1、Designation: E2809 13Standard Guide forUsing Scanning Electron Microscopy/X-Ray Spectrometry inForensic Paint Examinations1This standard is issued under the fixed designation E2809; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, t
2、he 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 guide is an outline of methods for scanningelectron microscopy (SEM) intended for use by forensic pain
3、texaminers. This guide is intended to supplement informationpresented in Guide E1610.1.2 The methods used by each examiner or laboratory orboth depend upon sample size, sample suitability, and labora-tory equipment.1.3 The term “scanning electron microscopy” occasionallyrefers to the entire analytic
4、al system including energy disper-sive X-ray spectrometry (EDS) or wavelength dispersive X-rayspectrometry (WDS) or both.1.4 This guide does not cover the theoretical aspects ofmany of the topics presented.1.5 This guide cannot replace knowledge, skill, or abilityacquired through appropriate educati
5、on, training, and experi-ence and should be used in conjunction with sound profes-sional judgment.1.6 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.7 This standard does not purport to address all of thesafety concerns, if an
6、y, 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 Standards:2E766 Practice for Calibrating the Magnification of
7、 a Scan-ning Electron MicroscopeE1492 Practice for Receiving, Documenting, Storing, andRetrieving Evidence in a Forensic Science LaboratoryE1508 Guide for Quantitative Analysis by Energy-Dispersive SpectroscopyE1610 Guide for Forensic Paint Analysis and ComparisonE1732 Terminology Relating to Forens
8、ic Science3. Terminology3.1 DefinitionsFor additional terms commonly employedfor general forensic examinations, see Terminology E1732.3.1.1 background X-rays (Bremsstrahlung, brakingradiation, continuous spectrum), nnonspecific X-ray radia-tion with a continuous energy range from zero up to the beam
9、voltage in which background radiation results from the decel-eration of beam electrons in the atomic Coulombic field.3.1.1.1 DiscussionA typical X-ray spectrum consists ofboth a continuous background and peaks from characteristicX-rays.3.1.2 backscattered electrons, nprimary beam electronsthat are s
10、cattered from the sample after undergoing fewinelastic interactions.3.1.2.1 DiscussionThe probability of backscattering isproportional to the atomic number.3.1.3 bulk analysis, ntype of scanning electron micros-copy (SEM) analysis that determines the average elementalcomposition of a material in whi
11、ch the area of analysis is aslarge as possible and may be achieved by a single large arearaster or the summed results from multiple smaller area rasters.3.1.4 cathodoluminescence, nemission of photons in theultraviolet (UV), visible (Vis), and infrared (IR) regions of theelectromagnetic spectrum as
12、a result of electron beam interac-tion with certain materials.3.1.5 characteristic X-rays, nX-ray emission resultingfrom de-excitation of an atom following inner shell ionizationin which the energy of the X-rays is related to the atomicnumber of the atom, providing the basis for energy dispersiveX-r
13、ay spectrometry (EDS).3.1.5.1 DiscussionA typical X-ray spectrum consists ofboth a continuous background and peaks from characteristicX-rays.1This guide is under the jurisdiction of ASTM Committee E30 on ForensicSciences and are the direct responsibility of Subcommittee E30.01 on Criminalis-tics.Cur
14、rent edition approved Feb. 15, 2013. Published April 2013. DOI: 10.1520/E2809-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page
15、 onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.6 charging, nnegative charge accumulation on either anonconductive sample or a sample that is not properlygrounded.3.1.6.1 DiscussionThis effect may interfere wit
16、h imageformation and X-ray analysis because of beam deflection. Itcan usually be eliminated by the application of a conductivecoating.3.1.7 detector fluorescence peak (dead-layer peak, siliconinternal fluorescence peak), npeak resulting from the emis-sion of characteristic X-rays in a thin layer of
17、inactive crystalarea in the front of an EDS detector.3.1.7.1 DiscussionThe peak is characteristic of the type ofdetector, such as silicon for a lithium-drifted silicon detector. Ina silicon detector, this peak may appear at 0.2 % apparentconcentration.3.1.8 electron probe microanalyzer (EPA, EPMA, E
18、MMA),nelectron beam instrument designed for quantitative X-rayanalysis (electron probe microanalysis).3.1.8.1 DiscussionIt is related to SEM but with multiplewavelength spectrometers and is designed to work at repro-ducible and stable beam currents and specimen-beam-X-raydetector geometries. Electro
