www.hkltechnology.com

Electron Back-Scatter Diffraction in the Scanning Electron Microscope:

An Overview

• What is EBSD?

• Historical Perspective

• Crystallography & pattern formation

• Data Collection

• Recent Developments

• Conclusions

Talk Outline

What is EBSD?• EBSD - electron backscatter diffraction• SEM based technique to measure crystal

orientations• Applicable to any crystalline material (in theory)• Provides the absolute crystal orientation with sub-

micron resolution• A useful tool for discriminating between phases

EBSD or EBSP?• EBSD - electron backscatter diffraction• EBSP – electron backscatter diffraction pattern• BKD – Backscattered Kikuchi DiffractionAnd some commercial names....• (C)OM – (Crystal) Orientation Mapping• ACOM – Automated Crystal Orientation

Mapping• OIM™ - Orientation Imaging Microscopy

• What is EBSD?

• Historical Perspective

• Crystallography & pattern formation

• Data Collection

• Recent Developments

• Conclusions

Talk Outline

EBSD History –Early Work

• EBSP like patterns were first observed by Kikuchi (1928) in the Transmission Electron Microscope (TEM).

• Von Boersch (1937) extended Kikuchi’s work

Mica

EBSD History –Alam et al.

• Alam, Blackman and Pashley (1954) used a cylindrical specimen chamber and film camera to produce high-angle Kikuchi patterns from cleaved LiF, KI, NaCl, PbS2 crystals.

Lead Sulphide

EBSD History – the birth of modern EBSD

• Venables and Harland (1972) observed EBSPs in the Scanning Electron Microscope (SEM) by using a 30mm diameter fluorescent imaging screen and a closed circuit television camera.

• Dingley (later 1980s) developed the combination of phosphor and television camera, and combined them with a graphical overlay.

EBSP from Dingley's group – note

calibration marks

EBSD History – continued experiments in the 1980s

• Commercial software (1989) was developed to analyse Electron Channeling Patterns (ECP) and EBSPs.

• EM film for high quality EBSPs & phase identification (1980s)

EBSP from a superalloy – collected with EM film

EBSD History – commercial systems in the 1990s

• Automatic methods for indexing EBSPs (1990s) and control of SEMs gave rise to mapping and phase discrimination.

• Digital cameras, EDX data and phase databases provide information for phase identification (1999 - ) Phase map from

duplex steel

EBSD History – the present day

• High speed mapping becomes a reality

• Dual/Cross beam system (Electron + Ion beam) for 3D microscopy

• Combined chemical and crystallographic mapping

Orientation map of Ni-superalloy, collected at

>65 points / sec

EBSD set up:

Resulting diffraction pattern (EBSP)

EBSD

Performance

• Spatial resolution: down to 10s of nm

• Max sample size: SEM dependent (typically up to 100 x 50mm)

• Angular resolution: 0.25-1° at present

• Probe current: >0.25 nA

• Accelerating voltage: >5 kV

• Specimen tilt: 60-75°

• Working distance: 10-40 mm

• Speed: 0.010 - 1 second per measurement

• Sample preparation: electropolishing, collidal silica polishing , ion beam milling or etching

• What is EBSD?

• Crystallography & pattern formation

• Data Collection

• Recent Developments

• Conclusions

Talk Outline

• EBSP symmetry comes from lattice symmetry – Crystal system, Laue group, space group

• To build a crystal– Start with unit cell– Add a basis– Repeat ad infinitum...

[uvw] is a crystal direction, <uvw> is a family of directions(hkl) is a crystal plane,{hkl}is a family of planes.

EBSP crystallography

EBSP formation

Spherical Kikuchi map

Phosphor

• Electron beam strikes specimen

• Scattering produces electrons travelling in all directions

• Electrons that satisfy the Bragg condition (nλ=2d.sinθ) for a plane (hkl) are channeled ⇒ Kikuchi bands

• Electrons strike the phosphor and produce light

• Which is detected by a CCD camera and digitised

• The resulting EBSP is automatically analysed and indexed...

Iron unit cell

• Although EBSPs are created by backscattered electrons, the signal does not come from the whole BSE interaction volume

• Instead, the diffraction signal effectively originates from a "point source" in the top few nm

• This means that the EBSD technique can obtain very high resolutions (<20nm)

EBSD Resolution

• Copper interconnect test sample

• Analysed on the LEO Supra 55VP

Resolution Example 1

Twin domains 10-20 nm wide are clearly resolved using a 5nm step size

• Pt thin film• Analysed on the JEOL

6500F

Resolution Example 2

Grains with a mean diameter of 35nm are clearly resolved using a 5nm step size

=0.08 µm; BC; Step=0.005 µm; Grid55x49

=0.08 µm; GB+tri-x; Step=0.005 µm; Grid55x49

{100}

[100] [010][011]

[001]

{110}(011)

c

ba

[100]

[001]

[111][101]

[201][311]

[210]

[011]

[110][010]

Body centred cubic Iron

Iron EBSP<111> is central

Note: <111> has 3 fold symmetry, but is

close to 6 fold.

