ISO 19214:2017

INTERNATIONAL ISO
STANDARD 19214
First edition
2017-04
Microbeam analysis — Analytical
electron microscopy — Method of
determination for apparent growth
direction of wirelike crystals by
transmission electron microscopy
Analyse par microfaisceaux — Microscopie électronique analytique
— Méthode de détermination de la direction apparente de croissance
des cristaux filiformes par microscopie électronique en transmission
Reference number
ISO 19214:2017(E)
©
ISO 2017

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ISO 19214:2017(E)

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ISO 19214:2017(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Specimens . 2
5 Analysis procedure . 2
5.1 Setting the TEM operating condition . 2
5.1.1 Preparation of the TEM . 2
5.1.2 Accelerating voltage . 2
5.1.3 Setting the specimen . 2
5.1.4 Calibration of the rotation angle . 2
5.2 Data acquisition . 3
5.2.1 Select the target crystal . 3
5.2.2 Obtaining diffraction patterns . 3
5.2.3 Determining interplanar spacing . 4
5.2.4 Index diffraction patterns . 4
5.2.5 Non-uniqueness of the indexing result . 5
5.3 Determination of the crystalline direction . 5
5.3.1 General approach . 5
5.3.2 Simplified procedure for special situations . 8
5.3.3 Convert the crystallographic index . 8
5.3.4 Result of the multiplicity factor . 9
6 Uncertainty estimation . 9
7 Test report .10
Annex A (informative) Relationships of Miller notation and Miller-Bravais notation for
hexagonal crystals .11
-1
Annex B (informative) Matrix G and G for the crystal systems .12
Annex C (informative) Example of a test report .14
Bibliography .15
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ISO 19214:2017(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
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different types of ISO documents should be noted. This document was drafted in accordance with the
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This document was prepared by Technical Committee ISO/TC 202, Microbeam analysis, Subcommittee
SC 3, Analytical electron microscopy.
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ISO 19214:2017(E)

Introduction
Wirelike crystals (including beltlike crystals) are a main component in some advanced materials,
especially nanomaterials, and also appear in traditional materials, such as needle-shaped precipitates
in steels and alloys. Controlling the microstructure of these materials during fabrication is very
important for quality control considerations. To control the microstructure and thereby improve the
service properties of the relevant materials, the apparent growth direction or the longest axis of the
wires is one of the essential parameters. This direction is generally determined for wirelike crystals
whose diameter or thickness and width is ranged from tens to hundreds of nanometres by transmission
electron microscopy (TEM).
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INTERNATIONAL STANDARD ISO 19214:2017(E)
Microbeam analysis — Analytical electron microscopy —
Method of determination for apparent growth direction of
wirelike crystals by transmission electron microscopy
1 Scope
This document prescribes a method for the determination of apparent growth direction by transmission
electron microscopy. It is applicable to all kinds of wirelike crystalline materials fabricated by various
methods. This document can also guide in ascertaining an axis direction of the second-phase particles
with a rod-like or polygonal shape in steels, alloys or other materials. The applicable diameter or
width of the crystals to be tested is in the range of tens to hundreds of nanometres, depending on the
accelerating voltage of the TEM and the material itself.
NOTE In the present document, wirelike crystals, beltlike crystals, needle-shaped second-phase particles,
etc. are all subsumed by the broad category of wirelike crystals.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 24173, Microbeam analysis — Guidelines for orientation measurement using electron backscatter
diffraction
ISO 25498:2010, Microbeam analysis — Analytical electron microscopy — Selected-area electron
diffraction analysis using a transmission electron microscope
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 24173 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
wirelike crystal
crystal resembling a thread with a diameter or width measuring in nanometres
3.2
apparent growth direction
crystalline direction which is parallel to the longest dimension of a single crystal
Note 1 to entry: Apparent growth direction does not involve mechanisms of the phase interface migration.
3.3
Miller notation
indexing system for diffraction patterns, which describes a crystal lattice by three axes coordinate
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ISO 19214:2017(E)

3.4
Miller-Bravais notation
indexing system for diffraction patterns of hexagonal crystal, which describes the lattice by four axes
coordinate
4 Specimens
4.1 The sample crystals shall be clean, without contamination or oxidation. They are stable under
electron beam irradiation during TEM analysis.
4.2 Powder or extracted powder specimens of the crystals may be analyzed. The sample powder shall
be well dispersed by a suitable technique so that individual crystals can be observed under the TEM.
NOTE One of the techniques in common use is ultrasonic dispersion. In this method, the sample powder
is immersed in ethanol or pure water and dispersed by ultrasonication for about 0,5 h to 1 h, then dropped
onto the supporting film surface of a microgrid. Afterward, the microgrids are dried at room temperature. The
wirelike crystals are usually parallel to the supporting film plane. Other techniques to prepare individual crystal
[2]
specimens can also be adopted, depending upon the physical characteristics of the sample .
4.3 The precipitates or second-phase particles in steels, alloys and the like may be extracted, then
treated as powder specimens; see 4.2.
4.4 Thin-foil specimens of various solid substances prepared by suitable methods are applicable. The
[3]
specimen shall be thin enough to transmit the electron beam .
5 Analysis procedure
5.1 Setting the TEM operating condition
5.1.1 Preparation of the TEM
The TEM working condition shall comply with ISO 25498:2010, 8.1.
5.1.2 Accelerating voltage
The applicable accelerating voltage of the TEM for the analysis mainly depends upon the thickness of
the specimen to be studied. Stability of the crystals under electron beam irradiation is also important
for the accelerating voltage setting. As long as the structure and/or morphology of the specimen are not
altered during the analysis, clear images and sharp diffraction patterns can be obtained on the TEM.
The corresponding accelerating voltage or higher may be suitable for the work.
5.1.3 Setting the specimen
Place the specimen to be tested firmly in the double-tilting or tilting-rotation specimen holder, then
insert the holder into the specimen chamber. It is recommended to use the cold finger of TEM before
conditioning.
5.1.4 Calibration of the rotation angle
As specified in ISO 25498:2010, 8.1.6, to be able to successfully correlate the axis of interest in an
image with the corresponding diffraction pattern, the rotation angle between the micrograph and its
corresponding diffraction pattern may need to be calibrated. A molybdenum trioxide crystal specimen
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ISO 19214:2017(E)

