ISO 14594:2014

INTERNATIONAL ISO
STANDARD 14594
Second edition
2014-10-15
Microbeam analysis — Electron
probe microanalysis — Guidelines for
the determination of experimental
parameters for wavelength dispersive
spectroscopy
Analyse par microfaisceaux — Analyse par microsonde électronique
(Microsonde de Castaing) — Lignes directrices pour la détermination
des paramètres expérimentaux pour la spectrométrie à dispersion de
longueur d’onde
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 Experimental parameters . 2
5.1 General . 2
5.2 Parameters related to the primary beam . 2
5.3 Parameters related to wavelength dispersive X-ray spectrometers . 3
5.4 Parameters related to the specimen . 4
6 Procedures and measurements . 5
6.1 General . 5
6.2 Beam current . 5
6.3 Parameters related to measured peaks . 6
6.4 Parameters related to the specimen . 8
7 Test report . 9
Annex A (informative) Methods of estimating analysis area .10
Annex B (informative) Methods of estimating analysis depth .12
Annex C (informative) Method of estimating X-ray analysis volume by applying the Monte Carlo
(MC) simulation .14
Bibliography .18
Foreword
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electrotechnical standardization.
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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
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to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 202, Microbeam analysis, Subcommittee SC 2,
Electron probe microanalysis.
This second edition cancels and replaces the first edition (ISO 14594:2003), of which it constitutes a
minor revision. It also incorporates the Technical Corrigendum ISO 14594:2003/Cor 1:2009.
iv © ISO 2014 – All rights reserved

INTERNATIONAL STANDARD ISO 14594:2014(E)
Microbeam analysis — Electron probe microanalysis
— Guidelines for the determination of experimental
parameters for wavelength dispersive spectroscopy
1 Scope
This International Standard gives the general guidelines for the determination of experimental
parameters relating to the primary beam, the wavelength spectrometer, and the sample that need to be
taken into account when carrying out electron probe microanalysis. It also defines procedures for the
determination of beam current, current density, dead time, wavelength resolution, background, analysis
area, analysis depth, and analysis volume.
This International Standard is intended for the analysis of a well-polished sample using normal beam
incidence, and the parameters obtained can only be indicative for other experimental conditions.
This International Standard is not designed to be used for energy dispersive X-ray spectroscopy.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 17025:2005, General requirements for the competence of testing and testing laboratories
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
analysis area
two-dimensional region of sample surface from which the full signal or a specified percentage of that
signal is detected
3.2
analysis depth
distance from the sample surface to the bottom normal to the surface from which the full signal or a
specified percentage of that signal is detected
3.3
analysis volume
three-dimensional region of a sample from which the full signal or a specified percentage of that signal
is detected
3.4
background
non-characteristic component of an X-ray spectrum arising from the X-ray continuum
3.5
beam current
electron current contained within the focused beam
3.6
beam current density
beam current incident on the sample per unit area
3.7
dead time
time associated with the measurement of a signal photon in a detector and/or counting system,
representing the time that the system is unavailable to process the next photon
3.8
wavelength resolution
full peak width at half maximum of a characteristic X-ray peak
4 Abbreviated terms
EPMA Electron Probe Microanalysis
FWHM Full Width at Half Maximum
WDX Wavelength Dispersive X-ray
5 Experimental parameters
5.1 General
The parameters given in 5.2.1, 5.2.3, and 5.2.4 should be known and recorded. Checking the calibration
of beam energy, beam current, and magnification together with counter dead time should be included in
the maintenance schedule of the instrument.
5.2 Parameters related to the primary beam
5.2.1 Beam energy
The beam energy typically ranges from 2 keV to 30 keV. In most cases, the calibration of the beam energy
is not critical for qualitative analysis.
NOTE Calibration is very critical in the case of use of low overvoltage ratio or during measurements relating
to layer thickness or elemental depth distributions.
5.2.2 Beam current
Because X-ray peak intensity is directly proportional to beam current, the precision of the measurement
of the beam current should be better than the precision required for quantitative analysis.
The beam current stability over long periods of time is absolutely essential for consistent quantitative
analysis. The beam current stability should be tested periodically, especially prior to quantitative
calibration and analysis. It is possible to compensate for small changes in beam current if this is recorded
prior to and following each measurement. Then all X-ray peak and background measurements should be
scaled appropriately by I /I where I is the initial beam current and I is the beam current at the time
i m, i m
of the measurement.
5.2.3 Beam current density
Beam current density is especially important when analyzing beam sensitive materials. The current
4 -2
density in a focused probe can exceed 10 A m . The effective current density can be reduced for a
measurement by lowering the incident electron beam current or, where lateral resolution is not critical,
2 © ISO 2014 – All rights reserved

by either defocusing or rastering the probe. If a rastered probe is used, a similar scan should be used
for comparative measurements on standards and other specimens because the effective spectrometer
efficiency for the selected wavelength decreases as a function of the beam deflection. See 5.3.5.
5.2.4 Magnification
To properly define the dimensional scale for line-scans and images acquired by deflecting the primary
electron beam, it is essential to calibrate the magnification scale while operating in the scanning electron
mode.
5.3 Parameters related to wavelength dispersive X-ray spectrometers
5.3.1 General
An instrument may be fitted with one or more WDX spectrometers, each with a number of diffracting
crystals that may be selected to cover a particular range of X-ray wavelengths depending on the line
of the analysed element. The following parameters are important for the proper operation of WDX
spectrometers.
5.3.2 Take-off angle
The take-off angle affects quantitative analysis. Any comparison of measurements from instruments
with different take-off angles should be taken into account and the procedures used be noted in the
analysis report.
NOTE The value of this angle, which is normally fixed, is provided by the instrument manufacturer.
5.3.3 Wavelength resolution
The spectral resolution depends on the following parameters:
— crystal material (and Miller indices of the crystal planes);
— the radius of curvature of the diffracting crystal (fully focusing vs. semi-focusing crystal);
— the presence of a crystal mask (if semi-focusing crystal);
— the size and position of the counter entrance window or of the entrance slit if present.
All these settings determine the wavelength resolution of the measured X-ray spectrum and the observed
line-width (FWHM) of the characteristic X-ray peaks.
Resolution can also influence the ability of the system to discriminate against overlapping peaks,
background signals, and the sensitivity of measurements to specimen height and beam position on the
specimen.
5.3.4 X-ray detector and counting chain
Many spectrometers use a gas-filled proportional counter to detect X-rays. The magnitude of the output
pulses from these detectors is determined by the incident X-ray energy and/or the voltage applied to
the counters. Two discriminators are used to select the pulse of interest. A low discriminator setting is
used to eliminate pulses due to noise, while a high discriminator setting excludes pulses from high order
reflections of more energetic X-rays. Optimum settings depend on the X-ray lines of interest.
It is important to set the discriminator to ensure that any unintended shift in pulse amplitude, for
example, due to high count rates or changes in atmospheric temper
...