Two-dimensional transition metal sulfide nanoplatelets and methods of making the same

Abstract

The application discloses a two-dimensional transition metal sulfide nanosheet and a preparation method thereof. The two-dimensional transition metal sulfide and the preparation method thereof comprise the following steps: taking a sulfur source and a transition metal source as raw materials, performing a chemical vapor deposition reaction on a substrate, and growing the two-dimensional transition metal sulfide; the sulfur source is a discharge-treated polyacrylonitrile sulfide, the transition metal source is one of molybdenum trioxide, tungsten trioxide or manganese dioxide, and the carrier gas is argon or nitrogen. The preparation method provided by the application can obtain the two-dimensional transition metal sulfide nanosheet with low defect density, high crystal quality and excellent optical performance, and the two-dimensional transition metal sulfide nanosheet has a wide application prospect in the field of high-performance electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional semiconductor material preparation technology, specifically relating to a two-dimensional transition metal sulfide nanosheet and its preparation method. Background Technology

[0002] For more than half a century, semiconductor materials, represented by silicon, have greatly promoted the development of electronic information technology. Against this backdrop, the size of electronic devices has continued to shrink. However, when the thickness of traditional semiconductors (such as silicon, germanium, and III-V compounds) is reduced to the nanometer scale, surface dangling bonds and surface electronic state effects significantly degrade their electrical properties, and reduce the uniformity and reliability of devices, making it difficult to meet application requirements. Therefore, the search for and development of new semiconductor materials is an inevitable trend in the development of information technology and a cutting-edge direction in condensed matter physics, materials science, information science, and technology.

[0003] In recent years, two-dimensional semiconductor materials, represented by two-dimensional transition metal sulfides (TMS), have been considered ideal candidates for continuing Moore's Law in the post-silicon semiconductor era due to their combination of characteristics such as the absence of surface dangling bonds, high mobility, ultra-large specific surface area, flexibility, and ease of planar integration. The latest International Roadmap for Devices and Semiconductors (IDS) indicates that atomically thin TMS materials not only possess highly efficient carrier transport capabilities under quantum confinement in a two-dimensional plane and various excellent physical properties, but are also compatible with classical complementary metal-oxide-semiconductor (CMOS) technology, potentially extending Moore's Law to below the 2nm node. However, currently reported TMS crystals have low quality and contain numerous point defects. These defects act as carrier scattering centers, significantly reducing device mobility and leading to a substantial decrease in electrical performance. Therefore, developing efficient techniques for preparing high-quality TMS with low point defect density is a prerequisite for their application.

[0004] As one of the most commonly used methods in industry and laboratories, chemical vapor deposition (CVD) can directly deposit gas-phase reaction products on a specified substrate or allow material generation reactions to occur on the substrate surface, thereby obtaining atomic-scale flakes or films. This is beneficial for the preparation of large-area, high-quality two-dimensional transition metal sulfide nanosheets. However, the defect density of two-dimensional transition metal sulfide nanosheets prepared by traditional CVD is still much higher than that of traditional semiconductor materials. To address these issues, researchers have improved the quality of molybdenum disulfide nanosheets by controlling and optimizing the reactants, substrate, reaction temperature, and reaction time in CVD. For example, researchers have used reconstituted sulfur blocks as a sulfur source to provide a stable sulfur supply to the reaction system, achieving large-area uniformly distributed two-dimensional transition metal sulfide nanosheets, but the samples still contain a significant number of defects. Other researchers have used sulfur vapor to pre-sulfidate the substrate, directly growing two-dimensional transition metal sulfide nanosheets with lower defect density. However, these methods have limited effect on reducing the defect density of two-dimensional transition metal sulfide nanosheets, and the resulting materials still have a high defect density, requiring further improvement in material quality. In summary, further reducing the defect density of the prepared two-dimensional transition metal sulfide nanosheets is a major challenge in this field. Researchers need to further improve and optimize the preparation methods to enhance their controllability and versatility, thereby reducing the defect density of these materials, improving their crystal quality, and ultimately promoting their application in high-performance electronic devices. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. To this end, the present invention provides a two-dimensional transition metal sulfide nanosheet with excellent morphology, optical properties, and crystal quality, and has broad application prospects in optics, electronics, and other fields.

