A method for preparing a single-layer molybdenum disulfide by dual sulfur source chemical vapor deposition

Abstract

This application relates to the field of two-dimensional semiconductor material preparation technology, specifically to a method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition, comprising the following steps: Step 1, providing a chemical vapor deposition reaction chamber having an upstream region, a growth region, and a downstream region; Step 2, arranging a molybdenum-containing precursor in the growth region, and arranging a substrate above or opposite to the molybdenum-containing precursor; Step 3, arranging a first sulfur-containing precursor in the upstream region and a second sulfur-containing precursor in the downstream region; Step 4, introducing a carrier gas into the reaction chamber and heating it to cause the first sulfur-containing precursor, the second sulfur-containing precursor, and the molybdenum-containing precursor to volatilize and undergo a chemical vapor deposition reaction on the substrate surface to form a monolayer molybdenum disulfide. This invention employs a dual-sulfur source strategy, achieving large-size, uniform, and low-defect preparation of monolayer MoS2, facilitating widespread application.

Description

Technical Field

[0001] This application relates to the field of two-dimensional semiconductor material preparation technology, specifically to a method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition. Background Technology

[0002] Two-dimensional transition metal dichalcogenides (TMDCs) exhibit broad application prospects in next-generation electronic devices, optoelectronic devices, sensors, and flexible devices due to their atomic-level thickness, excellent carrier transport performance, and unique optoelectronic properties. Among them, molybdenum disulfide (MoS2), as a typical two-dimensional semiconductor material, possesses a single-layer direct bandgap, a high on / off ratio, and good environmental stability, thus becoming an important target for current two-dimensional material research and application development.

[0003] Among existing technologies, chemical vapor deposition (CVD) is considered one of the most promising methods for synthesizing monolayer MoS2 thin films due to its suitability for the controllable preparation of large-area, high-quality films. By controlling process parameters such as precursor type, temperature conditions, carrier gas flow rate, and substrate type, MoS2 nucleation and growth can be achieved on the substrate surface, thereby obtaining two-dimensional thin films with a certain grain size and coverage.

[0004] However, traditional CVD processes generally employ a single sulfur source layout, typically placing the sulfur source only in the low-temperature upstream region of the tube furnace, while the molybdenum source and substrate are positioned in the central high-temperature region or downstream growth region. During carrier gas transport, the sulfur vapor concentration exhibits significant attenuation along the gas flow direction, resulting in a large spatial concentration gradient within the reaction chamber. Because the concentration of sulfur precursor received at different locations within the growth region varies, it easily disrupts the thermodynamic equilibrium required for uniform MoS2 nucleation and epitaxial growth, leading to significant differences in nucleation density, grain size, layer number distribution, and defect density in different regions of the substrate, including the upstream, midstream, and downstream areas.

[0005] More importantly, under traditional single-sulfur-source processes, the unstable and spatially uneven distribution of sulfur atmosphere easily introduces intrinsic defects such as sulfur vacancies into the MoS2 crystal during growth. These defects typically act as non-radiative recombination centers, weakening exciton recombination luminescence, reducing the material's optical quality and electrical properties, and ultimately affecting its application in high-performance optoelectronic devices. Therefore, insufficient or uneven distribution of sulfur precursor supply has become one of the key factors restricting the high-quality and controllable preparation of monolayer MoS2.

[0006] Currently, existing technologies mainly focus on molybdenum source modification, substrate modification, growth temperature adjustment, or nucleation promotion. Although they can improve the growth behavior of MoS2 to some extent, they usually cannot fundamentally solve the problem of uneven spatial distribution of sulfur precursors in the reaction chamber, nor can they simultaneously achieve multiple goals such as large-size grain growth, global uniformity improvement, and sulfur vacancy defect suppression. Summary of the Invention

[0007] To address the above problems, this invention provides a method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition, comprising the following steps: Step 1: Provide a chemical vapor deposition reaction chamber with an upstream region, a growth region, and a downstream region; Step 2: Arrange the molybdenum-containing precursor in the growth region, and arrange the substrate above or opposite the molybdenum-containing precursor; Step 3: Arrange the first sulfur-containing precursor in the upstream region and the second sulfur-containing precursor in the downstream region; Step 4: Introduce carrier gas into the reaction chamber and heat it up to cause the first sulfur-containing precursor, the second sulfur-containing precursor, and the molybdenum-containing precursor to volatilize and undergo a chemical vapor deposition reaction on the substrate surface to form a monolayer of molybdenum disulfide.

