A method for preparing two-dimensional ultrathin hexagonal boron nitride nanosheets

Abstract

The application discloses a preparation method of two-dimensional ultrathin hexagonal boron nitride nanosheets, which comprises the following steps: placing a substrate at one end of a reaction furnace cavity and placing a boron-nitrogen precursor in a high-temperature zone of the reaction furnace cavity, introducing a reducing carrier gas into the cavity to replace the internal air, and closing valves at the gas inlet end and the gas outlet end; the reaction furnace is heated to a gas deposition temperature, the substrate is pushed and pulled to be placed above the boron-nitrogen precursor to form a micro-reaction space, and the substrate is kept warm and deposited for a period of time; after the growth is completed, the substrate and the boron-nitrogen precursor are pushed to the one end of the reaction furnace cavity, and after the temperature of the cavity is reduced to room temperature, the substrate with the two-dimensional ultrathin hexagonal boron nitride nanosheet deposited and grown thereon is taken out. The two-dimensional ultrathin hexagonal boron nitride nanosheet prepared by the method is a high-quality crystal and has excellent environmental and chemical stability, thereby laying a foundation for the research and application of the two-dimensional ultrathin hexagonal boron nitride nanosheet in the fields of electronic devices, optoelectronic devices, high-strength thin films, high-transmittance thin films, high-thermal-conductivity thin films, high-dielectric thin films and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of synthesis of two-dimensional materials, and particularly relates to a preparation method of two-dimensional ultrathin hexagonal boron nitride nanosheets. BACKGROUND

[0002] The successful exfoliation of graphene opened the door to the research of two-dimensional materials. Two-dimensional materials have broad application prospects in the fields of electronics, optoelectronics, information, energy, environment, aerospace, etc. due to their excellent electrical, optical, thermal and mechanical properties. Hexagonal boron nitride is a two-dimensional material similar to graphene. Both of them belong to hexagonal system, and their lattice constants and layer thicknesses are very similar. Therefore, hexagonal boron nitride is also known as white graphene. However, the physical and chemical properties of hexagonal boron nitride and graphene are completely different. Single-layer graphene is a semi-metal, while hexagonal boron nitride is an insulator. This means that hexagonal boron nitride can be used as a tunnel barrier layer, as a UV light emitting source, and as an epitaxial growth substrate for other two-dimensional layered materials. The emergence of hexagonal boron nitride not only enriches the physical and chemical properties in the field of two-dimensional materials, but also can be used to stack with other two-dimensional materials to form electronic devices with novel properties. However, although the chemical vapor deposition method of two-dimensional hexagonal boron nitride has been widely studied, the long growth time, single growth substrate, and high risk and environmental unfriendliness of the precursor limit the large-area preparation of two-dimensional hexagonal boron nitride film, hindering its wide application. Therefore, the present application provides a preparation method of two-dimensional ultrathin hexagonal boron nitride nanosheets to solve the above technical problems. SUMMARY

[0003] The purpose of the present application is to overcome the defects in the prior art and provide a preparation method of two-dimensional ultrathin hexagonal boron nitride nanosheets. The method can use various metal and non-metal materials as growth substrates, and use boron-nitrogen precursors that can volatilize or decompose boron-nitrogen elements. By using a simple vapor deposition method in a normal pressure high-temperature static reducing atmosphere, the method realizes the rapid preparation of large-size two-dimensional ultrathin hexagonal boron nitride nanosheets with uniform thickness. The prepared two-dimensional ultrathin hexagonal boron nitride nanosheets can be further transferred to any substrate. The two-dimensional ultrathin hexagonal boron nitride nanosheet preparation method of the present application has the characteristics of simple and fast preparation process, easy control of product thickness and size, easy large-area film preparation, and environmental friendliness. The two-dimensional ultrathin hexagonal boron nitride nanosheet preparation method of the present application obtains two-dimensional ultrathin hexagonal boron nitride nanosheets which are high-quality crystals with excellent environmental and chemical stability. This lays a foundation for the research and application of two-dimensional ultrathin hexagonal boron nitride nanosheets in the fields of electronic devices, optoelectronic devices, high-strength films, high-transparency films, high-thermal-conductivity films, high-dielectric films, etc.

[0004] To achieve the above object, the technical scheme of the present application is to design a preparation method of two-dimensional ultrathin hexagonal boron nitride nanosheet, comprising the following steps:

[0005] S1: placing the substrate at one end of the reaction furnace cavity, placing the boron-nitrogen precursor in the high-temperature zone of the reaction furnace cavity, opening the valves at the gas inlet and outlet ends of the reaction furnace, introducing a reducing carrier gas into the interior of the reaction furnace cavity to replace the air inside, then stopping the introduction of the carrier gas, and closing the valves at the gas inlet and outlet ends of the reaction furnace;

[0006] S2: raising the temperature of the reaction furnace to a vapor deposition temperature, then pushing and pulling the substrate to be placed above the boron-nitrogen precursor to form a micro-reaction space, and depositing and growing for a period of time under heat preservation;

[0007] S3: after the deposition and growth under heat preservation is completed, pushing and pulling the substrate and the boron-nitrogen precursor together from the high-temperature zone of the reaction furnace cavity to one end, and after the temperature of the reaction furnace cavity is reduced to room temperature, taking out the substrate with the two-dimensional ultrathin hexagonal boron nitride nanosheet deposited and grown thereon from the reaction furnace.

[0008] In the preferred technical scheme, in step S1, the substrate material is one of copper, nickel, gold, platinum, iron, silicon dioxide, silicon, aluminum oxide, mica, and gallium nitride, the shape of the substrate is sheet-shaped, powder-shaped, or foamed porous, the boron-nitrogen precursor is hexagonal boron nitride or cubic boron nitride, the shape of the boron-nitrogen precursor is powder-shaped or sheet-shaped, the particle size range of the powder-shaped boron-nitrogen precursor is 20 nm to 200 µm, and the carrier gas is hydrogen or a mixture of hydrogen and inert gas, wherein the volume percentage of hydrogen is ≥10%.

