Optimizing detector resolution and efficiency in CCD arrays

Abstract

The effective use of a CCD camera to record TEM images requires the use of a scintillator to convert the energy of the incident electrons into light. In order to record the image with the highest resolution possible from the given CCD array we require that the broadening of the electron beam that occurs as it travels through the scintillator be less than, or comparable to, the diameter of the pixel. Beam spreading that is greater than the pixel size not only reduces the line-pair resolution, but also causes correlation between adjacent pixels which may result in the measured detector quantum efficiency (DQE) apparently exceeding unity. At the same time we need the electron to transfer the maximum possible amount of energy to the scintillator since the intensity of the signal produced by the CCD array depends directly on the energy deposited. Clearly these two requirements are mutually opposed since the conditions which minimize the beam spreading will also likely be the conditions under which the least energy is transferred.