direct electron detector

The direct electron detector is a detector in which accelerated electrons are directly received by an image sensor of CCD or CMOS instead of using a scintillator. Those electrons are converted directly into electric signals, whereas in a usual case, the accelerated electrons are received by a scintillator, converted to light and then the light is transferred to a CCD or CMOS using a lens system or an optical fiber system. Very large electric signals are produced in the case of the direct detector because the scintillator converting electron signals to light signals is not used and the incident electrons possess a very high energy than the light signals produced in the scintillator. The direct electron detector has 10 to 100 times higher sensitivity for electron detection than the scintillator - CCD system. Taking advantage of this high sensitivity, the direct electron detector is effectively used for cryo-electron microscopy (observation of biological materials with cooling), which requires a very low electron dose to avoid specimen damage. In addition, nonuse of the scintillator enables the spatial resolution of a TEM image to be improved. Furthermore, the advantage of its high read-out rate is utilized as a detector taking scanning images.
However, damage to the detector due to electron-beam irradiation is unavoidable. Thus, replacement of the sensor is necessary if the total electron dose reaches approximately 10⁹.

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