Corner double-layer molybdenum disulfide and preparation method thereof

Abstract

The preparation method comprises the following steps: (1) uniformly mixing ammonium phosphomolybdate hydrate and sodium chloride, loading the mixture into a porcelain boat, inversely placing a silicon wafer above the porcelain boat, and then placing the porcelain boat at the central position of a tubular furnace; loading sulfur powder into another porcelain boat, and then placing the porcelain boat at the pipe orifice of the gas inlet end of the tubular furnace; (2) introducing argon into the tubular furnace to remove foreign gases, then adjusting the flow of the argon, heating until the central position of the tubular furnace reaches 700-800 DEG C, then pushing the porcelain boat loaded with the sulfur powder to a position with the temperature of 250-350 DEG C, introducing hydrogen after a certain time to form disturbance, closing the hydrogen after the disturbance is finished until the reaction is finished, and cooling to room temperature to obtain the sulfur powder. The corner double-layer molybdenum disulfide is obtained. According to the method, controllable synthesis of TB-MoS2 with the torsion angle of 0-120 degrees and the size of 10-20 microns is realized through an H2 disturbance auxiliary dynamic regulation and control strategy.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic two-dimensional material preparation, and specifically relates to a corner double-layer molybdenum disulfide and a preparation method thereof. Background Art

[0002] Molybdenum disulfide (MoS2) is a typical transition metal dichalcogenide (TMDCs). Due to its layered structure, tunable band gap and significant exciton effect, it shows broad application prospects in optoelectronic devices, tribology and flexible sensing. However, traditional performance optimization strategies (such as size control, element doping and heterostructure construction) have gradually approached physical limits. In recent years, the introduction of the moiré superlattice effect by changing the interlayer twist angle (θ) has provided new degrees of freedom for the performance control of MoS2. TB-MoS2 is a 2D van der Waals homogeneous structure formed by stacking two monolayer MoS2 at specific twist angles other than 0° and 60°. As a typical representative of the corner 2D material system, TB-MoS2 has attracted extensive research in the fields of condensed matter physics and functional materials in recent years due to its interlayer coupling and novel quantum phenomena induced by the moiré superlattice.

[0003] However, the controllable preparation of TB-MoS2 still faces key scientific challenges. Existing physical stacking methods are prone to introduce interface contamination, resulting in a significant attenuation of the interlayer electronic coupling strength; and mechanical folding methods are limited by sample size and angle control accuracy. In contrast, chemical vapor deposition (CVD) is considered a better solution to these bottlenecks due to its intrinsic clean interface and large-area growth potential. However, the traditional CVD growth process is dominated by thermodynamic equilibrium, and bilayer MoS2 tends to form a 0° or 60° stacking structure, while the formation of "special twist angles (i.e., non-0° and 60°)" requires overcoming high energy barriers, which makes the CVD synthesis of TB-MoS2 face technical obstacles. Summary of the Invention

[0004] In response to the problems existing in the existing CVD preparation, the purpose of the present invention is to provide a twisted bilayer molybdenum disulfide and a preparation method thereof. Using ammonium phosphomolybdate hydrate and S as precursors, and through the H2 perturbation-assisted dynamic control strategy, the controllable synthesis of TB-MoS2 with a twist angle of 0°~120° and a size of 10~20μm is achieved.

[0005] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0006] A method for preparing a corner double-layer molybdenum disulfide comprises the following steps:

[0007] (1) Ammonium phosphomolybdate hydrate and sodium chloride are uniformly mixed and loaded into a porcelain boat, a silicon wafer is inverted on top of the porcelain boat, and then the porcelain boat is placed in the center of a tube furnace; sulfur powder is loaded into another porcelain boat, and then the porcelain boat is placed at the nozzle of the air inlet end of the tube furnace;

[0008] (2) Inert gas is continuously introduced into the tube furnace to remove impurity gases, and then the inert gas flow rate is adjusted and the temperature is raised to 700-800°C at the center of the tube furnace. Then, the porcelain boat loaded with sulfur powder is pushed along the air flow direction to a position with a temperature of 250-350°C, and hydrogen is introduced after a certain period of time to form a disturbance. After the disturbance ends, the hydrogen is turned off until the reaction ends, and the corner double-layer molybdenum disulfide is obtained.

