US2761991A

US2761991A - Electron microscopes

Info

Publication number: US2761991A
Application number: US243070A
Authority: US
Inventors: Eisfeldt Manfred
Original assignee: Siemens AG
Current assignee: Siemens and Halske AG; Siemens AG
Priority date: 1950-08-29
Filing date: 1951-08-22
Publication date: 1956-09-04
Anticipated expiration: 1973-09-04
Also published as: NL94737C; GB710960A; FR1043174A

Description

Sept; 4, 1956 M. ElsFl-:LDT ELECTRQN MICRoscoPEs Filed ug. 22. 1951 2 Sheets-Sheet 1 Flr.

United States Patent ELECTRON MCRUSCOPES Manfred Eisfeldt, Berlin-Tempelhof, Germanyhassiguor to Siemens @a Halske Aktiengesellschaft, Munich, Germany, a corporation of Germany Application August 22, 1951, Serial No. 243,070 Claims priority, appiication Germany August 29, 1950 22 Claims. (Cl. 313-84) This invention relates to electron microscopes, and is particularly concerned with a permanent magnetic electron lens system for such microscopes.

Permanent magnetic electron lens systems are known, comprising regulating means for adjusting the refractive power of the lenses. Such regulators are required, for example, for the focusing by changing the refractive power of the objective or tovregulate the nal magnification by changing the refractive power of the projective.

A prior regulator of this kind employs for the adjustment of the magnetic iux, a regulator nut which is associated with a cross-sectionally reduced portion of the outer casing surrounding the lenses. If relatively great regulation eiects are to be obtained, it is necessary to provide a narrow cross-section of the casing so that the tlux may be nearly completely interrupted. The result is a relatively great outwardly eiective stray magnetic iield.

Regulators have also been proposed in which a part of the lens pole shoe is axially displaced, making it impossible to provideV for a certain unalterably predetermined form of the pole shoe for all operating positions.

In accordance with the invention, there is provided for the adjustment of the refractive power of the lenses a regulating member which is disposed within the casing surrounding the pole shoe system and the permanent magnetic system. The regulator is magnetically connected with one pole of the magnetic system and is adjustable from the outside, and in all regulating positions is in series with the magnetic circuit.

As compared with the initially mentioned prior structures, the new lens system is free of an outwardly eective magnetic field, because the associated regulator does not coact with a cross-sectional defined part of the outer casing, but is completely disposed therein.

The regulator is furthermore a structural element which is entirely independent of the pole shoe system of the lenses. The shape of the pole shoe is not changed and is in no way affected by the regulator or by its operation.

Several structural forms are possible for carrying out the invention. A particularly simple structure is obtained by using an adjustable annular regulating member which is disposed ray-symmetrical, that is, symmetrical with respect to the optical axis. This regulating member may be provided with teeth for coaction with teeth extending from a part of the magnetic system. An annular regulating member without any teeth is used if it is to be disposed for axial displacement.

Other embodiments of the invention contemplate the use of rotatable regulating members. These members, as well as relatively stationary coacting parts, are provided with magnetically coacting teeth. These structures are indicated in axially short embodiments.

The regulating member and the stationary coacting part may be closely adjacent or may be in one terminal position in engagement.

The form of the regulator teeth may vary. They may,

T.faterrted Sept.v 4, 1956 ice one-half of the symmetrical structure of an embodiment comprising four pole shoe lenses of an image-forming or focusing system of an electron microscope;

Fig. la shows a portion of Fig. 1 and in diagrammatic manner additional details for operating certain parts thereof;

Figs. 2, 3, and 4 illustrate fragmentary views of different forms of rotatable regulator structures; and

Figs. 5 and 6 show one-half of the symmetrical struc-V ture of another embodiment of a lens system according to the invention.

Numeral 1 in Fig. 1 indicates the pole shoes of the objective; 2 and 3 are the pole shoes of two intermediate lenses; and 4 indicates the pole sh'oes of the projective. The magnetic outer casing of the lens'system comprises the two transverse walls or lids 5 and 6 and the cylindrical member forming the wall 7. The outer pole shoes of the lenses 1 and 4 extend directly from the transverse walls 5 and 6. The remaining pole shoes of thelenses are disposed on the

tubular parts

8, 9, 10 which form carriers therefor. The carriers 8 and lllhave annular radially outwardly directed

extensions

11, 12. Between the transverse Wall 5 and the extension 11 is disposed a ring-shaped permanent magnet 13, and a similar magnet 14 is disposed between the transverse wall 6 and the extension 12. The poles of the two magnets are so disposed that the outer casing comprising the walls. 5, 6, 7 is connected with poles of the identical sign.

