ASTM E1508-12a(2019)
(Guide)Standard Guide for Quantitative Analysis by Energy-Dispersive Spectroscopy
Standard Guide for Quantitative Analysis by Energy-Dispersive Spectroscopy
SIGNIFICANCE AND USE
5.1 This guide covers procedures for quantifying the elemental composition of phases in a microstructure. It includes both methods that use standards as well as standardless methods, and it discusses the precision and accuracy that one can expect from the 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 routine quantitative analysis of elements that are 1) heavier than or equal to sodium in atomic weight, 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 ultra-thin-window or windowless spectrometers, generally with less precision than is possible for heavier elements. Trace elements, defined as 2 can be analyzed but with lower precision compared with analyses of elements present in greater concentration.
SCOPE
1.1 This guide is intended to assist those using energy-dispersive spectroscopy (EDS) for quantitative analysis of materials with a scanning electron microscope (SEM) or electron probe microanalyzer (EPMA). It is not intended to substitute for a formal course of instruction, but rather to provide a guide to the capabilities and limitations of the technique and to its use. For a more detailed treatment of the subject, see Goldstein, et al. (1) This guide does not cover EDS with a transmission electron microscope (TEM).
1.2 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1508 − 12a (Reapproved 2019)
Standard Guide for
Quantitative Analysis by Energy-Dispersive Spectroscopy
This standard is issued under the fixed designation E1508; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
1.1 This guide is intended to assist those using energy-
dispersive spectroscopy (EDS) for quantitative analysis of
3. Terminology
materials with a scanning electron microscope (SEM) or
electron probe microanalyzer (EPMA). It is not intended to 3.1 Definitions—For definitions of terms used in this guide,
substitute for a formal course of instruction, but rather to
see Terminologies E7 and E673.
provide a guide to the capabilities and limitations of the
3.2 Definitions of Terms Specific to This Standard:
technique and to its use. For a more detailed treatment of the
3.2.1 accelerating voltage—the high voltage between the
subject,seeGoldstein,etal. (1)ThisguidedoesnotcoverEDS
cathode and the anode in the electron gun of an electron beam
with a transmission electron microscope (TEM).
instrument, such as an SEM or EPMA.
1.2 Units—The values stated in SI units are to be regarded
3.2.2 beam current—the current of the electron beam mea-
as standard. No other units of measurement are included in this
sured with a Faraday cup positioned near the specimen.
standard.
3.2.3 Bremsstrahlung—background X rays produced by in-
1.3 This standard does not purport to address all of the
elastic scattering (loss of energy) of the primary electron beam
safety concerns, if any, associated with its use. It is the
in the specimen. It covers a range of energies up to the energy
responsibility of the user of this standard to establish appro-
of the electron beam.
priate safety, health, and environmental practices and deter-
3.2.4 critical excitation voltage—the minimum voltage re-
mine the applicability of regulatory limitations prior to use.
quired to ionize an atom by ejecting an electron from a specific
1.4 This international standard was developed in accor-
electron shell.
dance with internationally recognized principles on standard-
3.2.5 dead time—the time during which the system will not
ization established in the Decision on Principles for the
process incoming X rays (real time less live time).
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
3.2.6 k-ratio—the ratio of background-subtracted X-ray in-
Barriers to Trade (TBT) Committee.
tensity in the unknown specimen to that of the standard.
3.2.7 live time—the time that the system is available to
2. Referenced Documents
detect incoming X rays.
2.1 ASTM Standards:
3.2.8 overvoltage—the ratio of accelerating voltage to the
E3 Guide for Preparation of Metallographic Specimens
critical excitation voltage for a particular X-ray line.
E7 Terminology Relating to Metallography
3.2.9 SDD (silicon drift detector)—An x-ray detector char-
E673 Terminology Relating to SurfaceAnalysis (Withdrawn
acterized by a pattern in the biasing electrodes which induces
2012)
generated electrons to move laterally (drift) to a small-area
anode for collection, resulting in greatly reduced capacitance
which to a first approximation does not depend on the active
ThisguideisunderthejurisdictionofASTMCommitteeE04onMetallography
area, in contrast to conventional detectors using flat-plate
and is the direct responsibility of Subcommittee E04.11 on X-Ray and Electron
electrodes. (2)
Metallography.
