ISO 20411:2018

INTERNATIONAL ISO
STANDARD 20411
First edition
2018-03
Surface chemical analysis —
Secondary ion mass spectrometry
— Correction method for saturated
intensity in single ion counting
dynamic secondary ion mass
spectrometry
Analyse chimique des surfaces — Spectrométrie de masse des ions
secondaires — Méthode de correction de l'intensité de saturation en
SIMS dynamique à comptage d'ions individuel
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 Outline of method . 3
6 Procedure for evaluating intensity linearity . 5
6.1 Obtaining reference sample . 5
6.2 Setting the sample . 5
6.3 Operating the instrument . 5
6.3.1 Setting the ion beam and the mass analyser. 5
6.3.2 Setting the charge compensation . 5
6.3.3 Setting the ion detector . 5
6.4 Acquiring the data . 5
6.5 Assessing the linearity without and with intensity correction . 6
6.5.1 Interpolating the minor isotope intensity . 6
6.5.2 Correcting the ratio of the isotope abundance to the instrument transmittance . 7
6.5.3 Assessing the linearity of intensity . 8
6.5.4 Correcting the saturated intensity . . 8
6.5.5 Assessing the uncertainty of the data .11
7 Reporting the results .12
8 Correcting saturated intensity to the measurement results of the analysis samples .12
Annex A (informative) Effect of the dead time correction with various instruments for
VAMAS study .13
Bibliography .15
Foreword
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This document was prepared by Technical Committee ISO/TC 201, Surface chemical analysis,
Subcommittee SC 6, Secondary ion mass spectrometry.
iv © ISO 2018 – All rights reserved

Introduction
For the quantitative analysis of materials using secondary ion mass spectrometry (SIMS), the abundance
of a species should be a linear function of its measured signal intensity. However, this relationship
can become nonlinear as the count rates rise because of saturation of the detector, which uses a
pulse counting system. This causes underestimation of an abundance of high-count-rate species. The
nonlinearity of the counting system can be corrected using the relevant method, so that the corrected
count rate gives a wider linear range.
This document explains how to assess the linearity in the high-count-rate region. The document also
provides a correction method for the saturated intensity in a certain situation. It uses a test based on
depth profile analysis of two isotopes in a reference material which has a gradual concentration change
between low and high concentration regimes. The correction method is based on the approximate
intermediate extended dead time model.
This document should be used when characterizing a new spectrometer so that it may be operated in an
appropriate intensity range or when applying a new analysis condition. It should then be repeated after
any substantive modification to the detection circuits, such as the multiplier voltage or the threshold,
after replacement of their multiplier, or at approximately 6-monthly intervals.
INTERNATIONAL STANDARD ISO 20411:2018(E)
Surface chemical analysis — Secondary ion mass
spectrometry — Correction method for saturated intensity
in single ion counting dynamic secondary ion mass
spectrometry
1 Scope
This document specifies a method for determining the maximum count rate for an acceptable limit of
divergence from linearity of the intensity scale in pulse counting magnetic sector-type secondary ion
mass spectrometers or quadrupole secondary ion mass spectrometers. It uses a test based on depth
profile analysis of two isotopes in a reference material which has a gradual concentration change
between low and high concentration regimes. It also includes a correction method for saturated
intensity caused by the dead time of the detector. The correction can increase the intensity range for
95 % linearity so that a higher maximum count rate can be employed for those spectrometers for which
the relevant correction equations have been shown to be valid.
This document does not apply to time of flight mass spectrometers.
This document is only applicable to elements with minor isotopes. It is not applicable if the element is
monoisotopic or contains isotopes with equal abundances.
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 18115-1, Surface chemical analysis — Vocabulary — Part 1: General terms and terms used in
spectroscopy
ISO 18115-2, Surface chemical analysis — Vocabulary — Part 2: Terms used in scanning-probe microscopy
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18115-1 and ISO 18115-2 and
the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
major isotope
isotope whose abundance is more than others of the same element
3.2
minor isotope
isotope whose abundance is less than a major isotope (3.1)
3.3
pulse counting system
ion detector system which counts an ion as a single pulse
Note 1 to entry: When an ion reaches the detector it generates some electrons, which are multiplied whenever
they collide with the multiplier or channeltron. Sufficient current is then produced so that the ion can be counted
as a single pulse.
3.4
medium intensity region
intensity region where the major isotope intensity is still linear and the minor isotope intensity is
sufficiently higher than background
3.5
saturation
phenomenon when too many ions reach the detector at the same time, their pulses are overlapped and
the detector cannot separate individual pulses
3.6
approximate intermediate extended dead time model
a-IED
model for detector saturation (3.5)
4 Symbols and abbreviated terms
The term “intensity” is used below and elsewhere. This refers to a measurement of count rate in the
depth profiles.
−1
I (t) measured intensity at the time t, expressed in counts per second (cts·s )
M
−1
I maximum measured intensity, expressed in counts per second (cts·s )
Max
−1
I (t) measured intensity of the major isotope at time t, expressed in counts per second (cts·s )
M-J
−1
I (t) measured intensity of the minor isotope at time t, expressed in counts per second (cts·s )
M-N
−1
I (t') I (t) interpolated at the measurement time of I (t'), expressed in counts per second (cts·s )
M-N-P M-N M-J
I maximum reliable intensity without saturated intensity correction, expressed in counts per second
M-Max
−1
(cts·s )
−1
I (t) corrected intensity at time t, expressed in counts per second (cts·s )
C
−1
I (t) corrected intensity of the major isotope at time t, expressed in counts per second (cts·s )
C-J
−1
I (t) corrected intensity of the minor isotope at time t, expressed in counts per second (cts·s )
C-N
−1
I (t') I (t) which is interpolated at the measurement time of I (t'), expressed in counts per second (cts·s )
C-N-P C-N C-J
−1
I maximum reliable intensity after saturated intensity correction, expressed in counts per second (cts·s )
C-Max
I maximum reliable measured intensity without intensity correction at I , expressed in counts per
C-m-Max C-Max
−1
second (cts·s )
R natural abundance of the major isotope
J
R natural abundance of the minor isotope
N
R practical isotope ratio; isotope ratio (R /R ) multiplied by the transmittance differential efficiency,
J N
also known as isotope ratio corrected for mass-fractionation
t maximum time within the medium intensity region, expressed in seconds (s)
MM
t minimum time within the medium intensity region, expressed in seconds (s)
ML
t time at I , expressed in seconds (s)
CM C-Max
N number of data points in the medium intensity region
Mid
N number of data points for the intensity from the I up to the I
Cor M-Max C-Max
ρ parameter corresponding to the
...