[0009] In the further preferred technical scheme, in step S1, the particle size range of the powder-shaped boron-nitrogen precursor is 100 nm to 50 µm, and when the carrier gas is a mixture of hydrogen and inert gas, the volume percentage of hydrogen is 50% to 100%.

[0010] In the preferred technical scheme, in step S2, the vapor deposition temperature is 600 to 1200 °C, the heat preservation deposition and growth time is 1 to 1200 min, and the micro-reaction space distance between the substrate and the boron-nitrogen precursor is 0.5 to 10 mm.

[0011] In the further preferred technical scheme, in step S2, the vapor deposition temperature is 900 to 1100 °C, the heat preservation deposition and growth time is 1 to 240 min, and the micro-reaction space distance between the substrate and the boron-nitrogen precursor is 0.5 to 5 mm.

[0012] In the preferred technical scheme, in step S3, the cooling rate of the reaction furnace cavity is 10 to 600 °C / min.

[0013] Further preferred technical solutions are that in the step S3, the temperature decreasing speed of the reaction furnace cavity is 200-600 DEG C / min.

[0014] The advantages and beneficial effects of the present application are that:

[0015] 1. The preparation method of the two-dimensional ultrathin hexagonal boron nitride nanosheet in the present application has the advantages of uniform structure, high crystal quality, excellent environmental, chemical, thermal stability and mechanical properties, and lays a foundation for the research and application of the two-dimensional ultrathin hexagonal boron nitride nanosheet in the fields of electronic devices, optoelectronic devices, high-strength thin films, high-transparency thin films, high-thermal-conductivity thin films, high-dielectric thin films, etc.

[0016] 2. The preparation method of the two-dimensional ultrathin hexagonal boron nitride nanosheet in the present application has the advantages of rapid preparation, simple operation, easy control and easy large-area preparation, and can obtain two-dimensional ultrathin hexagonal boron nitride nanosheets or large-area thin films of different thicknesses on various metal or non-metal substrates.

[0017] 3. The preparation method of the two-dimensional ultrathin hexagonal boron nitride nanosheet in the present application does not use common boron-nitrogen precursor hazardous chemicals such as ammonia (flammable and explosive), boron trichloride (BCl3, toxic), ammonia borane (toxic), borazine (explosive and toxic), etc., but uses boron nitride with high stability, non-toxicity and no toxic waste gas as the boron-nitrogen precursor, and the boron nitride precursor has low material cost, low temperature control requirement and high operation fault tolerance, which is conducive to large-scale industrialized preparation of the two-dimensional ultrathin hexagonal boron nitride nanosheet.

[0018] 4. The preparation method of the two-dimensional ultrathin hexagonal boron nitride nanosheet in the present application fills the reaction furnace cavity with non-flowing static reducing atmosphere (note: the static reducing atmosphere here means that after the reaction furnace cavity is filled with a reducing carrier gas atmosphere, the valves at the inlet and outlet of the reaction furnace are closed, no carrier gas is continuously introduced from the outside during the deposition and growth process, and no gas is discharged outside, and the reducing atmosphere in the reaction furnace cavity itself is still affected by the temperature gradient and flows in a small range in the reaction furnace cavity), which avoids the disadvantage that the flowing reducing atmosphere easily blows away the boron-nitrogen precursor, greatly improves the concentration of the boron-nitrogen precursor near the growth substrate, and thus promotes the increase of the growth speed of the two-dimensional ultrathin hexagonal boron nitride nanosheet; in addition, the presence of hydrogen in the reducing atmosphere makes the boron-nitrogen precursor at high temperature easy to produce volatile BH x and NH xThe gaseous source further increases the concentration of the boron-nitrogen precursor, which is beneficial to the rapid preparation of the two-dimensional ultra-thin hexagonal boron nitride nanosheet. Due to the high concentration of the boron-nitrogen precursor in the static reducing atmosphere, the high-quality two-dimensional ultra-thin hexagonal boron nitride nanosheet can also be grown on a non-metallic substrate, which is a result that cannot be obtained by previous research.

[0019] 5. The preparation method of the two-dimensional ultra-thin hexagonal boron nitride nanosheet provided by the application has a very fast deposition and growth speed, and high-quality two-dimensional ultra-thin hexagonal boron nitride nanosheets can be prepared in only 1 minute, which is beneficial to the large-scale industrialized preparation of the two-dimensional ultra-thin hexagonal boron nitride nanosheet.

[0020] 6. The preparation method of the two-dimensional ultra-thin hexagonal boron nitride nanosheet provided by the application can prepare hexagonal boron nitride nanosheets with a micron-level thickness through parameter adjustment, which lays a foundation for expanding the application range of two-dimensional materials. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a schematic diagram of an experimental device for growing the two-dimensional ultra-thin hexagonal boron nitride nanosheet by the vapor deposition method and a schematic diagram of the operation steps of the preparation method of the two-dimensional ultra-thin hexagonal boron nitride nanosheet provided by the application;

[0022] Figure 2 is an optical microscope photo of the two-dimensional ultra-thin hexagonal boron nitride nanosheet prepared in Examples 1-4 on a substrate, Figure 2 (a) of corresponds to Example 1, Figure 2 (b) of corresponds to Example 3, Figure 2 (c) of corresponds to Example 4, Figure 2 (d) of corresponds to the optical microscope photo of the two-dimensional ultra-thin hexagonal boron nitride nanosheet prepared in Example 2 and transferred to the SiO2 / Si substrate;

[0023] Figure 3 (a) of is an atomic force microscope photo of the two-dimensional ultra-thin hexagonal boron nitride nanosheet prepared in Example 1;

[0024] Figure 3 The curve in (b) is a thickness curve of the two-dimensional ultra-thin hexagonal boron nitride nanosheet prepared in Example 1 measured by an atomic force microscope;

[0025] Figure 3 (c) of is an atomic force microscope photo of the two-dimensional ultra-thin hexagonal boron nitride nanosheet prepared in Example 7;

[0026] Figure 3 The curve in (d) is a thickness curve of the two-dimensional ultra-thin hexagonal boron nitride nanosheet prepared in Example 7 measured by an atomic force microscope;

