Double-layer corner molybdenum disulfide and preparation method thereof

Abstract

The preparation method comprises the following steps: 1) annealing: placing a molybdenum disulfide raw material on a quartz carrier, and placing the quartz carrier in a temperature zone of a dual-temperature zone tubular furnace; introducing inert gas from the deposition zone to the temperature zone to remove foreign gas; raising the temperature until the temperature of the temperature zone reaches 1185-1195 DEG C, then reducing the temperature, reducing the temperature until the temperature of the temperature zone reaches 995-1005 DEG C, then keeping the temperature for a certain time, and cooling to room temperature; 2) growth: after raising the temperature to 995-1005 DEG C, reversely adjusting the flow direction of the inert gas, and after growing for a certain time, obtaining double-layer corner molybdenum disulfide; the prepared double-layer corner molybdenum disulfide has various angles, has SHG intensity change with high angle dependence, shows novel optical performance, and is beneficial to exploring potential application of a TB-TMD material in nonlinear optics.

Description

Technical Field

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

[0002] Since the emergence of graphene in 2004, two-dimensional material systems have gradually come into people's view. Under the action of interlayer van der Waals forces, different two-dimensional materials with atomic-level thickness can be stacked in any order to construct artificial van der Waals heterojunctions and superlattice structures with atomic-scale flat interfaces. When two atomic layers are stacked together with a small lattice mismatch or a specific twist angle to form a moiré superlattice, this superlattice introduces strong correlation effects and quantum confined excited states through moiré periodic potential, providing a new control dimension for the study of strong correlation effects such as superconductivity, magnetism, and topology.

[0003] Transition Metal Dichalcogenides (TMDCs) play an important role in the two-dimensional material system. The general formula of TMDCs is MX 2 , where M represents transition metal elements, such as Mo, W, Nb, etc., and X represents chalcogen elements, such as S, Se, Te, etc. As a typical TMDCs material, the growth process and characterization methods of MoS2 are relatively mature. At the current stage, the processes for preparing twisted MoS2 are mostly mechanical exfoliation and transfer and chemical vapor deposition. Although the mechanical exfoliation and transfer method has a certain degree of universality, the process is relatively complicated, and there may be problems such as polymer residue, poor angle control and low success rate during the preparation process; and although the chemical vapor deposition method has developed rapidly in recent years, there are still problems such as the process is not simple enough and the variables that need to be controlled are relatively complex. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a double-layer twisted molybdenum disulfide and a preparation method thereof. The prepared double-layer twisted molybdenum disulfide has various angles and highly angle-dependent SHG intensity changes, showing novel optical properties, which is helpful to explore the potential application of TB-TMD materials in nonlinear optics.

[0005] The embodiment of the present invention provides a method for preparing a double-layer corner molybdenum disulfide, comprising the following steps: 1) Annealing: Place the molybdenum disulfide raw material on a quartz carrier, and the quartz carrier is placed in the temperature zone of a dual-temperature zone tube furnace; introduce inert gas from the deposition zone to the temperature zone to remove impurity gases; then heat the temperature to 1185-1195°C in the temperature zone and then cool it down to 995-1005°C in the temperature zone, keep it for a certain time, and cool it to room temperature; 2) Growth: After heating to 995-1005°C, adjust the flow direction of the inert gas in the opposite direction. After a certain period of growth, a double-layer corner MoS2 is obtained; Before growth, the silicon wafer substrate is placed in the deposition zone of a dual-temperature zone tube furnace; and inert gas is introduced from the deposition zone to the temperature zone to remove impurity gases.

