Low-temperature sample stage capable of transferring samples for electron microscope

Abstract

The invention discloses a sample-transmittable low-temperature sample stage for an electron microscope. The sample-transmittable low-temperature sample stage comprises a sample stage assembly and a refrigeration unit for providing cooling capacity for the sample stage assembly, the sample stage assembly comprises: a sample plate thermally connected with the cold end of the refrigeration unit through a detachable heat conduction member; the positioning piece can move axially, when the positioning piece moves upwards in place in the axial direction, the heat conduction piece can make close contact with the sample plate, and after the positioning piece moves downwards, the heat conduction piece can be released to be separated from the sample plate; and the driving piece can drive the positioning piece to move axially. The sample table is compact in overall structure, the refrigeration chip is adopted for providing cooling capacity, and the space needed by a refrigeration system is greatly reduced; meanwhile, the heat conduction piece is of a detachable structure, the heat transfer state of the heat conduction piece can be rapidly controlled through the head of the sample transfer rod, and the sample table can be rapidly and conveniently transferred and conveyed through the head of the sample transfer rod.

Description

Technical Field

[0001] The present invention relates to the technical field of microscopes, and particularly to a low-temperature sample stage for an electron microscope that can transfer samples. Background Art

[0002] An electron microscope is a high-resolution microscopic device that forms an image of a sample through an electron beam and can observe details at the nanoscale or even atomic level that cannot be resolved by an optical microscope. In the fields of materials science, biology, and physics, electron microscopes are widely used to study the microstructure and composition of samples.

[0003] In an electron microscope, a low-temperature sample stage is an important auxiliary technology and plays a key role in fields such as biology and materials science. The low-temperature sample stage can maintain the sample at an extremely low temperature (such as liquid nitrogen or liquid helium temperature), effectively reducing the irradiation damage of the electron beam to the sample and maintaining the structural integrity of the sample. At the same time, low temperature can also slow down chemical reactions and prevent the loss of volatile components in the sample, enabling the sample to present a structure closer to its natural state under the electron microscope. This is particularly important for studying biological macromolecules, samples that are extremely susceptible to heat, and samples that require high-resolution imaging, greatly improving the resolution and accuracy of imaging.

[0004] Since most cryocoolers contain components such as compressors and expansion valves that move at high frequencies, they often have relatively high vibrations and can hardly be used in electron microscopes that require high-resolution imaging. Therefore, currently, the low-temperature sample stage for an electron microscope mainly uses the method of directly cooling the sample stage with liquid nitrogen. To reduce the vibrations caused by the cryogenic fluid during imaging, commercial sample stages mainly use two designs to ensure high-resolution imaging of the sample: 1. First, cool the pipeline with nitrogen flow outside the microscope cavity with liquid nitrogen, and the pipeline is directly connected to the bottom of the sample stage to reduce the vibrations caused by the boiling process of liquid nitrogen. 2. Place the liquid nitrogen in a thermal insulation Dewar, and the low-temperature area at the bottom of the Dewar is connected to the sample stage through a copper strip to completely isolate the vibrations caused by the fluid, so as to achieve the purpose of vibration reduction.

[0005] However, the refrigeration system based on the liquid nitrogen refrigeration principle mentioned above has two core problems: 1. The low-temperature sample stage system is huge and requires equipment such as large liquid nitrogen tanks, Dewars, and gas pipelines, making disassembly, installation, and transportation difficult. 2. Many areas other than the sample stage are also cooled, such as gas pipelines, Dewars, and connectors of liquid nitrogen tanks. During use, the liquid nitrogen consumption is huge, the economy is poor, and at the same time, liquid nitrogen needs to be replenished regularly, making it difficult to operate autonomously for a long time. Summary of the Invention

[0006] The present invention provides a low-temperature sample stage for an electron microscope that can transfer samples, aiming to solve the problems of complex system, short maintenance time, and low refrigeration efficiency in the prior art.