[0006] The present invention also provides a method for preparing two-dimensional transition metal sulfide nanosheets.

[0007] The first aspect of the present invention provides a method for preparing two-dimensional transition metal sulfide nanosheets, wherein the sulfided polyacrylonitrile powder is subjected to discharge treatment, and the metal source is at least one of molybdenum trioxide powder, tungsten trioxide powder, or manganese dioxide powder.

[0008] One technical solution of the present invention relating to the preparation method of two-dimensional transition metal sulfide nanosheets has at least the following beneficial effects:

[0009] Due to the readily available availability of sublimated sulfur powder, it is currently widely used as a sulfur source in chemical vapor deposition (CVD) methods for preparing two-dimensional transition metal sulfide nanosheets. However, this invention has found that sulfur powder, upon heating and volatilization, produces sulfur species primarily composed of long-chain sulfur. These long-chain sulfur species exhibit low reactivity and are difficult to suppress or heal the numerous sulfur defects generated during growth, resulting in crystals with numerous defects and low quality. Highly reactive single-atom sulfur, possessing the most negative adsorption energy with sulfur vacancies, readily adsorbs onto these vacancies, thereby healing and suppressing sulfur vacancy defects during growth and further reducing the defect density of the material. This invention further reveals that sulfurized polyacrylonitrile (PABN) obtained from discharged lithium-sulfur batteries can efficiently and selectively release single-atom sulfur without containing any other forms of sulfur. Therefore, the obtained sulfurized PABN can serve as a novel sulfur source for CVD, providing highly reactive single-atom sulfur during growth to prepare two-dimensional transition metal sulfide nanosheets with ultra-low defect density.

[0010] This invention uses sulfurized polyacrylonitrile (PAB) treated with electrical discharge as a sulfur source. This sulfur source exhibits higher activity (the released single-atom sulfur plays a role), overcoming the low activity problem of traditional sulfur sources. Therefore, the prepared molybdenum disulfide nanosheets have higher quality and lower defect density. The higher activity of the sulfur source is due to two factors: firstly, theoretical calculations show that single-atom sulfur has higher activity and the most negative adsorption energy with sulfur vacancies in molybdenum disulfide, thus effectively repairing and suppressing defects generated during growth; secondly, the electrical discharge treatment alters the chemical structure of the PAB (introducing lithium atoms), significantly reducing the energy required to release single-atom sulfur. This allows for selective release of single-atom sulfur at specific temperatures without generating other less active sulfur species, enhancing its effectiveness as a sulfur source. Other sulfur sources, such as sulfur powder and undischarged PAB, release single-atom sulfur at much higher energy than discharged PAB, and cannot selectively release single-atom sulfur for use in the growth process.

[0011] According to some embodiments of the present invention, in the chemical vapor deposition reaction, the heating temperature of the sulfur source is 100–500°C.

[0012] According to some embodiments of the present invention, in the chemical vapor deposition reaction, the heating temperature of the sulfur source is 150–450°C.

[0013] According to some embodiments of the present invention, in the chemical vapor deposition reaction, the heating temperature of the sulfur source is 380–420°C.

[0014] In some embodiments of the present invention, in the chemical vapor deposition reaction, the heating rate of the sulfur source is 15–55 °C / min.

[0015] In some embodiments of the present invention, the heating rate of the sulfur source in the chemical vapor deposition reaction is 35–45 °C / min.

[0016] According to some embodiments of the present invention, in the chemical vapor deposition reaction, the heating temperature of the transition metal source is 400–1200°C.

[0017] In some embodiments of the present invention, the temperature of the transition metal source in the chemical vapor deposition reaction is 550–1100°C.

[0018] In some embodiments of the present invention, the temperature of the transition metal source in the chemical vapor deposition reaction is 680–850°C.

[0019] In some preferred embodiments of the present invention, when the transition metal source is molybdenum trioxide, the temperature of the transition metal source in the chemical vapor deposition reaction is 650–820°C.

[0020] In some preferred embodiments of the present invention, when the transition metal source is tungsten trioxide, the temperature of the transition metal source in the chemical vapor deposition reaction is 700-850°C.

[0021] In some preferred embodiments of the present invention, when the transition metal source is manganese dioxide, the temperature of the transition metal source in the chemical vapor deposition reaction is 550–800°C.

