Scientific instrument with cryogenic sample stage
By using a cooling plate at the sample stage's resting position to achieve a high heat transfer rate and using flexible heat transfer connectors during movement, the problem of flexible copper braids being unable to simultaneously meet the requirements of high heat transfer rate and flexible movement was solved, thus achieving rapid cooling and temperature stabilization of the sample.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- FEI CO
- Filing Date
- 2024-12-02
- Publication Date
- 2026-07-17
AI Technical Summary
In existing scientific instruments, there is a contradiction between providing a high heat transfer rate and the flexible movement of the sample stage, making it difficult to simultaneously meet the requirements of high heat transfer rate and flexibility.
By providing a cooling plate with a high heat transfer rate at the sample stage's resting position, and then using flexible heat transfer connectors to maintain the target temperature, combined with an elastic support and flexible conductive components, the sample stage can be moved and cooled.
It enables rapid cooling of the sample to the target temperature and maintains temperature stability during movement, avoiding interference from flexible conductive components and meeting the requirements of high heat transfer rate and flexible movement.
Smart Images
Figure CN122422972A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to a scientific instrument with a cooling sample stage, a method for cooling a sample, and particularly, but not exclusively, the use of cryogenic cooling of samples for scientific research or imaging. Background Technology
[0002] Electron microscopes and other scientific instruments may include cooled, movable sample stages for fixing and cooling samples, such as to study the cryogenic behavior of samples or to protect samples from radiation damage. In some known devices, the sample stage is connected to a heat sink, such as a Dewar flask filled with liquid nitrogen, via a flexible copper braid or foil that is flexible enough to allow the stage to move while still providing a sufficient cooling rate. The flexibility of the braid or foil and the achievable cooling rate represent conflicting design requirements, as high heat transfer rates typically require thicker and therefore relatively stiff braids or foils. Summary of the Invention
[0003] The inventors have recognized that the conflicting design requirements associated with a movable cooled sample stage can be resolved by decoupling the initial cooling phase from maintaining the cooling temperature. This is achieved by providing a high heat transfer rate mediated by a cooling plate in contact with the sample stage while it is in its parking position until the desired target temperature is reached. Subsequently, once the sample stage leaves its parking position, the target temperature can be maintained at a lower heat transfer rate via a flexible heat transfer connector, such as a relatively thin copper braid. Therefore, the flexible heat transfer connector can be specified to provide sufficient heat transfer to maintain the target temperature while remaining relatively more flexible to facilitate the movement of the sample stage, for example, being thinner than a flexible heat transfer connector specified to provide a high heat transfer rate for initial cooling.
[0004] In a first aspect, a scientific instrument for studying a sample includes a movable stage. The movable stage includes a sample holder. The sample holder holds the sample. A finger-shaped cryostat contacts a heat sink and includes a cooling plate configured to contact the sample holder to cool the sample holder when the movable stage is positioned in a resting position. For cooling the sample holder, the cooling plate can contact the sample holder in any suitable manner, such as through direct mechanical contact between the cooling plate and the sample holder. When the movable stage is positioned away from the resting position, for example in a position where the sample can be studied, imaged, etc., a flexible heat-conducting component (e.g., a conductive braid, such as copper braid) thermally connects the sample holder and the finger-shaped cryostat to cool the sample holder via the flexible heat-conducting component.
[0005] The movable stage can be placed in the sample chamber, such as in a vacuum chamber.
[0006] Scientific instruments can be microscopes, such as optical microscopes or charged particle beam microscopes, such as electron microscopes, and the sample holder can be moved to an imaging position away from the parking position. Therefore, scientific instruments can include a beam source (e.g., a charged particle beam source) and a beam detector configured to emit a beam toward the sample holder in the imaging position, and the beam detector configured to receive the transmitted or reflected beam from the sample holder in the imaging position.
[0007] Scientific instruments may include a controller configured to: move a movable stage to a parking position while the sample holder is in contact with a cooling plate; monitor the temperature of the sample holder while the movable stage is in the parking position; and, in response to the temperature reaching a target temperature, move the movable stage away from the parking position to a location, such as an imaging or other research location, for studying the sample, such as imaging. Temperature can be monitored by any suitable device, such as a thermocouple or a non-contact infrared probe, and can be monitored by directly measuring the temperature or by measuring a temperature indicative of the sample holder's temperature (e.g., the temperature of the sample).
