1、Designation: E2108 10Standard Practice forCalibration of the Electron Binding-Energy Scale of anX-Ray Photoelectron Spectrometer1This standard is issued under the fixed designation E2108; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes a procedure for calibrating theelectron binding-energy (BE) scale of an X-ray
3、 photoelectronspectrometer that is to be used for performing spectroscopicanalysis of photoelectrons excited by unmonochromated alu-minum or magnesium Ka X-rays or by monochromatedaluminum Ka X-rays.1.2 The calibration of the BE scale is recommended afterthe instrument is installed or modified in an
4、y substantive way.Additional checks and, if necessary, recalibrations are recom-mended at intervals chosen to ensure that BE measurements arestatistically unlikely to be made with an uncertainty greaterthan a tolerance limit, specified by the analyst, based on theinstrumental stability and the analy
5、sts needs. Information isprovided by which the analyst can select an appropriatetolerance limit for the BE measurements and the frequency ofcalibration checks.1.3 This practice is based on the assumption that the BEscale of the spectrometer is sufficiently close to linear to allowfor calibration by
6、measurements of reference photoelectronlines having BEs near the extremes of the working BE scale. Inmost commercial instruments, X-ray sources with aluminum ormagnesium anodes are employed and BEs are typically mea-sured over the 01000 eV range. This practice can be used forthe BE range from 0 eV t
7、o 1040 eV.1.4 The assumption that the BE scale is linear is checked bya measurement made with a reference photoelectron line orAuger-electron line that appears at an intermediate position. Asingle check is a necessary but not sufficient condition forestablishing linearity of the BE scale.Additional
8、checks can bemade with specified reference lines on instruments equippedwith magnesium or unmonochromated aluminum X-raysources, with secondary BE standards, or by following theprocedures of the instrument manufacturer. Deviations fromBE-scale linearity can occur because of mechanical misalign-ments
9、, excessive magnetic fields in the region of the analyzer,or imperfections or malfunctions in the power supplies. Thispractice does not check for, nor identify, problems of this type.1.5 After an initial check of the BE-scale linearity andmeasurements of the repeatability standard deviation for them
10、ain calibration lines for a particular instrument, a simplifiedprocedure is given for routine checks of the calibration atsubsequent times.1.6 This practice is recommended for use with X-rayphotoelectron spectrometers operated in the constant-pass-energy or fixed-analyzer-transmission mode and for w
11、hich thepass energy is less than 200 eV; otherwise, depending on theconfiguration of the instrument, a relativistic equation could beneeded for the calibration. The practice should not be used forinstruments operated in the constant-retardation-ratio mode atretardation ratios less than 10, for instr
12、uments with an energyresolution above 1.5 eV, or in applications for which BEmeasurements are desired with tolerance limits of 60.03 eV orless.1.7 On instruments equipped with a monochromated alumi-num Ka X-ray source, a measurement of the position of aspecified Auger-electron line can be used, if d
13、esired, todetermine the average energy of the X-rays incident on thespecimen. This information is needed for the determination ofmodified Auger parameters.1.8 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.9 This standard doe
14、s not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Stan
15、dards:2E456 Terminology Relating to Quality and StatisticsE673 Terminology Relating to Surface AnalysisE902 Practice for Checking the Operating Characteristics of1This practice is under the jurisdiction of ASTM Committee E42 on SurfaceAnalysis and is the direct responsibility of Subcommittee E42.03
16、onAuger ElectronSpectroscopy and X-Ray Photoelectron Spectroscopy.Current edition approved Nov. 1, 2010. Published December 2010. Originallyapproved in 2000. Last previous edition approved in 2005 as E2108 05. DOI:10.1520/E2108-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org,
17、 orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.X-Ray Photoelec
18、tron SpectrometersE1016 Guide for Literature Describing Properties of Elec-trostatic Electron SpectrometersE1078 Guide for Specimen Preparation and Mounting inSurface AnalysisE1523 Guide to Charge Control and Charge ReferencingTechniques in X-Ray Photoelectron Spectroscopy2.2 ISO Standards:3ISO 9001
19、:2000 Quality Management SystemsRequirementsISO 15472:2001 Surface Chemical AnalysisX-Ray Pho-toelectron SpectrometersCalibration of Energy ScalesISO 18115:2001 Surface Chemical AnalysisVocabulary3. Terminology3.1 DefinitionsFor definitions of terms used in X-rayphotoelectron spectroscopy and surfac
20、e analysis, see Terminol-ogy E673 and ISO 18115:2001. For definitions of terms used instatistics, see Terminology E456.3.2 Symbols and AbbreviationsTable 1 shows definitionsof the symbols and abbreviations used in this practice.4. Summary of Practice4.1 A procedure is given for calibrating the BE sc
21、ale of anX-ray photoelectron spectrometer equipped with one or moreof the following sources of characteristic Ka X-rays: magne-sium (Mg) source; unmonochromated aluminum (Al) source;3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.
