Scanning Electron Microscopy


Magnetic fields are used in electron microscopy for a variety of purposes: image formation, energy analysis and correction of astigmatism, for example.

We are interested in the problems of designing short focal length lenses to be used for focusing high energy electrons in the energy range 1-3 MeV.

These lenses are generally very large and we have tried to reduce their dimensions to simplify their construction and use. From this point of view, it is necessary to diminish the magnetic coil and the magnetic circuit iron.

Several solutions have been proposed in the case of the coil. We have obtained good results with superconducting coils.

The reduction of the magnetic circuit is more difficult when we try to use a smaller volume of iron; we find that for high values of magnetizing current iron saturation appears. And we can observe a deterioration of the electron optical characteristics.

These problems can be solved by using a special magnetic circuit composed of elements of anisotropic magnetic material. These new types of lenses will be in valuable if we need to focus electrons with energies greater than 3 MeV and could lead to considerable simplification of the mechanical design of all high voltage instruments.

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