[0008] The cooling plate can be resiliently mounted on the finger-shaped freezer to ensure close contact with the sample holder in a range of orientations. The cooling plate can be mounted using any resilient support (e.g., one or more springs). Heat transfer to the cooling plate can occur solely through the support, through a separate thermal connector, or both. The separate thermal connector can be a relatively thick thermal braid (compared to flexible heat-conducting components) or any other suitably deformable resilient heat conductor. The resilient support can be provided as a resilient deformable plate or other resilient deformable component made of copper alloy or other suitable resilient alloy or other material.
[0009] The movable stage may include a base connected to a power mechanism for moving the movable stage. The sample holder may be mounted to the base via a thermally insulating component. A cooling plate may include holes for receiving the insulating component. The cooling plate may additionally include a cooling surface for contacting the sample holder's base-facing side.
[0010] The radiator may include a Dewar flask to contain cooling fluid. The Dewar flask may be positioned outside the sample chamber, and a finger-shaped freezer may extend from inside the Dewar flask into the sample chamber.
[0011] In another aspect, a method for cooling a sample disposed on a sample holder thermally connected to a finger-shaped freezer via a flexible heat-conducting component is disclosed. The method includes moving the sample holder to direct contact with the finger-shaped freezer, thereby cooling the sample on the sample holder at a first cooling rate; monitoring the temperature of the sample holder; and, in response to the temperature reaching a target temperature, moving the sample holder away from the finger-shaped freezer while continuing to cool the sample using the flexible heat-conducting component at a second cooling rate lower than the first cooling rate. More generally, in addition to moving the sample holder or instead of moving the sample holder, the finger-shaped freezer may be moved, selectively positioning the sample holder and the finger-shaped freezer in a first configuration for cooling via direct mechanical contact between the finger-shaped freezer and the sample holder, or in a study configuration where cooling is achieved via the flexible component. After moving the sample holder away from the finger-shaped freezer, the method may include studying the sample while maintaining the sample holder at the target temperature. Studying a sample can include any form of interaction with the sample to determine its properties, such as irradiating the sample with a beam to image it (e.g., using a charged particle beam, such as an electron beam). The sample holder, finger-shaped cryostat, and flexible heat-conducting components can be configured as described above.
[0012] In another aspect, a scientific instrument includes means for moving a finger-shaped cryostat connected to a heat sink and a sample holder for holding a sample relative to each other, thereby moving the scientific instrument between a first configuration and a second configuration for studying the sample. In the first configuration, the sample holder can be cooled at a first cooling rate by direct mechanical contact with the finger-shaped cryostat. In the second configuration, the finger-shaped cryostat and the sample holder are not in direct mechanical contact, and the sample holder is cooled at a second cooling rate lower than the first cooling rate via a flexible heat transfer connection between the finger-shaped cryostat and the sample holder, the flexible heat transfer connection accommodating the relative movement between the finger-shaped cryostat and the sample holder. Advantageously, cooling at a higher first rate by direct mechanical contact with the finger-shaped cryostat allows the sample to reach temperature rapidly, and cooling at a second rate in the second configuration is sufficient to maintain the sample temperature while allowing the flexible heat transfer connection to be sufficiently flexible, for example, thin enough not to interfere with the movement of the sample holder. Attached Figure Description
[0013] The disclosed embodiments will now be described with the aid of examples and reference to the accompanying drawings, in which:
[0014] Figure 1 shows a cross-sectional view of a scientific instrument with a cooling device;
[0015] Figure 2 shows the scientific instrument of Figure 1 operating in reflective imaging mode to image a sample;
[0016] Figure 3 shows a variant of the scientific instrument of Figure 1 operating in transmission imaging mode to image a sample;
[0017] Figure 4 shows a detailed top view of the finger-shaped freezer of the cooling device that interacts with the sample holder;
[0018] Figure 5 shows a side view of the sample holder near the finger-shaped freezer;
[0019] Figure 6 shows a side view of the sample holder in direct mechanical contact with the finger-shaped cryostat; and
[0020] Figure 7 illustrates the method of operating scientific instruments. Detailed Implementation
[0021] Referring to Figures 1 and 2, the disclosed electron microscope includes a vacuum chamber 2 and an electron beam source 4, a detector 6, a sample stage 8, and a cooling device 10. It should be understood that while a specific configuration of an electron microscope has been described, this disclosure is equally applicable to any charged particle beam microscope or scientific instrument in general. In this general case, any one of the vacuum chamber 2, the beam source 4, or the detector 6 may be present or absent, and / or the vacuum chamber 2 may be any other type of chamber, for example, under atmospheric pressure. This disclosure does not relate to the imaging operation of the electron microscope, which is conventional and well known to those skilled in the art. A controller 11 is connected to the components of the electron microscope and is configured to control the operation of the electron microscope, as disclosed below, for example.
