High-ratio large-angle cornered double-layer molybdenum disulfide nanosheet and preparation method thereof

Abstract

The application discloses a high-proportion large-angle corner double-layer molybdenum disulfide nanosheet and a preparation method thereof. The preparation process of the nanosheet is as follows: sequentially placing a sulfur source and a molybdenum source in a quartz tube along an airflow direction, placing the sulfur source in a low-temperature zone and the molybdenum source in a high-temperature zone, then laying a porous material above the molybdenum source, and placing a substrate directly above the molybdenum source on which the porous material is laid; reserving air in the quartz tube, placing the quartz tube in a furnace to perform a chemical deposition reaction, and naturally cooling the furnace to room temperature after the reaction is completed, so that the high-proportion large-angle corner double-layer molybdenum disulfide nanosheet is obtained. The method uses a normal pressure chemical vapor deposition method, uses thermodynamic and kinetic regulation means, changes a growth unit step in a growth process, breaks a traditional MoS2 double-layer material steady-state growth process, reduces the growth proportion of a 0° or 60° corner system material, and finally increases the growth proportion of a non-thermodynamic stable-state double-layer corner molybdenum disulfide sample.

Description

Technical Field

[0001] This invention relates to a method for preparing bilayer molybdenum disulfide nanosheets, specifically to a high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheet and its preparation method, belonging to the field of two-dimensional semiconductor materials technology. Background Technology

[0002] Since the discovery of correlated insulating states and unconventional superconductivity in magic-angle graphene, the field of twist electronics has developed rapidly. Interlayer rotation and stacking patterns, as core degrees of freedom in two-dimensional van der Waals materials, provide key dimensions for controlling physical properties. Besides graphene and its heterostructures, moiré superlattices also exist in transition metal dichalcogenides (TMDs) and their heterostructures. Among them, moiré superlattices based on semiconductor TMDs exhibit significant advantages compared to twisted graphene systems. First, the flat bands of moiré superlattices in TMDs can be achieved under more relaxed conditions, such as twisted homojunctions within a larger rotation range (typically less than 4-5°). In contrast, twisted bilayer graphene must be precisely close to the magic angle (less than 1.1°) to produce strong correlation effects. Second, monolayer TMDs possess strong spin-orbit coupling characteristics and offer a wide range of material choices, allowing for tuning in degeneracy and lattice symmetry. The interaction of multiple degrees of freedom promises to generate a wealth of physical phenomena. Third, monolayer TMDs, as direct bandgap semiconductors, possess strong optical response characteristics, and their electronic correlations can be detected using mature optical methods such as photoluminescence and reflection spectroscopy. Therefore, the TMD moiré superlattice system has attracted widespread attention both experimentally and theoretically over the past decade.

[0003] The controllable fabrication of two-dimensional moiré superlattice materials fundamentally relies on precise control of interlayer angles. Existing fabrication methods include physical-mechanical exfoliation and dry stacking transfer, as well as chemical vapor deposition (CVD). Among these, physical-mechanical exfoliation and dry stacking transfer played a crucial role in the early stages of research, providing technical support for exploring the control mechanisms of interlayer coupling and correlated electronic states, and demonstrating significant advantages in the exploration of novel two-dimensional semiconductor corner systems and their properties. However, this method has inherent drawbacks: achieving precise corner angles is difficult; the inhomogeneity of the corner superlattice in a single device leads to poor repeatability of experimental observations; and it is prone to introducing external interference caused by additional strain or local structures. Furthermore, it faces challenges such as difficulty in controlling sample uniformity and weak controllability of interlayer coupling due to interface contamination, severely restricting its expansion in practical research and applications. The fabrication of two-dimensional TMD semiconductor bilayer systems using CVD also faces bottlenecks. Due to the high thermodynamic nucleation barrier of the corner moiré superlattice system, it is difficult to generate during the vapor deposition process. Currently, bilayer systems prepared by chemical vapor deposition (CVD) primarily utilize thermodynamically stable stacking patterns, making it difficult to fabricate thermodynamically unstable bilayer samples with corner stacking. However, corner bilayer samples prepared by CVD offer significant advantages, including high sample quality, strong interlayer coupling, and uniform Mohr's superlattice. Therefore, developing CVD methods for preparing large-area, high-quality, thermodynamically unstable samples with uniform Mohr's rotation and strong interlayer coupling is crucial for meeting the needs of various experimental techniques and applications requiring high-quality samples.