For the regulation of the objective lens 1, there is proi vided a ring-shaped regulating member 15, also shown in Fig. la. Suitable known means Stl'to 57, shown in Fig. la are provided for axially displacing this member 15 relative to the pole shoe carrier 8 in the direction indiv cated by the double arrow 16. This regulator serves for the focusing or sharp adjustment of the electron stream forming the specimen image.

The means for eiecting the displacement of the member 15 from the outside may comprise suitable guide means or waysalong which the member 15 may be moved and the gearing extending therefrom in vacuumtight manner to the outside and having operating means, for example, a handle or knob 57 (Fig. la) or the like for effecting ythe displacement. Such operating means may be constructed generally along the lines of gearings disclosed and described, for example, in Patents Nos. 2,215,794 and 2,247,524 and in copending application Ser. No. 244,195, led Aug. 29, 1951, now Patent No. 2,714,678 dated August 2, 1955.

Between the outer shell wall 7 and the pole shoe carrier 9 is provided a rotatable regulator 17 for continuously varying the flux conducted to the carrier 9 for the purpose of continuously varying the iinal image magnication. This regulator may receive different forms'. Three examples are illustrated in Figs. 2-4 which show the structure in diagrammatic fragmentary views as seen when looking along the sectional line A-A of Fig. l. The means for operating the regulator comprises, as shown in Fig. la, an annular inner member 63 having alateral extension 66 provided with an external gear meshing with the gear wheel 67, the latter carryinga pinion 69 meshing with a pinion 68 on a rod 70 which extends invacuumtight manner through the casing Wall 7 and carries a knob 71. The annular member 63 isV provided with a dovetail disposed in aV guideway in thestationary part 4G. Rota- 10 for securing the pole shoe carriers and associated parts on ythe inside ofthe casing 7. Referring again to the structurefor axially displacing the ,regulator member is', the screw 5.0; carries a key @which slides in a groove in the annular rib 11' extending from the pole shoe carrier 8. The serewis thus moved only-axially to displace the member 15.' Numeral 80 indicates a scale and numeral 81 indicates a pointer rotatable with a knob 71 for indicating on the'scale adjustments etected by the knob.

ln lthe structure shown in Fig. 2, there are provided teeth 18 which project radially inwardly from the casing wall 7. The pole shoe carrier 9is provided with an annular member disposed rotatable thereon and having teeth 19 which extend -therefrom'radially outwardly for coaction with the teeth i3.l The faces of the

teeth

18, 19 are inclined as shown. teeth are in engagement so that the magnetic flux to the pole shoe carrier member 9,.and therefore to the lenses 2 and 3, is at its greatest value. vAs a result the refractive power of the lenses and therewith the final image magnification are greatest. By rotating the annular member carrying the teeth`19 in the direction of the arrow 2t) (Fig. 2), the refractive power will be continuously varied or adjusted, i. e., it will Vbe progressively reduced, thereby progressively reducing the final image magnification down to a minimal value when the .teeth V19 are in the dotted terminal position 21.

The means for effecting from the outside the rotation of the annular-member on the carrier 9 from which extend the teeth 19, may again be a'suitable gearing constructed and disposed in vacuumtight relationship to the lens system, for example, along the teaching of the previously mentioned copending application Ser. No. 244,195, now Patent No. 2,714,678.

The pole shoe carrier 9is disposed in stationary position by a ringlike member 40, which will be referred to later on. Suitable journal means for the annular regulating member carrying the teeth 19 is provided thereon, and this annular regulating member may have a gear for coaction with a gear wheel on a suitably journalled shaftY which extends in vacuumtight manner to the outside through a bushing in oneV of the casing walls. An operating handle Yor knob or the like may be carried by the shaft on the outside for effecting the adjustment of the annular regulating member-and therewith of the teeth 19 relative to the teeth 18.

Fig. 3 shows an embodiment in which the regulator comprises an annular rotatable member having radially outwardly directed teeth 23 for coaction with teeth 22 extending radially inwardly from the casing wall 7. The coacting faces of the teeth are in this case cut on a cylindrical line which is symmetrical to the path of the electron stream. The gearing required and the operation resulting therefrom may correspond to those explained in connection with Fig. 2.

