Transcript Obtaining CBED Patterns

EM Course – CBED Patterns
Professor Rodney Herring
CBED Patterns - Introduction
CBED Patterns - Introduction
probe
The electron probe can be made on the order of 0.1
nm so very small volumes can be sampled.
CBED Patterns - Introduction
Perfect for the characterization of nanoparticles
CBED Patterns - Introduction
Energy-filtered TEM
CBED vs SAD Patterns
CBED vs SAD Patterns
A wealth of crystal information
Making a TEM CBED Pattern
Making a TEM CBED Pattern
Making a STEM CBED Pattern
L, camera length
Making (S)TEM CBED Patterns
If the specimen is uniform, its CBED pattern
doesn’t move while the beam is scanned through
the specimen.
Experimental Variables
CBED Convergence Angle, a
CBED Cameral Length, L
Beam Diameter, specimen thickness
CBED Patterns - Focus
DF = Dark Field; BF = Bright Field
CBED – Kikuchi & HOLZ Lines
Diffraction of elastically scattered electrons at large angles creates the Laue Zone Lines.
CBED – Kikuchi & HOLZ Lines
CBED Pattern
Change focus of probe either by
using objective lens or manually
changing the eucentric height
Defocused probe
Defocus CBED
Back-focal plane
CBED – ZOLZ, HOLZ lines
CBED – ZOLZ, HOLZ lines
CBED – Energy Filtering
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.
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.
HOLZ Line Strain Measurement
Beam direction
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.
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.
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) selfinterference of the split HOLZ line by the biprism and d) same as c) but increased biprism
voltage.
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 2011. Submitted.
K-M – Kossel - MÖllenstedt