Zero-consumption liquid helium circulating refrigeration system and liquid helium temperature range electron microscope

Abstract

This application relates to a zero-liquid helium consumption circulating refrigeration system, the configuration of which includes a liquid-free helium refrigerator, a copper shield tube (one end of which is connected to the shield tube of the liquid-free helium refrigerator, and the other end of which is provided with a first-stage cold head connecting member and a second-stage cold head connecting member), a first-stage cooling shield (connected to the first-stage cold head connecting member via a copper braided wire and positioned on the outer circumference of the μ-metal shield), a μ-metal shield (connected to the first-stage cold head connecting member via a copper braided wire and also connected to the first-stage cooling shield via a copper braided wire for the first-stage cooling shield, and further, the μ-metal shield is vacuum-connected to the lower pole piece of the electron microscope as a fixing ring, and at the same time, the μ-metal shield is connected to the Z-axis piezoelectric ceramic support of the sample chamber via an insulating spacer), and a sample holder fixing member (connected to the second-stage cold head connecting member via a copper braided wire). According to this application, it is possible to achieve a desired liquid helium temperature range environment for extended periods, significantly reducing experimental costs, minimizing mechanical vibrations, improving lateral resolution, and realizing ultra-high resolution in electron microscopes.

Description

Technical Field

[0001] This application relates to the field of electron microscopy technology, specifically to a zero-liquid-helium consumption circulation refrigeration system and an electron microscope in the liquid helium temperature range.

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 it has been recognized that they play important roles in a number of applications. Among the various experimental tools available, the cathode lens microscope has played an important role in identifying and interpreting many complex phenomena on the surface. Since the invention of the low-energy electron microscope (LEEM) by Bauer, LEEM has evolved into an important technique for studying surface structure, morphology, and kinetic processes in situ.

[0003] LEEM is a cathode lens microscope that uses a low-energy electron beam (energy less than 100 eV, usually less than 10 eV) to probe a sample, and collects elastically backscattered electrons from the sample surface for imaging. Since the mean free path of low-energy electrons is short, LEEM is an extremely sensitive probing technique for the surface. In addition, by modulating a precise electron optical system, LEEM has both a real-space image mode and a momentum-space image mode, and when combined with the highly coherent electron source provided by a cold cathode field emission electron gun, it is also used for studying phenomena such as quantum interference. Therefore, it has become one of the powerful techniques in the research of surface physics or surface chemistry. LEEM has the following remarkable advantages.

[0004] The first is that important surface processes such as surface growth, phase transition processes, and reactions can be realized as spatially resolved real-time dynamic imaging.

[0005] Secondly, the LEEM system has extremely high spatial resolution, with vertical resolution reaching the atomic level and lateral resolution reaching 3-4 nm, and it can also image localized areas on the sample surface.

[0006] The third advantage is that the LEEM system can perform low-energy electron diffraction (μ-LEED) on minute regions (down to 185 nm in the lateral direction), enabling the evaluation of the local structure and properties of surfaces.

[0007] The fourth advantage is that the energy of the exploration electron beam can be varied with high precision over a relatively large range, and the interaction between electrons and surfaces can be studied based on a curve (intensity I-voltage V curve) in which the image brightness of the selected region changes with respect to the electron beam energy.

[0008] With the advancement of research and applications in surface science, new technologies based on LEEM / PEEM are continuously being developed and applied. Traditionally, LEEM / PEEM has been primarily used to study surface dynamic processes, such as phase transitions and in-situ growth phenomena at high temperatures, and has been proven to be a very powerful technology. However, even in the low-temperature range below room temperature, many novel physical and chemical phenomena exist, such as low-temperature magnetism and electronic phase transitions of complex oxides. Current LEEM / PEEM systems typically have a sample temperature range of 300K to 1800K, and there are few systems that can cool samples below room temperature, and even then, the temperature usually does not fall below 100K.

[0009] Currently, the Hong Kong University of Science and Technology has reported that its LEEM system can be cooled to 50K using a static liquid helium dewar. Furthermore, previously reported LEEM systems that can reach temperatures below 77K all achieve low sample temperatures using a static dewar method, which consumes large amounts of liquid helium during operation. Even with low liquid helium consumption, maintaining low temperatures requires several liters per day. Currently, the global supply and demand for helium is tight, causing prices to skyrocket and significantly increasing experimental costs. Moreover, helium is a non-renewable resource with limited reserves, and it has been pointed out that it may face resource depletion within a few decades. In addition, many cities in the country lack adequate helium supply infrastructure, which further increases liquid helium prices. These factors significantly restrict scientific research requiring low-temperature LEEM / PEEM.

[0010] Most importantly, cooling experiments using a static liquid helium dewar consume large amounts of liquid helium, significantly increasing experimental costs. When cooling with a static liquid helium dewar, it's necessary to use liquid nitrogen as a pre-cooling agent to reduce liquid helium consumption. However, the large evaporation of liquid nitrogen and liquid helium increases the mechanical vibration of the entire system, affecting lateral resolution. Furthermore, because the entire sample is under a high voltage of -15kV, even slight, noticeable vibrations can cause vacuum discharge (breakdown) in the sample, risking damage to the electron microscope's high-voltage power supply and precision components such as the nose cone, potentially leading to significant economic losses. Additionally, the static liquid helium dewar requires manual liquid helium injection as needed, which is time-consuming and labor-intensive, and the cryogenic flow path can become blocked, potentially leading to accidents and injuries. In cities without liquid helium supply infrastructure, securing sufficient experimental time becomes difficult, severely limiting cryo-electron microscopy research.