The structure illustrated in Fig. 4 employs a regulator comprising arms or members 25 which are angularly dis- -placeable about pivot means 24 extending alongside the l intermediate lenseszandsis -held in position byasta- In the'full-line position 'these f .4 tionary ring 40 (Fig. l) of magnetic material which engages the carrier 9 as shown.- The ring 443 may be secured in any desirable and suitable manner, for example, by nonmagnetic axially extending annular` spacing rings disposed on each side thereof and engaging with their other ends the extensions 11 Vand 12 of the pole shoe bodies 8 and 11)..

Parts of the 'embodiment shown in Figs. 5 and 6, which are marked by numerals corresponding to the numerals in Fig. l, indicatefidentical-elements. Identical poles of the permanent magnets 31,` 32 are in thisembodiment disposed in engagement with the

annular extensions

11 and 12 projecting radially outwardly` from the pole shoe carriers 8`V and 10. .The other polesofthese

permanent magnets

31, 32 extend axially inwardly for coaction with a

rotatable regulator

33, 34,35 which is disposed centrally of the pole shoe carrier 9 having the pole shoes for the ltwo lenses 2 and 3.. The regulator 33,-.34-35 serves 4the purpose o'f'varying the magnetic Alux to the pole shoe carrier9 for the purpose of adjusting or regulating the final image magnification. Numerals 36;-37 Vand33-39 indicate two rotatable regulators lfor coaction, respectively with the projective 4 andl with the objective 1. The regulator 38-39 serves forthe focusing, and the regulator 36-37 for additional `'regulation of theV nal'image magnification.

The means for operating the regulators of Figs. 5 and 6 from the youtside cor'n'prises suitable known gearing of the type alreadyexplained in vconnection Vwith thedescription of the previousgures; t v v It will be appreciated from the examples described above, that the inventionpermits construction of a simple and efiicient image-forming system for electron microscopes comprising four lenses'which arefexcited by permanent magnets and Yhaving a regulating member or deviceV which Vforms a bridge between the outer casingzof 'the lenses and a pole shoe`member which carries the secondl p ole shoe of the second lens and the first pole shoe o f the third lens. The examples show that the adjustmentsrequired in an electron microscope (focusing and ymagniication) can be eectedin a very simple manner,` resulting in full illumination of the final imagein all operating positions. i Y

The handle portions of theregulators, which are on the outside, are preferably .provided with or coact with index marksy or suitable scale means which may be calibrated, for example, so as :to obtain direct reading ofthe nal image magniication. f

-. indicate that the structure provides satisfactoryV possi-` The casing forming the walls S, 6, 7 is preferably made of a plurality of parts.` Thus, as indicated in Fig.V y1 the transverse wall members S and 6 are separate members,

and the cylindrical wall member 7 is made of two parts suitably assembled with the transverse .walls 5 and 6 so as to facilitate assembly, adjustments, and also the mag! netization of the unit comprising the-permanent magnet` system and its coacting pole shoes.

The evacuating holes i1 in Fig 5 have been shown to bilities for evac'uatingV the cathode arearbyV connecting a high-vacuum pump to exhaust the space underneath the last projective. j

The invention is particularly suitable for use4V with electron microscopes, but may find uses in other types of apparatus for producing and/ or projecting particle beams.V Changes may be made within the scope and spirit of the Iappended claims-.which define what isbelieved `new and desired to have'protected by Letters Patent.

Iclaim: Y l. An electron microscope or the like h aVinga-casing and comprising pole shoe means and permanentuma'gnet means disposed in said casing, means for connecting said casing with one pole of said magnet means,an adjustable regulator within saidv casing, said regulator comprising aV movable member whichris separate from saidperrnan ei itV magnet means and disposed in a magneticfcircuit in series with said pole shoe means, control means in said casing for moving said movable member, and actuating means extending from said control means to the outside for operating said control means to move said movable member so as to adjust the refractive power of said lens system.

2. The structure defined in claim 1, wherein said movable regulator member is `an annular member carrying teeth the free ends of which are cut on a cylindrical line which is symmetrical to the optical axis, and stationary members for coaction with said teeth.

3. The structure defined in claim 1, wherein said movable regulator member is an .annular member carrying teeth the free ends of which are cut on a cylindrical line which is symmetrical to the optical axis, and a stationary toothed member forming teeth for coaction with the teeth of said movable regulator member.