[0007] A cryogenic sample stage for an electron microscope, comprising a sample stage assembly and a refrigeration unit for providing cooling capacity to the sample stage assembly;

[0008] The sample stage assembly includes:

[0009] A sample plate, which is thermally connected to the cold end of the refrigeration unit through a detachable heat conducting member; to achieve the transfer of cooling capacity;

[0010] A positioning member that can move axially. When the positioning member moves up axially to the in-place position, it can make the heat conducting member in close contact with the sample plate, and after moving down, it can release the heat conducting member to disengage it from the sample plate;

[0011] A driving member capable of driving the positioning member to move axially.

[0012] As a specific technical solution, the heat conducting member is an elastic heat conducting member, which is not in contact with the sample plate in the free state; it can only be in contact with the sample plate for heat conduction when it is subjected to an upward force from the positioning member. During actual processing, the elastic heat conducting member can be selected as an elastic heat conducting flexible strip, and the material can be selected from high heat conducting materials such as copper or graphite.

[0013] The sample plate can be selected as a copper plate for placing samples and the like.

[0014] The refrigeration unit is a throttling refrigeration chip system. In the throttling refrigeration chip system, the cooling capacity is mainly provided by a centimeter-sized throttling refrigeration chip. The throttling refrigeration chip is formed by bonding glass etched with multi-layer microchannels, and internally integrates microchannel structures such as a working fluid inlet, an outlet, a partition heat exchanger, a throttling channel, an evaporator, etc. During the working process, the high-pressure working fluid flows in from the inlet, flows through the high-pressure side of the heat exchanger, is throttled into a low-temperature two-phase flow in the throttling channel and enters the evaporator to provide refrigeration capacity for the sample, and then flows out of the throttling refrigeration chip from the low-pressure side of the heat exchanger.

[0015] Furthermore, in the present invention, the inlets and outlets of the throttling refrigeration chip are connected to the flange of the electron microscope cavity through a gas path, and the flange can be connected to a high-pressure gas cylinder or a compressor to provide high-pressure working fluid for the throttling refrigeration chip.

[0016] In the above throttling refrigeration chip, its cold end is connected to the bottom of the sample plate through a heat conducting flexible strip, such as a copper strip, a graphene strip, etc., for reducing the thermal resistance during the refrigeration process. Both the heat conducting flexible strip and the surface of the refrigeration chip are gold-plated to achieve the electron export during the electron microscope imaging process and ensure the imaging quality. At the same time, during the working process of the throttling refrigeration chip, the heat conducting strip cools down faster than the sample and has a lower minimum temperature. Therefore, it can pre-condense the gas impurities in the cavity and achieve the purpose of a cold screen.

[0017] Furthermore, the sample stage assembly further includes:

[0018] A mounting base that can be fixed to the inner cavity of an electron microscope;

[0019] A mounting block, on the top surface of which the sample plate is fixed; the mounting block can be detachably fixed to the sample transfer rod so as to realize the transfer of the sample, etc.;

[0020] The positioning member is axially movably arranged in the mounting block.

[0021] The mounting block is horizontally movably mounted in a mounting base, and through this mounting base, the sample stage assembly can be fixedly mounted relative to the inner cavity of the microscope.

[0022] Furthermore, the mounting block is a wedge-shaped copper block (trapezoidal); a dovetail groove matching with the wedge-shaped copper block is provided in the mounting base. With this structure, it not only ensures that the mounting block can move in the horizontal direction under the action of an external force (such as the sample transfer rod), but also ensures the stability of the mounting block in the vertical direction.

[0023] Generally, a positioning block with a dovetail groove for mutual fixation with the electron microscope displacement stage is provided at the bottom of the mounting base.

[0024] The positioning member can be selected as a shaft member or a column member, which is vertically arranged and can move axially up and down under the action of a driving member.

