A method for preparing a uniform monolayer MA2Z4 thin film

Abstract

The present application relates to ternary compound MA2Z4 thin film material preparation field, concretely is a kind of preparation method of uniform single-layer MA2Z4 thin film.The copper foil is used as growth substrate, a layer of thin film containing transition group metal M is deposited on the surface of copper foil using physical vapor deposition technology, the pre-storage of M-A or M-Z source in copper foil substrate is realized by annealing treatment in the environment with A source or Z source, then the third element Z or A is introduced, and the stored element is reacted at high temperature not higher than the melting point of copper to grow uniform single-layer MA2Z4 thin film, and the copper foil substrate is etched to be transferred to any substrate subsequently.The present application has the characteristics of simple preparation process, fast film formation rate, easy to enlarge the size of thin film, suitable for large-area high-quality thin film preparation and other characteristics, which provides the possibility for the industrialization application of two-dimensional MA2Z4 material in the fields of electronic devices, optoelectronic devices, valley electronic devices, high-strength thin films, high-transparency thin films, catalysis and other fields.

Description

Technical fields:

[0001] This invention relates to the field of chemical vapor deposition (CVD) preparation of two-dimensional layered MA2Z4 thin film materials, specifically a method for preparing uniform monolayer MA2Z4 (M is a transition metal element, A is a group 4 element, and Z is a group 5 element) thin films, suitable for the preparation of large-area, high-quality, uniform monolayer MA2Z4 thin films. Background technology:

[0002] Since the successful exfoliation and preparation of graphene, a variety of novel two-dimensional materials, including h-BN, transition metal chalcogenides, oxides, and black phosphorus, have been successively prepared. Their unique two-dimensional structures endow them with excellent electrical, optical, thermal, and mechanical properties, and they hold broad application prospects in electronics, optoelectronics, information technology, energy, environment, and aerospace. Currently, most of the obtained two-dimensional materials are single-element or binary structures with relatively simple compositions and structures, limiting their corresponding property exploration and application development. Therefore, exploring novel two-dimensional materials is of great significance for expanding the family of two-dimensional materials and for researching their corresponding properties and applications.

[0003] Recent research has shown that a novel two-dimensional layered ternary compound, MA2Z4, has been successfully prepared, and its corresponding bulk parent material does not exist in nature. The monolayer structure of this compound consists of seven atomic layers, ZAZMZA-Z, bonded together by van der Waals forces. High-quality two-dimensional layered MA2Z4 single crystals or thin films can be obtained by chemical vapor deposition using a bimetallic layer consisting of an upper copper foil and a lower transition metal M foil as the growth substrate. However, in this method, the transition metal M atoms need to diffuse from the lower transition metal foil upwards to the upper Cu surface to catalyze the growth reaction. The size of the resulting two-dimensional layered MoSi2N4 thin film is severely limited by the size of the transition metal foil, achieving a maximum size only in the centimeter range. Furthermore, the diffusion mechanism requiring crossing the catalytic substrate results in a long growth time for some MA2Z4 materials (only a 6 μm WSi2N4 single crystal can be grown in 18 hours). Size limitations and extremely slow growth rates severely restrict the study of the properties of two-dimensional layered MA2Z4 thin films and their application in large-scale, low-cost fabrication. Therefore, it is urgent to develop an efficient and rapid fabrication method to lay the foundation for large-area, high-quality growth of two-dimensional MA2Z4 materials and to explore their related properties and applications. Summary of the Invention:

[0004] The purpose of this invention is to provide a method for preparing a uniform monolayer MA2Z4 thin film, which solves the problems of small material size and slow growth rate obtained in current research, and lays the foundation for achieving efficient and rapid growth of two-dimensional MA2Z4 thin films and exploring related properties and applications.

[0005] The technical solution of this invention is:

[0006] A method for preparing a uniform monolayer MA2Z4 thin film involves using copper foil as a growth substrate, depositing a thin film containing a transition metal M on the surface of the copper foil using physical vapor deposition, pre-storing the MA source or MZ source in the copper foil substrate through annealing in an environment with an A source or a Z source via chemical vapor deposition, introducing a third element Z or A, and reacting it with the stored element precipitated on the surface of the copper foil at a reaction temperature not higher than the melting point of copper to grow a uniform monolayer MA2Z4 thin film, and subsequently etching the copper foil substrate to transfer it to any substrate.

