ISO 22493:2014

INTERNATIONAL ISO
STANDARD 22493
Second edition
2014-04-15
Microbeam analysis — Scanning
electron microscopy — Vocabulary
Analyse par microfaisceaux — Microscopie électronique à balayage
— Vocabulaire
Reference number
ISO 22493:2014(E)
©
ISO 2014

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ISO 22493:2014(E)

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© ISO 2014
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Published in Switzerland
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ISO 22493:2014(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Abbreviated terms . 1
3 Terms and definitions used in the physical basis of SEM . 1
4 Terms and definitions used in SEM instrumentation . 5
5 Terms and definitions used in SEM image formation and processing .12
6 Terms and definitions used in SEM image interpretation and analysis .16
7 Terms and definitions used in the measurement and calibration of SEM image
magnification and resolution .18
Bibliography .20
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ISO 22493:2014(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
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
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
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 202, Microbeam analysis, Subcommittee SC 1,
Terminology.
This second edition cancels and replaces the first edition (ISO 22493:2008), of which it constitutes a
minor revision.
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ISO 22493:2014(E)

Introduction
The scanning electron microscopy (SEM) technique is used to observe and characterize the surface
morphology and structure of solid materials, such as metal alloys, ceramics, glasses, minerals, polymers,
powders, etc., on a spatial scale of micrometer down to nanometer laterally. In addition, three-dimensional
structure can be generated by using a combination of focused ion beam and scanning-electron-based
analysis techniques. The SEM technique is based on the physical mechanism of electron optics, electron
scattering and secondary electron emission.
As a major sub-field of microbeam analysis (MBA), the SEM technique is widely applied in diverse sectors
(high-tech industries, basic industries, metallurgy and geology, biology and medicine, environmental
protection, trade, etc.) and has a strong business base that needs standardization.
Standardizing the terminology of a technical field is one of the basic prerequisites for development of
standards on other aspects of that field.
This International Standard is relevant to the need for an SEM terminology that contains consistent
definitions of terms as they are used in the practice of scanning electron microscopy by the international
scientific and engineering communities that employ the technique. This International Standard is the
second one developed in a package of standards on electron probe microanalysis (EPMA), scanning
electron microscopy (SEM), analytical electron microscopy (AEM), energy-dispersive X-ray spectroscopy
(EDS), etc., developed or to be developed by Technical Committee ISO/TC 202, Microbeam analysis,
Subcommittee SC 1, Terminology, to cover the complete field of MBA.
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INTERNATIONAL STANDARD ISO 22493:2014(E)
Microbeam analysis — Scanning electron microscopy —
Vocabulary
1 Scope
This International Standard defines terms used in the practice of scanning electron microscopy (SEM).
It covers both general and specific concepts, classified according to their hierarchy in a systematic order,
with those terms that have already been defined in ISO 23833 also included, where appropriate.
This International Standard is applicable to all standardization documents relevant to the practice of
SEM. In addition, some clauses of this International Standard are applicable to documents relevant to
related fields (e.g. EPMA, AEM, EDS) for the definition of terms which are relevant to such fields.