[0006] Before growth, the silicon wafer substrate is placed in the deposition zone of the dual-temperature zone tubular furnace, that is, the silicon wafer substrate can be placed in the deposition zone of the dual-temperature zone tubular furnace during annealing, or the silicon wafer substrate can be placed in the deposition zone of the dual-temperature zone tubular furnace after annealing is completed and before growth. In the present invention, before growth, an inert gas is introduced from the deposition zone to the temperature zone to remove impurity gases. If the silicon wafer substrate needs to be placed after annealing and before growth, the inert gas needs to be introduced again after the placement is completed to remove the impurity gases. If the silicon wafer substrate does not need to be re-placed, the impurity gases can be directly removed during annealing without the need to re-introduce the inert gas to remove the impurity gases.

[0007] Preferably, the edge of the silicon wafer substrate penetrates into the temperature zone, and the penetration length is 0.5-1.5 cm.

[0008] Preferably, the inert gas is argon.

[0009] Preferably, the flow rate of the inert gas in the scrubbing stage is 250-350 sccm, and the flow rate in other stages is 120-150 sccm. The scrubbing stage is the initial stage of passing the inert gas.

[0010] Preferably, during annealing, the temperature is raised to 1190° C. in the temperature zone and then cooled to 1000° C. in the temperature zone and then maintained for 15 minutes.

[0011] Preferably, during growth, the flow direction of the inert gas is adjusted in the reverse direction, and after 3-5 minutes of growth, a double-layer corner molybdenum disulfide is obtained.

[0012] Preferably, when heating, the heating rate is 20 ℃·min -1 .

[0013] Preferably, the mass of the molybdenum disulfide raw material is 2 g.

[0014] Preferably, the size of the silicon wafer substrate is 1.5 cm×3 cm.

[0015] The embodiment of the present invention provides a double-layer corner molybdenum disulfide, which is prepared by the preparation method.

[0016] The beneficial effect of the present invention is that the present invention optimizes the process of preparing double-layer corner molybdenum disulfide based on the traditional chemical vapor deposition method. 2The powder is used as raw material to directly grow double-layer corner MoS2 by physical vapor deposition.

[0017] The present invention provides a method for preparing double-layer corner molybdenum disulfide based on physical vapor deposition technology, using MoS 2 Powder is used as raw material and prepared in a high-temperature tube furnace. The prepared double-layer twisted molybdenum disulfide has a wide angle range and a high yield. The prepared double-layer twisted molybdenum disulfide at different angles has different optical properties, and the material exhibits high crystal properties.

[0018] The present invention overcomes the problems of complex process, poor controllability, sample contamination and possible polymer residue in the process of preparing double-layer corner molybdenum disulfide by mechanical stripping and transfer method. The prepared double-layer corner molybdenum disulfide has good quality and novel optical properties.

[0019] The present invention overcomes the problems of complex growth system construction and high controllable precision requirements for growth conditions in the process of preparing double-layer corner molybdenum disulfide by chemical vapor deposition, and has a simple preparation process and strong controllability of parameter adjustment.

[0020] The present invention mainly includes two steps: annealing and growth. The first is the annealing step: the molybdenum disulfide raw material carried on a quartz carrier is placed in the central area of ​​the temperature zone of the double-temperature zone tubular furnace, and the silicon wafer substrate is placed in the deposition area of ​​the adjacent temperature zone of the double-temperature zone tubular furnace. Inert gas argon is introduced from the silicon wafer substrate to the temperature zone, and the gas is washed for three minutes to remove the impurity gas in the temperature zone tubular furnace. Then the temperature is increased at a heating rate of 20 ℃・min⁻¹. When the temperature of the temperature zone reaches 1190 ℃, the heating is stopped and it is allowed to cool naturally. After it drops to 1000 ℃, it is kept at a constant temperature for 15 minutes, and then the heating is stopped. It is allowed to cool naturally to room temperature, and the annealing step is completed.

