A low-temperature thermostat

Abstract

The present invention provides a low-temperature thermostat and its application. The low-temperature thermostat includes a liquid inlet pipe, a liquid inlet port, an air return pipe, an air outlet port, a cold head, a cold end heat exchanger, a flexible connecting wire, a sample stage, a temperature measuring and controlling instrument, a cold shield, and a vacuum shell. The liquid inlet pipe and the air return pipe are made of round tubes, and the positional relationship between the two is concentric. A gap sandwich is formed between the liquid inlet pipe and the air return pipe. At the same time, the liquid inlet pipe, the air return pipe, the cold end heat exchanger, and the cold head form a closed gas circuit. A layer of cold shield is fixed on the periphery of the return pipe to reduce heat leakage and improve heat exchange efficiency. A flexible connecting wire connects the cold head and the sample stage to ensure rapid transfer of cold and free movement of the sample stage, thereby expanding its application scenarios. An electric heating wire and thermal insulation material are arranged on the periphery of the tail end of the return pipe to prevent condensation and frost on the surface from affecting the service life and stability. The low-temperature thermostat can be used for temperature control of the sample stage of a scanning electron microscope.

Description

Technical Field

[0001] The present invention relates to the field of low-temperature refrigeration technology, and in particular to a low-temperature thermostat. Background Art

[0002] A scanning electron microscope (SEM) is a common laboratory device that allows for high-magnification microscopic observation of samples without damaging them. To ensure accurate and stable observations, the sample stage must be kept at an extremely low temperature. This is where a cryostat becomes crucial.

[0003] Cryostats are used in SEMs in the following key areas: 1. Providing a stable low-temperature environment: A cryostat controls the temperature of the sample stage, maintaining it at an extremely low temperature, which helps improve the accuracy and stability of SEM observations. 2. Protecting samples: A low temperature environment slows the decay of samples, protecting them from damage. 3. Improving observations: In a low-temperature environment, the physical and chemical properties of samples change, enabling scientists to more accurately observe their morphology and structure.

[0004] At present, cryogenic thermostats mainly adopt two technical forms: one is a liquid helium or liquid nitrogen continuous flow cryogenic thermostat, which uses liquid helium or liquid nitrogen in the liquid helium or liquid nitrogen Dewar to transport the cryogenic liquid to the cold end of the cryogenic thermostat through a low-temperature transmission pipeline, and uses the latent heat and sensible heat of the phase change of the cryogenic liquid to cool the cold end to achieve a low-temperature effect; the other is a technical method that uses a combination of a compressor and a low-temperature refrigerator to expand and cool high-pressure gas to achieve the purpose of low temperature.

[0005] Most existing cryostats are designed for optical electron microscopes (EMs), and their cold ends generally feature a transparent glass window. Optical EMs utilize the principles of geometric optics to acquire images. The geometric light emitted by these microscopes easily penetrates glass and reaches the sample being measured. SEMs, on the other hand, utilize a high-energy electron beam to bombard the sample surface, stimulating various physical signals. These signals are then received by various detectors and converted into image information. The electron beam emitted by the SEM's high-energy electron gun is absorbed by any material it passes through, even transparent glass. Therefore, glass windows for samples cannot be directly applied to SEMs, and existing cryostats are incompatible with these applications. Furthermore, because the spatial position of the sample requires multiple adjustments during observation, the SEM's sample stage must be moved in the X, Y, and Z axes, as well as in the circumferential direction. This requires the low-temperature cold stage connected to the sample stage to move with it. Existing cryostats cannot meet this requirement for cold-end mobility. Third, after the cryogenic liquid in existing cryostats exchanges heat with the cold end, the gas temperature at the exhaust port remains low, which can easily cause frost, adversely affecting users and affecting the lifespan and stability of the thermostat. Fourth, the heat exchange structure in existing cryostats suffers from large temperature differences, low heat exchange efficiency, and high cryogenic gas consumption, which urgently need to be addressed. Summary of the Invention

