ISO 22581:2021

Surface chemical analysis — Near real-time information from the X-ray photoelectron spectroscopy survey scan — Rules for identification of, and correction for, surface contamination by carbon-containing compounds

This document is provided to assist in the surface analysis of thin films on materials which are not thought to contain carbon compounds as intended components but for which a C1s peak is observed in the survey spectrum. The films can be those generated on metals and alloys by aerobic or electrochemical oxidation or be those deposited on inert substrates. The procedure described is not suitable for discontinuous deposits of particles on a substrate. With this exception, a simple procedure is provided for identifying the C1s signal from carbon-containing surface contamination. When the C1s peak is identified as arising from an adventitious over-layer the composition derived from the survey spectrum can be corrected for its influence. Recommended procedures are provided in the form of simple Rules structured in the 'If - Then` format with the intention that the information they embody might be utilised by automated procedures in data-systems. The rules provided utilize only information retrieved from the XPS survey scan.

Analyse chimique des surfaces — Informations en temps quasi réel issues du balayage d’ensemble par spectroscopie photoélectronique à rayonnement X (XPS) — Règles portant sur l'identification et la correction d'une contamination des surfaces par des composés contenant du carbone

General Information

• Status: Published
• Publication Date: 11-Mar-2021
• ICS: 71.040.40 - Chemical analysis
• Technical Committee: ISO/TC 201/SC 3 - Data management and treatment
• Drafting Committee: ISO/TC 201/SC 3 - Data management and treatment
• Current Stage: 6060 - International Standard published
• Start Date: 12-Mar-2021
• Due Date: 05-Jul-2021
• Completion Date: 12-Mar-2021

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 22581
First edition
2021-03
Surface chemical analysis — Near
real-time information from the X-ray
photoelectron spectroscopy survey
scan — Rules for identification of, and
correction for, surface contamination
by carbon-containing compounds
Analyse chimique des surfaces — Informations en temps quasi réel
issues du balayage d’ensemble par spectroscopie photoélectronique
à rayonnement X (XPS) — Règles portant sur l'identification et
la correction d'une contamination des surfaces par des composés
contenant du carbone
Reference number
ISO 22581:2021(E)
©
ISO 2021

---------------------- Page: 1 ----------------------
ISO 22581:2021(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 22581:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 Sample contamination. 2
5.1 General . 2
5.2 Causes of contamination . 2
5.3 Recognition of contamination . 3
5.3.1 Construction of rules based on sample description . 3
5.3.2 Rules for use of the sample history . 4
5.3.3 Rules for use of peak positions . 4
5.3.4 Rule to establish carbon type . 6
5.3.5 Rules identifying C1s as arising from absorbed material in the form of a
thin film . . . 7
5.3.6 Achievement of the goal . 9
6 Estimation of film thickness and correction for its impact . 9
6.1 Film thickness . 9
6.2 Correction of substrate composition .10
Annex A (informative) Flow diagrams for operation of rules .11
Bibliography .16
© ISO 2021 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 22581:2021(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 3, Data management and treatment.
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 2021 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 22581:2021(E)

Introduction
The basis of X-ray photoelectron spectroscopy is irradiation of a sample surface by soft X-rays and
examination of the excited emission in the form of photo- and Auger electrons. In its most widely used
mode the X-ray flux is of low intensity and spread over a large area. Thus, the technique is generally
regarded as one of the least destructive of the available ‘beam’ techniques used for analysis of materials’
surfaces. The increasingly wide use of the technique makes the development of rule sets, that enable
accurate information retrieval, highly important and this document helps to meet this need.
In many cases the surface for which a composition is desired will have accreted a film of contamination,
frequently organic in nature and arising from adsorption of molecules from the atmosphere, from the
exposure to a working or test environment, or from the spectrometer itself. This film attenuates the
different regions of the spectrum to a different extent, depending on the kinetic energy of the electron
emitted in that region. Thus correction and removal of this influence is necessary for the desired
surface composition of the substrate to be achieved. The procedure to be described enables recognition
of the presence of carbon-containing contamination, an estimate of its thickness, and the removal
of its influence on the measured surface composition. It is thus an integral part of data reduction in
quantitative evaluation of the XPS Survey Scan. This could be automated within a data system and
would be an essential first step in provision of a means for automatic retrieval of information from the
survey scan for a number of technologies dependent on surface analysis.
All procedures described are intended to be based only on an XPS survey scan obtained in the fashion
[9] [10]
recommended in the conclusions of the IUVSTA Workshops 22 and 34 : they can be carried out in
a manner which does not require intervention by an expert spectroscopist and could be adopted in an
automated data system.
© ISO 2021 – All rights reserved v