[0007] Wherein, M is a transition metal element, including but not limited to molybdenum, tungsten, titanium, zirconium, hafnium, vanadium, niobium, tantalum, or chromium; A is a group IV element, including but not limited to silicon or germanium; Z is a group V element, including but not limited to nitrogen, phosphorus, or arsenic.

[0008] The method for preparing a uniform monolayer MA2Z4 thin film allows the size of the two-dimensional layered MA2Z4 thin film to be controlled by changing the size of the copper foil substrate or the deposition area of ​​the transition metal M film, ultimately achieving the growth of a high-quality uniform monolayer thin film.

[0009] The method for preparing the uniform monolayer MA2Z4 thin film involves using a flat copper foil with a purity greater than 98 wt% and a thickness of 8 μm to 2 mm. A transition metal M thin film is physically vapor-deposited on the copper foil to obtain a transition metal / copper bimetallic growth substrate. The physical vapor deposition method includes magnetron sputtering, electron beam evaporation, or ion beam sputtering. The deposition conditions are: deposition rate of 0.01 to 1 nm / s, and the thickness of the transition metal M layer on the copper foil surface is 0.2 to 1000 nm. The target materials used include, but are not limited to, pure transition metal targets, alloy targets of transition metal and copper, and alloy targets of transition metal and Group IV or V elements.

[0010] The method for preparing a uniform monolayer MA2Z4 thin film involves introducing A and Z elements by using a precursor containing A and Z. The precursor is a solid, powder, liquid, or gas that volatilizes or decomposes to release A or Z at high temperature; or, it can be introduced by coating in the form of an MA alloy or an MZ alloy.

[0011] The method for preparing the uniform monolayer MA2Z4 thin film, wherein A is a Group 4 element, including but not limited to silicon or germanium, and silicon precursors include but are not limited to elemental silicon, quartz or silane, and germanium precursors include but are not limited to elemental germanium or germanane; Z is a Group 5 element, including but not limited to nitrogen, phosphorus or arsenic, and nitrogen precursors include but are not limited to ammonia or nitrogen, phosphorus precursors include but are not limited to white phosphorus or red phosphorus, and arsenic precursors include but are not limited to elemental arsenic.

[0012] The method for preparing a uniform monolayer MA2Z4 thin film involves using hydrogen or a mixture of hydrogen and an inert gas as the carrier gas during the chemical vapor deposition reaction. The temperature for growing a large-area, high-quality monolayer MA2Z4 thin film by chemical vapor deposition is 600℃ to 1083℃, and the growth time is 1 minute to 480 minutes.

[0013] The method for preparing the uniform monolayer MA2Z4 film involves uniformly coating a layer of polymer or organic small molecule protective layer on the surface of the MA2Z4 film before transfer to protect it, etching away the copper foil substrate, transferring the resulting protective layer / MA2Z4 composite film to other substrates, and dissolving away the protective layer.

[0014] The method for preparing the uniform monolayer MA2Z4 film uses a polymer that is one or a mixture of two or more of polymethyl methacrylate, polyethylene, polystyrene, and polypropylene; and uses an organic small molecule that is one or a mixture of two or more of paraffin, rosin, and camphor.

[0015] The method for preparing the uniform monolayer MA2Z4 thin film involves etching a copper foil substrate with a copper etching solution, which may be an aqueous solution of ammonium persulfate, an aqueous solution of tin tetrachloride, an aqueous solution of ferric chloride, concentrated ammonia, or dilute hydrochloric acid.

[0016] The method for preparing the uniform monolayer MA2Z4 film uses one or more of the following organic solvents to remove the polymer protective layer: ketones, chlorinated hydrocarbons, halogenated hydrocarbons, and aromatic hydrocarbons; and uses one or more of the following organic solvents to remove the small molecule protective layer: ethanol, diethyl ether, chloroform, hexane, acetone, and petroleum ether.

