Electron microprobe
An electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. It works similarly to a
History
The electron microprobe (electron probe microanalyzer) developed from two technologies:
There have been at several historical threads to electron beam microanalysis. One was developed by
A second thread developed in France in the late 1940s. In 1948–1950,
The 1950s was a decade of great interest in electron beam X-ray microanalysis, following Castaing's presentations at the First European Microscopy Conference in Delft in 1949[10] and then at the National Bureau of Standards conference on Electron Physics[11] in Washington, DC, in 1951, as well as at other conferences in the early to mid-1950s. Many researchers, mainly material scientists, developed their own experimental electron microprobes, sometimes starting from scratch, but many times using surplus electron microscopes.
One of the organizers of the Delft 1949 Electron Microscopy conference was Vernon Ellis Cosslett at the Cavendish Laboratory at Cambridge University, a center of research on electron microscopy,[12] as well as scanning electron microscopy with Charles Oatley as well as X-ray microscopy with Bill Nixon. Peter Duncumb combined all three technologies and developed a scanning electron X-ray microanalyzer for his PhD thesis (1957), which was commercialized as the Cambridge MicroScan.
Pol Duwez, a Belgian material scientist who fled the Nazis and settled at the California Institute of Technology and collaborated with Jesse DuMond, encountered André Guinier on a train in Europe in 1952, where he learned of Castaing's new instrument and the suggestion that Caltech build a similar instrument. David Wittry was hired to build such an instrument as his PhD thesis, which he completed in 1957. It became the prototype for the ARL[13] EMX electron microprobe.
During the late 1950s and early 1960s there were over a dozen other laboratories in North America, the United Kingdom, Europe, Japan and the USSR developing electron beam X-ray microanalyzers.
The first commercial electron microprobe, the "MS85" was produced by
Operation
A beam of electrons is fired at a sample. The beam causes each element in the sample to emit
Detailed description
Low-energy electrons are produced from a
When the beam electrons (and scattered electrons from the sample) interact with bound electrons in the innermost electron shells of the atoms of the various elements in the sample, they can scatter the bound electrons from the electron shell producing a vacancy in that shell (ionization of the atom). This vacancy is unstable and must be filled by an electron from either a higher energy bound shell in the atom (producing another vacancy which is in turn filled by electrons from yet higher energy bound shells) or by unbound electrons of low energy. The difference in binding energy between the electron shell in which the vacancy was produced and the shell from which the electron comes to fill the vacancy is emitted as a photon. The energy of the photon is in the X-ray region of the electromagnetic spectrum. As the electron structure of each element is unique, the series X-ray line energies produced by vacancies in the innermost shells is characteristic of that element, although lines from different elements may overlap. As the innermost shells are involved, the X-ray line energies are generally not affected by chemical effects produced by bonding between elements in compounds except in low atomic number (Z) elements ( B, C, N, O and F for Kalpha and Al to Cl for Kbeta) where line energies may be shifted as a result of the involvement of the electron shell from which vacancies are filled in chemical bonding.
The characteristic X-rays are used for chemical analysis. Specific X-ray wavelengths or energies are selected and counted, either by
Chemical composition is determined by comparing the intensities of characteristic X-rays from the sample with intensities from standards of known composition. Counts from the sample must be corrected for
Volume from which chemical information is gathered (volume of X-rays generated) is 0.3 – 3 cubic micrometers.
Limitations
- WDS cannot determine elements below number 3 (lithium). This restricts WDS when analyzing geologically important elements such as H, Li, and Be.[20]
- Despite the improved spectral resolution of elemental peaks, some peaks exhibit significant overlap that causes analytical challenges (e.g., VKα and TiKβ). WDS analyses are unable to distinguish the valence states of elements (e.g. Fe2+ vs. Fe3+) which must be obtained by other techniques such as Mössbauer spectroscopy or electron energy loss spectroscopy.[20]
- Element isotopes cannot be determined by WDS, but are most commonly obtained with a mass spectrometer.[20]
Applications
Materials science and engineering
The technique is commonly used for analyzing the chemical composition of metals, alloys, ceramics, and glasses.[21] It is particularly useful for assessing the composition of individual particles or grains and chemical changes on the scale of a few micrometres to millimeters. The electron microprobe is widely used for research, quality control, and failure analysis.
