1、Designation: E 827 02Standard Practice forIndentifying Elements by the Peaks in Auger ElectronSpectroscopy1This standard is issued under the fixed designation E 827; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice outlines the necessary steps for the iden-tification of elements in a given Auger spectrum obtained usingcon
3、ventional electron spectrometers. Spectra displayed as ei-ther the electron energy distribution (direct spectrum) or thefirst derivative of the electron energy distribution are consid-ered.1.2 This practice applies to Auger spectra generated byelectron or X-ray bombardment of the specimen surface an
4、dcan be extended to spectra generated by other methods such asion bombardment.1.3 This standard does 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 deter
5、mine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:E 673 Terminology Relating to Surface Analysis2E 983 Guide for Minimizing Unwanted Electron BeamEffects In Auger Electron Spectroscopy2E 984 Guide for Identifying Chemical Effects and MatrixEffec
6、ts in Auger Electron Spectroscopy2E 1523 Guide to Charge Control and Charge ReferencingTechniques in X-Ray Photoelectron Spectroscopy23. Terminology3.1 Terms used in Auger electron spectroscopy are definedin Terminology E 673.4. Summary of Practice4.1 The Auger spectrum is obtained with appropriate
7、instru-mental parameters from a low kinetic energy limit of approxi-mately 30 eV to an upper kinetic energy limit of approximately2000 eV or higher to include all the principal Auger electronenergies of all elements (except H and He which do not haveAuger transitions).4.2 This practice assumes the e
8、xistence of appropriatereference spectra from pure element or stoichiometric com-pound standards, or both, with which an unknown spectrumcan be compared (1, 2).3It may be useful to note that althoughAuger energies in some data bases are referenced to the Fermilevel, other data collections have been
9、referenced to thevacuum level. Auger kinetic energies referenced to the Fermilevel would be approximately 5 eV larger than values refer-enced to the vacuum level.4.3 An element in an Auger spectrum is considered posi-tively identified if the peak shapes, the peak energies, and therelative signal str
10、engths of peaks from the unknown coincidewith those from a standard reference spectrum of the elementor compound.5. Significance and Use5.1 Auger analysis is used to determine the elementalcomposition of the first few atomic layers, typically 0.5 to 2.0nm thick, of a specimen surface. In conjunction
11、 with inert gasion sputtering, it is used to determine the sputter depth profileto a depth of a few micrometres.5.2 The specimen is normally a solid conductor, semicon-ductor, or insulator. For insulators, provisions may be requiredfor control of charge accumulation at the surface (see GuideE 1523).
12、 Typical applications include the analysis of thin filmdeposits or segregated overlayers on metallic or alloy sub-strates. The specimen topography may vary from a smooth,polished specimen to a rough fracture surface.5.3 Auger analysis of specimens with volatile species thatevaporate in the ultra-hig
13、h vacuum environment of the Augerchamber and substances which are susceptible to electron orX-ray beam damage, such as organic compounds, may requirespecial techniques not covered herein. (See Guide E 983.)6. Apparatus6.1 Electron Energy Analyzers, a retarding field analyzer,cylindrical mirror analy
14、zer (single or double pass), or hemi-spherical analyzer is typically used.1This practice is under the jurisdiction of ASTM Committee E42 on SurfaceAnalysis and is the direct responsibility of Subcommittee E42.03 on Auger ElectronSpectroscopy and XPS.Current edition approved April 10, 2002. Published
15、 April 2002. Originallypublished as E 827 81. Last previous edition E 827 95.2Annual Book of ASTM Standards, Vol 03.06.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken,
16、 PA 19428-2959, United States.6.2 Standard Equipment, typically an electron gun or X-raysource is used for excitation, an electron multiplier is used foramplification of the Auger electron signal, and recordingdevice is used to output the data.6.2.1 A vacuum capability in the test chamber is require
17、d toallow analysis without contamination from the ambient atmo-sphere; depending on specimen surface conditions, analysis isperformed in the pressure range from 103to 108Pa.7. Procedure7.1 Identify the peak having the largest signal strength in thespectrum and note its peak energy and characteristic