[0004] In summary, the controllable preparation and property study of molybdenum disulfide (MoS2) moiré superlattices are extremely challenging, involving many aspects such as growth mechanism, kinetic control of the preparation process and large-area sample growth. In particular, the controllable preparation of high-quality, uniformly rotated, and strongly coupled interlayer bilayer materials is still difficult to achieve with current technology. Summary of the Invention

[0005] To address the problems existing in the prior art, the first objective of this invention is to provide a high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheet. This nanosheet possesses advantages such as uniform molar rotation, strong interlayer coupling, and high quality. Statistical analysis of all bilayer molybdenum disulfide on the substrate shows that the proportion of large-angle-rotation bilayer molybdenum disulfide nanosheets obtained by the above method is 40-50%, demonstrating excellent yield.

[0006] The second objective of this invention is to provide a method for preparing high-proportion, large-angle-turn bilayer molybdenum disulfide nanosheets. This method utilizes atmospheric pressure chemical vapor deposition, employing thermodynamic and kinetic control techniques to alter the growth unit steps during the growth process. This breaks the traditional steady-state growth process of MoS2-like bilayer materials, reduces the growth ratio of 0° or 60° turn systems, and ultimately increases the growth ratio of non-thermodynamically stable bilayer-turn molybdenum disulfide samples.

[0007] To achieve the above-mentioned technical objectives, this invention provides a method for preparing high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheets, comprising:

[0008] A sulfur source and a molybdenum source are placed sequentially in a quartz tube along the airflow direction. The sulfur source is placed in the low-temperature zone and the molybdenum source is placed in the high-temperature zone. Then, a porous material is laid on top of the molybdenum source, and the substrate is placed directly above the molybdenum source with the porous material laid on it. The air inside the quartz tube is retained, and the tube is placed in a furnace for chemical deposition reaction. After the reaction is completed, the furnace is opened and the tube is allowed to cool naturally to room temperature to obtain the final product.

[0009] The chemical deposition reaction process is as follows: under the environment of continuous carrier gas supply, the high temperature zone and the low temperature zone are heated simultaneously. The low temperature zone is heated to the sulfur source evaporation temperature in one stage, and the high temperature zone is heated to the molybdenum source evaporation temperature in two stages, and the reaction is maintained at the temperature.

[0010] During the heating process in the high-temperature zone, the amount of carrier gas introduced in the first stage is less than that in the second stage.

[0011] In the technical solution provided by this invention, air is retained inside the quartz tube before heating the tube furnace, so that the carrier gas for the chemical vapor deposition reaction is a weakly oxygen-rich mixture. This atmosphere can partially oxidize the molybdenum source, forming a small amount of MoO. x As a precursor; furthermore, during the heating process in the high-temperature zone, by changing the amount of carrier introduced, airflow disturbance is generated during the reaction, thereby promoting the formation of large-angle bilayer molybdenum disulfide nanosheets.

[0012] As a preferred embodiment, the sulfur source is elemental sulfur powder, and the molybdenum source is metallic molybdenum sheet.

[0013] As a preferred embodiment, the high-temperature zone temperature is 800~1000℃, and the low-temperature zone temperature is 100~200℃. Temperature control has a significant impact on the reaction process and the morphology of the products. If the temperature is below the lower limit of the preferred range, the chemical reaction between the molybdenum source and the sulfur source is slow, and monolayer molybdenum disulfide nanosheets are easily formed. If the temperature is above the upper limit of the preferred range, the supply of molybdenum source and sulfur source is faster, and molybdenum disulfide thin films are easily formed, making it difficult to obtain corner bilayer MoS2 nanosheets.

