Transmission electron microscope sample preparation device and method based on supercritical fluid dispersion

Abstract

The invention discloses a transmission electron microscope sample preparation device and method based on supercritical fluid dispersion. The method comprises the following steps: placing a dried molecular sieve to be detected in a high-pressure treatment unit; fixing a transmission electron microscope grid in a porous support structure, and suspending the support structure in the high-voltage processing unit; the high-pressure treatment unit is sealed, fluid is introduced, the temperature and the pressure are increased to a supercritical state, and under the stirring and / or fluid forced circulation condition, the molecular sieves and the fluid are in full contact and flow and are directly dispersed and adsorbed on the carrying net. By utilizing the characteristics of the supercritical fluid, in-situ direct dispersion and adsorption of the sample on the carrier net and synchronous cleaning of the molecular sieve sample are realized, and the method has the advantages of uniform dispersion, no organic solvent residue, high sample cleanliness, capability of effectively weakening the electron beam induced carbon deposition effect and the like.

Description

Technical Field

[0001] This invention relates to the field of sample preparation technology, and specifically to a transmission electron microscope sample preparation apparatus and method based on supercritical fluid dispersion. Background Technology

[0002] Scanning transmission electron microscopy (STEM), especially integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM) under double spherical aberration correction, has become an important characterization tool for studying the microstructure of molecular sieves, nanomaterials, porous materials, and functional materials.

[0003] The aforementioned techniques enable high-resolution imaging of light elements and pore structures under relatively low electron dose conditions, but impose stricter requirements on sample dispersion, surface cleanliness, and structural integrity. During dual-spherical-aberration-corrected iDPC-STEM characterization, the uniformity of sample dispersion on the transmission electron microscope grid directly affects the selectivity and stability of the imaging region; while the cleanliness of the sample surface and pore interior plays a decisive role in the imaging signal-to-noise ratio, phase contrast uniformity, and atomic-level structural resolution. Especially under long-term exposure or high magnification conditions, trace organic residues in the sample are highly susceptible to carbonaceous deposition under electron beam action, severely interfering with the accurate characterization of light elements and pore structures by iDPC-STEM imaging.

[0004] Currently, the preparation methods for transmission electron microscopy (iDPC) samples still primarily rely on liquid-phase dispersion. Typically, solvents such as water, ethanol, and acetone are used to ultrasonically disperse the sample before it is dropped onto a copper grid, followed by natural or heat drying to obtain the sample for analysis. However, this method generally suffers from the following drawbacks: Firstly, solvent evaporation can easily induce particle migration and aggregation, resulting in uneven sample distribution on the grid and failing to meet the requirement for single-particle dispersion under double spherical aberration correction conditions. Secondly, residual solvent or introduced organic impurities are easily adsorbed onto the sample surface or inside the pores, undergoing decomposition and carbon deposition under electron beam irradiation, significantly reducing the contrast and spatial resolution of iDPC-STEM imaging. Furthermore, the liquid-phase dispersion and drying processes may cause swelling, dissolution, or surface reconstruction in some structure-sensitive materials, affecting their intrinsic microstructure characteristics and thus reducing the reliability of iDPC-STEM characterization results.

[0005] To improve sample cleanliness, existing technologies have attempted to use post-treatment methods such as plasma cleaning, ultraviolet ozone treatment, or multiple solvent rinsing. However, these methods often have problems such as complex process flow, poor repeatability, and easy introduction of new surface defects or electron beam sensitive sites. Furthermore, it is difficult to achieve simultaneous cleaning during sample dispersion.

[0006] Therefore, there is an urgent need for a transmission electron microscopy (TEM) sample preparation method that does not require the introduction of traditional liquid solvents. This method should enable uniform dispersion of molecular sieve samples during sample preparation, and allow for in-situ deposition and simultaneous cleaning on the TEM grid. This would effectively improve the dispersion uniformity and surface and pore cleanliness of the samples, and significantly reduce the carbon deposition effect caused by the electron beam during dual aberration-corrected iDPC-STEM imaging. This would meet the increasingly demanding technical requirements of high-resolution, multi-mode electron microscopy characterization for sample quality. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing a transmission electron microscopy (TEM) sample preparation device and method based on supercritical fluid dispersion. It incorporates a high-pressure processing unit and, under stirring and / or forced fluid circulation conditions, achieves in-situ dispersion and adsorption of the molecular sieve on a carrier mesh through contact between the molecular sieve and the supercritical fluid. This method eliminates the need for traditional solvents and offers advantages such as uniform dispersion, absence of organic solvent residue, high sample cleanliness, and effective reduction of electron beam-induced carbon deposition. It significantly improves the dispersion quality and imaging stability of TEM samples and is applicable to various material systems, including molecular sieves, nanomaterials, and porous materials, demonstrating promising application prospects.

