ISO 18554:2016

Surface chemical analysis — Electron spectroscopies — Procedures for identifying, estimating and correcting for unintended degradation by X-rays in a material undergoing analysis by X-ray photoelectron spectroscopy

ISO 18554:2016 provides a simple procedure for identifying, estimating and correcting for unintended degradation in the elemental composition or chemical state of a material which occurs as a result of X-radiation during the time that a specimen material is exposed to the X-rays used in X-ray photoelectron spectroscopy (XPS). ISO 18554:2016 does not address comparisons between different types of material nor does it address the mechanisms, depth, or chemical nature of the degradation that occurs. The correction procedure proposed is only valid if the changes are caused by the X-rays and result in less than a 30 % reduction or increase in intensity of a chosen photoelectron peak from the sample material.

Analyse chimique des surfaces — Spectroscopie d'électrons — Procédures pour l'identification, l'estimation et la correction de la dégradation involontaire par rayons X pendant une analyse de matériau par spectroscopie de photoélectrons par rayons X

General Information

• Status: Published
• Publication Date: 17-Mar-2016
• ICS: 71.040.40 - Chemical analysis
• Technical Committee: ISO/TC 201/SC 7 - Electron spectroscopies
• Drafting Committee: ISO/TC 201/SC 7 - Electron spectroscopies
• Current Stage: 9093 - International Standard confirmed
• Start Date: 17-Jun-2021
• Completion Date: 17-Jun-2021