[0006] The present invention aims to address the deficiencies of the prior art and provide a cryostat that can be used for temperature control of a sample stage of a scanning electron microscope.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions: a low-temperature thermostat, including a liquid inlet pipe, a liquid inlet, an air return pipe, an air outlet, a cold head, a cold end heat exchanger, a flexible connecting line, a sample table, a temperature measuring and controlling instrument, a cold screen, and a vacuum shell; wherein one end of the liquid inlet pipe is connected to the liquid inlet, and the other end of the liquid inlet pipe is connected to the cold end heat exchanger, the cold end heat exchanger is connected to the cold head, the cold head is connected to the air return pipe, and the tail end of the return pipe is connected to the air outlet; the liquid inlet pipe and the air return pipe are made of round pipes, and the positional relationship between the two is a concentric relationship, and a gap interlayer is formed between the liquid inlet pipe and the air return pipe. At the same time, the liquid inlet pipe, the air return pipe, the cold end heat exchanger, and the cold head form a closed gas circuit; a layer of cold screen is fixed on the periphery of the return pipe; one end of the flexible connecting line is connected to the cold head, and the other end is connected to the sample table.

[0008] The temperature measuring and controlling instrument described in this application is used for measuring and controlling the temperature of a sample stage.

[0009] In a specific embodiment, the flexible connecting wire and the sample stage are connected by welding, screwing, etc.

[0010] In one embodiment, a cold shield structure is fixed to the periphery of the return air duct by screwing or clamping. The cross-section of the cold shield can be circular, square, or other special shapes, which are not specifically limited here.

[0011] In a specific embodiment, the cold head is connected to the flexible connecting line through a cold head extension section.

[0012] In a specific embodiment, the cold shield is connected to the cold shield extension section, and the cold shield extension section is installed on the periphery of the cold head extension section, and its function is consistent with that of the cold shield.

[0013] In a specific embodiment, the cold head and the cold head extension are in close contact with each other, and a low-temperature thermal interface material is installed on the contact surface.

[0014] In a specific embodiment, the cold head extension section and the flexible connecting wire are connected by welding, screw connection, clamping or the like.

[0015] In a specific embodiment, the cold shield and the cold shield extension section are seamlessly connected, which can be done in various ways such as screw connection, clip connection, embedding, etc.

[0016] In a specific embodiment, the flexible connecting wire is made by welding multiple strands of oxygen-free copper wire or pressing and welding multiple layers of oxygen-free copper sheets; the outer surface of the flexible connecting wire is mirror-coated.

[0017] In a specific embodiment, an electric heating wire is wound around the outer periphery of the return air pipe at the tail end thereof, and a heat-insulating material is used as a protective layer on the outer layer of the electric heating wire.

[0018] In a specific embodiment, a temperature sensor is provided at the tail end of the return air pipe and is connected to a temperature control system.

[0019] In a specific embodiment, a mounting hole for an electrical connector is provided on the housing of the temperature measuring and controlling instrument. The electrical connector is installed and fixed through the mounting hole. The electrical connector connects the temperature sensor and heater components used for temperature measurement and control of the sample stage.

[0020] The present application also provides an application of the cryostat, which is used to control the temperature of a sample stage of a scanning electron microscope. When the cryostat is used on a scanning electron microscope, the vacuum housing, the housing of the temperature measurement and control instrument, and the microscope chamber are connected to form a vacuum space.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The cryostat of this application uses a flexible cable to connect the cold head and sample stage. This ensures that the cooling energy generated by the cold head can be quickly transferred to the sample stage. It also allows the sample stage to move freely in the X, Y, and Z axes and in the circumferential direction during use, unaffected by the fixed structure of the cryostat. This expands the use range and application scenarios of the cryostat. The flexible cable is made of oxygen-free copper material with a mirror-coated surface. It has good thermal conductivity at low temperatures, high flexibility, and strong resistance to thermal radiation, which can reduce thermal resistance and heat leakage.

[0023] 2. An electric heating wire and insulation material are arranged on the periphery of the return air pipe at the tail end of the low-temperature thermostat. Through heating and insulation measures, the outer surface temperature of the return air pipe tail end is increased to at least above the dew point temperature of the moisture in the air, thereby preventing the occurrence of condensation and frost on the surface. This avoids the problem of condensation of moisture on the surface of the low-temperature thermostat during operation, causing excessive local humidity and affecting the service life and stability of the thermostat, and also prevents adverse effects on users.

[0024] 3. The cold shield structure can shield the impact of thermal radiation on the low-temperature cold head, reduce heat leakage and improve heat exchange efficiency.

[0025] 4. A cold-end heat exchanger is provided at the cold head position of the low-temperature thermostat of the present application, which has the characteristics of large heat exchange area and compact structure. It can fully exchange heat with the low-temperature liquid entering the cold head position, improve the flow heat transfer coefficient, reduce the heat transfer thermal resistance, and achieve the effects of fast cooling, high heat exchange efficiency, and high utilization rate of low-temperature gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 FIG2 shows a structural schematic diagram of a specific embodiment of the low-temperature thermostat of the present invention.

