Circulating refrigeration system without liquid helium consumption, and electron microscope operating in liquid-helium temperature range
Patent Information
- Application Number
- PCT/CN2024/117956
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-07-12
- Filing Date
- 2024-09-10
- Publication Date
- 2026-01-08
Smart Images
Figure CN2024117956_08012026_PF_FP_ABST
Abstract
Description
Liquid helium consumption-free circulating refrigeration system and liquid helium temperature zone electron microscope Technical Field
[0001] The present application relates to the technical field of electron microscopes, and in particular to a circulating refrigeration system without liquid helium consumption and a liquid helium temperature zone electron microscope. Background Art
[0002] Over the past few decades, extensive research on surfaces, thin films, and interfaces has led to a deeper understanding of many of their fundamental physical and chemical properties and the recognition that they play a key role in numerous applications. Among the various experimental tools available, cathode lens microscopy has played a significant role in identifying and interpreting many complex surface phenomena. Since its invention by Bauer, low-energy electron microscopy (LEEM) has developed into a vital technique for in situ investigation of surface structure, morphology, and dynamic processes.
[0003] LEEM is a cathode lens microscope that uses a low-energy electron beam (energy below 100eV, usually less than 10eV) to detect samples. It collects elastic backscattered electrons from the sample surface for imaging. Due to the short mean free path of low-energy electrons, LEEM is a very sensitive surface detection technology. Moreover, LEEM uses precise electron optical path modulation and has both real space and momentum space imaging modes. Combined with the high coherence electron source provided by the cold field electron gun, it can study phenomena such as quantum interference, making it one of the most powerful technologies for studying surface physics or chemistry. It has several outstanding advantages:
[0004] First, it can realize spatial real-time dynamic imaging of important surface processes such as surface growth, phase change, and reaction;
[0005] Second, the LEEM system has a very high spatial resolution capability, with a vertical resolution of up to the atomic level and a lateral resolution of 3-4 nm, and can image the local area of the sample surface.
[0006] Third, the LEEM system can realize the micro-area (lateral minimum up to 185nm) low-energy electron diffraction (μ-LEED) function to characterize the local structure and properties of the surface;
[0007] Fourth, the energy of the detection electron beam can be accurately changed over a large range, and the interaction between electrons and surfaces can be studied based on the curve of the image brightness of the selected area changing with the electron beam energy (i.e., intensity I-voltage V).
[0008] With the development of surface science research and applications, new technologies based on LEEM / PEEM are also being developed and applied. In the past, LEEM / PEEM was mainly used to study surface dynamic processes, such as high-temperature phase transitions and in-situ growth phenomena, and has been proven to be a very powerful technology. However, there are also many novel physical and chemical phenomena at temperatures below room temperature, such as the magnetic and electronic phase transitions of complex oxides at low temperatures. Current LEEM / PEEM systems typically have a sample temperature range of 300K-1800K. Only a few LEEM / PEEM systems can cool samples below room temperature, but usually not below 100K.
[0009] The Hong Kong University of Science and Technology has reported that its LEEM system can be cooled to 50K using a liquid helium static dewar. Existing reports claiming that LEEM systems can reach temperatures below 77K utilize static dewars to achieve sample cryogenics, requiring significant consumption of liquid helium. To maintain sustained low temperatures, even minimal liquid helium consumption can reach several liters per day. Currently, global helium supply exceeds demand, and prices are skyrocketing, significantly increasing experimental costs. Because helium is a non-renewable resource with limited reserves, it is estimated to be depleted within decades. Furthermore, many cities in China lack helium supply systems, further driving up liquid helium prices. This significantly restricts research requiring cryogenic LEEM / PEEM.
[0010] The most important thing is that the liquid helium static dewar method consumes a large amount of liquid helium in the cooling experiment, which will greatly increase the cost of the experiment. The use of liquid helium static dewar method for cooling must use liquid nitrogen as a pre-stage cooling stage to reduce the consumption of liquid helium. However, the large amount of evaporation of liquid nitrogen and liquid helium will increase the mechanical vibration of the entire system, thereby affecting the lateral resolution. At the same time, the entire sample is under a high voltage of -15kV, and even a slight significant vibration may cause the sample to undergo vacuum breakdown, which may damage the high-voltage power supply and precision components such as the nose of the electron microscope, resulting in serious economic losses. In addition, the liquid helium static dewar method requires manual perfusion of liquid helium at any time, which is time-consuming and labor-intensive. Due to the extremely low temperature, the flow channel may become clogged, which will cause experimental accidents and may even lead to experimental injuries. For cities without a liquid helium supply system, the duration of each experiment cannot be guaranteed, which greatly restricts the scientific research work of low-temperature electron microscopes.
[0011] Therefore, there is an urgent need for a liquid helium-free circulating refrigeration system and a liquid helium temperature zone electron microscope that can provide good cooling effects and does not require liquid helium replenishment after operation. This breakthrough technology greatly reduces the amount of liquid helium used in the electron microscope system and greatly reduces experimental costs. At the same time, it is simple and convenient, and is also suitable for scientific research in areas where liquid helium is difficult to obtain, without regional restrictions, to solve the problems existing in existing technologies.
[0012] Summary of the Invention
[0013] The purpose of this application is to address the above-mentioned problems existing in the prior art and to provide a circulating refrigeration system without liquid helium consumption and a liquid helium temperature zone electron microscope.
