US3257554A - Electron microscope specimen holder having means for heating the specimen - Google Patents

Description

June 21, 1966 J. H. LUCAS 3,257,554

ELECTRON MICROSCOPE SPECIMEN HOLDER HAVING MEANS FOR HEATING THE SPECIMEN Filed Aug. 12, 1963 United States Patent The present invention relates to specimen holders for use in electron microscopes, and in particular to specimen holders of the type which comprise means for heating the specimen.

In specimen holders of this type, the heating of the specimen is conveniently performed by mounting the specimen in good thermal contact with an electrically conducting support and passing a current through the support so as to heat up the support and heat the specimen by conduction. The current for the support is supplied along two conductors, and a magnetic field will be induced adjacent these conductors by the current flowing therein.

In the operation of the electron microscope an electron beam is passed through the specimen while it is being heated and the current is flowing, and the field induced by the current may deflect the electron beam by an unpredictable amount.

In order to prevent the deflection of the electron beam by these fields it is known to shield the conductors so as to restrict the fields, but this is not always convenient or possible in some designs of specimen holder.

The object of the present invention is to provide an improved specimen holder of the above type.

According to the present invention a specimen holder for use in an electron microscope comprises a pair of jaw members extending longitudinally on opposite sides respectively ot'the electron beam axis and electrically insulated from each other, the jaw members being channelled to form a beam passage, a pair of clamp members supported by the jaw members with each clamp member making electrical connection with one of the jaw members, lugs extending inwardly from each of the clamp members, a metal mesh specimen support extending across the electron beam path with opposite edges resting on and supported by the lugs respectively, and means for passing an electrical current through the series path formed by the clamp members, the jaw members and the mesh support to heat a specimen resting on the mesh support. Preferably the electric current is supplied to the series circuit by electrical supply leads twisted together and extending from external supply terminals through a passage defined in a metal body from which the pair of flanged jaw members extend longitudinally.

Preferably said support is a mesh of electrically conducting material between the strands of which there is very good electrical and thermal contact. The mesh may be cold-rolled, so as to produce the required good contact between the strands, or may be electro-deposited in the form of a continuous mesh.

The support may be connected to the conductors so that it can easily be removed for cleaning or replacement.

In order that the invention may be more readily understood reference will now be made to the accompanying drawing, in which:

FIG. 1 is a side view sectioned on an axial plane of a specimen holder embodying the invention;

FIG. 2 is a side view of the specimen holder partly sectioned and viewed in the direction II in FIG. 1;

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FIG. 3 is an exploded view of the components of the lower part of the specimen holder, and

FIG. 4 is a general view of an electron microscope illustrating the specimen holder in its operative position.

With reference to FIGS. 1, 2 and 3, the specimen holder comprises a hollow metal body 1, on the lower end of which are supported two metal jaws 2, 3, adapted to hold a mesh 4 which acts as a support for the specimen. The mesh is secured to the lower ends of the two jaws by means of an integral assembly of twoclamps 5, 6 and a clamping ring 7 which fits over the outer surfaces of the jaws. The inner surfaces of the clamps fit closely against the outer surfaces of the jaws so that as the assembly is pushed axially on to the jaws the clamps are secured in position. The ends of the clamps are formed respectively with lugs 8, 9, which are forced towards the ends of the jaws and hold the mesh 4 securely against the ends of the aws.

The jaws 2, 3 are spaced apart and are electrically insulated from each other. The lower end of the body 1 is formed with a boss 11, and an insulating washer 12 with a central aperture 13 is located over the end of the body. The boss 11 extends through the aperture 13 and engages in a circular recess provided by two semicircular recesses 14, 15 formed in jaws 2, 3 respectively. The jaws 2, 3 are attached to the body 1 by means of studs 16 which are secured within recesses 17 by means of a suitable insulating adhesive. This construction ensures that the jaws are held firmly against the lower end of the body, are accurately located and are insulated from the body and from each other. The jaws 2, 3 are arcuate in cross-section and are reduced in width at their lower ends. The sides of the jaws are spaced apart by only a fraction of a millimetre, and the gap between the jaws across which the mesh 4 is secured is aligned with the hollow centre of the body 1. The jaws extend coaxially with the body and are made as short as possible.

In order to insulate the lower ends of the jaws a flanged bushing 18 of electrically insulating material is located between the clamping ring 7 and the clamps 5, 6 so that these clamps are insulated from each other.

The body 1 is formed with a longitudinally extending bore 19 which is closed at its upper end by a terminal plug 21 and extends to the lower end of the body. This bore 19 provides a location for a pair of flexible conductors 22, 23 which are connected at their lower ends to jaws 2, 3 respectively, and at their upper ends to terminals 24, 25 respectively. These conductors are insulated from each other and are twisted together closely in spiral form.

The specimen holder is supported in a conical recess in a suitable frame when in use in an electron microscope. The recess closely encloses the body 1 which is provided with bars 26, 27 by which it may be removed from the frame.