[0011] Therefore, there is a strong demand for a liquid helium-free circulating refrigeration system and a liquid helium temperature range electron microscope that provide excellent cooling and eliminate the need for liquid helium replenishment after operation. This groundbreaking technology would significantly reduce liquid helium usage in electron microscope systems, greatly lowering experimental costs and simplifying the process. Furthermore, it would enable application to research purposes without regional constraints, even in areas where liquid helium is difficult to obtain, thus solving the problems of conventional technologies. [Overview of the project] [Problems that the invention aims to solve]

[0012] The object of this application is to provide a liquid helium consumption zero-recirculation refrigeration system and a liquid helium temperature range electron microscope, in view of the above-mentioned problems in the prior art. [Means for solving the problem]

[0013] To achieve the above objective, the present invention employs the following technical means: a liquid helium-free circulating refrigeration system for cooling the sample chamber of an electron microscope, comprising a liquid helium-free refrigerator, and further comprising the following:

[0014] Copper shield tube: One end is connected to the shield tube of the liquidless helium refrigerator, and the other end is equipped with a first-stage cold head connecting member and a second-stage cold head connecting member.

[0015] First-stage cooling shield: Connected to the first-stage cold head connecting member via copper braided wire (copper blade), and positioned on the outer periphery of the μ metal shield.

[0016] μ-metal shield: Connected to the first stage cold head connecting member via copper braided wire, and connected to the first stage cooling shield via copper braided wire, and further connected to the lower pole piece of the electron microscope as a fixing ring via vacuum, and connected to the Z-axis piezoelectric ceramic support of the sample chamber via an insulating spacer.

[0017] Sample holder fixing member: Connected to the second stage cold head connecting member via copper braided wire, and used to insert and fix the sample holder so that it can be cooled.

[0018] Here, the first-stage cold head connecting member, the first-stage cooling shield, and the μ-metal shield constitute the first-stage low-temperature system. This configuration primarily provides the following effects.

[0019] Low-temperature cooling: This system transfers cold energy to the sample chamber via the first-stage cold head connecting member and the second-stage cold head connecting member, thereby achieving cooling of the sample chamber. The first-stage low-temperature system consists of the first-stage cold head connecting member, the first-stage cooling shield, and the μ-metal shield, and can provide a relatively low temperature.

[0020] Shielding and Isolation: Copper shielding tubes and μ metal shields provide shielding and isolation functions, isolating the cryogenic system from the external environment (e.g., the vacuum environment below an electron microscope) to suppress heat inflow and interference.

[0021] Cooling of the sample holder: The sample holder fixing member is connected to the second-stage cold head connecting member, thereby achieving cooling of the sample holder. This makes it possible to observe and study the sample in a low-temperature environment.

[0022] Stability and Precision: The zero-consumption liquid helium circulating refrigeration system offers more stable and precise temperature control compared to conventional liquid nitrogen or liquid helium cooling systems. It enables long-term continuous operation without the need for frequent refrigerant replenishment.

[0023] Furthermore, the sample holder fixing member is provided with a copper braided wire fixing member, and the copper braided wire is connected by this copper braided wire fixing member. This configuration primarily provides the following effects.

[0024] Thermal Conductivity: The main function of the copper braided wire fixing member is to connect the copper braided wire to the sample holder fixing member. Since copper is a good thermal conductive material, heat can be efficiently transferred to the sample holder through the connection by the copper braided wire fixing member, improving the cooling effect of the sample holder.

[0025] Stability and Reliability: By using the copper braided wire fixing member, the copper braided wire can be securely fixed to the sample holder fixing member, providing better stability and reliability. This prevents the copper braided wire from falling off or loosening during operation and ensures the continuity of heat transfer.

[0026] Mechanical Support: The copper braided wire fixing member provides mechanical support and fixation, making the attachment of the copper braided wire to the sample holder fixing member stronger. This prevents unnecessary movement or loosening during operation or vibration.

[0027] Protection Performance: The copper braided wire fixing member protects the braided wire and has the function of preventing damage or wear. This extends the service life of the braided wire and reduces the frequency of maintenance or replacement.

[0028] Furthermore, the Z-axis piezoelectric ceramic supports are evenly arranged along the circumferential direction of the μ-metal shield. Each Z-axis piezoelectric ceramic support is provided with a Z-axis nano-level piezoelectric ceramic, and the sample is reciprocally moved in the Z-axis direction. Each Z-axis nano-level piezoelectric ceramic is connected to the Z-axis fixing frame via a connecting piece. The Z-axis fixing frame is further connected with an X-axis nano-level piezoelectric ceramic, and the X-axis nano-level piezoelectric ceramic reciprocally moves the sample in the X-axis direction. An X-axis piezoelectric ceramic fixing plate is connected to the X-axis nano-level piezoelectric ceramic, and a Y-axis nano-level piezoelectric ceramic is connected to the X-axis piezoelectric ceramic fixing plate. The Y-axis nano-level piezoelectric ceramic reciprocally moves the sample in the Y-axis direction. A Y-axis piezoelectric ceramic fixing plate is connected to the Y-axis nano-level piezoelectric ceramic, and a sapphire insulating tube is provided at the center of the Y-axis piezoelectric ceramic fixing plate. The sapphire insulating tube is fixed to the Y-axis piezoelectric ceramic fixing plate via the sample holder cooling disk, and the tip of the sapphire insulating tube is connected to the sample holder fixing member. With this configuration, the following effects are mainly achieved.

[0029] Multi-axis movement: This system can achieve high-precision control and movement of the sample in three axial directions (Z-axis, X-axis, Y-axis) by the Z-axis nano-level piezoelectric ceramic, X-axis nano-level piezoelectric ceramic, and Y-axis nano-level piezoelectric ceramic. Thereby, multi-dimensional positioning, rotation, and adjustment of the sample can be performed to meet different experimental requirements.

[0030] Nano-level control: By applying the nano-level piezoelectric ceramic, extremely fine movement control can be realized. Displacement and position control on the order of nanometers are possible by voltage adjustment, enabling fine adjustment of the sample position and precise operation.

[0031] Stability and reproducibility: The piezoelectric ceramic has high stability and reproducibility. With high movement accuracy and the ability to maintain consistent position and motion control in multiple experiments, reliable experimental results and data reproducibility can be provided.