[0017] The design concept of this invention is:

[0018] This invention uses copper foil as a growth substrate and employs physical vapor deposition (PVD) technology to deposit a thin film containing transition metal M on the surface of the copper foil. The MA source or MZ source is pre-stored in the copper foil substrate by annealing in an environment with an A source or a Z source. Then, a third element Z or A is introduced and reacts with the stored element precipitated on the surface of the copper foil at a reaction temperature not higher than the melting point of copper, thereby achieving efficient and rapid growth of a uniform monolayer MA2Z4 thin film.

[0019] The advantages and beneficial effects of this invention are:

[0020] 1. This invention proposes a chemical vapor deposition method for preparing uniform monolayer MA2Z4 thin films, which can be carried out under normal pressure, is convenient to operate and easy to control, and can efficiently and quickly obtain uniform monolayer MA2Z4 thin films. The film size depends on the size of the transition metal M film and the furnace tube size. The preparation process is simple, the film formation rate is fast, and the film size is easy to scale up, making it suitable for the preparation of large-area high-quality thin films.

[0021] 2. In the preparation process of this invention, the transition metal M source can be pre-stored inside the copper foil together with the A source after the annealing process, without having to cross the catalytic substrate to reach the copper foil surface for growth, which greatly improves the growth rate of MA2Z4 film.

[0022] 3. The present invention can also grow and prepare large-size single-layer or multi-layer MA2Z4 crystals on the back side of coated copper foil.

[0023] 4. The uniform monolayer MA2Z4 film prepared by this invention is grown on a flexible substrate, which is expected to realize large-area roll-to-roll transfer. Attached image description:

[0024] Figure 1 This is a schematic diagram of the experimental setup for growing a uniform monolayer MA2Z4 thin film using the CVD method. In the diagram, 1 is the gas inlet; 2 is the metal substrate: 21 is the copper foil; 22 is the transition metal thin film; 3 is the heating furnace; 4 is the quartz tube; and 5 is the gas outlet.

[0025] Figure 2 A photograph of a 3cm × 4cm MoSi2N4 thin film grown by CVD on a Mo / Cu substrate.

[0026] Figure 3 Photographs showing the transfer of MoSi2N4 thin films grown on Mo / Cu substrates via CVD onto 2 square-inch SiO2 / Si and PET substrates. Wherein: a) SiO2 / Si substrate; b) PET substrate.

[0027] Figure 4 The image shows a planar high-resolution scanning transmission electron micrograph of a monolayer MoSi2N4 thin film grown by CVD, revealing that the sample has high crystallinity.

[0028] Figure 5 The optical properties of monolayer MoSi2N4 films grown by CVD are characterized. Figure a shows the absorption spectrum of the monolayer MoSi2N4 film transferred to PET, with the horizontal axis representing wavelength (nm) and the vertical axis representing absorbance (au). Figure b shows the Tauc plot converted from the absorption spectrum in Figure a, with the horizontal axis representing photon energy (eV) and the vertical axis representing (αhν). 0.5The variable (au) represents the absorption coefficient. The intersection of the extended linear segment of the curve in the figure with the horizontal axis represents the indirect band gap value of the material.

[0029] Figure 6 This is a photograph of a 3cm × 4cm WSi2N4 thin film grown by CVD on a W / Cu substrate.

[0030] Figure 7 Photographs showing the transfer of WSi2N4 thin films grown on W / Cu substrates by CVD onto 2 square-inch SiO2 / Si and PET substrates. Wherein: a) SiO2 / Si substrate; b) PET substrate.

[0031] Figure 8 A photograph of an 8cm×9cm WSi2N4 thin film grown on a W / Cu substrate by CVD after being oxidized in air at 180℃ for 30 minutes.

[0032] Figure 9 The image shows a planar high-resolution scanning transmission electron micrograph of a monolayer WSi2N4 thin film grown by CVD, revealing that the sample has high crystallinity.

