What is the difference between the SEM and the electron microprobe?

Both use an electron beam, but the SEM is optimized for high-resolution imaging while the electron microprobe is optimized for accurate quantitative chemical analysis, typically with wavelength-dispersive spectrometers.

Does electron microprobe analysis destroy the sample?

It is essentially non-destructive at the scale of a polished thin section; the focused beam may cause minor local damage in beam-sensitive minerals but leaves the sample intact for further study.

Electron Microprobe and Microanalysis

Electron-beam microanalysis measures the chemical composition of minerals in situ at the micron scale by detecting the characteristic X-rays they emit.

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Definition

The set of electron-beam techniques, chiefly the electron microprobe and scanning electron microscope, used to determine the chemical composition and image the microtexture of minerals at the micron scale.

Scope

This topic covers the electron microprobe (EPMA) and scanning electron microscope (SEM), the generation of characteristic X-rays under electron bombardment, wavelength- and energy-dispersive spectrometry, quantitative analysis with matrix corrections, and imaging by backscattered and secondary electrons. It is the principal method for obtaining quantitative mineral chemistry.

Core questions

How does an electron beam generate characteristic X-rays in a mineral?
How do wavelength- and energy-dispersive spectrometers differ?
How are matrix corrections used to obtain quantitative concentrations?
What do backscattered-electron images reveal about composition?

Key theories

Characteristic X-ray generation and quantification: An electron beam ejects inner-shell electrons, and the resulting characteristic X-rays identify elements and, after correction for atomic number, absorption, and fluorescence effects, yield quantitative concentrations of mineral constituents.
Compositional imaging: Backscattered-electron intensity increases with mean atomic number, so images map compositional variation and zoning within grains, guiding quantitative spot analyses.

Clinical relevance

Quantitative microanalysis underpins geothermobarometry, the study of compositional zoning and diffusion, mineral identification of tiny phases, and ore characterization, making it one of the most widely used analytical tools in the earth sciences.

History

Raymond Castaing built and described the first electron microprobe in the early 1950s, establishing quantitative in-situ chemical analysis; subsequent decades brought energy-dispersive detectors, automated correction procedures, and combined SEM imaging that made microanalysis routine in geology.

Key figures

Raymond Castaing
Joseph I. Goldstein
S. J. B. Reed

Seminal works

reed2005
goldstein2018

Frequently asked questions

What is the difference between the SEM and the electron microprobe?: Both use an electron beam, but the SEM is optimized for high-resolution imaging while the electron microprobe is optimized for accurate quantitative chemical analysis, typically with wavelength-dispersive spectrometers.
Does electron microprobe analysis destroy the sample?: It is essentially non-destructive at the scale of a polished thin section; the focused beam may cause minor local damage in beam-sensitive minerals but leaves the sample intact for further study.