ISO 19318:2021

INTERNATIONAL ISO
STANDARD 19318
Second edition
2021-06
Surface chemical analysis — X-ray
photoelectron spectroscopy —
Reporting of methods used for charge
control and charge correction
Analyse chimique des surfaces — Spectroscopie de photoélectrons
— Indication des méthodes mises en œuvre pour le contrôle et la
correction de la charge
Reference number
ISO 19318:2021(E)
©
ISO 2021

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ISO 19318:2021(E)

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Published in Switzerland
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ISO 19318:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 1
5 Apparatus . 2
6 Calibration of binding-energy scale . 2
7 Reporting of information related to charge control . 2
7.1 General . 2
7.2 Information about specimen. 2
7.2.1 Specimen form . 2
7.2.2 Specimen dimensions . 2
7.2.3 Specimen mounting methods . 2
7.2.4 Specimen treatment prior to or during analysis . 3
7.3 Instrument and operating conditions . 3
7.4 General method for charge control . 3
7.5 Reasons for needing charge control and for choosing the particular method for
charge control . 3
7.6 Values of experimental parameters . 4
7.7 Information on the effectiveness of the method of charge control . 4
7.7.1 Adequacy of charge control . 4
7.7.2 Damage assessment . 4
8 Reporting of method(s) used for charge correction and the value of that correction .4
8.1 General . 4
8.2 Approach . 4
8.3 Value of correction energy . 5
Annex A (informative) Description of methods of charge control and charge correction .6
Bibliography .12
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ISO 19318:2021(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 of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .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 19318:2004), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— Clause 7 has been reorganized and 7.7 (effectiveness of charge control) has been updated;
— Annex A has been updated, in particular A.2.1 (specimen damage), A.2.5.2 (specimen isolation) and
A.3.3 (adventitious-hydrocarbon referencing);
— up-to-date bibliographical references have been added throughout the document.
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.
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ISO 19318:2021(E)

Introduction
X-ray photoelectron spectroscopy (XPS) is widely used for the characterization of surfaces of materials.
Elements in the test specimen (with the exception of hydrogen and helium) are identified from
comparisons of the binding energies of their core levels, determined from measured photoelectron
spectra, with tabulations of these binding energies for the various elements. Information on the
chemical state of the detected elements can frequently be obtained from small variations (typically
between 0,1 eV and 10 eV) of the core-level binding energies from the corresponding values for the pure
elements. Reliable determination of chemical shifts often requires that the binding-energy scale of the
XPS instrument be calibrated with an uncertainty that could be as small as 0,1 eV.
The surface potential of an insulating specimen will generally change during an XPS measurement due
to surface charging, and it is then difficult to determine binding energies with the accuracy needed
for elemental identification or chemical-state determination. There are two steps in dealing with this
problem:
a) experimental steps can be taken to minimize the amount of surface charging (charge-control
methods);
b) corrections for the effects of surface charging can be made after acquisition of the XPS data (charge-
correction methods).
Although the build-up of surface charge can complicate analysis in some circumstances, it can be
creatively used as a tool to gain information about a specimen.
The amount of induced charge near the surface, its distribution across the specimen surface, and its
dependence on experimental conditions are determined by many factors including those associated
[6,7]
with the specimen and characteristics of the spectrometer. Charge build-up is a well-studied, three-
dimensional phenomenon that occurs along the specimen surface and into the material. Charge build-
up can also occur at phase boundaries or interface regions within the depth of the specimen that is
irradiated by X-rays. Some specimens undergo time-dependent changes in the level of charging because
of chemical changes or volatilization induced by photoelectrons and secondary electrons, X-rays, or
heating. It is possible that such specimens will never achieve steady-state potentials.
There is no universally applicable method or set of methods for charge control or for charge correction.
[8-10]
This document specifies the information to be provided to document the method of charge control
during data acquisition or the method of charge correction during data analysis, or both. Annex A
describes common methods for charge control and charge correction that can be useful for many
applications. The particular charge-control method that is chosen in practice depends on the type of
specimen (e.g. powder, thin film or thick specimen), the nature of the instrumentation, the size of the
specimen, and the extent to which the specimen surface might be modified by a particular procedure.
This document identifies information on methods of charge control or charge correction, or both, to be
included in reports of XPS measurements (e.g. from an analyst to a customer or in publications) in order
to evaluate, assess and reproduce data on insulating materials and to ensure that measurements on
similar materials can be meaningfully compared. It enables published binding energies to be used with
confidence by other analysts and will lead to the inclusion of more reliable data in XPS databases.
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INTERNATIONAL STANDARD ISO 19318:2021(E)
Surface chemical analysis — X-ray photoelectron
spectroscopy — Reporting of methods used for charge
control and charge correction
1 Scope
This document specifies the minimum amount of information spectroscopy to be reported with the
analytical results to describe the methods of charge control and charge correction in measurements of
core-level binding energies for insulating specimens by X-ray photoelectron. It also provides methods
for charge control and for charge correction in the measurement of binding energies.
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 and definitions
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/
4 Symbols and abbreviated terms
BE binding energy, in eV
BE corrected binding energy, in eV
corr
BE measured binding energy, in eV
meas
BE measured binding energy of a reference material, in eV
ref,meas
BE reference binding energy, in eV
ref
FWHM full width at half maximum amplitude of a peak in the photoelectron spectrum above the
background, in eV
XPS X-ray photoelectron spectroscopy
Δ correction energy to be added to measured binding energies for charge correction, in eV
corr
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ISO 19318:2021(E)