[0008] This invention addresses this issue by setting a first sulfur-containing precursor upstream and a second sulfur-containing precursor downstream of the growth region. This eliminates the reliance on a single upstream sulfur source for sulfur supply to the substrate region. Instead, it creates a synergistic sulfur supply and spatial compensation on both sides of the growth region during chemical vapor deposition. This reduces the concentration gradient caused by the gradual decay of sulfur vapor along the carrier gas flow direction under traditional single-sulfur-source conditions, resulting in a more uniform, stable, and sufficient sulfur chemical potential on the substrate surface. Furthermore, the more uniform sulfur atmosphere facilitates closer nucleation conditions at different locations on the substrate, reducing local over-dense or under-dense nucleation and promoting more consistent lateral epitaxial growth of grains. This leads to increased grain size and improved in-plane uniformity of monolayer MoS2. On the other hand, a sufficient and stable sulfur supply suppresses intrinsic defects such as sulfur vacancies caused by local sulfur deficiency during growth, reducing non-radiative recombination centers and mitigating the adverse effects of defects on exciton recombination and carrier transport. This, in turn, improves the material's crystal quality and enhances its absorption and luminescence optical properties. Therefore, this invention enables the fabrication of large-size, uniform, and low-defect monolayer MoS2.

[0009] Furthermore, the upstream and downstream regions are low-temperature zones, while the growth zone is a high-temperature zone. This facilitates the stable sublimation and release of sulfur vapor by the sulfur-containing precursor in the low-temperature zone, while simultaneously allowing the molybdenum-containing precursor to fully volatilize and undergo chemical vapor deposition on the substrate surface in the high-temperature zone, thus forming mutually matched precursor supply and surface reaction conditions. This partitioning is conducive to building a stable sulfur chemical potential environment, avoiding premature precursor reaction or supply imbalance, and thereby promoting uniform nucleation and high-quality growth of monolayer molybdenum disulfide.

[0010] Furthermore, both the first and second sulfur-containing precursors are sublimated sulfur powder; the molybdenum-containing precursor is molybdenum trioxide powder. This is advantageous for utilizing the mature and stable precursor system in existing chemical vapor deposition processes to form a controllable sulfur vapor and molybdenum source vapor supply process, thereby improving the stability and repeatability of the reaction. At the same time, the sublimated sulfur powder and molybdenum trioxide powder have good reaction compatibility, which is conducive to the formation of high-purity molybdenum disulfide crystals on the substrate surface and reduces the formation of impurity phases.

[0011] Furthermore, the mass ratio of the first sulfur-containing precursor, the molybdenum-containing precursor, and the second sulfur-containing precursor is 40:1:20. This helps to keep the sulfur supply at the growth interface within a relatively ideal range, ensuring sufficient sulfur source while avoiding localized weak or strong sulfur supply, thus more effectively compensating for the concentration gradient problem caused by the decay of sulfur vapor along the process in traditional single-sulfur-source processes. Under this ratio, it is beneficial to promote the lateral epitaxial growth of monolayer molybdenum disulfide, improving grain size, spatial uniformity, and crystal quality.

[0012] Furthermore, the substrate is a c-plane sapphire substrate. This provides molybdenum disulfide growth with a relatively stable surface state, good high-temperature resistance, and suitable substrate conditions for the nucleation and epitaxial growth of two-dimensional materials, thereby improving the controllability of the deposition process and the uniformity of the obtained film; at the same time, the c-plane sapphire substrate is conducive to obtaining monolayer molybdenum disulfide grains with regular morphology and high crystal quality.

