US3488493A - Mechanism for tilting specimens in electron microscopes and electron diffraction cameras - Google Patents

Description

Jan. @1970 J. c. MILLS 8 MECHANISM FOR TILTIN G SPECIMENS IN ELECTRON MICROSCQPES AND ELECTRON DIFFRACTION CAMERAS 2 Sheets-Sheet 1 Filed May 15. 1967 Jan. 6, 1970 J. c. MILLS 3,488,493 MECHANISM FOR TILTING SPECIMENS IN ELECTRON MICROSCOPES AND ELECTRON DIFFRAGTION CAMERAS Filed May 15. 196'? 2 Sheets-Sheet 2 United States Patent O US. Cl. 250-495 Claims ABSTRACT OF THE DISCLOSURE A mechanism for positioning specimens for examination within an electron microscope or electron diffraction camera, comprising a specimen holder pivotally mounted between adjacent ends of three substantially parallel arms which are movable in their longitudinal directions so as to tilt the specimen holder about two mutually perpendicular tilt axes.

BACKGROUND OF INVENTION Field of invention This invention relates to apparatus for positioning specimens for examination within electron microscopes and electron diffraction cameras and is concerned particularly with the provision of manipulating apparatus which enables a specimen to be tilted accurately.

Prior art In order to achieve high resolution, the pole piece of an electron microscope or diffraction camera should be cylindrical and have a central bore of very small diameter, preferably of the order of 6 mm. Conventional mechanisms for tilting specimens are so bulky that they prevent the specimen from being located within the bore of such a pole piece. For this reason it is present practice, when tilting of a specimen is required, to use, at some sacrifice of resolution, a pole piece having a larger diameter bore or an asymmetrical pole piece which is specially shaped at one end to receive a tilta'ble specimen holder.

SUMMARY The present invention provides a tilting mechanism which can be so constructed as to enable it to support a specimen within the 'bore of a normal, high resolution pole piece.

A mechanism according to the invention comprises a pair of substantially parallel arms, a specimen holder pivotally mounted between the arms by two pivot connections one to each arm, means to move the arms longitudinally and equally in opposite directions thereby to tilt the specimen holder about a fixed axis perpendicular to the moving axis extending through said pivot connections, and a further arm pivotally connected to the specimen holder and movable to tilt the holder about said moving axis.

More particularly, a mechanism according to the invention may comprise a body, a member pivotally mounted on the body to pivot about a first axis, a pair of arms connected to said member one to each side of the first axis and each extending transversely of that axis, a specimen holder pivotally mounted between the arms such that pivoting of said member about the first axis causes the holder to pivot about a fixed second axis parallel to the first axis and such as to allow pivoting of the holder about a third axis extending through the holder pivot mountings and perpendicularly of the second axis, a further arm pivotally connected to the holder such that movement 3,488,493 Patented Jan. 6, 1970 thereof causes the holder to pivot about the third axis, means conrollably to pivot said member about the first axis and means controllably to move the further arm.

Preferably the body is provided with a hollow stem located between said pair of arms and extending longitudinally thereof and each of the arms is held against the stem at a location between its ends by means of a leaf spring element and thereby given lateral support at said location.

Preferably further the hollow stem is tapered conically.

In order that the invention may be more fully explained two embodiments thereof will :now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS FIGURE 1 is an exploded perspective view of a specimen tilting cartridge constructed in accordance with the invention;

FIGURE 2 is a vertical section through the mechanism illustrated in FIGURE 1 when assembled;

FIGURE 3 is a cross-section on the line 3-3 in FIG- URE 2;

FIGURE 4 is a cross-section on the line 4-4 in FIG- URE 3;

FIGURE 5 is a vertical section of a modified cartridge embodying the invention;

FIGURE 6 is a cross-section on the line 6-6 in FIG- URE 5;

FIGURES 7 and 8 are perspective views of a pair of arms from the mechanism of FIGURES 5 and 6;

FIGURE 9 is a perspective view to an enlarged scale of a specimen holder incorporated in the mechanism of FIG- URES 5 and 6;

FIGURE 10 is an exploded perspective view of the holder illustrated in FIGURE 9; and

FIGURE 11 is a vertical section through the specimen holder illustrated in FIGURE 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The cartridge illustrated in FIGURES 1 to 4 comprises a body plate 11 having a central opening 12 encompassed by an upstanding hollow spigot 13 which carries a hollow conical stem 14. Three slots 16, 17, 18 are cut in the outer periphery of stem 14 so as to extend longitudinally of the stem. Slots 16 and 17 are on diametrically opposite sides of the stem and slot 18 is midway between slots 16 and 17. A hole 19 is formed in body plate 11 adjacent the lower end of slot 18 and an arcuate opening 21 is formed through body plate 11 to extend around the other side of the stem with its two ends adjacent the lower ends of slots 16, 17 respectively.