[0014] To achieve the above application objectives, the present application adopts the following technical solution: a liquid helium-free circulating refrigeration system for cooling the sample chamber of an electron microscope, including a liquid helium-free refrigerator, and further comprising:
[0015] A copper shielding tube, one end of which is connected to the shielding cylinder of the liquid helium-free refrigerator, and the other end of which is provided with a first-stage cold head connector and a second-stage cold head connector;
[0016] The first-stage cold screen is connected to the first-stage cold head connector through a copper braid and is located on the outer ring of the μ metal cover;
[0017] The μ metal cover is connected to the first-stage cold head connector through a copper braid and to the first-stage cold screen through a copper braid. The μ metal cover is vacuum-connected to the lower pole shoe of the electron microscope as a fixing ring. At the same time, the μ metal cover is connected to the Z-axis piezoelectric ceramic bracket of the sample chamber through an insulating gasket.
[0018] The sample holder fixing piece is connected to the secondary cold head connecting piece through a copper braid. The sample holder fixing piece is used for inserting and fixing the sample holder to enable cooling of the sample holder.
[0019] Among them, the first-level cold head connector, the first-level cold shield and the μ metal cover constitute the first-level low-temperature system. This setting has the following main effects:
[0020] Cryogenic cooling: The system cools the sample chamber by transferring cold energy to the sample chamber through the primary and secondary cold head connectors. The primary cryogenic system, consisting of the primary cold head connector, primary cold shield, and μ-metal cover, provides relatively low temperatures.
[0021] Shielding and isolation: Copper shielding tubes and μ-metal covers can provide shielding and isolation, isolating the cryogenic system from the external environment (such as the lower vacuum environment of an electron microscope) to prevent heat loss and interference.
[0022] Sample holder cooling: The sample holder fixture is connected to the secondary cold head connector to cool the sample holder. This ensures that the sample can be observed and studied in a low temperature environment.
[0023] Stability and precision: The non-liquid helium consumption circulating refrigeration system has more stable and precise temperature control than traditional liquid nitrogen or liquid helium refrigeration systems. It can provide long-term continuous operation without the need for frequent addition of cooling medium.
[0024] Furthermore, a copper braid fixing piece is provided on the sample holder fixing piece, through which the copper braid is connected. This arrangement has the following main effects:
[0025] Thermal Conductivity: The copper braid fixture primarily connects the braid to the sample holder. Since copper is a good thermal conductor, the braid fixture effectively transfers cold air to the sample holder, enhancing its cooling efficiency.
[0026] Stability and reliability: By using the copper braid fixture, you can ensure that the copper braid is firmly connected to the sample holder fixture, providing better stability and reliability. This helps prevent the copper braid from falling off or loosening during operation, ensuring the continuity of cooling transfer.
[0027] Mechanical Support: The braid holder provides mechanical support and fixation, making the braid more securely mounted on the specimen holder. This helps prevent unwanted movement or loosening during handling or vibration.
[0028] Protective performance: Copper braid fixings can protect the braids and prevent them from being damaged or worn. This can extend the service life of the braids and reduce the frequency of maintenance or replacement.
[0029] Furthermore, the Z-axis piezoelectric ceramic supports are evenly distributed along the circumference of the μ-metal cover. Each Z-axis piezoelectric ceramic support is provided with a Z-axis nano-scale piezoelectric ceramic, which is used to drive the sample to move back and forth along the Z-axis. Each Z-axis nano-scale piezoelectric ceramic is connected to the Z-axis fixed frame via a connecting piece. The Z-axis fixed frame is also connected to an X-axis nano-scale piezoelectric ceramic, which is used to drive the sample to move back and forth along the X-axis. The X-axis nano-scale piezoelectric ceramic is connected to an X-axis piezoelectric ceramic fixed plate. The X-axis piezoelectric ceramic fixed plate is connected to a Y-axis nano-scale piezoelectric ceramic, which is used to drive the sample to move back and forth along the Y-axis. The Y-axis nano-scale piezoelectric ceramic is connected to a Y-axis piezoelectric ceramic fixed plate. A sapphire insulating tube is provided at the center of the Y-axis piezoelectric ceramic fixed plate. The sapphire insulating tube is fixed to the Y-axis piezoelectric ceramic fixed plate via a sample holder cold plate, and the end of the sapphire insulating tube is connected to the sample holder fixing piece. The main effects of this arrangement are as follows:
[0030] Multi-axis movement: The system uses nano-scale piezoelectric ceramics on the Z axis, X axis, and Y axis to precisely control and move the sample along three axes (Z, X, and Y). This allows for multi-dimensional positioning, rotation, and adjustment of the sample to meet diverse experimental needs.
[0031] Nanoscale control: The application of nanoscale piezoelectric ceramics can achieve very fine movement control. By adjusting the voltage, nanoscale displacement and position control can be achieved, thereby achieving fine-tuning and precise operation of the sample position.
[0032] Stability and Repeatability: Piezoelectric ceramics offer high stability and repeatability. Their high movement precision allows for consistent position and motion control across multiple experiments, providing reliable experimental results and data repeatability.
[0033] Insulation: Sapphire insulation tubes provide electrical insulation and isolation, preventing current leakage and interference. This helps ensure the safety of electronic equipment and samples, and reduces the impact of unnecessary interference on experimental results.
[0034] Furthermore, the first-stage cooling screen is connected to the Z-axis fixing frame. This setting has the following main effects:
[0035] Thermal conductivity: The primary cold shield is a component connected to the cryogenic refrigerator's primary cold head connector. It is typically made of a material with good thermal conductivity, such as copper. By connecting the primary cold shield to the Z-axis mount, cooling capacity and temperature control can be effectively transferred to the Z-axis mount and related components.
