ISO 16129:2018

INTERNATIONAL ISO
STANDARD 16129
Second edition
2018-11
Surface chemical analysis — X-ray
photoelectron spectroscopy —
Procedures for assessing the day-
to-day performance of an X-ray
photoelectron spectrometer
Analyse chimique des surfaces — Spectroscopie de photoélectrons X
— Modes opératoires d'évaluation de la performance au jour le jour
d'un spectromètre de photoélectrons X
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, definitions and abbreviations . 1
4 Initial approach . 1
5 Initial instrument calibration, alignment and assessment . 2
6 Test specimen selection . 2
6.1 General information . 2
6.2 The conductive specimen . 3
6.3 The non-conductive specimen . 3
6.4 Specimen for assessing the X-ray source . 4
7 Collection of reference data . 5
7.1 General information . 5
7.2 Rapid test of the instrument using a conductive specimen . 5
7.2.1 Specimen mounting and pre-treatment . 5
7.2.2 Survey spectrum . 5
7.2.3 High-resolution spectrum . 7
7.3 Rapid test of the instrument using a non-conductive specimen . 8
7.3.1 Specimen mounting and positioning . 8
7.3.2 High-resolution spectrum . 8
7.4 Rapid test of the X-ray source using a phosphor specimen . 8
7.5 Rapid test of the X-ray source using a uniform conductive specimen . 9
8 Collection of subsequent performance data . 9
9 Analysis of the performance data .10
9.1 General information .10
9.2 Survey spectrum .10
9.3 High-resolution spectrum from the conductive specimen.10
9.4 High-resolution spectrum from the non-conductive specimen .10
9.5 Images from the phosphor specimen .10
9.6 Images from the uniform conductive specimen .10
9.7 Spectrum ratios .11
10 Control charts .15
Bibliography .18
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
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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
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.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 201, Surface chemical analysis,
Subcommittee SC 7, Electron spectroscopies.
This second edition cancels and replaces the first edition (ISO 16129:2012), which has been technically
revised.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2018 – All rights reserved

Introduction
XPS instruments are complex, and unsatisfactory performance is not always obvious to an operator. It
is therefore necessary to provide a test for the correct operation of the system that can be performed
regularly and frequently without interfering excessively with the normal work of the laboratory.
A full diagnostic test can require many hours or even days; such a test can be appropriate only when
the instrument is known to have a fault that needs to be remedied or following a major maintenance
procedure. Data acquired before a problem is uncovered become suspect if the spectrometer has not
been routinely tested, leading to a loss of confidence in those data. If a regular check of the instrument
is made, changes in performance can be monitored and corrective action taken in good time to ensure
that the data supplied are fit for purpose. In the event that a serious fault is uncovered, then only the
data since the last check can be in doubt and need to be repeated.
The purpose of this document is to provide users with a procedure which is not excessively time-
consuming so that it can be completed on a regular and frequent basis – daily if required. The user will
then gain an awareness of the current characteristics of the instrument so that a decision can be made
as to whether or not a more complete and time-consuming action is required to return the instrument
to a satisfactory level of performance.
This procedure is intended to be applied to an XPS instrument that has been correctly calibrated and
aligned in accordance with ISO standards or manufacturer’s instructions. It is designed to highlight
aspects of the instrument’s characteristics that differ significantly from those that were measured
immediately following the calibration procedure. The procedure does not show how the instrument can
be returned to its original state. Instead, it guides the user to possible areas of concern. The procedure
provides data that can be used in control charts, allowing trends to be observed and acted upon before
data quality deteriorates to an unacceptable level for the needs of the analyst.
INTERNATIONAL STANDARD ISO 16129:2018(E)
Surface chemical analysis — X-ray photoelectron
spectroscopy — Procedures for assessing the day-to-day
performance of an X-ray photoelectron spectrometer
1 Scope
This document is designed to allow the user to assess, on a regular basis, several key parameters of an
X-ray photoelectron spectrometer. It is not intended to provide an exhaustive performance check, but
instead provides a rapid set of tests that can be conducted frequently.
Aspects of instrument behaviour covered by this document include the vacuum, measurements of
spectra of conductive or non-conductive test specimens and the current state of the X-ray source. Other
important aspects of the instrument performance (e.g. lateral resolution) fall outside the scope of this
document.
The document is intended for use with commercial X-ray photoelectron spectrometers equipped with a
monochromated Al Kα X-ray source or with an unmonochromated Al or Mg Kα X-ray source.
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
3 Terms, definitions and abbreviations
For the purposes of this document, the terms and definitions given in ISO 18115-1 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/
The following abbreviations are used:
FWHM full width at half maximum
PET poly(ethylene terephthalate)
PTFE polytetrafluoroethylene
XPS X-ray photoelectron spectroscopy
4 Initial approach
Most instruments are fitted with a vacuum gauge or gauges. These shall be read frequently and the
reasons for large variations understood. A large increase in the pressure can be due to the properties
of a test specimen inside the instrument, a fault in the pumping system, an increase in the temperature
of the vacuum system or a leak.
