Conditions for Extending the Resolution Limit of the Electron Microscope

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Abstract
The limiting resolution obtainable with magnetic lenses of existing type may be reduced below 10 A by the use of a sufficiently high accelerating voltage, provided that the lens power is maintained at an optimum value which gives minimum aberration. This may be achieved either by increasing simultaneously the strength of the magnetic focusing field in a lens of fixed dimensions, or by increasing lens dimensions at a given value of field strength. In either case a resolving limit of 5-6 A is predicted in the first case for a field of 25,000 oersteds and a voltage of 350 kV. at a focal length of 2 mm., and in the 2d case at a focal length of 9 mm. and a voltage of 1 mV. at a field strength of 10,000 oersteds. Further improvement in resolution is only to be obtained by correction of lens aberrations.