[0032] Insulation Performance: The application of sapphire insulating tubes provides electrical insulation and isolation, preventing leakage current and interference. This ensures the safety of electronic equipment and samples, and reduces the impact of unwanted interference on experimental results.

[0033] Furthermore, the first-stage cooling shield is connected to the Z-axis fixed frame. This configuration primarily provides the following effects:

[0034] Thermal Conduction Performance: The first-stage cooling shield is a component connected to the first-stage cold head connecting member of a liquid-free helium refrigerator, and is usually made of a material with excellent thermal conductivity, such as copper. By connecting the first-stage cooling shield to the Z-axis fixed frame, cooling and temperature control can be efficiently transmitted to the Z-axis fixed frame and related components.

[0035] Cooling Effect: The first-stage cooling shield provides a temperature reduction function as one of the components of the low-temperature system. By connecting to the Z-axis fixed frame, it transfers cold energy to the Z-axis fixed frame and the sample chamber, achieving primary cooling of the sample and related components, while also blocking heat radiation from the surroundings and reducing low-temperature losses.

[0036] Stability and Thermal Equilibrium: Connecting the first-stage cooling shield to the Z-axis fixed frame improves system stability and thermal equilibrium. This contributes to the dispersion and homogenization of cooling and heat, preventing heat buildup and localized temperature fluctuations, and providing a more stable and uniform cooling effect.

[0037] Thermal insulation and shielding: The connection of the first-stage cooling shield also provides thermal insulation and shielding effects, suppressing the effects of heat transfer and external interference. By limiting the propagation of heat flow, the cooling effect of the sample chamber is ensured, and the required temperature environment can be maintained.

[0038] Furthermore, each Z-axis piezoelectric ceramic support includes a first ceramic support and a second ceramic support, the first and second ceramic supports connected via an insulating sphere, and the Z-axis nano-level piezoelectric ceramic is placed on the second ceramic support. This configuration primarily produces the following effects.

[0039] Thermal insulation performance: The connection using insulating spheres provides thermal insulation, reducing heat transfer and loss. This is important for ensuring a stable temperature environment for the Z-axis piezoelectric ceramic support and avoiding interference from external heat sources.

[0040] Thermal Stability: By arranging the Z-axis nano-level piezoelectric ceramic on a second ceramic support and connecting them using an insulated sphere, better thermal stability can be achieved. This reduces heat diffusion and leakage, allowing the Z-axis nano-piezoelectric ceramic to be maintained in a relatively constant temperature environment.

[0041] Insulation Performance: The insulating sphere placed between the first and second ceramic supports provides electrical insulation, preventing leakage current and interference. This is important for ensuring the electrical characteristics and signal stability of the Z-axis piezoelectric ceramic support and related components.

[0042] Structural Stability: The combination of the first and second ceramic supports provides better structural stability and support. This ensures stable mounting and operation of the Z-axis piezoelectric ceramic support, meeting the requirements for high-precision control and motion.

[0043] Furthermore, the sample holder fixing member has three evenly spaced notches, and each notch is equipped with a sample holder clamp (sample holder locking seat) to secure the sample holder. This configuration primarily provides the following effects.

[0044] Sample Fixation: The sample holder clamps at each notch are used to fix the sample holder, ensuring the stability and reliability of the sample during the experimental process. By inserting and fixing the sample holder in the clamp, accidental movement or shaking of the sample is prevented, and the accurate position of the sample can be maintained.

[0045] High-precision positioning: The evenly spaced notches and sample holder clamps enable high-precision positioning of the sample on the fixing member. The position and design of each notch ensure correct alignment of the sample holder, allowing the sample to be positioned and manipulated in the desired location.

[0046] Interchangeability: The design of the sample holder clamp allows for relatively easy replacement and adjustment of the sample holder. This enables rapid exchange of different samples or adjustment of sample placement to meet the demands of various experimental conditions.

[0047] Furthermore, the copper braided wire fixing member is connected to the sample holder fixing member and, via a heat transfer member, to the sample holder cooling disk. This configuration primarily provides the following effects.

[0048] Mechanical support: Mechanical support is obtained by connecting the copper braided wire fixing member and the sample holder fixing member, improving the stability and rigidity of the sample holder. This prevents unwanted vibrations or movement during experiments, ensuring the accuracy and reliability of the experiments.

[0049] Heat conduction: Heat conduction and control can be achieved by connecting the copper braided wire fixing member to the sample holder cooling disk via a heat transfer member. The heat transfer member typically has good thermal conductivity, efficiently transferring heat from the sample holder to the cooling disk and achieving sample cooling.

[0050] Temperature Stability: Temperature stability can be provided by connecting the copper braided wire fixing member and the sample holder cooling disk with a heat transfer member. The heat transfer member quickly equalizes the temperature difference and transmits the low temperature of the cooling disk to the sample holder, thereby maintaining a stable low-temperature environment for the sample holder.

[0051] Thermal control: By connecting copper braided wire fixing members and heat transfer members, the sample holder temperature can be controlled. By adjusting the temperature of the cooling disk and the heat transfer efficiency of the heat transfer members, the sample holder temperature can be controlled with high precision to meet experimental requirements.

[0052] Furthermore, each sample holder clamp exhibits an "η" shape. This configuration primarily produces the following effects.

[0053] Elastic Fixation: The "η"-shaped sample holder clamp has a predetermined elasticity. This elastic design ensures that a constant pressing force is applied when inserting the sample holder into the clamp, resulting in fastening and fixation within the clamp. This allows the sample holder to be held stably in the required position, preventing accidental movement or loosening during experiments.

[0054] Adaptability to diverse sample holder dimensions: The "η"-shaped sample holder clamp, due to its shape and elasticity, can adapt to sample holders of different dimensions. That is, it can securely fasten and fix both small and large sample holders within the clamp. This provides greater flexibility and allows for the accommodation of samples of different sizes.

