Circulating refrigeration system without liquid helium consumption, and electron microscope operating in liquid-helium temperature range

Abstract

A circulating refrigeration system without liquid helium consumption. The system comprises: a liquid-helium-free refrigerating machine (40); a copper shielding tube (10), one end of the copper shieldi

Description

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[0001] The present invention relates to the field of electron microscopy technology, specifically to a circulating refrigeration system without liquid helium consumption, and electron microscope operating in liquid-helium temperature range. BACKGROUND

[0002] Over the past few decades, extensive research on surfaces, thin films, and interfaces has led to a deeper understanding of many fundamental physical and chemical properties, and recognized their critical role in numerous applications. Among the various experimental tools, cathode lens microscopy has played a significant role in identifying and interpreting many complex phenomena on surfaces. Since Bauer's invention of the low-energy electron microscope (LEEM), LEEM has evolved into an important technique for in-situ studies of surface structure, morphology, and dynamic processes.

[0003] LEEM is a type of cathode lens microscope that uses a low-energy electron beam (with energy below 100 eV, typically less than 10 eV) to probe the sample. It images the sample by collecting elastically backscattered electrons from the surface. Due to the short mean free path of low-energy electrons, LEEM is a highly surface-sensitive probing technique. Additionally, LEEM, through precise modulation of the electron optical path, can operate in both real-space and momentum-space imaging modes. Combined with the high-coherence electron source provided by a cold field emission gun, LEEM can be used to study phenomena such as quantum interference, making it one of the most powerful techniques for studying surface physics or chemistry. It has several prominent advantages:

[0004] 1. Real-time dynamic spatial imaging of important surface processes such as growth, phase transitions, and reactions;

[0005] 2 The LEEM system has very high spatial resolution capabilities, with longitudinal resolution reaching the atomic level, and lateral resolution reaching 3-4 nm, and allowing for localized imaging of the sample surface;

[0006] 3. The LEEM system achieves micro-area low-energy electron diffraction (u-LEED) with a minimum lateral resolution of 185 nm, and allowing for the characterization of local surface structure and properties;

[0007] 4. The LEEM system precisely changes the energy of the probing electron beam over a wide range, where the interaction of electrons with the surface can be studied by analyzing the IV-curve (intensity I-voltage V) as a function of the electron beam energy for the selected region.

[0008] With the development of surface science and related applications, new technologies based on LEEM / PEEM are also being continuously developed and applied. LEEM / PEEM has primarily been used in past studies to investigate surface dynamics, such as phase transitions near or above room temperature and in-situ growth phenomena, and proven to be a very powerful technique. However, there are also extensive novel physical and chemical phenomena that occur at temperature below room temperature, such as magnetic and electronic phase transitions in complex oxides. Current LEEM / PEEM systems typically have a sample temperature range of 300K to 1800K. Only a few LEEM / PEEM systems can cool samples below room temperature, but usually not lower than 100 K.

[0009] Currently, the Hong Kong University of Science and Technology has reported that their LEEM system can be cooled to 50 K using a static liquid helium Dewar. Existing reports claim that LEEM systems achieving temperatures below 77 K use static Dewar to cool the samples, which consumes a significant amount of liquid helium during operation. To sustain low temperatures, the consumption of liquid helium can reach several liters per day. Currently, there is a global helium shortage, and prices are rising exponentially, which significantly increases experimental costs. Since helium is a non-renewable resource with limited reserves, and it is estimated that resources will be depleted within a few decades. Additionally, many cities in China lack helium supply systems, leading to even higher liquid helium prices. This poses a significant constraint on scientific research requiring low-temperature LEEM / PEEM.

[0010] Most importantly, the use of a static liquid helium Dewar for cooling in experiments must consume a large amount of liquid helium, significantly increasing the experimental costs. Using a static liquid helium Dewar for cooling necessarily requires liquid nitrogen as a pre-cooling stage to reduce liquid helium consumption. However, the substantial evaporation of both liquid nitrogen and helium increases mechanical vibrations in the system, which can affect the lateral resolution. Furthermore, a high voltage of -15 kV is applied to the entire sample, and even slight vibrations can cause breakdown, which pose a risk of damaging the high-voltage power supply and nose of the electron microscope, leading to significant economic losses. The static liquid helium Dewar method requires frequent manual refilling of liquid helium, which is time-consuming and labor-intensive. The extremely low temperature can cause blockages in the flow channels, leading to experimental accidents and potential injuries. For cities without a liquid helium supply system, the duration of each experiment cannot be guaranteed, which greatly restricts the research work involving low-temperature electron microscopy.

[0011] Therefore, there is an urgent need for a circulating refrigeration system without liquid helium consumption and a electron microscope operating in liquid-helium temperature range, that can provide excellent cooling performance without the need for liquid helium supplementation after operation. This technology significantly reduces the liquid helium consumption of electron microscopy systems, greatly lowering experimental costs. It is also simple and convenient to use and is suitable for research in areas where liquid helium is difficult to obtain, without being limited by geographical constraints, thus addressing the issues present in existing technologies. SUMMARY OF THE INVENTION

[0012] The present invention aims to address the aforementioned issues present in existing technologies by providing a circulating refrigeration system without liquid helium consumption and electron microscope for a liquid-helium temperature range.

