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Polarity CBED

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by

Andrew Scullion

on 5 October 2015

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Transcript of Polarity CBED

Polarity Determination
using CBED

GaAs Unit cell:
As
Ga
How can we distinguish between 110 and 110?
Bond directions alternate between planes
110
110
Simple solution:
HRTEM
Not possible with all microscopes
Not practical for all samples or checking large areas
C
1
C
2
Not to scale!
What is CBED?
α
α: convergence angle


θ: diffracted angle
condenser aperture
Still not to scale!
diffraction plane
[2] Williams, D. B., & Carter, C. B. (2009). Transmission Electron Microscopy.
What does CBED look like?
Simulated CBED pattern for InAs (110)
Phonons/Diffuse scattering are not considered
with diffuse scattering
θ
θ

Kossel Cone
Diffuse Scattering
Bragg Scattering
Kikuchi lines:
Diffuse scattering
+
Bragg scattering
More on Kikuchi lines
(000)
(300)

Not Bragg Condition
Bragg Condition
(000)
(300)

Ewald Sphere
Kikuchi lines are fixed to the crystal
(300)
(-300)
(-300)
(300)
Conclusion: (hkl) is under Bragg condition when (-h-k-l) Kikuchi line overlaps with (000) spot
What happens in the (000) spot?
From a particle perspective, the beam is
weakened
by the Bragg reflection
A
deficient
line is found in the spot
(000)
(002)
(004)
From a wave perspective,
destructive
interference occurs
(002)
ω: Phase change after reflection
φ: Phase of structure factor
(00-2)
How do we calculate the structure factor phase, φ?
ΔL
ΔX
h: first Miller index
a: lattice constant
Polarity of GaAs
GaAs near (230) at 300 kV
x
InP near (230) at 120 kV
When (hkl) Kikuchi lines up with (002) spot:
Δω(5,-3,5;0,0,2) = -4°
constructive
destructive
Δω(5,-3,-3;0,0,2) = -4°
Δω(5,-3,-7;0,0,2) = 184°
constructive
destructive
Δω(5,-3,-5;0,0,2) = 184°
Δω(5,-3,-7;0,0,-2) = -4°
constructive
destructive
Δω(5,-3,5;0,0,-2) = -4°
Δω(5,-3,-5;0,0,-2) = 184°
constructive
destructive
Δω(5,-3,3;0,0,-2) = 184°
Experimental results from Jaeger
Polarity of InP
Interference is less clear
Δω for constructive is around 55°
Simulated*
Experimental
(002)
(00-2)
Thick
Thin
*Stadelmann, P. A. (2012). JEMS
Thanks!
by Andrew Scullion
Bragg-lines:
Double scattering
+
Interference
Kikuchi lines
Zinc Blende Structure

Kikuchi Patterns:
Thickness
Huygens' model
forward peaked
Bragg lines
Full transcript