[0055] Vibration damping effect: The sample holder clamp has a specific elasticity and shape design, thus providing a predetermined vibration damping effect. During experiments, external vibrations or oscillations may occur, potentially adversely affecting the stability of the sample and the experimental results. However, the elastic "η"-shaped sample holder clamp can absorb and attenuate these vibrations to some extent, protecting the sample from external interference.

[0056] Simplified Operation: The "η"-shaped clamp design simplifies the operating procedure. Due to its elastic properties, the sample holder can be inserted and removed relatively easily, allowing for simpler and faster sample replacement or position adjustment.

[0057] Furthermore, a threaded section is provided at the upper end of the sapphire insulating tube, used for connecting a high-voltage electrode. This connects the high-voltage electrode to the vacuum feedthrough of the sample chamber via a high-voltage cable, enabling high-voltage application, and electrically connecting the upper part of the sample chamber to the high-voltage electrode. This configuration primarily provides the following effects:

[0058] High-voltage transmission: High voltage transmission to the sample can be achieved by connecting a high-voltage electrode to a sapphire insulating tube. The high-voltage electrode is connected to the sample chamber via a high-voltage cable, and the sapphire insulating tube provides electrical isolation and insulation protection, allowing for 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 can be ensured. This is essential for realizing high-voltage application experiments, ensuring an effective connection between the high-voltage electrode and the sample inside the sample chamber, and allowing for reliable voltage application to the sample.

[0060] Safety and Stability: The sapphire insulated tube design provides isolation and insulating protection against high voltages, ensuring directional transmission from high-voltage electrodes to the sample. This reduces the risk of electric shock and protects the stability of the experimental apparatus.

[0061] A liquid helium temperature range electron microscope includes an electron source, a lens system, an imaging system, a sample chamber, and a liquid helium zero-consumption circulating refrigeration system. The liquid helium zero-consumption circulating refrigeration system cools the sample chamber, and the imaging system forms an image. [Effects of the Invention]

[0062] Compared to the prior art, the present invention has the following advantageous effects.

[0063] This invention replaces conventional static Dewar cooling with a liquid helium-free circulating refrigerator and adds a circulating refrigeration system specifically designed for sample chamber cooling. The refrigerant is cooled by circulating through the circulation piping of the liquid helium-free circulating refrigerator, achieving heat exchange cooling for the sample chamber device. Therefore, the refrigerant does not evaporate and is consumed, allowing the desired liquid helium temperature range environment to be maintained for a long period of time, significantly reducing experimental costs, as well as reducing mechanical vibration, improving lateral resolution, and achieving ultra-high resolution for electron microscopes.

[0064] 2. This invention constitutes a first-stage low-temperature system with a first-stage cold head connecting member, a first-stage cooling shield, and a μ-metal shield, generating a low-temperature environment of 90-95K around the sample. Furthermore, a sample fixing member is connected via a second-stage cold head connecting member, allowing the sample holder to be cooled to approximately 30K, and even further to 10K. This enables the sample to be held for extended periods within the desired liquid helium temperature range. Moreover, this groundbreaking technology, which eliminates the need for liquid helium replenishment after operation, significantly reduces liquid helium usage in electron microscope systems, greatly lowering experimental costs and simplifying the process. It also allows for application to research purposes without regional limitations, even in areas where liquid helium is difficult to obtain. In addition, by reducing mechanical vibrations caused by refrigerant evaporation, lateral resolution can be further improved. [Brief explanation of the drawing]

[0065] [Figure 1] Figure 1 is a schematic diagram of a liquid helium temperature range electron microscope. [Figure 2] Figure 2 is a schematic front view of an example of the sample chamber in the liquid helium zero-electron microscope of the present invention. [Figure 3] Figure 3 is a schematic diagram of the liquidless helium refrigerator of the present invention. [Figure 4] Figure 4 is an enlarged schematic diagram of part A in Figure 3. [Figure 5] Figure 5 is a schematic diagram of the assembly structure of the refrigerator and sample chamber components in the liquid helium zero-electron microscope of the present invention. [Figure 6] Figure 6 is a schematic front view of the cryogenic sample chamber in the liquid helium zero-electron microscope of the present invention. [Figure 7] Figure 7 is a schematic front view of the cryogenic sample chamber in the liquid helium zero-electron microscope of the present invention when the first-stage cooling shield is not installed. [Figure 8] Figure 8 is a schematic diagram of the back structure of the low-temperature sample chamber in the liquid helium zero-electron microscope of the present invention when the first-stage cooling shield is not attached. [Figure 9] Figure 9 is a schematic diagram of the structure in the "AA" direction of Figure 7. [Figure 10] Figure 10 shows the low-energy electron diffraction (LEED) pattern of a Cu(110) single crystal obtained using the high-resolution imaging scheme of the liquid helium temperature range electron microscope of the present invention. [Figure 11] Figure 11 shows a real-space surface image of a Cu(110) single crystal obtained using the high-resolution imaging scheme of the liquid helium temperature range electron microscope of this application. [Figure 12] Figure 12 shows the resolution in section a of Figure 11. [Modes for carrying out the invention]

[0066] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the drawings relating to the embodiments of this application. Note that the embodiments described are only a selection of the embodiments of this application, not all of them. All other embodiments that a person skilled in the art could obtain based on the embodiments of this application are all within the scope of protection of this application.

[0067] Those skilled in the art will recognize that terms indicating direction or positional relationships, such as "vertical," "horizontal," "up," "down," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inside," and "outside," used in the disclosure of this application are based on the direction or positional relationships shown in the drawings and are used solely to facilitate and simplify the explanation of this application, and do not indicate that the indicated or implied devices or components necessarily have a specific direction, are composed of, or are operated in a specific direction. Therefore, the above terms should not be interpreted as limiting this application.