[0013] Furthermore, the substrate is positioned upside down on top of the molybdenum-containing precursor. This shortens the transport path of the molybdenum-containing precursor to the substrate surface after volatilization, allowing the molybdenum precursor to be transported more uniformly to the substrate growth surface. Combined with the more uniform sulfur atmosphere formed by the dual sulfur source, this promotes uniform nucleation and lateral growth of monolayer molybdenum disulfide. At the same time, this arrangement also helps to improve the precursor utilization efficiency and reduce the impact of external disturbances on the growth process.

[0014] Furthermore, the distance between the substrate growth surface and the molybdenum-containing precursor is 4-6 mm, which allows the molybdenum-containing precursor to reach the substrate surface within a suitable transport distance after volatilization. This balances the precursor supply intensity and transport uniformity, avoiding insufficient molybdenum source supply due to excessive distance, and also avoiding excessively rapid local deposition or growth imbalance due to insufficient distance.

[0015] Furthermore, argon is used as the carrier gas, which provides a stable inert atmosphere during the deposition process, reducing the adverse effects of impurities such as oxygen and water vapor on the volatilization, transport, and reaction processes of the precursor, reducing precursor oxidation and impurity introduction, and ensuring that the chemical vapor deposition process is stable and controllable. At the same time, argon helps maintain a relatively stable precursor transport environment, promoting the formation of high-quality monolayer molybdenum disulfide.

[0016] Furthermore, the first sulfur-containing precursor, the molybdenum-containing precursor, and the second sulfur-containing precursor were placed in the first quartz boat, the second quartz boat, and the third quartz boat, respectively. The quartz boats are heat-resistant and chemically stable, which helps to avoid interference from the container with the deposition reaction.

[0017] Furthermore, the third quartz boat is tilted relative to the horizontal plane and its opening is directed towards the growth region, which allows the sulfur vapor formed after the sublimation of the second sulfur-containing precursor to be transported more effectively toward the growth region. This enhances the compensating effect of downstream auxiliary sulfur supply on the growth region, further reduces the sulfur concentration gradient in the substrate region, and creates a more uniform and stable sulfur atmosphere environment. This helps to suppress the formation of intrinsic defects such as sulfur vacancies and promotes the large-size, uniform and high-quality growth of monolayer molybdenum disulfide.

[0018] The beneficial effects of this invention are: (1) This invention constructs a chemical vapor deposition layout with dual sulfur sources for synergistic sulfur supply by setting a first sulfur-containing precursor upstream of the growth region and a second sulfur-containing precursor downstream of the growth region. This fundamentally improves the problem of gradual attenuation of sulfur vapor along the carrier gas flow direction and large sulfur concentration gradient in the traditional single sulfur source process. Through the combined effect of upstream sulfur supply and downstream compensating sulfur supply, this invention forms a more uniform, stable and sufficient sulfur atmosphere environment in the growth region where the substrate is located, making the sulfur chemical potential distribution at the growth interface more reasonable, and providing good thermodynamic conditions for uniform nucleation and high-quality epitaxial growth of monolayer molybdenum disulfide.

[0019] (2) The present invention is beneficial to improving the grain size and spatial uniformity of monolayer molybdenum disulfide. Since the dual sulfur source layout reduces the difference in sulfur precursor concentration received at different locations on the substrate, it can reduce the inconsistency of nucleation conditions between different regions, reduce the phenomenon of excessively dense or sparse local nucleation, thereby promoting more uniform lateral epitaxial growth of monolayer molybdenum disulfide grains, increasing grain size, and improving the nucleation density, layer distribution and morphological consistency throughout the substrate.

[0020] (3) This invention is beneficial for suppressing the formation of intrinsic defects such as sulfur vacancies and reducing defect density. In the traditional single sulfur source process, due to the instability of the sulfur atmosphere and uneven spatial distribution, defects such as sulfur vacancies are easily introduced into the molybdenum disulfide crystal. However, this invention uses dual sulfur sources to supply sulfur in a coordinated manner, making the sulfur supply during the growth process more stable and sufficient, thereby effectively reducing the phenomenon of local sulfur deficiency, reducing the generation of intrinsic defects such as sulfur vacancies, reducing the number of non-radiative recombination centers, and improving the crystallization quality of the material.