A semi-circular rocker yoke 22 fits within arcuate opening 21 and is pivotally mounted on spigot 13 by means of a screw 23 which screws into a tapped hole 24 in the spigot and is provided with a bush 26 fitting within a journal 27 on the yoke. A spacing washer 28 holds the yoke spaced from spigot 13. The ends of yoke 22 are provided with a pair of slots 29, 30 the upper ends of which are provided with tapped holes 31, 32. A pair of upwardly extending arms 33, 34 are slidable in slots 16, 17 respectively and are pivotally connected to the ends of yoke 22, the lower ends of the arms being provided with eyes 36, 37 which fit within slots 29, 30 and receive pivot screws 38, 39 screwed into holes 31, 32.

A small ring shaped specimen holder 41, which supports a specimen grid 40, is pivotally mounted between the upper ends of arms 33, 34 by means of a pair of ruby balls 42, 43 which are secured to its outer periphery and fit within sockets 44, 45 formed in the upper ends of the arms. A third ruby ball 46 is secured to the outer periphery of specimen holder 19 midway between balls 42 and 43 and fits within a socket 47 formed in the upper end of a further arm 48 which extends along slot 18 in stem 14 through hole 19 in body plate 11.

Arms 33, 34 are held within slots 16, 17 and forced against stem 14 by means of two leaf springs 49, 50 which are anchored to body plate 11 by means of screws 51, 52 and slidably engage at their upper ends the arms 33, 34. In similar fashion, arm 48 is held within slot 18 and forced against stem 14 by means of a composite leaf spring 53 which is anchored to body plate 11 by means of a screw 54 and slidably engages rod 48 at two vertically spaced locations 56, 57.

Pivoting movement is imparted to yoke 22 by means of a push rod 58 the upper end of which is in the form of an eye 59 which fits into the lower end of slot 29 and receives a pivot screw 61 screwed into a tapped hole 62 in the yoke. Thus rod 58 is pivotally connected at its upper end to the end of yoke 22. Upward movement of push rod 58 causes yoke 22 to pivot such that arm 33 is raised and arm 34 is lowered by an equal amount whereby specimen holder ring 41 is tilted about a fixed axis parallel to the pivot axis of yoke 22 and extending diametrically of the ring and through ruby ball 46. Downward movement of push rod 58 causes opposite tilting of specimen holder ring 41 about the same fixed pivot axis. The tilting of holder 41 caused by movement of push rod 58 does not cause any raising or lowering of ruby ball 46. Up and down movement of arm 48 pivots holder 41 about a pivot axis extending diametrically of the holder and through ruby balls 42, 43. This latter axis is, of course, moved when the holder is tilted by movement of arms 33, 34. The two pivot axes are mutually perpendicular and intersect at the centre of the specimen holder 19. The centre of the specimen grid therefore remains stationary during all tilting movements.

The tilting cartridge illustrated in FIGURES l to 4 may be fitted to the positioning mechanism of an electron microscope or electron diffraction camera in place of a conventional type of tilting cartridge. The ends of push rod 58 and arm 48 may be connected to any of a number of common forms of tilting controls such that they can be controllably moved up and down. For example they may be connected to a pair of bars which are moved up and down by rotation from a pair of vertical control screws, the control screws being rotated by bevel gears driven by a pair of universally jointed shafts which extend through the wall of the chamber of the microscope or camera and provided outside the chamber with control knobs, This form of control screw drive is of entirely conventional construction and is not illustrated.