[0008] To address the aforementioned technical problems, the first aspect of this invention provides a method for preparing transmission electron microscopy samples based on supercritical fluid dispersion, comprising the following steps:

[0009] S1. Place the dried molecular sieve to be tested in the high-pressure processing unit;

[0010] S2. Fix the transmission electron microscope screen in the porous support structure, and suspend the support structure in the high-voltage processing unit;

[0011] S3. Seal the high-pressure processing unit, introduce a fluid medium and raise the temperature and pressure to a supercritical state. Under stirring and / or forced fluid circulation conditions, the molecular sieve comes into full contact with the supercritical medium to perform dispersion and cleaning, and is directly dispersed and adsorbed on the carrier network.

[0012] This invention incorporates a high-pressure processing unit, within which molecular sieves and transmission electron microscope (TEM) meshes are placed. Fluid is introduced and the temperature and pressure are increased to a supercritical state. Through stirring and / or forced fluid circulation, sufficient contact between the molecular sieves and the fluid is achieved. Utilizing the low viscosity, low surface tension, and strong diffusion capacity of the supercritical fluid, in-situ direct dispersion and adsorption of the sample on the mesh is realized. Simultaneously, during the dispersion process, the fluid is periodically replaced. The supercritical fluid can simultaneously clean weakly bound impurities and organic residues on the surface of the molecular sieve sample, thereby improving sample surface cleanliness, reducing electron beam-induced carbon deposition during TEM characterization, and significantly enhancing imaging quality and stability.

[0013] Furthermore, in S1, the drying process specifically involves drying in a vacuum drying oven at a temperature of 60-80°C for 6-10 hours.

[0014] Furthermore, in S2, the porous support structure is composed of n layers of metal mesh, where n≥1 and the mesh size is 800-1000 mesh.

[0015] Furthermore, in S3, the fluid medium is selected from carbon dioxide, or a mixture of carbon dioxide and one or more inert gases; the conditions for heating and pressurizing are a temperature of 35-180℃ and a pressure of 10-40MPa.

[0016] Furthermore, in S3, the stirring is mechanical stirring and / or ultrasonic stirring; the forced fluid circulation is driven by an external circulation device and / or a built-in centrifugal device.

[0017] Furthermore, in S3, the fluid in the high-pressure processing unit is replaced every 5-90 minutes to achieve cleaning of the molecular sieve.

[0018] Furthermore, step S3 also includes: depressurizing the air vent via an exhaust valve, removing the carrier mesh, and obtaining a sample for transmission electron microscopy characterization.

[0019] Another aspect of the present invention provides a transmission electron microscope sample preparation apparatus based on supercritical fluid dispersion to implement the preparation method described in the first aspect, comprising: a high-pressure processing unit, a heating unit for heating the high-pressure processing unit, a sealing cover for sealing the high-pressure processing unit, a porous support structure suspended in the high-pressure processing unit, a stirring and / or forced fluid circulation device, and a fluid inlet valve and an exhaust valve connected to the high-pressure processing unit.

[0020] Furthermore, the heating unit includes a housing, a heating element, and a heat-conducting medium filled inside the housing, and the high-pressure processing unit is placed inside the housing.

[0021] Furthermore, the sealing cover is placed on top of the high-pressure processing unit and is connected to the air inlet valve and the air outlet valve through an air pipe. The air inlet valve and the air outlet valve are connected to the high-pressure processing unit through the sealing cover.