[0025] Further, a groove for mounting the positioning member is provided on the top surface of the mounting block; a through hole I communicating with the groove is provided on the side surface of the mounting block; the driving member is a shaft member that can pass through the through hole I, contact with the positioning member, and apply a downward axial acting force to the positioning member.

[0026] Further, the positioning member is sleeved with a spring member at the bottom, and under the action of the spring member, the top end of the positioning member tightly abuts the heat conducting member against the sample plate.

[0027] Further, a mutually matching guiding structure is provided between the positioning member and the side wall of the groove.

[0028] Further, the positioning member is a spring column, and the guiding structure is a limiting boss and a guiding protrusion arranged on the periphery of the spring column; the limiting boss is used to limit the spring member on the spring column, the top end of the spring member abuts against the limiting boss, and the bottom end abuts against the bottom end of the groove, being in a compressed state. A guiding groove matching with the guiding protrusion is provided on the side wall of the groove, and the guiding groove is vertically arranged to ensure that the spring column only moves axially.

[0029] During actual installation, in order to reduce the heat conduction and heat leakage between the sample stage and the electron microscope displacement stage, the sample plate is fixed to the mounting block (which can be a copper block) through studs. A hole is opened in the center of the copper block, that is, the groove mentioned above, and a spring post is placed to fix and press the heat conduction strip against the sample stage. Both the above-mentioned studs and the spring post are made of low thermal conductivity materials, such as nylon, polyether ether ketone and other materials. The copper block (i.e., the mounting block) is wedge-shaped and fits with the groove on the mounting seat fixed to the electron microscope displacement stage on three sides. A threaded hole is opened on the other side of the copper block, which can be matched with the external thread at the end of the sample transfer rod to realize in-situ sample transfer in the electron microscope system.

[0030] Further, the shaft part is the head of the sample transfer rod, and the head of the sample transfer rod has a structure with a gradually decreasing diameter; a through hole II is provided on the side wall of the positioning part. When the positioning part moves up axially to the in-place position, the height of the lower edge of the inner wall of the through hole II is lower than the height of the end of the working end. Preferably, the head of the sample transfer rod is a conical or frustum-shaped structure. Further, the head of the sample transfer rod is a frustum-shaped structure or a conical structure; there is a threaded fit between the through hole I and the head of the sample transfer rod.

[0031] With the above structure, when the head of the sample transfer rod is screwed into the through hole I, its end can enter the through hole II of the positioning part. As the head of the sample transfer rod continues to be screwed in, the downward force of the conical side wall of the head of the sample transfer rod on the positioning part causes the positioning part to move downward axially, thereby releasing the heat conduction part.

[0032] Due to the limited length of the inlet and outlet gas paths of the throttling refrigeration chip, it cannot follow the copper block during the sample transfer process. Therefore, the heat conduction strip needs to be untied from the sample stage during the sample transfer process. To solve this problem, a frustum-shaped structure is machined at the front end of the threaded column of the sample transfer rod in the present invention, and at the same time, a through hole is opened on the side of the spring post. During the operation of the system: the spring post presses the heat conduction strip against the sample stage, and the sample maintains a low temperature state. At this time, the through hole on the side of the spring post is slightly higher than the threaded hole on the side of the copper block; when the system needs to perform sample transfer: as the sample transfer rod is gradually screwed into the threaded hole on the side of the copper block, the frustum at the front end of the stud of the sample transfer rod will extend into the through hole on the side of the spring post, and finally the through hole on the side of the spring post is concentric with the threaded hole on the side of the copper block, and the spring post descends, and the heat conduction strip is thus untied from the sample stage. Finally, the sample stage and the copper block are fixed to the sample transfer rod for the next sample transfer operation.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] The overall structure of the sample stage of the present invention is compact, and the cold quantity is provided by the refrigeration chip, greatly reducing the space required for the refrigeration system; at the same time, the heat conduction part adopts a detachable structure, and the heat transfer state of the heat conduction part can be quickly controlled by using the head of the sample transfer rod, and at the same time, the transfer and transmission of the sample stage can be quickly and conveniently realized by using the head of the sample transfer rod. Description of the Drawings