Since arms 33, 34, 48 are given lateral support a short distance below specimen holder 41 by the action of leaf springs 49, 50, 53 the position of the specimen holder is quite stable. The cone angle and length of stem 14 are such as to allow the divergent diffracted electron beam to pass through it and also such as to reduce contamination by stray molecules to a minimum. The cartridge enables extremely accurate two-way tilting of a specimen with very little mechanical hysterises. Furthermore it can readily be manufactured to such a scale that specimen holder 41 and the upper ends of stem 14 and arms 33, 34, 48 can be inserted into the 6 mm. diameter bore of a high resolution symmetrical pole piece. Therefore no special form of pole piece is required for examinations where tilting is required and such examinations can be carried out under high resolution conditions. Furthermore, this cartridge enables a far greater degree of tilting to be achieved than with conventional tilting cartridges. Conventional tilting cartridges are limited to tilting angles of approximately 30 but the construction of FIGURES 1 to 4 enables accurate and reproducible tilting through angles of 35 and more.

Decontamination and specimen heating and cooling facilities can readily be provided with the construction in accordance with the invention and FIGURES 5 to 11 illustrate a modified construction in which all of these facilities are available. The basic construction of this cartridge is essentially the same as that illustrated in FIG- URES l to 4 and like components are given the same reference numerals but with primes in the case of FIG- URES 5 to 11 (e.g. body plate 11 becomes 11).

In this case a collar 62 is provided to give lateral support to the arms 33, 34 and 48 instead of leaf springs. The collar is formed from an electrically and thermal insulating plastics material such as that marketed under the trade name Delrin. It is a tight friction fit on the 'top portion of stem 14' and holds arms 34' and 48 in grooves 17' and 18' respectively. However, in this case arm 33' is not held within groove 16' but instead passes through a long slit formed in collar 62 so that it is spaced from the outer periphery of stem 14. Furthermore, arm 33' is made much finer than arm 34' and is broken into upper and lower portions which are connected together by means of a Delrin thermal insulation block 63. The lower end of the upper portion of arm 33 fits into a slit formed in the block and is connected to the block by a grub screw 64 and the upper end of the lower portion of arm 33' is permanently embedded in the block. The block is slidable in groove 16'.

Specimen holder 41 is made in two portions 66, 67 which fit together as shown in FIGURES 9 and 10 to form a generally horse-shoe shaped holder the inner edge wall of which is shaped to form a dove-tail slideway. The dovetail slideway converges slightly toward the centre of the holder and a circular specimen grid 40 can be dropped clown this slideway whereupon it will be wedged therein to remain in position across the bight of the holder. The grid can be readily removed by means of tweezers.

Holder portions 66, 67 are both made of electrically conducting metal, for example brass, and are electrically insulated from one another. For example they may be joined together by a layer of an electrically insulating, hard setting resin. The upper ends of arms 33', 34' are provided with sockets but instead of these sockets receiving ruby balls attached to the specimen holder, they receive small conical projections 42, 43' formed from the same metal as portions 66, 67. Thus holder portions 66, 67 are in electrical contact with arms 33, 34 respectively but are electrically insulated from one another. An electrical lead 71 is clipped to the lower portion of arm 33' and the two portions of that arm are electrically connected with one another by means of a thin layer 72 of electrically conducting paint, for example aluminium paint, on the exterior surface of block 63. An earth lead 74 is connected to plate 11' by means of a clamping screw 76. The upper end of arm 48 is provided with a socket which receives a ruby ball 46' fastened to the outer periphery of holder 41 so that it is electrically insulated from the holder. The rocker yoke 22 is made of a thermally and electrically insulating material such as Delrin.

A copper braid strap 77 is clamped to body plate 11 by means of a clamping screw 78. The other end of braid 77 may be connected to a liquid nitrogen bath whereby the whole of the body including body plate 11', spigot 13' and stem 14' may be reduced to liquid nitrogen temperature. When the temperature of conical stem 14' is so reduced it forms a very effective anti-contamination shield. A metal cap 79 provided with a small opening 81 for the passage of an electron beam may be fitted to the upper end of collar 62 so as to provide a complete anti-contamination enclosure, the cap having an internal rib 80 which contacts the stem so that it too is reduced to liquid nitro-' gen temperature.