[0033] Figure 10 The optical properties of the monolayer WSi2N4 thin film grown by CVD are characterized. Figure a shows the absorption spectrum of the monolayer WSi2N4 thin film transferred to PET, with the horizontal axis representing wavelength (nm) and the vertical axis representing absorbance (au). Figure b shows the Tauc plot converted from the absorption spectrum in Figure a, with the horizontal axis representing photon energy (eV) and the vertical axis representing (αhν). 0.5 The variable (au) represents the absorption coefficient. The intersection of the extended linear segment of the curve in the figure with the horizontal axis represents the indirect band gap value of the material. Detailed implementation method:

[0034] In its specific implementation, the method for preparing a uniform monolayer MA2Z4 thin film of this invention uses copper foil as the growth substrate and employs physical vapor deposition (PVD) technology to deposit a thin film containing transition metal M on the surface of the copper foil. The MA source or MZ source is pre-stored in the copper foil substrate through annealing in an environment with an A source or Z source. Then, a third element Z or A is introduced, reacting with the stored element precipitated on the copper foil surface at a reaction temperature not exceeding the melting point of copper, thereby achieving efficient and rapid growth of a uniform monolayer MA2Z4 thin film. Subsequently, etching of the copper foil substrate transfers the MA2Z4 thin film to any substrate. The specific steps are as follows:

[0035] (1) CVD growth of uniform monolayer MA2Z4 thin film, taking two-dimensional layered transition metal silicon-nitrogen ternary compound MSi2N4 as an example: A transition metal M thin film is physically vapor deposited on copper foil to obtain a transition metal / copper bimetallic layer growth substrate. A silicon wafer or quartz wafer is placed above or in front of the growth substrate as a silicon source and ammonia as a nitrogen source. The composite substrate is annealed under high temperature and carrier gas atmosphere to achieve pre-storage of transition metal M and Si in the copper foil substrate. Subsequently, N element is introduced. At a reaction temperature not higher than the melting point of copper, M atoms and Si atoms that are uniformly diffused to the surface of the catalytically active copper foil substrate react with the introduced N atoms to grow a uniform monolayer MSi2N4 thin film.

[0036] The growth substrate used is a transition metal M thin film / copper bimetallic layer. The thickness of the transition metal M layer deposited by physical vapor deposition is 0.2–1000 nm, preferably 0.2–1 nm, and the deposition rate is 0.01–1 nm / s, preferably 0.01–0.03 nm / s. The thickness of the copper foil used is 8 μm–2 mm, preferably 12.5 μm–50 μm; the purity is 98 wt%–99.9999 wt%, preferably 99.5 wt%–99.9999 wt%. The nitrogen source used in the CVD growth process is ammonia or nitrogen, and the silicon source is silicon wafer, quartz wafer, or silane. When growing other two-dimensional MA2Z4 crystals, the germanium source is germanium wafer or germanane, the phosphorus source is elemental phosphorus, and the arsenic source is elemental arsenic. The carrier gas used in the CVD growth is hydrogen or a mixture of hydrogen and an inert gas (carrier gas flow rate is 20 mL / min–1000 mL / min). The CVD growth temperature is 600℃~1083℃, preferably 900℃~1070℃; the growth time is 1 minute~480 minutes, preferably 15 minutes~240 minutes; the cooling rate after the reaction is completed is 10℃ / minute~600℃ / minute, preferably 200℃ / minute~600℃ / minute.

[0037] (2) Coating of protective layer: A layer of polymer or organic small molecule protective layer is uniformly coated on the surface of the two-dimensional layered MA2Z4 film to prevent it from being damaged in subsequent processing; the polymer is one or more of polymethyl methacrylate, polyethylene, polystyrene, and polypropylene; the organic small molecule is one or more of paraffin, rosin, and camphor.

[0038] (3) Dissolution of copper foil substrate: The copper foil substrate is dissolved and removed with copper etching solution to obtain a protective layer / two-dimensional layered MA2Z4 composite film; the dissolving solution for removing the copper foil substrate is tin tetrachloride aqueous solution, ammonium persulfate aqueous solution, ferric chloride aqueous solution, concentrated ammonia or dilute hydrochloric acid, etc., and the molar concentration of the dissolving solution is 0.05mol / L to 2mol / L.

