Preparation method and application of hexagonal boron nitride / graphene suspended composite support membrane with strength and toughness

Abstract

The invention discloses a preparation method and application of a hexagonal boron nitride / graphene suspended composite support membrane with both strength and toughness. According to the method, a graphene grid is placed on the surface of hexagonal boron nitride in a face-to-face mode, hexagonal boron nitride and graphene are perfectly attached through a volatile organic solvent, and preparation of the clean and complete suspended two-dimensional composite film is achieved. The method solves the problems that the process of transferring the two-dimensional material Van der Waals composite film layer by layer is tedious and serious in pollution, the suspended composite supporting film is high in yield, high in integrity and clean in interface, and large-area preparation can be achieved. Meanwhile, the suspended composite support membrane shows excellent mechanical strength and fracture toughness, and is kept stable under an extreme high-temperature thermal shock condition. On the basis, the hexagonal boron nitride / graphene suspended composite support membrane has wide application prospects in the aspects of high-temperature synthesis, thermal shock synthesis, related electron microscope characterization, high-temperature sensing, thermoelectron luminescence, proton-ion screening and the like.

Description

Technical Field

[0001] The present invention belongs to the field of materials, and in particular relates to a preparation method and application of a hexagonal boron nitride / graphene suspended composite support membrane having both strength and toughness. Background Art

[0002] Graphene and hexagonal boron nitride (h-BN) are two similar two-dimensional materials that have received widespread attention. They both have a honeycomb hexagonal close-packed structure and can be as thin as a single atomic layer. At the same time, there are significant differences between the two. 2 The hybridized carbon atoms form a delocalized large π bond in the plane, so graphene has good conductivity; in hexagonal boron nitride, boron atoms and nitrogen atoms are arranged alternately, have in-plane polarity, and the delocalization is greatly weakened, so boron nitride is a commonly used dielectric material.

[0003] Existing studies have shown that graphene has excellent electrical, optical, thermal, mechanical and chemical stability, and has broad application prospects and potential in various fields. Thanks to the excellent properties of graphene, graphene-based two-dimensional functional membranes have played a prominent role in applications such as electron microscope support membranes, proton separation membranes, and fuel cell diaphragms.

[0004] However, graphene suspended support membranes have two disadvantages: on the one hand, because graphene is a brittle material, although a single-component graphene film has high mechanical strength, it is difficult to prevent the rapid expansion of cracks when damaged, which leads to catastrophic failure of the entire material; on the other hand, graphene itself has poor thermal stability and is easily oxidized in the air, which limits its application in high-temperature fields. Therefore, it is urgent to make improvements based on the graphene suspended support membrane to solve the above two problems.

[0005] A potential solution is to use two-dimensional hexagonal boron nitride as a suspended support membrane. Hexagonal boron nitride is a hexagonal honeycomb material formed by alternating B atoms and N atoms, with a lattice constant of 2.5 Å. Its fracture strength and elastic modulus are slightly lower than those of single-layer graphene, but because the hexagonal boron nitride lattice has triple symmetry, boron nitride has additional fracture toughness. Its fracture tip is divided into a B end and an N end with different energies, which then continuously deflect and bifurcate, greatly improving the fracture energy release rate. At the same time, the high chemical stability of hexagonal boron nitride allows it to remain stable even under normal pressure and 800 degrees Celsius. However, the mechanical properties of hexagonal boron nitride materials are poor, and the preparation of a suspended single-layer hexagonal boron nitride is extremely difficult, with a high probability of breakage, which is not conducive to its use as a suspended support membrane alone. Summary of the invention

[0006] In view of the defects existing in the prior art, the present invention utilizes the structural similarities and functional differences between graphene and hexagonal boron nitride to design and prepare a vertically stacked hexagonal boron nitride / graphene composite structure as an electron microscope grid support film. While the composite film has high mechanical strength, it introduces additional fracture toughness, so that it has the ability to resist fracture and crack propagation at the same time. Specifically, the present invention laminates the suspended graphene support film face to face with the hexagonal boron nitride, and uses a clean glue-free transfer method to transfer the boron nitride to the graphene surface, thereby realizing the layer-by-layer transfer of the composite film.