5 Apparatus
One or more of the charge-control techniques, also called charge-neutralization techniques, mentioned
in Clause A.2 can be employed in most XPS spectrometers. The XPS instrument shall be operated in
accordance with the manufacturer’s instructions or other documented procedures.
Some of the techniques outlined in Clause A.2 require special apparatus, such as an electron flood gun
or a source for evaporative deposition of gold.
[11]
Certain specimen-mounting procedures, such as mounting the specimen under a fine metal mesh ,
can enhance electrical contact of the specimen with the specimen holder, or reduce the amount of
surface charge build-up. This and other methods of specimen mounting to reduce static charge are
described in References [4] and [5].
6 Calibration of binding-energy scale
The binding-energy scale of the X-ray photoelectron spectrometer shall be calibrated using ISO 15472
or another documented method before application of this document.
7 Reporting of information related to charge control
7.1 General
Methods commonly used to control the surface potential and to minimize surface charging are
summarized in Clause A.2. Information on the critical specimen and experimental conditions, as
specified in 7.2 through 7.7, shall be reported for individual specimens or collections of similar
specimens.
7.2 Information about specimen
7.2.1 Specimen form
The form of the specimen shall be reported. The physical nature, source, preparation method and
[7]
specimen structure can influence charging behaviour.
EXAMPLE 1 Powder.
EXAMPLE 2 Thin film spin-cast on silicon.
EXAMPLE 3 Macroscopic mineral specimen.
7.2.2 Specimen dimensions
The size and shape of a specimen can have a significant effect on the extent of specimen charging. The
shape of the specimen shall be reported together with approximate values of the dimensions of the
specimen or of any relevant specimen features (e.g. particle diameters).
7.2.3 Specimen mounting methods
[2-5, 10]
Specimen mounting and contact with the specimen holder can significantly impact charging . The
method by which a specimen is mounted, including information about special methods used to increase
conductivity or isolate a specimen from ground, shall be reported.
EXAMPLE 1 Powder specimen pressed into foil, which was attached to a specimen holder using tape.
EXAMPLE 2 1 ml of contaminated liquid deposited on a silicon substrate and dried prior to analysis.
EXAMPLE 3 Specimen held to specimen holder using conductive adhesive tape of a specified type.
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ISO 19318:2021(E)

EXAMPLE 4 Corroded specimen held on specimen holder by metal screw.
7.2.4 Specimen treatment prior to or during analysis
The specimen treatment prior to or during analysis shall be reported, including any physical or chemical
treatment that can affect charging of the specimen during XPS measurements.
EXAMPLE 1 Gold deposition.
EXAMPLE 2 Ar gas implantation from sputter ion source.
NOTE Such treatment of the specimen can modify the surface composition as well as the electrical
conductivity, and hence charging, of the surface region.
7.3 Instrument and operating conditions
The instrument operating conditions shall be reported, including details of the:
— particular XPS instrument;
— nature of the X-ray source;
— approximate size of the X-ray beam on the specimen surface;
— analyser pass energy;
— measure of energy resolution such as the FWHM of the silver 3d photoelectron line for the
5/2
selected operating conditions;
— angle between the specimen normal and the X-ray source;
— use or not of a magnetic lens.
7.4 General method for charge control
The particular instrumental component(s) used for charge control shall be identified.
EXAMPLE 1 Electron flood gun.
EXAMPLE 2 Electron flood gun in combination with an ion gun.
EXAMPLE 3 Specimen heating.
EXAMPLE 4 Irradiation with ultraviolet light.
[10]
EXAMPLE 5 Vendor XYZ charge neutralization system.
If the components used are not standard for the XPS instrument, information shall be provided on the
manufacturer or on the relevant design characteristics.
7.5 Reasons for needing charge control and for choosing the particular method for
charge control
The reasons for needing charge control and for choosing a particular method shall be reported.
EXAMPLE 1 The portion of the specimen of interest was isolated from ground. Flood gun electrons were
supplied for charge compensation using the standard flood gun for this instrument.
EXAMPLE 2 Experience with similar specimens indicated that differential charging was likely. To obtain good
spectra, these specimens were totally isolated from ground. The application of the combined fluxes of a low-
energy electron flood gun and a low-energy ion flux produced well-resolved peaks.
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ISO 19318:2021(E)