[0021] (4) This invention can significantly improve the optical properties of monolayer molybdenum disulfide. Because defects such as sulfur vacancies are effectively suppressed, non-radiative recombination channels are reduced, and defect interference in the exciton recombination and absorption processes is weakened. Therefore, the resulting monolayer molybdenum disulfide exhibits superior exciton absorption characteristics and luminescence performance, which is beneficial for enhancing the material's application value in optoelectronic devices. The sample prepared by this method has enhanced A exciton emission, stronger and sharper A, B, and C exciton absorption peaks, and exhibits excellent spatial uniformity.

[0022] (5) The process of the present invention is simple, easy to implement, and has good controllability and repeatability. The present invention does not require complex substrate modification, additional catalyst assistance or special equipment modification. It mainly achieves effective control of the sulfur atmosphere distribution in the growth zone by optimizing the spatial layout of the precursor in the reaction chamber. Therefore, it has the advantages of simple operation, clear process window, stable process and good repeatability, and is easy to implement on the basis of existing chemical vapor deposition equipment.

[0023] (6) This invention has good prospects for promotion and application. The concept of synergistic sulfur supply from two sulfur sources proposed in this invention is not only applicable to the preparation of monolayer molybdenum disulfide, but also provides a reference technical path for the uniform growth of other two-dimensional transition metal dichalcogenide materials and related heterostructures. Therefore, it has strong versatility and scalability.

[0024] Based on the above beneficial effects, this invention has good application prospects in the field of two-dimensional semiconductor material preparation technology. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of dual-sulfur source CVD in Example 1 of the present invention.

[0026] Figure 2 The curves show the spatial distribution of sulfur concentration across the entire temperature range in Example 1 of this invention using dual-sulfur source CVD and in the comparative example using traditional single-sulfur source CVD. (Curve ① represents MoS2 prepared by the dual-sulfur source CVD strategy, and curve ② represents MoS2 prepared by the traditional single-sulfur source CVD strategy).

[0027] Figure 3 This is an optical microscope image of MoS2 prepared by the dual-sulfur-source CVD strategy in Example 1 of the present invention.

[0028] Figure 4 This is a SEM image of MoS2 prepared by the dual-sulfur-source CVD strategy in Example 1 of this invention.

[0029] Figure 5 This is a comparison of nucleation density analysis curves for different regions of the substrate prepared by the dual-sulfur-source CVD strategy in Example 1 of this invention and the conventional single-sulfur-source CVD in the comparative example. The upstream of the substrate corresponds to 3 mm, the midstream to 6 mm, and the downstream to 9 mm.

[0030] Figure 6 The XPS spectra of DS-MoS2 in Example 1 of this invention are as follows: (a) is the Mo 3d spectrum, and (b) is the S 2p spectrum.

[0031] Figure 7 This is a comparison of the UV-Vis absorption spectra of DS-MoS2 in Example 1 of the present invention and TS-MoS2 in the comparative example.

[0032] Figure 8 This is a temperature-dependent photoluminescence characteristic diagram of DS-MoS2 in Example 1 of the present invention.

[0033] In the diagram: 1. Upstream region; 2. Growth region; 3. Downstream region. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Example 1

[0035] This embodiment provides a method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition, and the apparatus used is as follows: Figure 1 As shown, the CVD process includes, from left to right, an upstream region 1, a growth region 2, and a downstream region 3, with upstream region 1 and downstream region 3 positioned on either side of growth region 2. A molybdenum source is placed in a quartz boat in the central high-temperature region, a first sulfur-containing precursor source is placed in a quartz boat in the upstream low-temperature region, and a second sulfur-containing precursor is placed in a quartz boat in the low-temperature region downstream of the substrate. The preparation method specifically includes the following steps: Step 1: Provide a chemical vapor deposition reaction chamber with an upstream region 1, a growth region 2, and a downstream region 3. Specifically, provide a three-temperature zone horizontal tubular chemical vapor deposition reaction chamber with an upstream low-temperature zone, a central high-temperature zone, and a downstream low-temperature zone.