[0007] The purpose of the present invention is to provide a method for preparing a hexagonal boron nitride / graphene suspended composite support membrane and demonstrate its excellent mechanical properties. The present invention solves the problem of brittle fracture and failure of graphene electron microscope carriers, and the obtained composite support membrane has a high yield rate and can be prepared in batches. It also has the advantages of good cleanliness and high integrity, which is conducive to achieving high-resolution electron microscope characterization in a variety of environments.

[0008] The method for preparing a hexagonal boron nitride / graphene suspended composite support membrane provided by the present invention comprises the following steps: 1) placing a graphene grid on a hexagonal boron nitride / substrate so that one side of the graphene in the graphene grid contacts the hexagonal boron nitride, dripping a volatile organic liquid until the entire surface of the boron nitride is covered, and waiting for the volatile organic liquid to dry; 2) placing the structure obtained in step 1) in an etching solution to remove the substrate in the hexagonal boron nitride / substrate, and obtaining the hexagonal boron nitride / graphene suspended composite support membrane after washing and drying.

[0009] In step 1) of the above method, the hexagonal boron nitride / substrate can be selected from at least one of the following: sapphire wafer-copper-nickel alloy-hexagonal boron nitride, sapphire wafer-copper-hexagonal boron nitride, sapphire wafer-nickel-hexagonal boron nitride, copper foil-hexagonal boron nitride, copper-nickel alloy foil-hexagonal boron nitride, nickel foil-hexagonal boron nitride; specifically sapphire wafer-copper-nickel alloy-hexagonal boron nitride.

[0010] In step 1) of the above method, the hexagonal boron nitride is single crystal, twin crystal or polycrystalline hexagonal boron nitride; specifically single crystal boron nitride.

[0011] In step 1) of the above method, the number of layers of the hexagonal boron nitride is a single layer, a double layer, or 3-10 layers; specifically, a single layer.

[0012] Furthermore, the hexagonal boron nitride / substrate is sapphire wafer-copper-nickel alloy-single crystal hexagonal boron nitride; the sapphire wafer-copper-nickel alloy-single crystal hexagonal boron nitride can be prepared according to the method recorded in application number: CN202410836113.9, and the specific method includes the following steps: (1) sputtering a layer of nickel film on sapphire by magnetron sputtering, and then sputtering a layer of copper film on the nickel film to obtain copper / nickel / sapphire; (2) subjecting the copper / nickel / sapphire to high temperature annealing to obtain a single crystal copper-nickel alloy wafer; (3) growing hexagonal boron nitride on the single crystal copper-nickel alloy wafer by low pressure chemical vapor deposition to obtain the single crystal hexagonal boron nitride wafer.

[0013] In step 1) of the above method, the graphene grid is a graphene suspended support membrane prepared using graphene as raw material and an electron microscope grid having a porous membrane.

[0014] Furthermore, the graphene raw materials include graphene grown on foil and graphene grown on wafer; the types of the foil and wafer include copper, copper-nickel alloy, nickel, etc.; specifically, it can be sapphire wafer-copper-graphene.

[0015] Furthermore, the number of layers of the graphene includes a single layer, a double layer, a few layers of 3-5 layers, etc., and specifically can be a single layer.

[0016] Furthermore, the electron microscope grid with a porous membrane includes commercial Quantifoil carbon membrane, GIG carbon membrane, independently prepared porous membrane (electron microscope grid recorded in ZL202110333466.3, ZL 202410168665.7 or ZL 202410883073.3), etc., and specifically can be Quantifoil carbon membrane or independently prepared porous membrane (electron microscope grid recorded in ZL202110333466.3, ZL202410168665.7 or ZL 202410883073.3).

[0017] Furthermore, the electron microscope grid with a porous membrane is a grid with a transmission electron microscope support membrane as described in ZL202110333466.3, and its preparation method comprises the following steps: (A) Preparation of transmission electron microscope support film Using vacuum coating to sequentially coat a water-soluble sacrificial layer and a porous electron microscope support film layer on the array template, and then separating the porous electron microscope support film layer from the array template in water to obtain the transmission electron microscope support film; (B) placing a batch of carrier meshes under the transmission electron microscope support film layer, scooping up the film from bottom to top in the liquid, and obtaining a carrier mesh with a transmission electron microscope support film after drying.

