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

Overview

ISO 22581:2021 gives rules for identifying and correcting carbon-containing surface contamination using the X‑ray photoelectron spectroscopy (XPS) survey scan. It is intended for near real‑time or automated interpretation of XPS survey spectra where a C1s peak appears on materials not expected to include carbon as an intended component. The standard provides a simple, structured approach (in If - Then rule format) to decide whether the C1s signal is adventitious contamination, estimate an overlayer’s thickness, and correct measured composition for its attenuation effect.

Key topics and requirements

• Scope and limitations
  • Applies to thin, continuous contamination films on metals, alloys or films on inert substrates.
  • Not suitable for discontinuous particle deposits on substrates.
• Data source
  • Rules use only information from the XPS survey scan (recommended to include the C KVV Auger region).
  • Recommended acquisition parameters cited (e.g., step size ≤ 0.4 eV as per IUVSTA guidance).
• Rule set and decision logic
  • Identification rules are expressed as straightforward If - Then statements, enabling machine implementation for automated systems.
  • Criteria include presence of a C1s peak, expected sample composition (whether carbon is anticipated), spectral characteristics consistent with contamination, and evidence of a thin surface overlayer.
• Correction and quantification
  • Procedures for estimating film thickness and correcting substrate elemental intensities for attenuation by the carbon overlayer are provided.
  • Rules support near real‑time adjustment of composition derived from the survey scan without expert intervention.
• Practical considerations
  • Notes on contamination sources (airborne organics, packaging, spectrometer vacuum), charging reference usage, and risks of ion sputter removal altering surface chemistry.
  • Angle‑resolved XPS (ARXPS) can provide more detail but is not required by this standard.

Applications and users

• Surface chemists, materials scientists, corrosion researchers, and quality‑control labs using XPS/X‑ray photoelectron spectroscopy to analyze thin films and surfaces.
• Instrument manufacturers and software developers implementing automated spectral interpretation and near‑real‑time data reduction.
• Laboratories needing standardized, reproducible procedures to identify adventitious carbon, estimate contamination thickness, and correct quantitative surface composition rapidly.

Related standards and guidance

• References IUVSTA Workshop recommendations (acquisition guidance) and cross‑references ISO 19318 (charging correction considerations).
• Prepared by ISO/TC 201 (Surface chemical analysis) - aligns with other XPS data‑management standards.

Keywords: ISO 22581:2021, XPS survey scan, C1s peak, adventitious carbon, surface contamination, film thickness correction, automated XPS analysis, near real‑time surface analysis.

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 2021
© ISO 2021
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ii © ISO 2021 – 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 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
Foreword
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This document was prepared by Technical Committee ISO/TC 201, Surface chemical analysis,
Subcommittee SC 3, Data management and treatment.
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iv © ISO 2021 – All rights reserved

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.
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.
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

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
...