[0027] Among them, 1-liquid inlet; 2-air outlet; 3-temperature measurement and control instrument housing; 4-electrical connector; 5-vacuum housing; 6-cold screen; 7-cold screen extension section; 8-cold head; 9-cold end heat exchanger; 10-return air pipe; 11-liquid inlet pipe; 12-return air pipe tail end; 13-cold head extension section; 14-flexible connecting line; 15-sample table. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0029] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0030] like Figure 1 As shown, the cryostat of the present invention includes a liquid inlet pipe 11, a liquid inlet port 1, a gas return pipe 10, a gas outlet 2, a cold head 8, a cold end heat exchanger 9, a flexible connecting line 14, a sample stage 15, a temperature measuring and controlling instrument, a cold shield 6, and a vacuum housing 5. The liquid inlet pipe 11 is connected to the liquid inlet port 1 at one end, and to the cold end heat exchanger 9 at the other end. The cold end heat exchanger 9 is connected to the cold head 8, which is connected to the gas return pipe 10. The tail end 12 of the gas return pipe is connected to the gas outlet 2. The liquid inlet pipe 11 and the gas return pipe 10 are made of circular tubes and are concentric with each other. A gap is formed between the liquid inlet pipe 11 and the gas return pipe 10. At the same time, the liquid inlet pipe 11, the gas return pipe 10, the cold end heat exchanger 9, and the cold head 8 form a closed gas circuit. A cold shield 6 is fixed to the periphery of the gas return pipe 10. One end of the flexible connecting line 14 is connected to the cold head 8, and the other end is connected to the sample stage 15. The temperature measuring and controlling instrument described in this application is used for measuring and controlling the temperature of the sample stage 15 .

[0031] When the cryostat is working, the cryogenic liquid enters the internal cavity of the liquid inlet pipe 11 from the liquid inlet 1, reaches the cold end heat exchanger 9, and after heat exchange with the cold head 8, the cryogenic liquid changes from liquid to gas, and enters the air interlayer formed between the liquid inlet pipe 11 and the return air pipe 10 from the cold head 8. The gas reaches the air outlet 2 along the direction of the interlayer and is then discharged into the atmosphere.

[0032] In a specific embodiment, the flexible connecting wire 14 and the sample stage 15 are connected by welding, screwing, etc.

[0033] In one embodiment, a cold shield 6 is secured to the periphery of the return air duct 10 via screwing or clamping. The cross-sectional shape of the cold shield can be circular, square, or other shapes, without specific limitation. The function of the cold shield 6 is to shield the low-temperature cold head from the effects of thermal radiation and reduce heat leakage.

[0034] In a specific embodiment, the cold head 8 is connected to the flexible connecting line 14 through a cold head extension section 13 .

[0035] In a specific embodiment, the cold shield 6 is connected to the cold shield extension section 7, and the cold shield extension section 7 is installed on the periphery of the cold head extension section 13, and its function is consistent with that of the cold shield.

[0036] In a specific embodiment, the cold head 8 and the cold head extension 13 are in close contact with each other, and a low-temperature thermal interface material is installed on the contact surface to conduct heat and reduce thermal resistance.

[0037] In a specific embodiment, the cold head extension section 13 and the flexible connecting wire 14 are connected by welding, screwing, clamping, etc.

[0038] In a specific embodiment, the cold shield 6 and the cold shield extension section 7 are seamlessly connected, which can be done in various ways such as screw connection, clip connection, embedding, etc.

[0039] In a specific embodiment, the flexible connecting wire 14 is made by welding multiple strands of oxygen-free copper wire or pressing and welding multiple layers of oxygen-free copper sheets, and the outer surface of the flexible connecting wire is mirror-coated to enhance the ability to resist thermal radiation.

[0040] In one embodiment, an electric heating wire is wrapped around the outer surface of the return air duct at the rear end 12, and an insulating material is used as a protective layer on the outer surface of the electric heating wire. The electric heating wire and the insulating material heat and insulate the outer surface of the return air duct to at least the dew point of the air, thereby preventing condensation and frost on the surface.

[0041] In a specific embodiment, a temperature sensor is provided at the tail end 12 of the return air duct and is connected to a temperature control system. When the temperature sensor detects that the temperature is lower than the dew point temperature, the electric heating wire is started to increase the temperature of the outer surface of the tail end to above the dew point temperature, and the temperature control system is used to keep the temperature of the outer surface of the tail end above the dew point temperature.