[0036] Step 2: Arrange the molybdenum-containing precursor in growth region 2, and place the substrate above or opposite the molybdenum-containing precursor. Specifically, 0.5 mg of molybdenum trioxide powder is placed in the second quartz boat in the central high-temperature region as the molybdenum-containing precursor. A c-plane sapphire (0001) substrate is selected as the growth substrate. The substrate is ultrasonically cleaned sequentially in acetone, anhydrous ethanol, and deionized water for 10 min each to remove surface impurities and organic contaminants, and then dried with high-purity nitrogen. The pretreated c-plane sapphire substrate is placed upside down above the second quartz boat, with the distance between the substrate growth surface and the molybdenum-containing precursor approximately 5 mm.

[0037] Step 3: Arrange the first sulfur-containing precursor in the upstream region 1 and the second sulfur-containing precursor in the downstream region 3. Specifically, 20 mg of sublimed sulfur powder is placed as the first sulfur-containing precursor in the first quartz boat in the upstream low-temperature region; and 10 mg of sublimed sulfur powder is placed as the second sulfur-containing precursor in the third quartz boat in the downstream low-temperature region.

[0038] Step 4: Introduce carrier gas into the reaction chamber and raise the temperature to allow the first sulfur-containing precursor, the second sulfur-containing precursor, and the molybdenum-containing precursor to volatilize and undergo chemical vapor deposition on the substrate surface, forming a monolayer of molybdenum disulfide. Specifically, high-purity argon gas is introduced into the reaction chamber and purged at a flow rate of 600 sccm for 10 min to fully remove oxygen and water vapor from the reaction chamber, preventing precursor oxidation and impurity introduction; subsequently, the argon flow rate is adjusted to 20 sccm and kept constant. The upstream low-temperature zone, the central high-temperature zone, and the downstream low-temperature zone are simultaneously programmed to increase the temperature. The upstream and downstream low-temperature zones are both heated to 290°C at a rate of 8°C / min and held at this temperature to ensure stable sublimation of the first and second sulfur-containing precursors; the central high-temperature zone is heated to 900°C at a rate of 8°C / min and held at this temperature to allow molybdenum trioxide to volatilize and undergo chemical vapor deposition with sulfur vapor on the substrate surface. Deposition is carried out at 900°C for 3 min. After the deposition reaction was completed, heating was stopped, and the substrate was naturally cooled to room temperature under argon protection at 20 sccm to obtain a sapphire substrate sample with a monolayer of molybdenum disulfide. For ease of description, the molybdenum disulfide prepared by the dual-sulfur source strategy is referred to as DS-MoS2, while that prepared by the conventional single-sulfur source is referred to as TS-MoS2.

[0039] Comparative Example The comparative example uses a traditional single-sulfur-source chemical vapor deposition method to prepare molybdenum disulfide. The difference between this example and Example 1 is that: a second sulfur-containing precursor is not set in the downstream region 3, that is, sublimed sulfur powder is not placed in the third quartz boat, and the downstream region 3 does not provide auxiliary sulfur supply; only 20 mg of sublimed sulfur powder is placed in the first quartz boat in the upstream low-temperature region as a single sulfur source, and 0.5 mg of molybdenum trioxide powder is placed in the second quartz boat in the central high-temperature region. The c-plane sapphire substrate is placed upside down on top of the second quartz boat, and the distance between the substrate growth surface and the molybdenum-containing precursor is about 5 mm. The remaining process conditions are the same as in Example 1.