[0039] (4) Removal of the protective layer: The obtained protective layer / two-dimensional MA2Z4 composite film is placed on the target substrate, and the protective layer covering the surface of the two-dimensional MA2Z4 film is dissolved and removed using an organic solvent. The organic solvent used to remove the polymer protective layer is one or more of the following: acetone, ethyl lactate, dichloroethane, trichloroethylene, chloroform, etc., ketones, chlorinated hydrocarbons, halogenated hydrocarbons, aromatic hydrocarbons, etc.; the organic solvent used to remove the small molecule protective layer includes, but is not limited to, one or more of the following: ethanol, diethyl ether, chloroform, hexane, acetone, petroleum ether, etc.

[0040] The uniform monolayer MA2Z4 film obtained by this invention can reach a size of up to 4 square inches. The film size depends on the size of the transition metal M film deposited by physical vapor deposition. The prepared MA2Z4 film has a uniform composition and is strictly controlled to be a monolayer film with a thickness of about 1 nm, exhibiting high crystallinity.

[0041] The present invention will now be described in further detail with reference to embodiments and accompanying drawings.

[0042] Example 1

[0043] First, such as Figure 1 As shown, this invention uses a horizontal reactor to grow a uniform monolayer MoSi2N4 thin film. The horizontal reactor has a gas inlet 1 and a gas outlet 5 at each end. A molybdenum / copper bimetallic substrate foil (molybdenum obtained by physical vapor deposition on the copper foil surface, with a thickness of 0.4 nm and a molybdenum target purity of 99.95 wt%; the copper foil is 3 cm × 4 cm × 25 μm, with a purity of 99.5 wt%) is placed in the central high-temperature region of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm); under hydrogen gas... The mixture was annealed in an atmosphere at 1070°C for 2 hours (with a hydrogen flow rate of 200 mL / min and a heating rate of 20°C / min). Then, a mixture of ammonia and hydrogen was introduced (with a flow rates of 6 mL / min for ammonia and 200 mL / min for hydrogen) to begin the growth of two-dimensional MoSi2N4. The growth time was 2 hours. After the growth was completed, the mixture was rapidly cooled at a rate of 500°C / min to obtain a 2 square inch MoSi2N4 film with a thickness of approximately 1 nm on the copper foil surface.

[0044] Then, molten paraffin wax heated to 150°C was dropped onto the surface of a copper foil with a MoSi2N4 thin film grown on it. The sample stage temperature of the spin coater was set to 40°C and the rotation speed was set to 2000 rpm to spin coat a 600 nm thick paraffin wax film. After curing at room temperature for 5 minutes, it was placed in a 0.15 mol / L ferric chloride aqueous solution and reacted at 70°C for 20 minutes to dissolve the copper foil substrate. The paraffin / MoSi2N4 film was then repeatedly washed in deionized water and transferred to a SiO2 / Si substrate (a uniform silicon dioxide SiO2 film on the surface of the silicon wafer Si). The substrate was then kept at 40°C for 24 hours to dry the moisture. The paraffin wax was dissolved in petroleum ether at 55°C, and finally, a 2 square inch MoSi2N4 film was successfully transferred.

[0045] The composition, crystal structure, morphology and thickness of the MoSi2N4 thin film were characterized by optical microscopy, transmission electron microscopy and atomic force microscopy. The results showed that the obtained MoSi2N4 was a monolayer polycrystalline MoSi2N4 thin film with a hexagonal structure. The film size was 3 cm × 4 cm and the thickness was about 1 nm. It was a strictly uniform monolayer film with high crystal quality and semiconductor properties.

