ASTM E1508-2012a Standard Guide for Quantitative Analysis by Energy-Dispersive Spectroscopy《用能量分散能谱学作定量分析的标准指南》.pdf

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1、Designation: E1508 12E1508 12aStandard Guide forQuantitative Analysis by Energy-Dispersive Spectroscopy1This standard is issued under the fixed designation E1508; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev

2、ision. 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 guide is intended to assist those using energy-dispersive spectroscopy (EDS) for quantitative analysis of materials witha

3、 scanning electron microscope (SEM) or electron probe microanalyzer (EPMA). It is not intended to substitute for a formal courseof instruction, but rather to provide a guide to the capabilities and limitations of the technique and to its use. For a more detailedtreatment of the subject, see Goldstei

4、n, et al. (1) This guide does not cover EDS with a transmission electron microscope (TEM).1.2 UnitsThe values stated in SI units are to be regarded as standard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of the safety concerns, if any

5、, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E3 Guide for Preparation of Metallographic SpecimensE7

6、 Terminology Relating to MetallographyE673 Terminology Relating to Surface Analysis (Withdrawn 2012)3E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method3. Terminology3.1 DefinitionsFor definitions of terms used in this guide, see Terminologies E7 and E67

7、3.3.2 Definitions of Terms Specific to This Standard:3.2.1 accelerating voltagethe high voltage between the cathode and the anode in the electron gun of an electron beaminstrument, such as an SEM or EPMA.3.2.2 beam currentthe current of the electron beam measured with a Faraday cup positioned near t

8、he specimen.3.2.3 Bremsstrahlungbackground X rays produced by inelastic scattering (loss of energy) of the primary electron beam in thespecimen. It covers a range of energies up to the energy of the electron beam.3.2.4 critical excitation voltagethe minimum voltage required to ionize an atom by ejec

9、ting an electron from a specificelectron shell.3.2.5 dead timethe time during which the system will not process incoming X rays (real time less live time).3.2.6 k-ratiothe ratio of background-subtracted X-ray intensity in the unknown specimen to that of the standard.3.2.7 live timethe time that the

10、system is available to detect incoming X rays.3.2.8 overvoltagethe ratio of accelerating voltage to the critical excitation voltage for a particular X-ray line.3.2.9 SDD (silicon drift detector)An x-ray detector characterized by a pattern in the biasing electrodes which inducesgenerated electrons to

11、 move laterally (drift) to a small-area anode for collection, resulting in greatly reduced capacitance whichto a first approximation does not depend on the active area, in contrast to conventional detectors using flat-plate electrodes. (2)1 This guide is under the jurisdiction of ASTM Committee E04

12、on Metallography and is the direct responsibility of Subcommittee E04.11 on X-Ray and ElectronMetallography.Current edition approved May 1, 2012Dec. 1, 2012. Published November 2012February 2013. Originally approved in 1993. Last previous edition approved in 20082012as E1508 98E1508 12.(2008). DOI:

13、10.1520/E1508-12.10.1520/E1508-12A.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The last approved versio

14、n of this historical standard is referenced on www.astm.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all chan

15、ges accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. Un

16、ited States13.2.10 shaping timea measure of the time it takes the amplifier to integrate the incoming charge; it depends on the timeconstant of the circuitry.3.2.11 spectrumthe energy range of electromagnetic radiation produced by the method and, when graphically displayed, is therelationship of X-r

17、ay counts detected to X-ray energy.4. Summary of Practice4.1 As high-energy electrons produced with an SEM or EPMA interact with the atoms within the top few micrometres of aspecimen surface, X rays are generated with an energy characteristic of the atom that produced them. The intensity of such X r

18、aysis proportional to the mass fraction of that element in the specimen. In energy-dispersive spectroscopy, X rays from the specimenare detected by a solid-state spectrometer that converts them to electrical pulses proportional to the characteristic X-ray energies.If the X-ray intensity of each elem