[0027] Figure 3(e) is an optical microscope image of the two-dimensional ultrathin hexagonal boron nitride nanosheets prepared in Example 8;

[0028] Figure 3 The curve in (f) is the thickness curve of the two-dimensional ultrathin hexagonal boron nitride nanosheets prepared in Example 8, measured by a step tester;

[0029] Figure 4 The Raman spectrum of the two-dimensional ultrathin hexagonal boron nitride nanosheets prepared in Example 1;

[0030] Figure 5 (a) is a transmission electron micrograph of the two-dimensional ultrathin hexagonal boron nitride nanosheets prepared in Example 1;

[0031] Figure 5 (b) is Figure 5 The electron diffraction pattern of the sample in the area selected in (a);

[0032] Figure 6 (a) is an optical microscope image of the two-dimensional ultrathin hexagonal boron nitride nanosheets prepared in Exercise 5 on the substrate;

[0033] Figure 6 (b) is an optical microscope image of the two-dimensional ultrathin hexagonal boron nitride nanosheets prepared in Exercise 6 on the substrate.

[0034] In the diagram: 1. Carrier gas inlet; 2. Substrate; 3. Crucible; 4. Heating element in the high-temperature zone of the reactor; 5. Boron-nitrogen precursor; 6. Quartz tube; 7. Carrier gas outlet. Detailed Implementation

[0035] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1

[0037] like Figure 1 As shown, the method of the present invention for preparing two-dimensional ultrathin hexagonal boron nitride nanosheets includes the following steps:

[0038] S1: A quartz tube 6 (quartz tube diameter of 22 mm, reaction zone length of 20 mm) is installed in a horizontal reaction furnace, one end of the horizontal reaction furnace is provided with a carrier gas inlet 1, the other end is provided with a carrier gas outlet 7, a growth substrate 2 (copper foil with a size of 10 mm x 10 mm x 10 microns, purity of 99.9999 wt%) is placed at one end of the cavity of the quartz tube 6, a boron-nitrogen precursor 5 (50 mg, hexagonal boron nitride powder with a particle size of 10 microns, purity of 99.9 wt%) is placed in a crucible 3, and the crucible 3 is located in the high-temperature zone of the cavity of the horizontal reaction furnace; pure hydrogen gas is introduced into the cavity of the quartz tube 6 as a reducing atmosphere, and after the hydrogen atmosphere in the quartz tube 6 is filled, the valves at the carrier gas inlet 1 and the carrier gas outlet 7 are closed to ensure that no external atmosphere enters and no internal gas is discharged (see Figure 1 (a) of FIG. 1;

[0039] S2: The quartz tube 6 of the horizontal reaction furnace is heated to 1070°C (heating rate of 20°C / min), when the furnace temperature reaches 1070°C, the substrate 2 (copper foil) is pushed to the high-temperature zone of the cavity of the horizontal reaction furnace and located directly above the boron-nitrogen precursor 5 by using a push-pull device, so that the lower surface of the copper foil is spaced apart from the upper surface of the boron-nitrogen precursor 5 (hexagonal boron nitride powder) by 0.5 mm, and the growth of two-dimensional ultrathin hexagonal boron nitride nanosheets is started, and the growth time is 1 minute (see Figure 1 (b) of FIG. 1;

[0040] S3: After the deposition growth is completed, the growth substrate 2 and the crucible 3 loaded with the boron-nitrogen precursor 5 are pushed out together to one end of the cavity of the quartz tube 6 by using the push-pull device, and then cooled to room temperature at a speed of 500°C / min, and then the substrate 2 on which the two-dimensional ultrathin hexagonal boron nitride nanosheets are deposited is taken out of the reaction furnace, and the copper foil surface on which the two-dimensional ultrathin hexagonal boron nitride nanosheets are grown and deposited (see Figure 1 (c) of FIG. 1.

[0041] Figure 2 (a) of FIG. 2 is an optical microscope photo of the copper foil surface on which the two-dimensional ultrathin hexagonal boron nitride nanosheets are grown and deposited prepared in Example 1, and from Figure 2 (a) of FIG. 2, it can be seen that the two-dimensional ultrathin hexagonal boron nitride nanosheets grown and deposited on the copper foil surface are high-quality crystals, and present a regular triangle shape, and the average size is 1 micron.

[0042] Figure 3 (a) of FIG. 3 is an atomic force microscope photo of the copper foil surface on which the two-dimensional ultrathin hexagonal boron nitride nanosheets are grown and deposited prepared in Example 1, Figure 3 the curve in (b) of FIG. 3 is a thickness curve of the two-dimensional ultrathin hexagonal boron nitride nanosheets prepared in Example 1 measured by an atomic force microscope, and from Figure 3As can be seen in (b) of FIG. 1, the thickness of the two-dimensional ultra-thin hexagonal boron nitride nanosheet deposited on the surface of the copper foil is 0.4 nm, i.e. a single-layer two-dimensional crystal of hexagonal boron nitride.

[0043] Figure 4 FIG. 2 is a Raman spectrum of the two-dimensional ultra-thin hexagonal boron nitride nanosheet prepared in Example 1, and the peak position thereof proves that it is a single-layer boron nitride crystal.

[0044] Figure 5 (a) of FIG. 3 is a transmission electron microscopy photograph of the two-dimensional ultra-thin hexagonal boron nitride nanosheet prepared in Example 1, Figure 5 (b) of FIG. 3 is Figure 5 (a) of FIG. 4 is an electron diffraction pattern of the boxed region sample in (a) of FIG. 4, showing that the sample is a high-quality single crystal.