[0009] Preferably, in step (1), the mass ratio of the ammonium phosphomolybdate hydrate to sodium chloride is 2 to 5:1; and the mass ratio of sulfur powder to ammonium phosphomolybdate hydrate is 30 to 40:1.

[0010] Preferably, in step (1), the size of the silicon wafer substrate is 1 cm × 2 cm, and it is placed in a watch glass containing a piranha solution (prepared by 30% H2O2 and analytical grade H2SO4 in a volume ratio of 3:7), heated to 100 ° C. and kept for 1 hour for pretreatment to remove surface impurities, and then washed several times with ultrapure water and then blown dry with N2 for use.

[0011] Preferably, in step (2), the inert gas is argon.

[0012] Preferably, in step (2), the flow rate of argon gas during the process of removing impurity gas is 250-350 sccm, and the adjusted flow rate of argon gas is 30-80 sccm.

[0013] Preferably, in step (2), the time for introducing hydrogen is 30 to 120 seconds; the flow rate of hydrogen is 2 to 12 sccm; and the disturbance time is 1 to 6 minutes.

[0014] More preferably, in step (2), the time for introducing hydrogen is 60 s; the flow rate of hydrogen is 10 sccm; and the disturbance time is 4 min.

[0015] Preferably, in step (2), the timing starts from when the porcelain boat loaded with sulfur powder is pushed along the airflow direction to a position with a temperature of 250-350° C., and continues until the reaction is completed, and the total reaction time is 7 minutes.

[0016] The present invention also provides a corner double-layer molybdenum disulfide prepared by the above preparation method.

[0017] The present invention uses ammonium phosphomolybdate hydrate as the molybdenum source precursor. As the reaction temperature gradually increases, ammonium phosphomolybdate hydrate begins to undergo a complex thermal decomposition process. When the temperature reaches about 600°C, ammonium phosphomolybdate hydrate decomposes to form non-stoichiometric phosphomolybdate (P2O5Mo 24 O 66 ). When the temperature is further increased, P2O5Mo 24 O 66 Continue to decompose and eventually generate molybdenum oxide (Mo x O y ), since NaCl exists as molten salt, Mo x O y It can also react with NaCl to generate Mo x O y Cl z These molybdenum-related compounds act as key active intermediates and participate in the subsequent synthesis process of MoS2.

[0018] The present invention uses hydrogen as a disturbing gas flow. After hydrogen is introduced into the reaction system, sulfur powder reacts with hydrogen to generate hydrogen sulfide. Since hydrogen sulfide is significantly more reducible than elemental sulfur, it can react with the molybdenum active precursor more efficiently, thereby significantly improving the overall reaction activity. More importantly, the introduction of a hydrogen atmosphere will lead to more local high-temperature areas in the temperature field. This effect has the following important effects: 1) promoting the thermal decomposition process of reactants; 2) enhancing the diffusion capacity of atoms; 3) significantly increasing the concentration of active molecules. These changes significantly change the number of active molecules at the nucleation site and their motion characteristics, providing the necessary conditions for the torsional growth of the second layer of crystal nuclei. In short, hydrogen not only has a disturbing effect in the process of CVD growth of TB-MoS2, but also has the effects of etching and promoting growth.