may be used as a reference for the rotation angle calibration. The analyst may refer to textbooks such
as References [4] and [5] for the experimental procedure for this calibration.
NOTE For some transmission electron microscopes, the rotation angle has been compensated by the
manufacturer. In this case, step 5.1.4 can be ignored.
5.2 Data acquisition
5.2.1 Select the target crystal
On the viewing screen, TV monitor, or computer screen of the TEM, get an overview image of the
specimen in low magnification mode. Select an individual crystal which is clean and free from damage
or distortion as the target. Under bright-field imaging mode, adjust the magnification to get a clear
magnified image of the target crystal. Adjust the specimen height (Z axis) to the eucentric position.
Focus the image.
5.2.2 Obtaining diffraction patterns
5.2.2.1 General
Various electron diffraction techniques may be applicable for determination of the crystal axis
direction. The selected area electron diffraction (SAED) and microbeam diffraction techniques are in
common use; however, for the present purpose, the spot diffraction patterns or the patterns formed by
the incident beam through a small angle aperture are preferred.
5.2.2.2 Procedure
The procedure for taking diffraction patterns and images of the target crystal is as follows.
a) Select a suitable position of the target crystal in the specimen and select a diffraction mode (SAED,
microdiffraction, or other suitable mode). Switch to the diffraction mode to get a spot diffraction
pattern. Tilt the specimen slightly so that the brightness distribution on the diffraction pattern is
symmetrical and a zero-order Laue zone pattern is displayed. Therefore, the zone axis, Z (with
1
index [u v w ]), of this diffraction pattern is nearly reverse parallel to the incident beam direction,
1 1 1
B. Record this diffraction pattern, Z and take note of the reading on the X and Y tilting angle of the
1,
double tilting specimen stage as X and Y respectively.
1 1,
Refer to the instruction manual provided by the microscope manufacturer for the operation
procedure for each diffraction mode.
b) Switch back to the imaging mode without changing the specimen orientation to get a correlative
bright field image, M , of the target crystal. Check the focus of this image and take a photo or save
1
it in the computer system. This image, M is formed under the incident beam direction, B , which is
1, 1
approximately reversely parallel to the zone axis, Z .
1
c) Return to the diffraction mode and tilt the specimen to produce a second diffraction pattern with
zone axis Z . Record this diffraction pattern, Z , and take note of the reading on the X and Y tilt
2 2
angle of the specimen holder as X and Y , respectively.
2 2
d) Repeat step b) to form the second bright field image, M , of the target crystal. This image, M , is
2 2
formed under the incident beam direction, B , which is nearly reversely parallel to the zone axis,
2
Z , of the specimen.
2
e) The angle, ψ, between the two specimen holder positions (that is, the angle ψ* between the zone
axis, Z , with index [u v w ] and Z , with index [u v w ]) can be obtained from the differences
1 1 1 1 2 2 2 2
between the readings on the X and Y tilting angles at each position (see ISO 25498:2010, 8.2).
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ISO 19214:2017(E)

5.2.3 Determining interplanar spacing
To determine the interplanar spacing, d , of the plane (hkl) in crystals, the simplified Bragg law, as
hkl
shown in Formula (1), shall be followed.
R × d = Lλ (1)
hkl hkl
where
L is the camera length;
λ is the wavelength of the incident electron beam;
Lλ is the camera constant;
R is the distance between the central spot and the diffracted spot of crystalline plane (hkl) in
hkl
the diffraction pattern.
When the camera constant Lλ is known, the interplanar spacing d can be found, in principle, using
hkl
Formula (1) by measuring the distance R . However, in practice, 2R (the distance between the spots
hkl hkl
hkl and hkl ) shall be measured, then divided by two to calculate the distance R .
hkl
In most cases, the camera constant, Lλ, shall be calibrated for the present work. The practical procedure
for camera constant calibration is specified in ISO 25498:2010, 8.3.
Camera constant, Lλ, calibration is usually performed by using a reference specimen such as
polycrystalline pure gold or pure aluminium. At a given accelerating voltage, record the ring diffraction
pattern of the reference specimen. Index the diffraction rings and measure the diameters 2R of the
hkl
corresponding ring (hkl), respectively. Find the interplanar spacing d for plane (hkl) of the reference
hkl
specimen by the crystallographic formulae. The diffraction constant, Lλ, can then be calculated using
Formula (1). In practice, either the Lλ ∼
...