[0022] In some embodiments of the present invention, the heating rate of the transition metal source in the chemical vapor deposition reaction is 15–50 °C / min.

[0023] In some embodiments of the present invention, the heating rate of the transition metal source in the chemical vapor deposition reaction is 25–45 °C / min.

[0024] The temperature of the transition metal source is positively correlated with the size of the two-dimensional transition metal sulfide nanosheets.

[0025] According to some embodiments of the present invention, the chemical vapor deposition reaction is carried out with the assistance of a carrier gas.

[0026] According to some embodiments of the present invention, the carrier gas includes at least one of nitrogen and argon.

[0027] According to some embodiments of the present invention, the sulfur source is located upstream of the metal source and the substrate is located above the metal source relative to the flow direction of the carrier gas.

[0028] This positioning is more conducive to balancing the deposition rates of the sulfur source and the transition metal source on the substrate. At the same time, the growth of the two-dimensional transition metal sulfide nanosheets and the volatilization of the transition metal source require a high-temperature region, while the volatilization of the sulfur source requires a low-temperature region. Therefore, the sulfur source is placed upstream.

[0029] In some embodiments of the present invention, the vertical distance between the transition metal source and the substrate is 0.3 to 3 mm.

[0030] In some preferred embodiments of the present invention, the vertical distance between the transition metal source and the substrate is approximately 1.2 mm.

[0031] In some embodiments of the present invention, the holding time for the chemical vapor deposition reaction is 0 to 50 minutes.

[0032] In some embodiments of the present invention, the holding time for the chemical vapor deposition reaction is 2 to 25 minutes.

[0033] The heat preservation time is positively correlated with the size of the molybdenum disulfide nanosheets.

[0034] In some embodiments of the present invention, the pressure of the chemical vapor deposition reaction is 0.05 to 760 torr.

[0035] The pressure of the chemical vapor deposition reaction is the pressure in the environment where the sulfur source and molybdenum source are located; for example, when the instrument for the chemical vapor deposition reaction is a tube furnace, the pressure is the pressure inside the quartz tube of the tube furnace.

[0036] In some embodiments of the present invention, the chemical vapor deposition reaction is carried out with the assistance of a carrier gas.

[0037] In some embodiments of the present invention, the flow rate of the carrier gas is 50 to 180 sccm.

[0038] In some embodiments of the present invention, the chemical vapor deposition process includes the following steps:

[0039] S1. Place the sulfur source and transition metal source in the heating zone;

[0040] S2. Introduce carrier gas for gas replacement, wherein the direction of introduction of the carrier gas should satisfy the condition that it flows from the sulfur source to the molybdenum source;

[0041] S3. During the carrier gas flow, the sulfur source and transition metal source are heated and kept at that temperature;

[0042] S4. Cool down the system obtained in step S3.

[0043] In some embodiments of the present invention, in step S3, the heating should satisfy the condition that the time when the sulfur source reaches the preset temperature is earlier than or equal to the time when the transition metal source reaches the preset temperature, so that the chemical vapor deposition reaction has a sulfur-rich environment.

[0044] In some embodiments of the present invention, in step S4, the cooling rate has no significant effect on the result of the chemical vapor deposition reaction. Those skilled in the art can perform at least one of natural cooling and artificial intervention cooling as needed.

[0045] In some embodiments of the present invention, the molar ratio of the transition metal source to the sulfur source is 1:3 to 200.

[0046] It is understood that the molar ratio of the transition metal source to the sulfur source can be any value of 1:10, 1:50, 1:100, 1:150 and 1:200 or a range of any two, such as 1:10 to 100.

[0047] According to some embodiments of the present invention, the substrate comprises silicon dioxide, sapphire, or mica.

[0048] According to some embodiments of the present invention, the method for preparing the sulfurized polyacrylonitrile powder after discharge treatment includes: assembling the sulfurized polyacrylonitrile as the positive electrode of a lithium-sulfur battery, and subjecting the battery to constant current discharge treatment.

[0049] According to some embodiments of the present invention, the current is 0.1C.

[0050] According to some embodiments of the present invention, the discharge time is 10 hours.

