1、BSI Standards PublicationBS ISO 18554:2016Surface chemical analysis Electron spectroscopies Procedures for identifying,estimating and correcting forunintended degradation by X-rays in a material undergoinganalysis by X-ray photoelectronspectroscopyBS ISO 18554:2016 BRITISH STANDARDNational forewordT
2、his British Standard is the UK implementation of ISO 18554:2016.The UK participation in its preparation was entrusted to TechnicalCommittee CII/60, Surface chemical analysis.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not pur
3、port to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2016. Published by BSI StandardsLimited 2016ISBN 978 0 580 82619 1ICS 71.040.40Compliance with a British Standard cannot confer immunity fromlegal obligation
4、s.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 March 2016.Amendments issued since publicationDate Text affectedBS ISO 18554:2016 ISO 2016Surface chemical analysis Electron spectroscopies Procedures for identifying, estimating and correct
5、ing for unintended degradation by X-rays in a material undergoing analysis by X-ray photoelectron spectroscopyAnalyse chimique des surfaces Spectroscopie dlectrons Procdures pour lidentification, lestimation et la correction de la dgradation involontaire par rayons X pendant une analyse de matriau p
6、ar spectroscopie de photolectrons par rayons XINTERNATIONAL STANDARDISO18554First edition2016-03-15Reference numberISO 18554:2016(E)BS ISO 18554:2016ISO 18554:2016(E)ii ISO 2016 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2016, Published in SwitzerlandAll rights reserved. Unless otherwise sp
7、ecified, 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
8、 ISOs member body in the country of the requester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749 09 47copyrightiso.orgwww.iso.orgBS ISO 18554:2016ISO 18554:2016(E)Foreword ivIntroduction v1 Scope . 12 Terms and definitions . 13 S
9、ymbols and abbreviated terms . 14 Sample degradation 24.1 Causes of degradation . 24.2 Sample degradation 34.3 Measurements for identifying, and correcting for, degradation . 34.3.1 Recognition of degradation 34.3.2 The first survey scan. 34.3.3 The detail scans 44.3.4 The final survey scan 44.3.5 I
10、nverting the order of acquisition for unstable compounds 44.3.6 Check for degradation . 44.3.7 Deduce the undegraded intensity . 44.4 Assessing the likelihood of degradation . 64.4.1 Determining the value of AZ64.5 Reporting degradation . 64.6 Suggested procedures for minimising degradation 64.7 Inf
11、luence of contamination 74.7.1 Contamination formation during spectrum acquisition 74.7.2 Reporting contamination . 7Annex A (informative) Materials reported to degrade during analysis . 8Annex B (informative) Examples of degradation . 9Annex C (informative) Compensation for formation of a contamina
12、tion layer.14Bibliography .16 ISO 2016 All rights reserved iiiContents PageBS ISO 18554:2016ISO 18554:2016(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is n
13、ormally 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 i
14、n 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
15、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 doc
16、ument 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.o
17、rg/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 on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the WTO p
18、rinciples in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information.The committee responsible for this document is ISO/TC 201, Surface chemical analysis, Subcommittee SC 7, Electron spectroscopies.iv ISO 2016 All rights reservedBS ISO 18554:2016ISO 18554:20
19、16(E)IntroductionThe 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.