[0018] In the above step (A), the array template is a circular hole array template, a square hole array template or a polygonal array template; the material constituting the template is at least one of silicon, silicon nitride and silicon dioxide; in the circular hole array template, the diameter of the circular hole is 1-10 μm; the depth of the circular hole groove is 0.5-5 μm; the vacuum coating is thermal evaporation coating or sputtering coating; the vacuum pressure is 10 -3 ~10 -6 Pa.

[0019] In the above step (A), the substance constituting the water-soluble sacrificial layer is an inorganic salt; the inorganic salt is specifically selected from at least one of sodium metaphosphate, sodium chloride, and potassium chloride; the coating thickness of the water-soluble sacrificial layer is 10~100 nm; the coating speed is 0.1 Å / s~1 Å / s; the porous electron microscope support film layer is a gold film, a nickel-titanium alloy film or a carbon film; the coating thickness of the porous electron microscope support film layer is 10~100 nm; the coating speed is 0.1 Å / s~1 Å / s; the separation step includes: immersing the circular hole array template in water at a certain inclination angle until the circular hole array template is separated from the porous electron microscope support film layer; the inclination angle is 20~60 degrees; in the separation step, the separation speed is 0.05~0.5 cm / s.

[0020] In the above step (B), the material constituting the carrier grid is selected from at least one of gold, copper, molybdenum and silicon nitride; the mesh size of the carrier grid is 200-400 meshes; the liquid is selected from any one of water, a mixture of water and ethanol, a mixture of water and isopropanol, and a mixture of water and acetone; the film scooping step includes: fixing the carrier grid in batches on a flat substrate, then immersing it in water, and scooping up the porous electron microscope support film from bottom to top; in the drying step, the time is 0.5 to 5 days; the temperature is room temperature.

[0021] Furthermore, the method for preparing the graphene suspended support membrane can be prepared by referring to the method for preparing an ultra-flat graphene electron microscope grid in ZL202110333466.3; the specific method is as follows: place a grid with a transmission electron microscope support membrane (corresponding to the aforementioned electron microscope grid with a porous membrane) on an ultra-flat wafer graphene (corresponding to the aforementioned graphene raw material), so that the side with the membrane is in contact with the ultra-flat wafer graphene, and add volatile organic liquid until the entire wafer surface is covered. After the volatile organic liquid is dried, place it in an etching solution to remove the growth substrate of the ultra-flat wafer graphene, and obtain the ultra-flat graphene electron microscope grid after washing and drying.

[0022] The ultra-flat graphene is sapphire-copper-graphene, sapphire-copper-nickel alloy-graphene or sapphire-copper-silicon alloy-graphene; the ultra-flat graphene is prepared according to the method provided in Chinese patent ZL201710523050.1, and the ultra-flat graphene is the graphene single crystal film in the patent.

[0023] Furthermore, the method for preparing the graphene suspended support film can also be prepared by referring to a method for controllable preparation and transfer of a self-supporting two-dimensional material recorded in ZL 202210107288.7; the specific method includes the following steps: (1) growing a two-dimensional material film (such as a graphene film) on a metal substrate, retaining the two-dimensional material film on one side of the metal substrate, and uniformly dripping a surfactant solution on the two-dimensional material film until it is completely soaked; (2) after the solvent evaporates, the surfactant molecules form a self-assembled structure on the surface of the two-dimensional material film; then the metal substrate with the two-dimensional material film on the surface is floated on the etching solution to remove the metal substrate; (3) after the metal substrate is completely etched, a self-supporting two-dimensional material film is obtained on the gas-liquid interface, the etching solution is replaced with deionized water, and then the self-supporting two-dimensional material film on the gas-liquid interface is transferred to the target substrate (such as an electron microscope grid with a porous membrane); (4) After the two-dimensional material / target substrate is fully dried, it is immersed in a solvent for washing to remove the self-assembled structure on the surface of the two-dimensional material, and after drying again, a two-dimensional material film on the target substrate is obtained; in the step (1), the surfactant molecule is at least one of the following: stearic acid, palmitic acid, oleic acid, lauric acid, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate; the solvent in the surfactant solution is alcohol, ketone, ester, ether, water, carboxylic acid, alkane, amide, aldehyde; the mass fraction of the surfactant in the surfactant solution is 0.001%~0.1%; in the step (2), the self-assembled structure is a thermodynamically spontaneously formed monolayer assembly structure with a thickness of 1~10nm; the floating method is that the self-assembled monolayer / two-dimensional material film is in contact with the atmosphere, and the metal substrate is in contact with the etching liquid surface.