[0045] Example 2

[0046] As shown in FIG. 5, the preparation of the two-dimensional ultra-thin hexagonal boron nitride nanosheet by the method of the present application comprises the following operation steps: Figure 1 S1: A quartz tube 6 (quartz tube diameter is 22 mm, and the reaction zone length is 20 mm) is installed in a horizontal reaction furnace, one end of the horizontal reaction furnace is provided with a carrier gas inlet 1, and the other end is provided with a carrier gas outlet 7. A growth substrate 2 (copper foil with a size of 10 mm x 10 mm x 10 microns, and a purity of 99.9999 wt%) is placed at one end of the cavity of the quartz tube 6, and a boron-nitrogen precursor 5 (50 mg, hexagonal boron nitride powder with a particle size of 10 microns, and a purity of 99.9 wt%) is placed in a crucible 3, and the crucible 3 is located in the high-temperature zone of the cavity of the horizontal reaction furnace. Pure hydrogen gas is introduced into the cavity of the quartz tube 6 as a reducing atmosphere. After the hydrogen atmosphere is filled in the quartz tube 6, the valves at the carrier gas inlet 1 and the carrier gas outlet 7 are closed to ensure that no external atmosphere enters and no internal gas is discharged (see

[0047] a) of FIG. 6; Figure 1 S2: The quartz tube 6 of the horizontal reaction furnace is heated to 1070°C (the heating rate is 20°C / min), and when the furnace temperature reaches 1070°C, the substrate 2 (copper foil) is pushed to the high-temperature zone of the cavity of the horizontal reaction furnace and located directly above the boron-nitrogen precursor 5 by using a push-pull device, so that the lower surface of the copper foil is spaced apart from the upper surface of the boron-nitrogen precursor 5 (hexagonal boron nitride powder) by 2 mm. The growth of the two-dimensional ultra-thin hexagonal boron nitride nanosheet is started, and the growth time is 5 minutes (see

[0048] b) of FIG. 6; Figure 1

[0049] ​S3: After the end of the growth of the deposition by keeping warm, the growth substrate 2 and the crucible 3 loaded with the boron-nitrogen precursor 5 are pushed out together to one end of the cavity of the quartz tube 6 by using the push-pull device, and then cooled to room temperature at a speed of 500℃ / min, and then the substrate 2 with the deposited two-dimensional ultra-thin hexagonal boron nitride nanosheets is taken out of the reaction furnace, and the copper foil surface is grown with the deposited two-dimensional ultra-thin hexagonal boron nitride nanosheets (see Figure 1 c) of the specification.

[0050] Figure 2 (d) of the specification is an optical microscope photo of the two-dimensional ultra-thin hexagonal boron nitride nanosheets prepared in Example 2 transferred to the SiO2 / Si substrate (the transfer step uses a mature wet transfer method, i.e. first spin-coating and solidifying an organic layer on the surface of the two-dimensional material, then using a corresponding etchant to selectively etch the corresponding substrate and use the target substrate to fish the organic layer / two-dimensional material composite film, and after drying, using an organic solvent to dissolve the organic coating to complete the transfer of the two-dimensional material), from Figure 2 As can be seen from (d) of the specification, the two-dimensional ultra-thin hexagonal boron nitride nanosheets are high-quality crystals, present a regular triangle shape, and the average size is 1μm.

[0051] The composition, crystal structure, morphology and thickness of the two-dimensional ultra-thin hexagonal boron nitride nanosheets prepared in Example 2 are characterized by using an atomic force microscope, a Raman spectrometer and a transmission electron microscope, and the results show that the obtained two-dimensional ultra-thin hexagonal boron nitride nanosheets are high-quality crystals, present a regular triangle shape, the average size is 1μm, the thickness is about 0.4nm, i.e. a single-layer hexagonal boron nitride crystal, and several nanosheets are connected together.

[0052] Example 3

[0053] As shown in Figure 1 , the method for preparing the two-dimensional ultra-thin hexagonal boron nitride nanosheets comprises the following operation steps:

[0054] S1: A quartz tube 6 (the quartz tube has a diameter of 22mm and a reaction zone length of 20mm) is installed in a horizontal reaction furnace, a carrier gas inlet 1 is arranged at one end of the horizontal reaction furnace, and a carrier gas outlet 7 is arranged at the other end of the horizontal reaction furnace, a growth substrate 2 (a copper foil with a size of 10mm×10mm×10μm and a purity of 99.9999wt%) is placed at one end of the cavity of the quartz tube 6, a boron-nitrogen precursor 5 (50mg, hexagonal boron nitride powder with a particle size of 10μm and a purity of 99.9wt%) is placed in a crucible 3, and the crucible 3 is located in the high-temperature zone of the cavity of the horizontal reaction furnace; pure hydrogen gas is introduced into the cavity of the quartz tube 6 as a reducing atmosphere, and after the hydrogen gas atmosphere is filled in the quartz tube 6, the valves at the carrier gas inlet 1 and the carrier gas outlet 7 are closed to ensure that no external atmosphere enters and no internal gas is discharged (see Figure 1 a) of the specification;

[0055] S2: The quartz tube 6 of the horizontal reaction furnace is heated to 1070℃ (the heating rate is 20℃ / min), when the furnace temperature reaches 1070℃, the substrate 2 (copper foil) is pushed to the high temperature zone of the horizontal reaction furnace cavity by the push-pull device and is located directly above the boron-nitrogen precursor 5, the lower surface of the copper foil is spaced apart from the upper surface of the boron-nitrogen precursor 5 (hexagonal boron nitride powder) by 3mm, and the growth of two-dimensional ultra-thin hexagonal boron nitride nanosheets is started, and the growth time is 12 minutes (see Figure 1 b) of FIG. 1;

[0056] S3: After the deposition growth is completed, the growth substrate 2 and the crucible 3 loaded with the boron-nitrogen precursor 5 are pushed out to the end of the cavity of the quartz tube 6 by the push-pull device, and then the deposition growth substrate 2 with two-dimensional ultra-thin hexagonal boron nitride nanosheets grown on the copper foil surface is taken out of the reaction furnace, and the copper foil surface is grown with two-dimensional ultra-thin hexagonal boron nitride nanosheets (see Figure 1 c) of FIG. 1.

[0057] Figure 2 (b) of FIG. 1 is an optical microscope photo of the copper foil surface grown with two-dimensional ultra-thin hexagonal boron nitride nanosheets prepared in Example 3, and from Figure 2 (b) of FIG. 1, it can be seen that the two-dimensional ultra-thin hexagonal boron nitride nanosheets grown on the copper foil surface are high-quality crystals, present a regular triangle shape, and the average size is 1μm.