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 22581:2021(E)
Surface chemical analysis — Near real-time information
from the X-ray photoelectron spectroscopy survey scan
— Rules for identification of, and correction for, surface
contamination by carbon-containing compounds
1 Scope
This document is provided to assist in the surface analysis of thin films on materials which are not
thought to contain carbon compounds as intended components but for which a C1s peak is observed
in the survey spectrum. The films can be those generated on metals and alloys by aerobic or
electrochemical oxidation or be those deposited on inert substrates. The procedure described is not
suitable for discontinuous deposits of particles on a substrate. With this exception, a simple procedure
is provided for identifying the C1s signal from carbon-containing surface contamination. When the C1s
peak is identified as arising from an adventitious over-layer the composition derived from the survey
spectrum can be corrected for its influence. Recommended procedures are provided in the form of
simple Rules structured in the 'If – Then' format with the intention that the information they embody
might be utilised by automated procedures in data-systems. The rules provided utilize only information
retrieved from the XPS survey scan.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
region
part of the fully accessible photo-excited spectrum chosen for acquisition in a detail, i.e. ‘narrow’, scan
Note 1 to entry: The region may be chosen because it contains a major or minor peak of a given element or to
represent the shape or slope of a background within that energy range.
3.2
survey scan
scan or series of scans across the major part of the photo-electron spectrum excited by a given
X-ray source
3.3
goal
achievement of an objective which is part of the process of the interpretation of a spectrum
Note 1 to entry: For example, the completion of a quantitative analysis can be thought of as the achievement
of a goal.
© ISO 2021 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO 22581:2021(E)

4 Symbols and abbreviated terms
maximum value (cps) above a line drawn at constant intensity from a point on the linear
a
region of the energy-loss background following the C1s peak
interval (eV) between the point on the linear background chosen as a reference in the
b measurement of ‘a’ and the position of the value (eV) at which ‘a’ is measured. It is an-
ticipated that the interval will be of the order of 30eV
C atomic fraction of carbon in the contamination layer
contamination
d thickness of the contamination layer
contamination
D parameter separation, in eV, of the maximum and deepest minimum peaks in the differential of
the C KVV Auger peak
E electron kinetic energy in eV of the peak to be corrected for overlayer contamination
I measured intensity of the peak corresponding to element Z
z,measured
I corrected intensity of the peak corresponding to element Z
z,corrected
IUVSTA International Union for Vacuum Science, Technique and Applications
k Shirley scattering factor
L attenuation length of C1s electrons in the contamination layer.
C
L attenuation length of electrons in the contamination layer corresponding to element Z
z
θ angle of emission of the detected electrons with respect to the surface normal
QUASES Quantitative Analysis of Surface Electron Spectra
SESSA Simulation of Electron Spectra for Surface Analysis
XPS X-ray photoelectron spectroscopy
5 Sample contamination
5.1 General
The C1s peak is frequently observed in the XP spectrum of material samples that are not thought to
include carbon in their composition. In a small number of cases, the peak is an important indicator of
an unexpected surface composition, e.g. the surface film on Aluminium-Lithium alloys that have been
exposed to air will often include lithium carbonate. However, in most cases, the C1s peak is an indicator
of the presence of an adsorbed film of organic compounds, normally referred to as a contamination
layer. Contamination may consist of an aliphatic chain having a polar end group which strongly adsorbs
to many surfaces. The film so formed can strongly attenuate the intended signal arising from the
substrate under investigation. Because of this, some analysts are tempted to remove the film by brief
use of a conventional monatomic ion gun. This procedure will greatly enhance the spectrum intensity
but only at the expense of serious and irrecoverable changes to the surface chemistry.
5.2 Causes of contamination
The sources of such contamination are widespread: surfactant molecules will be picked up from the
meniscus film of aqueous media during the course of electrochemical or other test procedures; the air
itself contains a wide variety of easily and strongly adsorbed molecules in the form of softening agents
used in laundry activities, personal care products, or petrochemical compounds released from transport
2 © ISO 2021 – All rights reserved