[0013] To achieve the aforementioned purposes, the present invention adopts the following technical solution: a circulating refrigeration system without liquid helium consumption for cooling the sample chamber of an electron microscope, comprising a liquid-helium-free refrigerating machine, and further including:

[0014] A copper shielding tube, one end of which is connected to the shielding cylinder of the liquid-helium-free refrigerating machine, and the other end is equipped with first-stage cold head connector and second-stage cold head connector;

[0015] A first-stage cold shield, connected to the first-stage cold head connector via copper braids located outside the p-metal shield;

[0016] A p-metal shield, connected to the first-stage cold head connector and the first-stage cold shield via copper braids. The p-metal shield serves as a mounting ring and is connected to the lower pole piece of the electron microscope. Additionally, the p-metal shield is connected to the Z-axis piezoelectric ceramic bracket of the sample chamber via thermally insulating washer.

[0017] A sample stage fixing member, connected to the second-stage cold head connector via copper braids. This sample stage fixing member is used to secure the sample holder, enabling the cooling of the sample holder;

[0018] Among these, the first-stage cold head connector, the first-stage cold shield, and the p-metal shield form the first-stage low-temperature system. The main effects of this setup are as follows:

[0019] Low-temperature cooling: The system transfers cooling power to the sample chamber through the first-stage cold head connector and the second-stage cold head connector, thereby achieving cooling of the sample. The first-stage low-temperature system, consisting of the first-stage cold head connector, the first-stage cold shield, and the p-metal shield, can provide a relatively low temperature.

[0020] Shielding and Isolation: The copper shielding tube and the p-metal shield provide shielding and isolation, separating the low-temperature system from the external environment (such as the vacuum environment of the electron microscope) to prevent heat loss and interference.

[0021] Sample Holder Cooling: The sample stage fixing member is connected to the second-stage cold head connector, achieving cooling of the sample holder. This ensures that the sample can be observed and studied for a liquid-helium temperature range.

[0022] Stability and Precision: The circulating refrigeration system without liquid helium consumption offers more stable and precise temperature control compared to traditional liquid nitrogen or liquid helium cooling systems. It can provide long-term continuous operation without the need for frequent addition of cooling medium.

[0023] Further, the sample stage fixing member is equipped with a copper braid fixing piece, which is connected with the copper braid. The main effects of this setup are as follows:

[0024] Thermal Conductivity: The primary function of the copper braid fixing piece is to connect the copper braid to the sample stage fixing member. Since copper is an excellent thermal conductor, the connection through the copper braid fixing piece effectively transfers cooling to the sample holder, enhancing the cooling performance of the sample holder.

[0025] Stability and Reliability: By using the copper braid fixing piece, the copper braid can be securely attached to the sample stage fixing member, providing better stability and reliability. This helps prevent the copper braid from coming loose or detaching during operation, ensuring the continuous transfer of cooling.

[0026] Mechanical Support: The copper braid fixing piece provides mechanical support and fixation, making the installation of the copper braid on the sample stage fixing member more secure. This helps prevent unnecessary movement or loosening during operation or vibration.

[0027] Protective Performance: The copper braid fixing piece can protect the copper braid from damage or wear. This extends the lifespan of the braid and reduces the frequency of maintenance or replacement.

[0028] Furthermore, the Z-axis piezoelectric ceramic brackets are evenly distributed along the circumference of the p-metal shield. Each Z-axis piezoelectric ceramic bracket is equipped with a Z-axis nanometer-level piezoelectric ceramic, which is used to move the sample back and forth along the Z-axis. Each Z-axis nanometer-level piezoelectric ceramic is connected to the Z-axis fixed frame via a connecting piece. The Z-axis fixed frame is also equipped with X-axis nanometer-level piezoelectric ceramics, which are used to move the sample back and forth along the X-axis. The X-axis nanometer-level piezoelectric ceramics are equipped with an X-axis piezoelectric ceramic mounting plate, which is further connected to Y-axis nanometer-level piezoelectric ceramics. The Y-axis nanometer-level piezoelectric ceramics are used to move the sample back and forth along the Y-axis and are equipped with a Y-axis piezoelectric ceramic mounting plate. The center of the Y-axis piezoelectric ceramic mounting plate is equipped with a sapphire insulating tube, which is fixed to the Y-axis piezoelectric ceramic mounting plate via the sample holder cold plate. The end of the sapphire insulating tube is equipped with the sample stage fixing member. This setup has the following main effects:

[0029] Multi-axis Movement: The system achieves precise control and movement of the sample in three axes (Z-axis, X-axis, and Y-axis) through the use of Z-axis nanometer-level piezoelectric ceramics, X-axis nanometer-level piezoelectric ceramics, and Y-axis nanometer-level piezoelectric ceramics. This allows for multi-dimensional positioning, rotation, and adjustment of the sample to meet various experimental requirements.

[0030] Nanometer-level Control: The application of nanometer-level piezoelectric ceramics can achieve very fine movement control. By adjusting the voltage, nanometer-level displacement and position control can be achieved, thus allowing for fine-tuning and precise manipulation of the sample position.

[0031] Stability and Reproducibility: Piezoelectric ceramics have high stability and reproducibility. They offer high precision of movement and can maintain consistent position and motion control across multiple experiments, thus providing reliable experimental results and data reproducibility.

[0032] Insulation Performance: The application of the sapphire insulating tube provides electrical insulation and isolation, preventing current leakage and interference. This helps ensure the safety of electronic equipment and the sample, and reduces the impact of unnecessary interference on the experimental results.

[0033] Moreover, the first-stage cold shield is connected to the Z-axis fixed frame. This setup has the following main effects:

[0034] Thermal Conductivity: The first-stage cold shield is a component connected to the first-stage cold head connector of the liquid-helium-free refrigerating machine. It is typically made of materials with good thermal conductivity, such as copper. By connecting the first-stage cold shield to the Z-axis fixed frame, it can effectively transfer cooling and temperature control to the Z-axis fixed frame and related components.