19、n probe microanalysis is the deter-mination of elemental concentration by X-ray emission fromthe microvolume of material in which a static electron beaminteracts.3.1.9 embedding, nprocedure for casting a sample in ablock of material that polymerizes, or otherwise hardens, topermit handling during fu
20、rther preparation.3.1.10 energy dispersive X-ray spectrometry (EDS, EDXA,EDX), nEDX spectrometry is complementary to wavelengthdispersive spectrometry (WDS).3.1.11 escape peak, npeak resulting from incompletedeposition of the energy of an X-ray entering the EDS detector.3.1.11.1 DiscussionThis peak
21、is produced when an in-coming X-ray excites a silicon atom within the detector crystaland the resulting silicon (Si) K-alpha fluorescence X-ray exitsthe detector crystal. It occurs at the principal peak energyminus the energy of the Si K-alpha fluorescence X-ray (1.74KeV). The escape peak intensity
22、is about 1 to 2 % of the parentpeak.3.1.12 extraneous material, nmaterial originating from asource other than the specimen (synonyms: contaminant andforeign material).3.1.13 final aperture, nlast beam-restricting orifice in anelectron optical column.3.1.13.1 DiscussionThe orifice diameter influences
23、 thebeam current and depth of focus.3.1.14 interaction volume, nsample volume in which theelectron beam loses most of its energy.3.1.14.1 DiscussionIt is generally thought of as the vol-ume in which detectable X-rays are produced. The actualvolume varies depending upon beam voltage, average atomicnu
24、mber, and density of the sample.3.1.15 live time, ntime in which the EDS electronics areavailable to accept and process incoming X-rays.3.1.15.1 DiscussionLive time is often expressed as apercentage of real time.3.1.16 microtomy, nsample preparation method that se-quentially passes a blade at a shal
25、low depth through a sampleresulting in sections of selected thickness as well as a flatblock.3.1.16.1 DiscussionEach may be used for the determina-tion of sample characteristics.3.1.17 particle analysis, nanalytical method intended todetermine the elemental composition of a single particle suchas a
26、pigment particle in a paint layer.3.1.17.1 DiscussionUsually performed with a static (non-scanning) electron beam.3.1.18 pulse processor time constant, noperator-selectedvalue for pulse-processing time in which a higher value (longertime) results in a more accurate determination of the detectorampli
27、fier pulse height (better spectral resolution) and a lowervalue results in a higher count rate but with reduced spectralresolution.3.1.19 raster, nrectangular pattern scanned by the electronbeam on a sample.3.1.19.1 DiscussionThe raster dimensions change in-versely with magnification.3.1.20 represen
28、tative sample, nrepresentative portion ofthe specimen selected and prepared for analysis that is believedto exhibit all of the elemental characteristics of the parentspecimen.3.1.21 sample polishing, nsample preparation method us-ing progressively finer abrasives to achieve a flat, smoothsample surf
29、ace.3.1.21.1 DiscussionGenerally, this is required for quanti-tative analysis.3.1.22 scanning electron microscopy (SEM), ntype ofelectron microscope in which a focused electron beam isscanned in a raster on a solid sample surface.3.1.22.1 DiscussionThe strength of resulting emissions ofsignals varie
30、s according to sample characteristics such ascomposition or topography. As the electron beam of the SEMscans the surface of a sample, a signal is continuouslyregistered by the imaging system which produces a two-dimensional image of the sample on the display monitor. Bypopular usage, the term SEM ma
31、y also include the analyticaltechniques EDS and WDS.3.1.23 secondary electrons (SE), nlow-energy electronsproduced from the interaction of beam electrons and conduc-tion band electrons of atoms within the interaction volume thatare produced throughout the interaction volume, but only thosenear the s
32、urface have enough energy to escape.3.1.23.1 DiscussionThe secondary electron signal is typi-cally used to form topographic images.3.1.24 smear, ntransfer of paint resulting from contactbetween two objects and consisting of comingled particles,fragments, and possible pieces of one or both surfaces.3
33、.1.25 specimen, nmaterial submitted for examination.3.1.25.1 DiscussionSamples are removed from a speci-men for analysis.E2809 1323.1.26 spectral artifacts, nspectral peaks other than char-acteristic peaks produced during the EDS detection process.3.1.26.1 DiscussionExamples are escape peaks and sum
34、peaks.3.1.27 spectral resolution, nmeasure of the ability todistinguish between adjacent peaks in an X-ray spectrum and itis usually determined by measuring peak width at half themaximum value of the peak height or full-width half-maximum.3.1.28 sum peak, npeak occurring at the sum of the energyof t
