BS ISO 20903-2011 Surface chemical analysis Auger electron spectroscopy and X-ray photoelectron spectroscopy Methods used to determine peak intensities and information required whe.pdf

1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 20903:2011Surface chemical analysis Auger electron spectroscopyand X-ray photoelectronspectroscopy Methods usedto determine peak intensitiesand information required whenre

2、porting resultsBS ISO 20903:2011 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 20903:2011. Itsupersedes BS ISO 20903:2006 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee CII/60, Surface chemical analysis.A list o

3、f organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. BSI 2011ISBN 978 0 580 74520 1ICS 71.040.40Compliance with a British Stan

4、dard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 30 November 2011.Amendments issued since publicationDate Text affectedBS ISO 20903:2011Surface chemical analysis Auger electron spectroscopy and

5、Xray photoelectron spectroscopy Methods used to determine peak intensities and information required when reporting resultsAnalyse chimique des surfaces Spectroscopie des lectrons Auger et spectroscopie de photolectrons par rayons X Mthodes utilises pour la dtermination de lintensit des pics et infor

6、mations requises pour lexpression des rsultats ISO 2011Reference numberISO 20903:2011(E)Second edition2011-11-01ISO20903INTERNATIONAL STANDARDBS ISO 20903:2011ISO 20903:2011(E)COPYRIGHT PROTECTED DOCUMENT ISO 2011All rights reserved. Unless otherwise specified, no part of this publication may be rep

7、roduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase postale 56 CH-1211 Geneva 20Tel. + 41 22 74

8、9 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in Switzerlandii ISO 2011 All rights reservedBS ISO 20903:2011ISO 20903:2011(E) ISO 2011 All rights reserved iiiContents PageForeword ivIntroduction v1 Scope 12 Normative references .13 Terms and definitions .14 Symbols and

9、abbreviated terms .15 Methods for peakintensity determination Direct spectrum .15.1 General .15.2 Selection and subtraction of an inelastic background .35.3 Measurement of peak intensity .35.4 Measurement of a peak intensity with computer software 45.5 Measurement of peak intensities for a spectrum

10、with overlapping peaks 55.6 Uncertainty in measurement of peak area 56 Methods for peak intensity determination Augerelectron differential spectrum .66.1 General .66.2 Measurement of Augerelectron differential intensity .66.3 Uncertainties in measurement of Augerelectron differential intensity .77 R

11、eporting of methods used to measure peak intensities 87.1 General requirements .87.2 Methods used to determine peak intensities in direct spectra .87.3 Methods used to obtain and determine peak intensities in Augerelectron differential spectra.9Annex A (informative) Instrumental effects on measured

12、intensities 10Annex B (informative) Useful integration limits for determination of peak intensities in XPS spectra 11Bibliography .13BS ISO 20903:2011ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work

13、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-government

14、al, 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.International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.The main

15、task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.Attent

16、ion 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.ISO 20903 was prepared by Technical Committee ISO/TC 201, Surface chemical analysis, Subcommittee SC 5, Auge

17、r electron spectroscopy.This second edition cancels and replaces the first edition (ISO 20903:2006), which has been revised to include an additional annex (Annex B) giving advice on the selection of the limits between which the peak intensity is measured in X-ray photoelectron spectroscopy.ISO 20903

18、:2011(E)iv ISO 2011 All rights reservedBS ISO 20903:2011IntroductionAn important feature of Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) is the ability to obtain a quantitative analysis of the surface region of a solid sample. Such an analysis requires the determinati

19、on of the intensities of spectral components.There are several methods of peak-intensity measurement that are applicable to AES and XPS. In practice, the choice of method will depend upon the type of sample being analysed, the capabilities of the instrumentation used, and the methods of data acquisi

20、tion and treatment available.This International Standard is expected to have two main areas of application. First, it provides a description of methods that may be used in the determination of the intensity of a peak for an element in a given spectrum. Information is given on the origin of uncertain

21、ties in the processes involved, and on how these uncertainties may be reduced. Second, this International Standard specifies reporting requirements for the methods used for peak-intensity measurements so that other analysts may use published results with confidence.ISO 20903:2011(E) ISO 2011 All rig

22、hts reserved vBS ISO 20903:2011BS ISO 20903:2011INTERNATIONAL STANDARD ISO 20903:2011(E)Surface chemical analysis Auger electron spectroscopy and Xray photoelectron spectroscopy Methods used to determine peak intensities and information required when reporting results1 ScopeThis International Standa

23、rd specifies the necessary information required in a report of analytical results based on measurements of the intensities of peaks in Auger electron and X-ray photoelectron spectra. Information on methods for the measurement of peak intensities and on uncertainties of derived peak areas is also pro

24、vided.2 Normative referencesThe following referenced documents are indispensable for the application 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 c

25、hemical analysis Vocabulary Part 1: General terms and terms used in spectroscopy3 Terms and definitionsFor the purposes of this document, the terms and definitions given in ISO 18115-1 apply.4 Symbols and abbreviated termsA peak areaAES Auger electron spectroscopyb number of channels over which inte

26、nsities are averaged to obtain a baselineeV electron voltsn number of channels in a spectrumXPS X-ray photoelectron spectroscopyyinumber of counts in the ith channel of a spectrumE channel width (in electron volts)t dwell time per channel (in seconds)(A) standard deviation of calculated peak area5 M

27、ethods for peakintensity determination Direct spectrum5.1 GeneralFigure 1 a) shows a portion of an X-ray photoelectron spectrum in which intensity is plotted as a function of kinetic energy increasing to the right or of binding energy increasing to the left. The intensity is plotted usually in units