[0024] In step 1) of the above method, the volatile organic liquid is selected from at least one of isopropanol, ethanol and acetone; the drying time of the volatile organic liquid is 2 min to 30 min, and specifically can be 10 min.

[0025] In step 2) of the above method, in the etching step, the etching solution is ammonium persulfate, sodium persulfate or ferric chloride, specifically ammonium persulfate.

[0026] In step 2) of the above method, the etching solution concentration is 0.1 mol / L to saturated solution, specifically 0.5 mol / L; In step 2) of the above method, the etching temperature is 0°C to 60°C, specifically 25°C. In step 2) of the above method, in the washing step, the washing method is washing in water and an organic solvent in sequence; the organic solvent can specifically be isopropanol or acetone.

[0027] Furthermore, the washing time in water may be 0.1 to 5 h, specifically 2 to 3 h.

[0028] Furthermore, the washing time in the organic solvent may be 0.5 to 5 min, specifically 1 min. In step 2) of the above method, the drying time after washing is 5 to 100 min, specifically 15 min.

[0029] Furthermore, the method also includes: repeating step 1) and step 2) at least once, or replacing the hexagonal boron nitride / substrate (such as a hexagonal boron nitride wafer) in step 1) and step 2) with graphene / substrate (such as a graphene wafer), to prepare a boron nitride and graphene composite structure with a stacking layer number greater than or equal to three layers.

[0030] More specifically, the method further includes: using the hexagonal boron nitride / graphene suspended composite support membrane prepared in step 2) as the graphene carrier grid, repeating the operations of step 1) and step 2) to prepare a boron nitride / graphene / boron nitride structure.

[0031] More specifically, the method further includes: using the hexagonal boron nitride / graphene suspended composite support film or the boron nitride / graphene / boron nitride structure as the hexagonal boron nitride / substrate, repeating step 1) to prepare a boron nitride and graphene composite structure with a stacking layer number greater than or equal to three layers.

[0032] The hexagonal boron nitride / graphene suspended composite support film prepared according to the above method and the boron nitride and graphene composite structure with a stacking layer number greater than or equal to three layers both fall within the protection scope of the present invention.

[0033] The application of the hexagonal boron nitride / graphene suspended composite support film or the boron nitride and graphene composite structure with three or more stacked layers prepared according to the above method in high-temperature synthesis, electron microscopy characterization, proton-ion screening, thermal shock synthesis, high-temperature sensing, thermal electron luminescence, etc. also falls within the protection scope of the present invention.

[0034] Compared with the prior art, the present invention has the following beneficial effects: 1. The process of the present invention is simple and realizes the layer-by-layer controllable transfer preparation of the two-dimensional material van der Waals suspended composite support membrane without the need for traditional polymer assistance.

[0035] 2. The present invention solves the problem that the traditional composite film construction method is prone to introduce interlayer contamination. The van der Waals force between two-dimensional materials is used to make the two spontaneously bond to form a composite film, so the interface of the obtained suspended composite support film is clean.

[0036] 3. The present invention constructs a hexagonal boron nitride / graphene suspended composite support membrane, and utilizes the unique fracture behavior and high effective energy release rate of hexagonal boron nitride when it fractures to toughen the graphene suspended support membrane, which greatly improves the problem of failure caused by brittle fracture of the graphene suspended support membrane, making it have a longer service life and a wider range of application scenarios.

