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

Continuum X-rays

Characteristic X-rays

Characteristic X-rays

Characteristic X-rays

X-ray counting: EDS and WDS

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

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!)

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).

Energy-Dispersive X-ray Spectrum

Complexities in X-ray production Production, (z) Pure Cu Cu-Al alloy

Complexities in X-ray production Absorption

Complexities in X-ray production Absorption

Complexities in X-ray production Secondary Fluorescence

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

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

EBSD

EBSD configuration

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.

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

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

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

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

Kikuchi pattern formation The monument to Kikuchi in Kumamoto (?)

Kikuchi pattern formation

Kikuchi pattern formation

Kikuchi pattern formation

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

Pattern indexing Good pattern match determines crystal structure and orientation

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

EBSD experiment modes Orientation mapping

EBSD experiment modes Grain mapping

EBSD experiment modes Texture

EBSD experiment modes Phase discrimination (automated point counting!)