Electron microscopy
Faraday Cage for Probe Current Measurement in EMs
- Practical Electron Microscopy and Database -
- An Online Book -
Microanalysis | EM Book                                                                                   http://www.globalsino.com/EM/        



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:
         i) Calibrate the zero current with a Faraday cage as shown in Figure 3115 (a).
         ii) As shown in Figure 3115 (b), rotate the Faraday cage and record the beam current by reading a current meter.

Faraday cage used to measurement electron beam current: (a) Calibration of zero current. (b) Beam current measurement.

Figure 3115. Faraday cage used to measure electron beam currents: (a) Calibration of zero current. (b) Beam current measurement.