[0037] 4. The present invention constructs a hexagonal boron nitride / graphene suspended composite support membrane, filling the application gap of graphene suspended support membrane in high temperature environment. The hexagonal boron nitride / graphene suspended composite support membrane is only atomic-level thick, and compared with the traditional suspended support membrane, it has high stability in high temperature environment.

[0038] 5. When the hexagonal boron nitride-graphene suspended composite support film prepared by the present invention is used as a transmission electron microscope grid, it can meet commercial standards and achieve high-resolution imaging of various samples such as nanoparticles and two-dimensional materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The process flow diagram and interface cleanliness characterization of the present invention include a) a flow diagram of the layer-by-layer adhesive-free clean transfer method; b) a schematic diagram of the bonding structure of the layer-by-layer transfer method; c) a schematic diagram of the cross-section of the bonding process of the layer-by-layer transfer method; d) a cross-sectional transmission image of the composite film obtained by the layer-by-layer transfer method.

[0040] Figure 2 The results of the hexagonal boron nitride / graphene suspended composite support film prepared by the invention are characterized. Among them, a) the actual image of the hexagonal boron nitride / graphene suspended support network; b) the statistics of the integrity of the support film and the typical scanning electron microscope image; c) the statistics of the single crystallinity of the hexagonal boron nitride / graphene suspended composite support film and the typical selected area electron diffraction image; d) the typical transmission electron microscope image of the hexagonal boron nitride / graphene suspended composite support film; e) the atomic-level transmission electron microscope image of the hexagonal boron nitride / graphene suspended composite support film; f) the electron energy loss spectrum of the hexagonal boron nitride / graphene suspended composite support film.

[0041] Figure 3 The mechanical properties of the hexagonal boron nitride / graphene suspended composite support membrane prepared by the invention are characterized. A) the fracture strength of the hexagonal boron nitride / graphene suspended composite support membrane and the double-layer graphene support membrane is tested by pressure using an atomic force microscope probe; B) the fracture toughness (fracture energy release rate J) of the hexagonal boron nitride / graphene suspended composite support membrane and the double-layer graphene support membrane is calculated by molecular dynamics simulation.

[0042] Figure 4 The high temperature shock stability test of the hexagonal boron nitride / graphene suspended composite support film prepared by the invention. Among them, a) the typical temperature-time curve of the thermal shock high temperature stability experiment and the schematic diagram of the flash Joule heating device used in the test; b) the stability statistics of the hexagonal boron nitride / graphene suspended composite support film at different thermal shock temperatures and cycle times; c) the high temperature thermal shock integrity comparison of the hexagonal boron nitride / graphene suspended composite support film and the single-layer and double-layer graphene support films, with the highest temperature being about 1800K; d) and e) are scanning electron microscope images of the hexagonal boron nitride / graphene suspended composite support film before and after 200 high temperature thermal shocks respectively; f) is an atomic level scanning transmission electron microscope image of the film in e).

[0043] Figure 5 The application of hexagonal boron nitride / graphene suspended composite support membrane. Taking the thermal shock synthesis of high entropy alloy nanoparticles as an example, single-crystal high entropy alloy nanoparticles with uniform distribution and concentrated particle size were successfully synthesized on the hexagonal boron nitride / graphene suspended composite support membrane, containing eight metal elements such as Fe, Co, Ni, Cu, Zn, Pd, Pt, and Au. Among them a) Scanning transmission electron microscope image of high entropy alloy nanoparticles on the hexagonal boron nitride-graphene suspended composite support membrane; b) Contrast intensity map of the white line area in a, reflecting the low background noise of the hexagonal boron nitride / graphene suspended composite support membrane c) Diameter distribution map of high entropy alloy nanoparticles, the inset is an image of the statistical range; d) High-resolution scanning transmission electron microscope image of high entropy alloy nanoparticles, the inset is a fast Fourier transform map; e) Element distribution map of high entropy alloy nanoparticles. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments, and any modifications or improvements made within the spirit of the present invention should be included in the protection scope of the present invention.

[0045] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials and reagents used are all commercially available unless otherwise specified.