[0042] In a specific embodiment, a mounting hole for an electrical connector 4 is provided on the housing 3 of the temperature measuring and controlling instrument, and the electrical connector 4 is installed and fixed through the mounting hole. The function of the electrical connector 4 is to connect the temperature sensor and heater components used when the sample stage 15 measures and controls the temperature.

[0043] The cryostat described herein can be used in a scanning electron microscope to control the temperature of the sample stage. When the cryostat is used on a scanning electron microscope, the vacuum housing 5 and the instrument housing 3 communicate with the microscope chamber, forming a vacuum space. This vacuum space serves to reduce the effects of air convection on the cold head temperature and minimize heat leakage.

[0044] In the description of this specification, the reference terms "one specific embodiment", "some embodiments", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0045] The scope of protection of the present invention is not limited to the above-described embodiments. Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the scope and spirit of the present invention. If such modifications and variations fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations.

Claims

1. A cryostat, comprising a liquid inlet pipe, a liquid inlet, an air return pipe, an air outlet, a cold head, a cold end heat exchanger, a flexible connecting line, a sample stage, a temperature measuring and controlling instrument, a cold screen, and a vacuum housing; wherein one end of the liquid inlet pipe is connected to the liquid inlet, the other end of the liquid inlet pipe is connected to the cold end heat exchanger, the cold end heat exchanger is connected to the cold head, the cold head is connected to the air return pipe, and the tail end of the air return pipe is connected to the air outlet; the liquid inlet pipe and the air return pipe are made of circular tubes, and the positional relationship between the two is concentric, forming a gap sandwich between the liquid inlet pipe and the air return pipe. At the same time, the liquid inlet pipe, the air return pipe, the cold end heat exchanger, and the cold head form a closed gas loop; the cryogenic liquid changes from liquid to gas and enters the gap sandwich formed between the liquid inlet pipe and the air return pipe; A cold screen is fixed on the periphery of the return air pipe; one end of the flexible connecting wire is connected to the cold head, and the other end is connected to the sample stage, and the flexible connecting wire and the sample stage are welded or screwed; An electric heating wire is wound around the outer periphery of the return air pipe at the tail end thereof, and a heat-insulating material is used as a protective layer on the outer layer of the electric heating wire. 2 . The cryostat according to claim 1 , wherein the cross-section of the cold shield is circular, square or other special shapes.

3. The cryostat according to claim 1 or 2, characterized in that The cold head is connected to one end of the flexible connecting line through the cold head extension section.

4. The cryostat according to claim 3, wherein The cold screen is connected to the cold screen extension section, and the cold screen extension section is installed on the periphery of the cold head extension section.

5. The cryostat according to claim 4, wherein The cold head and the cold head extension are in close contact with each other, and a low-temperature thermal interface material is installed on the contact surface.

6. The cryostat according to claim 5, wherein The cold screen and the cold screen extension section are seamlessly connected.

7. The cryostat according to any one of claims 1-2, 4-6, characterized in that The flexible connecting wire is made of multiple strands of oxygen-free copper wire welded or multi-layer oxygen-free copper sheets pressed and welded; the outer surface of the flexible connecting wire is mirror-coated.

8. The cryostat according to claim 3, wherein The flexible connecting wire is made of multiple strands of oxygen-free copper wire welded or multi-layer oxygen-free copper sheets pressed and welded; the outer surface of the flexible connecting wire is mirror-coated.

9. The cryostat according to claims 1-2, 4-6, characterized in that A temperature sensor is provided at the tail end of the return air pipe and is connected to a temperature control system.

10. The cryostat according to claim 3, wherein A temperature sensor is provided at the tail end of the return air pipe and is connected to a temperature control system.

11. The cryostat according to claim 1, wherein The housing of the temperature measuring and controlling instrument is provided with a mounting hole for the electrical connector, through which the electrical connector is installed and fixed, and the electrical connector is connected to the temperature sensor and heater components used for temperature measurement and control of the sample stage.

12. Use of the cryostat according to any one of claims 1 to 11, characterized in that: It is used to control the temperature of the sample stage of a scanning electron microscope.

13. The use according to claim 12, characterized in that The vacuum housing, the temperature measuring and controlling instrument housing and the electron microscope chamber are communicated with each other to form a vacuum space.

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