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Volume 107, Number 6, November–December 2002Journal of Research of the National Institute of Standards and Technology

[J. Res. Natl. Inst. Stand. Technol. 107, 627–638 (2002)]

Sample Preparation for Electron ProbeMicroanalysis—Pushing the Limits

Volume 107 Number 6 November–December 2002

Joseph D. Geller andPaul D. Engle

Geller MicroAnalytical Laboratory,Topsfield, MA 01983-1216

There are two fundamental considerationsin preparing samples for electron probemicroanalysis (EPMA). The first one mayseem obvious, but we often find it isoverlooked. That is, the sample analyzedshould be representative of the populationfrom which it comes. The second is adirect result of the assumptions in thecalculations used to convert x-ray intensityratios, between the sample and standard,to concentrations. Samples originate froma wide range of sources. During theirjourney to being excited under the electronbeam for the production of x rays thereare many possibilities for sample alteration.Handling can contaminate samples byadding extraneous matter. In preparation,the various abrasives used in sizing thesample by sawing, grinding and polishingcan embed themselves. The mostaccurate composition of a contaminatedsample is, at best, not representative ofthe original sample; it is misleading. Ourlaboratory performs EPMA analysis oncustomer submitted samples and preparesover 250 different calibration standardsincluding pure elements, compounds, alloys,glasses and minerals. This large varietyof samples does not lend itself tomass production techniques, includingautomatic polishing. Our manualpreparation techniques are designedindividually for each sample. The use of

automated preparation equipment doesnot lend itself to this environment, and isnot included in this manuscript. Thefinal step in quantitative electron probemicroanalysis is the conversion of x-rayintensities ratios, known as the “k -ratios,”to composition (in mass fraction oratomic percent) and/or film thickness. Ofthe many assumptions made in the ZAF(where these letters stand for atomicnumber, absorption and fluorescence)corrections the localized geometry betweenthe sample and electron beam, or takeoffangle, must be accurately known. Smallangular errors can lead to significanterrors in the final results. The samplepreparation technique then becomes veryimportant, and, under certain conditions,may even be the limiting factor in theanalytical uncertainty budget. This paperconsiders preparing samples to getknown geometries. It will not addressthe analysis of samples with irregular,unprepared surfaces or unknowngeometries.

Key words: electron probe microanaly-sis; grinding; mounting; polishing; quantita-tive analysis; sample preparation; sawing.

Accepted: September 20, 2002

Available online: http://www.nist.gov/jres

1. Sample Collection, Transport, andParticulate Mounting

EPMA samples originate from a large variety ofsources. They may be powders, corrosion scales on ahost surface, coated substrates or from bulk specimenssuch as metals, ceramics, glasses, and plastic or organicmaterial. In collecting the sample one must be certainthat nothing is added that will later be analyzed andmistaken for the analyte. One area of analysis where thisoften happens is with the analysis of small particles,which have to be collected and transported.

The challenge here is to collect the particles andembed them in a media suitable for grinding and polish-ing. The purpose of embedding or mounting is to holdthe particle during preparation so known geometriescan be established between the electron beam and x-raydetector. During analysis small airborne particles, thatmay range in size from sub-micrometer and up, areoften filtered or collected electrostatically. Particlesmay also be suspended in liquid form. How can such

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small particles be collected and transported for analysis?Air and liquid filtration may embed these particles intothe depth of three-dimensional filters, preferably singlesurface filters can be used with the particles populatingon a single surface (polycarbonate materials preferreddue to its chemical inertness), but with much reducedconductance resulting in far less volume filtered. Withdepth filtering the filter can be dissolved concentratingthe particles for later surface filtration or embedding.There is a risk, however, that the solvent used will reactwith the analyte by either putting it into solution,corroding the sample, or causing a chemical reactionresulting in a new compound or that impurities in thefilter itself be mistaken for the analyte. Larger particlesmay exist as scale and be simply scraped off a surfacetaking care not to sacrifice the scraping tool in theprocess. For instance, this author has had the unfortu-nate experience of finding tungsten in unknownparticles. With no tungsten used in the process thatgenerated these particles the origin was later determinedto be a tungsten probe that was used to dislodge theparticle. Unknowingly, a result was produced that hadnothing to do with the sample.