[0035] Figure 1Schematic diagram of the low-temperature sample stage system;

[0036] Figure 2 Schematic diagram of the refrigeration system;

[0037] Figure 3 Exploded view of the sample stage system;

[0038] Figure 4 (a) Schematic diagram of the working state of the sample stage (b) Schematic diagram of the sample transfer process of the sample stage. Specific implementation manner

[0039] The present invention will be further described below in conjunction with the accompanying drawings by taking two groups of high and low pressure channels as examples:

[0040] As Figure 1 shown, a transferable low-temperature sample stage for a scanning electron microscope includes a throttling refrigeration chip gas supply system 101-104, a throttling refrigeration chip system 201-208, and a sample stage assembly 301-308. The throttling refrigeration chip gas supply system and the throttling refrigeration chip system are arranged in the cavity of the scanning electron microscope. In the throttling refrigeration chip gas supply system, it is fixed to the flange opening reserved by the electron microscope through the metal flange 103 thereon. The throttling refrigeration chip system is installed and fixed to the moving stage of the electron microscope through the dovetail groove 206; the sample stage assembly is installed and fixed to the moving stage of the electron microscope through the dovetail groove 307; the head 305 of the sample transfer rod is a part of the sample transfer rod of the electron microscope and serves as a driving part in this embodiment.

[0041] The gas supply system mainly includes a metal flange 103 that matches the vacuum cavity of the electron microscope. Outside the vacuum cavity, the flange is provided with a gas inlet 101 and a gas outlet 102. The gas inlet 101 can be connected to the high-pressure side of the compressor or a high-pressure gas cylinder to provide high-pressure gas for throttling. Correspondingly, the gas outlet 102 is connected to the low-pressure side of the compressor or directly discharged into the atmosphere; inside the vacuum cavity, the flange is connected to the throttling refrigeration chip system through a pair of stainless steel capillary hoses 104, finally forming a closed or open cycle.

[0042] As Figure 2As shown in the figure, the throttling refrigeration chip system mainly consists of a throttling refrigeration chip 203, a thermally conductive flexible strip 204 and related fixing components. The throttling refrigeration chip adopts an existing structure, such as the structure shown in CN 113329593 A; the throttling refrigeration chip is generally formed by bonding three glass sheets with microchannels, namely an upper plate 203a, a middle plate 203b and a lower plate 203c. A through hole is opened at the head of the lower plate 203c, corresponding to the air inlet and outlet holes on the chip base 207. In the working state, the high-pressure gas flows through the high-pressure side of the partition-type convective heat exchanger on the lower plate 203c of the chip, throttles to a low-temperature two-phase flow in the throttling channel to provide cooling capacity, and then flows through the low-pressure side of the partition-type convective heat exchanger on the middle plate 203b of the chip. The stainless-steel capillary hose 104 is fixed on the pipeline base 208, pressed and limited by the pipeline pressing plate 201. The end of the hose is brazed to the chip base 207, and is aligned and conducted with the air vent on one side of the chip base 207 at the same time. Finally, it is connected to the air hole of the chip through the air vent on the upper surface of the base. The air hole inside the chip base 207 extends to the back and is brazed to the stainless-steel hose 104. The stainless-steel hose is fixed and limited to the copper plate 205 through the pressing plate 201 and the base 208. The chip 203 is fixed to the base 207 through the pressing plate 202 on the copper plate 205. The copper plate 205 is fixed to the first positioning block 206 with a dovetail groove structure at the bottom to realize the function of adapting to the electron microscope displacement stage. The copper plate 205 is provided with a strip-shaped hole. By passing bolts and other through the positioning hole and the strip-shaped hole of the first positioning block 206, the relative fixation of the copper plate 205 and the first positioning block 206 can be realized; at the same time, by moving the positions of the copper plate 205 and the first positioning block 206 relative to the strip-shaped hole, the convenient adjustment of the specific installation position of the copper plate 205 can also be realized. The upper surface of the two-phase flow region at the end of the chip is fixed to a thermally conductive flexible strip 204, and the material can be selected from high-thermal-conductivity materials such as copper or graphite. The other end of the heat-conducting strip is fixed to the sample stage to realize the transfer of cooling capacity.