[0022] Furthermore, the stirring and / or forced fluid circulation device is selected from one or more of the following: a mechanical stirrer, an ultrasonic stirrer, an external circulation device, and a built-in centrifugal device; the mechanical stirrer extends into the high-pressure processing unit through a stirring shaft passing through the sealed cover; the ultrasonic stirrer extends into the high-pressure processing unit through an ultrasonic probe passing through the sealed cover; the built-in centrifugal device is located at the bottom of the high-pressure processing unit and is driven by a pump to rotate the impeller at high speed; the external circulation device is connected to the high-pressure processing unit through a pipeline and is driven by a circulation pump to circulate the supercritical fluid within the system.

[0023] The beneficial effects of this invention are:

[0024] This invention places the molecular sieve sample to be tested and the transmission electron microscope (TEM) grid together in a supercritical fluid high-pressure processing unit, utilizing the characteristics of supercritical fluid—low viscosity, low surface tension, and strong diffusion ability—to achieve in-situ direct dispersion of the sample on the grid.

[0025] In the molecular sieve dispersion process, the present invention replaces the fluid with a supercritical fluid, which can simultaneously clean weakly bound impurities and organic residues on the sample surface, thereby improving the cleanliness of the sample surface, reducing the electron beam-induced carbon deposition phenomenon during transmission electron microscopy characterization, and significantly improving imaging quality and stability.

[0026] The method of this invention does not require the introduction of traditional liquid solvents, which can effectively avoid particle agglomeration, redeposition and impurity contamination caused by solvent evaporation. It has the advantages of uniform dispersion, no organic solvent residue, high sample cleanliness and effective reduction of electron beam-induced carbon deposition effect.

[0027] The method of this invention has a simple process flow and is easy to operate. The supercritical fluid can be completely vaporized and discharged from the system after depressurization, without producing solvent residue, and the fluid medium can be recycled and reused. Based on solving the problems of complex sample preparation process, poor repeatability and environmental pollution in the prior art, it realizes a solvent-free, clean and environmentally friendly transmission electron microscopy sample preparation method. It has good versatility and repeatability, and is applicable to a variety of material systems such as molecular sieves, nanomaterials and porous materials, and has broad application prospects. Attached Figure Description

[0028] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the transmission electron microscopy sample preparation device based on supercritical fluid dispersion according to the present invention. Figure 1 ;

[0030] Figure 2 This is a schematic diagram of the transmission electron microscopy sample preparation device based on supercritical fluid dispersion according to the present invention. Figure 2 ;

[0031] Figure 3 This is a schematic diagram of the transmission electron microscopy sample preparation device based on supercritical fluid dispersion according to the present invention. Figure 3 ;

[0032] Figure 4 This is a schematic diagram of the transmission electron microscopy sample preparation device based on supercritical fluid dispersion according to the present invention. Figure 4 ;

[0033] Figure 5 The transmission electron microscopy characterization results of the molecular sieve sample prepared in Example 1 of the present invention are as follows: (a) TEM image, scale bar: 2 μm; (b) High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image, scale bar: 50 nm; (c) HAADF-STEM high-magnification image, scale bar: 5 nm.

[0034] Figure 6 This is an integrated differential phase contrast scanning transmission electron microscope (iDPC-STEM) image of the molecular sieve sample prepared in Example 1 of the present invention;

[0035] Figure 7 The transmission electron microscopy characterization results of the molecular sieve sample prepared in Example 2 of the present invention are as follows: (a) TEM image, scale bar: 2 μm; (b) HAADF-STEM image, scale bar: 50 nm; (c) HAADF-STEM high magnification image, scale bar: 5 nm.

[0036] Figure 8The transmission electron microscopy characterization results of the molecular sieve sample prepared in Example 3 of the present invention are as follows: (a) TEM image, scale bar: 2 μm; (b) HAADF-STEM image, scale bar: 100 nm; (c) HAADF-STEM high magnification image, scale bar: 5 nm.

[0037] Figure 9 Transmission electron microscopy characterization results of molecular sieve samples prepared for Comparative Example 1 of this invention: (a) TEM image, scale bar: 2 μm; (b) HAADF-STEM image, scale bar: 100 nm; (c) HAADF-STEM high magnification image, scale bar: 5 nm;

[0038] Figure 10 Transmission electron microscopy characterization results of molecular sieve samples prepared for Comparative Example 2 of this invention: (a) TEM image, scale bar: 2 μm; (b) HAADF-STEM image, scale bar: 100 nm; (c) HAADF-STEM high magnification image, scale bar: 5 nm;

[0039] Figure 11 The image shows an integrated differential phase contrast scanning transmission electron microscope (iDPC-STEM) image of the molecular sieve sample prepared in Comparative Example 2 of this invention.