[0036] Cooling Effect: As part of the cryogenic system, the primary cooling shield provides a cooling function. Connected to the Z-axis fixture, it transfers cooling energy to the Z-axis fixture and sample chamber, providing primary cooling for the sample and related components while also shielding against external heat radiation and minimizing low-temperature losses.
[0037] Stability and Thermal Balance: Connecting the primary cooling shield to the Z-axis mount enhances system stability and thermal balance. It helps disperse and evenly distribute cooling, preventing heat buildup and localized temperature variations, providing more stable and uniform cooling.
[0038] Thermal Insulation and Shielding: The connection of the first-level cold screen can also provide thermal insulation and shielding, preventing heat transfer and the influence of external interference. It can limit the spread of heat flow, ensure the cooling effect of the sample chamber, and maintain the required temperature environment.
[0039] Furthermore, each Z-axis piezoelectric ceramic support includes a first ceramic support and a second ceramic support, which are connected by a heat-insulating ball, and the Z-axis nano-scale piezoelectric ceramic is placed on the second ceramic support. This arrangement has the following main effects:
[0040] Thermal Insulation: The connection of the insulation balls provides thermal insulation, reducing heat transfer and loss. This is crucial for maintaining a stable temperature environment for the Z-axis piezoelectric ceramic mount, preventing interference from external heat sources.
[0041] Thermal stability: By placing the Z-axis nano-scale piezoelectric ceramic on a second ceramic support and connecting it with a heat-insulating ball, better thermal stability can be achieved. This can reduce the diffusion and leakage of heat and ensure that the Z-axis nano-scale piezoelectric ceramic is in a relatively constant temperature environment.
[0042] Insulation: The insulation ball between the first and second ceramic supports provides electrical insulation, preventing current leakage and interference. This is crucial for ensuring the electrical performance and signal stability of the Z-axis piezoelectric ceramic support and related components.
[0043] Structural Stability: By using a combination of the first and second ceramic supports, better structural stability and support are provided. This helps ensure stable installation and operation of the Z-axis piezoelectric ceramic support to meet the requirements of precise control and movement.
[0044] Furthermore, the sample holder fixing piece is evenly distributed with three notches, each of which is provided with a sample holder holder for fixing the sample holder. This arrangement has the following main effects:
[0045] Sample Fixing: The sample holder on each notch can be used to fix the sample holder, ensuring the stability and reliability of the sample during the experiment. By inserting and fixing the sample holder into the holder, you can prevent accidental movement or shaking of the sample and maintain the accurate position of the sample.
[0046] Precise Positioning: Uniformly spaced notches and sample holders allow for precise positioning of the sample on the fixture. The location and design of each notch ensures the correct alignment of the sample holder, allowing the sample to be positioned and manipulated in the desired position.
[0047] Interchangeability: The design of the sample holder allows for easy replacement and adjustment. This allows for quick replacement of samples or adjustment of sample arrangement to meet varying experimental conditions.
[0048] Furthermore, the copper braid fixture is connected to the sample holder fixture and is connected to the sample holder cold plate via a heat transfer conductor. This arrangement has the following main effects:
[0049] Mechanical support: The connection between the copper braid fixture and the sample holder fixture provides mechanical support, increasing the stability and rigidity of the sample holder. This helps prevent unnecessary vibration or movement of the sample holder during the experiment, ensuring the accuracy and reliability of the experiment.
[0050] Heat conduction: Heat conduction and control is achieved by connecting the copper braid fixture to the sample holder cold plate through heat transfer components. Heat transfer components generally have good thermal conductivity and can effectively transfer heat from the sample holder to the cold plate, achieving sample cooling.
[0051] Temperature stability: The connection between the copper braid fixture and the sample holder cold plate provides temperature stability through a heat transfer element. The heat transfer element quickly equalizes temperature differences and transfers the cold temperature from the cold plate to the sample holder, maintaining a stable low temperature environment.
[0052] Thermal Control: The sample holder temperature can be controlled by connecting the copper braid fixture and the heat transfer guide. By adjusting the temperature of the cold plate and the heat transfer efficiency of the heat transfer guide, the sample holder temperature can be precisely controlled to meet experimental requirements.
[0053] Furthermore, each sample holder is This setting has the following main effects:
[0054] Elastic fixation: Due to the sample holder The sample holder is designed to be flexible and resilient. This elastic design allows the sample holder to be subjected to a certain amount of pressure when inserted into the holder, securing it firmly and securely in the holder. This ensures that the sample holder remains firmly in the desired position, preventing accidental movement or loosening during experiments.
[0055] Multiple sample size adaptability: Due to The shape and elasticity of the sample holder adapt to sample holders of varying sizes. This means that both smaller and larger sample holders can be secured and fixed in place. This provides greater flexibility, allowing the sample holder to accommodate samples of varying sizes.
[0056] Shock absorption effect: Due to the elasticity and shape design of the sample holder, it can play a certain shock absorption effect. During the experiment, there may be some external vibration or shock, which may have an adverse effect on the stability of the sample and the experimental results. However, the elastic The sample holder can absorb and slow down these vibrations to a certain extent, protecting the sample from external interference.
[0057] Simplified operation: sample holder The new cassette holder design simplifies the operation steps. Due to its elastic properties, the sample holder can be inserted and removed from the cassette holder relatively easily, making sample replacement or position adjustment more convenient and quick.
