Center for Electron Microscopy (ZELMI)

Element analysis

EDX - Energy Dispersive X-ray Analysis (all electron microscopes)

EDX can be used for chemical elements starting from beryllium (Be). The elements hydrogen, helium and lithium cannot be analyzed with EDX. The detection limit varies; but is generally at about 0.1 atomic percent. The lateral resolution for qualitative analysis is about 10 nm, and for quantitative analysis the lateral resolution is about 300 nm. For quantitative analysis, metallographic preparation is required or a flat surface with a homogeneous examination volume. As an alternative to energy dispersive X-ray analysis, wavelength dispersive X-ray analysis can be used to achieve more precise quantification and detection limits.

WDX - Wavelength Dispersive X-ray Analysis (Electron Beam Microprobe)

X-rays generated by an electron beam are emitted from the sample, diffracted at the net planes of a crystal (Bragg diffraction: nλ=2dsinθ) and detected by means of a proportional counter tube.

This allows much more accurate element identification than with EDX (less peak overlap) due to the very good spectral resolution. On the other hand, the detection limit is significantly better and thus the analysis of trace elements is also possible.

µRFA - Micro X-ray fluorescence analysis (electron beam microprobe)

X-rays generated at a rhodium target are focused onto the sample using polycapillary optics. X-rays are again generated in the sample and detected by the EDX detector or WDX spectrometers. This type of X-ray generation is called X-ray fluorescence and has the advantage that, compared to electron-excited X-rays, no bremsstrahlung is generated and one thus achieves a better detection limit (a few 10 ppm versus 1000 ppm).  The spot diameter of the X-ray beam on the sample is about 100 µm. The depth of information is in the order of a few 10 µm. This has the advantage that average concentrations can be measured over large volumes.

Furthermore, it is possible to analyze non-conducting substances, since no charge carriers are present.