Patent GB-720008-A (GB)
Title: Improvements in or relating to electron microscopes
IPC: H01J37/20
Filed: 1951-02-14
Abstract: 720,008. Electron microscopes. SIEMENS & HALSKE AKT.-GES. Feb. 14, 1951 [Oct. 1, 1948; Aug. 25, 1950]. No. 3628/51. Class 39 (1). An electron microscope has within the vacuum envelope a support 29, Fig. 1, carrying a stage 32 on which are mounted a plurality of object holders 33, the support being movable in two intersecting directions transverse to the beam axis, by means known per se, for fine adjustment of the position of the object holder in the operative position, and means extending outwardly through the vacuum wall are provided to adjust the stage relatively to the support 29 to change the object. In the form shown in Fig. 1, eight object holders 33 ... 40 are supported by stage 32, the stage being mounted on an intermediate member 31 pivoted on support 29 so that it is rocked to and fro between the dotted and full line positions as determined by cam surfaces 38 and stop 39 while being rotated step by step by suitable gearing, Figs. 2, 3 (not shown) to subject the objects successively to the beam. The full line position of the holder 40 is an operative one, this position being maintained by one or more e.g. two springs, Fig. 2 (not shown) which press members 31, 32 and cams 38 firmly against stop 39. The object holder is shown in detail in Fig. 4, the diaphragm 54 carrying the object being clamped between parts 52, 53 a beam entrance diaphragm 51 being provided in the holder and an exit diaphragm 50 in the stage 32. Gas may be pumped to the objects through tube 47, Fig. 1, and ducts 46, 48, Figs. 1, 4, holes 55, 56 allowing both sides of the object to be reached thereby. There are as many gas ducts 48 as object holders and in this way chemical reactions of the objects with the gas can be studied. The stage also has a built-in change-over valve so gas is supplied only to the object which is in operative position. The object chamber is sealed by rubber packings 57, 58. The beam is generated in chamber 11 and passes into the object supporting chamber 13 connected to the evacuating pump at 14, a tube 28 leading to the camera chamber (not shown) to allow the latter to be thoroughly exhausted. The focussing lenses are provided by permanent magnets 16, 17 mounted in a framework 15, 27 and clamped between soft iron plates 18, 19 and co-operate with pole pieces 21, 25; 23, 24. Members 21, 23 together with brass spacers 20, 22 form part of the evacuated tube wall. Member 29 is movable in two transverse directions against return springs. The object holders are introduced and removed by opening a sealing door 44 provided with'an observation window 45 through which indicating numerals on the stage can be seen by the observer. The objects may have a common stage separable from a support or pivotal intermediate member so that the stage and objects can be removed or introduced as a whole. In this case the object stage preferably moves rectilinearly Fig. 6, where stage 66 carries a plurality of objects and is moved step by step on a slideway on the support by gearing 69, 70, a spring 72 and co-operating catches 73 rendering the movement perceptible to the touch of the operator. The gear drive may also have a counting mechanism to indicate which object is in operative position. By opening cap 68 the object stage as a whole may be introduced or withdrawn from the tube. The lenses are permanent magnets and the object support is pressed by two springs against one pole piece Fig. 5 (not shown). The support is movable transversely in two inclined directions by means not shown. In another form the common stage for the objects is mounted rotatably on the support or on the pivotal intermediate member. The object holders may be introduced and removed, if necessary by tongs, without removing their common stage if desired. A prior art arrangement in which a plurality of object holders are supported on a rotatable stage and in which each object holder can be moved transversely against springs with which it is individually provided, is referred to.