Particles may be suspended in oil that were createdwhile an engine or mechanical device was in operation.Concentrating the particles can be done by removingthem from the liquid with a tweezers or fine probe whilebeing observed under a microscope. They can also befiltered, as described above, except care must be takento use solvents that are compatible with the filters andthe particles. Sometimes particles are collected withadhesive tape. While this may be easy for collection, itcan be difficult to completely and cleanly remove them.Adhesive residue on the particles may be very difficultto remove, even with solvents and sonication. If theparticles are embedded with adhesive residue they maymove during grinding and polishing. This results in poorsurface finish or loss of the particle. We prefer using thePost-It note type of adhesive paper. While particlebonding may not be as good the adhesive is thinnerand remains on the paper providing less chance forcontamination.

Once the particles are collected they are nextprepared for polishing, the purpose of which is toestablish the necessary take-off angle for analysis. Clearembedment media offers the technician the advantage ofbeing able to observe the particles during the prepara-tion process. We have had much success using two-partepoxies (available from the major metalographicsuppliers) that cure overnight. Epoxies generally havevery good adhesion to the samples. In general, slowercuring epoxies are harder and have better edge retention.Other embedment media, such as cold mounts andacrylics that cure very quickly may not bind well to

particles, have poor edge retention and decomposerapidly from electron beam irradiation. Clear hot mountmaterials that are hardened under high pressure andtemperature may cause the particles to be redistributedover too large a volume with the end result being only afew particles exposed over the polished surface at thesame time. A technique which we use, and may havebeen used by others, employs a cured, vacuum degassed,epoxy mount. Several small (�2 mm) holes are drilledto the same depth in the mount. The bottom of the holeshas a “V” shape from the drill point. The particles areplaced, using a probe, into each hole making sure theyfind their way to the bottom (Fig. 1). The holes are thenfilled with freshly mixed epoxy, vacuum degassed, andthen examined under the stereo microscope to insure theparticles are still at the hole bottoms. Some of the holesat the periphery of the mount can be filled with a markermaterial, such as small ball bearings or wires. This willenable the technician to rapidly locate the plane of theembedded particles. Since there will be entrappedgas bubbles in the uncured epoxy the mount should becarefully vacuum degassed, making sure not tovolatilize the hardener in the process. If this happens theepoxy will not harden.

The mount is then ground with successively finer gritabrasives while intermittently observing the depth of themarkers below the mount surface. When the particlesbecome exposed, or nearly exposed, the final polishingsteps are initiated. This technique also works well foranalyzing wires and glass cylinders, such as fiber optics.

2. Preparing Samples or CalibrationStandards That are Available Onlyin Particulate Form

1. The choice of calibration standards can be equallyas important as the preparation to reduce the analyticaluncertainty. The ZAF calculation is used in a two-stepprocess. The first is to convert the intensities of thecompound standard used for x-ray intensity calibrationinto k -ratios, where the k -ratio is the counting rate ratiobetween the unknown and standard. After the sampledata is collected those x-ray intensities are converted tok -ratios then run through the ZAF calculation programfor determining concentrations. There are manyvariables in the ZAF calculation that affect the outcome.The selection of mass absorption coefficients, stoppingpower, fluorescence corrections, and errors in the takeoff angle result in variations of several percent. How-ever, if the standard chosen is the same composition asthe unknown no corrections need to be made. If an exactmatch is not available the analyst should choose astandard whose elements were in the same type of