[0046] Example 2

[0047] First, such as Figure 1 As shown, this invention uses a horizontal reactor to grow a uniform monolayer MoSi2N4 thin film. The horizontal reactor has a gas inlet 1 and a gas outlet 5 at each end. A molybdenum / copper bimetallic substrate foil (molybdenum obtained by physical vapor deposition on the copper foil surface, with a thickness of 0.4 nm and a molybdenum target purity of 99.95 wt%; the copper foil is 8 cm × 9 cm × 25 μm, with a purity of 99.5 wt%) is placed in the central high-temperature region of the horizontal reactor (furnace tube diameter 105 mm, reaction zone length 200 mm); under hydrogen gas... Annealing was performed by heating to 1070℃ and holding for 2 hours in an atmosphere (hydrogen flow rate was 400 mL / min and heating rate was 20℃ / min). Then, a mixture of ammonia and hydrogen was introduced (gas flow rates were 10 mL / min for ammonia and 400 mL / min for hydrogen) to begin the growth of two-dimensional MoSi2N4. The growth time was 4 hours. After the growth was completed, the film was rapidly cooled at a rate of 500℃ / min to obtain a 4 square inch MoSi2N4 film with a thickness of about 1 nm on the copper foil surface.

[0048] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the surface of a copper foil on which a MoSi2N4 film was grown. A PMMA film with a thickness of 200 nm was coated by spin coating at 5000 rpm. After baking at 120°C for 10 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70°C for 20 minutes to dissolve the copper foil substrate, thus transferring the PMMA / MoSi2N4 film onto a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55°C, finally achieving a successful transfer of a 4 square inch MoSi2N4 film.

[0049] The composition, crystal structure, morphology and thickness of the MoSi2N4 thin film were characterized by optical microscopy, transmission electron microscopy and atomic force microscopy. The results showed that the obtained MoSi2N4 was a monolayer polycrystalline MoSi2N4 thin film with a hexagonal structure. The film size was 8 cm × 9 cm and the thickness was about 1 nm. It was a strictly uniform monolayer film with high crystal quality and semiconductor properties.

[0050] Example 3

[0051] First, such as Figure 1 As shown, this invention uses a horizontal reactor to grow a uniform monolayer MoSi2N4 thin film. The horizontal reactor has a gas inlet 1 and a gas outlet 5 at each end. A molybdenum / copper bimetallic substrate foil (molybdenum obtained by physical vapor deposition on the copper foil surface, with a thickness of 0.6 nm and a molybdenum target purity of 99.95 wt%; the copper foil is 3 cm × 4 cm × 25 μm, with a purity of 99.5 wt%) is placed in the central high-temperature region of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm); under hydrogen gas... Annealing was performed by heating to 1030℃ and holding for 2 hours in an atmosphere (hydrogen flow rate of 200 mL / min and heating rate of 20℃ / min during heating). Then, a mixture of ammonia and hydrogen was introduced (gas flow rates of 6 mL / min for ammonia and 200 mL / min for hydrogen) to start the growth of two-dimensional MoSi2N4. The growth time was 4 hours. After the growth was completed, the film was rapidly cooled at a rate of 500℃ / min to obtain a 2 square inch MoSi2N4 film with a thickness of about 1 nm on the copper foil surface.

[0052] Then, molten paraffin wax heated to 150°C was dropped onto the surface of a copper foil on which a MoSi2N4 thin film was grown. The sample stage temperature of the spin coater was set to 40°C and the rotation speed was set to 2000 rpm to spin coat a 600 nm thick paraffin film. After curing at room temperature for 5 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70°C for 20 minutes to dissolve the copper foil substrate. The paraffin / MoSi2N4 film was then repeatedly washed in deionized water and transferred to a SiO2 / Si substrate. The film was then dried at 40°C for 24 hours. The paraffin wax was dissolved in petroleum ether at 55°C, and finally, a 2 square inch MoSi2N4 film was successfully transferred.

[0053] The composition, crystal structure, morphology and thickness of the MoSi2N4 thin film were characterized by optical microscopy, transmission electron microscopy and atomic force microscopy. The results showed that the obtained MoSi2N4 was a monolayer polycrystalline MoSi2N4 thin film with a hexagonal structure. The film size was 3 cm × 4 cm and the thickness was about 1 nm. It was a strictly uniform monolayer film with high crystal quality and semiconductor properties.