28、 of counts or sometimes in units of counts per second. Intensities may also be plotted as a digitized ISO 2011 All rights reserved 1BS ISO 20903:2011voltage; this procedure is often used when the intensity of an Auger differential spectrum is obtained from an analogue detection system. Energies are

29、commonly expressed in electron volts.KeyX1 binding energy (eV)X2 kinetic energy (eV)Y intensityFigure 1 Illustration of procedure involved in the determination of the intensity of a single peak in an Xray photoelectron spectrum (as described in 5.2 and 5.3)The intensity of a single peak in an X-ray

30、photoelectron spectrum can be measured by using the procedure described in the following two subclauses (5.2 and 5.3) or by using computer software as described in 5.4. The measurement of peak intensities for a spectrum containing overlapping peaks is described in 5.5. Information on the uncertainty

31、 of a measured peak area for a single peak is given in 5.6.The intensity of a single peak in a direct Auger-electron spectrum can be measured by following the procedure described in 5.2 and 5.3, although it may be necessary first to subtract a secondary-electron background12. Alternatively, computer

32、 software can be used to measure the peak intensity as described in 5.4.In some cases, the peak of interest may be superimposed on a sloping background. This background could arise from multiple inelastic scattering of Auger electrons or photoelectrons of initially high energy, from multiple inelast

33、ic scattering of primary electrons (in AES), or from photoemission by bremsstrahlung radiation (for XPS with an unmonochromated X-ray source). It may be necessary (e.g. with use of the Tougaard inelastic background described in 5.2) or desirable to subtract this background from the spectrum in the v

34、icinity of the peak before proceeding with the peak-intensity measurements described in 5.2 to 5.5. This subtraction can usually be performed by fitting a straight line to the sloping background at energies between about 10 eV and 30 eV above the peak of interest, extrapolating this line to lower en

35、ergies, and subtracting the spectral intensities from this linear background. If a linear function is judged to be invalid for describing the sloping background over the spectral range of interest (e.g. for modelling the background of scattered primary electrons in AES), an exponential function can

36、be utilized3.ISO 20903:2011(E)2 ISO 2011 All rights reservedBS ISO 20903:20115.2 Selection and subtraction of an inelastic backgroundIt is necessary to select an appropriate inelastic background and then to subtract this background from the measured spectrum. Three types of inelastic background are

37、in common use:a) linear background;b) integral or Shirley background4;c) Tougaard background567and Werner background89, based on physical models describing inelastic electron scattering in solids.Information on procedures and software for determining the Shirley, Tougaard and Werner backgrounds is g

38、iven in the scientific literature4-13and ISO/TR 1839214.From a practical viewpoint, the selection of a particular background will depend on (a) whether the relevant software is conveniently available and (b) the type of sample analysed. For insulators, the linear background is often satisfactory, wh

39、ile the Shirley background is often employed for metals. While these two backgrounds are simple and convenient to apply, the limits of these two backgrounds (the starting and ending points on the energy scale) should be chosen carefully so that the background is as nearly continuous as possible with

40、 the spectrum in the region of overlap.Tougaards approach, in particular, for background determination and subtraction567has found favour over the Shirley background because it describes the physics of the inelastic-scattering process more accurately15 16. The Tougaard and the Werner approaches have

41、 a further advantage in that they are insensitive to the precise positions of the starting and ending energy points providing they are clearly in the spectral region well away from the main peak of interest (typically starting at an energy at least 10 eV higher than that of the peak of interest and

42、ending at an energy at least 50 eV lower). This requirement is a disadvantage in that spectra have to be recorded over a larger energy range than if the linear or Shirley background is used.As an example, Figure 1 a) shows an XPS peak whose intensity is to be measured. Vertical lines have been drawn

43、 to indicate suitable limits for use of the Shirley background. The spectrum after subtraction of this background is shown on an expanded energy scale in Figure 1 b). For clarity of display, the zero of the intensity scale in Figure 1 b) has been placed at 2 % of the ordinate axis. The end points in

44、 Figure 1 b) are at the same positions as those in Figure 1 a).Averaging over neighbouring channels may be helpful in defining the signal level at the selected end points, thus improving the precision of peak-height or peak-area measurement. The sets of points to be averaged may be located inside or

45、 outside of the chosen end points or may be symmetrically placed about the end points. It is important that the end points are chosen to be sufficiently far from the peak so that the averaging process does not include significant peak intensity. Harrison and Hazell17have derived an expression for th

46、e estimated uncertainty in a peak-area measurement (see 5.6) and have shown that a large contribution to this uncertainty comes from uncertainties arising from the choice of end points and the intensities at these end points.Smoothing of a spectrum, using a Savitzky-Golay18convolution with a width l

47、ess than 50 % of the full width at half-maximum intensity of the peak, may improve the precision of a peak-height determination. However, smoothing should be avoided for peak-area determination since it cannot improve the precision and, if over-done, will distort the spectrum.Annex B gives informati

48、on on the choice of suitable energy limits for the determination of peak intensities or areas in XPS spectra.5.3 Measurement of peak intensity5.3.1 Measurement of peak heightA peak height is determined (i) by direct measurement from a chart output using a ruler, (ii) by using computer software to ob

49、tain the intensity difference from the baseline to the peak maximum or (iii) by using computer software to fit an appropriate analytical peak shape (Gaussian, Lorentzian or a mixture of the two101112) to the experimental spectrum (that is, the group of data points defining the peak of interest). The length of the ISO 20903:2011(E) ISO 2011 All rights reserved 3BS ISO 20903:2011vertical line with arrows in Figure 1 b) is a measure of the peak height in units defined by t