[0035] Cooling Effect: The first-stage cold shield, as a part of the low-temperature system, can provide a cooling function. By connecting it to the Z-axis fixed frame, it can transfer cooling to the Z-axis fixed frame and the sample chamber, achieving primary cooling of the sample and related components. It also blocks external thermal radiation, reducing heat loss in the low-temperature environment.

[0036] Stability and Thermal Equilibrium: Connecting the first-stage cold shield to the Z-axis fixed frame can enhance the stability and maintain thermal equilibrium of the system. It helps to distribute and evenly spread the cooling, preventing heat accumulation and local temperature variations, thus providing a more stable and uniform cooling effect.

[0037] Thermal Insulation and Shielding: The connection of the first-stage cold shield also provides thermal insulation and shielding, preventing heat transfer and external interference. It can limit the propagation of heat flow, ensuring the cooling effectiveness of the sample chamber and maintaining the required temperature environment.

[0038] Further, 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 sphere, and the Z-axis nanometer-level piezoelectric ceramic is mounted on the second ceramic bracket. This setup has the following main effects:

[0039] Thermal Insulation: The connection via the insulating sphere provides thermal insulation, reducing heat transfer and loss. This is crucial for maintaining a stable temperature environment for the Z-axis piezoelectric ceramic bracket, preventing external heat sources from causing interference.

[0040] Thermal Stability: By placing the Z-axis nanometer-level piezoelectric ceramic on the second ceramic bracket and using the insulating sphere for connection, better thermal stability can be achieved. This reduces heat diffusion and leakage, ensuring that the Z-axis nanometer-level piezoelectric ceramic remains in a relatively constant temperature environment.

[0041] Electrical Insulation: The insulating sphere between the first ceramic bracket and the second ceramic bracket 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 bracket and related components.

[0042] Structural Stability: The combination of the first ceramic bracket and the second ceramic bracket provides better structural stability and support. This helps ensure the stable installation and operation of the Z-axis piezoelectric ceramic bracket, meeting the requirements for precise control and movement.

[0043] Additionally, the sample stage fixing member is uniformly equipped with three notches, and each notch has a sample holder clamp for securing the sample holder. This setup has the following main effects:

[0044] Sample Fixation: Each sample holder clamp on the notches can be used to secure the sample holder, ensuring stability and reliability during the experiment. By inserting and fixing the sample holder into the clamp, it prevents accidental movement or shaking of the sample, maintaining its precise position.

[0045] Precise Positioning: The uniform distribution of the notches and sample holder clamps allows for precise positioning of the sample on the sample stage fixing member. The position and design of each notch ensure the correct alignment of the sample holder, enabling the sample to be positioned and operated according to the predetermined location.

[0046] Replaceability: The design of the sample holder clamps allows for the sample holder to be relatively easily replaced and adjusted. This enables quick replacement of different samples or adjustment of the sample arrangement according to experimental needs, meeting the requirements of various experimental conditions.

[0047] Further, the copper braid fixing piece is connected to the sample stage fixing member, and is connected to the sample holder cold plate via a thermal conductor. This setup has the following main effects:

[0048] Mechanical Support: The connection between the copper braid fixing piece and the sample stage fixing member provides mechanical support, increasing the stability and rigidity of the sample holder. This helps prevent unnecessary vibrations or movements of the sample holder during the experiment, ensuring the precision and reliability of the experiment.

[0049] Thermal Conductivity: By connecting the copper braid fixing piece to the sample holder cold plate via a thermal conductor, heat transfer and control can be achieved. The thermal conductor typically has good thermal conductivity, effectively transferring heat from the sample holder to the cooling plate, thus cooling the sample.

[0050] Temperature Stability: The connection between the copper braid fixing piece and the sample holder cold plate via the thermal conductor provides temperature stability. The thermal conductor can quickly balance temperature differences and transfer the low temperature from the cooling plate to the sample holder, maintaining a stable low-temperature environment for the sample holder.

[0051] Thermal Control: The connection between the copper braid fixing piece and the thermal conductor allows for control of the sample holder's temperature. By adjusting the temperature of the cooling plate and the heat transfer efficiency of the thermal conductor, the temperature of the sample holder can be precisely controlled to meet the experimental requirements.

[0052] Further, each sample holder clamp is shaped like a "rj". This setup has the following main effects:

[0053] Elastic Fixation: Due to the "q" shape of the sample holder clamp, it has a certain degree of elasticity. This elastic design allows the sample holder to be subjected to a certain pressure when inserted into the sample holder clamp, and to be securely fixed in the sample holder clamp. This ensures that the sample holder remains firmly in the desired position, avoiding any unintended movement or loosening during the experiment.

[0054] Adaptability to Multiple Sample Sizes: Due to the shape and elasticity of the "q" shaped sample holder clamp, it can accommodate sample holders of different sizes. This means that whether the sample holder is smaller or larger, it can be securely fixed in the holder. This provides greater flexibility, allowing the sample holder to accommodate samples of different sizes.

[0055] Shock Absorption: Due to the elasticity and shape design of the sample holder clamp, it can provide a certain shock absorption effect. During the experiment, there may be some external vibrations or shocks, which can adversely affect the stability of the sample and the experimental results. However, the elastic "q" shaped sample holder clamp can absorb and mitigate these vibrations to a certain extent, protecting the sample from external interference.

[0056] Simplified Operation: The "q" shaped design of the sample holder clamp can simplify the operational steps. Due to its elastic characteristics, the sample holder can be relatively easily inserted and removed from the sample holder clamp, making it more convenient and quickly to change or adjust the sample position.

