Electron Microprobe Laboratories

The electron microprobe technique employs an electron beam accelerated to a selected voltage of 3-20 kV, and focused on the surface of the sample. The electron beam is typically operated at probe currents of 5 to 50nA and the beam spot size can vary from 0.04 to 20 µm. The volume excited by the electron beam varies in the range of about 0.03 to 4.5 cubic microns, depending on sample density and acceleration voltage, corresponding to a sample mass of a few picograms. The target (sample) generates characteristic X-rays, whose intensities are measured with wavelength or energy dispersive spectrometers. Quantitative analysis employing these characteristic X-rays and reference standards can be made of all elements except H, He and Li. Detection limits are typically between 20 and 400 ppm depending on the beam current and voltage, the X-ray line chosen and the counting time.
Digital X-ray maps show variations in chemical compositions on the surface of a sample. The resolution of the image, and time of acquisition, depend of the pixel number in each direction, whereby every pixel represent an individual analysis. For example, a pixel map of 512 x 512 contains 262144 analyses for each selected element.

The GeoForschungsZentrum maintains two electron microprobes, a JEOL Hyperprobe JXA-8500F with a thermal field-emission cathode (see Figure) and a JEOL Superprobe JXA 8230 with tungsten or LaB6 cathodes.

The JEOL Hyperprobe JXA-8500F has the following parameters:

  • Accelerating voltage: 1 to– 30 kV
  • Electron Gun: Schottky-Field emitter
  • Beam current: 0.01 to– 4500 nA
  • Minimum Beam Size: 40 nm at 10 kV and 10 nA
  • 5 Spectrometers


Profile photo of  Dr. Franziska Wilke

Dr. Franziska Wilke
Inorganic and Isotope Geochemistry

Building D, room 222
14473 Potsdam
tel. +49 331 288-1317