[0046] The graphene grid used in the following embodiments is prepared according to the method provided in Example 1 of Chinese Patent ZL202110333466.3, and the graphene grid is the ultra-flat graphene grid prepared in Example 1 of the patent; the hexagonal boron nitride used is prepared according to the method described in Example 2 of Application Number: CN202410836113.9 (CN118745594A), and the hexagonal boron nitride is the single crystal hexagonal boron nitride / CuNi (111) wafer prepared in Example 2 of the patent.

[0047] Example 1: Preparation method and property characterization of a hexagonal boron nitride / graphene suspended composite support membrane with both strength and toughness.

[0048] 1) Preparation of hexagonal boron nitride / graphene suspended composite support membrane: The graphene surface of the graphene grid is placed downward on the hexagonal boron nitride wafer to make the graphene contact with the hexagonal boron nitride. Isopropyl alcohol is added until the entire surface of the hexagonal boron nitride wafer is covered. After drying for 10 minutes, the two are tightly attached. It is placed in 0.5 mol / L ammonium persulfate and etched at room temperature for 20 to 30 minutes to remove the copper-nickel alloy substrate on which the hexagonal boron nitride grows, so that the hexagonal boron nitride is transferred to the graphene grid. The graphene grid with the hexagonal boron nitride film transferred is then transferred to water for washing for 2 to 3 hours, then immersed in isopropyl alcohol for 40 seconds and dried for 1 hour to obtain a hexagonal boron nitride / graphene suspended composite support film.

[0049] Figure 1 The process flow diagram and interface cleanliness characterization of this example are shown in Figure 1. a) Flow diagram of the layer-by-layer adhesive-free clean transfer method; b) Schematic diagram of the bonding structure of the layer-by-layer transfer method; c) Schematic diagram of the cross-section of the bonding process of the layer-by-layer transfer method; d) The cross-sectional transmission image of the composite film obtained by the layer-by-layer transfer method proves that there is a clean van der Waals interface between boron nitride and graphene.

[0050] Figure 2 The results of the hexagonal boron nitride / graphene suspended composite support film prepared in this example are characterized. Among them, a) the actual image of the hexagonal boron nitride / graphene suspended support network; b) the statistics of the integrity of the support film and the typical scanning electron microscope image; c) the statistics of the single crystallinity of the hexagonal boron nitride / graphene suspended composite support film and the typical selected area electron diffraction image; d) the typical transmission electron microscope image of the hexagonal boron nitride / graphene suspended composite support film; e) the atomic-level transmission electron microscope image of the hexagonal boron nitride / graphene suspended composite support film, showing its moiré fringe structure; f) the electron energy loss spectrum of the hexagonal boron nitride / graphene suspended composite support film, proving its elemental composition.

[0051] 2) Mechanical strength evaluation of hexagonal boron nitride / graphene suspended composite support membrane: The prepared hexagonal boron nitride / graphene suspended composite support membrane is placed in an atomic force microscope, and a diamond atomic force microscope probe (ART D160, ART D300) is used to press the center of the suspended membrane until it breaks. During this process, the deformation of the membrane and the force applied by the probe are recorded.

[0052] 3) Fracture toughness evaluation of hexagonal boron nitride / graphene suspended composite support membrane: Using molecular dynamics simulation, a hexagonal boron nitride / graphene suspended composite support membrane with a central defect was constructed, and then biaxial vertical stretching was performed to simulate its crack propagation mode. During the crack propagation process, the energy release rate was calculated as a function of the effective crack length.

[0053] Figure 3 The mechanical properties of the hexagonal boron nitride / graphene suspended composite support membrane prepared in this example are characterized. a) The fracture strength of the hexagonal boron nitride / graphene suspended composite support membrane and the double-layer graphene support membrane is tested by pressure using an atomic force microscope probe; b) The fracture toughness (fracture energy release rate J) of the hexagonal boron nitride / graphene suspended composite support membrane and the double-layer graphene support membrane is calculated by molecular dynamics simulation. Figure 3 It can be seen that the mechanical fracture strength of the hexagonal boron nitride / graphene suspended composite support film is comparable to that of the double-layer graphene support film, but its fracture energy release rate is higher than that of the double-layer graphene, showing stronger fracture toughness.