[0057] Furthermore, the top of the sapphire insulating tube is equipped with threads for connecting the high-voltage electrode. This allows the high-voltage electrode to be connected to the vacuum feedthrough of the sample chamber via a high-voltage wire, enabling the application of high voltage, and ensures electrical connection between the top of the sample chamber and the high-voltage electrode. This setup has the following main effects:

[0058] High-Voltage Transmission: By connecting the high-voltage electrode to the 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.

[0059] Electrical Connection: By electrically connecting the top of the sample chamber to the high-voltage electrode, effective voltage feedthrough is ensured. This is necessary for high-voltage experiments, ensuring the effective connection between the high-voltage electrode and the sample in the sample chamber, allowing the voltage to be successfully applied to the sample.

[0060] Safety and Stability: The design of the sapphire insulating tube provides isolation and insulation protection for high voltage, ensuring the directed transmission of high voltage between the electrode and the sample. This helps prevent electrical shock risks and maintains the stability of the experimental equipment.

[0061] The liquid-helium-free cryogenic electron microscope includes an electron source, a lens system, an imaging system, a sample chamber, and the aforementioned circulating refrigeration system without liquid helium consumption. The sample chamber is cooled by the circulating refrigeration system without liquid helium consumption, and imaging is performed by the imaging system.

[0062] Compared to existing technologies, The present invention has the following beneficial effects:

[0063] 1. The present invention replaces traditional static Dewar cooling with a liquid-helium-free refrigerating machine and additionally designs a circulating refrigeration system specifically for cooling the sample chamber. The refrigerant circulates within the circulation pipes of the liquid-helium-free refrigerating machine to achieve heat exchange and cooling of the sample chamber equipment. Therefore, the refrigerant does not evaporate and can maintain the required liquid-helium temperature environment for a long time, significantly reducing experimental costs, reducing mechanical vibrations, and improving lateral resolution to achieve ultra-high resolution in electron microscopy.

[0064] 2 The present invention achieves a primary low-temperature system using a first-stage cold head connector, a first-stage cold shield, and a p-metal shield to create a low-temperature environment of 90 - 95 K around the sample. By connecting the sample holder to a second-stage cold head connector, the sample holder can be cooled to approximately 20 K, and even as low as 10 K, allowing the sample to remain in the required liquid-helium temperature environment for an extended period. Moreover, no liquid helium needs to be replenished after operation, which significantly reduces the liquid helium consumption of the electron microscope system, greatly reducing experimental costs. This technology is simple and convenient and is also suitable for scientific research in regions where liquid helium is difficult to obtain. Additionally, it reduces mechanical vibrations caused by refrigerant evaporation, thereby improving lateral resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 is a schematic diagram of the liquid-helium temperature range electron microscope.

[0066] Figure 2 is main view structural diagram of the sample chamber of the liquid-helium-free closed-cycle cryogenic electron microscope of the present invention.

[0067] Figure 3 is a schematic diagram of the liquid-helium-free refrigerating machine of the present invention.

[0068] Figure 4 is a local enlarged view of area A in Figure 3

[0069] Figure 5 is a structural diagram of the assembly of the liquid-helium-free refrigerating machine and the sample chamber components of the present invention.

[0070] Figure 6 is main view schematic diagram of the low-temperature sample chamber of liquid-helium-free closed-cycle cryogenic electron microscope of the present invention.

[0071] Figure 7 is a front view structural diagram of the low-temperature sample chamber of the liquid-helium-free closed-cycle cryogenic electron microscope of the present invention, without the first-stage cold shield.

[0072] Figure 8 is a rear view structural diagram of the low-temperature sample chamber of the liquid-helium-free closed-cycle cryogenic electron microscope of the present invention, without the first-stage cold shield.

[0073] Figure 9 is a structural diagram in the "A-A" direction of Figure 7.

[0074] Figure 10 is a low-energy electron diffraction (LEED) pattern of a Cu(110) single crystal obtained using the high-resolution imaging method of the liquid-helium temperature range electron microscope according to the present invention.

[0075] Figure 11 is a real-space surface image of a Cu(l 10) single crystal obtained using the high-resolution imaging method of the liquid-helium temperature range electron microscope according to the present invention.

[0076] Figure 12 is the resolution at a in Figure 11.

[0077] In the figures: 1. helium gas pipe interface; 2. heating source interface; 3. U-shaped protective bracket; 4. anti-vibration bellows; 5. shielding cylinder; 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. the first copper braid; 14.2. the second copper braid; 14.3. the third copper braid; 15.1. the first-first-stage cold shield; 15.2. the second-first-stage cold shield; 16. tail first-stage cold shield copper braid; 17. copper braid fixing piece; 18.1. the first p-metal shield; 18.2. the second p-metal shield; 19.1. the first Z-axis piezoelectric ceramic bracket; 19.2. the second Z-axis piezoelectric ceramic bracket; 20. Z-axis nanometer-level piezoelectric ceramic; 21. connecting plate; 22. X-axis nanometer-level piezoelectric ceramic; 23. Z-axis fixed frame; 24. Y-axis nanometer-level piezoelectric ceramic; 25.1. the second insulating zirconia washer; 25.2. the first insulating zirconia washer; 26.1. the first copper braid fixing piece; 26.2. the second copper braid fixing piece; 27. sample holder; 28. sample stage fixing member; 29. sample holder clamp; 30. sample holder cold plate; 31. Y-axis piezoelectric ceramic mounting plate; 32. tungsten wire; 33. thermal conductor; 34. copper braid cold plate fixing piece; 35. high-voltage electrode; 36. sapphire insulating tube; 37. zirconia ceramic sphere; 38. X-axis piezoelectric ceramic mounting plate; 39. molybdenum nose; 40. liquid-helium-free refrigerating machine. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0078] The following description of the embodiments of the present invention, in conjunction with the accompanying figures, is provided to clearly and completely describe the technical solutions of the embodiments of the present invention. It should be understood that the embodiments described herein are only a part of the embodiments of the present invention and not all of them. Any other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0079] It should be understood by those of ordinary skill in the field that, in the disclosure of the present invention, terms such as “longitudinal,” “transverse,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” “outer,” etc., are used to indicate directions or positional relationships based on the directions or positional relationships shown in the figures. These terms are used merely for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or suggest that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, these terms should not be construed as limiting the present invention.

