Faraday Cage for Probe Current Measurement in EMs
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Probe currents in TEM and SEM systems can be measured with a picoammeter at the large phosphorus viewing screen or the small phosphorus viewing screen, and at the sample with a faraday cup holder.
The electron probe (beam) current can be directly and simply measured with a Faraday cage. Therefore, the currents obtained at the Faraday cup can be the currents used for dose calculations. For instance, in some TEM cases, the Faraday cages are mounted on a removable specimen rod. The current measurement can be done as follows:
Figure 3115. Faraday cage used to measure electron beam currents: (a) Calibration of zero current. (b) Beam current measurement.