[0058] The composition, crystal structure, morphology and thickness of the two-dimensional ultra-thin hexagonal boron nitride nanosheets prepared in Example 3 are characterized by atomic force microscopy, Raman spectroscopy and transmission electron microscopy, and the results show that the obtained two-dimensional ultra-thin hexagonal boron nitride nanosheets are high-quality crystals, present a regular triangle shape, and the average size is 1μm, and the thickness is about 0.4nm, i.e. a single-layer hexagonal boron nitride crystal, and several nanosheets are connected to each other, and the coverage rate reaches about 85%.

[0059] Example 4

[0060] As shown in Figure 1 , the method for preparing two-dimensional ultra-thin hexagonal boron nitride nanosheets according to the present application comprises the following operation steps:

[0061] S1: A quartz tube 6 (quartz tube diameter of 22 mm, reaction zone length of 20 mm) is installed in a horizontal reaction furnace, one end of the horizontal reaction furnace is provided with a carrier gas inlet 1, the other end is provided with a carrier gas outlet 7, a growth substrate 2 (copper foil with a size of 10 mm x 10 mm x 10 microns, purity of 99.9999 wt%) is placed at one end of the cavity of the quartz tube 6, and boron-nitrogen precursors 5 (50 mg, hexagonal boron nitride powder with a particle size of 10 microns, purity of 99.9 wt%) are placed in a crucible 3, and the crucible 3 is located in the high temperature zone of the cavity of the horizontal reaction furnace; pure hydrogen gas is introduced into the cavity of the quartz tube 6 as a reducing atmosphere, and after the hydrogen atmosphere in the quartz tube 6 is filled, the valves at the carrier gas inlet 1 and the carrier gas outlet 7 are closed to ensure that no external atmosphere enters and no internal gas is discharged (see Figure 1 a) of the accompanying drawings;

[0062] S2: The quartz tube 6 of the horizontal reaction furnace is heated to 1070°C (heating rate of 20°C / min), when the furnace temperature reaches 1070°C, the substrate 2 (copper foil) is pushed to the high temperature zone of the cavity of the horizontal reaction furnace and located directly above the boron-nitrogen precursors 5 by using a push-pull device, so that the lower surface of the copper foil is spaced apart from the upper surface of the boron-nitrogen precursors 5 (hexagonal boron nitride powder) by 5 mm, and the growth of two-dimensional ultra-thin hexagonal boron nitride nanosheets is started, and the growth time is 15 minutes (see Figure 1 b) of the accompanying drawings;

[0063] S3: After the deposition growth is completed, the growth substrate 2 and the crucible 3 loaded with the boron-nitrogen precursors 5 are pushed out together to one end of the cavity of the quartz tube 6 by using the push-pull device, and then cooled to room temperature at a speed of 500°C / min, and then the substrate 2 with the two-dimensional ultra-thin hexagonal boron nitride nanosheets deposited thereon is taken out of the reaction furnace, and the copper foil surface is grown with the two-dimensional ultra-thin hexagonal boron nitride nanosheets (see Figure 1 c) of the accompanying drawings.

[0064] Figure 2 (c) of the accompanying drawings is an optical microscope photo of the copper foil surface grown with the two-dimensional ultra-thin hexagonal boron nitride nanosheets prepared in Example 4, and from Figure 2 (c) of the accompanying drawings, it can be seen that the copper foil surface is grown with complete two-dimensional ultra-thin hexagonal boron nitride film, and the film size depends on the size of the growth substrate and the size of the reaction cavity.

[0065] The composition, crystal structure, morphology and thickness of the two-dimensional ultra-thin hexagonal boron nitride film prepared in Example 4 are characterized by using an atomic force microscope, a Raman spectrometer and a transmission electron microscope, and the results show that the obtained two-dimensional ultra-thin hexagonal boron nitride film is a high-quality crystal, the thickness is about 0.4 nm, i.e. a single-layer hexagonal boron nitride crystal, and several nanosheets are connected together, and the coverage rate reaches 100%.

[0066] Example 5

[0067] As Figure 1 shown, the method for preparing two-dimensional ultrathin hexagonal boron nitride nanosheets according to the present application comprises the following steps:

[0068] S1: A quartz tube 6 (quartz tube diameter of 22 mm, reaction zone length of 20 mm) is installed in a horizontal reaction furnace, a carrier gas inlet 1 is arranged at one end of the horizontal reaction furnace, and a carrier gas outlet 7 is arranged at the other end of the horizontal reaction furnace. A growth substrate 2 (nickel foil with a size of 10 mm x 10 mm x 10 microns, purity of 99.99wt%) is placed at one end of the cavity of the quartz tube 6, and a boron-nitrogen precursor 5 (50 mg, hexagonal boron nitride powder with a particle size of 10 microns, purity of 99.9wt%) is placed in a crucible 3, and the crucible 3 is located in the high-temperature zone of the cavity of the horizontal reaction furnace. Pure hydrogen gas is introduced into the cavity of the quartz tube 6 as a reducing atmosphere. After the quartz tube 6 is filled with a hydrogen atmosphere, the valves at the carrier gas inlet 1 and the carrier gas outlet 7 are closed to ensure that no external atmosphere enters and no internal gas is discharged (see Figure 1 (a) of FIG. 1);

[0069] S2: The quartz tube 6 of the horizontal reaction furnace is heated to 900°C (heating rate of 20°C / min), and when the furnace temperature reaches 900°C, the substrate 2 (nickel foil) is pushed to the high-temperature zone of the cavity of the horizontal reaction furnace and located directly above the boron-nitrogen precursor 5 (hexagonal boron nitride powder) by using a push-pull device, so that the lower surface of the nickel foil is spaced apart from the upper surface of the boron-nitrogen precursor 5 (hexagonal boron nitride powder) by 2 mm. The growth of two-dimensional ultrathin hexagonal boron nitride nanosheets is started, and the growth time is 10 minutes (see Figure 1 (b) of FIG. 1);

[0070] S3: After the deposition growth is completed, the growth substrate 2 and the crucible 3 loaded with the boron-nitrogen precursor 5 are pushed out together to one end of the cavity of the quartz tube 6 by using the push-pull device, and then cooled to room temperature at a speed of 400°C / min. Then, the substrate 2 with the two-dimensional ultrathin hexagonal boron nitride nanosheets deposited thereon is taken out of the reaction furnace. The nickel foil surface is grown with two-dimensional ultrathin hexagonal boron nitride nanosheets (see Figure 1 (c) of FIG. 1).