[0054] 4) Thermal shock stability evaluation of hexagonal boron nitride / graphene suspended composite support membrane: a) Build a Joule thermal shock device, including a high-power power supply (150 A, 32V), a thermal shock test chamber, a gas path (argon and gas flowmeter), a vacuum device (mechanical pump), a controller computer, etc. b) Construct a heating path, fix the two ends of the carbon cloth or carbon felt between the copper sheet and the graphite base, place a piece of alumina ceramic on the carbon cloth or carbon felt, and then place the hexagonal boron nitride / graphene suspended composite support film on the ceramic. c) Place the heating device in the experimental chamber, evacuate and purge with argon three times, and finally fill the chamber with argon at near-normal pressure. d) Set the heating program, select the time pulse mode, and determine the heating voltage, current, heating time, cooling time, and number of cycles. e) Perform multiple cycles of thermal shock experiments, and perform structural characterization after the end.

[0055] Figure 4 This is a high temperature shock stability test of the hexagonal boron nitride / graphene suspended composite support film prepared in this example. It includes: a) a typical temperature-time curve of the thermal shock high temperature stability experiment and a schematic diagram of the flash Joule heating equipment used in the test; b) stability statistics of the hexagonal boron nitride / graphene suspended composite support film at different thermal shock temperatures and cycle numbers; c) a comparison of the high temperature thermal shock integrity of the hexagonal boron nitride / graphene suspended composite support film with single-layer and double-layer graphene support films, with the highest temperature being about 1800K; d) and e) are scanning electron microscope images of the hexagonal boron nitride / graphene suspended composite support film before and after 200 high temperature thermal shocks, respectively; f) is an atomic-level scanning transmission electron microscope image of the film in e). Figure 4It can be seen that the hexagonal boron nitride / graphene suspended composite support membrane has both high mechanical strength and fracture toughness, and can maintain structural stability under repeated thermal shock conditions. 4 K / s heating rate and 1800 K impact temperature, after 200 cycles, the integrity of the hexagonal boron nitride / graphene suspended composite support membrane reached 95%.

[0056] Example 2: A hexagonal boron nitride / graphene suspended composite support membrane with both strength and toughness as a substrate for high-temperature thermal shock synthesis and a support membrane for structural characterization 1) Prepare mixed aqueous solutions of various metal salt precursors, including FeCl 2 、CoCl 3 6H 2 O、NiCl 2 , CuCl 2 6H 2 O、ZnCl 2 , PdCl 2 , H 2 PtCl 6 HAuCl 4 , the concentration of each salt is 0.002 mol / L. The mixed solution is used to synthesize high entropy alloy nanoparticles; 2) The hexagonal boron nitride / graphene suspended composite support membrane was prepared as a substrate by the same method as in Example 1, and treated in an oxygen plasma with a flow rate of 5 sccm and a power of 30 W for 30 seconds to enhance its hydrophilicity; 3) Add 0.5 μL of the above precursor solution onto the hexagonal boron nitride / graphene suspended composite support film treated in step 2) and dry it at room temperature.

[0057] 4) The whole device was placed in a flash Joule heating device and subjected to three 30 ms thermal shocks at 90 A and 32 V. The highest temperature of the thermal shock was about 1600~1700 K, and the cooling time of each thermal shock was 1970 ms.

[0058] 5) Structural and elemental characterization using scanning transmission electron microscopy.

[0059] Figure 5The application of hexagonal boron nitride / graphene suspended composite support membrane as a substrate for high-temperature thermal shock synthesis and a support membrane for structural characterization is demonstrated. a) Scanning transmission electron microscope image of high entropy alloy nanoparticles on hexagonal boron nitride-graphene suspended composite support membrane; b) Contrast intensity map of the white line area in a, reflecting the low background noise of the hexagonal boron nitride / graphene suspended composite support membrane; c) Diameter distribution map of high entropy alloy nanoparticles, the inset is an image of the statistical range; d) High-resolution scanning transmission electron microscope image of high entropy alloy nanoparticles, the inset is a fast Fourier transform map; e) Element distribution map of high entropy alloy nanoparticles.