35、wo individual peaks.3.1.29 dead time, ntime during which the EDS is not ableto process X-rays.3.1.29.1 DiscussionDead time is typically expressed as apercentage of real time during which the detector is notcollecting X-ray data.3.1.30 system peaks (stray radiation), npeaks that mayoccur in the X-ray
36、 spectrum resulting from interaction of theelectron beam or fluorescent radiation with components of theSEM itself3.1.31 takeoff angle, nangle between the specimen surfaceand the detector axis.3.1.32 transmission electron microscopy (TEM), ntype ofelectron microscopy in which an image of a sample pr
37、epared asa thin section is formed by the interaction of the beam passingthrough the sample.3.1.33 variable pressure scanning electron microscopy (LV,CP, VP, ESEM), ntype of SEM that is designed to operate athigher chamber pressure than the conventional in which theneed for application of a conductiv
38、e coating is minimized whenusing a variable pressure SEM; however, EDS may be com-plicated because of the electron beam spread experienced athigher operating pressures.3.1.34 wavelength dispersive spectroscopy (WDS, WDXA),nX-ray spectroscopy that separates and identifies X-raysbased on their differe
39、nces in wavelength.3.1.34.1 DiscussionWDS is a complementary spectros-copy to EDS.3.2 Definitions of Terms Specific to This Standard:3.2.1 concentration, nfor the purpose of this guide, thefollowing ranges shall apply: major: greater than 10 %; minor:1 to 10 %; and trace: less than 1 %.3.2.2 sample
40、size, nfor the purposes of this guide, thefollowing terms are used to describe sample size with theactual size demarcation between each being somewhat arbi-trary.3.2.2.1 fragment, nonly within this guide, sample orspecimen smaller than approximately 0.2 mm.(1) DiscussionIf the material from which th
41、e fragmentoriginated was layered, then the fragment may also show alayered structure with light microscopy inspection and SEManalysis. A fragment is frequently not of sufficient size topermit multiple tests.3.2.2.2 particle, nonly within this guide, sample or speci-men whose greatest dimension is le
42、ss than approximately 50m.(1) DiscussionMaterial of this size generally has none ofthe overall structural characteristics that can be associated withthe material from which the particle originated. A particle isgenerally not of sufficient size to permit multiple tests.3.2.2.3 piece, nsample or speci
43、men larger than approxi-mately 0.2 mm.(1) DiscussionIf the material from which the piece origi-nated was layered, then the piece may show a layered structure.A sample of this size is sufficient to perform all of thesuggested cross-sectional preparation and analytical methods.3.2.3 thick section, nfo
44、r the purpose of this guide, asample that is 2 m or thicker.3.2.4 thin section, nfor the purpose of this guide, a samplewith a thickness of less than 2 m.4. Significance and Use4.1 The SEM can be used to define and compare the layerstructure of multilayered samples, the structure of individuallayers
45、, the bulk elemental composition of individual layers, andthe elemental composition of individual particulate compo-nents within paints and coatings.4.2 The test methods described in this guide may have somelimitations. They include the inability to detect elements intrace concentrations, the need f
46、or a conductive coating of thesample, the inability to remove a sample from most embeddingmaterials after analysis, and the discoloration of materials byirradiation.4.3 Although quantitative and semiquantitative methods areavailable for EDS (see Guide E1508), they are not appropriatefor most paint a
47、nalyses because of the typical heterogeneity ofpaint. Application of quantitative methods is further compli-cated by an inability to predict what compounds may bepresent (see 7.12.1).4.4 The information available from a specimen may dimin-ish as its size is reduced and its condition degrades.The sma
48、llera specimen is, the less valuable it becomes for association witha known because it may contain fewer characteristics of theoriginal material.As specimen size is reduced, it may no longerbe representative of the original material. This may also be trueof a degraded sample.4.5 This guide is intend
49、ed to advise and assist laboratoryanalysts in the effective application of scanning electronmicroscopy to the analysis of paint evidence. It is intended tobe applicable to most modern scanning electron microscopestypically used in the forensic laboratory.4.6 It is not the intention of this guide to present compre-hensive methods of SEM. It is necessary that the analyst havean understanding of SEM operation and general concepts ofspecimen preparation before using this guide. This informationis available from manufactur
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