[0071] Figure 6 (a) of FIG. 1 is an optical microscope photo of the nickel foil surface grown with two-dimensional ultrathin hexagonal boron nitride nanosheets prepared in Example 5. As can be seen from Figure 6 (a) of FIG. 1, the two-dimensional ultrathin hexagonal boron nitride nanosheets grown on the nickel foil surface are high-quality crystals, present a regular triangle shape, and have an average size of 8 microns.

[0072] The composition, crystal structure, morphology and thickness of the two-dimensional ultrathin hexagonal boron nitride nanosheets prepared in Example 5 were characterized by atomic force microscopy, Raman spectrometer and transmission electron microscopy. The results show that the obtained two-dimensional ultrathin hexagonal boron nitride nanosheets are high-quality crystals, present a regular triangle shape, have an average size of 8 μm, and a thickness of about 0.4 nm, i.e. a single-layer hexagonal boron nitride crystal. Moreover, several nanosheets are connected to each other, and the coverage is about 50%.

[0073] Example 6

[0074] As shown in Figure 1 , the preparation of two-dimensional ultrathin hexagonal boron nitride nanosheets by the method of the present application comprises the following operation steps:

[0075] S1: A quartz tube 6 (quartz tube diameter of 22 mm, reaction zone length of 20 mm) is installed in a horizontal reaction furnace, a carrier gas inlet 1 is arranged at one end of the horizontal reaction furnace, and a carrier gas outlet 7 is arranged at the other end. A growth substrate 2 (10 mm x 10 mm x 10 μm of silicon dioxide, purity of 99.9999 wt%) is placed at one end of the cavity of the quartz tube 6, a boron-nitrogen precursor 5 (50 mg, hexagonal boron nitride powder with a particle size of 10 μm, purity of 99.9 wt%) is placed in a crucible 3, and the crucible 3 is located in the high-temperature zone of the cavity of the horizontal reaction furnace. Pure hydrogen gas is introduced into the cavity of the quartz tube 6 as a reducing atmosphere. After the quartz tube 6 is filled with a hydrogen atmosphere, the valves at the carrier gas inlet 1 and the carrier gas outlet 7 are closed to ensure that no external atmosphere enters and no internal gas is discharged (see Figure 1 a) of the drawings;

[0076] S2: The quartz tube 6 of the horizontal reaction furnace is heated to 600 ℃ (heating rate of 20 ℃ / min). When the furnace temperature reaches 600 ℃, the substrate 2 (silicon dioxide) is pushed to the high-temperature zone of the cavity of the horizontal reaction furnace and located directly above the boron-nitrogen precursor 5 (hexagonal boron nitride powder) by using a push-pull device, so that the lower surface of the silicon dioxide is spaced apart from the upper surface of the boron-nitrogen precursor 5 by 10 mm. The growth of two-dimensional ultrathin hexagonal boron nitride nanosheets is started, and the growth time is 60 minutes (see Figure 1 b) of the drawings;

[0077] S3: After the deposition growth is completed, the growth substrate 2 and the crucible 3 loaded with the boron-nitrogen precursor 5 are pushed out together to one end of the cavity of the quartz tube 6 by using the push-pull device, and then cooled to room temperature at a rate of 200 ℃ / min. Then, the substrate 2 on which the two-dimensional ultrathin hexagonal boron nitride nanosheets are deposited is taken out of the reaction furnace. The two-dimensional ultrathin hexagonal boron nitride nanosheets are grown and deposited on the surface of the silicon dioxide (see Figure 1 c) of the drawings.

[0078] Figure 6(b) is an optical microscope image of the silica surface grown and deposited with two-dimensional ultrathin hexagonal boron nitride nanosheets prepared in Example 6. Figure 6 As can be seen in (b), the two-dimensional ultrathin hexagonal boron nitride nanosheets grown and deposited on the silica surface are high-quality crystals, exhibiting an equilateral triangle shape, with an average size of 10 μm.

[0079] The composition, crystal structure, morphology and thickness of the two-dimensional ultrathin hexagonal boron nitride nanosheets prepared in Example 5 were characterized by atomic force microscopy, Raman spectroscopy and transmission electron microscopy. The results showed that the obtained two-dimensional ultrathin hexagonal boron nitride nanosheets were high-quality crystals, exhibiting equilateral triangles, with an average size of 10 μm and a thickness of about 0.4 nm, i.e., monolayer hexagonal boron nitride crystals, and several nanosheets were interconnected, with a coverage of about 70%.

[0080] Example 7

[0081] like Figure 1 As shown, the method of the present invention for preparing two-dimensional ultrathin hexagonal boron nitride nanosheets includes the following steps:

[0082] S1: A quartz tube 6 (22 mm in diameter, 20 mm in reaction zone length) is installed in a horizontal reactor. One end of the horizontal reactor has a carrier gas inlet 1, and the other end has a carrier gas outlet 7. The growth substrate 2 (10 mm × 10 mm × 10 μm nickel foil, 99.99 wt% purity) is placed at one end of the cavity of the quartz tube 6. The boron-nitrogen precursor 5 (100 mg, 150 nm hexagonal boron nitride powder, 99.9 wt% purity) is placed in the crucible 3, which is positioned in the high-temperature zone of the horizontal reactor cavity. Pure hydrogen gas is introduced into the cavity of the quartz tube 6 as a reducing atmosphere. After the quartz tube 6 is filled with hydrogen gas, the valves at the carrier gas inlet 1 and the carrier gas outlet 7 are closed to ensure that no external atmosphere enters and no internal gas is discharged (see [reference]). Figure 1 a);

