Rotatable stage

Abstract

A rotatable stage for an analytical apparatus. The rotatable stage has a stator, a heat exchanger in thermal connection with the stator, a rotor and a bearing located between the stator and the rotor. The bearing provides a thermal connection between the stator and rotor.

Claims

1. A rotatable stage for an analytical apparatus, the rotatable stage comprising: a stator; a heat exchanger in thermal connection with the stator; a rotor; and a bearing located between the stator and the rotor, the bearing providing a thermal connection between the stator and rotor, wherein the bearing comprises a canted coiled spring, wherein one or more portions of the bearing engage with one or more portions of the rotor to limit an axial motion of the rotor.

2. A rotatable stage according to claim 1, wherein the bearing comprises a material having a thermal conductivity of greater than about 170 Wm.sup.−1K.sup.−1.

3. A rotatable stage according claim 1, wherein the bearing is configured to provide multiple points of contact between the bearing and the stator and multiple points of contact between the bearing and the rotor.

4. A rotatable stage according to claim 3, wherein the bearing is configured to provide at least 12 points of contact between the bearing and the stator and at least 12 points between the bearing and the rotor.

5. A rotatable stage according to claim 1, wherein the bearing comprises one continuous component.

6. A rotatable stage according to claim 1, wherein the material of the bearing comprises at least one of copper, phosphor, bronze, and CuBe.sub.2.

7. A rotatable stage according to claim 1, wherein the heat exchanger comprises a gas tube configured to receive cooled gas.

8. A rotatable stage according to claim 1, wherein the heat exchanger comprises a thermally conductive braid.

9. A rotatable stage according to claim 8, wherein the braid comprises a copper braid.

10. A rotatable stage according to claim 1, comprising a connection providing thermal conduction between the heat exchanger and a second heat exchanger, wherein the connection is flexible.

11. A rotatable stage according to claim 1, wherein the stator comprises a temperature sensor.

12. A rotatable stage according to claim 11, further comprising means for: receiving a temperature input from the temperature sensor indicative of the temperature of the stator; and determining automatically from the temperature input whether the temperature of the stator is within a predetermined range; and controlling the temperature of the heat exchanger to ensure that the temperature of the stator stays within the predetermined range.

13. A rotatable stage according to claim 12, wherein the heat exchanger comprises a gas tube configured to receive cooled gas and wherein controlling the temperature of the heat exchanger comprises controlling the flow of cooled gas through the gas tube.

14. An electron microscope comprising a vacuum chamber and a rotatable stage according to claim 1, wherein the stator, rotor and bearing are located in the vacuum chamber.

15. An electron microscope according to claim 14, comprising a specimen stage and wherein the stator is mounted on the specimen stage via a thermally insulated support.

16. An electron microscope according to claim 14, comprising a stage rotate module, mounted on the specimen stage, wherein the rotor is mounted via thermally isolating supports to the stage rotate module.

17. A method for cooling the rotor of a rotatable stage comprising a stator, a heat exchanger in thermal connection with the stator, a rotor and a bearing located between the stator and the rotor, wherein the bearing comprises a canted coil spring, the bearing providing a thermal connection between the stator and rotor and wherein one or more portions of the bearing engage with one or more portions of the rotor to limit an axial motion of the rotor, the method comprising: thermally cooling the heat exchanger of the stator to thereby cool the rotor via the thermally conductive bearing.

18. A method according to claim 17, wherein the bearing comprises a material having a thermal conductivity of greater than about 170 Wm.sup.−1K.sup.−1.

19. A method according to claim 17, wherein the heat exchanger comprises a gas tube, and the method comprises the step of passing cooled gas through the gas tube.

20. A method according to claim 19, wherein the gas is cooled to at least −170° C.

21. A rotatable stage according to claim 1, wherein the canted coil spring comprises a pair of canted coil springs.

22. The method of claim 17, wherein the canted coil spring comprises a pair of canted coil springs.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic view of an embodiment of the rotatable stage in a scanning electron microscope;

(3) FIG. 2 is a top plan view of the rotatable stage of FIG. 1; and

(4) FIG. 3 is a cross sectional view of the rotate stage of FIG. 2.

DETAILED DESCRIPTION

(5) FIG. 1 shows an embodiment of the rotatable stage in a scanning electron microscope. The scanning electron microscope 10 is provided with a vacuum chamber 12 which houses an electron microscope specimen stage 14.

(6) The rotatable stage comprises a static part of the rotatable stage (stator) 16, a rotating part of the rotatable stage (rotor) 18 and bearing 20 between them. The rotor 18 is mounted inside the stator 16, with the bearing 20 enabling rotation between the stator 16 and rotor 18. The rotor 18 is mounted on a microscope stage rotate module mounted on the electron microscope specimen stage 14, via a thermally isolating support (not shown). The stator 16 is mounted by thermally insulating supports (not shown) to the main electron microscope specimen stage 14.

(7) A heat exchanger in thermal connection with the stator 16 is provided in the form of a cooling tube 32 located around the outer circumference of the stator 16. Nitrogen gas cooled close to −196° C. is passed through the cooling tube 32, to thereby cool the stator.

(8) The supply of cooled nitrogen gas is provided via a second heat exchanger 22 placed in a liquid nitrogen Dewar flask 24. A flow of warm, dry nitrogen gas 26 is passed through the heat exchanger submerged in liquid nitrogen where it is cooled to close to −196° C. The cooled nitrogen gas 28 is passed through a vacuum feedthrough 30 into the vacuum chamber 12 and into the cooling tube 32.

(9) The bearing 20 acts as a high efficiency thermal link which connects the stator to the rotor. In this embodiment, the bearing is a circular copper canted coiled spring.

(10) FIG. 2 is a plan view of the rotatable stage in more detail, showing the stator 16 and rotor 18. A sample holder 34 is shown on the rotor 18. The stator 16 is connected to the electron microscope specimen stage 14 via a thermally isolated locator 36. A cooling tube 32 is shown around the outer circumference of the stator 16, enabling the cooled nitrogen gas to circulate around it, thereby cooling the stator.

(11) FIG. 3 is a section through the rotatable stage of FIG. 2. The rotor 18 is shown mounted on the microscope stage rotate module 15 via thermal insulator 38. The rotor 18 is mounted in stator 16 via bearing 20, which comprises a circular copper canted coiled spring. The cooling tube 32 is shown around the periphery of the stator 16.

(12) In an alternative embodiment, the cooling tube could be replaced by a cooling braid.

(13) The cold parts of the system (for example the cooling tube 32 and sample holder 34) are made of gold plated copper for high thermal conductivity and corrosion resistance. The insulating parts (for example thermally isolated locator 36 and thermal insulator 38) are of ceramic and Torlon™ (a high vacuum compatible polymer).

(14) A temperature sensor on the stator (not shown) is used in a feedback loop to maintain a set, fixed temperature by varying the gas flow through the cooling tube 32.

(15) The use of a canted coiled spring has the advantage of ease of assembly, as the rotor, stator and bearing to simply click together.

(16) Using this set up, sample temperatures of less than −175° C. are achieved, well below the required temperature of −165° C.