EXAMPLE 3 Initial spectra without any charge control showed peak shifting and broadening. Placing a
grounded fine grid above the specimen solved these problems without leading to a significant signal due to the
grid material. This method is easy to apply and is used routinely in measurements with similar specimens.
7.6 Values of experimental parameters
Values of parameters used to control charge, such as flood gun settings, shall be reported. Information
about typical parameters for some charge neutralization systems on modern instruments is provided
in Reference [10].
EXAMPLE For the flood gun, the cathode voltage was −5 V (with respect to instrumental ground), the
emission current was 20 mA, and the gun cathode was 5 cm from the specimen.
7.7 Information on the effectiveness of the method of charge control
7.7.1 Adequacy of charge control
The adequacy of the charge-control methods for the type of analysis being conducted shall be
established. FWHMs and the binding energies (BE ) of peaks in the measured spectra, after charging
meas
effects have been minimized, but before any charge correction has been made, provide one useful
method for determining adequacy of the charge-control method. To document the effectiveness of the
procedure(s) used to produce appropriate BE and FWHM measurements, it can be useful to have as a
comparison a measurement of the FWHM of at least one photoelectron peak of similar chemistry in
another specimen that is known to be conductive or for which the method of charge control is believed
to be effective.
EXAMPLE 1 The FWHM of the oxidized Si 2p photoline was reduced from 2,4 eV to 1,6 eV by application of a
flood gun. The 1,6 eV width is consistent with measurements made on a thin SiO layer on Si.
2
EXAMPLE 2 The ability to control charge compensation over a wide energy range can be documented by
measuring the energy separation between different photoelectron peaks from the same element. The adequacy
of such a measurement assumes that there are no complications due to chemical state changes with depth or the
presence of second phases.
7.7.2 Damage assessment
It is recommended that specimens be examined for the presence or absence of specimen damage due
to sample charging or the impact of the charge neutralization method (see A.2.1) and that the results
be recorded. If damage is observed, changes to the charge neutralization parameters can need to be
adjusted and the changes recorded.
EXAMPLE Survey scans at the start and end of data collection showed no changes suggestive of intensity of
peak structure changes due to damage.
8 Reporting of method(s) used for charge correction and the value of that
correction
8.1 General
Many of the methods commonly used for charge correction are summarized in Clause A.3. The critical
specimen and experimental parameters in 8.2 and 8.3 shall be reported.
8.2 Approach
The general method for correcting measured binding energies (peak positions) for charging effects
shall be specified in sufficient detail so that the method can be reproduced and the effectiveness judged.
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ISO 19318:2021(E)

8.3 Value of correction energy
Information shall be given on the magnitude of the correction energy (Δ ) for each spectrum and
corr
how this correction energy was determined. The corrected binding energies and values of the reference
energies shall be reported.
The correction energy (Δ ) is determined by taking the difference between the measured binding
corr
energy of a reference line (BE ) and an appropriate binding energy value (BE ) for the reference
ref,meas ref
line (obtained from the literature or other trusted source) using Formula (1):
Δ = BE – BE (1)
corr ref ref,meas
The corrected binding energy for another photoelectron peak in the same spectrum (BE ) can then
corr
be found from the sum of the measured binding for that peak (BE ) and the correction energy:
meas
BE = BE + Δ (2)
corr meas corr
NOTE Formulae (1) and (2) apply only when charge compensation has adequately removed differential
charging effects.
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ISO 19318:2021(E)