[0040] Figure 2 The graphs show the spatial distribution of sulfur concentration across the entire temperature range in the tube furnaces using the dual-sulfur-source strategy in Example 1 and the traditional single-sulfur-source strategy in the comparative example. The upstream curve corresponds to x-axis = 10 cm, and the downstream curve corresponds to x-axis = 12 cm. In the dual-sulfur-source system of Example 1, the sulfur concentrations upstream and downstream of the substrate are 29680 μmol·m⁻¹. -3 and 27560 μmol·m -3 The concentration difference was only 2120 μmol·m -3 The corresponding concentration gradient is 0.106 μmol·m -4 In the comparative example, in the traditional single-sulfur source system, the sulfur vapor concentration decreased from 21200 μmol·m⁻¹ upstream. -3 The temperature dropped sharply to 6360 μmol·m -3 The concentration gradient is as high as 0.742 μmol·m -4 It is about 7 times that of the disulfide source system.

[0041] Figure 3 The image shows an optical microscope image of the MoS2 prepared in Example 1. It can be seen that the MoS2 is in the form of an equilateral triangle, uniformly covering the substrate.

[0042] Figure 4 The image shows a SEM image of MoS2 prepared in Example 1. The grain size is approximately 70 μm, and the triangular edges are clear and sharp.

[0043] Figure 5 This is a comparison of the nucleation density of molybdenum disulfide prepared on the substrate using the dual-sulfur-source strategy in Example 1 and the conventional single-sulfur-source strategy in the comparative example. The difference in nucleation density between the upper, middle, and lower regions of the substrate decreased from 3.5 times that of the single-sulfur-source sample to less than 1.5 times, and the average nucleation density increased by about 43%, demonstrating excellent macroscopic uniformity.

[0044] Figure 6 The image shows the XPS spectrum of DS-MoS2 in Example 1. Figure 6 (a) is the Mo 3d spectrum. Figure 6(b) is the S 2p spectrum. The Mo 3d spectrum shows two characteristic peaks at binding energies of 229.2 eV and 232.3 eV, corresponding to Mo, respectively. 4+ The 3d5 / 2 and 3d3 / 2 energy levels. In the S 2p spectrum, the doublets at 161.7 eV and 162.9 eV are attributed to the S 3d5 / 2 and 3d3 / 2 energy levels, respectively. 2- The 2p3 / 2 and 2p1 / 2 energy levels. The peak positions of these binding energies are consistent with standard data for 2H phase MoS2, and MoO was not detected. x The presence of impurity peaks indicates that the precursor MoO3 has been completely sulfided, resulting in high-purity 2H phase MoS2.

[0045] Figure 7 The UV-Vis absorption spectra of molybdenum disulfide prepared using the dual sulfur source strategy in Example 1 and the conventional single sulfur source strategy in the comparative example are compared. The A, B, and C exciton absorption peaks of DS-MoS2 are stronger and the peak shapes are sharper than those of TS-MoS2.

[0046] Figure 8 The image shows the temperature-varying PL spectrum of DS-MoS2 in Example 1. Even with excitation using a 380 nm laser, which is more sensitive to defects, a weak sulfur vacancy-related defect peak was only observed at an extremely low temperature of 80 K. Example 2

[0047] Based on Example 1, when placing the second sulfur-containing precursor in the downstream region, the third quartz boat is no longer placed horizontally, but is tilted relative to the horizontal plane, with its opening directed towards the growth region. This makes it easier for the sulfur vapor formed after the sublimation of the second sulfur-containing precursor to be transported towards the growth region, thereby enhancing the compensation effect of downstream auxiliary sulfur supply on the substrate area, further reducing the sulfur concentration gradient in the growth region 2, improving the uniformity and stability of the sulfur atmosphere, and thus being more conducive to suppressing the formation of intrinsic defects such as sulfur vacancies, promoting the large-size, uniform and high-quality growth of monolayer molybdenum disulfide; the remaining steps and conditions are the same as in Example 1. Example 3