[0060] The present invention has been described in detail above. It will be apparent to those skilled in the art that the present invention may be implemented in a wide range under equivalent parameters, concentrations and conditions without departing from the spirit and scope of the present invention and without the need for unnecessary experimentation. Although the present invention provides specific embodiments, it should be understood that further improvements may be made to the present invention. In short, according to the principles of the present invention, this application intends to include any changes, uses or improvements to the present invention, including changes made by conventional techniques known in the art that depart from the scope disclosed in this application. Applications of some of the basic features may be made within the scope of the following appended claims.

Claims

1. A method for preparing a hexagonal boron nitride / graphene suspended composite support membrane having both strength and toughness, comprising the following steps: 1) placing a graphene grid on a hexagonal boron nitride / substrate so that one side of the graphene in the graphene grid contacts the hexagonal boron nitride, dripping a volatile organic liquid until the entire surface of the hexagonal boron nitride is covered, and waiting for the volatile organic liquid to dry; 2) placing the structure obtained in step 1) in an etching solution to remove the substrate in the hexagonal boron nitride / substrate, and obtaining the hexagonal boron nitride / graphene suspended composite support membrane after washing and drying.

2. The method according to claim 1, characterized in that: In the step 1), the hexagonal boron nitride / substrate is selected from at least one of the following: sapphire wafer-copper-nickel alloy-hexagonal boron nitride, sapphire wafer-copper-hexagonal boron nitride, sapphire wafer-nickel-hexagonal boron nitride, copper foil-hexagonal boron nitride, copper-nickel alloy foil-hexagonal boron nitride, nickel foil-hexagonal boron nitride; And / or, in the step 1), the hexagonal boron nitride is single crystal, twin crystal or polycrystalline hexagonal boron nitride; And / or, in the step 1), the number of layers of the hexagonal boron nitride is a single layer, a double layer or 3-10 layers.

3. The method according to claim 1 or 2, characterized in that: In the step 1), the volatile organic liquid is selected from at least one of isopropanol, ethanol and acetone; and the drying time of the volatile organic liquid is 2 min to 30 min.

4. The method according to any one of claims 1 to 3, characterized in that: In the step 1), the graphene grid is a graphene suspended support membrane prepared by using graphene as raw material and using an electron microscope grid with a porous membrane.

5. The method according to claim 4, characterized in that: The graphene raw materials include graphene grown on foil and graphene grown on wafer; the types of the foil and wafer include copper, copper-nickel alloy and nickel; And / or, the number of layers of the graphene is a single layer, a double layer, or a few layers of 3-5 layers.

6. The method according to any one of claims 1 to 5, characterized in that: In the step 2) of etching, the etching solution is ammonium persulfate, sodium persulfate or ferric chloride; And / or, the concentration of the etching solution is 0.1 mol / L to a saturated solution; And / or, the etching temperature is 0°C to 60°C; And / or, the etching time is 5 to 100 minutes; And / or, in the washing step, the washing method is washing in water and an organic solvent in sequence; the washing time in water is 0.1 to 5 h; the washing time in the organic solvent is 0.5 to 5 min; And / or, the drying time is 5 to 100 min.

7. The method according to any one of claims 1 to 5, characterized in that: The method further includes: the method further includes: repeating step 1) and step 2) at least once, or replacing the hexagonal boron nitride / substrate in step 1) and step 2) with graphene / substrate to prepare a boron nitride and graphene composite structure with a stacking layer number greater than or equal to three layers.

8. A hexagonal boron nitride / graphene suspended composite support membrane prepared by the method of any one of claims 1 to 6.

9. The boron nitride and graphene composite structure having a stacking layer number greater than or equal to three layers prepared by the method of claim 7.

10. Application of the hexagonal boron nitride / graphene suspended composite support membrane described in claim 8 or the boron nitride and graphene composite structure with three or more stacked layers described in claim 9 in at least one of the following aspects: high temperature synthesis, thermal shock synthesis, correlated electron microscopy characterization, high temperature sensing, thermal electron luminescence, and proton-ion screening.

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