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 18554
First edition
2016-03-15
Surface chemical analysis — Electron
spectroscopies — Procedures for
identifying, estimating and correcting
for unintended degradation by X-rays
in a material undergoing analysis by
X-ray photoelectron spectroscopy
Analyse chimique des surfaces — Spectroscopie d’électrons —
Procédures pour l’identification, l’estimation et la correction de
la dégradation involontaire par rayons X pendant une analyse de
matériau par spectroscopie de photoélectrons par rayons X
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Terms and definitions . 1
3 Symbols and abbreviated terms . 1
4 Sample degradation . 2
4.1 Causes of degradation . 2
4.2 Sample degradation . 3
4.3 Measurements for identifying, and correcting for, degradation . 3
4.3.1 Recognition of degradation . 3
4.3.2 The first survey scan. 3
4.3.3 The detail scans . 4
4.3.4 The final survey scan . 4
4.3.5 Inverting the order of acquisition for unstable compounds . 4
4.3.6 Check for degradation . 4
4.3.7 Deduce the undegraded intensity . 4
4.4 Assessing the likelihood of degradation . 6
4.4.1 Determining the value of A . 6
Z
4.5 Reporting degradation . 6
4.6 Suggested procedures for minimising degradation . 6
4.7 Influence of contamination . 7
4.7.1 Contamination formation during spectrum acquisition. 7
4.7.2 Reporting contamination . 7
Annex A (informative) Materials reported to degrade during analysis . 8
Annex B (informative) Examples of degradation . 9
Annex C (informative) Compensation for formation of a contamination layer.14
Bibliography .16
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
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electrotechnical standardization.
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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
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The committee responsible for this document is ISO/TC 201, Surface chemical analysis, Subcommittee
SC 7, Electron spectroscopies.
iv © ISO 2016 – 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-electrons 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 the
surface chemical analysis of materials. However, since the time of its inception as a technique for surface
[1]-
analysis, there have been reports of changes in composition arising during the course of analysis.
[4]
These reports indicated that, for some materials, a form of degradation during analysis needs to
be taken into account and, where possible, a correction made. This International Standard addresses
these issues and describes a method by which the extent of degradation can be estimated and a suitable
correction obtained.
INTERNATIONAL STANDARD ISO 18554:2016(E)
Surface chemical analysis — Electron spectroscopies —
Procedures for identifying, estimating and correcting for
unintended degradation by X-rays in a material undergoing
analysis by X-ray photoelectron spectroscopy
1 Scope
This International Standard provides a simple procedure for identifying, estimating and correcting for
unintended degradation in the elemental composition or chemical state of a material which occurs as
a result of X-radiation during the time that a specimen material is exposed to the X-rays used in X-ray
photoelectron spectroscopy (XPS).
This International Standard does not address comparisons between different types of material nor does
it address the mechanisms, depth, or chemical nature of the degradation that occurs. The correction
procedure proposed is only valid if the changes are caused by the X-rays and result in less than a 30 %
reduction or increase in intensity of a chosen photoelectron peak from the sample material.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
region
part of the photo-excited spectrum chosen for detailed acquisition and analysis
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, e.g. a detail scan.
Note 2 to entry: This usage of region is not to be confused with the area of analysis.
2.2
time zero
time at which the X-rays start to irradiate the sample
3 Symbols and abbreviated terms
A deduced linear rate of change of I as a result of degradation for a given element or state
Z t,Z
C atomic fraction of contamination carbon from the quantification computation
d thickness of a contamination layer on the surface of the sample
contamina-
tion
DI degradation index
E kinetic energy, in eV, of the detected electrons
FWHM full width at half maximum (intensity)
I intensity of a given photoelectron peak after correction for the formation of a layer of con-
Z,corrected
tamination
I measured intensity of a given photoelectron peak that is influenced by the presence of a layer of
Z,measured
contamination
I undegraded photoelectron intensity of a given element or state, Z
0,Z
I final photoelectron intensity of a given element in the survey spectrum
f,S
I initial photoelectron intensity of a given element in the survey spectrum
i,S
I intensity of a given element or state measured after a period of X-ray exposure, t
t,Z m,Z
L attenuation length of detected electrons in the contamination layer
c
PTI photo threshold index
PVC poly(vinyl chloride)
θ angle of emission of the detected electrons from the surface normal
t elapsed time of exposure to X-rays at the start of data collection for a particular element, Z
i,Z
t elapsed time of exposure to X-rays at the termination of data collection for a given element, Z
f,Z
t mean time of X-ray exposure for a given element or state, Z
m,Z
t time at which the sample was first exposed to X-rays
t mean time at which the initial survey scan was acquired
i,S
t mean time at which the final survey scan was acquired
f,S
XPS X-ray photoelectron spectroscopy
NOTE t may be the same for all elements if, for example, the scans for individual elements are acquired in
m,Z
a pseudo-parallel mode, but can be very different for each element if element regions are acquired serially, i.e. in
turn, after the previous one has been completed.
4 Sample degradation
Reports of sample degradation during acquisition of a photoelectron spectrum are widespread and
affect most, if not all, classes of materials under certain circumstances. A list of materials reported to
degrade under XPS analysis is provided for information in Annex A.
4.1 Causes of degradation
Sample degradation in the course of analysis by XPS occurs, mainly, because of bonding changes in the
sample caused by the X-ray beam through the direct interaction with the X-rays (characteristic X-rays
or bremsstrahlung) or the electrons emitted from un-monochromated sources or the photoelectrons.
It will occur when the sample is exposed to the X-ray beam before analysis and in the period between
survey or detail scans, as well as in the scans themselves; it does not occur solely during data acquisition.
Degradation can occur also through heating, especially from twin anode sources which are close to
the sample and emit heat. These anodes operate close to 100 °C and are often as close as 5 mm to the
sample stage, covering a large solid angle.
Minor damage can occur from exposure of samples to the vacuum of the instrument and in other cases
from exposure to the low-energy secondary electron flux within the spectrometer chamber. The former
is outside the scope of this International Standard while damage from secondary electrons is likely to
be a concomitant factor of the X-ray flux and does not need to be treated as an independent factor.
Degradation also arises from electron flood guns which may have to be run at high current to neutralize
focused monochromated X-ray sources or may be set at an unnecessarily high value by default. Low-
energy ions used for charge neutralization, also, can have a deleterious effect. Such devices may be on
for some time before analysis starts. Control of some or al
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