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Sběrová účinnost detektoru sekundárních elektronů v REM
Konvalina, Ivo ; Müllerová, Ilona
In order to collect the secondary electrons (SE), scanning electron microscopes (SEM) are equipped with the Everhart-Thornley (ET) type detector. The electrostatic field of the front grid, biased to a positive potential of several hundred volts , is to attract all SE of kinetic energy below 50 eV or at least those from the SE spectrum peak at 1(3 eV. However, the detection quantum efficiency (DQE) of such detectors has been found to be significantly lower than one, which is mainly given by their low collection efficiency. The electrostatic field of the grid cannot sufficiently penetrate toward the specimen and influence the trajectories of SE owing to grounded electrodes surrounding the specimen (specimen alone and its holder, specimen stage, pole piece of the objective lens, etc)
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Rastrovací elektronová mikroskopie pomalými elektrony
Hrnčiřík, Petr ; Müllerová, Ilona
The largest sample thickness usable for transmission electron microscopy (TEM) is determined by the inelastic and elastic mean free paths (IMFP and EMFP). At primary electron energies normally used for TEM (>50 keV), both the mean free paths decrease as the primary energy is lowered. Attaining a sufficient penetration through a transmission sample of a given thickness is then simply a question of using a suitably high primary energy. As the primary energy is lowered below about 100 eV, however, IMFP is predicted to stop decreasing and to begin to grow again. This opens up the exciting possibility of very low voltage TEM, with poorer resolution but greatly reduced radiation damage compared to conventional TEM
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