19、ent is compared to that of a standard of known or calculated composition and suitably correctedfor the effects of other elements present, then the mass fraction of each element can be calculated.5. Significance and Use5.1 This guide covers procedures for quantifying the elemental composition of phas

20、es in a microstructure. It includes bothmethods that use standards as well as standardless methods, and it discusses the precision and accuracy that one can expect fromthe technique. The guide applies to EDS with a solid-state X-ray detector used on an SEM or EPMA.5.2 EDS is a suitable technique for

21、 routine quantitative analysis of elements that are 1) heavier than or equal to sodium in atomicweight, 2) present in tenths of a percent or greater by weight, and 3) occupying a few cubic micrometres, or more, of the specimen.Elements of lower atomic number than sodium can be analyzed with either u

22、ltra-thin-window or windowless spectrometers,generally with less precision than is possible for heavier elements. Trace elements, defined as 100 %. For quantitative analysis using standards, the beam current(not specimen current) must be the same for both the specimen and the standards or one must b

23、e normalized to the other.8.2.6 The geometric configuration of the sample and detector, shown schematically in Fig. 1, also affects the analysis. Thenumber of X-ray photons that reach the detector is a function of the solid angle and take-off angle, including the effect of specimenand detector tilt.

24、 The count rate incident on an X-ray detector is directly proportional to the size of the solid angle defined asfollows for a detector normal to the line of sight to the specimen:5A/r2 (2)where: = solid angle in steradians,A = active area of the detector crystal; for example, 30 mm2, andE1508 12a3r

25、= sample-to-detector distance, mm.The larger the active area of the detector, the more counts will be collected, but at the expense of spectral resolution. Mostdetectors have a movable slide and can be brought closer to the sample if a higher count rate at a given beam current is needed.The take-off

26、 angle is defined as the angle between the surface of the sample and a line to the X-ray detector. If the sample is nottilted, the take-off angle is defined as follows:5arctanW 2V!/S (3)8.2.6.1 The larger the active area of the detector, the more counts will be collected, but at the expense of spect

27、ral resolution.Most detectors have a movable slide and can be brought closer to the sample if a higher count rate at a given beam current isneeded. The take-off angle is defined as the angle between the surface of the sample and a line to the X-ray detector. If the sampleis not tilted, the take-off

28、angle is defined as follows:5arctanW 2V!/S (3)where: = take-off angle,W = working distance,V = vertical distance, andS = spectrometer distance.where: = take-off angle,W = working distance,V = vertical distance, andS = spectrometer distance.8.2.6.2 Working distance is measured in the microscope; its

29、accuracy depends on the method used to measure it and thespecimen position. Vertical distance is the distance from the bottom of the pole piece of the final lens to the centerline of thedetector; it usually can be measured within the microscope with a ruler or obtained from the manufacturer. Spectro

30、meter distanceis the horizontal distance from the spectrometer to the beam; it is measured using the scale provided by the manufacturer on thespectrometer slide.All distances must be in the same units. The take-off angle should be as high as possible to minimize absorptionof X rays within the specim

31、en and maximize the accuracy of quantitative analysis. If the specimen is tilted such that the beam isnot perpendicular to the specimen surface, an effective take-off angle is used. There are several expressions in use by commercialmanufacturers to calculate this, and all produce similar results if

32、the tilt angle is not extreme.When analysis is performed on a tiltedspecimen, the azimuthal angle between the line from the analysis point to the EDS detector and the line perpendicular to the stagetilt axis must be known. If standards are used, they must be collected under the identical geometrical

33、 conditions as the unknowns.To set W, move the stage in the z-axis until it is in focus with the objective lens, preset to the desired W.Working distance is measured in the microscope; its accuracy depends on the method used to measure it and the specimenposition. Vertical distance is the distance f

34、rom the bottom of the pole piece of the final lens to the centerline of the detector; itusually can be measured within the microscope with a ruler. Spectrometer distance is the horizontal distance from the spectrometerto the beam; it is measured using the scale provided by the manufacturer on the sp

