Impacting primary electrons (PE) are elastically distributed in the atom nucleus area. The higher the positive charge, the stronger the PE deflection at the atom nucleus This helps to scatter more electrons back from the sample surface with increasing atomic numbers (increasing atomic weight). These areas are displayed with a brighter color → Material contrast.
In addition, the back-scattering coefficient depends on the crystal orientation → Orientation contrast.
Electron probe micro analysis
Energy dispersive x-ray spectrometry
Scanning electron microscope
Wave-length dispersive x-ray spectrometry
Schröttner H. : Die Elektronenmikroskopie in der Materialforschung / Electron Microscopy in Materials Research.