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matrix and concentration to minimize the corrections.This was the basis for the early Bence-Albee [1]program for mineral analysis—and it worked quite well.The difficulty in using this technique is the lack ofreliable standards. Well characterized mineral standards,in particular, are in collections in museums such as theSmithsonian Institution in Washington, DC and manyuniversities that have EPMA laboratories. Since they

are inshort supply they are difficult to acquire, oftenavailable only on a barter basis. Even so, there are manynaturally occurring standards that are simply unavail-able. If the sample is not flat causing unknown errors inthe take off angle the proper corrections to the data willnot be made. For instance, for 1 % carbon in steel(Fig. 2) a 1� error in take off angle at 40� results in a 2 %relative error for carbon.

Fig. 1. Epoxy mount prepared for sectioning micrometer sized particles. A metal sample (10 �m) is at the hole bottom.

Fig. 2. Take off angle variation for carbon in iron where a 1� error in take off angle at 40� resultsin a 2 % relative error for carbon.

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3. A System of Calibration Standards

We have developed a system of standards (UHV-EL) that uses a 25 mm diameter stainless steel holderwith up to 37 holes, each being 3 mm in diameter. Inthis system each standard is individually prepared, withno materials other than the embedding medium, toprevent cross contamination that occurs when preparingmaterials of differing hardness. The holder is designedso that the polished surface of each standard whenplaced in the holder is top referenced. This auto-matically aligns the standard with the plane of the holderand provides for a predictable take off angle and aconstant working distance when moving betweenstandards. The holder is laser engraved uniquely identi-fying the position of each standard. These engravedmarkings are imaged either optically or with theelectron image. The 250, or so, standard materialsavailable can be selected from pure elements, com-pounds, glasses, alloys and minerals. Each standard ispolished using a procedure developed specifically forthat material, rather than polishing a surface containinga large range of materials with different hardness. Thisalso prevents cross contamination where materialsof different hardness contaminate each other. Thestandards are held in place with a stainless steel clip andare easily removable. General preparation guidelineswill be given later in this manuscript.

We try to select standards that can be directlyfabricated into 3 mm disks. The easiest to work with arefoils that can be punched. Ceramic materials and glassescan be cored with mechanical or ultrasonic drill.However, many materials are only available in powderform. Unfortunately, chemical suppliers often engineertheir processes to produce the minimum size powdergrains. A small number of these materials, all com-pounds, are sieved, and while they pass through 300mesh screens and often are agglomerated and haveindividual sizes approaching 1 �m. This is too smallfor microanalysis considering the electron scatteringvolume. However, other sources may not be available.A few examples are WO3 and MoO3, for which thecorrection factors, including the mass absorptioncoefficient, is not well known. These powder grainsmust be mounted for grinding and polishing.

We have selected silver flake (or tin flake for prepar-ing sulfides since sulfides reacts with silver) as a mount-ing medium since they have good electrical conductiv-ity, bleed the charge and help to conduct away the heatgenerated from the electron beam sample interactionand do not add an excessive number of peaks to the x-rayspectrum at analysis time. These metals are mixed withthe analyte, pressed at �1.4�103 GPa pressure andmildly annealed to densify and help keep the disctogether for further processing. The composite disc isthen ground and polished, revealing the polished analytesurfaces. As an example the SEM photograph in Fig. 3shows iron oxide grains in silver.

Fig. 3. FeO calibration (powder grains) standard mounted in silver and flat polished.

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4. Sizing the Sample

In many cases samples need to be reduced in sizeto fit into the analytical position in the EPMA chamber,into a metallurgical mount, or a polished section. Thesizing method used, if too aggressive, can cause deepdamage to both morphology and chemistry which maynot be removed during preparation. Sizing methodsused involve cleaving, scribing fractioning scissors,sawing, cutting, torching, and wire EDM (electrodischarge machining). In all cases it is imperative tobe aware of the damage depth caused. Subsequentoperations must completely remove the damagedmaterial.