[0068] Currently, there are no reports of commercially available liquid helium temperature range electron microscopes. The main reason for this is that stationary dewars require the storage of large amounts of liquid helium during the cooling process. During use, a large amount of refrigerant evaporates and is consumed, which causes relatively significant mechanical vibrations that affect the lateral resolution of the electron microscope. More importantly, the entire sample is suspended under a high voltage of -15kV, and even slight oscillations can cause serious discharge phenomena throughout the electron microscope, potentially damaging the high-voltage power supply and nose cone, leading to significant economic losses. In addition, maintaining the sample in a low-temperature environment for extended periods requires the consumption of large amounts of liquid helium, significantly increasing experimental costs. Furthermore, the constraints are even greater in areas where liquid helium is difficult to obtain. Moreover, the liquid helium stationary dewar system requires manual injection of liquid helium as needed, which is time-consuming and labor-intensive, and the cryogenic flow path may become blocked, leading to experimental accidents and the risk of injury.

[0069] Therefore, this application solves the problems that exist in the prior art based on a liquid-free helium refrigerator.

[0070] To facilitate understanding of this invention, the imaging principle of the liquid helium zero-electron microscope is explained as shown in Figure 1. First, the liquid helium compressor is started, and the refrigerator operates to lower the sample temperature to approximately 30K. After the sample temperature stabilizes, the cold cathode field emission electron gun generates an electron beam with an energy of 15 keV, and a focusing electromagnetic lens array focuses the electron beam with variable magnification. Next, the electrons pass through a magnetic prism array, are deflected by 90°, and head towards the objective lens and the sample. Since the sample itself is floating at a negative potential close to the field emission of the electron gun, the electrons can be decelerated to energies in the range of 0 to 100 eV. After the electrons interact with the sample, they are reflected and accelerated again to 15 keV via the objective lens, and a magnified image of the sample is formed on the diagonal of the prism array by the transport lens. The electrons are deflected again by 90° by a second prism array. The intermediate planes of the two prism arrays coincide with the diffraction planes. Electrons are incident on 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.

[0071] Example 1 As shown in Figures 2 and 3, this zero-liquid-helium-consumption circulating refrigeration system is used to cool the sample chamber 8 of an electron microscope and includes a liquid-free helium refrigerator 40. The liquid-free helium refrigerator 40 is a refrigeration device used for cooling purposes, and its operating principle does not depend on the use of liquid helium. Compared to conventional liquid helium refrigerators, the liquid-free helium refrigerator 40 can provide a simpler, more economical, and more environmentally friendly cooling solution.

[0072] The liquid-free helium refrigerator 40 typically achieves its cooling effect through a compression refrigeration cycle or thermoelectric cooling technology. For example, it achieves low-temperature refrigeration by utilizing the expansion and compression of gas based on the pulse tube effect. The gas is compressed within the refrigerator to become a high-pressure gas, which is then introduced into a pulse tube bundle via an expansion valve. The gas then expands within the pulse tubes to absorb heat from the surrounding environment, lowering the gas temperature within the bundle. Subsequently, the compressor compresses the cooled gas again, releasing the heat into the environment via a heat exchanger, and continuously circulating the gas.

[0073] The connection between the liquid helium refrigerator and the electron microscope sample chamber 8 is crucial for bringing the liquid helium zero-electron microscope to the liquid helium temperature range. As shown in Figures 2 and 3, the liquid helium refrigerator 40 mainly includes a U-shaped protective frame 3, vibration-damping bellows 4, shielding cylinder 5, copper shielding tube 10, first-stage cold head connecting member 11, and second-stage cold head connecting member 13. The vibration-damping bellows 4 mainly reduces the mechanical vibration of the entire electron microscope as the refrigerant circulates and cools through the fluidized piping, improving the lateral resolution of the microscope and enabling the electron microscope to operate safely. The liquid helium refrigerator 40 is connected to the sample chamber via a vacuum flange.

[0074] The vibration-damping bellows 4 of the liquidless helium refrigerator 40 connect the U-shaped protective frame 3 and the shield cylinder 5, and the U-shaped protective frame 3 is provided with a helium gas piping interface 1 and a heat source interface 2. The sample chamber 8 of the electron microscope is further provided with a low-temperature sample stage 9, a sample chamber interface 6, and an objective lens lower pole piece 7. All of these structures are conventional, and this invention achieves sample chamber cooling of the electron microscope by utilizing the advantages and characteristics of the liquidless helium refrigerator 40 and designing an additional circulating refrigeration system structure.

[0075] Preferably, in order 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 turbomolecular pump, and a mechanical dry pump, and the sample chamber 8 and the shield cylinder 5 are evacuated by the vacuum pump system, and the vacuum level can reach 5.0 × 10^-11 mbar, ensuring an ultra-high vacuum environment throughout the sample chamber 8.

[0076] As shown in Figures 3 to 9, this zero-liquid-helium-consumption circulating refrigeration system specifically includes the following:

[0077] Copper shield tube 10: One end is connected to the liquid helium inlet end inside the shield tube 5 of the liquid-free helium refrigerator 40, and the other end is provided with a first-stage cold head connecting member 11 and a second-stage cold head connecting member 13.

[0078] First-stage cooling shield: Connected to the first-stage cold head connecting member 11 via copper braided wire, and positioned on the outer circumference of the μ metal shield and on the sample.

[0079] In this embodiment, the first-stage cooling shield is connected to the Z-axis fixed frame 23. The first-stage cooling shield is intended to reduce heat exchange between the outside and inside, and belongs to the first-stage cooling system.

[0080] The μ-metal shield is connected to the first-stage cold head connecting member 11 via a copper braided wire, and also to the first-stage cooling shield via a copper braided wire for the first-stage cooling shield. Furthermore, the μ-metal shield is vacuum-connected to the lower electrode pole piece of the electron microscope as a fixed ring, and is also connected to the Z-axis piezoelectric ceramic support of the sample chamber 8 via an insulating pad (e.g., an insulating zirconia pad).

