Radiant energy – Inspection of solids or liquids by charged particles – Analyte supports
Patent
1983-12-19
1986-05-27
Smith, Alfred E.
Radiant energy
Inspection of solids or liquids by charged particles
Analyte supports
H01J 3720
Patent
active
045917221
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a low temperature specimen stage for use in microanalysis, primarily in the microanalysis of thin specimens in a transmission electron microscope by X-ray spectrum examination.
In analysing biological specimens by X-ray analysis in the TEM, it is necessary to prepare the specimens at cryogenic temperatures, and to maintain the specimens at such temperatures during analysis, in order to prevent movement of soluble and unfixed ions. This presents problems in design of the specimen stage, since it must hold the specimen at a cryogenic temperature, and yet present elastomeric seals at approximately room temperature to accommodate movement in a goniometer mounting. At the same time, the stage must be mechanically stiff to give accurate and constant positioning of the specimen in the electron beam.
An object of the present invention is to overcome or mitigate these problems.
According to the invention a low-temperature stage for use in an electron microscope comprises a main body, a holder for a specimen mount, a heat exchanger within the main body, conduit means for supplying coolant to the heat exchanger, a bar of relatively large cross-section and relatively high thermal conductivity interconnecting the heat exchanger and the specimen mount holder to form a heat transfer path therebetween, and a support member of relatively small cross-section and relatively low thermal conductivity interconnecting the specimen mount holder and the main body, the support member being a generally box-shaped member disposed around said bar.
Preferably the bar is of copper and the support member of stainless steel sheet.
In a preferred form, a forward O-ring seal is disposed around the stage between the support member and the body, a rear O-ring seal is provided to form a vacuum seal for the interior of the body, and the rear O-ring seal is connected to the conduit means by a tubular member of thin sheet material acting as a thermal isolator.
From another aspect, the invention provides an anticontaminator for an electron microscope, comprising a metallic cryogenic shield, a tank for holding a cryogenic liquid maintained at boiling point, and a thermal pathway between the shield and the tank.
Preferably, said thermal pathway includes flexible metal foil.
An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a cross-sectional side view of a specimen stage in accordance with the invention;
FIG. 2 is a cross-section to an enlarged scale on the line 2--2 of FIG. 1;
FIG. 3a is a perspective view from above of a specimen mount holder used in the embodiment of FIG. 1;
FIG. 3b is a perspective view from below of the same mount holder;
FIG. 4 is a perspective view from above of an alternative specimen mount holder; and
FIG. 5 is a diagrammatic cross-sectional side view of an anticontaminator.
Referring to FIG. 1, the stage has a specimen mount holder 10 at one end. A bearing 12 is formed from fused silica tubing to give a spherical surface which seats in a conical mount (not shown) of the TEM. Nitrogen gas at approximately -190.degree. C. is supplied through an inner tube 14 to a copper heat exchanger 16 and exhausts via a concentric outer tube 18. A thermocouple (not shown) is provided to monitor the temperature of the heat exchanger 16. The heat exchanger 16 is thermally coupled to the specimen mount holder 10 by a copper bar 22 of relatively massive cross-section. A further thermocouple (not shown) monitors the temperatures at the specimen mount itself.
Vacuum sealing of the stage in the TEM is provided by a forward O-ring 24 and a rear O-ring 26. The forward 0-ring 24 also accommodates movement of the stage in the goniometer mounting. These O-rings must be maintained at approximately room temperature to retain their resilience and thus their sealing properties. To this end, the forward O-ring is thermally separated from the specimen area by a thin stainless steel member 28 which forms a box-section around the copper ba
REFERENCES:
patent: 3958124 (1976-05-01), Koch et al.
patent: 4162401 (1979-07-01), King et al.
Eades, "A Helium-Cooled Specimen Stage . . . ", J. Phys. E. Sci. Instrum., vol. 15, 1982, pp. 184-186.
Pross et al, "Transportable Cryostat . . . ", Rev. Sci. Instrum., vol. 47, No. 3, Mar. 1976, pp. 353-355.
Biddlecombe William H.
Elder Hugh Y.
Nicholson W. A. Patrick
Berman Jack I.
Ferguson Jr. Gerald J.
Smith Alfred E.
The University Court of the University of Glasgow
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