[0019] Beneficial effects of the present invention:

[0020] Given that the traditional CVD growth process is dominated by thermodynamic equilibrium, bilayer MoS2 tends to form stacked structures at 0° or 60°. However, the formation of "special twist angles (i.e., non-0° and non-60°)" requires overcoming high energy barriers, which makes the CVD synthesis of TB-MoS2 face technical obstacles. The present invention uses ammonium phosphomolybdate hydrate and S as precursors and achieves the controllable synthesis of TB-MoS2 through an H2 perturbation-assisted kinetic regulation strategy. The ratio can reach as high as 51.22%, and an average of 48 TB-MoS2 are generated on each silicon wafer. These products exhibit a rich range of twist angles in the range of 0° to 120°. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the reaction process.

[0022] Figure 2 OM image of the sample prepared in Comparative Example 1 (scale bar: 5 μm).

[0023] Figure 3 OM images of the sample obtained by the torsion angle measurement method (a) and the introduction of H2 perturbation at 30s (b) in Example 1 (scale bar: 5μm).

[0024] Figure 4 This is the OM image of the sample obtained by introducing H2 perturbation at 60s in Example 1 (scale bar: 5μm).

[0025] Figure 5 OM images of the sample obtained by introducing H2 perturbation at 90s (a) and 120s (b) in Example 1 (scale bar: 5μm).

[0026] Figure 6 This is the evolution diagram of the percentage, number and morphology of TB-MoS2 when H2 is introduced at different times in Example 1 (scale: 5μm).

[0027] Figure 7 OM images of the samples prepared in Example 1 when the H2 flow rate was 2 sccm (a) and 4 sccm (b) (scale bar: 5 μm).

[0028] Figure 8 OM images of the samples prepared in Example 1 when the H2 flow rate was 6 sccm (a) and 8 sccm (b) (scale bar: 5 μm).

[0029] Figure 9 OM image of the sample prepared in Example 1 when the H2 flow rate is 10 sccm (scale bar: 5 μm).

[0030] Figure 10 OM image of the sample prepared in Example 1 when the H2 flow rate is 12 sccm (scale bar: 5 μm).

[0031] Figure 11 This is the evolution diagram of TB-MoS2 percentage, number and morphology at different H2 flow rates in Example 1 (scale: 5μm).

[0032] Figure 12 OM images of the samples prepared when H2 was introduced for 1 min (a), 2 min (b), and 3 min (c) in Example 1 (scale bar: 5 μm).

[0033] Figure 13 This is the OM image of the sample prepared when the H2 introduction time was 4 min in Example 1 (scale bar: 5 μm).

[0034] Figure 14This is the OM image of the sample prepared when the H2 introduction time was 5 min in Example 1 (scale bar: 5 μm).

[0035] Figure 15 This is the OM image of the sample prepared when the H2 introduction time was 6 min in Example 1 (scale bar: 5 μm).

[0036] Figure 16 This is the evolution diagram of the percentage, number and morphology of TB-MoS2 with different H2 introduction time in Example 1 (scale: 5μm). DETAILED DESCRIPTION

[0037] The following is further described in conjunction with specific examples to make the technical solution of the present invention easier for those skilled in the art to understand. Unless otherwise specified, the raw materials used in the following examples are all commercially available conventional products, such as:

[0038] Table 1 Some experimental reagents

[0039]

[0040]

[0041] Comparative Example 1

[0042] (1) Substrate processing

[0043] Cut the SiO2 / Si substrate into 1cm×2cm pieces and place them in a watch glass for later use. To obtain a substrate with a clean surface, it needs to be treated. Prepare 20mL of piranha solution, which consists of 30% H2O2 and analytically pure H2SO4 in a volume ratio of 3:7. Place the cut silicon wafer in the piranha solution and heat it on a hot plate (100°C for 1 hour). The principle of its action is that the piranha solution has extremely strong oxidizing properties and can remove impurities on the surface of the silicon wafer. After heating, cool the silicon wafer to room temperature and then rinse it several times in ultrapure water. After rinsing, blow it dry with N2 for later use.

