Electron microprobe analyser (EMPA)

Group Leader

Dr. Christina Günter

E-mail:
guenter@geo.uni-potsdam.de
Phone:
+49 331 977 5605
Fax:
+49 331 977 5700
Arbeitsgruppenbild Allgemeine Geologie

Description

The electron microprobe analyser (EMPA) allows to determine the chemical composition of minerals and glasses in-situ and non-distructively.

A beam of electrons excites a small volume underneath the solid target surface (interaction volume of a few µm3) that subsequently emits different types of waves. These include secondary electrons (SE), back-scattered electrons (BSE) and X-rays. The intensity of SE preserves information of the sample surface, that of BSE of the target's mean atomic number and X-rays are characteristic in wavelength to the elements being analysed.

If the beam is in scanning mode, then topographic images (SE) and images recording the spatial variation of mean atomic numbers (BSE) across sample surfaces can be obtained. Acquisition of element specific X-rays allows the distribution of element concentrations at the sample surface to be determined (X-ray mapping).

If in spot mode, X-ray wavelengths are statistically counted using either energy dispersive spectrometer (EDS) or wavelength dispersive spectrometer (WDS). The former accumulates all wavelengths produced from the interaction volume simultaneously, whereas the latter uses the Bragg diffraction from an analytical crystal to select and count a specific X-ray wavelength of interest.

Instrumentation

Our system comrises a JEOL JXA-8200 equipped with:

  • five wavelength dispersive spectrometer (WDS) for quantitative mineral chemical analysis,
  • an Oxford Scientific energy dispersive spectrometer (EDS) used for qualitative mineral chemical analysis,
  • a cold-cathode cathodoluminescence detector for examining internal structures on minerals related to composition, growth and thermal re-equilibration.