Similarly, most instruments have status indicators, either for the system as a whole or for sub-systems
or modules. Examples of such indicators include water flow rate, data system communications status
and electrical power. These can be visible as part of the instrument hardware itself or on screen through
an instrument control (data acquisition) system. Such indicators again shall be carefully monitored,
along with any measured values that are reported.
5 Initial instrument calibration, alignment and assessment
Before undertaking the procedure described in the following clauses, it is essential that the instrument
be calibrated and aligned to an optimum performance level. This is achieved by following the relevant
International Standards (References [5] to [9]) or the manufacturer’s instructions. Choose the two
settings of the instrument operating conditions that are needed to obtain survey spectra and high-
resolution spectra. These should be settings that you regularly use and are described in Clause 7. Since
this is a rapid check, only these two settings are chosen, but these can show faults that are common
to all settings. These settings shall always be used in future checks unless they are later found to be
less effective than other settings. If the designated settings are changed, data at both the new and old
settings shall be recorded at the time of change.
6 Test specimen selection
6.1 General information
Three types of test specimen are required for the full procedure described in this document: a
conductive specimen, a non-conductive specimen and a specimen suitable for assessing the quality
of the X-ray beam (e.g. X-ray spot size, shape and uniformity). The conductive specimen provides
information that the basic energy and intensity calibrations of the instrument are consistent from day
to day. When using a non-monochromatic X-ray source with more than one anode material, the survey
spectrum shall be examined to check for peaks arising from specimen irradiation from the anode that
is not currently being used (this is due to “cross-talk” within the X-ray source). Similarly, when anode
coatings wear, X-rays can be emitted from the substrate material, which is often copper. The survey
spectrum shall be examined for peaks arising from X-rays produced from the substrate material. When
using a magnesium anode, there can be peaks due to radiation from O Kα arising from oxidation of
the anode coating. These peaks are often called ghost peaks. In some instances, ghost peaks may be
removed from the spectrum by degassing the X-ray source (following the instrument manufacturer's
recommended procedure). Table 1 shows the approximate positions of commonly encountered ghost
peaks when acquiring an XPS spectrum from silver using Mg Kα radiation.
Table 1 — Examples of approximate positions on the binding-energy scale of frequently
encountered ghost peaks in a silver spectrum collected using a magnesium anode
Peak position on the
Radiation giving rise to Photon energy Possible origin of radia-
binding-energy scale
ghost peaks eV tion
eV
Al Kα 1 486,6 From second anode in a 135
twin anode source
O Kα 524,9 From oxide on the surface 1 097
of the magnesium anode
Cu Lα 929,7 From anode substrate 692
NOTE  The photon energy of Mg Kα radiation is 1 253,6 eV.
The non-conductive specimen is required to confirm that the charge compensation system is operating
satisfactorily when non-conducting specimens are being analysed. The nature of the specimen that is
required for assessing the X-ray beam depends upon the type of instrument being used. If the analysis
position is visible during the normal operation of the instrument, the quality of the focus and the
alignment of the X-ray beam from a monochromated source can be assessed using a phosphor specimen.
If the analysis position is not visible in normal operation and the instrument is capable of imaging, a
2 © ISO 2018 – All rights reserved

uniform (there should be no features visible in an image of the specimen when the instrument is in its
optimum condition), conductive specimen can be used; this can be the conductive specimen mentioned
previously. All specimens used shall be large enough to completely fill the defined analysis region of the
spectrometer.
6.2 The conductive specimen
A suitable conductive specimen shall be selected. This should be a material that produces several peaks
in the photoelectron spectrum. Preferably, these peaks should be widely spaced in binding energy. The
specimen shall be one whose surface can be cleaned easily by sputtering with noble-gas ions.
A pure (≥99,8 %) specimen of silver foil is suitable for this measurement and is recommended. If,
however, a different material is commonly analysed in the user’s laboratory and conforms to the above
criteria, this may be used instead. For convenience, it is assumed here that silver has been selected as
the conductive reference material. The same conductive specimen shall be used for all measurements.
6.3 The non-conductive specimen
Non-conductive specimens, and conductive specimens with a non-conductive surface layer, charge
under the X-ray flux, resulting in shifts in the peak binding energies relative to the uncharged state.
Select a non-conductive material often studied in your laboratory, of which you have a good stock and
which can be maintained with a surface in a reproducible state. If you are unsure of a material to use,
examples that have been found to be useful for tests of instrumental performance are shown in Table 2.
Examples are given with different forms. You might wish to select a specimen with a form similar to
that of the specimens most commonly analysed with the instrument. Care shall be taken to select a
material which does not exhibit degradation under the X-ray beam during the analysis.