For semiconductor wafers cleaving is accomplishedby placing a sharp pointed object on one side of thewafer and applying pressure at the opposite side startingthe cleave. If the cleave direction is oriented with thecrystallographic plane a straight cleave will follow.Unfortunately the cleaved edge will rarely be at rightangles to the wafer resulting in an unknown geometry.For EPMA instruments, with an optical microscopehaving a shallow depth of field, it may be possible tofind a location with the proper geometry for analysis.

Scribing thin, brittle samples is accomplished byusing carbide or diamond pointed tools to define afracture plane. The revealed surface will usually requirepolishing unless suitable areas for analysis can belocated.

Metal foils and soft coated materials can be cut withscissors or shears. Care must be taken to removedmaterial smeared across the cut surface.

Sawing operations require careful consideration ofdamage depth and possible sample contamination whenusing abrasive coated wheels. Over-aggressive sawingcan cause deep sample damage, generating cracksand heat affected zones beyond the depth for whichgrinding operations can remove them. Metallographiccut-off saws using ceramic blades may generate heatburning the sample surface causing melting, oxidationor the removal of surface coatings. Liquid coolingduring the cut is recommended. Low speed diamondsaws cut slowly, but leave a smooth surface and causevery low sample deformation. To prevent contaminationfrom the cooling liquid used during cutting the samplecan be dry cut. Rotation of the sample during cutting1

helps to increase the cutting speed (up to ten times),polishes the surface, and allows for a larger area to becut. The choice of blade used is critical.

1 Counter-Rota-Cutter, patent �4,949,605 from Geller MicroAnalyti-cal Lab, Topsfield, MA 01983

Metal samples can be cut with shears or pliers.Sample deformation again is a concern. Using a weldingtorch to cut a sample brings concerns about heatmodification of the sample. Finally, the wire EDM(electro discharge machine) is a very useful way to cutelectrically conductive samples. The wire EDM cuts bysparking its way through the sample, which is immersedin high resistivity water. It is very useful for cuttingsmall samples from large pieces. The deformation zoneis rather shallow so it is easy to grind through thedamage. The down side to this technique is the high costof the equipment and operator skill required, since wireEDMs are generally computer controlled.

5. Mounting the Sized Sample

Samples large enough to be held by hand or anothermechanical device during grinding and polishing maynot need to be mounted. There are several choices tobe made for mounting materials. Some of these arethermoplastic, acrylic cold mount materials, epoxies,and bakelite, diallyl phthalate or methyl methacrylatehot mount materials.

Sample orientation in the mount is often important.Many times multiple small sized samples are placed inthe same mount for simultaneous polishing. They can beheld in place in a number of ways. The metallurgicalsupply houses sell metal and plastic clips. Samples canalso be placed in sparing amounts of glue or epoxy andallowed to set before final mounting. They can also beplaced on double sided tape. All the mounting materialsbelow, except the hot mount materials, do not move thesamples excessively. The mounting pressure with hotmount materials may cause differential movementchanging the orientation.

Special consideration should be given to the mountingtechnique if EPMA analysis is done at the samplesedge, to prevent contamination from the electron beamdegrading the mount. One application is in the measure-ment of low concentration (<1 %) carbon in steels todetermine case hardening depths. Contamination fromdecomposed acrylic or epoxy will increase the carbonx-ray intensity giving false high readings. The mountingmedia formed at higher temperatures (carbon or metalfilled hot mounts) have the best characteristics since noadditional conductive coating is necessary.

Thermoplastic materials, like Crystalbond2 509have low melting temperature (�80 �C) and are soluble

2 Crystalbond 509 is manufactured by Armeco, Ossining, NY.

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in acetone. This material should not be placed in avacuum system due to outgassing and degradation ifstruck by an electron beam. 509 is very useful forholding samples in position for low speed sawing andpolishing. It is also useful for final polishing and thenremoving the mount materials so that the polishedsurface can be viewed along with the adjacent non-polished area (which could be a fracture, crack orsurface contamination or scale).