4. The structure dened in claim l, wherein said movable member is a rotatable member.

5. The structure defined in claim 1, wherein said movable member is an axially displaceable member.

6. The structure defined in claim 1, comprising a stationary regulating member for coaction with said movable regulating member, said stationary and said movable members being substantially in engagement in one terminal position of said movable member.

7. The structure defined in claim 1, wherein said movable member is a rotatable member carrying a plurality of radially outwardly directed teeth, a plurality of radially stationary inwardly directed teeth extending from the wall of said casing for coaction with the teeth of said movable member, the coacting outer faces of said teeth being cut on a cylindrical line which is symmetrical to the optical axis of the structure.

8. The structure defined in claim l, wherein said movable member is a rotatable member carrying a plurality of radially outwardly directed teeth, a plurality of radially stationary inwardly directed teeth extending from the wall of said casing for coaction with the teeth of said movable member, the coacting outer faces of said teeth being angularly inclined to provide for engagement thereof in one terminal position of said movable member.

9. ln an electron microscope having an image-forming system comprising four magnetic lenses and permanent magnet excitation means therefor and having a casing for surrounding said lenses and said permanent magnet means, a regulator for adjusting the refractive power of said lens system, said regulator being disposed inside of said casing Iand forming a bridge extending between said casing and the pole shoe body of said system which carries the second pole shoe of the second lens and the rst pole shoe of the third lens.

10. The structure deined in claim 9, together with a relatively stationary ring-shaped member of magnetic material for securing the pole shoe body of the two intermediate lenses substantially centrally thereof.

11. The structure delined in claim 9, wherein said permanent magnet means comprises two cylindrically shaped permanent magnets for the excitation of all four lenses, one of said magnets being associated with the objective lens and the other magnet being associated with the projective lens.

12. The structure deiined in claim 9, together with operating means for said regulator, and scale means for said operating means to indicate the adjustment of the regulator in terms of magnication of the final image.

13. In an electron microscope comprising a cylindrical casing, a lens-forming pole shoe system and permanent magnet excitation means therefor disposed within said casing and completely enveloped thereby, a device also disposed within said casing for adjusting the refractive power of said lens system, said device comprising movable adjusting means disposed on the outside of said pole shoe means for altering the magnetic flux affecting said pole means, control means for operating said movable adjusting means, yand means extending to the outside of said casing for actuating said control means.

i4. The structure defined in claim 13, wherein said movable adjusting means is an annular member which is axially movably disposed on the outside of said pole shoe means.

15. The structure defined in claim 13, wherein said movable adjusting means comprises a plurality of members which extend radially outwardly from said pole shoe means for coaction with similar stationary members which extend radially inwardly from the wall of said casing.

16. The structure defined in claim 13, wherein said movable adjusting means comprises an arm which is pivotally secured on the inside of said casing, .and means for angularly moving said :arm to adjust the position of its free end relative to said pole shoe means.

17. The structure dened in vclaim 13, wherein said movable adjusting means comprises a plurality of arms which are pivotally disposed on the inside of said casing, 'and means for angularly moving said arms to adjust the free ends thereof relative to said pole shoe means.

18. In an electron microscope, three axially serially disposed annular pole shoe means forming lenses including an objective lens and intermediate lenses and a projective lens, an annular extension projecting radially from each of the two pole shoe means forming the lenses for said objective lens and projective lens, respectively, a casing, ring-shaped permanent magnet means connected with each of said extensions for establishing a magnetic circuit between said objective lens and projective lens pole shoe means and the inside wall of said casing, and a rotatable regulator carried by the pole shoe means forming said intermediate lenses for varying the magnetic iiux therefrom to said casing.

19. The structure defined in claim 18, together with an axially movable regulator for eecting the magnetic liux of the pole shoe means which forms the objective lens.

20. The structure dened in claim 18, together with rotatable regulator means for varying the magnetic ux in the magnetic circuit from said permanent magnet means to said casing.

21. The structure defined in claim 18, wherein said rotatable regulator comprises an -annular hub which is rotatable on the corresponding pole shoe means, a plurality of teeth extending radially outwardly from said hub, and a plurality of coacting teeth extending radially inwardly from the inside wall of said casing.

22. The structure defined in claim 18, together with gear means for operating said rotatable regulator.

References Cited in the le of this patent UNITED STATES PATENTS 2,220,973 Marton Nov. 12, 1940 2,305,458 Rusk-a et al. Dec. 15, 1942 2,305,761 Bor-ries et al. Dec. 22, 1942 2,503,173 Reisner Apr. 4, 1950 2,533,687 Quam Dec. 12, 1950