[0058] Furthermore, the top of the sapphire insulating tube is provided with a thread for connecting a high-voltage electrode, so that the high-voltage electrode can be connected to the vacuum feedthrough of the sample chamber via a high-voltage wire to achieve high voltage application, and the top of the sample chamber is electrically connected to the high-voltage electrode. This setting has the following main effects:
[0059] High-voltage transmission: By connecting a high-voltage electrode and a sapphire insulating tube, high voltage can be transmitted to the sample. The high-voltage electrode is connected to the sample chamber via a high-voltage wire, while the sapphire insulating tube provides electrical isolation and insulation protection, ensuring the safe transmission of high voltage to the sample.
[0060] Electrical connection: By electrically connecting the top of the sample chamber to the high-voltage electrode, effective voltage feedthrough can be ensured. This is necessary for high-voltage electrical experiments, ensuring effective connection between the high-voltage electrode and the sample chamber sample so that voltage can be successfully applied to the sample.
[0061] Safety and stability: The sapphire insulating tube design provides isolation and insulation protection from high voltage, ensuring directional transmission between the high voltage electrode and the sample. This helps prevent the risk of electric shock and protects the stability of experimental equipment.
[0062] The liquid helium temperature zone electron microscope includes an electron source part, a lens system, an imaging system, a sample chamber and the above-mentioned liquid helium consumption-free circulating refrigeration system. The sample chamber is cooled by the liquid helium consumption-free circulating refrigeration system, and images are formed by the imaging system.
[0063] Compared with the prior art, this application has the following beneficial effects:
[0064] 1. This application uses a liquid helium-free circulation machine to replace the traditional static Dewar cooling, and additionally designs a circulating refrigeration system for cooling the sample chamber. The refrigerant circulates and cools in the circulation tube of the liquid helium-free circulation machine to achieve heat exchange refrigeration of the sample chamber equipment. Therefore, the refrigerant will not evaporate and consume, and the required liquid helium temperature zone environment can be achieved for a long time, which greatly reduces experimental costs, reduces mechanical vibration, improves lateral resolution, and realizes ultra-high resolution of electron microscopes.
[0065] 2. This application constructs a primary cryogenic system using a primary cold head connector, a primary cold shield, and a μ-metal cover to create a low-temperature environment of 90-95K around the sample. Connecting the sample holder via a secondary cold head connector allows the sample holder to be cooled to ~30K, or even 10K, thereby maintaining the sample in the desired liquid helium temperature range for extended periods. Furthermore, no liquid helium needs to be replenished after operation. This breakthrough technology significantly reduces the amount of liquid helium used in electron microscope systems, significantly reducing experimental costs. Simultaneously, it is simple and convenient, and is also suitable for scientific research in areas where liquid helium is difficult to obtain, without regional restrictions. Furthermore, it reduces mechanical vibrations caused by refrigerant evaporation, thereby improving lateral resolution. BRIEF DESCRIPTION OF THE DRAWINGS
[0066] FIG1 is a diagram of an electron microscope instrument in a liquid helium temperature zone;
[0067] FIG2 is a schematic diagram of the main structure of a sample chamber embodiment of a cryogen-free electron microscope of the present application;
[0068] FIG3 is a schematic diagram of a liquid helium-free refrigerator of the present application;
[0069] FIG4 is a partial enlarged schematic diagram of point A in FIG3 ;
[0070] FIG5 is a schematic diagram of the assembly structure of the cryogen-free electron microscope refrigerator and the sample chamber assembly of the present application;
[0071] FIG6 is a schematic diagram of the main view of the cryogenic sample chamber of the liquid helium-free electron microscope of the present application;
[0072] FIG7 is a schematic diagram of the front view structure of the cryogenic sample chamber of the liquid helium-free electron microscope without a first-stage cold shield of the present application;
[0073] FIG8 is a schematic diagram of the rear view structure of the cryogenic sample chamber of the liquid helium-free electron microscope without a first-stage cold shield of the present application;
[0074] FIG9 is a schematic structural diagram of the “AA” direction of FIG7 ;
[0075] FIG10 is a low energy electron diffraction (LEED) pattern of a Cu(110) single crystal obtained using the liquid helium temperature zone electron microscope high resolution imaging scheme of the present application;
[0076] FIG11 is a real-space surface image of a Cu(110) single crystal obtained using the liquid helium temperature zone electron microscope high-resolution imaging solution of the present application;
[0077] FIG12 shows the resolution at point a in FIG11 .
[0078] In the figure, 1. Helium tube interface; 2. Heating source interface; 3. U-shaped protection frame; 4. Shockproof bellows; 5. Shielding tube; 6. Sample chamber interface; 7. Objective lower pole piece; 8. Sample chamber; 9. Low-temperature sample stage; 10. Copper shielding tube; 11. First-stage cold head connector; 12. Aluminum connector; 13. Second-stage cold head connector; 14.1. First copper braid; 14.2. Second copper braid; 14.3. Third copper braid; 15.1. First-stage cold screen; 15.2. Second-stage cold screen; 16. Tail-stage cold screen copper braid; 17. Copper braid fixing; 18.1. First μ metal cover; 18.2. Second μ metal cover; 19.1. First Z-axis piezoelectric ceramic holder; 19.2. Second Z-axis piezoelectric ceramic holder; 20. Z-axis nano-scale piezoelectric ceramics; 21. Connecting piece; 22. X-axis nano-scale piezoelectric ceramics; 23. Z-axis fixing frame; 24. Y-axis nano-scale piezoelectric ceramics; 25.1. Second thermal insulation zirconia gasket; 25.2. First thermal insulation zirconia gasket; 26.1. First copper braid fixing piece; 26.2. Second copper braid fixing piece; 27. Sample holder; 28. Sample holder fixing piece; 29. Sample holder holder; 30. Sample holder cold plate; 31. Y-axis piezoelectric ceramic fixing plate; 32. Tungsten filament; 33. Heat transfer conductor; 34. Copper braid cold plate fixing piece; 35. High-voltage electrode; 36. Sapphire insulating tube; 37. Zirconia ceramic ball; 38. X-axis piezoelectric ceramic fixing plate; 39. Molybdenum nose; 40. Liquid helium refrigerator. DETAILED DESCRIPTION
[0079] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of this application.