[0014] As a preferred embodiment, the porous material is a high-temperature resistant molecular sieve with a pore size of 0.2~0.8 nm. More preferably, the pore size of the porous material is 0.5 nm. From the perspective of thermodynamic and kinetic control, the high-temperature resistant porous material acts as a disturbance to the gas flow during chemical vapor deposition. Therefore, by controlling the transition from regular laminar flow to fully random turbulent flow during the movement of gas molecules in the chemical vapor deposition process, the controllable preparation of unstable bilayer rotational MoS2 can be achieved.

[0015] As a preferred embodiment, the surface area ratio of the molybdenum source to the sulfur source is 1:0.5~1.5cm². 2 / g.

[0016] As a preferred embodiment, the mass ratio of the porous material to the sulfur source is 1:8~12.

[0017] As a preferred embodiment, the carrier gas is argon, with an injection rate of 6-18 sccm in the first stage and 30-50 sccm in the second stage during the high-temperature heating process. If the carrier gas flow rate in the first stage is lower than the lower limit of the selected range, the molybdenum sheet will be over-oxidized under high oxygen concentration, resulting in insufficient MoO2. x Excessive amounts will easily lead to the deposition of MoO on the substrate. x Nanosheets. If the carrier gas flow rate in the first stage exceeds the upper limit of the selected range, the molybdenum sheet will not oxidize sufficiently at low oxygen concentrations, resulting in insufficient MoO₂ production. x If the flow rate is insufficient, a small amount of monolayer MoS2 nanosheets will be prepared. If the carrier gas flow rate in the second stage is lower than the selected lower limit, the sulfur provided by the carrier gas will be insufficient, and MoO will easily deposit on the substrate. x Nanosheets. If the carrier gas flow rate in the second stage exceeds the upper limit of the preferred range, the sulfur source will be supplied too quickly, which will easily generate a molybdenum disulfide film and make it difficult to obtain bilayer twisted MoS2 nanosheets.

[0018] As a preferred embodiment, the heating process of the low-temperature zone is as follows: the low-temperature zone is heated from room temperature to 140-180℃ at a rate of 50-60℃ / min, and then maintained at a constant temperature.

[0019] As a preferred embodiment, the heating process in the high-temperature zone is as follows: In the first stage, the temperature is increased from room temperature to 810-850℃ at a rate of 50-60℃ / min, while increasing the carrier gas flow rate; in the second stage, the temperature is further increased to 900-950℃ at a rate of 50-60℃ / min, and held for 5-13 minutes. In the first stage, the molybdenum source is oxidized to MoO under a high oxygen concentration. x As a metal precursor, the chemical reaction at this stage is relatively slow. At the end of the first stage, most of the deposits on the SiO2 / Si substrate are monolayer MoS2 nanosheets. Within this temperature range, especially around 830℃, the MoS2 nanosheets complete the nucleation growth of the bottom layer, and some nanosheets begin to nucleate the top layer. At this time, a sudden increase in the carrier amount disturbs the nucleation of the top layer MoS2 nanosheets, causing the airflow to change instantaneously into chaotic airflow conditions. During the nucleation of the top layer MoS2, it is easy to form a double-layer stacking mode with higher stacking energy and a corner relative to the bottom layer MoS2 nanosheets.

[0020] As a preferred embodiment, the size of the molybdenum source is 3~5×1~3×0.1~0.3 mm, and the distance between its upper surface and the substrate is 6~10 mm. If the vertical distance between the substrate and the molybdenum source is greater than 10 mm, the molybdenum precursor supply is insufficient, and most of the substrate surface area is composed of small single-layer MoS2 nanosheets; if the vertical distance between the substrate and the molybdenum source is less than 6 mm, the molybdenum precursor supply is excessive, and most of the substrate surface area is composed of multilayer MoS2 nanosheets.

[0021] As a preferred embodiment, the substrate is a SiO2 / Si substrate with a total thickness of 490~510μm and a SiO2 layer thickness of 275~295μm.