[0051] According to some embodiments of the present invention, the method for preparing the discharge-treated sulfurized polyacrylonitrile powder further includes collecting the discharge-treated sulfurized polyacrylonitrile powder, washing it sequentially with N-methylpyrrolidone and anhydrous ethanol, and drying it. The collected black powder is the discharge-treated sulfurized polyacrylonitrile powder.

[0052] According to some embodiments of the present invention, the molar ratio of the metal source to the sulfur source is 1:3 to 150.

[0053] A second aspect of the present invention provides a two-dimensional transition metal sulfide nanosheet, which is prepared by the method of the first aspect of the present invention.

[0054] According to some embodiments of the present invention, the point defect density of the two-dimensional transition metal sulfide nanosheet is ≤10. 13 pcs / cm 2 .

[0055] According to some embodiments of the present invention, the thickness of the two-dimensional transition metal sulfide nanosheet is 0.7-10 nm.

[0056] According to some embodiments of the present invention, the domain size of the two-dimensional transition metal sulfide nanosheet is 5 to 100 μm.

[0057] One of the technical solutions of the present invention concerning two-dimensional transition metal sulfide nanosheets has at least the following beneficial effects:

[0058] Since the two-dimensional transition metal sulfide nanosheets provided by this invention have the above-mentioned parameters, they have good morphology, optical properties and crystal quality, and have broad application prospects in the fields of optics and electronics. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the growth process of the two-dimensional transition metal sulfide nanosheets of the present invention.

[0060] Figure 2 This is a schematic diagram of the process of obtaining vulcanized polyacrylonitrile after discharge treatment in Example 1.

[0061] Figure 3 This is a schematic diagram showing the relative positions of the components in the chemical vapor deposition method in Example 1.

[0062] Figure 4 This is an optical microscope image of the two-dimensional transition metal sulfide nanosheets of Example 1.

[0063] Figure 5 This is an atomic force microscopy height image of the two-dimensional transition metal sulfide nanosheets of Example 1.

[0064] Figure 6 This is a fluorescence microscope image of the two-dimensional transition metal sulfide nanosheets from Example 1.

[0065] Figure 7 The Raman spectrum of the two-dimensional transition metal sulfide nanosheets of Example 1 is shown.

[0066] Figure 8 This is an optical microscope image of the two-dimensional transition metal sulfide nanosheets from Example 2.

[0067] Figure 9 This is an atomic force microscopy height image of the two-dimensional transition metal sulfide nanosheets of Example 2.

[0068] Figure 10 The image shows the Raman spectrum of the two-dimensional transition metal sulfide nanosheets from Example 2.

[0069] Figure 11This is an optical microscope image of the two-dimensional transition metal sulfide nanosheets of Example 3.

[0070] Figure 12 This is an atomic force microscopy height image of the two-dimensional transition metal sulfide nanosheets of Example 3.

[0071] Figure 13 This is an optical microscope image of the molybdenum disulfide nanosheets obtained in Comparative Example 1.

[0072] Figure 14 This is an optical microscope image of the molybdenum disulfide nanosheets obtained in Comparative Example 2.

[0073] Figure 15 The photoluminescence spectrum at room temperature of the two-dimensional transition metal sulfide nanosheets of Example 1 is shown.

[0074] Figure 16 The low-temperature photoluminescence spectrum of the two-dimensional transition metal sulfide nanosheets in Example 1 is shown.

[0075] Figure 17 The photoluminescence spectrum at room temperature of the two-dimensional transition metal sulfide nanosheets of Example 2 is shown.

[0076] Figure 18 The photoluminescence spectrum of molybdenum disulfide nanosheets obtained in Comparative Example 1 is shown at room temperature.

[0077] Figure 19 The low-temperature photoluminescence spectrum of the molybdenum disulfide nanosheets obtained in Comparative Example 1 is shown.

[0078] Figure 20 The image shows the room-temperature photoluminescence spectrum of the two-dimensional transition metal sulfide nanosheets in Comparative Example 2.

[0079] Figure 21 This is a scanning transmission electron microscope image of the two-dimensional transition metal sulfide nanosheets from Example 1. Detailed Implementation

[0080] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0081] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0082] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0083] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0084] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0085] Example 1

[0086] This embodiment prepares a two-dimensional transition metal sulfide nanosheet, the process of which is as follows: Figure 1 As shown.

