GB1210210A - Electron beam apparatus - Google Patents

Abstract

1,210,210. Electron lenses. NIHON DENSHI K.K. 25 April, 1969 [26 April, 1968], No. 21359/69. Heading H1D. An electromagnetic lens comprising a winding on a ferromagnetic core has an associated correction lens comprising a further winding on a smaller core of similar material, the two windings being energized with proportional currents and the correction lens being adjustable to correct for the effects of leakage flux from the main lens. In one arrangement for use in an electron microscope the correction lens is 1/ 5 to 1/20 the size of the associated objective lens and comprises a yoke 23 energized by a coil 25 and including a non-magnetic gap 24; magnetic arms 26 couple two points on the yoke to polepieces 27 which surround the path of the electron beam. The polepiece 27b is slidable to adjust the strength and direction of the transverse component of the compensating magnetic field. In a modification, Fig. 5 (not shown) the yoke is C-shaped and two coils are wound on to it. In another arrangement, Fig. 6 (not shown), the compensation core is elongate, and one or a number of such cores extend to an adjustable extent through the wall of a specimen chamber. In a further arrangement, Fig. 7, the core 14a is symmetrically arranged about the axis of the electron beam and adjoins a ferromagnetic diaphragm 36 which forms one polepiece of the correction lens. The core 14a is adjustable by means of rods 38 and is surrounded by a non-magnetic case. Two such systems may be arranged back-to-back (Fig. 8, not shown), one being used to correct for deflection caused by the objective lens and the other to correct for deflection caused by the condenser lens, the intermediate lens, and the projector lens. The microscope may include a fluorescent screen (13, Fig. 1, not shown) observable through a window (12).