Preparation method of large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide film

Abstract

This invention discloses a method for preparing a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film. First, a silicon substrate is immersed in a piranha solution for cleaning and drying. High-purity (NH4)2MoS4 and cobalt salt are dissolved in a mixed solvent of N,N-dimethylformamide and ethylene glycol to obtain a mixed solution. The mixed solution is then spin-coated onto the cleaned and dried silicon substrate, followed by drying to form a silicon wafer with a thin film structure. Finally, the silicon wafer with the thin film structure undergoes a two-step annealing process to form a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film on the silicon wafer. This invention enables the uniform and controllable deposition of a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film on a large-area substrate, while maintaining its magnetic and structural stability.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional magnetic material preparation, specifically a method for preparing a large-area room-temperature room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film. Background Technology

[0002] As a two-dimensional material, molybdenum disulfide (MoD) possesses excellent electrical, optical, and mechanical properties, making it a promising candidate for fabricating high-performance electronic devices, sensors, and optoelectronic devices. However, its lack of magnetism in its natural state limits its applications in magnetism and related fields. The ability to fabricate large-area magnetic MoD film materials would significantly expand its application scope, enabling applications such as magnetic storage, magnetic sensors, and magnetic spintronics. Currently, numerous methods exist to impart room-temperature ferromagnetism to MoD, including introducing stress, defects, and doping with magnetic ions. Ion doping is considered the simplest and most reliable method for preparing stable magnetic MoD. However, increasing the fabrication area of ​​two-dimensional magnetic materials remains a significant bottleneck hindering their widespread application. Developing new methods to fabricate larger-area, high-quality two-dimensional ferromagnetic MoD films is crucial. Currently, chemical vapor deposition (CVD) is the most widely used method for preparing MoD films, but this method suffers from drawbacks such as complex fabrication processes, high costs, low reproducibility, small fabrication area, and lack of scalability. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film, which uniformly and controllably deposits a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film on a large-area substrate, while maintaining its magnetic and structural stability.

[0004] The technical solution of this invention is as follows:

[0005] A method for preparing a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film specifically includes the following steps:

[0006] (1) Soak the silicon substrate in piranha solution to clean off the organic stains on the surface of the silicon substrate, and then dry it at 75-85℃ for 10-15 minutes before use.

[0007] (2) Dissolve high-purity (NH4)2MoS4 and cobalt salt in a mixed solvent of N,N-dimethylformamide and ethylene glycol, and then sonicate to obtain a mixed solution.

[0008] (3) Spin-coating the mixed solution onto the cleaned and dried silicon substrate using a spin-coating method, and then drying it at 75-85℃ for 25-35 minutes to form a silicon wafer with a thin film structure;

[0009] (4) Place the silicon wafer with the thin film structure into a tube furnace. In a reducing atmosphere, raise the furnace temperature to 450-550°C and push the silicon wafer with the thin film structure into the reaction zone of the furnace. React at 450-550°C for 50-70 minutes to complete the first step of annealing and form the thin film. Then move the silicon wafer to the cooling zone of the tube furnace, raise the temperature of the reaction zone of the furnace to 800-850°C, switch the reducing atmosphere to an inert atmosphere, and perform sulfuring. When the temperature of the sulfuring zone rises to 160-180°C and the temperature of the reaction zone of the furnace rises to 800-850°C, push the silicon wafer back into the reaction zone of the furnace and react at 800-850°C for 25-35 minutes to complete the second step of annealing. After the reaction is completed, finally remove the silicon wafer from the reaction zone of the furnace and cool it. This forms a large-area room temperature ferromagnetic cobalt-doped molybdenum disulfide thin film on the silicon wafer.

[0010] The silicon substrate was immersed in a piranha solution for 45-50 hours.

[0011] The cobalt salt is selected from Co(NO3)2 or CoCO3.

[0012] The mass ratio of the high-purity (NH4)2MoS4 to the cobalt salt is 90-99:1-10.

