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 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

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) self-interference 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