The holder described above is adapted to be used in an electron microscope as illustrated diagrammatically in FIG. 4. The electron microscope comprises a hollow body 31 adapted to be evacuated, an electron source 32, two electron lens systems 33, 34 and a fluorescent viewing screen 35. The specimen holder 36 is located between the two lens systems and is of the type described above. The specimen is mounted on the supporting mesh 4, and the beam of electrons 37 passes through the hollow body 1 of the holder and between the jaws 2, 3 to strike the specimen on the mesh 4. The electron beam continues so as to strike the fluorescent screen 35 in the Well known manner.

If it is desired to heat the specimen on the mesh 4 the terminals 24, 25 on the holder are connected to a source of current, and this current flows along the conductors 22,

23 and the jaws 2, 3 and through the mesh 4 so as to heat the mesh and to heat the specimen by conduction. Since the conductors 22, 23 are closely twisted together the magnetic field produced by the current passing along these conductors, and the electric field due to the voltage between the conductors, are reduced to a minimum and have only a negligible effect on the electron beam asit passes through the hollow body 1.

Fields will be induced between the jaws 2, 3 but since these jaws are made as short as possible the fields are reduced to a minimum. Hence heating of the specimen does not cause any appreciable deflection of the electron beam.

In order to ensure that there is good electrical conductivity between all the strands of the mesh 4 and between the mesh and the jaws, and that there is good thermal conductivity between the mesh and the specimen and the mesh and the jaws, the mesh is made as flat as possible. This can be arranged either by forming the mesh by an electro-deposition process, so that the strands are continuous, or by cold-rolling a mesh made by well known methods, so that the strands are forced together. Each of these operations ensures that the strands of the mesh are in close contact and that the strands cannot work loose.

As a result there is very good electrical and thermal contact between the jaws and the mesh, and very good thermal contact between the mesh and the specimen and the jaws. The nature of the electrical and thermal contact will be constant, and, therefore, for a given current through the mesh the heat generated and the heat lost will be constant, and, therefore, the change in temperature of the specimen will be the same.

By using meshes made of different materials the temperature range of the holder can be varied. For example a range of 30-1450 C. can be obtained using a stainless steel mesh, and a range of 30120 C. can be obtained using a copper mesh. For higher temperature applications platinum or tungsten, for example, can be used for the material of the mesh.

What I claim is:

1. In an electron microscope a specimen holder assembly comprising a pair of jaw members extending longitudinally on opposite sides respectively of the electron beam axis and electrically insulated from each other, surfaces on said jaw members defining longitudinal channelling in each said member to form a beam passage, a

men support extending across the electron beam path with opposite edges resting on and supported by said lugs respectively, and means for passing an electrical current through the series path formed by the clamp members, the jaw members and the mesh support to heat a specimen resting on the mesh support.

2. In an electron microscope a specimen holder assembly comprising a hollow metal body encircling the electron beam path, a pair of flanged jaw members extending longitudinally from said metal body on opposite sides respectively of the electron beam axis, said jaw members being electrically insulated from each other and from the metal body, surfaces on said jaw members defining longitudinal channelling in said members to define a beam passage, a pair of clamp members supported by said jaw members and each clamp member making electrical connection with one of said jaw members, lugs extending inwardly from each of said clamp members, a metal mesh specimen support extending across the electron beam path with opposite edges resting on said lugs respectively, means defining a longitudinal passage in the wall of said metal body, electrical supply leads twisted together and extending from external supply terminals through said passage to respective jaw members, and means for passing electric current through the series circuit formed by the clamp members, the jaw members, the mesh support and the electrical supply leads.

References Cited by the Examiner UNITED STATES PATENTS 2,266,082 12/1941 Ruska 250-495 2,423,158 7/1947 Runge 25049.5 2,753,458 7/1956 Kazato et al 25049.5 3,151,241 9/1964 Hermann et al 25049.5

- FOREIGN PATENTS 1,130,615 5/1962 Germany.

730,203 5/ 1955 Great Britain.

RALPH G; NILSON, Primary Examiner.

H. S. MILLER, G. E. MATTHEWS, A. L. BIRCH,

Assistant Examiners.

Claims (1)

1. IN AN ELECTRON MICROSCOPE A SPECIMEN HOLDER ASSEMBLY COMPRISING A PAIR OF JAW MEMBERS EXTENDING LONGITUNDINALLY ON OPPOSITE SIDES RESPECTIVELY OF THE ELECTRON BEAM AXIS AND ELECTRICALLY INSULATED FROM EACH OTHER, SURFACES ON SAID JAW MEMBERS DEFINING LONGITUDINAL CHANNELLING IN EACH SAID MEMBERS TO FORM A BEAM PASSAGE, A PAIR OF CLAMP MEMBERS SUPPORTED BY SAID JAW MEMBERS AND EACH CLAMP MEMBER MAKING ELECTRICAL CONNECTION WITH ONE OF SAID JAW MEMBERS, LUGS EXTENDING INWARDLY FROM EACH OF SAID CLAMP MEMBERS, A METAL MESH SPECI-

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