35、ectrometer slide. All distances must be in theFIG. 1 Schematic Diagram of Electron Microscope SystemE1508 12a4same units. The take-off angle should be as high as possible to minimize absorption of X rays within the specimen and maximizethe accuracy of quantitative analysis. If the specimen is tilted

36、 such that the beam is not perpendicular to the specimen surface, aneffective take-off angle is used. There are several expressions in use by commercial manufacturers to calculate this, and all producesimilar results if the tilt angle is not extreme. When analysis is performed on a tilted specimen,

37、the azimuthal angle between theline from the analysis point to the EDS detector and the line perpendicular to the stage tilt axis must be known. If standards areused, they must be collected under the identical geometrical conditions as the unknowns.8.3 Spectral Artifacts:8.3.1 There are a number of

38、artifacts possible with EDS, and these are discussed by Fiori, et al.(5) Most of them are related todetector electronics and are rarely seen in a properly functioning system. However, two artifacts that are commonly seen are pulsepileup peaks and silicon escape peaks. Pileup peaks occur when several

39、 X-ray photons reach the detector at the same time, andthe pulse processing electronics erroneously record the sum of their energies rather than each one individually. Lowering the beamcurrent to lower the count rate usually eliminates the problem. The ratio of pileup peak to parent peak(s) is propo

40、rtional to the inputcount rate of the parent peak(s). For the same total input count rate, a complex spectrum will have smaller relative pileup peaksthan a simple spectrum having a few dominant peaks. The pileup peak for two parent peaks of different energies is larger than fora single peak with the

41、 same count rate as the two-peak pair. Relative pileup peak height is inversely related to energy for the samecount rate. Systems with SDDs generally have smaller pileup peaks under the same conditions, because the reduced capacitanceof the SDD makes it easier for the pulse processing electronics to

42、 recognize close coincidences as separate events. EDS systemsoften have software to model pileup peaks and correct for them.8.3.2 Asilicon escape peak occurs when an ionized atom of silicon in the detector generates an X ray. If that X ray escapes fromthe detector, its energy that would ordinarily h

43、ave been measured is lost. The result is a peak at 1.74 keV (Si K) below the properpeak. This artifact is greatest at about 2 keV, near the P K or Zr L peaks. The artifact cannot occur at energies below theabsorption edge of the Si K line, and it becomes negligible at higher energies such as the Cu

44、K line. SDDs have larger escapepeaks relative to the parent peak because they are thinner (typically 0.4 to 0.5 mm compared to several mm for Si(Li) detectors)and thus have a higher surface-to-volume ratio.9. Quantification Analysis9.1 Before performing a quantitative analysis on an unknown specimen

45、, the elements present must be identified, that is, aqualitative analysis must be performed. Qualitative analysis may be performed on polished specimens or on flat regions ofunpolished surfaces, see 7.1.9.1.1 All manufacturers of EDS systems provide some sort of automatic identification routine. The

46、 ability of these systems toidentify all of the elements present varies from one EDS system to another and with the nature of the specimen, particularly fortrace elements. These programs are quite helpful but should be viewed with caution. For a discussion of their pitfalls, see Newbury(6). The anal

47、yst can use his knowledge of chemical principles and of the specimen. Be careful not to disregard elements reportedby the computer too quickly. The peaks of these elements may be overlapped with those of other elements. For critical analyses,it is essential for the analyst to confirm the computer ou

48、tput with a manual systematic procedure such as outlined in 9.2. Remember,the analyst is responsible for the results.9.2 Step-by-Step IdentificationThe following procedure is similar to the one described by Lyman et al. (7) and is sometimesreferred to as the “Lehigh Method.”9.2.1 Begin with the most

49、 intense line towards the high-energy region of the spectrum where lines within a family are wellseparated. If it falls above 3.5 keV, it will be either a K or L line.9.2.2 Using the KLM markers, compare the location of each peak to that of the marker. If it is off by one channel or less, thesame should be true for all nearby lines. If the markers can be scaled, check the relative intensities. If you identified a K line,then the K line should be about 10 % of the K intensity. K and K lines are typically resolved at sulfur and above. If a K lineis