[0081] In this embodiment, the Z-axis piezoelectric ceramic supports are evenly arranged along the circumferential direction of the μ metal shield, and each Z-axis piezoelectric ceramic support is provided with a Z-axis nano-level piezoelectric ceramic 20, which reciprocates the sample in the Z-axis direction. Each Z-axis nano-level piezoelectric ceramic 20 is connected to a Z-axis fixed frame 23 via a connecting piece 21. An X-axis nano-level piezoelectric ceramic 22 is further connected to the Z-axis fixed frame 23, and this X-axis nano-level piezoelectric ceramic 22 reciprocates the sample in the X-axis direction. An X-axis piezoelectric ceramic fixed plate 38 is connected to the X-axis nano-level piezoelectric ceramic 22, and a Y-axis nano-level piezoelectric ceramic 24 is connected to the X-axis piezoelectric ceramic fixed plate 38, and this Y-axis nano-level piezoelectric ceramic 24 reciprocates the sample in the Y-axis direction. A Y-axis piezoelectric ceramic fixed plate 31 is connected to the Y-axis nano-level piezoelectric ceramic 24, and a sapphire insulating tube 36 is provided in the center of the Y-axis piezoelectric ceramic fixed plate 31. The sapphire insulating tube 36 is fixed to the Y-axis piezoelectric ceramic fixing plate 31 via the sample holder cooling disk 30, and a sample holder fixing member 28 is assembled to the end of the sapphire insulating tube 36.

[0082] In this embodiment, a threaded portion is provided at the upper end of the sapphire insulating tube 36 and is used to connect the high-voltage electrode 35. As a result, the high-voltage electrode 35 is connected to the vacuum feedthrough of the sample chamber 8 via a high-voltage cable to apply a high voltage, and the upper part of the sample chamber 8 is electrically connected to the high-voltage electrode 35.

[0083] The sample holder fixing member 28 is connected to the second stage cold head connecting member 13 via a copper braided wire. The sample holder fixing member 28 is used to insert and fix the sample holder 27, thereby allowing the sample holder 27 to be cooled.

[0084] In this embodiment, a copper braided wire fixing member 17 is provided on the sample holder fixing member 28, and the copper braided wire is connected by the copper braided wire fixing member 17. Preferably, the sample holder fixing member 28 has three evenly spaced notches, and a sample holder clamp 29 is provided in each notch to fix the sample holder 27. The copper braided wire fixing member 17 is connected to the sample holder fixing member 28 and is also connected to the sample holder cooling disk 30 via a heat transfer member 33. Each sample holder clamp 29 has an "η" shape.

[0085] The first-stage cold head connecting member 11, the first-stage cooling shield, and the μ-metal shield constitute the first-stage low-temperature system.

[0086] Furthermore, each Z-axis piezoelectric ceramic support includes a first ceramic support and a second ceramic support, the first and second ceramic supports being connected via an insulating sphere (e.g., a zirconia ceramic sphere 37), and the Z-axis nano-level piezoelectric ceramic 20 is placed on the second ceramic support.

[0087] Specifically, referring to Figure 5, the first-stage cold head connecting member 11 of the liquid-free helium refrigerator is connected to the first-stage cooling shield and the first μ metal shield 18.1 and second μ metal shield 18.2 via the second copper braided wire 14.2 and the third copper braided wire 14.3. The second μ metal shield 18.2 is also connected to the first-stage cooling shield via the copper braided wire 16 for the tail first-stage cooling shield. This constitutes the first-stage low-temperature system, creating a low-temperature environment of 90-95K around the sample. When the sample temperature becomes even lower, heat exchange with components such as the cooling shield is reduced, allowing the sample temperature to be lowered to the liquid helium temperature range. The second-stage cold head connecting member 13 of the liquid-free helium refrigerator is connected to the sample holder fixing member 28 via the copper braided wire and the copper braided wire fixing member 17, allowing the sample holder fixing member 28 to reach the liquid helium temperature range. When the sample holder 27 is inserted, the entire sample holder 27 is cooled to approximately 30K, and then further to 10K.

[0088] Referring to Figures 6 to 9, the first μm metal shield 18.1 is connected to the objective lens lower pole piece 7 as a fixing ring (the left end of the first μm metal shield 18.1 is vacuum-connected to the objective lens member, but the objective lens portion is not described herein as it is outside the scope of the patent). A second first-stage cooling shield 15.2 is also covered on the outside of the first μm metal shield 18.1. The first μm metal shield 18.1 is connected to the second μm metal shield 18.2 via a first insulating zirconia pad 25.2, and the second μm metal shield 18.2 is connected to the first Z-axis piezoelectric ceramic support 19.1 via a second insulating zirconia pad 25.1. Here, both insulating zirconia pads are used for insulation.

[0089] The first Z-axis piezoelectric ceramic support 19.1 and the second Z-axis piezoelectric ceramic support 19.2 are evenly arranged on the second μ metal shield 18.2, with four of each. Zirconia ceramic spheres 37 are interposed between the first Z-axis piezoelectric ceramic support 19.1 and the second Z-axis piezoelectric ceramic support 19.2, thereby ensuring the movement of the second Z-axis piezoelectric ceramic support 19.2 and reducing heat transfer between them.

[0090] Each second Z-axis piezoelectric ceramic support 19.2 is fitted with a Z-axis nano-level piezoelectric ceramic 20, thereby providing sufficient driving force to move the entire sample section from side to side. Each Z-axis nano-level piezoelectric ceramic 20 is connected to the Z-axis fixing frame 23 via a connecting piece 21, thereby moving the entire sample section from side to side.

[0091] The first stage cooling shield 15.1 is attached to the Z-axis fixed frame 23, thereby reducing heat exchange between the sample section and the first copper braided wire 14.1 and the external environment, and allowing the entire sample section to be kept at a low temperature.