18、 shape.Note that by convention, the peak energy is measured at theenergy of the maximum intensity in the direct N(E) spectrumand at the minimum value in the derivative spectrum. Thesetwo energies are generally not the same.7.2 Consult a list of peak energies for elements and note thepossible energy
19、matches. The peak position can vary by up to20 eV because of slightly differing chemistries, so includeelements within a wide range of energies around the peakposition noted in 7.1.7.3 Consult the standard elemental spectrum for one of theelements identified by 7.2, and look for the presence ofaddit
20、ional lines in the specimen spectrum that match thestandard spectrum (1, 2). Direct and derivative standard spectraare available (1, 2). Compare the shape of the peaks as well. Ifa good match is found, label all lines from the standardspectrum that are visible in the specimen spectrum. If a matchis
21、not found, eliminate that element from further considerationand select another element from the list found in 7.2 and repeat7.3.7.4 If all of the elements from 7.2 have been exhausted,widen the energy range and choose additional elements.Remember, charging may shift the energy spectrum substan-tiall
22、y. In this event, look for the carbon and oxygen peak shapes(or other known elements) by shape and relative position todetermine the extent of charging. Correct for charging andrepeat 7.2 and 7.3.7.5 If a match is still not found, temporarily ignore the mostintense peak and repeat 7.1-7.3 for the ne
23、xt most intense peak.Recall that relative Auger peak intensities may change becauseof the specimen chemistry. A weaker peak may become moreintense and the primary peak may become less intense.7.6 Repeat 7.1-7.3 with peaks of decreasing signal strengthuntil all peaks are positively identified.7.7 It
24、should be noted that since the Auger signal strengthvaries proportionally with the concentration of the elementdetected, an element present at a small concentration mayregister only its strongest Auger peak(s). The identification ofsuch weak peaks should be verified by optimizing the signal-to-noise
25、 ratio in separate scans, for example, by repetitivescans of the energy range of interest.7.8 When extending the technique to Auger transitionsgenerated by an X-ray source, it is important to note that thekinetic energy of the Auger electrons does not change when theenergy of the incident X-rays is
26、changed. This may allow theAuger peaks to be distinguished from the photoelectron peaks.7.9 Auger features generated by incident ions may haverelative intensities and energies that differ substantially fromthose generated by electrons or X-rays (3).8. Interferences8.1 The procedure for positive elem
27、ental identificationgiven in Section 7 is valid except when the characteristic shapeof an Auger peak is subject to change (which is not caused byinstrumental parameters such as different analyzer resolutions).This can arise from two situations:8.1.1 Peak overlap occurs when Auger peak energies fromt
28、wo or more different elements coincide within the energywidth ranges of the peaks. The spectrum of a possiblecomponent element can be subtracted from the composite data.This subtraction or spectrum stripping can be performednumerically, and the residual intensity can be compared withreference spectr
29、a for another possible element (4). Sometimes,for qualitative analysis, spectrum stripping can be adequatelyperformed by an experienced eye. It may be necessary to takeadditional data on an expanded scale (perhaps with increasedenergy resolution and improved signal-to-noise ratio) to per-form the sp
30、ectrum stripping with the desired precision.8.1.2 Changes in peak energy, peak shape, or relative signalstrengths of peaks may be due to Auger chemical effects ormatrix effects (see Guide E 984). In this case, the referencespectrum should be that of the particular compound containingthe element.8.2
31、In spectra obtained using X-ray generation there willgenerally be photoelectron peaks in the spectrum. These mayinterfere with the Auger peaks. As noted above, if possible,changing the energy of the incident X-rays will change thekinetic energy of the photoelectron peaks, while the kineticenergy of