[0013] The volume ratio of N,N-dimethylformamide to ethylene glycol is 1:1-1.1.

[0014] The reducing atmosphere is a mixture of argon and hydrogen, with a volume ratio of argon to hydrogen of 4:1; the flow rate of the reducing atmosphere is 50-100 sccm, and the pressure in the furnace reaction zone is controlled at 1 torr.

[0015] The inert atmosphere is argon, the flow rate of the inert atmosphere is 50-100 sccm, and the pressure in the reaction zone of the furnace cavity is controlled at atmospheric pressure.

[0016] Advantages of this invention:

[0017] This invention employs a spin-coating method to uniformly coat a mixed solution over a large area onto a silicon substrate, thereby spin-coating a layer of MoS2 precursor onto the silicon substrate and doping it with an appropriate amount of Co ions. This invention directly obtains high-quality, large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin films through a two-step annealing method, eliminating the need for expensive and demanding equipment, saving time and money by eliminating the long deposition process. At the same time, by controlling the deposition temperature and atmosphere, the problem of excessive annealing of crystals at high temperatures, which would lead to the destruction of the film structure and magnetism, is avoided, thus obtaining a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film. Attached Figure Description

[0018] Figure 1This is an optical microscope image of a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film prepared in the embodiments of the present invention, under a 1cm scale.

[0019] Figure 2 This is an optical microscope image of a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film prepared in the embodiments of the present invention under a 100 μm scale.

[0020] Figure 3 This is a transmission electron microscope (TEM) image of a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film prepared in an embodiment of the present invention.

[0021] Figure 4 This is the XRD pattern of a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film prepared in an embodiment of the present invention.

[0022] Figure 5 The graphs show the M(emu / g)-H(Oe) curves obtained by VSM testing of the large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film prepared in the embodiments of the present invention and the control sample.

[0023] Figure 6 The FC-ZFC curve is obtained by VSM testing of a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film prepared in the embodiments of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] A method for preparing a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film specifically includes the following steps:

[0026] (1) Soak the silicon substrate in piranha solution for 48 hours to clean off the organic stains on the surface of the silicon substrate, and then dry it at 80°C for 10 minutes before use.

[0027] (2) Dissolve 80 mg of high-purity (NH4)2MoS4 and 5 mg of Co(NO3)2 in a mixed solvent of 5 ml DMF and 5 ml ethylene glycol, and sonicate for 20 min to obtain a mixed solution.

[0028] (3) Spin-coating the mixed solution onto the cleaned and dried silicon substrate using a spin-coating method, and then drying it at 80°C for 30 min to form a silicon wafer with a thin film structure;

[0029] (4) Place the silicon wafer with the thin film structure into a tube furnace. Under a reducing atmosphere (Ar / H2 = 4 / 1), a flow rate of 100 sccm, and a pressure of 1 torr, raise the furnace temperature to 500°C. Then, push the silicon wafer with the thin film structure into the reaction zone of the furnace and react at 500°C for 60 minutes to complete the first annealing operation and form the thin film. The purpose of the first annealing operation is to thermally decompose (NH4)2MoS4 to generate MoS2. The purpose of hydrogen gas is to reduce and promote the formation of MoS2 from (NH4)2MoS4. However, the crystallinity of MoS2 is poor at this time. Then, transfer the silicon wafer to the tube furnace. In the furnace cooling zone, the temperature of the furnace reaction zone is raised to 800°C. The reducing atmosphere is switched to an inert atmosphere (Ar), the flow rate is 100 sccm, and the pressure is normal. At the same time, sulfur is introduced (the purpose of sulfur introduction is to ensure better crystallinity of MoS2 and reduce the generation of sulfur vacancies). When the temperature of the sulfur introduction zone rises to 170°C and the temperature of the furnace reaction zone rises to 800°C, the silicon wafer is pushed back into the furnace reaction zone and reacted at 800°C for 30 minutes to complete the second annealing operation. After the reaction is completed, the silicon wafer is finally removed from the furnace reaction zone for cooling, thus forming a large-area room temperature ferromagnetic cobalt-doped molybdenum disulfide film on the silicon wafer.