[0021] Then enter the growth step: after the annealing stage, the silicon wafer substrate is placed in the deposition area of ​​the adjacent temperature zone of the double temperature zone tube furnace again, and inert gas argon is introduced from the silicon wafer substrate to the temperature zone, and the impurity gas is removed by washing for three minutes. The temperature is increased at a rate of 20 ℃・min⁻¹. When the temperature of the temperature zone reaches 1000 ℃, the direction of the gas flow is adjusted from the temperature zone to the silicon wafer substrate. Grow at a constant temperature of 1000 ℃ for 3-5 minutes, during which the double-layer corner molybdenum disulfide begins to deposit. After the growth is completed, stop heating, wait for it to cool naturally, and take out the silicon wafer to obtain the double-layer corner molybdenum disulfide.

[0022] By adopting the method of the present invention, a large number of samples (up to dozens) can be prepared in one growth process. The angles of the samples include common angles such as 0° and 60°, as well as angles other than 0° and 60°. Then, the required samples can be screened out, and samples with precise angle requirements can be obtained.

[0023] Traditional TMD materials, the means of regulating interlayer coupling are mostly focused on the number of layers, interlayer spacing, stacking order and doping, while the existence of interlayer angles provides a new degree of freedom for regulating the performance of MoS2. The change in interlayer angles is highly correlated with many properties, such as SHG intensity. This feature will help explore the potential application of TB-TMD materials in nonlinear optics. The preparation of double-layer angled MoS2 by the present invention is of great significance for the frontier exploration of the current field and the accumulation of technology that may promote its industrialization in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the experimental equipment for preparing double-layer corner MoS2 by PVD method.

[0025] Figure 2 Actual picture of the experimental equipment for preparing double-layer corner molybdenum disulfide by PVD method.

[0026] Figure 3 This is an optical photograph of the double-layer corner molybdenum disulfide prepared in Example 1.

[0027] Figure 4 This is a photoluminescence scan of the double-layer corner molybdenum disulfide prepared in Example 1.

[0028] Figure 5 Single photoluminescence spectra of double-layer twisted molybdenum disulfide at different angles prepared in Example 1.

[0029] Figure 6 This is the Raman scan image of the double-layer corner molybdenum disulfide prepared in Example 1.

[0030] Figure 7 These are single Raman spectra of double-layer twisted molybdenum disulfide at different angles prepared in Example 1.

[0031] Figure 8 This is the deposition morphology on the silicon wafer substrate prepared in Comparative Example 1.

[0032] Fig. 9 This is the deposition morphology on the silicon wafer substrate prepared in Comparative Example 2.

[0033] Fig.10 For MoS annealed in direct contact with the quartz boat 2 EDS spectrum analysis of raw materials. (A) and (B) are MoS 2 High-power optical imaging of the raw material after annealing ((A) is 500nm, (B) is 50nm), (C) is the energy spectrum analysis diagram of each element at this position, and (D) is the energy spectrum mapping scan diagram of the four elements Mo, S, Si, and O at this position. These four elements are the four elements that may exist in the growth system.

[0034] Fig.11 Schematic diagram of a double-layer molybdenum disulfide, with the upper and lower layers twisted relative to each other by 0° (left) and 60° (right).

[0035] Fig.12 Statistics of the number of double-layer rotated MoS2 and 0° / 60° samples. The red counts are double-layer rotated MoS2 samples (scale bar: 50μm).

[0036] Fig.13 is the angle-dependent change in SHG relative intensity.

[0037] In the figure, 1 is deposition zone, 2 is temperature zone, 3 is silicon wafer substrate, and 4 is molybdenum disulfide raw material. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below by specific examples, wherein the raw materials are all industrial products. The examples are only used to explain the present invention and cannot be construed as limiting the present invention. Changes or modifications to the equivalent forms of the present invention by those skilled in the art also fall within the scope defined by the appended claims of the present application.

[0039] Example 1 The present invention provides a method for preparing double-layer MoS2 with angles. The experiment of growing double-layer MoS2 with various interlayer angles is carried out in a double-temperature zone tubular furnace. The experimental device is as follows: Figure 1-2 shown.