---------------------- Page: 7 ----------------------
ISO 22581:2021(E)

vehicles; or films can be generated from the packaging used to convey samples to the laboratory
(especially when plasticizing agents have been used in manufacture of the ‘plastic’ bags often used for
transport). Adsorption can occur within the spectrometer from contamination of the vacuum by vapour
from the diffusion or oil pumps or from vapours released from prior examination of other samples, or
even in cases of technological samples, from the analysed sample itself. Adsorption of contaminants
is influenced by the hydrophobic/hydrophilic character of the surface, or in aqueous media, by the
electropotential of the surface and so differing materials may have differing susceptibilities to the
formation of a contaminant layer.
It should be noted that the presence and composition of a contaminating surface film can be obtained
using ARXPS (angle-resolved XPS) but this degree of detail may not be available, either because of a lack
of suitable equipment or because of a constraint on the time available for such a study.
5.3 Recognition of contamination
The correct identification of a given C1s peaks as being derived from and indicative of the presence of
a thin film of adsorbed organic compounds is important. The ubiquitous character of a contamination
film has given rise to the advice that its C1s peak can be used as a reference peak (nominally 285 eV)
for correction of any electrostatic charging (see ISO 19318); it is important that it is not confused with
an actual component of the material surface; and it is important that it is recognised as having the
characteristics of a surface film since it is only in this case that the whole spectrum can be corrected
for the consequential attenuation. Recognition is based on a mix of probabilities that a contamination is
present; that it is not anticipated to be present in the material sample; and that it has the characteristics
of a surface film. The means to assess that these attributes are associated with the C1s peak are
outlined in the following paragraphs. Each single identifier of an attribute is given in Table 1 in the form
of ‘If – Then’ statements which can be utilised for computer-based, near real-time correction of the XP
spectrum for the effect of a contamination film.
[11],[12],[13]
In published work it was shown that the identification and characterisation of a contamination
layer is reached by setting a goal, defined by an object, 'Carbon_Contamination', having the value 'Yes'.
The achievement of this goal marks the end of a stage in the analysis and enables further interpretation
of the spectrum. It should be noted that analysts who are experts in reviewing the XPS survey spectrum
will recognise the C1s peak on many materials for what it is – contamination. For them, this document
will give some guidance in answering the client who asks 'how do you know'. For non-experts it will
give some assurance that they may safely assume the carbon peak to be generated by contamination
but for those designing machine-assisted interpretation of a survey spectrum the analysis set out here
is essential. A useful discussion of the suggested methodology, and possible pitfalls have been given by
[14] [15]
Vegh and an example of its actual use in near real-time surface analysis has been given by Lea et al .
To reach the goal with 100 % certainty, it shall be established:
— that a photoelectron peak for carbon is present in the spectrum;
— that it is not expected for carbon to be part of the sample material, i.e. it is adventitious in character;
— that it has certain characteristics of contamination carbon;
— that it has an impact on the sp
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 22581
ISO/TC 201/SC 3
Surface chemical analysis — Data
Secretariat: BSI
management and treatment - Near
Voting begins on:
2020­12­14 real time information from the X-ray
photoelectron spectroscopy survey
Voting terminates on:
2021­02­08
scan — Rules for identification of, and
correction for surface contamination
by carbon-containing compounds
Analyse chimique des surfaces — Gestion et traitement des données -
Informations en temps quasi réel issues du balayage d’ensemble par
spectroscopie photoélectronique à rayonnement X (XPS) — Règles
portant sur l'identification et la correction d'une contamination des
surfaces par des composés contenant du carbone
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 22581:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
©
NATIONAL REGULATIONS. ISO 2020

---------------------- Page: 1 ----------------------
ISO/FDIS 22581:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH­1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/FDIS 22581:2020(E)

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 Sample contamination. 2
5.1 General . 2
5.2 Causes of contamination . 2
5.3 Recognition of contamination . 3
5.3.1 Construction of rules based on sample description . 3
5.3.2 Rules for use of the sample history . 4
5.3.3 Rules for use of peak positions . 4
5.3.4 Rule to establish carbon type . 6
5.3.5 Rules identifying C1s as arising from absorbed material in the form of a
thin film . . . 7
5.3.6 Achievement of the goal . 9
6 Estimation of film thickness and correction for its impact .10
6.1 Film thickness .10
6.2 Correction of substrate composition .10
Annex A (informative) Flow diagrams for operation of rules .11
Bibliography .16
© ISO 2020 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/FDIS 22581:2020(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 non­governmental, 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 3, Data Management and Treatment.
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 2020 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/FDIS 22581:2020(E)

