information limit

Information limit indicates the wave number at which phase information carried by the phase-contrast transfer function disappears. That is, it is determined as the wave number at which the envelope function reaches practically zero. The envelope function which gives damping of the phase contrast is determined by an energy spread of the electron beam and stability of the accelerating voltage (these two factors are related to chromatic aberration of the objective lens), stability of the objective lens and the divergence angle of the incident electron beam. The information limit is used as an indication of the resolution of a high resolution image. The resolution of the structure image is given by "first zero" of the phase-contrast transfer function in the ordinary sense. Phase information between the first zero and the information limit can be utilized to obtain a higher resolution of the structure image by computer-processing.

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