Scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX)

Scanning electron microscopy (SEM: Scanning Electron Microscopy)

Principle
Device similar to the optical microscope but where the light rays are replaced by an incident electron flux. The reflected electrons provide an image of the surface of the object or the sample. The shades of grey of the picture are directly related to the atomic weight of the analysed materials.

Applications

  • Multiple.
Advantages

  • Possibility of examining an extremely tenuous particle;
  • No problem of field shallowness;
  • Study of the stratigraphy;
  • Very important magnifying power.
X-ray detector (EDX: Energy dispersive X-ray spectroscopy)

Principle

Consists in connecting to a scanning electron microscope a system of elementary analysis based on the X-ray micro-fluorescence in order to be able to analyze very definite zones of a sample. Combined to the SEM, the energy dispersive X-ray spectroscopy makes it possible to analyse samples in the range of the nanometer and to provide their elementary composition. The secondary X-rays produced at the moment of the impact of the electron beam on the sample are typical of the elements present in the analysed material. This technique is not a properly so called spectrometry since the excitation source is not of an electro-magnetic origin.

Applications

  • Extremely varied.
Advantages
In addition to those linked to electron microscopy, ultramicroanalysis allows, among other things:

  • To identify the mineral constituents of each stratum of a pictorial layer;
  • To identify and proportion the components of an alloy;
  • To identify the corrosion products;
  • To check the nature of the metallic concretions which form crystallizations on the surface of archaeological objects ;
  • To focus the excitation source on a precise dot of the sample or else to scan the whole surface or a determined zone of the sample;
  • To study the way the elements are combining with each other using the “mapping” process (image of the distribution of each element in the sample).