[0080] Currently, there are no reports of commercialized liquid-helium temperature range electron microscopes. This is mainly due to the fact that static Dewar, during the cooling process, require a large amount of liquid helium to be stored. During operation, the refrigerant will evaporate in large quantities, which can cause significant mechanical vibrations, thereby affecting the lateral resolution of the electron microscope. More critically, the entire sample will be suspended at a high voltage of -15 kV. Even slight vibrations can cause severe discharge phenomena in the electron microscope, which can damage the high-voltage power supply and the nose, leading to significant economic losses. Additionally, maintaining the sample at a low temperature for extended periods requires a large amount of liquid helium, which significantly increases the experimental costs. Furthermore, regions where liquid helium is difficult to obtain are severely restricted. The static Dewar method also requires frequent manual refilling of liquid helium, which is time-consuming and labor-intensive. The extremely low temperature flow channels may also become blocked, leading to experimental accidents and potential injuries.

[0081] Therefore, the present invention is based on a liquid-helium-free refrigerating machine to solve the problems existing in the current technology.

[0082] To facilitate understanding of the present invention, as shown in Figure 1, the imaging principle of the liquid-helium-free closed-cycle cryogenic electron microscope is as follows: First, the liquid helium compressor is turned on, and the refrigeration machine begins to operate, cooling the sample to around 20 K. Once the sample temperature stabilizes, a cold field emission electron gun generates an electron beam with an energy of -15 keV. The electron beam is focused by a combination of electromagnetic lenses at a variable magnification. Then, the electrons pass through a magnetic prism array, deflecting 90° towards the objective lens and the sample. The sample itself is suspended at a potential close to the negative potential of the electron gun field emission, so the electrons can be decelerated to an energy range of 0-100 eV. After interacting with the sample, the electrons are reflected and again accelerated to 15 keV by the objective lens. The transfer lens then places the magnified image of the sample on the diagonal of the prism array. A second prism array deflects the electrons another 90°. The intermediate plane between the two prism arrays coincides with the diffraction plane. The electrons enter the projection system, and by changing the settings of the projection electromagnetic lenses, either a real-space image or a diffraction pattern can be projected onto the image screen.

[0083] Embodiment One

[0084] As shown in Figures 2-3, the circulating refrigeration system without liquid helium consumption is used to cool the sample chamber 8 of the electron microscope. The system includes a liquid-helium-free refrigerating machine 40, which is a cooling device designed for cooling applications that does not rely on the using of liquid helium. Compared to traditional liquid-helium-free refrigerating machines, the liquid-helium-free refrigerating machine 40 provides a more convenient, economical, and environmentally friendly cooling solution.

[0085] The liquid-helium-free refrigerating machine 40 typically uses compression refrigeration cycles or thermoelectric cooling technology to achieve the cooling effect. For example, it can be based on the pulse tube effect, which utilizes the expansion and compression of gases to achieve low-temperature cooling. In the refrigeration machine, the gas is compressed into a high-pressure state, which then passes through an expansion valve into the pulse tube bundle. In the pulse tube, the gas expands and absorbs heat from the surrounding environment, causing the temperature of the gas inside the tube bundle to decrease. Subsequently, the compressor re-compresses the cooled gas and expels the heat through a heat exchanger, allowing the gas to continue circulating.

[0086] To achieve the liquid-helium temperature range in a liquid-helium-free closed-cycle cryogenic electron microscope, the key is the connection between the liquid-helium-free refrigerating machine and the sample chamber 8 of the electron microscope. As shown in Figures 2 and 3, the liquid-helium-free refrigerating machine 40 mainly includes a U-shaped protective bracket 3, an anti-vibration bellows 4, a shielding cylinder 5, a copper shielding tube 10, a first-stage cold head connector 11, and a second-stage cold head connector 13. The anti-vibration bellows 4 primarily reduces the mechanical vibrations of the entire electron microscope when the refrigerant circulates through the flow pipes, improving the lateral resolution of the microscope and ensuring the safe operation of the electron microscope. The liquid-helium-free refrigerating machine 40 is connected to the sample chamber via a vacuum flange.

[0087] The anti-vibration bellows 4 of the liquid-helium-free refrigerating machine 40 are connected to the U-shaped protective bracket 3 and the shielding cylinder 5. The U-shaped protective bracket 3 is equipped with a helium gas pipe interface 1 and a heating source interface 2. The sample chamber 8 of the electron microscope is also equipped with a low-temperature sample stage 9, a sample chamber interface 6, and an objective lower pole piece 7. These structures are all part of existing technology. The present invention leverages the advantages and characteristics of the liquid-helium-free refrigerating machine 40 and achieves cooling of the electron microscope's sample chamber by designing an additional circulating refrigeration system.

[0088] Preferably, to maintain the ultra-high vacuum stability of the sample chamber 8, a vacuum pump system is equipped at this location. The vacuum pump system includes an ion pump, a titanium sublimation pump, a magnetically levitated turbo molecular pump, and a mechanical pump. The vacuum pump system evacuates the sample chamber 8 and the shielding cylinder 5, achieving a vacuum of 5.0 x 10 11 mbar, ensuring the ultra-high vacuum environment throughout the sample chamber 8.