[0048] Based on Example 1, multiple micro-pits are formed at the bottom of the second quartz boat, and the molybdenum-containing precursor is dispersed and contained in each micro-pit. This prevents the molybdenum trioxide powder from being concentrated at the bottom of the second quartz boat, but instead arranges it in multiple micro-regions in a dispersed and quantitative manner. During the heating deposition process, the molybdenum-containing precursor in each micro-pit can be heated more uniformly and gradually volatilize, thereby reducing the supply fluctuations caused by excessively fast or slow local evaporation, improving the consistency and stability of molybdenum precursor release, and making the distribution of molybdenum source reaching the substrate surface more uniform. This is beneficial to improving the nucleation uniformity, grain size and crystal quality of monolayer molybdenum disulfide. Example 4

[0049] Based on Example 1, the third quartz boat adopts an asymmetric structural design, with one side of the boat wall being higher and the other side being lower, and the lower boat wall facing the growth region. Through this structure, the sulfur vapor formed after the sublimation of the second sulfur-containing precursor is more constrained on the side of the higher boat wall, and is more easily released and transported towards the growth region from the side of the lower boat wall. This provides directional guidance for the release direction of sulfur vapor, making the downstream auxiliary sulfur supply more concentrated in the area where the substrate is located, further enhancing the compensation effect on the sulfur atmosphere in the growth region, reducing the sulfur concentration gradient, improving the uniformity and stability of the sulfur chemical potential, and thus helping to suppress the formation of intrinsic defects such as sulfur vacancies, promoting the large-size, uniform and high-quality growth of monolayer molybdenum disulfide.

[0050] In summary, this invention provides a method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition. By setting sulfur-containing precursors upstream and downstream of the growth region 2, the concentration gradient caused by the decay of sulfur vapor along the path in the traditional single-sulfur source process is compensated, creating a more uniform, stable, and sufficient sulfur atmosphere environment. This promotes the uniform nucleation and lateral epitaxial growth of monolayer molybdenum disulfide and effectively suppresses the formation of intrinsic defects such as sulfur vacancies. Ultimately, this method achieves the preparation of large-size, uniform, and low-defect monolayer MoS2, which has good optical properties, process controllability, and promising prospects for widespread application.

[0051] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition, characterized in that, Includes the following steps: Step 1: Provide a chemical vapor deposition reaction chamber with an upstream region, a growth region, and a downstream region; Step 2: Arrange the molybdenum-containing precursor in the growth region, and arrange the substrate above or opposite the molybdenum-containing precursor; Step 3: Arrange a first sulfur-containing precursor in the upstream region and a second sulfur-containing precursor in the downstream region; Step 4: Introduce carrier gas into the reaction chamber and heat it up to cause the first sulfur-containing precursor, the second sulfur-containing precursor and the molybdenum-containing precursor to volatilize and undergo a chemical vapor deposition reaction on the substrate surface to form a monolayer of molybdenum disulfide.

2. The method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition as described in claim 1, characterized in that: The upstream and downstream regions are low-temperature regions, and the growth region is a high-temperature region.

3. The method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition as described in claim 1, characterized in that: Both the first sulfur-containing precursor and the second sulfur-containing precursor are sublimed sulfur powder; the molybdenum-containing precursor is molybdenum trioxide powder.

4. The method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition as described in claim 3, characterized in that: The mass ratio of the first sulfur-containing precursor, the molybdenum-containing precursor, and the second sulfur-containing precursor is 40:1:

20.

5. The method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition as described in claim 1, characterized in that: The substrate is a c-plane sapphire substrate.

6. The method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition as described in claim 5, characterized in that: The substrate is disposed on top of the molybdenum-containing precursor in an inverted manner.

7. The method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition as described in claim 6, characterized in that: The distance between the substrate growth surface and the molybdenum-containing precursor is 4-6 mm.

8. The method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition as described in claim 1, characterized in that: The carrier gas is argon.

9. The method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition as described in claim 1, characterized in that: The first sulfur-containing precursor, the molybdenum-containing precursor, and the second sulfur-containing precursor are respectively placed in the first quartz boat, the second quartz boat, and the third quartz boat.

10. The method for preparing monolayer molybdenum disulfide by dual-sulfur source chemical vapor deposition as described in claim 9, characterized in that: The third quartz boat is inclined relative to the horizontal plane, and its opening is directed towards the growth zone.

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