[0092] Between the two first Z-axis piezoelectric ceramic supports 19.1 and the second Z-axis piezoelectric ceramic support 19.2, the X-axis nano-level piezoelectric ceramic 22 is connected to the Z-axis fixing frame 23, and another X-axis nano-level piezoelectric ceramic 22 is assembled at a symmetrical position rotated 180°, thereby moving the entire sample section in the X-axis direction (direction of the arrow in Figure 6). Next, the X-axis piezoelectric ceramic fixing plate 38 is attached to the two X-axis nano-level piezoelectric ceramics 22.

[0093] Two Y-axis nano-level piezoelectric ceramics 24 are mounted symmetrically on an X-axis piezoelectric ceramic fixing plate 38 that intersects with the two X-axis nano-level piezoelectric ceramics 22, thereby moving the sample section in the Y-axis direction. Next, a Y-axis piezoelectric ceramic fixing plate 31 is attached to the two Y-axis nano-level piezoelectric ceramics 24, and a sapphire insulating tube 36 is attached to its center. The ends of the sapphire insulating tube 36 are fixed to the Y-axis piezoelectric ceramic fixing plate 31 by a sample holder cooling disk 30, and the sample holder fixing member 28 is further fixed on the sample holder cooling disk 30.

[0094] The sample holder fixing member 28 has three evenly spaced notches (120° apart), and a sample holder clamp 29 is attached to each notch, with the sample holder clamp 29 having an "η" shape. This allows the three teeth on the rear end of the sample holder 27, which holds the sample, to engage with the sample holder clamp 29, and the sample holder 27 can be fixed by rotating it slightly.

[0095] Furthermore, the second copper braided wire fixing member 26.2 is fixed to one end of the sample holder fixing member 28 and connected to the sample holder cooling disk 30 via the heat transfer member 33. The second copper braided wire fixing member 26.2 is connected to the first copper braided wire fixing member 26.1 by the copper braided wire, and further connected to the second stage cold head connecting member 13 via the copper braided wire. As a result, the second stage cold head cools the entire sample holder 27 through this connection method, and also cools the sapphire insulating tube 36.

[0096] This cooling method allows the temperature of the sample holder 27 to be reduced to approximately 30K. A threaded section is formed at the upper end of the sapphire insulating tube 36, and the high-voltage electrode 35 is screwed in and attached. Next, the high-voltage electrode 35 is connected to the vacuum feedthrough of the sample chamber 8 via a tungsten wire 32 (high-voltage wire), and a high voltage of -15kV is applied. As a result, the upper surface of the sample comes into contact with the high-voltage electrode 35, and a high voltage of -15kV is applied to the sample, allowing the electron microscope to form an image as usual.

[0097] As shown in Figure 9, a molybdenum nose 39 (nose-objective lens) is provided on the lower pole piece 7 of the objective lens of the electron microscope.

[0098] Example 2 The liquid helium temperature range electron microscope includes an electron source, a lens system, an imaging system, a sample chamber 8, and a liquid helium zero consumption circulation refrigeration system. The liquid helium zero consumption circulation refrigeration system cools the sample chamber 8, and the imaging system forms an image.

[0099] Referring to Figure 10, an inverse-space image of a Cu(110) single crystal sample was obtained in the liquid helium temperature range using the liquid helium temperature range electron microscope of Example 2, and a good low-energy electron diffraction (LEED) image showing the long-range ordered structure of the surface was obtained. Referring to Figure 11, a real-space LEEM image of a Cu(110) single crystal sample was obtained in the liquid helium temperature range, and a good surface morphology was obtained. Figure 12 shows the resolution analysis of part a in Figure 11, indicating that the spatial resolution of the LEEM reached 5.5 nm, almost reaching the resolution limit of non-aberration-corrected low-energy electron microscopy (Non-aberration-corrected LEEM).

[0100] Since the parts not described in detail in this application are prior art, they will not be explained in detail here.

[0101] The term "one" should be understood to mean "at least one" or "one or more." That is, in one embodiment, the quantity of an element may be 1, and in another embodiment, the quantity of that element may be multiple. The term "one" should not be interpreted as a limitation of quantity.

[0102] This specification refers to the helium gas piping interface 1, heating source interface 2, U-shaped protective frame 3, vibration-damping bellows 4, shield cylinder 5, material chamber interface 6, objective lens pole piece 7, material chamber 8, low-temperature test stage 9, shield section 10, first cold head connecting member 11, aluminum connecting member 12, second cold head connecting member 13, first cavity braided shield 14.1, second cavity braided shield 14.2, third cavity braided shield 14.3, first first-stage cooling shield 15.1, second first-stage cooling shield 15.2, tail section first-stage cooling shield oscillating braided shield 16, tail section braided shield base member 17, first μm metal shield 18.1, second μm metal shield 18.2, first Z-axis piezoelectric ceramic support 19.1, second Z-axis piezoelectric ceramic support 19.2, and Z-axis level While many terms such as piezoelectric ceramic 20, lotus link 21, X-axis level piezoelectric ceramic 22, Z-axis fixing frame 23, Y-axis level piezoelectric ceramic clamp 24, second insulating zirconia pad 25.1, first insulating zirconia pad 25.2, first braided wire fixing member 26.1, second braided wire fixing member 26.2, data holder 27, data holder fixing member 28, data holder lamp 29, data holder cooling disk 30, Y-axis piezoelectric ceramic fixing plate 31, tungsten wire 32, electric heating element 33, same type cooling disk fixing member 34, high-voltage electrode 35, sapphire insulating element 36, zirconia ceramic sphere 37, X-axis piezoelectric ceramic fixing plate 38, molybdenum nose 39, and liquidless helium refrigerator 40 are used, this does not rule out the possibility of using other terms. These terms are used solely to more easily describe and explain the essence of this application, and interpreting them as any additional limitation would be contrary to the spirit of this application.

