Pre-evaporated large-area single-layer molybdenum diselenide thin film and preparation method thereof

Abstract

The invention discloses a pre-evaporated large-area single-layer molybdenum diselenide thin film and a preparation method thereof. The method comprises the following steps: sequentially placing a first quartz boat loaded with a selenium source and a second quartz boat loaded with a molybdenum source mixture at the upstream and the downstream of a multi-temperature-zone tubular furnace, and pre-evaporating in a normal-pressure sealed state after gas washing; and after the pre-evaporation is finished, respectively supplementing a selenium source and molybdenum source mixture, placing the substrate right above a second quartz boat, carrying out gas washing, and carrying out a selenylation reaction in a normal-pressure ventilation state, so as to obtain the product. According to the method, normal-pressure growth of molybdenum diselenide is achieved at a low temperature based on the synergistic effect between pre-evaporation and selenylation reaction, the preparation cost of the film is greatly reduced, the molybdenum diselenide film obtained through the method is high in crystallinity, the area can reach the centimeter level, the uniformity is good, and it is detected that the size of the obtained film is larger than or equal to 0.5 cm, and the surface is uniform and flat.

Description

Technical Field

[0001] The present invention relates to a preparation method of a monolayer molybdenum diselenide film, and in particular to a pre-evaporated large-area monolayer molybdenum diselenide film and a preparation method thereof, belonging to the technical field of the preparation of molybdenum diselenide film materials. Background Art

[0002] Two-dimensional materials refer to materials in which electrons can move freely only in two dimensions and have excellent physical, chemical, optical, electronic, mechanical and other properties. In recent years, two-dimensional materials have made remarkable progress in many fields such as optoelectronics, radio frequency, logic, storage, biology, sensing, and medical treatment. Common two-dimensional materials include transition metal chalcogenides (TMDs), black phosphorus (BP), hexagonal boron nitride (h-BN), and metal-organic framework compounds (MOFs). Among them, graphene-like MX2 compounds (where M represents two transition metal elements, Mo and W, and X represents three chalcogen elements, S, Se, and Te) have attracted wide attention from researchers. MoSe2 (molybdenum disulfide) has different phase structures, mainly including the following types: The 2H phase is the most common phase structure of MoSe2 and has D 3h symmetry, showing semiconductor properties. In this structure, molybdenum atoms are six-coordinated in a trigonal prism, and two Se-Mo-Se units form a unit cell. The 1T phase has octahedral O h symmetry and shows metallic properties. The 1T-phase MoSe2 has significant differences in electronic structure from the 2H phase. Among them, molybdenum atoms are octahedrally coordinated with a coordination number of 6, and one molybdenum atom forms a unit cell. However, the 1T-phase MoSe2 is thermodynamically unstable and will gradually transform into the 2H-phase MoSe2. The 3R-phase structure has also been reported in MoSe2, but it is less common than the 2H and 1T phases. In the 3R-phase MoSe2, molybdenum atoms are six-coordinated in a trigonal prism, and three Se-Mo-Se units form a unit cell. The thermodynamic stabilities of different phases are different, and these phases can be transformed into each other. For example, the 2H phase of MoSe2 is the most stable in nature. As the number of layers of MoSe2 decreases, the bandgap will increase and change from an indirect bandgap to a direct bandgap. This means that in monolayer MoSe2, the valence band top and the conduction band bottom are at the same k-space position, which is beneficial to improving the light absorption efficiency and electron mobility. Its direct bandgap is about 1.55 eV, which is close to the optimal value of solar cells. Unsaturated Se atoms at its edge and defect positions can induce electrocatalytic activity for hydrogen evolution reactions and similar electrocatalytic reactions. In addition, due to the large spin splitting energy of about 180 meV at the top of the valence band of the monolayer MoSe2 film, it can be applied to spintronic devices.

[0003] Common preparation methods of MoSe2 include mechanical exfoliation, pulsed laser deposition (PLD), hydrothermal method, chemical vapor deposition (CVD), solvothermal method, etc. These methods all have certain defects, such as different sizes of thin film areas, uneven thickness, poor repeatability, high operation difficulty, high cost, etc. Therefore, there is an urgent need in the market for a new preparation method to obtain high-quality MoSe2 thin films with large area, good uniformity, strong operability, high crystallinity and can be mass-produced and applied. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the first object of the present invention is to provide a pre-evaporated large-area single-layer molybdenum diselenide thin film. This molybdenum diselenide thin film is based on a pre-evaporation process, with high crystallinity, and the area can reach the centimeter level. Moreover, the epitaxial edge of the thin film can be regulated according to the ratio between reaction raw materials to generate various stacking configurations such as AA stacking, AB stacking, AAA stacking, ABA stacking, etc., thus showing different physical properties, greatly expanding the development and applicable scenarios of the van der Waals structure of molybdenum diselenide thin films.

