METHODS TO MEASURE PROPERTIES OF SLOW-SCAN CCD CAMERAS FOR ELECTRON DETECTION

New ways to measure detection properties of slow-scan charge-coupled device (CCD) cameras suitable for electron microscopy, mainly based on the statistics of single-electron events, are discussed. The experiments concentrate on the newly introduced Gatan 679 slow-scan CCD camera. It has been established that for this instrument (if equipped with a thin YAG scintillator) 20% of the true intensity is recorded at the highest detectable spatial frequency (Nyquist frequency), limited mostly by the modulation transfer function of the YAG scintillator. The detection quantum efficiency is 0.45 for single 100-kV electrons and 0.15 for single 400-kV electrons, and is approaching unity for intensities higher than ten electrons. Furthermore, nonlinearity of the response is smaller than deviations in the image intensity due to shot noise. Examples are presented illustrating the detection properties of slow-scan CCD cameras for electron imaging, which also include high dynamic range and negligible geometric distortion.