[0043] As Figure 3As shown in the figure, the sample stage assembly is composed of a copper plate 301 (i.e., the sample plate), a stud 303, a wedge-shaped copper block 304 (i.e., the mounting block), the head 305 of the sample transfer rod, a copper block mounting seat 306 with a wedge-shaped groove, a second positioning block 307 with a dovetail groove, and a spring post 308. Among them, the stud and the spring post are made of nylon or polyether ether ketone materials, which are used to form heat insulation between the copper plate 301 and the copper block 304. The wedge-shaped groove of the copper block mounting seat 306 matches the outer shape of the wedge-shaped copper block 304, which is used to position the latter. The copper plate 301 is provided with through holes, which correspond one by one to the threaded holes of the copper block 304, and are fixed by four studs 303. A threaded hole 309 (i.e., through hole I) is opened on the side of the copper block, which is matched with the external thread of the head 305 of the sample transfer rod to realize the relative fixation of the sample transfer rod and the copper block during the sample transfer process. There is a frustum structure 310 at the front end of the external thread of the head 305 of the sample transfer rod, which is matched with the through hole 311 (i.e., through hole II) on the side of the spring post 308 to realize the downward displacement of the spring post during the sample transfer process, and further the purpose of the copper strip detaching from the sample stage system. Below the through hole on the side of the spring post is a cylindrical structure with a guiding protrusion 312 and a limiting boss 313. The guiding protrusion 312 is matched with the guiding groove 316 provided on the copper block 304, and the cylindrical structure is matched with the cylindrical groove 315 at the center of the copper block 304. A spring 314 is sleeved on the cylindrical structure below the limiting boss 313. The top end of the spring 314 abuts against the bottom surface of the limiting boss 313, and the bottom end abuts against the inner wall of the bottom end of the cylindrical groove 315, which can realize the up and down movement of the spring post. The spring 314 is in a compressed state, which can ensure that when not restricted by the head of the sample transfer rod, an upward thrust can be applied to the thermally conductive flexible strip 204 to ensure that the thermally conductive flexible strip 204 is closely attached to the copper plate 301. The copper block mounting seat 306 with a wedge-shaped groove is matched with the copper block 304. Under the action of an external force, the copper block 304 can slide horizontally relative to the copper block mounting seat 306, and at the same time, it cannot move vertically under the limiting action of the wedge-shaped groove. The copper block mounting seat 306 is fixed on the second positioning block 307, and the function of adapting to the electron microscope displacement stage is realized through the dovetail groove at the bottom of the second positioning block 307. The guiding protrusion 312 is matched with the guiding groove 316 provided on the copper block 304, which mainly realizes the guiding of the axial movement of the spring post 308 and plays a guiding and limiting role.

[0044] The frustum structure 310 of the head 305 of the sample transfer rod can also be replaced with a conical structure, mainly to apply a downward force to the spring post 308 when contacting the through hole 311 of the spring post 308, so as to promote the downward movement of the spring post.