[0080] Those skilled in the art should understand that, in the disclosure of this application, the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the above terms cannot be understood as limiting this application.
[0081] There are currently no reports on commercially available liquid helium temperature zone electron microscopes. This is mainly because the static Dewar needs to store a large amount of liquid helium during the cooling process. During use, a large amount of refrigerant will evaporate and be consumed, which will produce relatively obvious mechanical vibrations, thereby affecting the lateral resolution of the electron microscope. A more critical point is that the entire sample will be suspended under a high voltage of -15kV. Even a slight shake will cause serious discharge in the entire electron microscope, which will damage the high-voltage power supply and nose of the electron microscope, causing serious economic losses. At the same time, if the sample is in a low-temperature environment for a long time, a large amount of liquid helium must be consumed, which will greatly increase the cost of the experiment. Moreover, areas where liquid helium is difficult to obtain will be greatly restricted. In addition, the liquid helium static Dewar method requires manual perfusion of liquid helium at any time, which is time-consuming and labor-intensive. The extremely low temperature flow channel may be blocked, which will cause experimental accidents and may lead to experimental injuries.
[0082] Therefore, the present application is based on a liquid helium-free refrigerator to solve the problems existing in the prior art.
[0083] To facilitate understanding of the present application, the imaging principle of a cryogenic electron microscope is shown in Figure 1: First, the liquid helium compressor is turned on, and the refrigerator starts working, lowering the sample temperature to approximately 30K. After the sample temperature stabilizes, a cold-field electron gun generates an electron beam with an energy of 15keV. A focusing electromagnetic lens assembly focuses the electron beam with variable magnification; the electrons then pass through a magnetic prism array and are deflected 90° toward the objective lens and sample. The sample itself is suspended at a negative potential close to the field emission of the electron gun, so the electrons can be decelerated to an energy range of 0-100eV. After the electrons interact with the sample, they are reflected through the objective lens and accelerated again to 15keV. The magnified image of the sample is placed on the diagonal line of the prism array by a transfer lens. A second prism array deflects the electrons again by 90°. The middle plane of the two prism arrays coincides with the diffraction plane. The electrons enter the projection system, and by changing the settings of the projection electromagnetic lens, either a real-space image or a diffraction pattern can be projected onto the image screen.
[0084] Example 1
[0085] As shown in Figures 2-3, this liquid helium-free circulating refrigeration system, used to cool the specimen chamber 8 of an electron microscope, includes a liquid helium-free refrigerator 40. This refrigerator 40 is a type of refrigeration device used for cooling applications that operates independently of liquid helium. Compared to traditional liquid helium refrigerators, this refrigerator 40 provides a more convenient, economical, and environmentally friendly cooling solution.
[0086] Liquid-free helium refrigerators 40 typically use compression refrigeration cycles or thermoelectric refrigeration technology to achieve cooling. For example, this is based on the pulse tube effect, which utilizes the expansion and compression of gas to achieve low-temperature refrigeration. In the refrigerator, gas is compressed into high-pressure gas, which enters the pulse tube bundle through an expansion valve. It then expands within the pulse tube, absorbing heat from the surrounding environment, causing the gas temperature within the bundle to drop. Subsequently, the compressor compresses the cooled gas again and discharges the heat to the environment through a heat exchanger, allowing the gas to continue circulating.
[0087] Among them, if the liquid helium-free electron microscope wants to reach the liquid helium temperature zone, the key is the connection between the liquid helium-free refrigerator and the electron microscope sample chamber 8. Referring to Figures 2 and 3, the liquid helium-free refrigerator 40 mainly includes a U-shaped protective frame 3, a shock-proof bellows 4, a shielding tube 5, a copper shielding tube 10, a first-level cold head connector 11, and a second-level cold head connector 13. The shock-proof bellows 44 mainly reduces the mechanical vibration of the entire electron microscope when the refrigerant circulates in the flow tube for cooling, thereby improving the lateral resolution of the entire microscope and allowing the electron microscope to operate safely. The liquid helium-free refrigerator 40 is connected to the sample chamber via a vacuum flange.
[0088] The shockproof bellows 4 of the liquid-free helium refrigerator 40 connects to the U-shaped protective frame 3 and the shielding tube 5. The U-shaped protective frame 3 is equipped with a helium pipe interface 1 and a heating source interface 2. The electron microscope's sample chamber 8 also has a low-temperature sample stage 9, a sample chamber interface 6, and an objective lens lower pole piece 7. These structures are all existing technologies. This application utilizes the advantages and characteristics of the liquid-free helium refrigerator 40 by additionally designing a circulating refrigeration system to achieve cooling of the electron microscope's sample chamber.
[0089] Preferably, to maintain the ultra-high vacuum stability of the sample chamber 8, the sample chamber 8 is equipped with a vacuum pump system. The vacuum pump system includes an ion pump, a titanium sublimation pump, a magnetic levitation molecular pump, and a mechanical dry pump. The vacuum pump system evacuates the sample chamber 8 and the shielding tube 5 to a vacuum of up to 5.0×10-11 mbar, ensuring an ultra-high vacuum environment throughout the sample chamber 8.