[0040] Figure 12 Solid state of samples before and after supercritical carbon dioxide treatment according to this invention 13 C nuclear magnetic resonance (C 13 C NMR spectrum;

[0041] The following are the labels in the diagram: 1. High-pressure processing unit; 2. Sealing cover; 3. Support structure; 4. Inlet valve; 5. Exhaust valve; 6. Housing; 7. Heating element; 8. Mechanical stirrer; 9. Stirring shaft; 10. Ultrasonic probe; 11. Centrifugal structure; 12. Drive pump; 13. Circulation pump; 14. Circulation inlet valve; 15. Circulation exhaust valve. Detailed Implementation

[0042] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] In this invention, unless otherwise stated, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," indicating orientation or positional relationships, are merely for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this patent can be understood according to the specific circumstances.

[0044] refer to Figure 1-4 This embodiment relates to a transmission electron microscope sample preparation device based on supercritical fluid dispersion, comprising: a high-pressure processing unit 1, a heating unit for heating the high-pressure processing unit 1, a sealing cover 2 for sealing the high-pressure processing unit 1, a porous support structure 3 suspended in the high-pressure processing unit 1, a stirring and / or forced fluid circulation device, and a fluid inlet valve 4 and an exhaust valve 5 connected to the high-pressure processing unit 1.

[0045] In a preferred embodiment, the heating unit includes a housing 6, a heating element 7, and a heat-conducting medium filled inside the housing 6; the high-pressure processing unit 1 is placed inside the housing 6; the sealing cover 2 is placed on top of the high-pressure processing unit 1 and is connected to the inlet valve 4 and the exhaust valve 5 via an air pipe; the inlet valve 4 and the exhaust valve 5 are connected to the high-pressure processing unit 1 via the sealing cover 2; the stirring and / or forced fluid circulation device is selected from one or more of a mechanical stirrer 8, an ultrasonic stirrer, an external circulation device, and / or a built-in centrifugal device; Reference Figure 1 As shown, the mechanical stirrer 8 passes through the sealing cover 2 and extends into the high-pressure processing unit 1 via the stirring shaft 9; Reference Figure 2 As shown, the ultrasonic stirrer passes through the sealed cover 2 and extends into the high-pressure processing unit 1 via the ultrasonic probe 10; Reference Figure 3 As shown, the built-in centrifugal device includes a centrifugal mechanism 11 disposed within the housing 6 and located at the bottom of the high-pressure processing unit 1, the centrifugal mechanism 11 being driven to rotate by a drive pump 12; Reference Figure 4As shown, the external circulation device includes a circulation pump 13 and a circulation inlet valve 14 and a circulation exhaust valve 15 connected to the high-pressure processing unit 1. The circulation pump 13 forms a circulation loop with the high-pressure processing unit 1 through the circulation inlet valve 14 and the circulation exhaust valve 15.

[0046] Another embodiment provides a transmission electron microscopy sample preparation method based on supercritical fluid dispersion, comprising the following steps:

[0047] S1. Place the dried molecular sieve to be tested in the high-pressure processing unit;

[0048] S2. Fix the transmission electron microscope screen in the porous support structure, and suspend the support structure in the high-voltage processing unit;

[0049] S3. Seal the high-pressure processing unit, introduce fluid and raise the temperature and pressure to a supercritical state. Under stirring and / or forced fluid circulation conditions, the molecular sieve comes into full contact with the supercritical medium to perform dispersion and cleaning, and is directly dispersed and adsorbed on the carrier network.

[0050] In a preferred embodiment, in S1, the drying process specifically involves drying in a vacuum drying oven at a temperature of 60-80°C for 6-10 hours.

[0051] In a preferred embodiment, in S2, the porous support structure consists of n layers of metal mesh, where n≥1 and the mesh size is 800-1000 mesh.