[0040] The double-temperature zone tubular furnace includes a deposition zone 1 and a temperature zone 2 connected in sequence. Quartz boats are placed in both deposition zone 1 and temperature zone 2. A silicon wafer substrate 3 is placed in the quartz boat in deposition zone 1, and a molybdenum disulfide raw material 4 (in powder form) is placed in the quartz boat in temperature zone 2.

[0041] Other known supporting equipment of the supporting dual-temperature zone tubular furnace also includes an argon tank, a three-way pipe, a flange, a switch, a quartz boat, a quartz tube, a silicon wafer, etc.

[0042] The preparation method of double-layer corner molybdenum disulfide specifically comprises the following steps: Step 1: Annealing.

[0043] 1) Weigh 2 g of molybdenum disulfide raw material 4 (powder), spread it evenly on the base of a quartz boat (the quartz boat container is 11 cm long and 1.5 cm wide), and place the quartz boat carrying the molybdenum disulfide raw material 4 in the center area of ​​temperature zone 2 of a dual-temperature zone tubular furnace.

[0044] 2) Assemble the flange components at both ends of the furnace tube of the dual-temperature zone tubular furnace and close the gas circuit.

[0045] 3) Introduce inert gas argon from the silicon wafer substrate 3 to the temperature zone 2 (i.e. Figure 1 From right to left), the gas flow rate is 300 sccm, and the purge is performed for three minutes to remove the impurity gas in the dual-temperature zone tube furnace. After the purge is completed, the gas flow rate is adjusted to 120 sccm until the entire annealing process is completed.

[0046] 4) Heating: The temperature in temperature zone 2 is increased at a rate of 20 °C per minute. When the temperature reaches 1190 °C, heating is stopped and the temperature is naturally cooled. After the temperature drops to 1000 °C, the temperature is kept constant for 15 minutes and then heating is stopped. After it is naturally cooled to room temperature, the annealing step is completed.

[0047] Step 2: Growth.

[0048] 1) After the annealing stage in step 1, select SiO 2 / Si substrate (i.e. silicon wafer substrate 3) is placed in the temperature changing area (i.e. deposition area 1) of the dual temperature zone tube furnace adjacent to temperature zone 2. The left end of silicon wafer substrate 3 extends into temperature zone 2 by about 1 cm.

[0049] 2) Introduce inert gas argon (i.e. Figure 1 The gas flow rate is 300 sccm, and the purge is performed for three minutes to remove the impurity gas in the dual-temperature zone tube furnace. After the purge is completed, the gas flow rate is adjusted to 150 sccm until the entire growth process is completed.

[0050] 3) Then the temperature is raised, and the temperature of temperature zone 2 is raised at 20 °C per minute. After the temperature reaches 1000 °C, the direction of the incoming airflow is adjusted from temperature zone 2 to silicon wafer substrate 3. Constant temperature growth is carried out at 1000 °C for 4 minutes, and double-layer corner MoS2 begins to be deposited.

[0051] 4) After the growth is completed, stop heating, wait for it to cool naturally, take out the silicon wafer, and you can get a double-layer corner molybdenum disulfide.

[0052] The performance of the double-layer corner molybdenum disulfide obtained in Example 1 was tested and the following results were obtained: Figure 3-7 Performance table shown.

[0053] from Figure 3-4 It can be seen that the double-layer corner molybdenum disulfide can be prepared by the above method.

[0054] Figure 5 It can be shown that the double-layer MoS2 has an adjustable Raman peak position corresponding to the rotation angle, showing an angle-dependent E 1 2g Mode and A 1g The peak position of the mode changes.

[0055] Figure 7 It can be shown that double-layer rotated MoS2 has an angle-dependent PL response, and as the rotation angle changes, the PL response is special at certain specific angles (such as 11.8° and 42.3°), which means that changes in the interlayer rotation angle may affect the band structure of MoS2.

[0056] The present invention is more advantageous in that the temperature is raised again for growth after the annealing is completed and the temperature is lowered than in direct growth without lowering the temperature. The possible reason is that the existence of the temperature lowering process is conducive to the formation of the growth atmosphere in the furnace tube.