[0090] As shown in Figure 3-9, this non-liquid helium consumption circulating refrigeration system specifically includes:
[0091] A copper shielding tube 10, one end of which is connected to the liquid helium inlet port in the shielding tube 5 of the liquid helium-free refrigerator 40, and the other end of which is provided with a first-stage cold head connector 11 and a second-stage cold head connector 13;
[0092] The first-stage cold shield is connected to the first-stage cold head connector 11 through a copper braid and is located on the outer ring of the μ metal cover and the sample;
[0093] In this embodiment, the first-stage cooling screen is connected to the Z-axis fixing frame 23. The first-stage cooling screen is used to reduce the heat exchange between the outside and the inside, and belongs to the first-stage cooling system.
[0094] The μ metal cover is connected to the first-stage cold head connector 11 through a copper braid and is connected to the first-stage cold screen through a copper braid of the first-stage cold screen. The μ metal cover is vacuum-connected to the lower pole shoe of the electron microscope as a fixed ring. At the same time, the μ metal cover is connected to the Z-axis piezoelectric ceramic support of the sample chamber 8 through an insulating gasket (such as an insulating zirconia gasket);
[0095] In this embodiment, the Z-axis piezoelectric ceramic supports are evenly distributed along the circumferential direction of the μ metal cover. Each Z-axis piezoelectric ceramic support is provided with a Z-axis nano-scale piezoelectric ceramic 20 for driving the sample to move back and forth along the Z axis. Each Z-axis nano-scale piezoelectric ceramic 20 is connected to the Z-axis fixing frame 23 through a connecting piece 21. The Z-axis fixing frame 23 is also connected to an X-axis nano-scale piezoelectric ceramic 22. The X-axis nano-scale piezoelectric ceramic 22 is used to drive the sample to move back and forth along the X axis. The X-axis nano-scale piezoelectric ceramic 22 is connected to the X-axis piezoelectric ceramic. Ceramic fixing plate 38, the X-axis piezoelectric ceramic fixing plate 38 is connected to the Y-axis nano-scale piezoelectric ceramic 24, which is used to drive the sample to move back and forth along the Y-axis. The Y-axis nano-scale piezoelectric ceramic 24 is connected to the Y-axis piezoelectric ceramic fixing plate 31, and a sapphire insulating tube 36 is provided at the center of the Y-axis piezoelectric ceramic fixing plate 31. The sapphire insulating tube 36 is fixed to the Y-axis piezoelectric ceramic fixing plate 31 through the sample holder cold plate 30, and the sample holder fixing part 28 is assembled at the end of the sapphire insulating tube 36.
[0096] In this embodiment, a thread is provided at the top of the sapphire insulating tube 36 for connecting the high-voltage electrode 35, so that the high-voltage electrode 35 can be connected to the vacuum feedthrough of the sample chamber 8 through a high-voltage line to achieve high voltage application, and the top of the sample chamber 8 is electrically connected to the high-voltage electrode 35.
[0097] The sample holder fixing part 28 is connected to the secondary cold head connecting part 13 through a copper braid. The sample holder fixing part 28 is used for inserting and fixing the sample holder 27 to enable cooling of the sample holder 27;
[0098] In this embodiment, the sample holder fixture 28 is provided with a copper braid fixture 17, through which the copper braid is connected. Preferably, the sample holder fixture 28 is evenly distributed with three notches, each of which is provided with a sample holder holder 29 for fixing the sample holder 27. The copper braid fixture 17 is connected to the sample holder fixture 28 and is connected to the sample holder cold plate 30 via a heat conducting member 33. Each sample holder holder 29 is type.
[0099] Among them, the first-level cold head connector 11, the first-level cold shield and the μ metal cover constitute a first-level low-temperature system.
[0100] Each Z-axis piezoelectric ceramic bracket includes a first ceramic bracket and a second ceramic bracket, the first ceramic bracket and the second ceramic bracket are connected by an insulating ball (such as a zirconia ceramic ball 37), and the Z-axis nano-scale piezoelectric ceramic 20 is provided on the second ceramic bracket.
[0101] Specifically, as shown in Figure 5 , the liquid helium-free refrigerator's primary cold head connector 11 is connected to the primary cold shield, first μ metal cover 18.1, and second μ metal cover 18.2 via second and third copper braids 14.2 and 14.3. The second μ metal cover 18.2 is connected to the primary cold shield via the tail copper braid 16. This primary cryogenic system creates a low-temperature environment of 90-95K around the sample. When the sample temperature drops even lower, heat exchange with components such as the cold shield is reduced, allowing the sample temperature to drop to the liquid helium range. The secondary cold head connector 13 of the liquid helium-free refrigerator is connected to the sample holder fixture 28 via a copper braid and braid fixture 17, allowing the sample holder fixture 28 to reach the liquid helium range. When the sample holder 27 is inserted, the entire sample holder 27 cools to ~30K, or even 10K.
[0102] Referring to Figures 6-9 , the first μ-metal cover 18.1 serves as a retaining ring connected to the objective lens lower pole piece 77 (the left end of the first μ-metal cover 18.1 is vacuum-connected to the objective lens assembly; since this is not covered by the patent, the objective lens portion is not described here). The first μ-metal cover 18.1 is enclosed by a second, primary cold shield 15.2. The first μ-metal cover 18.1 is connected to the second μ-metal cover 18.2 via a first, thermally insulating zirconia gasket 25.2. The second μ-metal cover 18.2 is connected to the first Z-axis piezoelectric ceramic support 19.1 via a second, thermally insulating zirconia gasket 25.1. Both thermally insulating zirconia gaskets function as thermal insulation.