[0087] The specific preparation process is as follows:

[0088] D1. Obtaining vulcanized polyacrylonitrile after discharge treatment. Wherein:

[0089] The first step is to mix sulfur powder and polyacrylonitrile powder at a mass ratio of 4:1 by grinding; then the mixture is annealed at 330°C for 450 min in an argon atmosphere to obtain the original vulcanized polypropylene.

[0090] The second step involves assembling the original sulfurized polyacrylonitrile as the positive electrode of a lithium-sulfur battery, subjecting the battery to constant current discharge at 0.1C for 10 hours, collecting the sulfurized polyacrylonitrile powder after discharge treatment, and washing and drying it sequentially with N-methylpyrrolidone and anhydrous ethanol solvent. The black powder collected afterward is the target sulfurized polyacrylonitrile after discharge treatment.

[0091] The process diagram for this step is shown below. Figure 2 As shown.

[0092] D2. Chemical Vapor Deposition Preparation: Place 300 mg of discharge-treated sulfurized polyacrylonitrile in a quartz boat and position it in the first heating zone of a 1-inch (quartz tube diameter) tube furnace. Place 1.5 mg of molybdenum trioxide in another quartz boat, with the silica substrate facing down 1 mm directly above it. Place this quartz boat in the second heating zone downstream of the first heating zone of the tube furnace. In specific embodiments, upstream or downstream refers to the direction of carrier gas flow. The specific placement and carrier gas flow direction are as follows: Figure 3 As shown, chemical vapor deposition is carried out in a tube furnace.

[0093] D3. Chemical vapor deposition: Argon gas is continuously introduced as the carrier gas at a flow rate of 80 sccm, with the argon gas flowing from the sulfur source to the molybdenum source. The gas pressure in the quartz tube of the tube furnace is 1 atmosphere, i.e. 760 torr.

[0094] After venting the air out of the tubular furnace for 10 minutes, the first heating zone (sulfur source) is heated to 150°C and the second heating zone (molybdenum source) is heated to 700°C at a rate of 35°C / min. The heating time of the first and second heating zones should be such that when the molybdenum source reaches 100°C below the preset temperature, the sulfur source reaches the preset temperature to provide a sulfur-rich environment. After holding at this temperature for 5 minutes, heating is stopped, and the furnace is allowed to cool naturally to room temperature. The flow rate of the carrier gas remains unchanged during the cooling process.

[0095] The obtained molybdenum disulfide nanosheets were deposited on a silica substrate. The microstructure and domain size of the nanosheets were measured using optical microscopy; the thickness of the nanosheets was measured using atomic force microscopy; and the luminescence uniformity and domain size were corroborated using fluorescence microscopy. The results showed:

[0096] Figure 4 This is a microscopic observation image of the two-dimensional transition metal sulfide nanosheets in this embodiment.

[0097] Depend on Figure 4 It can be seen that the synthesized nanosheets have a triangular morphology with neat edges and an average lateral dimension of about 40 μm.

[0098] Figure 5 The image shows the atomic force microscopy results of the two-dimensional transition metal sulfide nanosheets in this embodiment.

[0099] The thickness of the molybdenum disulfide nanosheets is 0.76 nm.

[0100] Figure 6 This is a fluorescence microscope image of the two-dimensional transition metal sulfide nanosheets in this embodiment.

[0101] This indicates that the obtained molybdenum disulfide nanosheets have uniform fluorescence luminescence properties.

[0102] Figure 7 The image shows the Raman diagram of the two-dimensional transition metal sulfide nanosheets in this embodiment.

[0103] The spectral peak corresponds to the Raman characteristic peak of molybdenum disulfide nanosheets, indicating that the obtained material is pure molybdenum disulfide nanosheet material.

[0104] Example 2

[0105] This embodiment prepares a two-dimensional transition metal sulfide nanosheet. The specific process differs from that in Example 1 in that:

[0106] (1) In step D2, the transition metal source is tungsten trioxide, not tungsten trioxide;

[0107] (2) In step D3, the temperature of the second heating zone (transition metal source) is 820℃.

[0108] Figure 8 This is a microscopic observation image of the two-dimensional transition metal sulfide nanosheets in this embodiment.

[0109] Depend on Figure 8 It can be seen that the synthesized tungsten disulfide nanosheets have a triangular morphology with neat edges and an average lateral size of about 47 μm.