[0022] The reason why the preparation method provided by this invention can controllably generate large-angle bilayer molybdenum disulfide nanosheets with high thermodynamic energy is mainly due to the following: First, this invention divides the growth process into two stages. When the nucleation and growth of the bottom nanosheets is completed, i.e., at the end of the first stage, the inert carrier gas is changed to a larger gas flow, introducing transient disturbances to the nucleation of the top nanosheets. Simultaneously, during the growth of bilayer MoS2, based on kinetic theory, a high-temperature resistant porous material is introduced to effectively reduce the supply rate of the metal precursor. In addition, during the second stage of heating and holding, i.e., the nucleation and growth of the top nanosheets, the tube furnace continuously fluctuates around the set holding temperature, which provides relatively continuous thermodynamic disturbances for the growth of bilayer molybdenum disulfide. In summary, this invention significantly improves the non-thermodynamically stable bilayer MoS2 stacking mode through thermodynamic and kinetic control, thereby stably and controllably growing large-angle bilayer molybdenum disulfide nanosheets.

[0023] The present invention also provides a high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheet, which is prepared by the method described in any one of the above methods.

[0024] As a preferred embodiment, the corner bilayer molybdenum disulfide nanosheet is composed of two stacked layers of MoS2 nanosheets, wherein the size of the top layer of molybdenum disulfide nanosheet is 3~12 μm and the size of the bottom layer of MoS2 nanosheet is 6~40 μm.

[0025] The bilayer corner MoS2 nanosheets provided by this invention are composed of two stacked MoS2 nanosheets, both of which are approximately triangular with independent crystal domains.

[0026] As a preferred embodiment, the proportion of large-angle double-layer molybdenum disulfide nanosheets in the corner double-layer molybdenum disulfide nanosheets is 40-50%.

[0027] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are as follows:

[0028] 1) The preparation method provided by the present invention uses atmospheric pressure chemical vapor deposition and thermodynamic and kinetic control methods to change the growth unit steps during the growth process, break the steady-state growth process of traditional MoS2-like bilayer materials, reduce the growth ratio of 0° or 60° corner system materials, and ultimately improve the growth ratio of non-thermodynamically stable bilayer corner molybdenum disulfide samples.

[0029] 2) The large-angle-turn bilayer molybdenum disulfide nanosheets provided by the present invention have the advantages of uniform molar rotation, strong interlayer coupling and high quality. According to statistics of all bilayer molybdenum disulfide on the substrate, the proportion of large-angle-turn bilayer molybdenum disulfide nanosheets obtained by the above method is 40~50%, which has excellent yield. Attached Figure Description

[0030] Figure 1 This is a schematic diagram illustrating the principle of the epitaxial growth of double-layer molybdenum disulfide at the growth corner in Embodiment 1 of the present invention;

[0031] Figure 2 This is a furnace temperature curve diagram from Embodiment 1 of the present invention;

[0032] Figure 3 This is an optical microscope image of the double-layered corner-rotated molybdenum disulfide nanosheets prepared in Example 1 of the present invention;

[0033] Figure 4 The Raman spectrum of the multilayer continuous molybdenum disulfide nanosheets prepared in Example 1 of this invention;

[0034] Figure 5 This is a statistical chart showing the proportions of the bilayer nanosheets prepared in Example 1 of this invention at various angles;

[0035] Figure 6 This is an optical microscope image of the large-scale double-layered corner-rotated molybdenum disulfide nanosheets prepared in Example 1 of the present invention;

[0036] Figure 7 This is an optical microscope image of the large-area double-layered corner molybdenum disulfide nanosheets prepared in Example 2 of the present invention;

[0037] Figure 8 This is an optical microscope image of the large-scale double-layered corner-rotated molybdenum disulfide nanosheets prepared in Example 3 of the present invention;

[0038] Figure 9 An optical microscope image of a small number of monolayer MoS2 nanosheets prepared in Comparative Example 1 of this invention.

[0039] Figure 10 An optical microscope image of a small number of monolayer MoS2 nanosheets prepared in Comparative Example 2 of this invention;

[0040] Figure 11 This is an optical microscope image of the monolayer MoS2 nanosheets prepared in Comparative Example 3 of this invention.