[0103] Four first and second Z-axis piezoelectric ceramic supports 19.1, 19.2 are evenly distributed on second μ-metal cover 18.2. Zirconia ceramic balls 37 separate first and second Z-axis piezoelectric ceramic supports 19.1, 19.2, ensuring movement of second Z-axis piezoelectric ceramic supports 19.2 while reducing heat transfer between them.
[0104] Each second Z-axis piezoelectric ceramic support 19.2 is equipped with a Z-axis nano-scale piezoelectric ceramic 20, which provides sufficient power to move the entire sample portion left and right. Each Z-axis nano-scale piezoelectric ceramic 20 is connected to the Z-axis fixed frame 23 via a connecting piece 21, thereby driving the entire sample portion left and right.
[0105] The first level cold shield 15.1 is mounted on the Z-axis fixing frame 23, so as to reduce the heat exchange between the sample portion and the first copper braid 14.1 and the environment, so that the entire sample portion is kept at a low temperature.
[0106] Between the first Z-axis piezoelectric ceramic holder 19.1 and the second Z-axis piezoelectric ceramic holder 19.2, an X-axis nano-scale piezoelectric ceramic 22 is attached to a Z-axis fixed frame 23. Rotated 180° (at a symmetrical position), another X-axis nano-scale piezoelectric ceramic 22 is then mounted, driving the entire sample portion to move along the X-axis (as indicated by the marked direction in Figure 6). The X-axis piezoelectric ceramic fixing plate 38 is then mounted on the two X-axis nano-scale piezoelectric ceramics 22.
[0107] Two Y-axis nanoscale piezoelectric ceramics 24 are symmetrically mounted on an X-axis piezoelectric ceramic mounting plate 38, which intersects the two X-axis nanoscale piezoelectric ceramics 22. This allows the sample portion to move along the Y-axis. Next, a Y-axis piezoelectric ceramic mounting plate 31 is mounted on the two Y-axis nanoscale piezoelectric ceramics 24, with a sapphire insulating tube 36 positioned at its center. The end of the sapphire insulating tube 36 is secured to the Y-axis piezoelectric ceramic mounting plate 31 using a sample holder cold plate 30. The sample holder fixture 28 is then secured to the sample holder cold plate 30.
[0108] The sample holder fixing part 28 is evenly distributed with three notches (120 degrees between the notches), and a sample holder holder 29 is assembled in each notch. In this way, the tail of the sample holder 27 with the sample is clamped into the sample holder holder 29 using three teeth, and the sample holder 27 can be fixed by a slight rotation.
[0109] The second copper braid fixture 26.2 is then fixed to one end of the sample holder fixture 28 and connected to the sample holder cold plate 30 via a heat transfer conductor 33. The second copper braid fixture 26.2 is connected to the first copper braid fixture 26.1 via a copper braid, and further connected to the secondary cold head connector 13 via the copper braid. This connection allows the secondary cold head to cool the entire sample holder 27 and also cool the sapphire insulating tube 36.
[0110] This cooling method ensures that the temperature of the sample holder 27 drops to ~30K. The top of the sapphire insulating tube 36 is threaded, allowing the high-voltage electrode 35 to be screwed onto it. This is then connected to the vacuum feedthrough of the sample chamber 8 via a tungsten filament 32 (high-voltage wire), which then applies a -15kV high voltage. This allows the top of the sample to contact the high-voltage electrode 35, applying a -15kV high voltage to the sample. This allows the electron microscope to perform normal imaging.
[0111] In FIG9 , a molybdenum nose 39 (nose-objective lens) is provided on the lower pole piece 7 of the objective lens of the electron microscope.
[0112] Example 2
[0113] The liquid helium temperature zone electron microscope includes an electron source part, a lens system, an imaging system, a sample chamber 8 and the above-mentioned liquid helium consumption-free circulating refrigeration system. The sample chamber 8 is cooled by the liquid helium consumption-free circulating refrigeration system, and images are formed by the imaging system.
[0114] Referring to FIG10 , the liquid helium temperature zone electron microscope of Example 2 was used to perform reciprocal space imaging of a Cu(110) single crystal sample in the liquid helium temperature zone, and an excellent low-energy electron diffraction (LEED) image was obtained, showing the long-range ordered structure of the surface. Referring to FIG11 , real-space LEEM imaging of a Cu(110) single crystal sample in the liquid helium temperature zone was performed, and an excellent surface morphology was obtained. Referring to FIG12 , the resolution analysis of point a in FIG11 was performed, and the LEEM spatial resolution was found to be 5.5 nm, which basically reached the resolution limit of non-aberration-corrected LEEM.
[0115] The parts not described in detail in this application are prior art, so this application does not describe them in detail.
[0116] It is to be understood that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the elements may be multiple, and the term "one" should not be understood as a limitation on the quantity.