[0110] Figure 9 The image shows the atomic force microscopy results of the two-dimensional transition metal sulfide nanosheets in this embodiment.

[0111] The thickness of the tungsten disulfide nanosheets is 0.79 nm.

[0112] Figure 10 This is a Raman image of the two-dimensional transition metal sulfide nanosheets in this embodiment.

[0113] The spectral peak corresponds to the Raman characteristic peak of tungsten disulfide nanosheets, indicating that the obtained material is pure tungsten disulfide nanosheet material.

[0114] Example 3

[0115] This embodiment prepares a two-dimensional transition metal sulfide nanosheet. The specific process differs from that in Example 1 in that:

[0116] (1) In step D2, the transition metal source is manganese dioxide, not tungsten trioxide;

[0117] (2) In step D3, the temperature of the second heating zone (transition metal source) is 720℃.

[0118] Figure 11 This is a microscopic observation image of the two-dimensional transition metal sulfide nanosheets in this embodiment.

[0119] Depend on Figure 11 It can be seen that the synthesized manganese sulfide nanosheets have a triangular morphology with neat edges and a lateral dimension of approximately 20 μm.

[0120] Figure 12 The image shows the atomic force microscopy results of the two-dimensional transition metal sulfide nanosheets in this embodiment.

[0121] Depend on Figure 12 It can be seen that the surface of the manganese sulfide nanosheets is clean, and its thickness is about 10 nm.

[0122] Comparative Example 1

[0123] This comparative example demonstrates a method for preparing molybdenum disulfide nanosheets, which differs from Example 1 in that:

[0124] (1) Step D1 is not included;

[0125] (2) In step D2, sulfur powder is used directly as the sulfur source.

[0126] Figure 13 This is an optical microscope image of the molybdenum disulfide nanosheets obtained in this comparative example.

[0127] The results show that the obtained nanosheets also have a triangular microstructure and a domain size of about 30 μm.

[0128] Comparative Example 2

[0129] This comparative example demonstrates a method for preparing molybdenum disulfide nanosheets, which differs from Example 1 in that:

[0130] (1) The vulcanized polyacrylonitrile was not subjected to discharge treatment.

[0131] (2) Use untreated sulfurized polyacrylonitrile as the sulfur source.

[0132] Figure 14 This is an optical microscope image of the molybdenum disulfide nanosheets obtained in this comparative example.

[0133] The results show that the obtained nanosheets have a concave triangular microstructure and a domain size of about 10 μm.

[0134] Effect verification

[0135] The optical and crystal quality of two-dimensional transition metal sulfide nanosheets were characterized using room temperature and low temperature photoluminescence spectroscopy and scanning transmission electron microscopy. The laser wavelength for the photoluminescence spectrum was 532 nm.

[0136] Figure 15 This is the room-temperature photoluminescence spectrum of the molybdenum disulfide nanosheets obtained in Example 1 of the present invention.

[0137] The results show that the obtained material has a very sharp photoluminescence peak with a half-maximum width of about 47 meV, which is the lowest value among all reported molybdenum disulfide nanosheets to date, indicating that the material has excellent optical properties.

[0138] Figure 16 This is the low-temperature (80K) photoluminescence spectrum of the molybdenum disulfide nanosheets obtained in Example 1 of the present invention.

[0139] The results show that the proportion of the defect peak area to the emission spectrum peak area is low, indicating that the sulfur defect density of the material is very low.

[0140] Figure 17 This is the room-temperature photoluminescence spectrum of the tungsten disulfide nanosheets obtained in Example 1 of the present invention.

[0141] The results showed that the photoluminescence peak of the obtained tungsten disulfide was also very sharp, with a half-maximum width of about 41 meV, indicating that the obtained tungsten disulfide nanosheets had excellent optical properties.

[0142] Figure 18 This is the room-temperature photoluminescence spectrum of the molybdenum disulfide nanosheets obtained in Comparative Example 1 of this invention.

[0143] In Comparative Example 1, sulfur powder was used as the sulfur source. The photoluminescence test conditions of the obtained molybdenum disulfide nanosheets were the same as those in Example 1. The results showed that the half-maximum width of the photoluminescence spectrum of the material in Comparative Example 1 was about 70 meV, indicating poor optical performance.