22、ansi.org.TABLE 1 Definitions of Symbols and Abbreviationsa measured energy scaling errorBE binding energy, in eVb measured zero offset error, in eVcinumber of counts in the i-th channeleV electron voltsEcorrcorrected result for the binding energy corresponding to a given Emeas,ineVEelembinding energ
23、y of a frequently measured element at which the indicated binding energy scale is set, aftercalibration, to read correctly, in eVEKkinetic energy of a peak, with reference to the Fermi level, in eVEmeasa measured binding energy, in eVEmeas naverage of the measured binding energies for the peak, n,in
24、Table 3,ineVEmeas nione of a set of measurements of binding energy for the peak, n,inTable 3,ineVEref nreference values for the position of peak, n,inTable 3, on the binding energy scale, in eVEppeak binding energy, in eVE0binding energy for first data channel at lower binding energy than the channe
25、l with the maximum number of counts,for a peak, in eVFWHM full width at half maximum peak intensity above the background, in eVg channel energy separation, in eVhvAleffective X-ray energy from an unmonochromated Al X-ray source, in eVhvAlmoneffective X-ray energy from a monochromated Al X-ray source
26、, in eVhvMgeffective X-ray energy from an unmonochromated Mg X-ray source, in eVi index to represent channel number, where i = 0 represents the first channel at lower binding energy than thechannel with the maximum number of counts, for a peak, in eVj number of repeat measurements for a new peakk nu
27、mber of repeat measurements for the Au 4f7/2,Cu2p3/2and Ag 3d5/2or Cu L3VV peaks in the repeatabilitystandard deviation and linearity determinationsm number of repeat measurements for the Au 4f7/2and Cu 2p3/2peaks in the regular calibrationsn designation of the peak identifier in Table 3p parameter
28、in Eq A1.1 defined in Eq A1.2q parameter in Eq A1.1 defined in Eq A1.3r parameter in Eq A1.1 defined in Eq A1.4txStudents t value for x degrees of freedom of a two-sided distribution for a confidence level of 95 %U95total uncertainty of the calibrated energy scale at a confidence level of 95 %, in e
29、VU95c(E) uncertainty at a confidence level of 95 % arising from the calibration using the Au 4f7/2and Cu 2p3/2peaks atbinding energy E, assuming perfect scale linearity, in eVU951uncertainty of 2or 3at a confidence level of 95 % from Eq 7,ineVU95cluncertainty of the calibration at a confidence level
30、 of 95 % in the absence of a linearity error, from Eq 12 and Eq13,ineVXPS X-ray photoelectron spectroscopya Auger parameter, in eVa8 modified Auger parameter, in eVDnoffset energy, given by the average measured binding energy for a calibration peak minus the reference energy, ineV, for n =1,2,3,4inT
31、able 3, for a given X-ray sourceDEcorrcorrection to be added to Emeas, after calibration, to provide the corrected result for the binding energy, in eVDEcorr nvalue of DEcorrfor peaks 1 and 4 in Table 3,ineVDEndrift of the binding-energy scale following a calibration for peaks 1 and 4 in Table 3,ine
32、VDf the average of D1and D4from Eq 16,ineVDhv difference between hvAlmonand hvAl,ineVd value for the tolerance limit of energy calibration at a confidence level of 95 % (set by the analyst), in eV2measured scale linearity error at the Ag 3d5/2peak from Eq 4,ineV3measured scale linearity error at the
33、 Cu L3VV peak from Eq 5 or Eq 6,ineVsRmaximum of sR1, sR2or sR3, and sR4,ineVsRnrepeatability standard deviation for the seven measurements of the binding energy of peak, n,inTable 3,ineVsRnewrepeatability standard deviation for a new peak, in eVE2108 102or monochromated Al source. This procedure is
34、 based onISO 15472:2001. In a first calibration for particular operatingconditions of the instrument, or after the instrument has beenmodified, measurements are made of the BEs of specified corelevels of copper and gold, and these values are then comparedwith corresponding reference energies (1).4Th
35、e linearity of theBE scale is checked at a single point on the scale using ameasurement of the position of either a specified core level ofsilver (monochromated Al source) or a specified Auger-electron transition of copper (Mg source or unmonochromatedAl source) (1,2); additional checks can be made,
36、 if desired,with secondary standards. Procedures are given for determin-ing the components of an uncertainty budget in BE measure-ments and for determining the uncertainties of BE measure-ments (at the 95 % confidence level) at various times followinga calibration. The analyst can thus establish tol