[0022] The sample stage 8 is mounted on a base 12, which houses a drive mechanism for moving the sample stage 8 between the parking position shown in FIG. 1 and the imaging position shown in FIG. 2, where the sample can be imaged by an available electron beam 14. The sample stage 8 includes a sub-stage 16 fixed to the drive mechanism in the base 12 and a sample holder 18 for holding the sample 20. The sample holder 18 is fixed to the sub-stage 16 by an insulating member 22. The sample holder is made of or includes a thermally conductive material, such as a metal, like copper, to ensure heat transfer to the sample 20. The insulating member 20 is made of or includes a thermally insulating material, such as a polymer, to thermally insulate the sample holder 18 from the sub-stage 16.
[0023] The cooling device 10 includes a finger-shaped cryostat 24 in the form of an elongated heat-conducting component (e.g., made of or including a metal such as copper) connected to a heat sink 26 (e.g., a Dewar flask 28 filled with a suitable cold fluid such as liquid nitrogen or helium), wherein the finger-shaped cryostat 24 is in contact with the liquid inside the Dewar flask 28. The finger-shaped cryostat 24 includes a cooling plate 30 for direct contact with the sample holder 18 when the sample stage 8 is in the parking position, e.g., direct mechanical contact with the sample holder 18, to enable heat transfer to the sample holder 18 via the cooling plate 30.
[0024] The finger-shaped cryostat 24 is further thermally connected to the sample holder 18 via a flexible heat-conducting component 32 (e.g., made of a metal such as copper or a conductive braid incorporating such metal, or other flexible heat-conducting components such as foil) to enable cooling of the sample holder 18 via the flexible heat-conducting component 32. The flexible component 32 is configured such that the sample stage 8 can be moved away from its parking position, for example, to the imaging position described below with reference to FIG2. For example, the flexible component 32 may be sized and sufficiently flexible (e.g., thin enough) to allow the sample stage 8 to be moved within a desired range without causing excessive mechanical disturbance or impact on the sample holder 18.
[0025] The heat conduction component 32 is shown in Figures 1 and 2 as being directly connected to the sample stage, but it should be understood that this disclosure is not limited thereto, and the component may be connected, for example, to different parts of the sample stage 8, such as substage 16, and to the sample holder 18 by other, for example, less flexible or rigid thermal connections, to thermally connect the finger freezer 24 to the sample holder 18 via the flexible component 32.
[0026] Figure 1 depicts the sample stage 8 in a parking position, in which the cooling plate 30 contacts the sample holder 18, cooling the sample holder at a first rate via the cooling plate 30, and also cooling the sample holder at a second rate via the flexible member 32. Figure 2 depicts the sample stage 8 in a spaced-out position, which is, for example, an imaging position where the sample on the sample holder 18 can be imaged using the beam 14.
[0027] The flexible component 32 is configured to move unimpeded between the parking position and the imaging position, and at the imaging position if the sample needs to be moved during imaging (or other studies). In the imaging position, the sample holder 18 is not in contact with the cooling plate 30, but is still cooled at a second rate via the flexible component 32. The cooling plate 30 is configured, for example by appropriately selecting the material and configuration of the cooling plate 30, such as the area of its contact with the sample holder 18, such that the first rate is higher than the second rate. The relatively high first cooling rate enables rapid cooling from, for example, room temperature to the desired target temperature, while the lower second cooling rate can be used to maintain the sample 20 at the target temperature.
[0028] Figure 2 The beam 14 reflected by sample 20 to detector 6 is depicted. Referring to Figure 3, in alternative arrangements, sample 20 can be imaged or studied in transmission, and detector 6 is positioned accordingly. In these arrangements, sample holder 18 may include aperture 34 to allow beam 14 to reach detector 6 unobstructed. Detector 6 may be configured not to interfere with the movement of sample stage 8, or may be movable away from the path of sample stage 8, allowing sample stage 8 to move between a parking position and an imaging position.
