ISO 17470:2014

INTERNATIONAL ISO
STANDARD 17470
Second edition
2014-01-15
Microbeam analysis — Electron
probe microanalysis — Guidelines
for qualitative point analysis
by wavelength dispersive X-ray
spectrometry
Analyse par microfaisceaux — Analyse par microsonde électronique
(Microsonde de Castaing) — Lignes directrices pour l’analyse
qualitative ponctuelle par spectrométrie de rayons X à dispersion de
longueur d’onde (WDX)
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 Apparatus . 2
6 Procedure for identification . 2
6.1 General . 2
6.2 Setting of analysis conditions . 2
6.3 Method for analysing an X-ray spectrum. 4
6.4 Detection limit . 5
7 Test report . 6
Annex A (informative) Example of the test report on qualitative analysis of a stainless steel
sample by EPMA . 7
Bibliography .10
Foreword
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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 17470:2004), of which it constitutes a
minor revision.
iv © ISO 2014 – All rights reserved

Introduction
Electron probe microanalysis is used to qualitatively identify the elements present in a specimen on a
micrometric scale. It is necessary to specify the measurement conditions and identification method in
order to avoid reporting erroneous or inconsistent results.
INTERNATIONAL STANDARD ISO 17470:2014(E)
Microbeam analysis — Electron probe microanalysis —
Guidelines for qualitative point analysis by wavelength
dispersive X-ray spectrometry
1 Scope
This International Standard gives guidance for the identification of elements and the investigation of
the presence of specific elements within a specific volume (on a μm scale) contained in a specimen,
by analysing X-ray spectra obtained using wavelength dispersive X-ray spectrometers on an electron
probe microanalyser or on a scanning electron microscope.
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 14594:2003, Microbeam analysis — Electron probe microanalysis — Guidelines for the determination
of experimental parameters for wavelength dispersive spectroscopy
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
higher order reflections
peaks appearing at the diffracted angles corresponding to n = 2, 3, 4…
Note 1 to entry: In WDS, X-rays are dispersed according to Bragg’s law, nλ = 2d sinθ, where λ is the X-ray wavelength,
d is the interplanar spacing of the diffraction crystal, θ is the diffraction angle, and n is an integer. The higher
order reflections are the peaks appearing at the diffracted angles corresponding to n = 2, 3, 4…
3.2
point analysis
analysis in which the primary beam is fixed, thus irradiating a selected region of a sample surface
Note 1 to entry: The method where the primary beam rapidly scans over a very small region on the sample surface
is also included. The maximum size of a static beam or a raster area should be chosen such that relative X-ray
intensities do not change when enlarging the analysis area.
3.3
Rowland circle
circle of focus along which the X-ray source, diffractor,
and detector must all lie in order to satisfy the Bragg condition and obtain constructive interference
3.4
X-ray line table
table of X-ray lines used for qualitative analysis by EPMA
Note 1 to entry: The X-ray line table for qualitative analysis by EPMA lists the wavelengths of K-, L-, and, M-lines
for the elements observed on each diffraction crystal. It can also list their relative intensities, the full width at
half maximum (FWHM) of each peak, the interplanar spacings of the diffraction crystals, and the wavelengths of
satellite peaks.
4 Abbreviated terms
EPMA electron probe microanalysis
WDS wavelength dispersive X-ray spectroscopy or spectrometry
5 Apparatus
Care should be taken to ensure the instrument is performing satisfactorily. In particular, that the
electron column is correctly aligned, the beam current is stable, the accelerating voltage and beam
current are appropriate for the sample, the sample surface is prepared suitably for quantitative analysis,
the working distance is correct, and the spectrometer crystals and X-ray counters are calibrated and
aligned so that the spectrum exhibits X-ray peaks with appropriate intensities and shapes.
NOTE 1 Operators should be aware that parameters such as peak position, relative peak heights, peak
resolutions, FWHM values, etc. can vary slightly from instrument to instrument, and also from sample to sample.
This can be largely corrected for by periodically comparing values with an appropriate X-ray line table and data
from appropriate laboratory reference materials.
NOTE 2 If the sample surface is not planar or polished or perpendicular to the beam, care should be taken in
determining the actual value of the local take-off angle and the ability of the spectrometer to properly analyse
this kind of sample.
6 Procedure for identification
6.1 General
X-ray spectra are obtained by directing the incident electron beam at the point to be analysed on the
sample surface and scanning the X-ray spectrometers over a specified wavelength range. Qualitative
analysis is performed by identifying each peak in the resulting X-ray spectra.
It is necessary to verify whether the peak identified interferes with a peak resulting from another
element. Particular care is needed for possible higher order reflections originating from other elements
in the sample, usually, but not always, at higher concentrations.
6.2 Setting of analysis conditions
6.2.1 Primary beam
The primary beam energy should be higher than the X-ray excitation energies of analysed elements,
but low enough to minimize sample damage, contamination of the sample, and saturation of the X-ray
detectors.
NOTE 1 The Bethe inner shell ionization cross section has a maximum for an overvoltage ratio equal to
Napier’s number (about 2,7). Taking into account the energy loss of the primary electrons, optimum excitation
occurs at overvoltage ratios slightly greater than Napier’s number. However, in the case of ultra-light elements
and low energy X-rays from other elements (i.e. low energy L- and M-lines), absorption from surface layers can
significantly affect the optimum overvoltage causing it to be substantially higher than 2,7.
NOTE 2 The intensity of a generated characteristic X-ray, I, is given approximately by Formula (1):
2 © ISO 2014 – All rights reserved

1,7
1,7
 
IC=×iE −EE =×Ci()U −1 (1)
()
0c c
 
where
C is the constant;
i is the primary beam current (A);
E is the primary beam energy (keV);
E is the critical excitation energy (keV);
c
U is the overvoltage ratio (E /E ).
0 c
Note that as the primary beam energy increases, the intensity of generated X-rays become larger.
Since the depth of the generation also increases, absorption of X-rays leaving the sample occurs, so the
intensities of the detected X-rays do not necessarily become proportionally larger. In samples where
absorption is particularly high, such as with light elements Be to F, it is recommended that a primary
beam energy of 15 keV or less be used to reduce the depth of X-ray generation and hence the absorption
effect. In the case of a thin film sample or a powder sample, primary beam energy should be determined
by referring to 5.2 of ISO 14594:2003.
The primary beam current should be also set in the range in which sample damage, sample contamination,
and saturation of the X-ray detectors are minimized.
6.2.2 X-ray spectrometer
6.2.2.1 Selection of diffraction crystals
The diffraction crystals selected should be capable of detecting the intended elements, with a maximum
peak-to-background ratio and peak resolution, but with minimum interference from peaks of other
elements in the sample. Since it is not always possible to optimize all of these parameters simultaneously,
the analyst should select the diffraction crystal that will provide the best compromise for the specific
analysis requirements.
6.2.2.2 Scanning speed
A scanning speed should be selected that will enable the detection of the anticipated elements at their
anticipated concentrations.
NOTE 1 The scanning speed of a digitally scanned spectrometer is defined by the number of steps, the length of
a step, and the sampling time per step. The number of steps should be high enough and the length of a step should
be short enough to sufficiently resolve the shape and height of the detected peaks. In practice, a measured peak
should contain a min
...