GB1444098A - Electron microscopes - Google Patents

Abstract

1444098 Electron microscopes SIEMENS AG 10 July 1973 [10 Julv 1972] 29861/73 Heading H1D An electron microscope comprises an auxiliary lens to produce a first image 9 of the cathode source at a fixed point between first anode 2 and a further lens provided to provide an image 12 of the first image, the further lens comprising acceleration electrode 3 in combination with further electrode 5 whose potential varies linearly proportionally with any variation in the acceleration voltage, the further lens thus acting to maintain the second image substantially unaffected by D.C. voltage supply variations, and in which the auxiliary lens is a single electrostatic lens with a centre electrode 4 maintained at a potential which varies linearly proportionally with any variation in the first anode voltage, separate voltage sources 6 and 7 being used for the acceleration electrode 3 and first anode 2. The proportional variations are obtained by potentiometers 8 and 10. The auxiliary lens may be a magnetic lens whose excitation current varies proportionally to the square root of any anode voltage variations (Fig. 2, not shown) which may use comparator (20) between source (17) and computer source (19) with resistor (18). Electrode 5 potential may be 0À5 V B in which case electrodes 2 and 5 form a lens, although virtually without effect for a cross over at the lens centre particularly when electrode 5 potential equals that of anode 2. Electrode potentials are specified. Cathode 1 as a field emission cathode may be cold, or also heated.