Current edition approved Nov. 1, 2019. Published November 2019. Originally 3.2.10 shaping time—a measure of the time it takes the
approved in 1993. Last previous edition approved in 2012 as E1508 – 12a. DOI:
amplifier to integrate the incoming charge; it depends on the
10.1520/E1508-12AR19.
time constant of the circuitry.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3.2.11 spectrum—the energy range of electromagnetic ra-
Standards volume information, refer to the standard’s Document Summary page on
diation produced by the method and, when graphically
the ASTM website.
displayed, is the relationship of X-ray counts detected to X-ray
The last approved version of this historical standard is referenced on
www.astm.org. energy.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1508 − 12a (2019)
4. Summary of Practice be insignificant with respect to the X-ray volume.The operator
must also be aware of the possibility of spurious X rays from
4.1 As high-energy electrons produced with an SEM or
parts of the chamber, polishing compound elements, or from
EPMAinteract with the atoms within the top few micrometres
adjacent phases or a combination thereof. Note that these
of a specimen surface, X rays are generated with an energy
requirements for surface preparation preclude the quantitative
characteristic of the atom that produced them. The intensity of
analysis of casual samples, such as unpolished surfaces like
such X rays is proportional to the mass fraction of that element
fracture surfaces and particles.Although data can be generated
in the specimen. In energy-dispersive spectroscopy, X rays
on these casual surfaces, the results would be of significantly
from the specimen are detected by a solid-state spectrometer
lower precision with unpredictable variations.
that converts them to electrical pulses proportional to the
characteristic X-ray energies. If the X-ray intensity of each 7.2 Unetched or lightly etched specimens are preferred. If
element is compared to that of a standard of known or
they are etched, the operator must make sure that the compo-
calculated composition and suitably corrected for the effects of sition in the region to be analyzed has not been altered and that
other elements present, then the mass fraction of each element
the region to be analyzed is flat.
can be calculated.
7.3 Nonconducting specimens should be coated with a
conductive material to prevent charging. Lowering the accel-
5. Significance and Use
erating voltage may reduce or eliminate the effect of charging
5.1 This guide covers procedures for quantifying the el-
in some samples, but applying a conductive coating is still the
emental composition of phases in a microstructure. It includes
most common method. Evaporated carbon is usually the most
both methods that use standards as well as standardless
suitable coating material. Heavy metals such as gold that are
methods, and it discusses the precision and accuracy that one
often used for SEM imaging are less suitable because they
can expect from the technique. The guide applies to EDS with
heavily absorb X rays; if the coating is thick enough, X-ray
a solid-state X-ray detector used on an SEM or EPMA.
lines from those metals will be seen in the spectrum. If one is
analyzing carbon in the specimen, then aluminum makes a
5.2 EDS is a suitable technique for routine quantitative
good coating. The coatings are usually applied in thicknesses
analysisofelementsthatare 1)heavierthanorequaltosodium
of several tens of nanometres. Carbon that appears to be tan in
in atomic weight, 2) present in tenths of a percent or greater by
color on the specimen surface, or on a piece of filter paper in
weight, and 3) occupying a few cubic micrometres, or more, of
theevaporator, isprobablythickenough. For themostaccurate
the specimen. Elements of lower atomic number than sodium
analysis,standardsandunknownsshouldbecoatedatthesame
can be analyzed with either ultra-thin-window or windowless
time to assure equal coating thicknesses. Specimens mounted
spectrometers,generallywithlessprecisionthanispossiblefor
in a nonconducting medium must make electrical contact with
heavier elements. Trace elements, defined as <1.0 %, can be
the microscope stage. This is often accomplished by painting a
analyzed but with lower precision compared with analyses of
stripe of carbon or silver paint from the specimen to the
elements present in greater concentration.
specimen holder.
6. Test Specimens
8. Spectrum Collection
6.1 Suitable specimens are those that are normally stable
under an electron beam and vacuum and are homogeneous
8.1 Calibration—The analyzer shall be calibrated on two
throughout the volume of X-ray production. If the specimen is
X-ray peaks or other methods implemented by the equipment
inhomogeneous at the micrometre level, then a truly quantita-
manufacturer in software to set the amplifier gain and offset.
tiveanalysisisnotpossible,andabulktechniquesuchasX-ray
Often aluminum and copper are used, and sometimes both the
fluorescence should be used.
K and L lines of copper are used. The two elements need not
be in the same specimen. A spectrum from pure aluminum
6.2 The concentration of each element to be analyzed
could be collected followed by pure copper in the same
should equal or exceed about 0.1 wt %. Lower limits of
spectrum. Single-peak (gain only) calibration is possible for
detection are possible with longer counting times, but the
pulse processing electronics with internal means of establish-
precision of trace element analysis is poorer than when the
ing the offset (location of zero eV). Software is usually
elementispresentatthepercentlevel.Thesilicondriftdetector
available to calibrate the EDS system, and one should consult
allows lower minimum detectable limits in practical counting
the system manual for the details of operation. To ensure
times, down to several hundred parts per million in favorable
reproducible results, calibration should be checked periodi-
cases,becauseitretainsgoodenergyresolutionatmuchshorter
cally.
shaping times (thus higher count rates) than Si(Li) detectors.