2 Abbreviated terms
AEM analytical electron microscope/microscopy
BSE (BE) backscattered electron
CPSEM controlled pressure scanning electron microscope/microscopy
CRT cathode ray tube
EBIC electron beam induced current
EBSD electron backscatter/backscattering diffraction
EDS energy-dispersive spectrometer/spectrometry
EPMA electron probe microanalyser/analysis
ESEM environmental scanning electron microscope/microscopy
FWHM full width at half maximum
SE secondary electron
SEM scanning electron microscope/microscopy
VPSEM variable-pressure scanning electron microscope/microscopy
3 Terms and definitions used in the physical basis of SEM
3.1
electron optics
science that deals with the passage of electrons through electrostatic and/or electromagnetic fields
3.1.1
electron source
device that generates electrons necessary for forming an electron beam in the electron optical system
3.1.1.1
energy spread
diversity of energy of electrons
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3.1.1.2
effective source size
effective dimension of the electron source
3.1.2
electron emission
ejection of electrons from the surface of a material under given excitation conditions
3.1.2.1
field emission
electron emission caused by the strong electric field on and near the surface of a material
3.1.2.1.1
cold field emission
field emission in which the emission process relies purely on the high-strength electrostatic field in a
high-vacuum environment with the cathode operating at ambient temperature
3.1.2.1.2
thermal field emission
Schottky emission
field emission in which the emission process relies on both the elevated temperature of the cathode tip
and an applied electric field of high voltage in a high-vacuum environment
3.1.2.2
thermionic emission
electron emission that relies on the use of high temperature to enable electrons in the cathode to
overcome the work function energy barrier and escape into the vacuum
3.1.3
electron lens
basic component of an electron optical system, using an electrostatic and/or electromagnetic field to
change the trajectories of the electrons passing through it
3.1.3.1
electrostatic lens
electron lens employing an electrostatic field formed by a specific configuration of electrodes
3.1.3.2
electromagnetic lens
electron lens employing an electromagnetic field formed by a specific configuration of electromagnetic
coil (or permanent magnet) and pole piece
3.1.4
focusing
aiming the electrons onto a particular point using an electron lens
3.1.5
demagnification
numerical value by which the diameter of the electron beam exiting a lens is reduced in comparison to
the diameter of the electron beam entering the lens
3.2
electron scattering
electron deflection and/or its kinetic energy loss as a result of collision(s) with target atom(s) or
electron(s)
3.2.1
elastic scattering
electron scattering in which energy and momentum are conserved in the collision system
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3.2.1.1
backscattering
electron scattering in which the incident electrons scatter backwards and out of the target after suffering
deflections
3.2.2
inelastic scattering
electron scattering in which energy and/or momentum are not conserved in the collision system
Note 1 to entry: For inelastic scattering, the electron trajectory is modified by a small angle, generally less than
0,01 rad.
3.2.3
scattering cross-section
hypothetical area normal to the incident radiation that would geometrically intercept the total amount
of radiation actually scattered by a scattering particle
2
Note 1 to entry: Scattering cross-section is usually expressed only as area (m ).
3.2.4
mean free path
mean distance between electron scattering events in any material
3.2.5
Bethe range
estimate of the total distance an electron can travel in any material (including vacuum and a target),
obtained by integrating the Bethe stopping power equation over the energy range from the incident
value to a low threshold value (e.g. 1 keV)
Note 1 to entry: This assumes that the electron loses energy continuously in the material rather than as occurs in
practice where energy is lost in discrete scattering events.
3.3
backscattered electron
BSE
electron ejected from the entrance surface of the specimen by the backscattering process
Note 1 to entry: By convention, an electron ejected with an energy greater than 50 eV may be considered as a
backscattered electron.
3.3.1
backscattering coefficient
BSE yield
η
ratio of the total number of backscattered electrons to the total number of incident electrons
3.3.2
BSE angular distribution
distribution of backscattered electrons as a function of their emitting angle relative to the specimen
surface normal
3.3.3
BSE atomic number dependence
variation of backscattering coefficient as a function of the atomic number of the specimen
3.3.4
BSE beam energy dependence
variation of backscattering coefficient with beam energy
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3.3.5
BSE depth distribution
distribution describing the locations of the electrons at their maximum depth in the specimen before
subsequently being backscattered from the specimen surface
3.3.6
BSE energy distribution
distribution of backscattered electrons as a function of their emitting energy
3.3.7
BSE escape depth
maximum depth in a specimen from which a backscattered electron may emerge
3.3.8
BSE lateral spatial distribution
two-dimensional distribution of backscattered electrons escaping as a function of the distance from the
beam impact point to the lateral position of escape
3.4
secondary electron
electron emitted from a specimen as a result of bombardment by the primary electrons
Note 1 to entry: By convention, an electron with energy less than 50 eV is considered as a secondary electron.