[0005] The second object of the present invention is to provide a preparation method for a pre-evaporated large-area single-layer molybdenum diselenide thin film. This method realizes the atmospheric-pressure growth of molybdenum diselenide at a lower temperature based on the synergistic effect between pre-evaporation and selenization reaction, greatly reducing the preparation cost of the thin film; and this method has high controllability, and the area and number of layers of molybdenum diselenide can be adjusted by regulating the process parameters in the pre-evaporation and selenization reactions, obtaining molybdenum diselenide thin films with different functional morphologies, meeting the requirements of industrial large-scale continuous production.

[0006] To achieve the above technical objects, the present invention provides a preparation method for a pre-evaporated large-area single-layer molybdenum diselenide thin film, including: placing a first quartz boat loaded with a selenium source and a second quartz boat loaded with a molybdenum source mixture in sequence at the upstream and downstream of a multi-temperature zone tube furnace, and performing pre-evaporation in an atmospheric-pressure sealed state after purging the gas; after the pre-evaporation ends, replenish the selenium source and the molybdenum source mixture respectively, place the substrate directly above the second quartz boat, and perform a selenization reaction in an atmospheric-pressure gas-passing state after purging the gas, then the product is obtained.

[0007] As a preferred solution, the selenium source is elemental selenium.

[0008] As a preferred solution, the molybdenum source mixture includes molybdenum oxide and a metal salt co-solvent.

[0009] As a preferred solution, when the molybdenum oxide is MoO3 and the metal salt co-solvent is NaCl, the mass ratio of MoO3 to NaCl in the pre-evaporation stage is 8 - 10:1, and the mass ratio of MoO3 to selenium powder is 1:1 - 3.

[0010] As a preferred solution, the process of pre-evaporation is as follows: Wash with an argon-hydrogen mixed gas for 3 to 10 minutes, start a multi-temperature zone tube furnace in an airtight state at normal pressure, and pre-evaporate for 3 to 5 minutes.

[0011] As a preferred solution, the supplementary amount of the selenium source after the pre-evaporation is 0.5 to 3.5 times the mass of the selenium source in the pre-evaporation stage.

[0012] As a preferred solution, the supplementary amount of the molybdenum source mixture after the pre-evaporation is 0.5 to 2 times the mass of the selenium source in the pre-evaporation stage.

[0013] The supplementary amounts of the selenium source and the molybdenum source mixture should be strictly in accordance with the above requirements. The amount of supplementation will directly affect the area and thickness of the molybdenum diselenide film. When the supplementary amount gradually increases to approach the mass of the materials during pre-evaporation, the area of the obtained molybdenum diselenide film is larger. However, when the supplementary amount exceeds the mass of the materials during pre-evaporation, the molybdenum diselenide not only has an increased area but also an increased thickness. If the supplementary amount is further increased beyond the above requirements range, it will result in a multi-layer and uneven-surface molybdenum diselenide film, which cannot meet the product requirements.

[0014] As a preferred solution, the substrate is any one of a silicon wafer substrate, a mica substrate, and a sapphire substrate.

[0015] As a preferred solution, the substrate is located 7 to 10 mm directly above the second quartz boat.

[0016] As a preferred solution, the process of the selenization reaction is as follows: Wash with an argon-hydrogen mixed gas for 3 to 10 minutes, start a multi-temperature zone tube furnace in a state of normal pressure ventilation, and pre-evaporate for 5 to 8 minutes.

[0017] As a preferred solution, the argon-hydrogen mixed gas is composed of 1 to 5% H2 and 95 to 99% Ar.

[0018] As a preferred solution, the flow rate of the argon-hydrogen mixed gas is 40 to 100 sccm.

[0019] As a preferred solution, the set temperature at the upstream of the multi-temperature zone tube furnace is 350 to 400 °C, and the set temperature at the downstream is 750 to 800 °C.

[0020] The present invention also provides a pre-evaporated large-area single-layer molybdenum diselenide film, which is prepared by the method described in any one of the above; the size of the single-layer molybdenum diselenide film is ≥ 500 μm.

[0021] Compared with the prior art, the beneficial technical effects of the technical solution provided by the present invention are as follows:

[0022] 1) The monolayer molybdenum diselenide film provided by the present invention is based on a pre-evaporation process, has a high crystallinity, an area that can reach the centimeter level, and the epitaxial edge of the film can be adjusted according to the ratio between reaction raw materials to generate various stacking configurations such as AA stacking, AB stacking, AAA stacking, ABA stacking, etc., thereby showing different physical properties, greatly expanding the development and applicable scenarios of the van der Waals structure of the molybdenum diselenide film.