8.2 Operating Parameters:
7. Specimen Preparation
8.2.1 The accelerating voltage of the SEM must be chosen
7.1 Specimens for quantitative EDS analysis should be to provide an adequate overvoltage to excite the X-ray lines of
prepared in accordance with standard metallographic or petro- interest. An overvoltage that is too low will not sufficiently
graphic techniques. Guidelines are given in Methods E3. The excite X rays; one that is too high yields low spatial resolution
specimen must be flat in the region to be analyzed. This and causes absorption as X rays escape from deep within the
requirement does not preclude scratches; however, any specimen. An overvoltage of at least 1.5 times the critical
scratchesintheimmediatevicinityoftheanalyzedregionmust excitationpotentialofthehighestenergyX-raylineanalyzedis
E1508 − 12a (2019)
recommended. When analyzing hard and soft X rays in the quantitative analysis, a shaping time of about 10 µs or greater
samespecimen,analysesattwovoltagesmaybenecessary.For is used for conventional detectors. SDDs are operated with
materials such as minerals and ceramics, which contain light shaping times between 3 and 10 times shorter than Si(Li)
elements (that is, of low atomic number), 15 kV is usually a detectors for the same spectral resolution, (in the 120-129 eV
goodcompromise.Formanymetalscontainingmediumatomic range) resulting in higher maximum throughput while remain-
number elements, 20 to 30 kV is a good choice. Heavy ingunder40%deadtime,providedthespecimencanwithstand
elements (those of higher atomic number) may be analyzed the required beam current without damage. The beam current
using L or M lines, and so higher voltages are not necessary. must remain stable throughout the analysis, because the counts
The actual accelerating voltage of the electron beam does not collected are directly proportional to the beam current. Thus, a
always correspond with the voltage selected on the instrument. 1 % upward drift in beam current will produce a 1 % increase
ItcanbedeterminedbyexpandingtheverticalscaleoftheEDS in all the reported mass fractions, resulting in a reported total
spectrum and observing the energy above which continuum X >100 %. For quantitative analysis using standards, the beam
rays do not occur. current (not specimen current) must be the same for both the
specimen and the standards or one must be normalized to the
8.2.2 Almost all elements can be analyzed using character-
other.
istic X-ray lines in the range of 0–10 keV. This range contains
8.2.6 The geometric configuration of the sample and
K lines of the first transition series (scandium–zinc (Sc-Zn)), L
detector, shown schematically in Fig. 1, also affects the
linesofthesecondtransitionseriesplusthelanthanides,andM
analysis. The number of X-ray photons that reach the detector
lines of the third transition series plus the actinides.
isafunctionofthesolidangleandtake-offangle,includingthe
Accordingly, most operators choose a 0–10 keV display at
effect of specimen and detector tilt. The count rate incident on
higher display resolution rather than a 0–20 keV display at
anX-raydetectorisdirectlyproportionaltothesizeofthesolid
lower resolution. Tables of X-ray energies can be found in
angle defined as follows for a detector normal to the line of
various texts, such as Goldstein, et al. (1) or Johnson and
sight to the specimen:
White. (3).
8.2.3 X-ray spatial resolution degrades with overvoltage, Ω 5 A/r (2)
because as the electrons penetrate deeper into the specimen, X
where:
rays are generated from a larger volume.An approximation of
Ω = solid angle in steradians,
the diameter of this tear-drop-shaped excitation volume, re-
A = active area of the detector crystal; for example, 30
ferred to as the X-ray range, can be obtained using the
mm , and
following equation. (4)
r = sample-to-detector distance, mm.
1.68 1.68
R 5 0.064 E 2 E /ρ (1)
~ !
o c
8.2.6.1 The larger the active area of the detector, the more
where:
counts will be collected, but at the expense of spectral
resolution. Most detectors have a movable slide and can be
R = the range in µm,
brought closer to the sample if a higher count rate at a given
E = the accelerating voltage in kV,
o
E = the critical excitation potential in keV, and beam current is needed. The take-off angle is defined as the
c
ρ = the density in g/cm . angle between the surface of the sample and a line to the X-ray
detector. If the sample is not tilted, the take-off angle is defined
...
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