[0044] (2) The growth experiment of single-layer MoS2 was carried out in a single-temperature zone tubular furnace. The quartz tube used was 100 cm long, 2.6 cm in inner diameter, and 0.2 cm thick. In the experiment, 15 mg of ammonium phosphomolybdate hydrate and 4 mg of NaCl were first accurately weighed using an analytical balance, and after uniformly mixing them, they were placed in the center of a high-temperature resistant alumina porcelain boat. Subsequently, the silicon wafer was placed upside down directly above the mixed powder, and the entire porcelain boat was placed in the center of the high-temperature zone of the tubular furnace. In addition, 500 mg of sulfur powder was weighed, loaded on the front end of another alumina porcelain boat, and placed at the nozzle of the air inlet end of the tubular furnace. In the experiment, ammonium phosphomolybdate was used as a molybdenum source, NaCl was used as a flux, and S was used as a sulfur source. The schematic diagram of the reaction process is shown in FIG. Figure 1 shown.

[0045] Before the experiment began, the tube furnace was sealed and Ar was introduced at a flow rate of 300 sccm for 10 minutes to expel air from the tube. After the purge was complete, the gas flow rate was adjusted to 50 sccm Ar, and the tube furnace temperature ramp was initiated, increasing the temperature to 770°C over 35 minutes. Once the set temperature was reached, S was pushed to a low-temperature range of approximately 300°C for a reaction time of 7 minutes. After the reaction was completed, the furnace was allowed to cool to room temperature before the sample was removed.

[0046] like Figure 2 The following is an OM image of the sample prepared in Comparative Example 1. No bilayer MoS2 formation was observed, and the primary product was single-layer MoS2. These single-layer MoS2 exhibited a regular shape, nearly an equilateral triangle, and had a high surface cleanliness with no obvious impurities or defects. This result indicates that in the absence of H2 perturbation, MoS2 growth tends to form a single-layer structure with high crystal quality.

[0047] Example 1

[0048] (1) Substrate processing

[0049] Cut the SiO2 / Si substrate into 1cm×2cm pieces and place them in a watch glass for later use. To obtain a substrate with a clean surface, it needs to be treated. Prepare 20mL of piranha solution, which consists of 30% H2O2 and analytically pure H2SO4 in a volume ratio of 3:7. Place the cut silicon wafer in the piranha solution and heat it on a hot plate (100°C for 1 hour). The principle of its action is that the piranha solution has extremely strong oxidizing properties and can remove impurities on the surface of the silicon wafer. After heating, cool the silicon wafer to room temperature and then rinse it several times in ultrapure water. After rinsing, blow it dry with N2 for later use.

[0050] (2) The growth experiment of TB-MoS2 was carried out in a single-temperature zone tubular furnace. The quartz tube used was 100 cm long, 2.6 cm in inner diameter, and 0.2 cm thick. In the experiment, 15 mg of ammonium phosphomolybdate hydrate and 4 mg of NaCl were first accurately weighed using an analytical balance, and after uniformly mixing them, they were placed in the center of a high-temperature resistant alumina porcelain boat. Subsequently, the silicon wafer was placed upside down directly above the mixed powder, and the entire porcelain boat was placed in the center of the high-temperature zone of the tubular furnace. In addition, 500 mg of sulfur powder was weighed, loaded on the front end of another alumina porcelain boat, and placed at the nozzle of the air inlet end of the tubular furnace. In the experiment, ammonium phosphomolybdate was used as a molybdenum source, NaCl was used as a flux, and S was used as a sulfur source. The schematic diagram of the reaction process is shown in FIG. Figure 1 shown.

