2. CBED Patterns - Introduction

3. CBED Patterns - Introduction
probe
The electron probe can be made on the order of 0.1 nm so very small volumes can be sampled.

4. CBED Patterns - Introduction
Perfect for the characterization of nanoparticles

5. CBED Patterns - Introduction
Energy-filtered TEM

6. CBED vs SAD Patterns

7. CBED vs SAD Patterns
A wealth of crystal information

8. Making a TEM CBED Pattern

9. Making a TEM CBED Pattern

10. Making a STEM CBED Pattern
L, camera length

11. Making (S)TEM CBED Patterns
If the specimen is uniform, its CBED pattern doesn’t move while the beam is scanned through the specimen.

12. Experimental Variables

13. CBED Convergence Angle, a

14. CBED Cameral Length, L

15. Beam Diameter, specimen thickness

16. CBED Patterns - Focus
DF = Dark Field; BF = Bright Field

17. CBED – Kikuchi & HOLZ Lines
Diffraction of elastically scattered electrons at large angles creates the Laue Zone Lines.

18. CBED – Kikuchi & HOLZ Lines

19. CBED Pattern Defocused probe Defocus CBED Back-focal plane
Change focus of probe either by using objective lens or manually changing the eucentric height
Defocused probe
Defocus CBED
Back-focal plane

20. CBED – ZOLZ, HOLZ lines

21. CBED – ZOLZ, HOLZ lines

22. CBED – Energy Filtering

23. CBED – Energy Filtering
There are many more details concerned with CBED imaging in Williams & Carter, which I don’t have time to present, that I want to review in Chapter 20.

24. CBED – Lattice Strain Measurements
Dd could be the change in interplanar spacing, d, due to strain. It causes the ZOLZ lines and HOLZ lines to split. This type of measurement of strain provides the highest resolution measurement of strain in crystals.

25. HOLZ Line Strain Measurement
Beam direction

26. HOLZ Line Strain Measurement
Unstrained
Strained
Experimental images of strain measurement by HOLZ lines at an interface between Si substrate and Si+Ge epilayer.
Next we will apply electron holography to split HOLZ lines to measure their phase.

27. Diffracted Beam Holography of HOLZ Line Strain Measurements
Split HOLZ line is self-interfered by placing an electron biprism between the lines and then applying a voltage.

28. Diffracted Beam Holography of HOLZ Line Strain Measurements
Fig 2 – Experimental images showing in a) a split HOLZ line running horizontally through the 000 disc, b) the same split HOLZ line running through a diffraction disc, c) self-interference of the split HOLZ line by the biprism and d) same as c) but increased biprism voltage.

29. Diffracted Beam Holography of HOLZ Line Strain Measurements
Higher magnification of Fig 2d showing the fringes more clearly and phase shifts existing at the intersections with other HOLZ lines, for example, at arrow.
The current challenge is to measure the 3D strain field from 2D information.
Herring et al, “Coherent Electron Interference of a split HOLZ line from a Strained Silicon Crystal” Microscopy & Microanalysis Submitted.

30. K-M – Kossel - MÖllenstedt