32、the Auger peaks will be unchanged.9. Discussion9.1 The state-of-the-art in Auger electron spectroscopy nowallows routine qualitative analysis without too many interpre-tational difficulties. It is assumed that the practitioner employscommon practice in generating an Auger spectrum in order touse thi
33、s procedure. Under normal circumstances, all elements(except H and He) present on a specimen surface beinganalyzed can be detected with a sensitivity limit of 1 atomic %or better.9.2 Electron Beam ExcitationTypical parameters used forelectron beam excitation are 2 to 20 keV beam energy and1010to 106
34、A beam current. The beam energy and beamcurrent are selected to obtain a sufficient Auger signal strength.High electron beam current densities may cause electron beamdamage in certain specimens (see Guide E 983). If phase-sensitive detection is used for obtaining the Auger spectrum,typical modulatio
35、ns used are 2 to 6 eVppsinusoidal orsquare-wave at 5 to 10 kHz.9.3 X-Ray ExcitationTypical parameters used in thesource for X-ray excitation are 10 to 50 mA electron emissionat 10 to 20 keV energy, resulting in a power dissipation of 100to 1000 W.9.4 Because this practice for chemical identification
36、 relieson comparison with reference spectra, the unknown spectrumshould ideally be generated using the same spectrometer typeE 8272and instrumental parameters employed for the reference spec-tra. Practical situations do not always meet these ideal condi-tions; therefore, systematic spectrum differen
37、ces should betaken into consideration when comparing with the standardspectra, such as the electron background shape which changeswith differing spectrometer type or primary electron beamenergy.9.5 Peaks other than those arising from interferences re-ferred to in Section 8 can arise from ionization
38、loss peaks(electron excitation), photoelectron peaks (X-ray excitation),ion-excited Auger peaks, or charging effects.9.5.1 Ionization loss peaks from primary electrons mayappear in the Auger spectrum, particularly when the primarybeam energy is relatively low. Changing the primary beamenergy shifts
39、the loss peak energy by the same amount and losspeaks may thus be identified. It is usually recommended thatthe primary beam energy should be at least three times greaterthan the Auger energies of interest to minimize the occurrenceof these loss peaks.9.5.2 Photoelectron peaks from characteristic X-
40、rays (forexample, Mg Ka) will occur in the spectrum. Changing thecharacteristic X-rays (for example, from Mg Kato Al Ka) willmove the photoelectron peaks relative to the Auger spectrum.9.5.3 Auger transitions can also be excited in certain mate-rials by ion beams typically used in sputter depth prof
41、iling (forexample, Ar+, 15 keV). Such materials include magnesium,aluminum, and silicon. Their ion excited Auger signal strengthsincrease with beam energy.9.5.4 Charging effects are manifested by shifts of the entirespectrum and are particularly prevalent during the analysis ofinsulating surfaces. S
42、evere charging may introduce spuriouspeaks. Unusually sharp peaks or peaks whose energy positionshifts in subsequent spectra are usually indicative of charging.Instrumental adjustments are necessary to eliminate this prob-lem. Care should be used in Auger peak identification sincesuch effects change
43、 the Auger peak energy and shape.10. Keywords10.1 Auger electron spectroscopy; AES; spectroscopyREFERENCES(1) Sekine, T., Nagasawa, Y., Kudoh M., Sakai, Y., Parkes, A. S., Geller,J. D., Mogami, A., and Hirata, K., Handbook of Auger ElectronSpectroscopy, JEOL, 1982.(2) Childs, K. D., Carlson, B. A.,
44、LaVanier, L. A., Moulder, J. F., Paul, D.F., Sitckle, W. F., and Watson, D. G., Handbook of Auger ElectronSpectroscopy, 3rd Edition, Physical Electronics Inc., Eden Prairie,1995.(3) Grant, J. T., Hooker, M. P., Springer, R. W., and Haas, T. W.,“Comparison of Auger Spectra of Mg, Al, and Si Excited b
45、yLow-Energy Electron and Low-Energy Argon-Ion Bombardment,”Journal of Vacuum Science and Technology, Vol 12, No. 1, 1975, pp.481-484.(4) Grant, J. T., Hooker, M. P., and Haas, T. W., “Spectrum SubtractionTechniques in Auger Electron Spectroscopy,” Surface Science, Vol 51,1975, pp. 318-322.ASTM Inter
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48、ld be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Stan
49、dards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).E 8273
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