Introduction
The basis of X-ray photoelectron spectroscopy is irradiation of a sample surface by soft X-rays and
examination of the excited emission in the form of photo- and Auger electrons. In its most widely used
mode the X-ray flux is of low intensity and spread over a large area. Thus, the technique is generally
regarded as one of the least destructive of the available ‘beam’ techniques used for analysis of materials’
surfaces. The increasingly wide use of the technique makes the development of rule sets, that enable
accurate information retrieval, highly important and this document helps to meet this need.
In many cases the surface for which a composition is desired will have accreted a film of contamination,
frequently organic in nature and arising from adsorption of molecules from the atmosphere, from the
exposure to a working or test environment, or from the spectrometer itself. This film attenuates the
different regions of the spectrum to a different extent, depending on the kinetic energy of the electron
emitted in that region. Thus correction and removal of this influence is necessary for the desired
surface composition of the substrate to be achieved. The procedure to be described enables recognition
of the presence of carbon­containing contamination, an estimate of its thickness, and the removal
of its influence on the measured surface composition. It is thus an integral part of data reduction in
quantitative evaluation of the XPS Survey Scan. This could be automated within a data system and
would be an essential first step in provision of a means for automatic retrieval of information from the
survey scan for a number of technologies dependent on surface analysis.
All procedures described are intended to be based only on an XPS survey scan obtained in the fashion
[9] [10]
recommended in the conclusions of the IUVSTA Workshops 22 and 34 : they can be carried out in
a manner which does not require intervention by an expert spectroscopist and could be adopted in an
automated data system.
© ISO 2020 – All rights reserved v

---------------------- Page: 5 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 22581:2020(E)
Surface chemical analysis — Data management and
treatment - Near real time information from the X-ray
photoelectron spectroscopy survey scan — Rules for
identification of, and correction for surface contamination
by carbon-containing compounds
1 Scope
This document is provided to assist in the surface analysis of thin films on materials which are not
thought to contain carbon compounds as intended components but for which a C1s peak is observed
in the survey spectrum. The films can be those generated on metals and alloys by aerobic or
electrochemical oxidation or be those deposited on inert substrates. The procedure described is not
suitable for discontinuous deposits of particles on a substrate. With this exception, a simple procedure
is provided for identifying the C1s signal from carbon-containing surface contamination. When the C1s
peak is identified as arising from an adventitious over-layer the composition derived from the survey
spectrum can be corrected for its influence. Recommended procedures are provided in the form of
simple Rules structured in the 'If – Then' format with the intention that the information they embody
might be utilised by automated procedures in data-systems. The rules provided utilize only information
retrieved from the XPS survey scan.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
region
part of the fully accessible photo-excited spectrum chosen for acquisition in a detail, i.e. ‘narrow’, scan
Note 1 to entry: The region may be chosen because it contains a major or minor peak of a given element or to
represent the shape or slope of a background within that energy range.
3.2
survey scan
scan or series of scans across the major part of the photo-electron spectrum excited by a given
X-ray source
3.3
goal
achievement of an objective which is part of the process of the interpretation of a spectrum
Note 1 to entry: For example, the completion of a quantitative analysis can be thought of as the achievement
of a goal.
© ISO 2020 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO/FDIS 22581:2020(E)

