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)
Cu-Alalloy
Pure Cu
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
•H
ough T
ransform
•5 to 7 lines is usually enough for phase ID
and orientation
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!)