[0023] 2) The preparation method provided by the present invention is based on the synergistic effect between pre-evaporation and selenization reaction, realizing the atmospheric-pressure growth of molybdenum diselenide at a lower temperature, greatly reducing the preparation cost of the film; and the method has high controllability, and the area and number of layers of molybdenum diselenide can be adjusted by adjusting the process parameters in the pre-evaporation and selenization reactions to obtain molybdenum diselenide films with different functional morphologies, meeting the requirements of industrial large-scale continuous production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a comprehensive characterization diagram of the MoSe2 film in Example 2 of the present invention;

[0025] Figure 1 (a) is the Raman spectrum diagram of the MoSe2 film, Figure 1 (b) is the PL spectrum of the MoSe2 film, Figure 1 (c) is the optical microscope image of the MoSe2 film, Figure 1 (d) is the physical image of the MoSe2 film. Among them, the left side is the original silicon wafer, and the right side is the silicon wafer on which the MoSe2 film is grown;

[0026] Figure 2 It is the optical microscope image of the MoSe2 films obtained in all Examples 2 to 6 and Comparative Examples 1 to 8 of the present invention;

[0027] Figure 3 It is a schematic diagram of the selenization reaction stage of the monolayer molybdenum diselenide film provided in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] To facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings of the specification and preferred embodiments. It should be noted that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0029] Example 1

[0030] This example provides a pre-evaporated large-area monolayer molybdenum diselenide film, and its preparation process is as follows:

[0031] 1) Weigh 15 mg of MoO3, 30 mg of selenium powder, and 1 mg of NaCl on weighing paper respectively. Place the weighed selenium powder in the first quartz boat, and after fully mixing the weighed MoO3 and NaCl, put them into a clean second quartz boat.

[0032] 2) Place the first quartz boat and the second quartz boat at the upstream and downstream of a multi-temperature zone tube furnace respectively. Then, introduce an argon-hydrogen mixed gas composed of 95% argon and 5% hydrogen to purge the tube furnace for 5 min.

[0033] 3) After the purging is completed, turn on the multi-temperature zone tube furnace, set the upstream temperature to 400 °C and the downstream temperature to 750 °C, and pre-evaporate for 5 min in an atmospheric pressure closed environment.

[0034] 4) After evaporation is completed, wait for the tube furnace to cool statically to below 100 °C. Add 30 mg of selenium powder to the first quartz boat, add 15 mg of MoO3 and 1 mg of NaCl to the second quartz boat, and place the substrate upside down 10 mm above the second quartz boat.

[0035] 5) Introduce an argon-hydrogen mixed gas composed of 95% argon and 5% hydrogen to purge the tube furnace for 5 min. After the purging is completed, turn on the multi-temperature zone tube furnace, set the upstream temperature to 400 °C and the downstream temperature to 750 °C, and continue to maintain the flow rate of the argon-hydrogen mixed gas at 50 sccm. Carry out the selenization reaction for 5 min under atmospheric pressure. Then, wait for the tube furnace to cool statically to below 100 °C, open the furnace, and take out the substrate to obtain the product.

[0036] Comparative Example 1

[0037] The preparation process of this comparative example is exactly the same as that of Example 1, and the differences are shown in Table 1. The product obtained in this comparative example is denoted as 1-1.

[0038] Example 2

[0039] The preparation process of this example is exactly the same as that of Example 1, and the differences are shown in Table 1. The product obtained in this example is denoted as 1-2.

[0040] Example 3

[0041] The preparation process of this example is exactly the same as that of Example 1, and the differences are shown in Table 1. The product obtained in this example is denoted as 1-3.

[0042] Example 4

[0043] The preparation process of this example is exactly the same as that of Example 1, and the differences are shown in Table 1. The product obtained in this example is denoted as 1-4.

[0044] Comparative Example 2

[0045] This comparative example has the exact same preparation process as Example 1. The differences are shown in Table 1, and the product obtained in this comparative example is denoted as 2-1.

[0046] Example 5

[0047] This example has the exact same preparation process as Example 1. The differences are shown in Table 1, and the product obtained in this example is denoted as 2-2.

[0048] Example 6

[0049] This example has the exact same preparation process as Example 1. The differences are shown in Table 1, and the product obtained in this example is denoted as 2-3.

[0050] Comparative Example 3

[0051] This comparative example has the exact same preparation process as Example 1. The differences are shown in Table 1, and the product obtained in this comparative example is denoted as 3-1.

[0052] Comparative Example 4

[0053] This comparative example has the exact same preparation process as Example 1. The differences are shown in Table 1, and the product obtained in this comparative example is denoted as 3-2.

[0054] Comparative Example 5

[0055] This comparative example has the exact same preparation process as Example 1. The differences are shown in Table 1, and the product obtained in this comparative example is denoted as 4-1.

[0056] Comparative Example 6

[0057] This comparative example has the exact same preparation process as Example 1. The differences are shown in Table 1, and the product obtained in this comparative example is denoted as 4-2.

