X-ray analysis and EBSD

2. Continuum X-rays

3. Characteristic X-rays

4. Characteristic X-rays

5. Characteristic X-rays

6. X-ray counting: EDS and WDS

7. X-ray counting: EDS and WDS • Spectral resolution determined by electron-hole pair production energy and thermal noise

8. X-ray counting: EDS and WDS • Silicon Drift Detector (SDD) – new! • Low capacitance allows MUCH higher counting rate • Reaches optimal resolution at higher temperature (LN2 not required!)

9. X-ray counting: EDS and WDS • Rise time of steps depends on capacitance of system, limits counting rate. • Conventional Si detector is periodically discharged. SDD is continuously discharged (less dead time).

10. Energy-Dispersive X-ray Spectrum

11. Complexities in X-ray production • Production, (z)

12. Complexities in X-ray production • Absorption

13. Complexities in X-ray production • Absorption

14. Complexities in X-ray production • Secondary Fluorescence

15. Complexities in X-ray production • Secondary Fluorescence 100 m From Milman-Barris et al. (2008)

16. Complexities in X-ray production • Quantitative analysis requires correction for production, absorption, and fluorescence effects • Physics-based methods: ZAF, (z) • Empirical method: Bence-Albee • Correction depends on composition, which is not known a priori, so quantification is an iterative procedure • Accurate analysis requires appropriate standards, as we will see when we learn electron probe analysis

17. EBSD

18. EBSD configuration

19. Diffraction: Bragg Equation • where n is an integer, λ is the wavelength of the electrons, d is the spacing of the diffracting planes, and θ is the angle of incidence of the electrons on the diffracting plane • Constructive interference between reflections off successive planes of charge in the lattice requires difference in path length to be an integer multiple of the wavelength.

20. Aside: X-ray Diffraction • X-ray diffraction is usually done with a plane-wave X-ray source • For monochromatic X-radiation and a single crystal, this gives a distribution of points of constructive interference around the sphere. • For monochromatic X-radiation and a powdered material, this gives a set of single cones with opening angle 2 around the irradiation vector. • For white incident X-ray source and powdered material, energy-dispersive detector at fixed 2 angle sees a set of discrete energy peaks

21. Aside: X-ray Diffraction • X-ray diffraction is usually done with a plane-wave X-ray source • For monochromatic X-radiation and a single crystal, this gives a distribution of points of constructive interference around the sphere. • For monochromatic X-radiation and a powdered material, this gives a set of single cones with opening angle 2 around the irradiation vector. • For white incident X-ray source and powdered material, energy-dispersive detector at fixed 2 angle sees a set of discrete energy peaks

22. Aside: X-ray Diffraction • X-ray diffraction is usually done with a plane-wave X-ray source • For monochromatic X-radiation and a single crystal, this gives a distribution of points of constructive interference around the sphere. • For monochromatic X-radiation and a powdered material, this gives a set of single cones with opening angle 2 around the irradiation vector. • For white incident X-ray source and powdered material, energy-dispersive detector at fixed 2 angle sees a set of discrete energy peaks So, for 10 keV, 1.24 angstroms

23. Kikuchi pattern formation • (Observed in TEM in 1928!) So, for 10 keV, 0.124 angstroms

24. Kikuchi pattern formation • The monument to Kikuchi in Kumamoto (?)

25. Kikuchi pattern formation

26. Kikuchi pattern formation

27. Kikuchi pattern formation

28. Band detection • Hough Transform • 5 to 7 lines is usually enough for phase ID and orientation

29. Pattern indexing • Good pattern match determines crystal structure and orientation

30. EBSD experiment modes • Point analysis: phase and orientation determined at each analytical point

31. EBSD experiment modes • Orientation mapping

32. EBSD experiment modes • Grain mapping

33. EBSD experiment modes • Texture

34. EBSD experiment modes • Phase discrimination (automated point counting!)