[0052] In a preferred embodiment, in S3, the fluid medium is selected from carbon dioxide, or a mixture of it with one or more inert gases; the conditions for heating and pressurizing are: temperature 35-180℃, pressure 10-40MPa; the stirring is mechanical stirring and / or ultrasonic stirring; the forced fluid circulation is driven by an external circulation device and / or a built-in centrifugal device. In S3, the fluid in the high-pressure processing unit is replaced every 5-90 minutes to achieve cleaning of the molecular sieve.

[0053] In a preferred embodiment, after S3, the method further includes: depressurizing the air filter by an exhaust valve, removing the carrier mesh, and obtaining a sample for transmission electron microscopy characterization.

[0054] Example 1

[0055] This embodiment relates to a transmission electron microscopy sample preparation method based on supercritical fluid dispersion, comprising the following steps:

[0056] (1) Take an appropriate amount of ZSM-5 molecular sieve sample, place it in a vacuum drying oven, and vacuum dry it at 60°C for 10 hours to remove the moisture and impurities adsorbed on the sample surface and in the pores.

[0057] (2) Weigh 0.0005 g of dried ZSM-5 molecular sieve sample and spread it evenly at the bottom of the high-pressure treatment unit.

[0058] (3) Fix the ultrathin carbon film (carrier) for transmission electron microscopy in a support structure consisting of three layers of metal mesh, wherein the mesh number of the metal mesh is 1000; then suspend the support structure inside the high-voltage processing unit so that the ultrathin carbon film is located in the central space of the processing unit.

[0059] (4) Seal the high-pressure treatment unit with a sealed cover, slowly introduce carbon dioxide, and simultaneously raise the temperature to 60°C and the pressure to 15 MPa to bring the carbon dioxide to a supercritical state; start the mechanical stirrer and control the stirring speed to 150 r / min. During the treatment process, replace the carbon dioxide in the high-pressure treatment unit every 30 minutes, for a total of three times, to ensure that the supercritical carbon dioxide is in full contact with the molecular sieve sample. Under the mass transfer and dispersion effect of the supercritical fluid, ZSM-5 particles are carried and deposited in situ on the ultrathin carbon film, realizing the direct dispersion of the sample.

[0060] (5) After the treatment is completed, stop stirring, open the exhaust valve to slowly depressurize the high pressure treatment unit, so that the pressure inside the unit drops to normal pressure; open the high pressure treatment unit, take out the ultrathin carbon film, and obtain a molecular sieve sample that can be directly used for transmission electron microscopy characterization.

[0061] Figure 5 The TEM characterization results of the molecular sieve sample prepared in Example 1 show that the molecular sieve sample exhibits good single-particle dispersion on the transmission electron microscope grid, with clear particle boundaries and obvious separation between particles. No significant aggregation or accumulation was observed (see reference). Figure 5 (a) Under further HAADF imaging conditions, the sample lattice fringes were clear, continuous, and regular, indicating that the molecular sieve crystal structure was effectively preserved after supercritical fluid treatment without significant damage (reference). Figure 5 (b and c).

[0062] Figure 6 The iDPC-STEM aberration-corrected characterization results of the molecular sieve sample prepared in Example 1 show that, under iDPC-STEM imaging mode, the sample surface and pore area exhibit high cleanliness and uniform contrast distribution, with clearly distinguishable pore contours and a high signal-to-noise ratio. No carbon deposition caused by residual organic solvents or their decomposition products was observed (see reference). Figure 6 (a and b).

[0063] Figure 5-6The results show that the method in Example 1 can effectively avoid the organic pollution problem introduced by traditional solvent dispersion methods during sample preparation, and significantly reduce the risk of carbon deposition in samples under high-resolution scanning transmission electron microscopy conditions. It achieves efficient, uniform dispersion and simultaneous clean preparation of molecular sieve samples on the transmission electron microscope grid, and is particularly suitable for material systems with high requirements for sample dispersibility, cleanliness and imaging stability, including but not limited to porous materials, molecular sieves and nanoparticles. It has significant technical advantages such as simplified process flow, excellent dispersion effect, high sample cleanliness and strong characterization adaptability.

