Secondary Electrons (SEs) are low energy electrons emitted from a localised area at the uppermost layers of samples surface (few nm depths); therefore, they provide high-resolution imaging suitable for detailed topographical characterization of samples. SEs are produced when primary electrons from the beam interact inelastically with the specimen. SEs have energies of < 50 eV.
SE images provide an excellent surface detail with well-defined edges. Regions of the sample facing the detector will appear brighter than those facing away or being blocked by the topography of the specimen creating the characteristic contrast in SE images. because of more SE electrons are emitted from Edges or sharp features of the specimen these regions will appear brighter.
The most common SE detector is the Everhart-Thornley (E-T) detector which is a type of scintillator-photomultiplier that provides high efficiency and reduced noise for collecting SE signal. A positively charged biased grid (set to a few hundreds of V) is used to attract emitted SEs (negatively charged) towards the E-T detector. The detector is placed off to one side of the sample inside the microscope chamber.
In-Beam SE detector
Another type of detector is the In-beam SE detector which is placed in the objective lens. The advantage of this detector is that it allows imaging at very short working distances thus better resolution can be achieved. The In-Beam SE detector enables to observe extraordinary sharp surface details and highlights topography.
All TESCAN systems are equipped with high-efficiency Everhart-Thornley (E-T) detectors as standard configuration. In-Beam SE detectors are optionally available for improved imaging quality in MIRA3, TIMA X, LYRA3, and FERA3, and, form a part of the standard configuration in MAIA3, GAIA3 and XEIA3.
Silicon substrate with nanocrystalline diamonds with Si vacancies Sample of LiFePO4 imaged at 3 keV with the In-Beam SE detector imaged at 2 keV with the In-Beam SE detector
Carbon fibres with silver nanoparticles imaged at 1 keV with the Wire bond in a microelectronic device imaged at 5 keV with the SE In-Beam SE detector