Annex A
(informative)

Description of methods of charge control and charge correction
A.1 General
This annex describes methods involving charge control, also called charge neutralization (the effort to
control or minimize the build-up of charge at a surface or to minimize its effect, or both), as described
in Clause A.2; charge correction (the effort to determine a reliable binding energy despite any build-up
of charge) as described in Clause A.3; or some combination of the two as described in Clause A.4.
For charge control, peak shape is one of the most important parameters to consider in assessing
the effectiveness of a method. Correcting a measured peak-energy position (i.e. binding energy) is
accomplished separately using an appropriate charge-correction technique. When both a photoelectron
line and a major Auger peak from the same element can be observed, the Auger parameter or the
modified Auger parameter, described in Clause A.5, can be used to provide chemical-state information
without the need to resort to charge corrections. Although the build-up of charge during XPS is often an
unwanted complication, it can also be used to obtain important information about a specimen as noted
in A.2.5.2 and A.2.5.3.
The amount and distribution of surface and near-surface charge for a specific experimental system are
determined by many factors, including specimen composition, homogeneity, magnitude of bulk and
surface conductivities, photoionization cross-section, surface topography, spatial distribution of the
exciting X-rays, and availability of neutralizing electrons. Charge build-up occurs along the specimen
[6,7]
surface and into the material. The presence of particles on or different phases in the specimen
surface can result in an uneven distribution of charge across the surface, a phenomenon known as
differential charging. Charge build-up can also occur at phase boundaries or interface regions within
the specimen that is irradiated by X-rays. Some specimens undergo time-dependent changes in the
amount of charging because of chemical and physical changes induced by electrons, X-rays or heat.
[8,10]
There is no single method to overcome all charging problems in all instruments. Several new
methods were developed in the 1990s, including those that involve electrons, ions or magnetic fields, or
both. All methods described in this annex assume that charging is not dependent on the kinetic energy
of the signal electrons. It is possible that this will not be the case for some spectrometers or when
differential charging occurs as a function of depth into the specimen. As reported in 2000, an inter-
laboratory comparison of static-charge stabilization methods for a variety of insulating specimens
using referencing to both gold and carbon showed that the standard deviation of the binding-energy
[9]
measurements from 27 laboratories was, at best, 0,15 eV. The report concluded that the reproducibility
was unsatisfactory and that considerable additional work was needed.
A.2 Methods of charge control
A.2.1 Damage caution
[6,10]
Both the build-up of surface charge during XPS and the methods that minimize charge accumulation
[10,12]
can induce damage in some samples. As some of the charge neutralization methods involve
charged-particle or photon irradiation or the addition of materials to the surface, the possibility of
specimen damage or specimen change from any such irradiations or treatments should be considered
[13,14]
and tested by comparing data at different times during data collection.
Multiple approaches can be used to check for damage. Some analysts take a rapid survey before and
after high resolution scans and examine for differences as an indication of damage. Especially for
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ISO 19318:2021(E)

known or suspected sensitive materials, analysts can take a rapid high-resolution scan of the sensitive
species before most of the data collection and compare the initial scan with a similar scan after the
majority of data is collected.
Reference [12] demonstrated that standard neutralizer operating conditions can be damaging to
particularly sensitive samples, however, it is possible to alter the operation conditions to get effective
charge neutralization while minimizing damage.
[15-18]
A.2.2 Electron flood gun
Low-energy electron flood guns are frequently used to stabilize the static charging of insulators
[16]
examined by XPS, in particular when monochromatized X-rays are employed. Optimum operating
conditions, for example, filament position, electron energy and electron current, depend upon the
orientation of the electron flood gun with respect to the specimen and upon the particular design of
the electron flood gun and should, in general, be determined by the user. Low electron energies (usually
10 eV or less) are used to maximize the neutralization effect and reduce the number of electron-
bombardment-induced reactions. Currents need to be high enough to be effective, but low enough to
avoid specimen damage or unwanted heating. A metal screen placed on or above the specimen can help.
[19,20]
[21]
A.2.3 Ultraviolet flood lamp
Ultraviolet radiation can produce low-energy electrons (e.g. from the specimen holder) that can be
useful in neutralizing specimen charge.
A.2.4 Specimen heating
For a limited number of specimens, heating can increase the electrical conductivity of the specimen,
[7]
thus decreasing charging. The effects of specimen temperature and possible surface segregation
need to be considere
...