SEM: Interaction with sample

• A SEM is like a large X-ray vacuum tube used in conventional X-ray diffraction systems. Electrons emitted from the filament (cathode) are accelerated to high energies where they strike the specimen target (anode). In the process, X-rays characteristics of atoms in the irradiated area are emitted. By an analysis of their energies, the atoms can be identified and by a count of the numbers of X-rays emitted the concentration of atoms in the specimen can be determined.

Figure 17.06: Variation of tear drop shape with accelerating voltage [5,6].

• These figures show the variations in the interaction volume with the atomic number in the materials and energy of the incident beam.

• While the high energy electron beam produces a very nice tear drop shape interaction volume in materials having low atomic number elements, the high atomic number elements produce a very wide interaction volume area which increases with increasing the electron beam energy.

Ref.[6]. http://www4.nau.edu/microanalysis/Microprobe-SEM/Signals.html.