When heating of the specimen is required, this may be achieved by passing current directly through the specimen grid. The current is supplied fromwire 71 and via arm 33 and to specimen holder portion 66 and holder portion 67 is earthed since it is in electrical contact with arm 34 whiq contacts conical stem 14 and the whole body is earthed by earth lead 74. The specimen grid is formed of copper, palladium, platinum or some other suitable electrically conducting metal so that it forms an electrical bridge between holder portions 66, 67 whereby it is heated by the passage of current therethrough. The grid has very low thermal capacity and may therefore be rapidly brought up to elevated temperatures of the order of 1,000 C. Such elevated temperatures may be achieved while the specimen is within the anti-contamination enclosure held at liquid nitrogen temperature.

If cooling of the specimen is required, no current is passed through the grid and heat is extracted from the grid through arm 34' to the stem 14 which is held at liquid nitrogen temperature. Block 63 then serves as a thermal barrier which obstructs the passage of heat from outside the instrument to the grid via arm 33'. The fact that arm 34 is very thin also helps to reduce such heat flow to a minimum.

The specimen holder end of the cartridge illustrated in FIGURES 5 to 11 can be inserted into the 6 mm. diameter bore of a high resolution symmetrical pole piece. This capsule provides combined heating, cooling, tilting, and anti-contamination facilities which are entirely compatible with one another and can all be employed while the speci men is being examined under high resolution conditions a result which has not hitherto been possible,

The particular conventions which have been illustrated and described herein are exemplary only and may be modified. For example the equal and opposite longitudinal movements of the arms 33, 34 (or 33 and 34) could be achieved by providing those arms with racks engaging a common pinion rotatably mounted on the body of the cartridge. The required movements would then be generated by rotating the pinion instead of by rocking of a yoke. This is only one example of many modifications and adaptations which may be made without departing from the scope of the invention as defined by the appended claims.

I claim:

1. A mechanism for positioning specimens for examinations within an electron microscope or electron diffraction camera, comprising a body, a pair of substantially parallel arms mounted on the body for movement along the body in their longitudinal directions, a specimen holder pivotally mounted between the arms by two pivot connections one to each arm, said pivot connections de' fining a first tilt axis extending through the connections, arm actuating means arranged for movement with respect to said body and connected to said arms to move the arms longitudinally and equally in opposite directions by pushing and pulling said arms thereby to tilt the specimen holder about a second tilt axis which is fixed relative to the body and is perpendicular to said first tilt axis, and a further arm pivotally connected to the specimen holder, said further arm being movable to tilt the holder about said first tilt axis.

2. A mechanism as claimed in claim 1, wherein the further arm is substantially parallel to said pair of arms.

3. A mechanism as claimed in claim 1, wherein the specimen holder is in the form of a circular ring and both said tilt axes extend diametrically of the ring.

4. A mechanism as claimed in claim 1, wherein said arm actuating means comprises a member pivotally mounted on said body to pivot about a pivot axis parallel to said first tilt axis, each of said pair of arms being pivotally connected to said member on opposite sides, respectively, of said pivot axis.

5. A mechanism as claimed in claim 1, wherein the body includes a hollow stem portion located between said pair of arms and extending longitudinally thereof, said body further including arm support means cooperating with the hollow stem at a location between the ends of the stem to provide lateral support to the arms at said location by causing the arms to be held against the body and guided longitudinally therealong.

6. A mechanism as claimed in claim 5 wherein said arm support means is constructed to provide similar lateral support for said further arm in the vicinity of said location.

7. A mechanism as claimed in claim 6, wherein said arm support means comprises a plurality of leaf spring elements each of which is anchored at one end to the body and at its other end bears against one of the arms to hold that arm in engagement with the hollow stem portion.

8. A mechanism as claimed in claim 6, wherein said arm support means comprises a collar which encompasses each of the arms and the stem at said location.

9. A mechanism as claimed in claim 5, wherein said hollow stem is conical and converges in the direction toward the specimen holder.

10. A mechanism as claimed in claim 1, wherein said specimen holder comprises first and second portions which are electrically insulated from one another the first portion being in electrical communication with one of said pair of arms via one of said pair of pivot connections and the second portion being in electrical communication with the other of said pair of arms via the other of said pivot connections.

References Cited UNITED STATES PATENTS 3,086,112 4/1963 Riecke. 3,230,365 1/ 1966 Nagahama. 3,307,035 2/ 1967 Grasenick et al.

RALPH G. NILSON, Primary Examiner S. C. SHEAR, Assistant Examiner

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