[0029] Referring to Figures 4 through 6, in a particular form of the cooling device 10, the cooling plate 30 is elastically movable relative to the finger-shaped freezer 24. Specifically, the cooling plate 30 is fixed to the finger-shaped freezer 24 by a resilient support 36, such as a set of one or more springs 38, such as springs made of a suitable metal. The resilient support 36 allows a certain amount of heat conduction from the finger-shaped freezer 24 through the cooling plate 30, for example, through the springs 38. In some forms, to achieve a higher heat transfer rate, the cooling plate 30 is further connected to the finger-shaped freezer 24 by a heat conductor 40, such as a metal such as copper, a braid, foil, or other flexible or ductile plate.
[0030] Considering the limited amount of movement required for the heat conductor 40 compared to the flexible component 32 (not shown in Figures 4 to 6), the heat conductor can be configured to be relatively thick to improve thermal conductivity. Furthermore, the shorter length required for the heat conductor 40 to connect the cooling plate 30 to the finger-shaped freezer 24 is beneficial for thermal conductivity. As shown in Figures 5 and 6, when the cooling plate 30 contacts the sample holder 18, the elastic support 36 is able to adapt its orientation to the orientation of the sample holder 18. In this way, a certain range of misalignment facilitates close contact between the sample holder 18 and the cooling plate 30, thereby providing tolerance for the relative orientation of the cooling device 10 and the sample stage 8. In the specific arrangement shown in Figures 4, 5, and 6, when the cooling plate 30 contacts the sample holder 18, the insulating component 22 of the sample stage 8 is accommodated in a hole in the cooling plate 30.
[0031] Referring to Figure 7, a method for cooling samples inside a scientific instrument (such as the electron microscope described above) includes contacting a sample holder with a finger-shaped cryostat 42 connected to a heat sink to cool the sample holder at a first cooling rate by making the sample holder mechanically contact the finger-shaped cryostat, for example, with a cooling plate as described above.
[0032] While the sample holder is in contact with the finger-shaped cryostat to cool it, the temperature of the sample holder is monitored 44 until a target temperature is reached. Once the target temperature is reached, the sample holder is removed 46 from the finger-shaped cryostat to a separate location where the sample on the sample holder can be studied (e.g., imaged). It should be understood that instead of moving the sample holder, the finger-shaped cryostat may be moved alternatively or additionally to contact the sample holder for cooling and to move away from the sample holder to position the scientific instrument in a configuration for studying the sample (such as imaging).
[0033] The sample holder is connected to the finger-shaped cryostat via a flexible thermal connector, and when not in direct mechanical contact with the finger-shaped cryostat, the sample holder is cooled by the flexible thermal connector at a second rate less than the first rate. The sample is studied, for example, by imaging, when the sample holder is in a separate location (or the instrument is in an imaging configuration, as appropriate).
[0034] The scientific instrument, and specifically the finger-shaped cryostat, sample holder, and flexible connector, can be configured as described above for an electron microscope, and the controller 11 can be configured to implement the method for cooling the sample.
[0035] It should be understood that the above description is intended to be illustrative and not restrictive. Many other embodiments will become apparent to those skilled in the art upon reading and understanding the above description. While this disclosure has been described with reference to specific exemplary embodiments, it should be recognized that this disclosure is not limited to the described embodiments, but can be implemented with modifications and variations within the spirit and scope of the appended claims.
[0036] For example, while the sample holder moves to position the sample holder and the cooling fingers relative to each other in a rapid cooling or imaging (or other) configuration, in some embodiments, it is the finger cryostat that moves. For example, the finger cryostat can be attached to a stage having at least one degree of freedom. The finger cryostat can move independently of the rest of the cooling device, for example, by being attached to the rest of the cooling device via a thick, flexible braid capable of achieving sufficiently rapid heat transfer, or the cooling device can be configured to move to the finger cryostat, for example, by moving the entire cooling device so that the rest of the cooling device moves together with the finger cryostat.
[0037] In various embodiments, one or both of the finger-shaped cryostat and the sample holder can be moved to position them in their various relative configurations. Correspondingly, one or both of the finger-shaped cryostat and the sample holder can be attached to a corresponding stage having at least one degree of freedom. Advantageously, the flexibility to move any component or both components enables the resolution of movement restrictions or volume conflicts within the vacuum chamber (or more generally, the sample chamber in non-vacuum embodiments).
[0038] The described embodiments use a Dewar flask filled with a cooling fluid such as liquid nitrogen or helium as a radiator or cold source. This disclosure is not limited to any particular cold source and alternative cold sources, such as Joule-Thompson or Stirling coolers, or even Peltier elements for less demanding cooling requirements.