[0045] The low temperature and sample transfer method of the sample stage are as Figure 4As shown. During the working process, the flexible heat-conducting strip 204 is fixed to the bottom of the copper plate 301 through the spring posts. The sample 302 is placed above the copper plate and fixed by means such as tape. At this time, the cold quantity is transmitted from the refrigeration chip to the sample through the heat-conducting flexible strip 204. At the same time, the flexible strip and the copper plate act as a cold shield to condense impurities such as moisture in the cavity during the cooling process, so as to ensure the clean and tidy surface of the sample. At this time, the center line 308a of the through hole on the side of the spring post is slightly higher than the center line 304a of the through hole on the side of the copper block 304. At the same time, the height of the lowest edge of the side wall of the through hole on the side of the spring post is lower than the height of the bottom side edge of the end of the frustum structure 310 of the head 305 of the sample transfer rod, ensuring that the frustum structure 310 of the head 305 of the sample transfer rod can enter the through hole on the side of the spring post. When sample transfer is required, as the sample transfer rod is screwed in, the frustum structure at the front end of the sample transfer rod enters the through hole on the side of the spring post. As the diameter of the cross section of the frustum extends and increases, the spring post gradually moves downward. Finally, the through hole on the side of the spring post is concentric with the threaded hole on the side of the copper block ( Figure 4 as shown in (b)), and the heat-conducting flexible strip is decoupled from the sample stage system, achieving the purpose that the refrigeration chip does not transfer samples synchronously with the sample stage.

[0046] As an alternative solution, the through hole on the side of the spring post can also be a non-cylindrical hole structure, as long as it can meet the requirement that the frustum structure 310 of the head 305 of the sample transfer rod can be inserted and apply a downward force to the spring post sufficient to move the spring post downward to the target position.

Claims

1. A transferable low-temperature sample stage for an electron microscope, characterized in that: It includes a sample stage assembly and a refrigeration unit that provides coldness to the sample stage assembly; The sample stage assembly comprises: a sample plate, the sample plate being thermally connected to the cold end of the refrigeration unit via a detachable heat conducting member; A positioning member that can move axially, when the positioning member moves axially upward to a position, the heat-conducting member can be in close contact with the sample plate, and when the positioning member moves downward, the heat-conducting member can be released to be separated from the sample plate; A driving member capable of driving the positioning member to move axially.

2. The transferable low-temperature sample stage for electron microscope according to claim 1, characterized in that: The sample stage assembly also includes: A mounting block, the sample plate is fixed on the top surface of the mounting block; the positioning member is axially movable in the mounting block; The mounting block is horizontally movably mounted in a mounting seat.

3. The transferable low-temperature sample stage for electron microscope according to claim 2, characterized in that: The top surface of the mounting block is provided with a groove for mounting the positioning member; the side surface of the mounting block is provided with a through hole I that penetrates the groove; the driving member is a shaft member that can pass through the through hole I and can contact the positioning member and can apply a downward axial force to the positioning member.

4. The transferable low-temperature sample stage for electron microscope according to claim 3, characterized in that: The shaft is the sample transfer rod head, and the working end of the sample transfer rod head is a structure with a gradually decreasing diameter; the side wall of the positioning member is provided with a through hole II, and when the positioning member moves axially upward to the right position, the height of the lower edge of the inner wall of the through hole II is lower than the height of the end of the working end.

5. The transferable low-temperature sample stage for electron microscope according to claim 4, characterized in that: The head of the sample transfer rod is a truncated cone structure or a conical structure; the through hole I and the head of the sample transfer rod are threadedly matched.

6. The transferable low-temperature sample stage for electron microscope according to claim 3, characterized in that: The positioning member is a spring column, and a spring member is sleeved on the bottom of the positioning member. Under the action of the spring member, the top end of the positioning member tightly contacts the heat conducting member and the sample plate.

7. The transferable low-temperature sample stage for electron microscope according to claim 3, characterized in that: A guiding structure that cooperates with each other is provided between the positioning piece and the side wall of the groove.

8. The transferable low-temperature sample stage for electron microscope according to claim 1, characterized in that: The heat-conducting member is an elastic heat-conducting member and does not contact the sample plate in a free state.

9. The transferable low-temperature sample stage for electron microscope according to claim 1, characterized in that: The refrigeration unit is a throttling refrigeration chip system.

10. The transferable low-temperature sample stage for electron microscope according to claim 1, characterized in that: It also includes a throttling refrigeration chip air supply system with a flange structure.

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