[0051] Before the experiment began, the tube furnace was sealed and Ar was introduced at a flow rate of 300 sccm for 10 minutes to expel air from the tube. After the purge was complete, the gas flow rate was adjusted to 50 sccm Ar, and the tube furnace temperature ramp was initiated, heating to 770°C over a 35-minute period. After reaching the set temperature, S was pushed to a low-temperature range of approximately 300°C. After a certain period of time (30s, 60s, 90s, and 120s), H2 (2sccm, 4sccm, 6sccm, 8sccm, 10sccm, and 12sccm) was introduced to create a turbulent flow. The turbulence continued for a certain period of time (1min, 2min, 3min, 4min, 5min, and 6min), after which H2 was turned off and the temperature was maintained at 770°C for a total reaction time of 7 minutes. After the reaction was completed, the furnace was cooled to room temperature before the sample was removed.

[0052] like Figure 3 (a) shows the method for determining the torsion angle. When H2 perturbation is introduced at 30 s, the resulting TB-MoS2 product is smaller in size. The limitation of the bottom layer size also limits the top layer size, with most top layers smaller than 5 μm (b).

[0053] like Figure 4 As shown in the figure, when H2 perturbation is introduced at 60s, more TB-MoS2 with a bottom size of 10μm and a top size of more than 5μm can be generated, and TB-MoS2 with a variety of twist angles are observed, including 20°, 23°, 28°, 30°, 34°, 40°, 80°, 82°, 85°, 88°, 90°, 95°, 97° and 104°. Figure 6 The Yield in the vertical axis represents the proportion of TB-MoS2 in the double-layer MoS2. When H2 perturbation is introduced at 60s, the average proportion of TB-MoS2 is the highest (31.77%), and the average number of TB-MoS2 produced on each silicon wafer is 31.

[0054] like Figure 5As shown in the figure, when H2 perturbation is introduced at 90s and 120s, although the bottom layer size increases, the top layer size decreases. This is because H2 is introduced at a later time point, and the top layer growth time is insufficient. This shows that as the introduction of H2 is delayed, the bottom layer size gradually increases, while the value of the top layer size / bottom layer size decreases. When H2 perturbation is introduced at 60s, the growth conditions of the bottom and top layers are most ideal, which is conducive to the formation of high-quality double-layer products.

[0055] like Figure 7 and 8 As shown in the figure, when the H2 flow rate is less than 10 sccm, the size of the generated TB-MoS2 products is mostly less than 10 μm, and the bottom layer is irregular in shape and severely deformed. This indicates that when the H2 flow rate is small, the degree of growth promotion is insufficient and the bottom layer growth is incomplete.

[0056] like Figure 9 As shown in Figure 2, when the turbulent gas flow reaches 10 sccm, the growth is more complete, more regular TB-MoS2 can be produced, the torsion angle distribution is wider, and the number of TB-MoS2 reaches 31 per silicon wafer, which is much higher than that under other conditions ( Figure 11 ), which shows that the H2 flow rate of 10sccm can effectively optimize the reaction environment, promote the uniform growth of the bottom and top layers, and thus obtain TB-MoS2 of better quality.

[0057] like Figure 10 As shown in Figure 2, by increasing the H2 flow rate to 12 sccm, the size of TB-MoS2 is greatly reduced, and the proportion and number of TB-MoS2 are greatly reduced ( Figure 11 ), which indicates that too high H2 flow rate may lead to enhanced etching effect. Figure 11 The morphological evolution of the TB-MoS2 further confirms that when the H2 flow rate is too high, the etching effect in the reaction system exceeds the growth effect, resulting in a decrease in product quality. Therefore, H2 not only has a perturbation effect during the CVD growth of TB-MoS2, but also has both growth and etching effects. Proper control of the gas flow rate is necessary to grow a high-quality product.

[0058] like Figure 12 As shown in the figure, when the H2 introduction time is short (1min, 2min, and 3min), the shape of the product shows a certain degree of deformation. Due to the insufficient H2 introduction time, the bottom and top MoS2 layers do not grow completely and fail to form a regular triangular shape. This shows that H2 promotes epitaxial growth during the CVD growth process. Too short an introduction time will limit the complete growth of the product, resulting in an irregular morphology.