[0057] Comparative Example 1 Comparative Example 1 is compared with Example 1, except that the annealing process is not performed, and the following steps are included: 1) Weigh 2 g of molybdenum disulfide raw material 4 (powder), spread it evenly on the base of a quartz boat (the quartz boat container is 11 cm long and 1.5 cm wide), and place the quartz boat carrying the molybdenum disulfide raw material 4 in the center area of ​​temperature zone 2 of a dual-temperature zone tubular furnace.

[0058] 2) Assemble the flange components at both ends of the furnace tube of the dual-temperature zone tubular furnace and close the gas circuit.

[0059] 3) Introduce inert gas argon from the silicon wafer substrate 3 to the temperature zone 2 (i.e. Figure 1 The gas flow rate is 300 sccm, and the purge is performed for three minutes to remove the impurity gas in the dual-temperature zone tube furnace. After the purge is completed, the gas flow rate is adjusted to 150 sccm until the entire growth process is completed.

[0060] 4) Heating: Temperature zone 2 is heated at a rate of 20 °C per minute. When the temperature reaches 1000 °C, the direction of the incoming airflow is adjusted from temperature zone 2 to silicon wafer substrate 1, and constant temperature growth is carried out at 1000 °C for 4 minutes.

[0061] 5) Stop heating, wait for it to cool naturally, and take out the silicon wafer.

[0062] The deposition morphology of the silicon wafer of Comparative Example 1 was observed under an optical microscope (see Figure 8 ), it can be seen that without the annealing process, under the same growth conditions, almost no molybdenum disulfide is deposited on the silicon wafer substrate 3.

[0063] The growth system without annealing treatment has no growth atmosphere, so no molybdenum sulfide is deposited on the silicon wafer substrate that is directly grown at high temperature.

[0064] Comparative Example 2 Compared with Example 1, the difference is that in step 4 of annealing, i.e., heating, the temperature zone 2 is heated at a rate of 20°C per minute, and after the temperature reaches 1190°C, the temperature is kept constant for 15 minutes and then the heating is stopped. After the temperature is naturally cooled to room temperature, the annealing step is completed. The rest is the same as Example 1.

[0065] The deposition morphology of the silicon wafer of Comparative Example 2 was observed under an optical microscope (see Fig. 9 ), it can be seen that after long-term high-temperature annealing treatment, under the same growth conditions, the deposition morphology is disordered.

[0066] Continuous annealing at high temperature for a long time will cause the growth atmosphere in the furnace tube to be destroyed, making it impossible to achieve good corner MoS2 sample deposition.

[0067] The present invention is kept warm at 1000°C to prevent excessive annealing. Although long-term annealing at an extremely high temperature of 1190°C does not affect the incorporation of O elements into the raw materials, it will damage the growth atmosphere in the furnace tube due to its high temperature for too long, and the optimal growth atmosphere cannot be achieved. Therefore, the process of reaching 1190°C is very important, because such a high temperature is required to adjust the growth atmosphere, but the time cannot be too long. However, since continuous annealing is required to oxygenate the raw materials, constant temperature annealing is selected at an appropriate temperature of 1000°C. This ensures that long-term annealing at this temperature will not affect the growth atmosphere, and also ensures that the raw materials are fully oxygenated.

[0068] The present invention promotes the decomposition of silicon dioxide in the quartz boat during the annealing process, and the oxygen element obtained by the decomposition is combined with the interior of the molybdenum disulfide raw material. The presence of the oxygen element reduces the binding energy of the molybdenum disulfide with a high binding energy, that is, it is not easy to form a double-layer corner, thereby reducing the difficulty of its formation, which leads to the deposition of double-layer corner molybdenum disulfide. MoS annealed in direct contact with the quartz boat 2 Raw material EDS spectrum analysis see Fig.10 , Fig.10 (C) shows the addition of MoS 2 In addition to the conventional element peaks, there is also an O element peak. Fig.10 (D) shows that the distribution of O element is highly consistent with the white area in the optical imaging, showing a significant enrichment of O element. It can be seen that after annealing, MoS 2 The raw material contains SiO 2 This means that after this treatment, the O element was successfully incorporated into MoS 2 In raw materials.

