Scientists at the University of Nantes (France) have recently developed a
novel technique to detect and quantify grain boundary segregations using wavelength
dispersive X-ray spectroscopy (WDS).
The instrument basis for the development of the new technique is the MERLIN®
Field Emission Scanning Electron Microscope from Carl
Zeiss, equipped with an Oxford WDS spectrometer. The experiment was performed
at the Laboratoire Génie des Matériaux et Procédés
Associés Polytech´ Nantes (LGMPA).
The main characteristic of the MERLIN FE-SEM enabling this novel technique
is the high probe current, of up to 300 nA. In the experiment it was even possible
to operate the system at 400 nA. Only by applying such a high probe current
can sufficient signal be excited. Due to the double condenser lens of the GEMINI®
II column within the MERLIN, the beam diameter is minimized to the extreme,
resulting in high spatial resolution of the WDS analysis.
Interfacial segregations can lead to a dramatic change of materials properties,
e.g. loss in ductility of iron, nickel or copper alloys. Until now, the characterization
of top surface layers is generally processed with Auger Electron Spectroscopy
or Electron Probe Micro Analysis. Both techniques have several drawbacks, e.g.
the need for ultra-high vacuum conditions or limitations in spatial resolution.
These drawbacks are overcome by the technique developed at the LGMPA, Nantes.