Scanning Electron Microscopy


The efficiency of the detector in an electron energy loss spectrometer is crucial to the performance of the system. The quality of this performance can be quantified in terms of the Detector Quantum Efficiency (DQE), the Modulation Transfer Function (MTF) and the radiation dose resistance (DR). The energy loss spectrum can be obtained either serially, by scanning the energy dispersion across a defining slit in front of a detector, or in parallel, by employing a detector or detectors with spatial resolution. The DQE, MTF and DR of serial detectors varies widely with the design chosen, but the fundamental limit to the DQE imposed by the sequential nature of the data collection process is such that serial detection, although simple, is never competitive with parallel collection. Present parallel detection schemes offer about an order of magnitude improvement in DQE over serial systems, but improvements in dynamic range, radiation resistance and fixed pattern noise are required before the full abilities of these detectors can be exploited.

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