GB1422398A - Scanning electron microscope - Google Patents

Abstract

1422398 Electron microscopes NIHON DENSHI KK 30 Jan 1973 [23 Oct 1972] 4723/73 Heading H1D [Also in Division H4] A scanning electron microscope comprises condensers 2, 3, an objective lens system 4 including a coil and pole-pieces defining at least one gap, and wherein the magnetic flux intensity in the gap or gaps is sufficient to form a first apparent lens just upstream from the specimen plane and a second apparent lens just downstream of the specimen plane so that the beam crosses the axis at least twice after passing the specimen plane (Fig. 3, not shown), deflection means 6 comprising at least one deflection stage for deflecting the scanning beam through the front focal point of the first apparent lens such that the beam scans the specimen perpendicularly, detector means 12 for detecting the transmitted beam at the second or more crossing point, first display means 13 connected to detector 12 and synchronized with deflection means 6, and second display means (e.g. apertured fluorescent screen 8) for displaying the diffraction pattern so that both displays may be viewed simultaneously. The screen 8 may be observed through window 9, deflection coil 16, ensures the diffraction pattern spot passes through the aperture, or alternatively, detector 12 and aperture 11 may be moved mechanically. Electric or magnetic fields may change the diffraction pattern position w.r.t. detector 12. Objective lens as in Fig. 2 (not shown) includes polepieces (20), (21), non-magnetic spacer (22), crystalline specimen (23), and deflection coil (6) attached to polepiece (20). Fig. 4 (not shown) includes apparent lenses (4a), (4b), (4c) produced by strong field (24), (Fig. 3). Fig. 5 (not shown) includes two coil pairs (6a, 6b) to deflect the beam twice, thereby varying the angle at which the beam crosses axis 26 at the front focal point of lens (4a). Perpendicular incidence ensures outer beam parts (25b, 25c) are diffracted while the central part (25a) is not. The lens of Fig. 6 (not shown) includes additional polepiece (29) producing two gaps with a single flux path, while Fig. 7 (not shown) includes further yoke (31), coil (30), polepieces (32, 33) and spacer (34), producing two flux paths and two gaps. For a high upper gap field, the low gap enlarges the diffraction pattern, but if that field is insufficient it acts as lenses (4a, 4b), while the lower gap field is lens (4c). Fig. 8 (not shown) includes semiconductor detector (35) at the plane of the deffraction pattern to produce the scanning microscope image, second detector (36) with aperture plate (37), additional deflection coil (38), detector (36) signal being supplied to the brightness control grid of cathode-ray tube (39). Detector (36) and plate (37) may be scanned mechanically. Fig. 9 (not shown) includes image pick up tube (43) as detector with incorpoated deflector coil (44). Cathode-ray tube (39) displays the signal. Reference is also made to diffraction patterns formed on a photographic plate.