[0041] Figure 12 This is an optical microscope image of the bilayer MoS2 nanosheets prepared in Comparative Example 4 of this invention. Detailed Implementation

[0042] The invention is further illustrated below with specific implementation examples. This invention employs atmospheric pressure chemical vapor deposition, placing a molybdenum source in the isothermal zone at the center of a quartz tube and a sulfur source in the low-temperature zone upstream of the quartz tube. The inner diameter of the quartz tube used in the embodiments and comparative examples of this invention is 20 mm. The operation steps of the embodiments are as follows: Argon gas is adjusted to the preferred flow rate at the end of the holding period; the sulfur source is turned off at the end of the holding period, the furnace is opened, and the furnace is allowed to cool naturally to room temperature, thereby preparing corner-turned bilayer MoS2 nanosheets on a SiO2 / Si substrate.

[0043] Example 1

[0044] This embodiment provides a method for preparing high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheets, such as... Figure 1 As shown, the specific preparation process is as follows:

[0045] 1) Weigh 6 mg of molecular sieve powder with a pore size of 0.5 nm, place it on a molybdenum sheet with a length, width, and thickness of 5×2×0.1 mm, and place it in a porcelain boat with a length, width, and thickness of 97×14×2.4 mm as a molybdenum source; separately weigh 100 mg of sulfur powder and place it in a porcelain boat with a length, width, and thickness of 72×12×2.2 mm as a sulfur source; wherein, the sulfur source and the molybdenum source are arranged sequentially along the airflow direction, the sulfur source is placed in the low-temperature region, the molybdenum source is placed in the high-temperature region, and the SiO2 / Si substrate is placed directly above the molybdenum source, with the vertical distance controlled at 8 mm;

[0046] 2) Before the reaction begins, the quartz tube is not evacuated or replaced with an inert gas; the air inside the quartz tube is retained. In the low-temperature zone, the temperature is increased from room temperature to 160℃ at a rate of 50-60℃ / min and held at 160℃. The high-temperature zone heating consists of two stages: In the first stage, 12 sccm of argon gas is introduced into the quartz tube, and the high-temperature zone is heated from room temperature to 830℃ at a rate of 55℃ / min. In the second stage, the argon gas flow rate is adjusted to 40 sccm, and the high-temperature zone is heated from 830℃ to 910℃ at a rate of 55℃ / min, finally held at 910℃ for 8 minutes. After the holding period, the furnace is opened and allowed to cool naturally to room temperature, yielding the corner-turned bilayer MoS2 nanosheets.

[0047] Microscopic images of the corner-rotated bilayer MoS2 nanosheets obtained in this embodiment are as follows: Figure 3As shown in the figure, this embodiment yielded high-quality MoS2 nanosheets with clear boundaries. Furthermore, Raman spectroscopy analysis yielded the following results: Figure 4 As shown, at 384 cm -1 E at the location 2g The interaction is an in-plane Coulomb interaction, insensitive to rotation, and hardly changes with the rotation angle. At 407 cm... -1 A at location 1g Due to interlayer van der Waals forces, it shifts with the change in torsion angle, and when the torsion angle is greater than 8°, A 1g Mohr phonon FA in the phonon branch 1g Appeared at 411cm -1 Its wavenumber varies sinusoidally with the rotation angle within the range of 8-30°. Raman data show that the bilayer rotated MoS2 nanosheets prepared in this invention have high crystal quality, uniform molar rotation angle, and strong interlayer coupling.

[0048] Furthermore, statistical analysis was performed on the MoS2 nanosheets prepared in this embodiment at various angles, and the results are as follows: Figure 5 As shown, the proportion of double-layer samples stacked at 0° / 60° was 56.41%, while the proportion of double-layer molybdenum disulfide with large-angle turns was 43.59%. The growth results of double-layer MoS2 with large-area turns are as follows... Figure 6 As shown in the figure, statistical data indicates that the preparation method proposed in this invention can significantly increase the proportion of large-angle twisted bilayer MoS2 nanosheets in the bilayer sample.