3.4.1
SE yield
secondary electron coefficient
total number of secondary electrons per incident electron
3.4.2
SE angular distribution
distribution of secondary electrons as a function of their emitting angle relative to the surface normal
3.4.3
SE energy distribution
distribution of secondary electrons as a function of their emitting energy
3.4.4
SE escape depth
maximum depth under a surface from which secondary electrons are emitted
3.4.5
SE tilt dependence
effect on secondary electrons of the specimen tilt which accompanies a change in incident beam angle
3.4.6
SE (SE )
1 I
secondary electrons that are generated by the incident beam electrons within the specimen
3.4.7
SE (SE )
2 II
secondary electrons that are generated by the backscattered electrons within the specimen
3.4.8
SE (SE )
3 III
secondary electrons that are generated by the electrons backscattered from the specimen somewhere
remotely beyond the point of incidence
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3.4.9
SE (SE )
4 IV
secondary electrons that are generated by the incident beam electrons within the electron optical
column
3.5
electron penetration
physical process of forwards travelling by an energetic incident beam electron before losing all its
energy within the target (specimen)
3.5.1
electron range
measure of the straight-line penetration distance of electrons in a solid
3.5.2
interaction volume
volume below the incident electron beam impact area at the specimen surface, within which the beam
electrons travel and experience elastic and inelastic scattering
3.5.3
information volume
volume of the specimen from which the measured signal originates
3.5.4
penetration depth
depth to which an incident electron travels in a target
3.5.5
Monte Carlo simulation
calculation that simulates stochastic physical processes (here: the electron diffusion in the solid state)
and thus can be used to model the electron probe - sample interaction and SEM image formation
3.6
electron channelling
physical process occurring in crystalline materials of greater electron penetration along directions of
low atomic density
3.7
electron diffraction
physical process of particularly strong scattering of the incident electron beam at certain angles relative
to the atomic planes in a crystal
3.7.1
electron backscattering diffraction
EBSD
diffracting process that arises between the backscattered electrons and the atomic planes of a specimen
illuminated by the incident electron beam
4 Terms and definitions used in SEM instrumentation
4.1
electron gun
component that produces an electron beam with a well-defined kinetic energy
4.1.1
field emission gun
electron gun employing field emission
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4.1.1.1
cold field emission gun
electron gun employing cold field emission
4.1.1.1.1
extracting electrode
electrode applying the electrostatic potential to extract electrons from the electron source
4.1.1.1.2
flashing
short-time heating process usually applied to a cold field emission gun to clean the surface of the electron
source tip
4.1.1.2
thermal field emission gun
electron gun employing thermal field emission
4.1.2
thermionic emission gun
electron gun employing thermionic emission
4.1.2.1
tungsten hairpin gun
thermionic emission gun employing a tungsten hairpin filament as its cathode
4.1.2.2
LaB gun
6
thermionic emission gun employing a heated block of single-crystal LaB as its cathode
6
4.1.2.3
anode
one of the electrodes making up the electron gun, to which a high positive voltage relative to the cathode
is applied to accelerate the emitted electrons from the cathode
4.1.2.4
cathode
one of the electrodes making up the electron gun, which is at a negative electric potential relative to the
anode
4.1.2.5
Wehnelt cylinder
cap-shaped electrode, placed between anode and cathode in the electron gun, which acts to focus
electrons inside the gun and to control the amount of electron emission
4.1.3
brightness
β
current per unit area at the focus position and per unit solid angle in the beam
Note 1 to entry: Brightness is given by the equation
2 2 2
β = 4I/(π d α )

where
I is the current, in amperes;
d is the beam diameter, in metres, at the focus position;
α is the beam half-angle, in radians.
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4.1.4
reduced brightness
β′
brightness (beam current density) normalized to the beam acceleration voltage
Note 1 to entry: Reduced brightness is given by the equation
β′ = β/V

where
β is the measured brightness;
V is the electron beam acceleration voltage.