37、erance limits,for example, at the same level of confidence, based on theinstrument stability and the analysts needs so that BE mea-surements statistically are likely to be made within these limitsduring specified time intervals following a calibration. Theinstrument is then adjusted or subsequent BE
38、 measurementsare corrected. For a routine check of the instrumental calibra-tion, either one or two measurements are made each of thesame core levels of copper and gold. Fig. 1 is a flow chart thatsummarizes the steps of the calibration procedure; referencesare given to relevant sections of this sta
39、ndard. An optionalprocedure is provided for determining the average energy ofthe X-rays from a monochromated Al X-ray source, using ameasured position of a copper Auger peak.5. Significance and Use5.1 X-ray photoelectron spectroscopy is used extensivelyfor the surface analysis of materials. Elements
40、 (with theexception of hydrogen and helium) are identified from com-parisons of the binding energies determined from photoelec-tron spectra with tabulated values. Information on chemicalstate can be derived from the chemical shifts of measuredphotoelectron andAuger-electron features with respect to
41、thosemeasured for elemental solids.5.2 Calibrations of the BE scales of XPS instruments arerequired for four principal reasons. First, meaningful compari-son of BE measurements from two or more XPS instrumentsrequires that the BE scales be calibrated, often with anuncertainty of about 0.1 eV to 0.2
42、eV. Second, identification ofchemical state is based on measurement of chemical shifts ofphotoelectron and Auger-electron features, again with anuncertainty of typically about 0.1 eV to 0.2 eV; individualmeasurements, therefore, should be made and literature sourcesneed to be available with comparab
43、le or better accuracies.Third, the availability of databases (3) of measured BEs forreliable identification of elements and determination of chemi-cal states by computer software requires that published dataand local measurements be made with uncertainties of about0.1 eV to 0.2 eV. Finally, the grow
44、ing adoption of qualitymanagement systems, such as, ISO 9001:2000, in many ana-lytical laboratories has led to requirements that the measuringand test equipment be calibrated and that the relevant measure-ment uncertainties be known.5.3 The actual uncertainty of a BE measurement depends oninstrument
45、 properties and stability, measurement conditions,and the method of data analysis. This practice makes use oftolerance limits 6d (chosen, for example, at the 95 % confi-dence level) that represent the maximum likely uncertainty ofa BE measurement, associated with the instrument in aspecified time in
46、terval following a calibration(ISO 15472:2001). A user should select a value of d based onthe needs of the analytical work to be undertaken, the likelymeasurement and data-analysis conditions, the stability of theinstrument, and the cost of calibrations. This practice givesinformation on the various
47、 sources of uncertainty in BEmeasurements and on measurements of instrumental stability.The analyst should initially choose some desired value for dand then make tests, as described in 8.14 to determine fromsubsequent checks of the calibration whether BE measure-ments are made within the limits 6d.
48、Information is given inAppendix X1 on how to evaluate for a material of interest theuncertainty of a BE measurement that is associated with theuncertainty of the calibration procedure. This information isprovided for four common analytical situations. It is importantto note that some BE measurements
49、 may have uncertaintieslarger than d as a result of poor counting statistics, large peakwidths, uncertainties associated with peak synthesis, and ef-fects of surface charging.5.4 Instrument settings typically selected for analysis shouldbe used with this practice. Separate calibrations should bemade if key operating conditions, such as choices of analyzerpass energy, aperture sizes, or X-ray source, are varied.Settings not specified in this practice are at the discretion of theuser, but those same settings should be recorded and consis-tently used whenever this practi
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