Ultimate resolution and information in electron microscopy II. The information limit of transmission electron microscopes

In this paper the factors affecting the information limit of transmission electron microscopes are described in a general framework. Separate information limits are given for the influence of chromatic aberration and beam convergence, for specimen drift and vibration and for the detection of the image with a limited number of resolved pixels. Their relative importance is discussed and constraints are derived relating all factors to the information limit as given by the chromatic aberration. By taking into account the brightness of the source and the noise explicitly, it has been possible to find optima for the exposure time and the convergence angle of the illumination, yielding the best information limit which can be achieved with a given microscope. The higher brightness of a field-emission gun improves the information limit because a smaller angle of beam convergence can be used, but also because the signal-to-noise ratio is improved.