Acrylic cold mount materials set very quickly butdo not bond well to surfaces and have low hardness.Some acrylics rise in temperature by about 55 �C duringcuring. Poor bonding leaves gaps that allow abrasivesand slurry to collect and come out during later prepara-tion steps where finer abrasives are used. This causesscratches and outgassing when placed in vacuum. Theoutgassed material can contaminate the sample surface.Acrylic materials offer low resistance to electron beamexposure, decomposition upon contact and contamina-tion of the sample. They are also too viscous to fill lowdensity samples.

Two part epoxies better than acrylics for mounting.They bond well to surfaces, have higher hardness andare of sufficiently low viscosity to fill low densitysample voids. They can also be filled with hardmaterial, such as alumina ceramic, matching thehardness of the sample to help maintain edge retention.They have longer set times than acrylics, up to 24 hours.During curing the exothermic reaction may raise thetemperature by about 80 �C, depending upon theamount of hardener used. More hardener and/or heatingthe mount in an oven decreases the cure time. Epoxiesdecompose under electron beam irradiation. Epoxymixes have a lot of air dissolved. The air bubbles in thecured mount may retain abrasives that can scratch thespecimens later when finer polishing grits are used. Afreshly mixed epoxy can be vacuum degassed, takingcare not excessively volatize the hardener, changing themix and interfering with proper curing. Vacuum mount-ing also helps the epoxy flow into porous surfaces muchbetter. To ensure edge retention samples can be electro-less nickel-coated or coated with epoxies filled withceramics, such as Varian3 Torr-Seal.

Bakelite hot mount materials require high tempera-ture (up to 150 �C) and pressure. They form hardmounts and offer good stability from electron beamirradiation. With the addition of carbon or metals likecopper some are electrically conductive. Unfortunately,they are too viscous to fill voids in porous samples. Onemust be careful how the sample is placed in the mount,

3 Torr-Seal is manufactured by Varian Associates, Lexington, MA.

if the sample is too large or too close to an edge themount may crack due to differential expansion causing-gaps between the sample and mount. Seepage of polish-ing oils in bonding gaps during polishing results insample scratching. Seepage can also occur when thesample is placed in a vacuum that results in contamina-tion of the sample, and possibly, the EPMA. Unfortu-nately, these high viscosity mounting materials do notfill porous samples as well as epoxy. Analysis of porousmaterials, like ceramic catalysts, is an important EPMAapplication. To prevent cracking the manufacturer’scooling recommendations must be carefully followedafter the hot mount is formed.

Some hot mount materials are filled with carbon orcopper to make them conductive. These materials aresupplied as pellets or spheres that liquefy at processtemperature and pressure. We find it helpful to grind thematerials into a fine powder before use—this minimizesmovement and helps the material flow around thesample.

A comparison of two different preparations (hotmount and epoxy) of a porous, loosely bound,honeycomb like ceramic sample is shown in Fig. 4a and4b. In the hot mount preparation (Fig. 4b) no flat surfaceis observed since the mounting material did not fill thevoids, while the epoxy preparation binds the sample forpolishing (Fig. 4a), and some flat surfaces are observed.The darker areas are epoxy. Figures 5a and 5b show aprofilometer scan across the mount for both prepara-tions. The upper figure is from the epoxy mountedsample. The large voids were epoxy filled. Epoxy ismuch softer than the ceramic and is preferentiallyremoved during preparation. The ceramic is muchflatter than that for the hot-mount preparation. Since thehot mount material did not hold the ceramic in placeduring polishing much material was lost in preparation.

6. Grinding

The next step in getting a flat polished surface is togrind the bare or mounted material. There is a range ofmedia available including alumina, silicon carbide, anddiamond abrasives. These materials are available for useas loose powders or fixed onto a substrate—like paperor metal, in the case of diamond. In our laboratory weprepare a large number of materials with different hard-ness and are always concerned about cross contamina-tion. For that reason we prefer to use low cost, dispos-able silicon carbide paper. While diamond discs mayoffer some advantages for production work on the samematerials day after day, we cannot afford to contaminateour standards or customer supplied materials.