20、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 analysis, there have been reports of changes in composition arising du
21、ring the course of analysis.1-4These 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 c
22、an be estimated and a suitable correction obtained. ISO 2016 All rights reserved vBS ISO 18554:2016BS ISO 18554:2016Surface chemical analysis Electron spectroscopies Procedures for identifying, estimating and correcting for unintended degradation by X-rays in a material undergoing analysis by X-ray
23、photoelectron spectroscopy1 ScopeThis 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
24、 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 onl
25、y 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 definitionsFor the purposes of this document, the following terms and definitions apply.2.1regionpart of the photo-exc
26、ited spectrum chosen for detailed acquisition and analysisNote 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 no
27、t to be confused with the area of analysis.2.2time zerotime at which the X-rays start to irradiate the sample3 Symbols and abbreviated termsAZdeduced linear rate of change of It,Zas a result of degradation for a given element or stateC atomic fraction of contamination carbon from the quantification
28、computationdcontamina-tionthickness of a contamination layer on the surface of the sampleDI degradation indexE kinetic energy, in eV, of the detected electronsFWHM full width at half maximum (intensity)IZ,correctedintensity of a given photoelectron peak after correction for the formation of a layer
29、of con-taminationIZ,measuredmeasured intensity of a given photoelectron peak that is influenced by the presence of a layer of contaminationI0,Zundegraded photoelectron intensity of a given element or state, ZIf,Sfinal photoelectron intensity of a given element in the survey spectrumIi,Sinitial photo
30、electron intensity of a given element in the survey spectrumINTERNATIONAL STANDARD ISO 18554:2016(E) ISO 2016 All rights reserved 1BS ISO 18554:2016ISO 18554:2016(E)It,Zintensity of a given element or state measured after a period of X-ray exposure, tm,ZLcattenuation length of detected electrons in
31、the contamination layerPTI photo threshold indexPVC poly(vinyl chloride) angle of emission of the detected electrons from the surface normalti,Zelapsed time of exposure to X-rays at the start of data collection for a particular element, Ztf,Zelapsed time of exposure to X-rays at the termination of d
32、ata collection for a given element, Ztm,Zmean time of X-ray exposure for a given element or state, Zt0time at which the sample was first exposed to X-raysti,Smean time at which the initial survey scan was acquiredtf,Smean time at which the final survey scan was acquiredXPS X-ray photoelectron spectr
33、oscopyNOTE tm,Zmay be the same for all elements if, for example, the scans for individual elements are acquired in 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
34、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 degradationSample
35、 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 wi
36、ll 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
37、 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 flu
38、x 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 whi
39、ch 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 o
40、f some or all of these factors can be helpful in reducing degradation; however, the procedure recommended in this International Standard considers only changes that occur once the sample is exposed to the X-rays (defined as time zero in the procedure described below).3456Material will also be remove
41、d from the surface during ion-etching; this is intentional but unintended changes in chemical state may result. Ion-beam sputtering is outside the scope of this International Standard but some concepts relating to chemical degradation may be helpful in understanding the phenomenon.2 ISO 2016 All rig
42、hts reservedBS ISO 18554:2016ISO 18554:2016(E)4.2 Sample degradationSample degradation is said to have occurred whenever there is a measurable change in the spectrum of a sample after a period of exposure to the X-ray flux. This change typically arises from a change in the atomic fraction or chemica
43、l state of one or more elements, giving rise to a relative shift in peak positions or to a change in intensity of one of more peaks and thus a change in the measured constitution of the sample. A good description of the overall effects of a photon beam has been given by Reference 5.The change in che
44、mical state can be due to photo-excited reduction of an ion, such as occurs when Cu(ll) is chemically reduced to Cu(l). Sometimes, but not always, this can be accompanied by oxidation of another element in the near-surface region. An example is given in Annex B. The change in composition can arise,
45、particularly in organic compounds, through the breaking of chemical bonds and the subsequent diffusion and escape of low-molecular weight species generated as a result. Some relative rates of degradation are given by Reference 6, e.g. using their degradation index, DI, which is proportional to the p
46、arameter, A, defined in this International Standard. Polypropylene has a DI value of 5 and polyethylene has a DI of 10; these are examples of various forms of degradation, including bond breaking, radical formation and cross-linking. Poly(vinyl chloride), which has been used to assess degradation ra
47、tes has a DI of 25 on this scale. An example of the loss of Cl from a poly(vinyl chloride) blend is described in Annex B.Although the degradation noticed in the X-ray photoelectron spectrum concerns only the outermost 10 nm, the X-rays penetrate to much greater depths and damage is not confined to t
48、he escape depth of photoelectrons. Thus, material lost from the surface layers may be compensated by material diffusing from deeper within the sample. This behaviour can give a dynamic plateau in the degradation of observed composition or chemical state. An illustration is given in Annex B. In the p
49、eriod prior to establishment of the plateau, an approximately linear rate of degradation is normally observed and the procedure recommended in this International Standard applies a correction by means of a linear extrapolation. Near-surface degradation may be particularly important in analysis of monolayer films because of disruption to the bond required for attachment to the substrate.784.3 Measurements for identifying, and correcting for, degradation4.3.1 Recognition of degradationRecognition of degradation is based pri