[0083] S2: The quartz tube 6 of the horizontal reactor is heated to 1200℃ (heating rate is 20℃ / min). When the furnace temperature reaches 1200℃, the substrate 2 (nickel foil) is pushed into the high-temperature zone of the horizontal reactor cavity using a push-pull device and positioned directly above the boron-nitrogen precursor 5, so that the distance between the lower surface of the nickel foil and the upper surface of the boron-nitrogen precursor 5 (hexagonal boron nitride powder) is 1mm. The growth of two-dimensional ultrathin hexagonal boron nitride nanosheets begins, with a growth time of 10 minutes (see [link]). Figure 1 b);

[0084] S3: After the end of the growth of the deposition by keeping warm, the growth substrate 2 and the crucible 3 loaded with the boron-nitrogen precursor 5 are pushed out together to one end of the cavity of the quartz tube 6 by using the push-pull device, and then cooled to room temperature at a speed of 600 ℃ / min, and then the substrate 2 with the deposition of the two-dimensional ultra-thin hexagonal boron nitride nanosheet is taken out of the reaction furnace, and the two-dimensional ultra-thin hexagonal boron nitride nanosheet is grown and deposited on the surface of the nickel foil (see Figure 1 (c) of FIG. 8.

[0085] Figure 3 (c) of FIG. 8 is an atomic force microscope photo of the two-dimensional ultra-thin hexagonal boron nitride nanosheet grown and deposited on the surface of the nickel foil prepared in Example 7, Figure 3 (d) of FIG. 8 is a curve of the thickness of the two-dimensional ultra-thin hexagonal boron nitride nanosheet prepared in Example 7 measured by the atomic force microscope, Figure 3 It can be seen from (d) of FIG. 8 that the thickness of the two-dimensional ultra-thin hexagonal boron nitride nanosheet grown and deposited on the surface of the nickel foil is 0.8 nm, that is, a double-layer hexagonal boron nitride two-dimensional crystal.

[0086] The composition, crystal structure, morphology and thickness of the two-dimensional ultra-thin hexagonal boron nitride nanosheet prepared in Example 7 are characterized by using an optical microscope, a Raman spectrometer and a transmission electron microscope, and the results show that the obtained two-dimensional ultra-thin hexagonal boron nitride nanosheet is a high-quality crystal, presents a regular triangle, has an average size of 10 μm, and has a thickness of about 0.8 nm, that is, a double-layer hexagonal boron nitride crystal, and a plurality of nanosheets are connected to each other.

[0087] Example 8

[0088] As shown in Figure 1 , the method for preparing the two-dimensional ultra-thin hexagonal boron nitride nanosheet according to the present application comprises the following operation steps:

[0089] S1: A quartz tube 6 (the quartz tube has a diameter of 22 mm and a reaction zone length of 20 mm) is installed in a horizontal reaction furnace, a carrier gas inlet 1 is arranged at one end of the horizontal reaction furnace, and a carrier gas outlet 7 is arranged at the other end of the horizontal reaction furnace, a growth substrate 2 (a copper foil with a size of 10 mm×10 mm×10 μm and a purity of 99.9999 wt%) is placed at one end of the cavity of the quartz tube 6, a boron-nitrogen precursor 5 (50 mg of hexagonal boron nitride powder with a particle size of 10 μm and a purity of 99.9 wt%) is placed in a crucible 3, and the crucible 3 is located in a high-temperature zone of the cavity of the horizontal reaction furnace; pure hydrogen gas is introduced into the cavity of the quartz tube 6 as a reducing atmosphere, and after the hydrogen gas atmosphere is filled in the quartz tube 6, the valves at the carrier gas inlet 1 and the carrier gas outlet 7 are closed to ensure that no external atmosphere enters and no internal gas is discharged (see Figure 1 (a) of FIG. 7;

[0090] S2: The quartz tube 6 of the horizontal type reaction furnace is heated to 1080℃ (the heating rate is 20℃ / min), when the furnace temperature reaches 1070℃, the substrate 2 (copper foil) is pushed to the high temperature zone of the horizontal type reaction furnace cavity by the push-pull device and is located directly above the boron-nitrogen precursor 5, the lower surface of the copper foil is spaced apart from the upper surface of the boron-nitrogen precursor 5 (hexagonal boron nitride powder) by 10mm, and the growth of two-dimensional ultra-thin hexagonal boron nitride nanosheets is started, and the growth time is 20 hours (see Figure 1 b) of FIG. 1;

[0091] S3: After the deposition growth is completed, the growth substrate 2 and the crucible 3 loaded with the boron-nitrogen precursor 5 are pushed out to the end of the cavity of the quartz tube 6 by the push-pull device, and then the substrate 2 with the two-dimensional ultra-thin hexagonal boron nitride nanosheets grown and deposited on the surface of the copper foil is taken out from the reaction furnace, and the copper foil surface with the two-dimensional ultra-thin hexagonal boron nitride nanosheets grown and deposited thereon (see Figure 1 c) of FIG. 1.

[0092] Figure 3 (e) of FIG. 1 is an optical microscope photo of the copper foil surface with the two-dimensional ultra-thin hexagonal boron nitride nanosheets grown and deposited thereon prepared in Example 8, Figure 3 the curve in (f) of FIG. 1 is a thickness curve of the two-dimensional ultra-thin hexagonal boron nitride nanosheets prepared in Example 8 measured by a step profiler, and Figure 3 from (f) of FIG. 1, it can be seen that the thickness of the two-dimensional ultra-thin hexagonal boron nitride nanosheets grown and deposited on the copper foil surface is micron level, about 6000 layers of hexagonal boron nitride crystals.

[0093] The composition, crystal structure, morphology and thickness of the two-dimensional ultra-thin hexagonal boron nitride nanosheets prepared in Example 8 are characterized by an atomic force microscope, a Raman spectrometer and a transmission electron microscope, and the results show that the obtained two-dimensional ultra-thin hexagonal boron nitride nanosheets are high-quality crystals, present a regular triangle, the average size is 8μm, the thickness is about 2μm, about 6000 layers of hexagonal boron nitride crystals, and a plurality of nanosheets are connected together.