[0117] Although this article uses more helium tube interface 1, heating source interface 2, U-shaped protection frame 3, shockproof bellows 4, shielding tube 5, sample chamber interface 6, objective lens lower pole shoe 7, sample chamber 8, low-temperature sample stage 9, copper shielding tube 10, first-level cold head connector 11, aluminum connector 12, second-level cold head connector 13, first copper braid 14.1, second copper braid 14.2, third copper braid 14.3, first-level cold screen 15.1, second-level cold screen 15.2, tail-level cold screen copper braid 16, copper braid fixing part 17, first μ metal cover 18.1, The following terms are used: second μ-metal cover 18.2, first Z-axis piezoelectric ceramic support 19.1, second Z-axis piezoelectric ceramic support 19.2, Z-axis nano-scale piezoelectric ceramic 20, connecting piece 21, X-axis nano-scale piezoelectric ceramic 22, Z-axis fixing frame 23, Y-axis nano-scale piezoelectric ceramic 24, second thermal insulating zirconia gasket 25.1, first thermal insulating zirconia gasket 25.2, first copper braid fixing member 26.1, second copper braid fixing member 26.2, sample holder 27, sample holder fixing member 28, sample holder holder 29, sample holder cold plate 30, Y-axis piezoelectric ceramic fixing plate 31, tungsten filament 32, heat transfer conductor 33, copper braid cold plate fixing member 34, high-voltage electrode 35, sapphire insulating tube 36, zirconia ceramic ball 37, X-axis piezoelectric ceramic fixing plate 38, molybdenum nose 39, liquid helium-free refrigerator 40, etc., but the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present application; interpreting them as any additional limitations is contrary to the spirit of the present application.
[0118] This application is not limited to the above-mentioned optimal implementation method. Anyone can derive various other forms of products based on the inspiration of this application. However, no matter what changes are made in their shape or structure, any technical solution that is the same or similar to that of this application falls within the scope of protection of this application.
Claims
1. A circulating refrigeration system without liquid helium consumption, for cooling a sample chamber of an electron microscope, comprising a liquid helium-free refrigerator, characterized in that: Also includes: A copper shielding tube, one end of which is connected to the shielding cylinder of the liquid helium-free refrigerator, and the other end of which is provided with a primary cold head connector and a secondary cold head connector; The first-level cold shield is connected to the first-level cold head connector through a copper braid and is arranged on the outer ring of the μ metal cover; A μ metal cover is connected to the primary cold head connector through a copper braid, and is connected to the primary cold screen through a primary cold screen copper braid, and the μ metal cover is vacuum-connected to the lower pole shoe of the electron microscope as a fixing ring, and is connected to the Z-axis piezoelectric ceramic support of the sample chamber through an insulating gasket; A sample holder fixing part, connected to the secondary cold head connecting part through a copper braid, the sample holder fixing part is used for inserting and fixing the sample holder to realize cooling of the sample holder; The first-level cold head connector, the first-level cold shield and the μ metal cover form a first-level low-temperature system; the sample holder fixture is provided with a copper braid fixture, and the copper braid is connected through the copper braid fixture; The Z-axis piezoelectric ceramic brackets are evenly distributed along the circumferential direction of the μ metal cover, each of the Z-axis piezoelectric ceramic brackets is provided with a Z-axis nano-level piezoelectric ceramic for driving the sample to move back and forth along the Z-axis, each of the Z-axis nano-level piezoelectric ceramics is connected to the Z-axis fixing frame through a connecting piece, the Z-axis fixing frame is also connected with an X-axis nano-level piezoelectric ceramic, the X-axis nano-level piezoelectric ceramic is used to drive the sample to move back and forth along the X-axis, the X-axis nano-level piezoelectric ceramic is connected with an X-axis piezoelectric ceramic fixing plate, the X-axis piezoelectric ceramic fixing plate is connected with a Y-axis nano-level piezoelectric ceramic, the Y-axis nano-level piezoelectric ceramic is used to drive the sample to move back and forth along the Y-axis, the Y-axis nano-level piezoelectric ceramic is connected with a Y-axis piezoelectric ceramic fixing plate, a sapphire insulating tube is provided at the center of the Y-axis piezoelectric ceramic fixing plate, and the sapphire insulating tube is connected to the sample holder cold plate through the sample holder cold plate. The Y-axis piezoelectric ceramic fixing plate is fixed, and the end of the sapphire insulating tube is connected to a sample holder fixing piece.
2. The liquid helium consumption-free circulating refrigeration system according to claim 1, characterized in that: The primary cold shield is connected to the Z-axis fixing frame.
3. The liquid helium consumption-free circulating refrigeration system according to claim 2, characterized in that: Each of the Z-axis piezoelectric ceramic supports comprises a first ceramic support and a second ceramic support, the first ceramic support and the second ceramic support are connected via a heat-insulating ball, and the Z-axis nanoscale piezoelectric ceramic is arranged on the second ceramic support.
4. The liquid helium consumption-free circulating refrigeration system according to claim 1, characterized in that: The sample holder fixing piece is evenly provided with three notches, and each notch is provided with a sample holder holder for fixing the sample holder.
5. The liquid helium consumption-free circulating refrigeration system according to claim 4, characterized in that: The copper braid fixing part is connected to the sample holder fixing part, and is connected to the sample holder cold plate through a heat transfer conductor.
6. The liquid helium consumption-free circulating refrigeration system according to claim 4, characterized in that: Each of the sample holders is type.
7. The liquid helium consumption-free circulating refrigeration system according to any one of claims 1 to 6, characterized in that: The top of the sapphire insulating tube is provided with a thread for connecting a high-voltage electrode, so that the high-voltage electrode can be connected to the vacuum feedthrough of the sample chamber through a high-voltage line to achieve high voltage application, and the top of the sample chamber is electrically connected to the high-voltage electrode.
8. Liquid helium temperature zone electron microscope, characterized in that: The invention comprises an imaging system, a sample chamber and the liquid helium consumption-free circulating refrigeration system according to any one of claims 1 to 7, wherein the sample chamber is cooled by the liquid helium consumption-free circulating refrigeration system and images are formed by the imaging system.