[0059] like Figure 13 and 14As shown in the figure, when the H2 introduction time is increased to 4min and 5min, the growth of the product tends to be complete, and the generated TB-MoS2 is larger in size and more regular in shape. This shows that within this time range, the etching effect and growth promotion effect of H2 reach the best balance, which is conducive to the formation of high-quality TB-MoS2. Figure 16 When H2 was introduced for 4 minutes, the proportion of TB-MoS2 reached 51.22%, and an average of 48 TB-MoS2 were generated on each silicon wafer. These products showed a rich variety of torsion angles, including 18°, 25°, 28°, 30°, 32°, 34°, 40°, 43°, 45°, 50°, 73°, 77°, 81°, 83°, 85°, 88°, 90°, 93°, 95°, 97°, 100°, etc. The bottom layer size was 10-20μm, and the size of the top layer MoS2 could reach more than 5μm.

[0060] like Figure 15 As shown in the figure, when the H2 introduction time is extended to 6 minutes, the product shape generally presents a truncated triangle, indicating that the long H2 introduction time will lead to etching starting from the top corner of the triangle.

[0061] comprehensive Figure 3-16 As shown, the present invention realizes the controllable synthesis of TB-MoS2 with a torsion angle of 0° to 120° and a size of 10 to 20 μm through the H2 perturbation-assisted dynamic control strategy.

Claims

1. A method for preparing a corner double-layer molybdenum disulfide, characterized in that: The steps include: (1) Ammonium phosphomolybdate hydrate and sodium chloride are uniformly mixed and loaded into a porcelain boat, a silicon wafer is inverted on top of the porcelain boat, and then the porcelain boat is placed in the center of a tube furnace; sulfur powder is loaded into another porcelain boat, and then the porcelain boat is placed at the nozzle of the air inlet end of the tube furnace; (2) Inert gas is continuously introduced into the tube furnace to remove impurity gases, and then the inert gas flow rate is adjusted and the temperature is raised to 700-800°C at the center of the tube furnace. Then, the porcelain boat loaded with sulfur powder is pushed along the air flow direction to a position with a temperature of 250-350°C, and hydrogen is introduced after a certain period of time to form a disturbance. After the disturbance ends, the hydrogen is turned off until the reaction ends, and the corner double-layer molybdenum disulfide is obtained.

2. The preparation method according to claim 1, characterized in that In step (1), the mass ratio of the ammonium phosphomolybdate hydrate to sodium chloride is 2-5:1; the mass ratio of sulfur powder to ammonium phosphomolybdate hydrate is 30-40:

1.

3. The preparation method according to claim 1, characterized in that In step (1), the silicon wafer substrate is 1 cm × 2 cm in size and is placed in a watch glass containing piranha solution. It is heated to 100°C and kept for 1 hour for pretreatment to remove surface impurities. It is then washed several times with ultrapure water and blown dry with N2 for later use.

4. The preparation method according to claim 1, characterized in that In step (2), the inert gas is argon.

5. The preparation method according to claim 1, characterized in that In step (2), the flow rate of argon gas during the process of removing impurity gas is 250-350 sccm, and the adjusted flow rate of argon gas is 30-80 sccm.

6. The preparation method according to claim 1, characterized in that In step (2), the time for introducing hydrogen is 30 to 120 seconds; the flow rate of hydrogen is 2 to 12 sccm; and the disturbance time is 1 to 6 minutes.

7. The preparation method according to claim 6, characterized in that In step (2), the time for introducing hydrogen is 60 seconds; the flow rate of hydrogen is 10 sccm; and the disturbance time is 4 minutes.

8. The preparation method according to claim 1, characterized in that In step (2), the timing starts from when the porcelain boat loaded with sulfur powder is pushed along the airflow direction to a position with a temperature of 250-350° C., and continues until the reaction is completed. The total reaction time is 7 minutes.

9. Corner double-layer molybdenum disulfide prepared by the preparation method according to any one of claims 1 to 8.

Images