[0069] During annealing, the annealing temperature of the present invention is a high temperature of about 1190°C and is kept constant at 1000°C for a period of time. This process not only promotes the decomposition of silicon dioxide, but also forms a growth atmosphere on the tube wall of the double-temperature zone tube furnace.

[0070] The double-layer MoS2 deposited by the present invention is different from the conventional double-layer MoS2. In the conventional double-layer MoS2, the relative angles between the upper and lower layers are usually 0° and 60°, which is a highly symmetrical situation (see Fig.11 ), so we usually refer to these two morphologies as "double-layer MoS2", which means that the relative angle between the layers is not special. Using the method of this application, it can be found that the relative angle between the upper and lower layers of MoS2 is not only 0° and 60°, but also a large number of double-layer MoS2 with angles other than 0° and 60°, and the proportion of their occurrence can reach about 50% (see Fig.12 ).

[0071] For double-layer MoS2 with non-0° and 60° angles, the different twist angles between the upper and lower layers provide a new degree of control freedom, thus developing many angle-tunable properties that are highly correlated with the angle between the layers. This is the most intuitive characteristic brought by the angle. For example, in our tests, we found that the change trend of the second harmonic signal of double-layer MoS2 with angles is highly correlated with the angle between the layers (see Fig.13 ).

[0072] A person skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of protection of the present application is limited to these examples. In line with the concept of the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0073] One or more embodiments of the present application are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the present application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a double-layer corner molybdenum disulfide, characterized in that: The steps include: 1) Annealing: Place the molybdenum disulfide raw material on a quartz carrier, and the quartz carrier is placed in the temperature zone of a dual-temperature zone tube furnace; introduce inert gas from the deposition zone to the temperature zone to remove impurity gases; then heat the temperature to 1185-1195°C in the temperature zone and then cool it down to 995-1005°C in the temperature zone, keep it for a certain time, and cool it to room temperature; 2) Growth: After heating to 995-1005°C, adjust the flow direction of the inert gas in the opposite direction. After a certain period of growth, a double-layer corner MoS2 is obtained; Before growth, the silicon wafer substrate is placed in the deposition zone of a dual-temperature zone tube furnace; and inert gas is introduced from the deposition zone to the temperature zone to remove impurity gases.

2. The preparation method according to claim 1, characterized in that: The edge of the silicon wafer substrate penetrates into the temperature zone, and the penetration length is 0.5-1.5 cm.

3. The preparation method according to claim 1, characterized in that: The inert gas is argon.

4. The preparation method according to claim 1, characterized in that: The flow rate of the inert gas in the purge stage is 250-350 sccm, and the flow rate in other stages is 120-150 sccm. The purge stage is the initial stage of passing the inert gas.

5. The preparation method according to claim 1, characterized in that: During annealing, the temperature is raised to 1190°C in the temperature zone and then cooled down to 1000°C in the temperature zone and maintained for 15 minutes.

6. The preparation method according to claim 1, characterized in that: During the growth, the flow direction of the inert gas is adjusted in the reverse direction, and after 3-5 minutes of growth, a double-layer corner molybdenum disulfide is obtained.

7. The preparation method according to claim 1, characterized in that: When heating, the heating rate is 20 ℃·min -1 .

8. The preparation method according to claim 1, characterized in that: The mass of the molybdenum disulfide raw material is 2 g.

9. The preparation method according to claim 1, characterized in that: The size of the silicon wafer substrate is 1.5 cm×3 cm.

10. A double-layer corner molybdenum disulfide, characterized in that: The preparation is obtained by the preparation method according to any one of claims 1 to 9.

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