[0058] Comparative Example 7

[0059] This comparative example has the exact same preparation process as Example 1. The differences are shown in Table 1, and the product obtained in this comparative example is denoted as 5-1.

[0060] Comparative Example 8

[0061] This comparative example has the exact same preparation process as Example 1. The differences are shown in Table 1, and the product obtained in this comparative example is denoted as 5-2.

[0062] Table 1

[0063]

[0064]

[0065] As can be seen from the above table, large-area MoSe2 thin films can be prepared by the pre-evaporation method. Under atmospheric pressure, at a high-temperature zone of 400 °C and a low-temperature zone of about 750 °C, they can be obtained after growing for 5 minutes, which has the advantages of an operating pressure of atmospheric pressure, a relatively low growth temperature, and a fast growth cycle. Further, it can be seen from the table that the amounts of selenium powder, MoO3, and NaCl during pre-evaporation, as well as the amounts of selenium powder, MoO3, and NaCl during the selenization reaction, are the main reasons affecting the quality of the MoSe2 thin film. At the same time, the gas flow rate and the growth time will also affect the size of the thin film. Among them, the thin film quality of Product 1-2 is the best, mainly manifested as a relatively large size, a uniform distribution of single-layer thin films, and only a few small-sized few-layer MoSe2 existing on the surface. Its optical micrograph is as shown in Figure 2-1 -2, while the size of Product 5-2 is the largest, and the thin film is mainly composed of partially epitaxial bilayer thin films. Its optical micrograph is as shown in Figure 2 -5-2.

Claims

1. A method for preparing a pre-evaporated large-area single-layer molybdenum diselenide film, characterized in that, Including: Place the first quartz boat loaded with a selenium source and the second quartz boat loaded with a molybdenum source mixture in sequence at the upstream and downstream of a multi-temperature zone tube furnace. After gas washing, perform pre-evaporation under an atmospheric pressure sealed state. After the pre-evaporation ends, supplement the selenium source and the molybdenum source mixture respectively, and place the substrate directly above the second quartz boat. After gas washing, perform a selenization reaction under an atmospheric pressure ventilation state, thus obtaining the product.

2. The preparation method of a pre-evaporated large-area single-layer molybdenum diselenide film according to claim 1, characterized in that: The selenium source is elemental selenium; the molybdenum source mixture includes molybdenum oxide and a metal salt co-solvent.

3. The preparation method of a pre-evaporated large-area single-layer molybdenum diselenide film according to claim 2, characterized in that: When the molybdenum oxide is MoO3 and the metal salt co-solvent is NaCl, the mass ratio of MoO3 to NaCl in the pre-evaporation stage is 8-10:1, and the mass ratio of MoO3 to selenium powder is 1:1-3.

4. The preparation method of a pre-evaporated large-area single-layer molybdenum diselenide film according to claim 1, wherein: The process of the pre-evaporation is: wash with an argon-hydrogen mixed gas for 3-10 min, start the multi-temperature zone tube furnace under an atmospheric pressure closed state, and pre-evaporate for 3-5 min.

5. The preparation method of a pre-evaporated large-area single-layer molybdenum diselenide film according to claim 1, characterized in that: The supplementary amount of the selenium source after the pre-evaporation ends is 0.5-3.5 times the mass of the selenium source in the pre-evaporation stage; the supplementary amount of the molybdenum source mixture after the pre-evaporation ends is 0.5-2 times the mass of the selenium source in the pre-evaporation stage.

6. The preparation method of a pre-evaporated large-area single-layer molybdenum diselenide film according to claim 1, characterized in that: The substrate is any one of a silicon wafer substrate, a mica substrate, and a sapphire substrate.

7. The preparation method of a pre-evaporated large-area single-layer molybdenum diselenide film according to claim 1, characterized in that: The process of the selenization reaction is: wash with an argon-hydrogen mixed gas for 3-10 min, start the multi-temperature zone tube furnace under an atmospheric pressure ventilation state, and pre-evaporate for 5-8 min.

8. The preparation method of a pre-evaporated large-area single-layer molybdenum diselenide film according to claim 4 or 7, characterized in that: The argon-hydrogen mixed gas is composed of 1-5% of H2 and 95-99% of Ar; the flow rate of the argon-hydrogen mixed gas is 40-100 sccm.

9. The preparation method of a pre-evaporated large-area single-layer molybdenum diselenide film according to claim 1, characterized in that: The set temperature at the upstream of the multi-temperature zone tube furnace is 350-400 °C, and the set temperature at the downstream is 750-800 °C.

10. A pre-evaporated large-area single-layer molybdenum diselenide thin film, characterized in that: Prepared by the method according to any one of claims 1-9; the size of the monolayer molybdenum diselenide film ≥ 500 μm.

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