{200}

bcc

fcc

x2410%{123}x413%{222}x1217%{013}x623%{220}x1232%{112}x651%{200}x6100%{110}No.IntensityPlane

x1213%{133}x1212%{240}

x316%{400}x423%{222}x1226%{113}x638%{220}x377%{200}x4100%{111}No.IntensityPlane

bcc h+k+l=2n (i.e. no {111})fcc h, k, l all odd or all even

Body and Face centred cubic Iron

• Differences in interplanar angles allow similar looking EBSPs from bcc and fcc Iron to be distinguished.

bcc Iron fcc Ironbcc Iron fcc Iron

Phase discrimination

• What is EBSD?

• Crystallography & indexing

• Data Collection

• Recent Developments

• Conclusions

Talk Outline

Indexing & Automation

• Automatic analysis– Beam/Stage control

Live EBSP

Detect Bands

Index EBSPPhase and orientation

Hough space

Move beam or stage

Save data to file

A single automated EBSD run provides a complete characterisation of the microstructure:

• Phase distribution• Texture strength• Grain size• Boundary properties• Misorientation data• Slip system activity• Intra-granular deformation• Plus much, much more

all provided while you get on with something else...!

Worked example of automated EBSD

• Analysis of polycrystalline samples of halite (NaCl – cubic)

• Some samples have been experimentally deformed

• Variations in grain size and in extent of subgrain development necessitate analysis at different scales

Data source: Utrecht University, using a Philips XL30 FEG

Stage scan orientation map of

polycrystalline halite

100×100 grid, step 100 µm.

4 mm

Analysis time: 4:04 hrs

500 µm

300×300 grid, 5 µm step

Beam scan orientation map of polycrystalline

halite

Analysis time: 36 minutes

Stage scan, 350×300 grid, 25 µm spacing

3.5 mm

Compression

Large area scan of polycrystalline

halite

EBSD on different scales I

200 µm 200 µm

A

B

Beam scan, 250×250 grid, 2.5 µm spacing

Viewing intragrain microstructure and local lattice orientation variations...

Reflected light image

EBSD on different scales II

0

1

2

3

4

5

6

0 100 200 300 400 500Distance / microns

Miso

rient

atio

n / d

egre

es

A B

Misorientations relative to 1st

data point

Misorientations between adjacent

data points

Absolute and relative misorientation changes across transect A-B.

A

B

Phase distribution, Texture, Grain size / shape, Boundary properties, Misorientation, Slip system activity, Intra-granular deformation....

EBSD data – Maps

Orientation bccOrientation fcc Phase map

EBSP quality

Misorientation angles for fcc

CSL map for fcc

Misorientation axis / angle 10-15° (49pts)

0 0 1

1 1 1

1 0 1

15-20° (59pts) 20-25° (76pts) 25-30° (78pts)

30-35° (120pts) 35-40° (253pts) 40-45° (168pts) 45-50° (132pts)

50-55° (231pts) 55-60° (5595pts) 60-65° (29pts)

Rot. Axes in crystal coordinates

[Duplex.cpr]Fe-FCC (m3m)Complete data set6790 data pointsEqual Area projectionUpper hemispheres

Forbidden zone limits:upper anglelower angle

Rot. Axes in crystal coordinates

[Duplex.cpr]Fe-FCC (m3m)Complete data set6790 data pointsEqual Area projectionUpper hemispheres

Forbidden zone limits:upper anglelower angle

EBSD data – Boundaries

φ2=0° φ2=5° φ2=10° φ2=15°

φ2=20° φ2=25° φ2=30° φ2=35°

φ2=40° φ2=45° φ2=50° φ2=55°

φ2=60° φ2=65° φ2=70° φ2=75°

φ2=80° φ2=85°

Φ=90°

φ1=90°11.522.5

EBSD data – texture

Pole Figures

ODFs

• What is EBSD?

• Crystallography & indexing

• Data Collection

• Recent Developments

• Conclusions

Talk Outline

Some Recent Developments

1. Improved camera technology – increased sensitivity and faster data acquisition

2. Combined EDX and EBSD – for integrated mapping and phase identification

3. Use of dual/cross beam instruments to obtain 3D EBSD (combined FIB and electron beam)

EBSD detectors• Low light EBSP camera

– Silicon intensified target (SIT)8 bit, very noisy

– CCD – TV type video signal8 bit less noisy

– Slow scan CCD 12 bit, low noise, high speed, binning

• Binning• Increases signal, reduces noise• Higher speed but at lower resolution

EBSPs - Feldspar

Old Camera New Camera

Halite - NaCl121,204 points48 minutes (42 pts / sec)93% indexing

Example Orientation Maps

Ni-superalloy60,000 points

17 minutes (63 pts / sec)93% indexing

Single Zircon Grain: substructured at one edge, but a single orientation in centre.21,545 points, 27 minutes (13 pts / s)

3D-EBSD

• What is EBSD?

• Crystallography & indexing

• Data Collection

• Recent Developments

• Conclusions

Talk Outline

Conclusions

• EBSD is an SEM-based technique that has been known for 50 years, but only widely applied in the last 10 years

• EBSD is now a fast, automated technique, applicable to most crystalline materials

• EBSD provides phase identification, texture and boundary characteristics.....