[0089] As shown in Figures 3-9, the circulating refrigeration system without liquid helium consumption specifically includes:

[0090] Copper Shielding Tube 10: One end of the copper shielding tube 10 is connected to the liquid helium inlet within the shielding cylinder 5 of the liquid-helium-free refrigerating machine 40. The other end is equipped with a first-stage cold head connector 11 and a second-stage cold head connector 13.

[0091] First-stage Cold Shield: The first-stage cold shield is connected to the first-stage cold head connector 11 via a copper braid. It is located outside the p-metal shield and the sample.

[0092] In this embodiment, the first-stage cold shield is connected to the Z-axis fixed frame 23. The first-stage cold shield is designed to reduce heat exchange between the external environment and the internal components, and it belongs to the first-stage cooling system.

[0093] p-metal Shield: The p-metal shield is connected to the first-stage cold head connector 11 via a copper braid and to the first-stage cold shield via a first-stage cold shield copper braid. The p-metal shield serves as a fixing ring and is connected to the lower pole piece of the electron microscope. Additionally, the p-metal shield is connected to the Z-axis piezoelectric ceramic bracket of the sample chamber 8 through an insulating washer (such as an insulating zirconia washer).

[0094] In this embodiment, the Z-axis piezoelectric ceramic bracket are evenly distributed around the circumference of the p-metal shield. Each Z-axis piezoelectric ceramic bracket is equipped with a Z-axis nanometer-level piezoelectric ceramic 20, which is used to move the sample back and forth along the Z-axis. Each Z-axis nanometer-level piezoelectric ceramic 20 is connected to the Z-axis fixed frame 23 via a connecting plate 21. The Z-axis fixed frame 23 is also equipped with an X-axis nanometer-level piezoelectric ceramic 22, which is used to move the sample back and forth along the X-axis. The X-axis nanometer-level piezoelectric ceramic 22 is equipped with an X-axis piezoelectric ceramic mounting plate 38, which is further connected to a Y-axis nanometer-level piezoelectric ceramic 24. The Y-axis nanometer-level piezoelectric ceramic 24 is used to move the sample back and forth along the Y-axis. The Y-axis nanometer-level piezoelectric ceramic 24 is equipped with a Y-axis piezoelectric ceramic mounting plate 31, which has a sapphire insulating tube 36 at its center. The sapphire insulating tube 36 is fixed to the Y-axis piezoelectric ceramic mounting plate 31 via a sample holder cold plate 30, and the end of the sapphire insulating tube 36 is equipped with a sample stage fixing member 28.

[0095] In this embodiment, the top of the sapphire insulating tube 36 has a thread for connecting the high-voltage electrode 35. This allows the high-voltage electrode 35 to be connected to the vacuum feedthrough of the sample chamber 8 via a high-voltage wire, enabling the application of high voltage. The top of the sample chamber 8 is electrically connected to the high-voltage electrode 35.

[0096] The sample stage fixing member 28 is connected to the second-stage cold head connector 13 via a copper braid. This sample stage fixing member 28 is used to secure the sample holder 27, allowing for the cooling of the sample holder 27.

[0097] In this embodiment, the sample stage fixing member 28 is equipped with a copper braid fixing piece 17, which connects to the copper braid. Preferably, the sample stage fixing member 28 is uniformly equipped with three notches, and each notch has a sample holder clamp 29 for securing the sample holder 27. The copper braid fixing piece 17 is connected to the sample stage fixing member 28 and is also connected to the sample holder cold plate 30 via a thermal conductor 33. Each sample holder clamp 29 is shaped like a "g".

[0098] The first-stage cold head connector 11, the first-stage cold shield, and the p-metal shield form the first-stage low-temperature system.

[0099] 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 via an insulating sphere (such as an insulating zirconia ceramic sphere 37). The Z-axis nanometer-level piezoelectric ceramic 20 is mounted on the second ceramic bracket.

[00100] Specifically, as shown in Figure 5, the first-stage cold head connector 11 of the liquid-helium-free refrigerating machine is connected to the first-stage cold shield, the first p-metal shield 18.1 and the second p-metal shield 18.2 via the second copper braid 14.2 and the third copper braid 14.3. The second p-metal shield 18.2 is connected to the first-stage cold shield via a tail first-stage cold shield copper braid 16. This first-stage low-temperature system creates a low-temperature environment of 90 - 95 K around the sample, reducing heat exchange with the cold shield and other components when the sample temperature is lower, thus allowing the sample temperature to reach the liquid-helium temperature range. The second-stage cold head connector 13 of the liquid-helium-free refrigerating machine is connected to the sample stage fixing member 28 via a copper braid and a copper braid fixing piece 17, enabling the sample stage fixing member 28 to reach the liquid-helium temperature range. When the sample holder 27 is inserted, the entire sample holder 27 will be cooled to ~20 K, and even down to 10 K.

[00101] As shown in Figures 6-9, the first p-metal shield 18.1 serves as a fixing ring and is connected to the lower pole piece 7 of the objective lens (the left end of the first p-metal shield 18.1 is connected to the objective lens components in vacuum, but the objective lens part is not described here, as it is not within the scope of the patent). The first p-metal shield 18.1 is covered by a second-first-stage cold shield 15.2. The first u-metal shield 18.1 is connected to the second p-metal shield 18.2 via a first insulating zirconia washer 25.2. The second p-metal shield 18.2 is connected to the first Z-axis piezoelectric ceramic bracket 19.1 via a second insulating zirconia washer 25.1. The function of both insulating zirconia washers is to provide thermal insulation.

