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Secondary electrons (SEs) are low energy electrons emitted from a localised area at the uppermost layers of samples surface (within a range of a few nm depths); therefore, they provide high-resolution imaging suitable for detailed topographical characterisation of samples. SEs are produced when primary electrons from the beam interact inelastically with the specimen. SEs have energies of < 50 eV, however.

Backscattered electrons (BSEs) are high-energy electrons generated as a result of elastic interactions between the primary electron beam and the sample. The range energy of BSEs is from 50 eV up to the energy of the electron beam. BSEs are emitted from a broad region within the interaction volume (the region in the sample where all the beam-sample interactions take place) with a range of penetration that can be as deep as a few microns for high-energy beams to hundreds or even a few tens of nanometres for low beam energies