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a

b

Fig. 4. a. Porous ceramic honeycomb material vacuum embedded in epoxy and polished. Some areas are flatfor analysis. b. Same material hot mounted. No flat surfaces are seen.

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The grinding technique is very important. Thesurface area being ground, and the loading weightshould be varied to optimum conditions for eachmaterial.

The grit size is also important. We find that 240, 400,followed by 600 silicon carbide grit is satisfactory formost samples. The basic idea behind grinding is thateach step should remove the damage from the previousgrit used. Embedding grit is a big problem, especiallywith soft materials. There is very little published litera-ture on this subject. Factors that affect embedding for agiven material are; the type and size of abrasive used,and the force applied during grinding and polishing andthe affinity between the grit and the sample.

The example in Fig. 6 shows a silicon substrate thatis coated with silver epoxy and then copper. The cracksseen in the silicon are from cutting with a high speedrotary grinder. At higher magnification, the SEMphotos in Fig. 7a shows fine damage at the silver/siliconinterface after final polishing, while Fig. 7b show theinterface after further grinding and polishing past thedamage layer.

7. Polishing

Polishing is the final step in sample preparation,although chemical or electro chemical etching may be

used (more about that later). Vander Voort’s metallo-graphy book is an excellent reference [2] on all phasesof metallograpy. The ASM Metals Handbook [3]also is a good source and has a lot of information on thepreparation of various materials.

Abrasives used for polishing are generally finerthan those used for grinding, although the choice ofmaterials is similar. We prefer not to use CrO2, SiO2,CeO2, or Al2O3 since they easily embed themselves intothe sample. In addition, many of the samples we ana-lyze contain Cr and Al. Diamond in a water solublepaste, for easy washing, is our choice in the sequence of6 �m, 3 �m, and 1 �m grit sizes. Embedded diamondin a sample is relatively easy to recognize and does notinterfere with most analytical jobs. For those samplesthat are water soluble, such a NaCl and KI we polishwith kerosene as a lubricant for the diamond paste in awater and oil soluble carrier. Clean up is then doneusing methanol. Another common final polish materialused in the industry is sub-micrometer silica gel. Thisproduces a high luster on the sample surface, but suffersfrom the possibility that this fine abrasive will embeditself in the sample.

The choice of polishing cloth is critical for somesamples. To keep samples flat the harder clothswith short naps are generally used. For softer samples along nap cloth with light sample pressure is preferable.

a

b

Fig. 5. a. Same sample as in Fig. 4. The softer epoxy areas are preferentially polished whilethe epoxy filled ceramic areas are relatively flat. b. The hot mounted sample surface is flushwith the void, but the porous ceramic areas are very rough.

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Some general recommendations for different types ofmaterials are given below:

7.1 Soft Metals

We have not found a mechanical way to polish indium,not that we haven’t seen a shiny scratch free surface(which was full of 0.1 �m diamond). Indium can be cutwith a glass or diamond microtome knife. Other softmetals like Pb, Au, Pt, Ag, and Pd are polished under thefollowing guidelines.

1. Remove as little material as possible. Start with aflat surface.

2. Load the silicon carbide paper with bees wax. Thishelp keeps the SiC from embedding in the metal.

3. Try to start polishing with 3 �m diamond withoutusing silicon carbide. Use light pressure for a longtime reverting to SiC when necessary.

4. Using a high nap cloth helps keeping the diamondout of the metal.

7.2 Hard Metals

For metals such as Ti, V, Nb, and Zr we have foundit is better to polish with 3 �m diamond and avoid using1 �m, going directly to 0.1 �m for a short time. The1 �m diamond leaves scratches that are difficult toremove.