[0064] Example 2

[0065] The difference between this embodiment and Embodiment 1 is that the number of metal mesh layers in the support structure is adjusted to two layers, while other steps and parameters remain unchanged. The dispersion state and imaging results of the transmission electron microscopy sample prepared using this embodiment are as follows: Figure 7 As shown in ac.

[0066] Example 3

[0067] The difference between this embodiment and Embodiment 1 is that in step (4), the temperature is simultaneously raised to 90°C and the pressure is raised to 18 MPa. The dispersion state and imaging results of the transmission electron microscopy sample prepared using this embodiment are as follows: Figure 8 As shown in ac.

[0068] refer to Figure 7-8 It can be seen that in the support structures with different numbers of layers as defined in this invention and under different supercritical conditions, molecular sieve samples can achieve uniform dispersion and stable in-situ deposition on ultrathin carbon film carriers, and maintain good crystal structure integrity and imaging stability under high-resolution imaging conditions, indicating that the method of this invention has good adaptability and stability to process parameters.

[0069] Comparative Example 1

[0070] The difference between this comparative example and Example 1 is that the number of metal mesh layers in the support structure is adjusted to one layer with a mesh size of 600 mesh, and the temperature is simultaneously raised to 30°C and the pressure is increased to 8 MPa in step (4). The dispersion state and imaging results of the transmission electron microscopy sample prepared using this comparative example are as follows: Figure 9 As shown in ac.

[0071] refer to Figure 9 Molecular sieve samples exhibited significant agglomeration on the transmission electron microscope (TEM) grid, with uneven particle distribution and multi-layer stacking in local areas, making it difficult to form a uniform, dispersed monolayer deposition structure (e.g., Figure 9 As shown in Figure a). Furthermore, under high-resolution imaging conditions, carbon deposition easily occurs in the sample area, significantly reducing imaging contrast and making it difficult to obtain clear and recognizable high-resolution images. Figure 9(b and c). Comparing Examples 1-3, it can be seen that when the processing conditions do not meet the supercritical processing temperature and pressure range and support structure conditions specified in this invention, the dispersion and transport capacity of carbon dioxide for molecular sieve samples is significantly insufficient, making it difficult to achieve uniform dispersion and in-situ deposition of molecular sieve samples. This further verifies the necessity and rationality of the supercritical processing conditions and support structure settings described in this invention.

[0072] Comparative Example 2

[0073] In this comparative example, anhydrous ethanol was introduced as a dispersion medium during sample preparation, and the molecular sieve samples were treated using conventional solvent dispersion methods. The specific steps are as follows:

[0074] (1) Take an appropriate amount of ZSM-5 molecular sieve sample, place it in a vacuum drying oven, and vacuum dry it at 60°C for 10 hours to remove the moisture and impurities adsorbed on the sample surface and in the pores.

[0075] (2) Add 5 mL of anhydrous ethanol to a centrifuge tube, add an appropriate amount of dried ZSM-5 molecular sieve, and treat it with ultrasound for about 30 minutes to fully disperse the molecular sieve sample in the ethanol and form a uniform dispersion system.

[0076] (3) The above dispersion is dropped onto an ultrathin carbon film for transmission electron microscopy. The ultrathin carbon film is placed on filter paper beforehand to adsorb excess solution, so as to obtain a molecular sieve sample that can be directly used for transmission electron microscopy characterization.

[0077] The samples prepared in the comparative example were characterized by TEM and iDPC-STEM spherical aberration correction, and the characterization results are as follows. Figure 10 Chinese AC and Figure 11 As shown in Figure ab, the samples prepared using this comparative method can be basically dispersed on the transmission electron microscope grid without large-area severe aggregation. However, local carbon deposits can still be observed under high-magnification and atomic-resolution imaging conditions. The uniformity of the imaging background and the signal-to-noise ratio are lower than those in Example 1, and the electron beam stability under continuous exposure conditions is also relatively weak. The results indicate that although the traditional ethanol dispersion method can meet the basic characterization requirements, it still has certain limitations in suppressing carbon formation during high-resolution imaging and improving sample cleanliness and imaging stability. In contrast, the supercritical fluid direct dispersion and in-situ deposition method used in Example 1 has significant advantages in terms of comprehensive characterization performance.