[0049] Example 2

[0050] This embodiment 2 is basically the same as embodiment 1, except that 13 sccm of argon gas is introduced in the first stage of heating.

[0051] The method described in this embodiment yielded a large-angle-rotated bilayer MoS2 with a content of 33.9%. Microscopic images of the large-area bilayer-rotated MoS2 nanosheets are shown below. Figure 7 As shown. The results indicate that the argon flow rate during the first heating stage is a key condition for controlling the large-angle twist bilayer MoS2 nanosheets. By changing the argon flow rate during the first heating stage, the oxygen content inside the quartz tube can be adjusted, thereby controlling the supply of the metal precursor. When the argon flow rate during the first heating stage is higher than the preferred parameters in Example 1, the remaining oxygen concentration inside the quartz tube is low, reducing the probability of secondary nucleation and formation of a twist bilayer structure on the monolayer MoS2 surface. Therefore, compared to Example 1, the proportion of large-angle twist bilayer MoS2 nanosheets in Example 2 is reduced to 33.9%.

[0052] Example 3

[0053] This embodiment 3 is exactly the same as embodiment 1, except that: in the second stage of heating in the high-temperature zone, 30 sccm of argon gas is introduced into the quartz tube.

[0054] In Example 3, the proportion of large-angle-rotated bilayer MoS2 nanosheets was 31.45%. Its microscopic image is shown below. Figure 8 As shown in the figure, even a small difference in flow rate from the optimal conditions can lead to a significant change in the proportion of corner bilayer MoS2. Specifically, the second stage of heating includes precursor transport, diffusion, and adsorption reactions on the substrate surface. These processes collectively determine the growth behavior of MoS2 nanosheets. Changes in the carrier gas flow rate affect the precursor transport flux, local concentration distribution, and nucleation epitaxial growth process on the substrate surface. When the carrier gas flow rate in the second stage is reduced from 40 sccm in Example 1 to 30 sccm, the transient gas flow disturbance effect decreases, and the probability of second-layer nucleation and formation of a corner bilayer structure on the monolayer MoS2 surface decreases. Therefore, the proportion of large-angle corner bilayer MoS2 nanosheets decreases to 31.45%.

[0055] Comparative Example 1

[0056] This comparative example is exactly the same as Example 1, except that the argon gas flow rate in the first stage of the high-temperature zone heating process is 5 sccm.

[0057] This comparative method yielded a small amount of monolayer MoS2 nanosheets and a large amount of MoO2. x Nanosheets, their microscopic images are as follows Figure 9 As shown in the figure, when the argon carrier gas flow rate in the first stage is too low, the residual oxygen content in the tube is high. Excessive supply of metal precursors and insufficient sulfur supply result in an excessively high Mo / S precursor ratio, leading to excessive MoO deposition on the substrate. x With a small amount of monolayer MoS2 nanosheets, it is difficult to prepare bilayer MoS2 nanosheets under these conditions.

[0058] Comparative Example 2

[0059] This comparative example is exactly the same as Example 1, except that the argon gas flow rate in the first stage of the high-temperature zone heating process is 18 sccm.

[0060] This comparative method yielded a small number of monolayer MoS2 nanosheets, the microscopic images of which are shown below. Figure 10 As shown in the figure, due to the excessive flow rate in the first stage, the supply of metal precursor is too low and insufficient for the epitaxial growth of bilayer MoS2 in the second stage. Therefore, the substrate is 100% monolayer MoS2.

[0061] Comparative Example 3

[0062] This comparative example is exactly the same as Example 1, except that the heating process in the high-temperature zone only involves the first stage of heating.

[0063] This comparative method yielded monolayer MoS2 nanosheets, the microscopic images of which are shown below. Figure 11 As shown in the figure, when the temperature of the first stage of heating is reached, the MoS2 nanosheets have completed the nucleation growth of the bottom layer and partially started the nucleation of the top layer. The comparison shows that the optimal temperature for nucleation of the second layer is 830 °C.