1. Aluminum and copper: these metals scratch easily,requiring 0.1 �m to finish.

2. Fluorides: water can leach out the fluorine,changing the stoichiometry.

3. Combined hard and soft materials: for instance,gold coatings on ceramic. In general, light pressureis used for long periods, with low nap cloth to helpkeep the sample flat. For refurbishing standardsthat are embedded and flat polished in one mount(this is not the way the UHV-EL standards aremade) one must be careful about water-solublestandards.

Fig. 6. Epoxy mount copper sample with silver epoxy and copper layers. Cracking in the silicon is from overaggressive grind with a high speed rotary tool.

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a

b

Fig. 7. a. Same sample in Fig. 6 after final polishing. Fine cracks are seen at the silver/silicon interface. b. Afterproperly removing the damaged layer the interface is free of cracks. 8. The flat polished flat surface in thesample from Fig. 2 was transformed into a pearlite structure after etching with HNO3. How can one determinethe take off angle?

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8. Etching

Etching is often used to reveal the samples grainstructure. The etching mechanism is selective removalof the sample by either chemical means (the etchantdissolving different phases in the sample at differentrates), by oxidation or reduction, or by removal of thesample at different rates according to the crystallo-graphic orientation. In any case the surface flatness iscompromised, as is the near surface density. Whilemicrostructure can be readily seen, the totals of theEPMA analysis are usually low. The 1 % carbon in steelsample shown in Fig. 2 was chemically etched withHNO3. The SEM photo in Fig. 8 shows that the flatpolished flat surface was transformed into a pearlitestructure. A profilometer scan revealed that the heightvariations are on the order of 1 �m, while the structuralvariations are much finer. Without even consideringchemical changes from etching one can visualize whata rough surface the electron beam sees. The take offangle on this surface is then indeterminate. An EPMAanalysis using a 1 �m beam is unlikely to be orthogonalto the surface.

9. Conclusion

Sample preparation for EPMA is critical to goodanalytical results. Like the proverbial “weakest link inthe chain” no data correction routine will fix errorsmade at the start of the process, which includecollection and transport of the sample to the analyticallaboratory. Once the sample is in the laboratory forpreparation, two areas that we have discussed are con-tamination of the sample with foreign material (that canbe either from sample handling prior to preparation orthe embedding of polishing abrasives during the prepa-ration process) and establishing known geometries(which are critical to the correction algorithms) betweenthe sample surface and electron beam. This encom-passes mounting, grinding and polishing the specimento achieve a flat surface.

Fig. 8. The flat polished flat surface in the sample from Fig. 2 was transformed into a perlite structure afteretching with HNO3. How can one determine the take off angle?

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10. References

[1] A. Bence and A.L. Albee, Empirical Correction on Factors for theElectron Microanalysis of Silicates and Oxides, J. Geol., JGEOA76, p. 382 1968,

[2] G.F. Vander Voort, Metallography Principles and Practice,McGraw-Hill Book Company, New York (1984).

[3] H.E. Boyer and T.L. Gail, Metals Handbook-Desk Edition,American Society for Metals, Metals Park, OH (1986).

About the authors: Joseph D. Geller is the proprietorof Geller MicroAnalytical Laboratory in Topsfield, MA.The company is certified to ISO-9001 and auditedto ISO-17025, a technical competency standard. Thecompany provides analytical services including EPMA,Auger electron spectroscopy surface analysis, metallo-graphy and optical microscopy. Products include(traceable) magnification and chemical calibrationstandards, and computer control systems for EPMAand Auger. Mr. Geller is the Chairman of the U.S. ISOTechnical Committee on Surface Analysis (TC-201)and an expert for TC-202, the Microbeam AnalysisCommittee.

Paul Engle is the laboratory manager, quality controldirector, and program manager for surface analysiscomputer control products. He has more than 10 yearsexperience preparing our samples and calibrationstandards.

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