[0094] from (f) of FIG. 1, it can be seen that the thickness of the two-dimensional ultra-thin hexagonal boron nitride nanosheets grown and deposited on the copper foil surface is micron level, about 6000 layers of hexagonal boron nitride crystals. Figure 2 It can be seen from FIG. 1 that the two-dimensional ultra-thin hexagonal boron nitride nanosheets prepared by the method of the present application present a regular triangle, with the extension of the growth time, the regular triangle is always unchanged, and the number of nanosheets gradually increases, and finally seamlessly connects together to form a complete film. In addition, the obtained two-dimensional ultra-thin hexagonal boron nitride nanosheets can be transferred from the initial substrate surface to the surface of other substrates to expand the application range.

[0095] from (f) of FIG. 1, it can be seen that the thickness of the two-dimensional ultra-thin hexagonal boron nitride nanosheets grown and deposited on the copper foil surface is micron level, about 6000 layers of hexagonal boron nitride crystals. Figure 3As can be seen from the above, the thickness of the two-dimensional ultrathin hexagonal boron nitride nanosheet can be regulated by regulating different growth parameters, the atomic force microscope photos show that the two-dimensional ultrathin hexagonal boron nitride nanosheet prepared is smooth and flat in surface, complete in structure, and the thinnest can reach the thickness of a single-layer hexagonal boron nitride, and the step gauge characterization results show that the sample with a micron-level thickness can be obtained by adjusting the growth parameters.

[0096] As can be seen from the above, the two-dimensional ultrathin hexagonal boron nitride nanosheet prepared by the method of the present application is a high-quality hexagonal boron nitride crystal. Figure 4 As can be seen from the above, the two-dimensional ultrathin hexagonal boron nitride nanosheet prepared by the method of the present application is a high-quality hexagonal boron nitride crystal.

[0097] Figure 5 As can be seen from the above, the two-dimensional ultrathin hexagonal boron nitride nanosheet prepared by the method of the present application is a high-quality hexagonal boron nitride crystal.

[0098] As can be seen from the above, the two-dimensional ultrathin hexagonal boron nitride nanosheet prepared by the method of the present application is a high-quality hexagonal boron nitride crystal. Figure 6 As can be seen from the above, the two-dimensional ultrathin hexagonal boron nitride nanosheet prepared by the method of the present application is a high-quality hexagonal boron nitride crystal.

[0099] The two-dimensional ultrathin hexagonal boron nitride nanosheet preparation method of the present application can use various metal materials and non-metal materials as growth substrates, use boron-nitrogen precursors capable of volatilizing or decomposing boron-nitrogen elements, and realize the rapid preparation of large-size two-dimensional ultrathin hexagonal boron nitride nanosheets with uniform thickness by a simple vapor deposition method in a normal-pressure high-temperature static reducing atmosphere. The two-dimensional ultrathin hexagonal boron nitride nanosheet prepared can be further transferred to any substrate. The two-dimensional ultrathin hexagonal boron nitride nanosheet preparation method of the present application has the characteristics of simple and rapid preparation process, easy thickness and size regulation, easy large-area thin film preparation, and environmental friendliness. The two-dimensional ultrathin hexagonal boron nitride nanosheet prepared by the method of the present application is a high-quality crystal, has excellent environmental and chemical stability, and lays a foundation for its research and application in the fields of electronic devices, optoelectronic devices, high-strength thin films, high-transmittance thin films, high-thermal-conductivity thin films, high-dielectric thin films, etc.

[0100] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the technical principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.​

Claims

1. A method for preparing two-dimensional ultrathin hexagonal boron nitride nanosheets, characterized in that, It comprises the following steps: S1: the substrate is placed at one end of the reaction furnace cavity, the boron-nitrogen precursor is placed in the high temperature zone of the reaction furnace cavity, the valves at the inlet and outlet of the reaction furnace are opened, the reducing carrier gas is introduced into the interior of the reaction furnace cavity to replace the air inside, then the carrier gas is stopped, and the valves at the inlet and outlet of the reaction furnace are closed, the substrate material is one of copper, nickel, gold, platinum, iron, silicon dioxide, silicon, aluminum oxide, mica and gallium nitride, the boron-nitrogen precursor is hexagonal boron nitride or cubic boron nitride, the carrier gas is hydrogen, or a mixture of hydrogen and inert gas, wherein the volume percentage of hydrogen is greater than or equal to 10%; S2: the reaction furnace is heated to the vapor deposition temperature, then the substrate is pushed and pulled above the boron-nitrogen precursor to form a micro-reaction space, and the substrate is deposited and grown for a period of time, the micro-reaction space between the substrate and the boron-nitrogen precursor is 0.5-10mm; S3: after the deposition and growth of the substrate and the boron-nitrogen precursor are completed, the substrate and the boron-nitrogen precursor are pushed and pulled from the high temperature zone of the reaction furnace cavity to one end, and after the temperature of the reaction furnace cavity is reduced to room temperature, the substrate with two-dimensional ultra-thin hexagonal boron nitride nanosheets is taken out of the reaction furnace, and the cooling rate of the reaction furnace cavity is 200-600℃ / min.

2. The method for preparing two-dimensional ultrathin hexagonal boron nitride nanosheets as described in claim 1, characterized in that, In the step S1: the shape of the substrate is sheet, powder or foamed porous; the shape of the boron-nitrogen precursor is powder or sheet, wherein the particle size of the powder boron-nitrogen precursor is 20nm-200μm.

3. The method for preparing two-dimensional ultrathin hexagonal boron nitride nanosheets as described in claim 2, characterized in that, In the step S1: the particle size of the powder boron-nitrogen precursor is 100nm-50μm; when the carrier gas is a mixture of hydrogen and inert gas, the volume percentage of hydrogen is 50%-100%.

4. The method for preparing two-dimensional ultrathin hexagonal boron nitride nanosheets as described in claim 1, characterized in that, In the step S2: the vapor deposition temperature is 600-1200℃, and the deposition and growth time is 1-1200min.

5. The method for preparing two-dimensional ultrathin hexagonal boron nitride nanosheets as described in claim 4, characterized in that, In the step S2: the vapor deposition temperature is 900-1100℃, the deposition and growth time is 1-240min, and the micro-reaction space between the substrate and the boron-nitrogen precursor is 0.5-5mm.

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