[0144] Figure 19 The low-temperature (80K) photoluminescence spectrum of the molybdenum disulfide nanosheets obtained in Comparative Example 1 of this invention is shown.

[0145] The results showed that the defect peak area of ​​the material accounted for a relatively high proportion of the emission spectrum peak area, indicating that the material prepared in Comparative Example 1 contained more defects.

[0146] Figure 20 This is the room-temperature photoluminescence spectrum of the molybdenum disulfide nanosheets obtained in Comparative Example 1 of this invention.

[0147] In Comparative Example 2, untreated sulfurized polyacrylonitrile was used as the sulfur source. The photoluminescence test conditions of the resulting molybdenum disulfide nanosheets were the same as those in Example 1. The results showed that the half-maximum width of the photoluminescence spectrum of the material in Comparative Example 1 was about 67 meV, indicating poor optical performance.

[0148] Figure 21 This is a scanning transmission electron microscope image of the molybdenum disulfide nanosheet material obtained in Example 1 of the present invention.

[0149] The results show a clear six-membered ring structure with a sulfur defect density ≤10. 13 pcs / cm 2This further demonstrates that the material has a low sulfur defect density and extremely high crystal quality.

[0150] In summary, the method provided by this invention can significantly reduce the sulfur vacancy defect density in the crystal lattice and improve the crystal quality and optical quality of the obtained two-dimensional transition metal sulfide nanosheets by replacing the sulfur source with sulfurized polyacrylonitrile that has undergone discharge treatment.

[0151] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing two-dimensional transition metal sulfide nanosheets, characterized in that, The method includes a step of performing a chemical vapor deposition reaction on a substrate using a sulfur source and a transition metal source as raw materials. The sulfur source is sulfurized polyacrylonitrile powder obtained from a discharged lithium-sulfur battery after discharge treatment, and the transition metal source is at least one of molybdenum trioxide powder, tungsten trioxide powder, or manganese dioxide powder. The method for preparing sulfurized polyacrylonitrile powder obtained from a discharged lithium-sulfur battery includes: assembling sulfurized polyacrylonitrile as the positive electrode of a lithium-sulfur battery, subjecting the battery to constant current discharge treatment, collecting the sulfurized polyacrylonitrile powder after discharge treatment, washing and drying it sequentially with N-methylpyrrolidone and anhydrous ethanol, and the collected black powder is the sulfurized polyacrylonitrile powder after discharge treatment.

2. The preparation method according to claim 1, characterized in that, In the chemical vapor deposition reaction, the heating temperature of the sulfur source is 100~500 ℃.

3. The preparation method according to claim 1, characterized in that, In the chemical vapor deposition reaction, the heating temperature of the transition metal source is 400~1200 ℃.

4. The preparation method according to claim 1, characterized in that, The chemical vapor deposition reaction is carried out with the assistance of a carrier gas.

5. The preparation method according to claim 4, characterized in that, The carrier gas includes at least one of nitrogen and argon.

6. The preparation method according to claim 4, characterized in that, The sulfur source is located upstream of the metal source, and the substrate is located above the metal source, relative to the flow direction of the carrier gas.

7. The preparation method according to claim 1, characterized in that, The substrate includes silicon dioxide, sapphire, or mica.

8. The preparation method according to claim 1, characterized in that, The current magnitude of the constant current discharge process is 0.1C.

9. The preparation method according to claim 1, characterized in that, The discharge time for the constant current discharge treatment is 10 hours.

10. The preparation method according to any one of claims 1 to 9, characterized in that, The molar ratio of the transition metal source to the sulfur source is 1:3 to 150.

11. A two-dimensional transition metal sulfide nanosheet, characterized in that, It is prepared by any one of claims 1 to 10.

12. The two-dimensional transition metal sulfide nanosheet according to claim 11, characterized in that, The point defect density of the two-dimensional transition metal sulfide nanosheets is ≤10. 13 pcs / cm 2 .

13. The two-dimensional transition metal sulfide nanosheet according to claim 11, characterized in that, The thickness of the two-dimensional transition metal sulfide nanosheets is 0.7-10 nm.

14. The two-dimensional transition metal sulfide nanosheet according to claim 11, characterized in that, The domain size of the two-dimensional transition metal sulfide nanosheets is 5~100 μm.

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