Table 2 — Examples of non-conductive specimens that may be used for this procedure
Material Form Cleaning
PET Sheet or fibre Not required
Laboratory filter
Sheet Not required
paper
Poly(ethylene terephthalate) (PET) has long been used to evaluate both the energy resolution and the
effectiveness of charge control in XPS. It shows a structure of three C 1s peaks together with shake-
up intensity. The minimum between the peak at the lowest binding energy and the adjacent peak at
a separation of ~1,5 eV is highly sensitive to the combination of the instrumental resolution and the
uniformity of the charge correction. The ease of achieving suitable and consistent energy resolution
will depend on both the operator and the instrumental capability.
An example of the C 1s spectrum from PET is shown in Figure 1.
Key
X binding energy (eV)
Y number of counts
Figure 1 — Example of a C 1s spectrum from PET
More recently, careful studies on cellulose-based materials (paper) have indicated that these are
suitable materials for use in this test (see References [1] and [2]). It has been shown that laboratory
1)
filter paper provides reproducible XPS spectra. If using paper, avoid releasing loose fibres into the
instrument, as they can cause a deterioration in performance.
Alternatively, the specimen can be one with which the user is familiar. It shall be a material that
provides a reliably reproducible spectrum with little or no specimen preparation.
6.4 Specimen for assessing the X-ray source
A phosphor specimen is suitable for those instruments that are fitted with a monochromatic X-ray
source and in which the analysis position is visible, preferably with a microscope and camera. The
phosphor specimen should be as flat and uniform as possible and produce easily visible light under the
X-ray bombardment.
Not all phosphor specimens are vacuum-compatible and not all phosphor materials are designed for
optimum excitation by X-rays. Ensure that a phosphor specimen of suitable quality is obtained from the
2)
supplier of the instrument or from another reputable supplier.
1) A suitable type of filter paper is S&S 589 Blue Ribbon Ashless, which can be obtained from Whatman plc,
Springfield Mill, James Whatman Way, Maidstone, Kent, ME14 2LE, UK, or one of this company’s international
distributors. This information is given for the convenience of users of this document and does not constitute an
endorsement by ISO of this product.
2) Suitable phosphor specimens can be obtained from a number of suppliers, including TMS Vacuum Components,
Unit 21 Stirling Road, Castleham Industrial Estate, Hastings, East Sussex, TN38 9NP, UK. This information is given for
the convenience of users of this document and does not constitute an endorsement by ISO of this supplier.
4 © ISO 2018 – All rights reserved

The uniform conductive specimen shall be used if an optical image of the analysis position is not
available during the normal operation of the instrument and the instrument is capable of producing
X-ray-induced images. The specimen shall be flat and of uniform composition over an area greater than
the maximum area that is imaged in the instrument. The silver specimen described in 6.2 is suitable for
this purpose.
7 Collection of reference data
7.1 General information
Once fully calibrated and functioning correctly at the designated settings described in Clause 5, the
instrument shall be used to collect a set of reference data. The specimens and the way in which data
shall be collected are described in this clause. If the spectrometer is routinely used for conductive
specimens, follow the procedure described in 7.2 regularly and that in 7.3 occasionally. For instruments
used mainly for insulating specimens, follow the procedure described in 7.3 regularly and that in 7.2
occasionally. The interpretation of “regular” and “occasional” depends on the use of the instrument
and its behaviour. If data are critical, “regular” might need to be interpreted as daily. For modern
instruments used daily in normal use, “regular” may be interpreted as “an interval of one week” and
“occasionally” as “a period of one month”, but it should be stressed that the appropriate interval does
depend on the instrument and its intended use. Document your reasons for your choice of the intervals.
The control charts in Clause 9 will also be useful in determining the frequency at which checks should
be made.
All electron optics have an optimum focal point. The specimens shall be at the common focal point of
the analyser, the ion gun (if used), the neutralizer (if used) and the X-ray source. If the spectrometer is
equipped with an X-ray source whose height above the specimen is adjustable, the X-ray source shall be
in the same position for each test.
7.2 Rapid test of the instrument using a conductive specimen
7.2.1 Specimen mounting and pre-treatment
Mount the specimen on an appropriate specimen holder. It is important that the specimen be in good
electrical contact with the specimen holder. Place the specimen in the optimum analysis position in the
spectrometer. Take care to follow the manufacturer’s recommendations for positioning the specimen
at the focal point, or use whatever documented procedure is required for analysis. Ensure that all
specimen stage parameters (X, Y, Z, rotation and tilt) are correctly set.
If the instrument is fitted with a noble-gas ion gun, the specimen surface shall be cleaned by ion etching,
using conditions commonly found to be successful for this purpose and which remove a minimum
amount of material. A typical sputtering fluence for cleaning silver is 20 A⋅s/m . A typical value for the
ion energy is 3 keV. Excessive sputtering leads to significant roughening of the specimen so that it needs
frequent replacement.
7.2.2 Survey spectrum
A survey or wide-scan spectrum shall be collected over the binding-energy range from −10 eV to a
value within 50 eV of the value of the photon energy used
...