[0078] Figure 12 Solid state of samples before and after supercritical carbon dioxide treatment 13 C nuclear magnetic resonance (C 13The C NMR spectrum, compared with the sample (ZSM-5) obtained in Comparative Example 2, shows that the broad and featureless carbon signal originally caused by residual organic template agents or amorphous carbon in the ZSM-5 sample after supercritical CO2 treatment in Example 1 was significantly weakened or even disappeared, indicating that the supercritical treatment process can effectively remove organic residues and amorphous carbon contaminants from the molecular sieve channels and surface.

[0079] In summary, the supercritical processing method of this invention not only achieves uniform dispersion and in-situ deposition of molecular sieve samples on the transmission electron microscope (TEM) grid, but also simultaneously completes the cleaning treatment of the sample surface and pore area, effectively suppressing the occurrence of electron beam-induced carbon deposition during TEM, especially aberration-corrected iDPC-STEM imaging, thereby improving the imaging stability and structural characterization reliability of the samples.

[0080] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing transmission electron microscopy samples based on supercritical fluid dispersion, characterized in that, Includes the following steps: S1. Place the dried molecular sieve to be tested in the high-pressure processing unit; S2. Fix the transmission electron microscope screen in the porous support structure, and suspend the support structure in the high-voltage processing unit; S3. Seal the high-pressure processing unit, introduce a fluid medium and raise the temperature and pressure to a supercritical state. Under stirring and / or forced fluid circulation conditions, the molecular sieve comes into full contact with the supercritical medium to perform dispersion and cleaning, and is directly dispersed and adsorbed on the carrier network.

2. The transmission electron microscopy sample preparation method based on supercritical fluid dispersion as described in claim 1, characterized in that, In S1, the drying process specifically involves drying in a vacuum drying oven at a temperature of 60-80℃ for 6-10 hours.

3. The transmission electron microscopy sample preparation method based on supercritical fluid dispersion as described in claim 1, characterized in that, In S2, the porous support structure is composed of n layers of metal mesh, where n≥1 and the mesh number is 800-1000 mesh.

4. The transmission electron microscopy sample preparation method based on supercritical fluid dispersion as described in claim 1, characterized in that, In S3, the fluid medium is selected from carbon dioxide, or a mixture of carbon dioxide and one or more inert gases; the conditions for heating and pressurizing are a temperature of 35-180℃ and a pressure of 10-40MPa.

5. The transmission electron microscopy sample preparation method based on supercritical fluid dispersion as described in claim 1, characterized in that, In S3, the stirring is mechanical stirring and / or ultrasonic stirring; the forced fluid circulation is driven by an external circulation device and / or a built-in centrifugal device.

6. The transmission electron microscopy sample preparation method based on supercritical fluid dispersion as described in claim 1, characterized in that, In S3, the fluid in the high-pressure processing unit is replaced every 5-90 minutes.

7. A transmission electron microscopy sample preparation apparatus based on supercritical fluid dispersion, characterized in that, The preparation method according to any one of claims 1-6 comprises: a high-pressure processing unit, a heating unit for heating the high-pressure processing unit, a sealing cover for sealing the high-pressure processing unit, a porous support structure suspended in the high-pressure processing unit, a stirring and / or forced fluid circulation device, and a fluid inlet valve and an exhaust valve communicating with the high-pressure processing unit.

8. The transmission electron microscopy sample preparation apparatus based on supercritical fluid dispersion as described in claim 7, characterized in that, The heating unit includes a housing, a heating element, and a heat-conducting medium filled inside the housing, and the high-pressure processing unit is placed inside the housing.

9. The transmission electron microscopy sample preparation apparatus based on supercritical fluid dispersion as described in claim 7, characterized in that, The sealing cover is placed on top of the high-pressure processing unit and is connected to the air inlet valve and the air outlet valve through an air pipe. The air inlet valve and the air outlet valve are connected to the high-pressure processing unit through the sealing cover.

10. The transmission electron microscopy sample preparation apparatus based on supercritical fluid dispersion as described in claim 7, characterized in that, The stirring and / or forced fluid circulation device is selected from one or more of the following: mechanical stirrer, ultrasonic stirrer, external circulation device, and built-in centrifugal device.

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