[00102] The first Z-axis piezoelectric ceramic bracket 19.1 and the second Z-axis piezoelectric ceramic bracket 19.2 are evenly distributed on the second p-metal shield 18.2, with four of each. The first Z-axis piezoelectric ceramic bracket 19.1 and the second Z-axis piezoelectric ceramic bracket 19.2 are separated by zirconia ceramic spheres 37. This arrangement ensures the movement of the second Z-axis piezoelectric ceramic bracket 19.2, while also reducing heat transfer between them.

[00103] Each second Z-axis piezoelectric ceramic bracket 19.2 is equipped with a Z-axis nanometer-level piezoelectric ceramic 20, providing sufficient power to move the entire sample stage back and forth. Each Z-axis nanometer-level piezoelectric ceramic 20 is connected to the Z-axis fixed frame 23 via a connecting plate 21, which allows the entire sample stage to move back and forth.

[00104] The first-first-stage cold shield 15.1 is installed to the Z-axis fixed frame 23. This arrangement reduces the heat exchange between the sample and the environment, as well as between the first copper braid 14.1 and the environment, ensuring that the entire sample remains at a low temperature.

[00105] Between the first Z-axis piezoelectric ceramic brackets 19.1 and the second Z-axis piezoelectric ceramic bracket 19.2, the X-axis nanometer-level piezoelectric ceramic 22 is installed on the Z-axis fixed frame 23. Another X-axis nanometer-level piezoelectric ceramic 22 is assembled at a 180° rotation (in the symmetrical position) to drive the entire sample stage to move along the X-axis (as shown in Figure 6). Subsequently, the X-axis piezoelectric ceramic mounting plate 38 is installed on the two X-axis nanometer-level piezoelectric ceramics 22.

[00106] On the X-axis piezoelectric ceramic mounting plate 38, which intersects with the two X-axis nanometer-level piezoelectric ceramics 22, two Y-axis nanometer-level piezoelectric ceramics 24 are symmetrically assembled. This allows the sample to move along the Y-axis. Subsequently, the Y-axis piezoelectric ceramic mounting plate 31 is installed on the two Y-axis nanometer-level piezoelectric ceramics 24, respectively. And a sapphire insulating tube 36 is assembled at the center position of Y-axis nanometer-level piezoelectric ceramics 24. The end of the sapphire insulating tube 36 is fixed to the Y-axis piezoelectric ceramic mounting plate 31 using a sample holder cold plate 30. Finally, the sample stage fixing member 28 is fixed to the sample holder cold plate 30.

[00107] Among these, the sample stage fixing member 28 has three evenly distributed notches (each 120° apart). A sample holder clamp 29, which is shaped like a "q," is assembled into each notch. The tail end of the sample holder 27, which carries the sample, uses three teeth to install into the sample holder clamp 29. A slight rotation is sufficient to secure the sample holder 27.

[00108] Subsequently, the second copper braid fixing piece 26.2 is fixed to one end of the sample stage fixing member 28 and is connected to the sample holder cold plate 30 via a thermal conductor 33. The second copper braid fixing piece 26.2 is connected to the first copper braid fixing piece 26.1 via a copper braid, and then is connected to the second-stage cold head connector 13 through the copper braid. This allows the secondary cold head to cool the entire sample holder 27 via this connection method, while also cooling the sapphire insulating tube 36.

[00109] This cooling method can ensure that the temperature of the sample holder 27 is reduced to approximately 20 K. The top of the sapphire insulating tube 36 has a threaded, where the high-voltage electrode 35 is screwed. The high-voltage electrode 35 is then connected to the vacuum feedthrough of the sample chamber 8 via a tungsten wire 32 (high-voltage wire), allowing the application of -15 kV high voltage. This ensures that the top of the sample contacts the high-voltage electrode 35, thereby applying -15 kV high voltage to the sample. Consequently, the electron microscope can image.

[00110] In Figure 9, objective lower pole piece 7 of the electron microscope is equipped with a molybdenum nose 39 (nose-objective).

[00111] Embodiment Two

[00112] The liquid-helium-free closed-cycle cryogenic electron microscope includes an electron source, a lens system, an imaging system, a sample chamber 8, and the aforementioned circulating refrigeration system without liquid helium consumption. The sample chamber 8 is cooled using the circulating refrigeration system without liquid helium consumption. And imaging is performed through the imaging system.

[00113] As shown in Figure 10, using the liquid-helium-free closed-cycle cryogenic electron microscope described in Example 2, reciprocal space imaging of a Cu(110) single crystal sample was performed at liquid-helium temperature range, resulting in very good low-energy electron diffraction (LEED), which shows the long-range ordered surface structure. In Figure 11, real-space LEEM imaging of the Cu(110) single crystal sample was performed at liquid-helium temperature range, yielding very good surface morphology images. In Figure 12, which is a detailed analysis of area a in Figure 11, the LEEM spatial resolution can reach 5.7 nm, achieving the limit of resolution for a non-aberration-corrected LEEM.

[00114] The parts not detailed in the present invention are considered to be existing technology. Therefore, they are not detailed in the present invention.

[00115] It is to be understood that the term "one" should be interpreted as "at least one" or "one or more." This means that in one embodiment, the quantity of a component can be one, while in another embodiment, the quantity of that component can be multiple. The term "one" should not be interpreted as a limitation on the quantity.