[0030] The prepared large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film was tested, and from... Figure 1 and Figure 2 As can be seen, the prepared film is a large-area film, with a size reaching the centimeter level; from Figure 3 As can be seen, the prepared film is a highly crystalline 2H phase MoS2 nanosheet; from Figure 4 As can be seen, the prepared film is pure phase MoS2, and no impurity peaks appear, indicating that Co does not form impurity particles of Co-related compounds in the film.

[0031] The prepared large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film and a control sample (undoped molybdenum disulfide thin film) were subjected to magnetic property testing (VSM test). Figure 5 As can be seen, the prepared film exhibits excellent magnetic properties, realizing intrinsic room temperature ferromagnetism. At 300K, its saturation magnetic moment is 0.1 emu / g, which is much higher than the 0.007 emu / g of the control sample. Figure 6 The results show that the Curie temperature of the prepared film is higher than 350K.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film, characterized in that: Specifically, it includes the following steps: (1) Soak the silicon substrate in piranha solution to clean off the organic stains on the surface of the silicon substrate, and then dry it at 75-85℃ for 10-15 minutes before use. (2) Dissolve high-purity (NH4)2MoS4 and cobalt salt in a mixed solvent of N,N-dimethylformamide and ethylene glycol, and then sonicate to obtain a mixed solution. (3) Spin-coating the mixed solution onto the cleaned and dried silicon substrate using a spin-coating method, and then drying it at 75-85℃ for 25-35 minutes to form a silicon wafer with a thin film structure; (4) Place the silicon wafer with the thin film structure into a tube furnace. In a reducing atmosphere, raise the furnace temperature to 450-550°C and push the silicon wafer with the thin film structure into the reaction zone of the furnace. React at 450-550°C for 50-70 minutes to complete the first step of annealing and form the thin film. Then move the silicon wafer to the cooling zone of the tube furnace, raise the temperature of the reaction zone of the furnace to 800-850°C, switch the reducing atmosphere to an inert atmosphere, and perform a sulfur-purifying operation. When the temperature of the sulfur-purifying zone rises to 160-180°C and the temperature of the reaction zone of the furnace rises to 800-850°C, push the silicon wafer back into the reaction zone of the furnace and react at 800-850°C for 25-35 minutes to complete the second step of annealing. After the reaction is completed, finally remove the silicon wafer from the reaction zone of the furnace and cool it, thus forming a large-area room temperature ferromagnetic cobalt-doped molybdenum disulfide thin film on the silicon wafer.

2. The method for preparing a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film according to claim 1, characterized in that: The silicon substrate was immersed in a piranha solution for 45-50 hours.

3. The method for preparing a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film according to claim 1, characterized in that: The cobalt salt is selected from Co(NO3)2 or CoCO3.

4. The method for preparing a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film according to claim 1, characterized in that: The mass ratio of the high-purity (NH4)2MoS4 to the cobalt salt is 90-99:1-10.

5. The method for preparing a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film according to claim 1, characterized in that: The volume ratio of N,N-dimethylformamide to ethylene glycol is 1:1-1.

1.

6. The method for preparing a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film according to claim 1, characterized in that: The reducing atmosphere is a mixture of argon and hydrogen, with a volume ratio of argon to hydrogen of 4:1; the flow rate of the reducing atmosphere is 50-100 sccm, and the pressure in the furnace reaction zone is controlled at 1 torr.

7. The method for preparing a large-area room-temperature ferromagnetic cobalt-doped molybdenum disulfide thin film according to claim 1, characterized in that: The inert atmosphere is argon, the flow rate of the inert atmosphere is 50-100 sccm, and the pressure in the reaction zone of the furnace cavity is controlled at atmospheric pressure.

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