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!)