4 Symbols and abbreviated terms
maximum value (cps) above a line drawn at constant intensity from a point on the linear
a
region of the energy-loss background following the C1s peak.
interval (eV) between the point on the linear background chosen as a reference in the
b measurement of ‘a’ and the position of the value (eV) at which ‘a’ is measured. It is an­
ticipated that the internal will be of the order of 30eV.
C atomic fraction of carbon in the contamination layer
contamination
d , thickness of the contamination layer
contamination
D parameter separation, in eV, of the maximum and deepest minimum peaks in the differential of
the C KVV Auger peak
E electron kinetic energy in eV of the peak to be corrected for overlayer contamination
I measured intensity of the peak corresponding to element Z
z,measured
I corrected intensity of the peak corresponding to element Z
z,corrected
IUVSTA International Union for Vacuum Science, Technique and Applications
k Shirley scattering factor
L attenuation length of C1s electrons in the contamination layer.
C
L attenuation length of electrons in the contamination layer corresponding to element Z
z
θ angle of emission of the detected electrons with respect to the surface normal
QUASES Quantitative Analysis of Surface Electron Spectra
SESSA Simulation of Electron Spectra for Surface Analysis
XPS X-ray photoelectron spectroscopy
5 Sample contamination
5.1 General
The C1s peak is frequently observed in the XP spectrum of material samples that are not thought to
include carbon in their composition. In a small number of cases, the peak is an important indicator of
an unexpected surface composition, e.g. the surface film on Aluminium-Lithium alloys that have been
exposed to air will often include lithium carbonate. However, in most cases, the C1s peak is an indicator
of the presence of an adsorbed film of organic compounds, normally referred to as a contamination
layer. Contamination may consist of an aliphatic chain having a polar end group which strongly adsorbs
to many surfaces. The film so formed can strongly attenuate the intended signal arising from the
substrate under investigation. Because of this, some analysts are tempted to remove the film by brief
use of a conventional monatomic ion gun. This procedure will greatly enhance the spectrum intensity
but only at the expense of serious and irrecoverable changes to the surface chemistry.
5.2 Causes of contamination
The sources of such contamination are widespread: surfactant molecules will be picked up from the
meniscus film of aqueous media during the course of electrochemical or other test procedures; the
air itself contains a wide variety of easily and strongly adsorbed molecules in the form of softening
agents using in laundry activities, personal care products, or petrochemical compounds released
2 © ISO 2020 – All rights reserved

---------------------- Page: 7 ----------------------
ISO/FDIS 22581:2020(E)

from transport vehicles; or films can be generated from the packaging used to convey samples to the
laboratory (especially when plasticizing agents have been used in manufacture of the ‘plastic’ bags
often used for transport). Adsorption can occur within the spectrometer from contamination of the
vacuum by vapour from the diffusion or oil pumps or from vapours released from prior examination of
other samples, or even in cases of technological samples, from the analysed sample itself. Adsorption
of contaminants is influenced by the hydrophobic/hydrophilic character of the surface, or in
aqueous media, by the electropotential of the surface and so differing materials may have differing
susceptibilities to the formation of a contaminant layer.
It should be noted that the presence and composition of a contaminating surface film can be obtained
using ARXPS (angle-resolved XPS) but this degree of detail may not be available, either because of a lack
of suitable equipment of because a constraints on the time available for such a study.
5.3 Recognition of contamination
The correct identification of a given C1s peaks as being derived from and indicative of the presence of
a thin film of adsorbed organic compounds is important. The ubiquitous character of a contamination
film has given rise to the advice that its C1s peak can be used as a reference peak (nominally 285 eV)
for correction of any electrostatic charging (see ISO 19318); it is important that it is not confused with
an actual component of the material surface; and it is important that it is recognised as having the
characteristics of a surface film since it is only in this case that the whole spectrum can be corrected
for the consequential attenuation. Recognition is based on a mix of probabilities that a contamination is
present; that it is not anticipated to be present in the material sample; and that it has the characteristics
of a surface film. The means to assess that these attributes are associated with the C1s peak are
outlined in the following paragraphs. Each single identifier of an attribute is given In Table 1 in the form
of ‘If – Then’ statements which can be utilised for computer­based, near­real­time correction of the XP
spectrum for the effect of a contamination film.
[11][12][13]
In published work it was shown that the identification and characterisation of a contamination
layer is reached by setting a goal, defined by an object, 'Carbon_Contamination', having the value 'Yes'.
The achievement of this goal marks the end of a stage in the analysis and enables further interpretation
of the spectrum. It should be noted that analysts who are expert in reviewing the XPS survey spectrum
will recognise the C1s peak on many materials for what it is – contamination. For them, this Standard
will give some guidance in answering the client who asks 'how do you know'. For non-experts it will
give some assurance that they may safely assume the carbon peak to be generated by contamination
but for those designing machine-assisted interpretation of a survey spectrum the analysis set out here
is essential. A useful discussion of the suggested methodology, and possible pitfalls have been given by
[14] [15]
Vegh and an example of its actual use in near-real-time surface analysis has been given by Lea et al .
To reach the goal with 100 % certainty, it shall be established:
— th
...