[0103] This application is not limited to the preferred embodiments described above, and those skilled in the art can obtain various other forms of products based on the disclosures herein. However, any modifications to the shape or structure of such products, which are identical or similar to the technical solutions of this application, are all covered by the scope of this application. [Explanation of Symbols]

[0104] 1. Helium gas piping interface 2. Heat source interface 3 U-shaped protective frame 4. Vibration-damping bellows 5 Shield tube 6. Sample Chamber Interface 7 Objective lens lower pole piece 8. Sample Room 9. Low-temperature sample stage 10 Copper shielded tubes 11. First stage cold head connecting member 12 Aluminum connecting members 13. Second stage cold head connecting member 14.1 Copper 1 Braided Wire 14.2 Cupric Braided Wire 14.3 Tertiary copper braided wire 15.1 First Stage Cooling Shield 15.2 Second first-stage cooling shield 16. Copper braided wire for the first stage cooling shield of the tail section. 17 Copper braided wire fixing member 18.1 First μm Metal Shield 18.2 Second μm Metal Shield 19.1 First Z-axis piezoelectric ceramic support 19.2 Second Z-axis piezoelectric ceramic support 20 Z-axis nano-level piezoelectric ceramics 21 Connecting piece 22 X-axis nano-level piezoelectric ceramics 23 Z-axis fixed frame 24 Y-axis nano-level piezoelectric ceramics 25.1 Second Insulating Zirconia Pad 25.2 First Insulating Zirconia Pad 26.1 First copper braided wire fixing member 26.2 Second copper braided wire fixing member 27 Sample holder 28 Sample holder fixing member 29. Sample holder clamp 30 Sample holder cooling disk 31 Y-axis piezoelectric ceramic fixing plate 32 Tungsten wire 33 Heat transfer components 34 Copper braided wire cooling disc fixing member 35 High-voltage electrodes 36 Sapphire Insulating Tubes 37 Zirconia ceramic balls 38 X-axis piezoelectric ceramic fixing plate 39 Molybdenum Nose 40 Liquid-free helium refrigerators

Claims

1. A zero-liquid-helium-consumption circulating refrigeration system for cooling the sample chamber of an electron microscope, comprising a liquid-free helium refrigerator, and further, A copper shield tube, one end of which is connected to the shield cylinder of the liquidless helium refrigerator, and the other end of which is provided with a first-stage cold head connecting member and a second-stage cold head connecting member, A first-stage cooling shield is connected to the first-stage cold head connecting member via a copper braided wire and is positioned on the outer circumference side of the μ metal shield, A μ-metal shield connected to the first stage cold head connecting member via a copper braided wire, and connected to the first stage cooling shield via a copper braided wire for the first stage cooling shield, wherein the μ-metal shield is vacuum-connected to the lower pole piece of the electron microscope as a fixing ring, and is connected to the Z-axis piezoelectric ceramic support of the sample chamber via an insulating spacer, The system includes a sample holder fixing member connected to the second stage cold head connecting member via a copper braided wire, which cools the sample holder by inserting and fixing the sample holder, The first stage cold head connecting member, the first stage cooling shield, and the μ metal shield constitute the first stage low-temperature system, and the sample holder fixing member is provided with a copper braided wire fixing member for connecting copper braided wire. A liquid helium-free circulating refrigeration system characterized in that the Z-axis piezoelectric ceramic supports are evenly arranged along the circumferential direction of the μ metal shield, each Z-axis piezoelectric ceramic support is provided with a Z-axis nano-level piezoelectric ceramic for reciprocating a sample in the Z-axis direction, each Z-axis nano-level piezoelectric ceramic is connected to a Z-axis fixing frame via a connecting piece, an X-axis nano-level piezoelectric ceramic is connected to the Z-axis fixing frame for reciprocating a sample in the X-axis direction, an X-axis piezoelectric ceramic fixing plate is connected to the X-axis nano-level piezoelectric ceramic, a Y-axis nano-level piezoelectric ceramic is connected to the X-axis piezoelectric ceramic fixing plate for reciprocating a sample in the Y-axis direction, a Y-axis piezoelectric ceramic fixing plate is connected to the Y-axis nano-level piezoelectric ceramic, a sapphire insulating tube is provided in the center of the Y-axis piezoelectric ceramic fixing plate, the sapphire insulating tube is fixed to the Y-axis piezoelectric ceramic fixing plate via a sample holder cooling disk, and the tip of the sapphire insulating tube is connected to the sample holder fixing member.

2. The liquid helium consumption zero-circulating refrigeration system according to claim 1, characterized in that the first-stage cooling shield is connected to the Z-axis fixed frame.

3. The zero-liquid helium consumption circulating refrigeration system according to claim 2, characterized in that each of the Z-axis piezoelectric ceramic supports includes a first ceramic support and a second ceramic support, the first ceramic support and the second ceramic support are connected via an insulating sphere, and the Z-axis nano-level piezoelectric ceramic is disposed on the second ceramic support.

4. The liquid helium consumption zero-circulating refrigeration system according to claim 1, characterized in that the sample holder fixing member is provided with three evenly spaced notches for fixing the sample holder, and each notch is provided with a sample holder clamp.

5. The liquid helium consumption zero-circulation refrigeration system according to claim 4, characterized in that the copper braided wire fixing member is connected to the sample holder fixing member and also connected to the sample holder cooling disk via a heat transfer member.

6. The liquid helium consumption zero-circulating refrigeration system according to claim 4, characterized in that each of the sample holder clamps is shaped like an "η".

7. The liquid helium consumption zero-circulating refrigeration system according to any one of claims 1 to 6, characterized in that a threaded portion is provided at the upper end of the sapphire insulating tube and connected to a high-voltage electrode, the high-voltage electrode is connected to the vacuum feedthrough of the sample chamber via a high-voltage line to apply a high voltage, and the upper part of the sample chamber is electrically connected to the high-voltage electrode.

8. A liquid helium temperature range electron microscope comprising an imaging system, a sample chamber, and a liquid helium zero-consumption circulating refrigeration system according to any one of claims 1 to 7, wherein the sample chamber is cooled by the liquid helium zero-consumption circulating refrigeration system and an image is formed by the imaging system.

Images