[0039] The disclosed embodiments are not limited to any particular scientific instrument and may include, for example, any type of charged beam (electron) microscope, or any type of optical microscope, such as a microscope with any suitable light source (e.g., LED or laser light source) and corresponding camera having any suitable wavelength range (e.g., visible light, infrared, far-infrared, ultraviolet, etc.). In some embodiments, an example of a microscope instrument is a confocal microscope.
[0040] Therefore, the specification and drawings should be considered illustrative rather than restrictive. Consequently, the scope of this disclosure should be determined by reference to the full scope of the appended claims and their equivalents.
Claims
1. A scientific instrument for studying samples, said instrument comprising: Sample holder; A finger-shaped freezer, the finger-shaped freezer being in contact with a radiator and including a cooling plate, the cooling plate being configured to contact the sample holder to cool the sample holder via the cooling plate; A flexible heat-conducting component thermally connects the sample holder and the finger-shaped freezer to cool the sample holder, wherein the sample holder and the finger-shaped freezer are movable relative to each other to position the sample holder and the finger-shaped freezer in a rapid cooling configuration and one or more other configurations for studying the sample held by the sample holder, wherein the cooling plate is in contact with the sample holder in the rapid cooling configuration and in the one or more other configurations the cooling plate is not in contact with the sample holder.
2. The scientific instrument of claim 1, wherein the scientific instrument includes a movable stage, the movable stage including the sample holder and movable between a rapid cooling position and one or more other positions, wherein the cooling plate is in contact with the sample holder in the rapid cooling position, and wherein the cooling plate is not in contact with the sample holder in the one or more other positions.
3. The scientific instrument according to any of the preceding claims, wherein the scientific instrument is a microscope and the one or more other configurations include an imaging configuration in which the sample holder is in the process of imaging, the scientific instrument comprising: A beam source configured to emit a beam toward the sample holder located in the imaging position; as well as A beam detector configured to receive a transmitted or reflected beam from the sample holder located at the imaging position.
4. The scientific instrument according to claim 3, wherein the scientific instrument is a charged particle microscope and the beam is a charged particle beam.
5. The scientific instrument according to claim 3, wherein the scientific instrument is an optical microscope and the beam is an electromagnetic beam.
6. The scientific instrument according to any preceding claim, wherein the scientific instrument includes a controller configured to: When the sample holder and the cooling plate are in the rapid cooling configuration, the temperature of the sample holder is monitored; and In response to the temperature reaching the target temperature, the sample holder and / or the finger-shaped freezer are moved to position the sample holder and the finger-shaped freezer in one of the one or more other configurations.
7. The scientific instrument according to claim 6, which is dependent on claim 3, claim 4 or claim 5, wherein the controller is configured to, in response to the temperature reaching a target temperature, place the sample holder and the finger cryostat in the imaging configuration.
8. The scientific instrument according to any of the preceding claims, wherein the cooling plate is resiliently mounted on the finger-shaped cryostat to facilitate close contact with the sample holder in a series of orientations.
9. The scientific instrument according to any of the preceding claims, wherein the sample holder is mounted on a base, the base being connected to a power mechanism for moving the sample holder.
10. The scientific instrument of claim 9, wherein the sample holder is mounted to the base via a thermally insulating component.
11. The scientific instrument of claim 10, wherein the cooling plate includes a cooling surface and a hole, the cooling surface being for contacting the sample holder facing the base, and the hole being for receiving the insulating component.
12. The scientific instrument of claim 11, wherein the sample holder is disposed in the sample chamber, the heat sink is disposed outside the sample chamber, and the finger-shaped freezer extends from the heat sink into the sample chamber.
13. A method for cooling a sample, the sample being disposed on a sample holder thermally connected to a finger-shaped freezer via a flexible heat-conducting component, the method comprising: Move the sample holder and / or the finger-shaped freezer to bring the sample holder into direct contact with the finger-shaped freezer, thereby cooling the sample on the sample holder at a first cooling rate; Monitor the temperature of the sample holder; and In response to the temperature reaching the target temperature, the sample holder and / or the finger-shaped freezer are moved to space the sample holder away from the finger-shaped freezer, while the flexible heat conduction component continues to cool the sample at a second cooling rate lower than the first cooling rate.
14. The method of claim 13, wherein the method comprises studying the sample after moving the sample holder and / or the finger freezer to space the sample holder away from the finger freezer, while keeping the sample holder at the target temperature.
15. The method of claim 13 or claim 14, the method comprising moving the sample holder to bring the sample holder into direct contact with the finger-shaped freezer and spaced the sample holder away from the finger-shaped freezer.