[0064] Comparative Example 4

[0065] This comparative example is exactly the same as Example 1, except that the argon flow rate is not changed during the heating process in the high-temperature zone and is uniformly 12 sccm.

[0066] This comparative method yielded bilayer MoS2 nanosheets, the microscopic images of which are shown below. Figure 12 As shown in the figure, without introducing transient gas flow disturbance during the nucleation of the second layer, the second layer will be stacked at a thermodynamically stable 0° or 60° for epitaxy. This also proves that the transient gas flow disturbance in this invention reduces the high nucleation barrier of bilayer turn MoS2 in chemical vapor deposition.

Claims

1. A method for preparing high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheets, characterized in that, include: A sulfur source and a molybdenum source are placed in a quartz tube in sequence along the airflow direction. The sulfur source is placed in the low-temperature zone and the molybdenum source is placed in the high-temperature zone. Then, a porous material is laid on top of the molybdenum source and the substrate is placed directly above the molybdenum source on which the porous material is laid. The air inside the quartz tube is retained, and it is placed in a furnace for chemical deposition reaction. After the reaction is completed, the furnace is opened and the tube is allowed to cool naturally to room temperature to obtain the product. The chemical deposition reaction process is as follows: under the environment of continuous carrier gas supply, the high temperature zone and the low temperature zone are heated simultaneously. The low temperature zone is heated to the sulfur source evaporation temperature in one stage, and the high temperature zone is heated to the molybdenum source evaporation temperature in two stages, and the reaction is maintained at the temperature. During the heating process in the high-temperature zone, the amount of carrier gas introduced in the first stage is less than that in the second stage.

2. The method for preparing a high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheet according to claim 1, characterized in that: The sulfur source is elemental sulfur powder, and the molybdenum source is metallic molybdenum sheet; the temperature of the high-temperature zone is 800~1000℃, and the temperature of the low-temperature zone is 100~200℃.

3. The method for preparing a high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheet according to claim 1, characterized in that: The porous material is a high-temperature resistant molecular sieve with a pore size of 0.2~0.8 nm; the surface area to mass ratio of the molybdenum source to the sulfur source is 1:0.5~1.5 cm². 2 / g; the mass ratio of the porous material to the sulfur source is 1:8~12.

4. The method for preparing a high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheet according to claim 1, characterized in that: The carrier gas is argon, and its introduction rate in the first stage of the high-temperature zone heating process is 6~18 sccm, and its introduction rate in the second stage is 30~50 sccm.

5. The method for preparing a high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheet according to claim 4, characterized in that: The heating process of the low-temperature zone is as follows: the low-temperature zone is heated from room temperature to 140-180℃ at a rate of 50-60℃ / min, and then held at that temperature; the heating process of the high-temperature zone is as follows: in the first stage, the temperature is increased from room temperature to 810-850℃ at a rate of 50-60℃ / min, and the carrier gas flow rate is increased; in the second stage, the temperature is further increased to 900-950℃ at a rate of 50-60℃ / min, and then held at that temperature for 5-13 minutes.

6. The method for preparing a high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheet according to claim 1, characterized in that: The molybdenum source has dimensions of 3~5×1~3×0.1~0.3 mm, and the distance between its upper surface and the substrate is 6~10 mm.

7. The method for preparing a high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheet according to claim 1, characterized in that: The substrate is a SiO2 / Si substrate with a total thickness of 490~510μm and a SiO2 layer thickness of 275~295μm.

8. A high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheet, characterized in that: It is prepared by the method described in any one of claims 1 to 7.

9. The high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheet according to claim 8, characterized in that: The corner bilayer molybdenum disulfide nanosheet is composed of two stacked MoS2 nanosheets, wherein the size of the top layer of molybdenum disulfide nanosheet is 3~12 μm and the size of the bottom layer of MoS2 nanosheet is 6~40 μm.

10. The high-proportion, large-angle-rotation bilayer molybdenum disulfide nanosheet according to claim 8, characterized in that: The proportion of large-angle double-layer molybdenum disulfide nanosheets in the corner double-layer molybdenum disulfide nanosheets is 40-50%.

Images