Mineralogy and petrology
This technique is most commonly used by mineralogists and
The change in elemental composition from the center (also known as core) to the edge (or rim) of a mineral can yield information about the history of the crystal's formation, including the temperature, pressure, and chemistry of the surrounding medium. Quartz crystals, for example, incorporate a small, but measurable amount of titanium into their structure as a function of temperature, pressure, and the amount of titanium available in their environment. Changes in these parameters are recorded by titanium as the crystal grows.
Paleontology
In exceptionally preserved fossils, such as those of the
Meteorite analysis
The chemical composition of meteorites can be analyzed quite accurately using EPMA. This can reveal much about the conditions that existed in the early Solar System.[citation needed]
Online tutorials
- Jim Wittke's class notes at Northern Arizona University[24]
- John Fournelle's class notes at the University of Wisconsin–Madison[25]
- John Donovan's class notes at the University of Oregon[26]
See also
References
- ^ Cosslett, V. E., and P. Duncumb. "Micro-analysis by a flying-spot X-ray method." Nature 177, no. 4521 (1956): 1172-1173.
- ^ Wittry, David B. (1958). "Electron Probe Microanalyzer", US Patent No 2916621, Washington, DC: U.S. Patent and Trademark Office
- .
- S2CID 15082304.[permanent dead link]
- S2CID 94191823.
- ^ "ChemTeam: Moseley Articles".
- .
- Application des sondes électroniques à une méthode d'analyse ponctuelle chimique et cristallographique: publication ONERA (Office national d'études et de recherches aéronautiques/ Institute for Aeronautical Research) N. 55(PhD Thesis). University of Paris.
- ^ http://www.microbeamanalysis.org/history/Castaing-Thesis-clearscan.pdf is equivalent to https://the-mas.org/castaings-famous-1951-thesis/
- ^ "Proceedings of the EM Conference" (PDF). geology.wisc.edu. July 1949. Retrieved 24 June 2023.
- ^ "Circular of the Bureau of Standards no. 527: Electron physics". National Bureau of Standards. 17 March 1954.
- ^ Long, J. V. P. "Microanalysis." Micron 24, no. 2 (1993): 143-148. https://doi.org/10.1016/0968-4328(93)90065-9
- ^ Eklund, Robert L. "Bausch & Lomb-ARL: Where We Come From, Who We are." Applied Spectroscopy 35, no. 2 (1981): 226-235.
- ^ Jansen, W.; Slaughter, M. (1982). "Elemental mapping of minerals by electron microprobe" (PDF). American Mineralogist. 67 (5–6): 521–533.
- ^ John Goodge, University of Minnesota-Duluth (23 July 2012). "Element mapping". Serc.carleton.edu. Retrieved 23 December 2015.
- ^ Duncumb P. and Reed S.J.B., NBS Spec. Publ. 298, Heinrich K.F.J. ed., 1968, p. 133
- ^ Bishop H.E., 4th Int. Congr. X-Ray Opt., Orsay, Hermann, Paris, 1966, p. 153
- ^ S.J.B. Reed, Electron microprobe analysis, Cambridge University Press, 1993
- ^ K.F.J. Heinrich, and D.E. Newbury eds., Electron probe quantitation, Plenum Press, 1991
- ^ a b c "Wavelength-dispersive spectroscopy (WDS)". Geochemical Instrumentation and Analysis. Retrieved 13 May 2016.
- ^ Llovet, Xavier, Aurélien Moy, Philippe T. Pinard, and John H. Fournelle. "Electron probe microanalysis: a review of recent developments and applications in materials science and engineering." Progress in Materials Science (2020): 100673. doi.org/10.1016/j.pmatsci.2020.100673
- doi:10.1111/j.1502-3931.2007.00013.x. Archived from the originalon 8 December 2012. Retrieved 20 August 2008.
- .
- ^ "Electron Microprobe Homepage". Archived from the original on 22 March 2017. Retrieved 4 July 2020.
- ^ "Geoscience 777 Lecture Notes". www.geology.wisc.edu. Retrieved 24 June 2023.
- ^ "Lecture Notes and PowerPoint Files". pages.uoregon.edu. Retrieved 24 June 2023.
Further reading
- Reed, Stephen (2005). Electron microprobe analysis and scanning electron microscopy in geology. Cambridge university press.
External links
- Media related to Electron microprobes at Wikimedia Commons
- Electron Probe Laboratory, Hebrew University of Jerusalem - web page of a lab describing their modern EPMA