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Questions?

Have questions about electron microprobe analysis? Want to know more about our facility? Send us an e-mail or visit our Contact Us page.

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What kind of materials can be analyzed?
	Many solid materials, both natural and synthetic, can be analyzed with the electron microprobe. We have analyzed rocks, minerals, sediments, ores, metals, alloys, thin films, ceramics, composites, microchips, teeth, archaeological artifacts, and more -- check out our image gallery to see some of these samples.

What kinds of solid materials cannot be analyzed?
	A few solid materials are not readily analyzed with an electron microprobe. Some materials are volatile and incompatable with a vacuum as low as 2E-6 torr. Other materials are susceptible to electron beam damage, which can then contaminate the interior of the microprobe. Thermal and electrical insulators tend to be susceptible to beam damage because energy (in the form of heat) from the electrons cannot be dispersed quickly enough. Materials like epoxy resin, paraffin wax, rubber, thermoplastics, and other hydrocarbon materials are highly susceptible to beam damage and should not be analyzed in the microprobe in order to avoid contamination.

Solid materials, huh? Can my samples be wet or sticky?
	No, the electron optical system operates under an ultra-high vacuum, so wet or sticky samples cannot be placed in the microprobe. All samples must be compatible with a vacuum as low as 2E-6 torr. If you have a wet or sticky sample (or you have a porous sample into which water may have seeped), it must be dried in an oven or desiccator first. If your sample cannot be dried out, you should look into the possibility of analysis with an environmental SEM (ESEM). An ESEM (a Phillips Electroscan) is housed at the University's Characterization Facility. Environmental SEMs are also commonly called variable-pressure SEMs (VP-SEMs).

What is the maximum specimen size?
	Specimens must be able to fit through the airlock and move around inside the microprobe without hitting any sensitive detectors. Normally the maximum specimen size is 100 x 100 x 50 mm (4 x 4 x 2 inches), but we can use special holders to slightly increase these dimensions. Any specimens that are much larger will not fit. Most of our holders are designed to accept petrographic thin sections (27 x 46 mm) and/or 1-inch round slides or epoxy plugs.

How are samples mounted for analysis?
	Samples for analysis are most often standard petrographic thin sections or embedded in epoxy resin mounts. We have various sample holders: ones that hold 1" round slides or epoxy plugs, and others that hold standard petrographic thin sections (27 x 46 mm), plus one that holds odd shapes. Please note that 1" round epoxy plugs must be less than 1" thick, and thin sections must be prepared without a cover slip. If you are planning probe work, be sure that your samples will fit into one of our holders -- if you have questions, we urge you to ask us ahead of time. Three of our eight sample holders: one that holds odd shapes (left), one that holds thin sections (center), and one that holds 1" round slides or epoxy plugs (right) Samples embedded in 1" round epoxy plugs Petrographic thin sections - 27 mm wide by 46 mm long

How are samples mounted for imaging?
	Samples for imaging, like those for analysis, could be petrographic thin sections or embedded in epoxy resin mounts. There are also options for samples that cannot be sectioned or polished. For instance, the samples of diatomite in the example pages were placed on conductive carbon tape, and a carbon coat was applied.

Is there any special sample preparation required?
	Specimens for EPMA have to be highly polished or quantitative analysis will not be possible. Without polishing, artifacts may be introduced into X-ray maps and electron images. Sample surfaces must also be cleaned so that they are free of dust, oils, polishing material, and such. Non-conductive samples must be conductively coated with a layer of carbon (for analysis) or gold (for imaging) prior to EPMA study.

Do you do sample preparation?
	Yes and no. We do not routinely prepare thin sections. There are several companies who will prepare thin sections for a modest fee -- we have had good luck with Petrographic International. Some universities will also prepare thin sections -- check with your local geology department. We will embed samples in resin epoxy plugs and then polish them for a fee and with sufficient time before the analyses are scheduled. There are companies who will do this as well.

How do I coat my samples with a carbon layer?
	Our lab is equipped with a JEOL JEE-400 Vacuum Evaporator that can be used to coat samples with a carbon layer prior to analysis. Lab personnel will coat samples prior to analysis for a small fee.

What happens to my sample after its analysis?
	We return it to you. Electron microprobe analysis is a non-destructive technique, but some material is usually expended in the sample preparation. Unlike most other analytical techniques, there is no induced radioactivity or chemical alteration of the sample. Some samples sustain a relatively small amount of heat damage under the beam. Other than a carbon coat, your sample is returned in the same condition it was before its analysis.

Content published on this Web Site is copyright the University of Minnesota Regents, the Electron Microprobe Laboratory, and/or the laboratory's users. Some content (particularly analyses and images of specimens) represents the intellectual property of laboratory users. Reproduction or distribution without permission is prohibited. Site content is available for educational and informational uses only, provided that the content is unmodified and that permission is granted by the author and/or the laboratory manager.
Geoarchaeology Archaeological Geology Geoarchaeology Archaeological Geology Obsidian Provenancing Obsidian Sourcing Obsidian Sourcing Obsidian Provenancing Electron Microprobe Analysis in Archaeology Electron Probe Microanalysis in Archaeology Electron Microprobe Analysis in Archaeology Electron Probe Microanalysis in Archaeology Petroarchaeology Petrography in Archaeology Petroarchaeology Petrography in Archaeology