GB1315945A - Electron microscopes and microanalysers - Google Patents

Abstract

1315945 Electron microscopes CAMBRIDGE SCIENTIFIC INSTRUMENTS Ltd 10 Feb 1972 [12 Feb 1971] 4604/71 Heading H1D [Also in Division G1] A scanning electron beam micro-analyser has provision for switching back and forth continuously between a first mode of operation in which the beam scans back and forth over a region of a specimen surface, and a second mode in which the beam rocks angularly about a fixed point on the specimen surface, Fig. 2, to cyclicly vary the angle of incidence of the beam. As shown, the device includes focusing coils L1, L2, and L3, and two pairs each of upper and lower scanning coils UC and LC (only one pair of each shown). The first image of the source is formed at point P2 in both modes, the lower deflection coil LC being switched on and off, with simultaneous change of the deflection current fed to the coils UC, to move the second image of the electron source from the specimen surface, corresponding to the rocking mode shown in Fig. 2, to the aperture of the lens L3 (Fig. 1 not shown), to provide the area scanning mode. In an alternative arrangement, Fig. 3, switching to the area scanning mode is achieved merely by an increase in current to the lens L3, raising the second image point above the specimen surface as shown, the resultant partial defocusing being accepted. Either the secondary or the backscattered electrons, the X-rays produced, or the specimen current, is detected and amplitude modulates the beam of a synchronously scanned cathode ray tube. Reference is made to the use of more than one detector, e.g. for back-scattered electrons and for X-rays respectively, and to the use of a conical or spiral, rather than rectangular, scan in the rocking mode. A circuit is described (Fig. 4, not shown), for switching the deflection current or the current to lens L3, with simultaneous change of gain of an amplifier in the detector circuit, and transfer of the detector output from a first to a second cathode ray tube.