[00116] Although the present invention frequently uses terms, such as helium gas pipe interface 1, heating source interface 2, U-shaped protective bracket 3, anti-vibration bellows 4, shielding cylinder 5, sample chamber interface 6, objective lower pole piece 7, sample chamber 8, low-temperature sample stage 9, copper shielding tube 10, first-stage cold head connector 11, aluminum connector 12, second-stage cold head connector 13, first-first-stage cold shield 15.1, second-first-stage cold shield 15.2, tail first-stage cold shield copper braid 16, copper braid fixing piece 17, first p-metal shield 18.1, second p-metal shield 18.2, first Z-axis piezoelectric ceramic bracket 19.1, second Z-axis piezoelectric ceramic bracket 19.2, Z-axis nanometer-level piezoelectric ceramic 20, connecting plate 21, X-axis nanometer-level piezoelectric ceramic 22, Z-axis fixed frame 23, Y-axis nanometer-level piezoelectric ceramic 24, second thermal insulating zirconia washer 25.1, first insulating zirconia washer 25.2, first copper braid fixing piece 26.1, second copper braid fixing piece 26.2, sample holder 27, sample stage fixing member 28, sample holder clamp 29, sample holder cold plate 30, Y-axis piezoelectric ceramic mounting plate 31, tungsten wire 32, thermal conductor 33, copper braid cold plate fixing piece 34, high-voltage electrode 35, sapphire insulating tube 36, zirconia ceramic sphere 37, X-axis piezoelectric ceramic mounting plate 38, molybdenum nose 39, and liquid-helium-free refrigerating machine 40, the use of these terms does not exclude the possibility of using other terms. These terms are used merely for the convenience of describing and explaining the essence of the present invention. Interpreting them as any form of additional limitation would be contrary to the spirit of the present invention.

[00117] The present invention is not limited to the best practices described above. Anyone inspired by the present invention can derive various other forms of products. However, regardless of any changes made in their shape or structure, any technical solutions that are the same as or similar to those of the present invention are all within the scope of protection of the present invention.

Claims

1. A circulating refrigeration system without liquid helium consumption for cooling the sample chamber of an electron microscope, comprising a liquid-helium-free refrigerating machine, is characterized in that it further includes:A copper shielding tube, one end of which is connected to the shielding cylinder of the liquid-helium-free refrigerating machine, and the other end is equipped with first-stage cold head connector and second-stage cold head connector;A first-stage cold shield, connected to the first-stage cold head connector via copper braids, and located outside the u-metal shield;A p-metal shield, connected to the first-stage cold head connector via copper braids, and also connected to the first-stage cold shield via copper braids. The p-metal shield serves as a mounting ring and is connected to the lower pole piece of the electron microscope in vacuum. Additionally, the p-metal shield is connected to the Z-axis piezoelectric ceramic bracket of the sample chamber via thermally insulating washer;A sample stage fixing member, connected to the second-stage cold head connector via copper braids, which is used to secure the sample holder and achieve cooling of the sample holder for liquid-helium temperature range;Wherein the first-stage cold head connector, the first-stage cold shield, and the p-metal shield form the first-stage cryogenic system. The sample stage fixing member is equipped with a copper braid fixing piece, which is connected to the copper braids;The Z-axis piezoelectric ceramic brackets are evenly distributed along the circumference of the p-metal shield. Each Z-axis piezoelectric ceramic bracket is equipped with a Z-axis nanometer-level piezoelectric ceramic, used to move the sample back and forth along the Z-axis. Each Z-axis nanometer-level piezoelectric ceramic is connected to a Z-axis fixed frame via a connecting plate. An X-axis nanometer-level piezoelectric ceramic, which is used to move the sample back and forth along the X-axis, is connected to the Z-axis fixed frame. The X-axis nanometer-level piezoelectric ceramic is connected to an X-axis piezoelectric ceramic mounting plate, which is equipped with a Y-axis nanometer-level piezoelectric ceramic. The Y-axis nanometer-level piezoelectric ceramic is used to move the sample back and forth along the Y-axis and is equipped with a Y-axis piezoelectric ceramicmounting plate. The center of the Y-axis piezoelectric ceramic mounting plate has a sapphire insulating tube, which is fixed to the Y-axis piezoelectric ceramic mounting plate via a sample holder cold plate. The end of the sapphire insulating tube is equipped with the sample stage fixing member.

2. According to claim 1, the circulating refrigeration system without liquid helium consumption is characterized in that the first-stage cold shield is connected to the Z-axis fixed frame.

3. According to claim 2, the circulating refrigeration system without liquid helium consumption is characterized in that 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 is connected via a thermal insulating sphere, and the Z-axis nanometer-level piezoelectric ceramic is mounted on the second ceramic bracket.

4. According to claim 1, the circulating refrigeration system without liquid helium consumption is characterized in that the sample stage fixing member is uniformly equipped with three notches, and each notch is provided with a sample holder clamp for securing the sample holder.

5. According to claim 4, the circulating refrigeration system without liquid helium consumption is characterized in that the copper braid fixing piece is connected to the sample stage fixing member, and is connected to the sample holder cold plate via a thermal conductor.

6. According to claim 4, the circulating refrigeration system without liquid helium consumption is characterized in that each sample holder clamp shows the shape of a "q".

7. According to any one of claims 1-6, the circulating refrigeration system without liquid helium consumption is characterized in that the top end of the sapphire insulating tube is threaded to connect to a high-voltage electrode, which allows the high-voltage electrode to be connected to the vacuum feedthrough of the sample chamber via a high-voltage wire to apply high voltage. And the top of the sample chamber is electrically connected to the high-voltage electrode.

8. The liquid-helium temperature range electron microscope is characterized in that it includes an imaging system, a sample chamber, and the circulating refrigeration systemwithout liquid helium consumption, according to any one of claims 1-7, wherein the sample chamber is cooled by the circulating refrigeration system without liquid helium consumption, and imaging is performed by the imaging system.

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