| 摘要 |
Particle-optical apparatus are normally embodied with a magnetic or electrostatic lens so as to focus a beam 1 of charged particles onto a sample 8. It is desirable to be able to use these apparatus at different beam energies. It is, however, undesirable that the focus position 9 of the beam, as a result hereof, should shift with respect to the sample 8. Use of a permanent-magnetic material 6 in a magnetic lens has advantages as regards compact construction, but is normally avoided because it is not easily possible to adjust the lens power to match varying beam energies. The invention shows how it is possible to keep constant the focus position 9, independent of the energy of the particles in the beam 1, by combining a magnetic lens-that has been furnished with permanent-magnetic material-with an electrostatic lens. The electrostatic lens is embodied in that case as an accelerating lens.
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