GB1364930A - Microscope employing a beam of chargedparticles - Google Patents

Abstract

1364930 Electron microscopes PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 18 Aug 1971 [21 Aug 1970] 38753/71 Heading H1D A microscope (e.g. electron microscope) includes an energy selection Wien type filter providing mutually transverse E and H fields in the same field space, also transverse to the charged particle path and in which the filter includes electrostatic and/or magnetic field producing means providing at least one multipolar focusing field for at least partially compensating for image focusing aberration introduced by the Wien filter. The field producing means may be quadrupolar and/or hexapolar fields. Fig. 1 (not shown), includes electrostatic two cylinder lens (5), (7), filter (1) and electrostatic two cylinder lens (8), (6). Filter (1), as in Fig. (2) (not shown), includes four electrostatic electrodes (8) and eight magnetic pole shoes (9), at least one being of adjustable strength. In operation at least one compensating multipolar field is formed as well as the energyselection field configuration. Electrodes (5), (6) are of high potential relative to electrodes (7), 8), lens (5), (7) decelerating and lens (7), (8) accelerating. Compensation of different order errors, one first order, and three second order, are discussed. Combinations include an electrostatic and magnetic quadrupolar lens producing focusing effect of a spherical lens and a second focusing error reduced by a magnetic hexapolar correction field, production of this being discussed in relation to the Fig. 2, arrangement, in most being differential poles with a corresponding increase or decrease in the pole strengths. Exit planes (2), (3) may be 5 cms. apart, the filter dispersion 20 Ám./v. and a resolving power 20 Š for a 100 keV. Fig. 3 includes objective lens 11, diffraction lens 12, projection lens 13, display screen 14, and filter 1 which may be elsewhere in the microscope or at a point beyond the final image, the screen 14 then having a 250 Ám. diameter aperture. The image may be scanned across the display screen and the filter output synchronously scanned across an output display screen. This arrangement enables removal of the filter without disassembly of the microscope. In Fig. 3, electrostatic lens 15 is preferably two-cylinder, a second corresponding lens 16 included, image 19 coincides with object focal plane 21, gap 23 may be displaced in direction of filter or the field strength in filter 1 varied to cover the entire energy spectrum. Filter 1 in position shown produces less aberrations since magnification (e.g. 150 x ) has already occurred. Lens 13 may magnify 125 Î. Lens 15, 16 preferably do not magnify.