In general, the current of incident electron beams in EMs may vary from one measurement to another depending on tip condition, extraction voltage, and parameters of the electron optics.
Figure 1970 shows the structure of the electron probe-forming system in STEM mode in JEOL JEM-2010F TEMs. The beam current decreases due to the probe-forming aperture.
Figure 1970. Schematic illustration of the probe-forming electron optics in STEM mode in JEOL JEM-2010F TEMs.
Furthermore, for TEM, STEM, and EELS measurements, the detected currents also depends on the beam spreading inside the specimens.