4.1.5
emission current
total electron current emitted from the cathode
4.1.6
saturation
specific cathode heating condition at which a change in the cathode heating current will result in only a
small change in the electron beam current, which is close to its maximum
4.2
electron lens system
combination of various electron lenses to obtain specific electron optics functions
4.2.1
aberration
divergence from ideal properties of an electron optical element, e.g. lens imperfections like spherical
aberration, chromatic aberration, diffraction, that degrade the lens optical performance
4.2.1.1
chromatic aberration
lens defect that arises because electrons from the same point but of slightly different energies will be
focused at different positions in the image plane
4.2.1.2
spherical aberration
lens defect which arises because electrons in trajectories further away from the optic axis are bent more
strongly by the lens magnetic field than those near the axis
4.2.2
aperture
diaphragm with an axial opening that defines the transmission of the lens
4.2.2.1
aperture angle
half of the angle subtended by the diameter of the aperture at the point of beam focus
4.2.2.2
aperture diffraction
defect that arises at very small aperture diameters because the wave nature of electrons gives rise to a
diffraction pattern instead of a point in the Gaussian image plane
4.2.2.3
objective aperture
aperture that restricts the cross-sectional area of the electron beam incident on the specimen
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4.2.2.4
virtual objective aperture
beam-limiting aperture located between the last condenser and the objective lens
4.2.3
astigmatism
phenomenon in which electrons emerging from a point object are focused to form two separate focal
lines at 90° to one another rather than a point focus as formed by a perfectly cylindrical lens
Note 1 to entry: It arises from the lens asymmetrical magnetic field caused by machining errors, inhomogeneities
in the pole pieces, asymmetry in the lens windings and imperfect apertures.
4.2.3.1
stigmator
device that applies weak supplementary magnetic fields to correct astigmatism
4.2.4
condenser lens
electron optical device used to converge or diverge transmitted electrons
Note 1 to entry: The principal function of the condenser is to set the beam current and control its three-dimensional
shape.
4.2.5
objective lens
lens in a microscope closest to the specimen
Note 1 to entry: The principal function of the objective lens is to focus the final probe.
4.2.5.1
conical lens
objective lens in the shape of a cone pointing towards the specimen
4.2.5.2
immersion lens
electron lens in which the object lies deep within the electric field so that the lens field varies rapidly in
its vicinity
4.2.5.3
snorkel lens
objective lens of asymmetric single-pole configuration with the ability to accommodate large specimens,
with low aberrations and with flexibility for through-lens electron detection and imaging
4.3
scanning system
device incorporated in the electron optical system for achieving time-controlled one- or two-dimensional
movement of the electron probe on the specimen surface and synchronized signal collection to generate
line scans or images
4.3.1
analogue scanning system
scanning system with an analogue circuit as its scanning signal source, in which the electron probe is
moved continuously, with a rapid scan along the x-axis (the line scan) and a slower scan at right angles
along the y-axis (the frame scan), so that a good approximation to an orthogonal scan is produced
4.3.2
digital scanning system
scanning system, with a digital circuit as its scanning signal source, in which the electron probe is
moved discretely from a point being addressed to a particular location (x, y) in a matrix, remains there
for a fixed time (the dwell time) and is then moved to the next data collection point
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4.3.3
double deflection
action of deflecting the electron beam at first off-axis and then to cross the optical axis again at the final
(beam defining) aperture
4.3.4
dwell time
time during which the electron probe stays in a particular location in digital scanning operation
4.4
specimen chamber
compartment just next to the objective lens where the specimen stage with specimen is accommodated
and manipulated
4.4.1
charge balance
condition at which the number of incident electrons impinging on the specimen surface equals the
number of electrons (secondary, backscattered, etc.) leaving the specimen
4.4.2
differential pumping
pumping method designed to achieve and maintain the different vacuum values for chambers connected
by diaphragms which prevent the exchange of large amounts of gas
4.4.3
gas path length
average distance electrons pass through gas to reach the specimen
4.4.4
gas amplification
effect of multiple ionization events leading to secondary electron cascade due to electron-gas interaction
under an applied electric field leading to a signal gain
4.4.5
CPSEM
controlled pressure SEM
variable pressure SEM
VPSEM
environmental SEM
ESEM
controlled pressure SEM which can operate with a pressure in the specimen chamber from 1 Pa up to
5 000 Pa so that direct secondary emission is no longer detectable and images are obtained with the
detection of electrons by gas amplification (4.4.4), environmental SE detector (4.6.2.6), ions, photoemission
or using other signals such as BSE or absorbed current
Note 1 to entry: This type of SEM can be also used with a normal vacuum in the chamber.
4.5
specimen
sampled material designated to be examined or analysed
4.5.1
specimen stage
device, located in the specimen chamber, which enables the specimen to be appropriately mounted,
manipulated and held in place
Note 1 to entry: It usually allows for some of the five degrees of freedom in motion, i.e. x-y-z displacements, tilting
and rotating.
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4.5.2
working distance
distance between the lower surface of the pole piece of the objective lens and the specimen surface
Note 1 to entry: In the past, this distance was defined as the distance between the principal plane of the objective
lens and the plane containing the specimen surface.
4.5.3
contamination
extraneous surface layer on the specimen surface and/or localized build-up of foreign material on the
surface arising from electron beam bombardment
4.5.4
coating
procedure of covering the specimen surface with a thin layer of material (usually conductive) which is
generally created by vacuum evaporation or sputtering
4.5.5
edge effect
signal enhancement at edge features of the specimen surface in SEM images
4.6
signal detection
collection of the physical signals generated by the electron-specimen interaction and their conversion
into electronic signals for further processing
4.6.1
detector
device employed to achieve signal collection and conversion into an electronic signal
4.6.2
electron detector
detector specifically designed for collection of electrons and their conversion into an electronic signal
4.6.2.1
BSE to SE conversion detector
version of the Everhart-Thornley detector for the collection of BSE signals through collection of remotely
generated SEs by the use of a specific electrode having a high BSE to SE conversion efficiency
4.6.2.2
EBSD CCD-based camera
detector system, used for imaging of EBSD patterns, which involves a fluorescent screen, an optical
camera lens system, a charge-coupled device and a computer to collect the data
4.6.2.3
IR camera
detector system used to observe the contents of the specimen chamber with infra-red light
4.6.2.4
channel plate detector
SE and BSE detector for all energy range operation and multiplication occurring within the capillaries
through the detector plate with an accelerating potential applied between the exit and the entrance
faces
4.6.2.5
combined scintillator/light guide BSE detector
dedicated BSE detector in which a large-area scintillator (made of the same material as the light guide) is
placed above the specimen surface, close to and symmetrical with the surface, to achieve BSE collection
over a solid angle of nearly 2π
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4.6.2.6
environmental SE detector
gas (or gaseous) SE detector
special type of SE detector, dedicated to VPSEM or CPSEM, which operates on the principle of amplified
ion signal current generated in the SE-gas ionization process by the accelerated SEs in the presence
of an electric field produced by positively biasing an electrode near the specimen placed in a gaseous
environment
4.6.2.7
Everhart-Thornley detector
type of SE detector named after its designers T. Everhart and R.F.M. Thornley
Note 1 to entry: The basic component of the detector is a scintillator that emits photons when hit by high-energy
electrons. The emitted photons are collected by a light guide and transported to a photomultiplier for detection.
4.6.2.8
solid-state diode detector
dedicated BSE detector which operates on the principle of electron-hole production induced in a
semiconductor by energetic electrons, with the features of flexible configuration, large solid angle,
multiple arrays, energy selectivity and self-amplification
4.6.2.9
through-the-lens (TTL) detector
special kind of SE/BSE detector, adapted to the objective lens, in which the SEs/BSEs emitted from the
specimen spiral up along the lens magnetic field, pass up through the lens bore and are collected by
electron detector(s) placed on one side of the column
4.6.2.10
in-lens detector
special kind of SE/BSE detector, placed between the pole pieces of the objective lens, in which the
SEs/BSEs emitted from the specimen spiral up along the lens magnetic field, pass up through the lens
bore and are collected by electron detector(s) coaxial with the beam
4.6.3
take-off angle
angle between the surface of the specimen and the line connecting the beam impact point on the
specimen surface to the centre of the detector face
Note 1 to entry: In this instance, the term does not apply to X-ray detector take-off angle. For X-ray detector take-
off angle, see “X-ray take-off angle” in ISO 23833.
4.7
signal processing
subsequent treatment and modification of electrical signals leaving the detector by electronic means for
further image processing and display
4.7.1
black level
dark level
minimum output signal from the amplifier that corresponds to the darkest possible level on the screen
4.7.2
dynamic range
difference between peak white and the black level
4.7.3
derivative processing
method of enhancing selected spatial frequencies in an image
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5 Terms and definitions used in SEM image formation and processing
5.1
scanning
action of obtaining time-controlled movement of the electron probe on the specimen surface with the
synchronized movement of the spot on the display screen
5.1.1
area scanning
scanning in an x-y pattern to obtain an SEM image display
5.1.2
line scanning
scanni
...