[0054] Example 4

[0055] First, such as Figure 1 As shown, this invention employs a horizontal reactor to grow a uniform monolayer MoSi2N4 thin film. The horizontal reactor has a gas inlet 1 and a gas outlet 5 at each end. A copper-molybdenum alloy / copper bimetallic substrate foil (molybdenum obtained through physical vapor deposition on the copper foil surface, with a thickness of 10 nm; the copper-molybdenum alloy target purity is 99.95 wt%; the copper-molybdenum ratio is 9:1; the copper foil is 8 cm × 9 cm × 25 μm, with a purity of 99.5 wt%) is placed in the center of the horizontal reactor (furnace tube diameter 105 mm, reaction zone length 200 mm) at a high temperature. The area was annealed by heating to 1070°C in a hydrogen atmosphere and holding for 2 hours (hydrogen flow rate was 400 mL / min, and heating rate was 20°C / min). Then, a mixture of ammonia and hydrogen was introduced (gas flow rates of 10 mL / min for ammonia and 400 mL / min for hydrogen) to begin the growth of two-dimensional MoSi2N4. The growth time was 6 hours. After the growth was completed, the area was rapidly cooled at a rate of 500°C / min to obtain a 4 square inch MoSi2N4 film with a thickness of approximately 1 nm on the copper foil surface.

[0056] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the surface of a copper foil on which a MoSi2N4 film was grown. A PMMA film with a thickness of 200 nm was coated by spin coating at 5000 rpm. After baking at 120°C for 10 minutes, the film was placed in a 0.15 mol / L ferric chloride aqueous solution and reacted at 70°C for 20 minutes to dissolve the copper foil substrate, thus transferring the PMMA / MoSi2N4 film onto a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55°C, finally achieving a successful transfer of a 4 square inch MoSi2N4 film.

[0057] The composition, crystal structure, morphology and thickness of the MoSi2N4 thin film were characterized by optical microscopy, transmission electron microscopy and atomic force microscopy. The results showed that the obtained MoSi2N4 was a monolayer polycrystalline MoSi2N4 thin film with a hexagonal structure. The film size was 8 cm × 9 cm and the thickness was about 1 nm. It was a strictly uniform monolayer film with high crystal quality and semiconductor properties.

[0058] Example 5

[0059] First, such as Figure 1 As shown, this invention uses a horizontal reactor to grow MoSi2N4 single crystal samples. The horizontal reactor has a gas inlet 1 and a gas outlet 5 at each end. A copper-molybdenum alloy / copper bimetallic substrate foil (molybdenum obtained by physical vapor deposition on the copper foil surface, with a thickness of 15 nm; the copper-molybdenum alloy target purity is 99.95 wt%; the copper-molybdenum ratio is 9:1; the copper foil is 3 cm × 4 cm × 25 μm, with a purity of 99.5 wt%) is placed upside down in the center of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm) at high temperature. The area was annealed by heating to 1070°C in a hydrogen atmosphere and holding for three hours (the hydrogen flow rate during heating was 200 mL / min, and the heating rate was 20°C / min). Then, a mixture of ammonia and hydrogen was introduced (the gas flow rates were 8 mL / min for ammonia and 200 mL / min for hydrogen) to begin the growth of two-dimensional MoSi2N4. The growth time was 6 hours. After the growth was completed, the area was rapidly cooled at a rate of 500°C / min to obtain a single layer or multiple layers of MoSi2N4 crystals with a thickness of about 1 nm on the copper foil surface.

[0060] Then, molten paraffin wax heated to 150℃ was dropped onto the surface of a copper foil on which MoSi2N4 crystals were grown. The sample stage temperature of the spin coater was set to 40℃ and the rotation speed was set to 2000 rpm to spin coat a 600 nm thick paraffin film. After curing at room temperature for 5 minutes, the film was placed in a 0.15 mol / L ferric chloride aqueous solution and reacted at 70℃ for 20 minutes to dissolve the copper foil substrate. The paraffin / MoSi2N4 film was then repeatedly washed in deionized water and transferred to a SiO2 / Si substrate. The film was then dried at 40℃ for 24 hours. The paraffin wax was dissolved in petroleum ether at 55℃, thus achieving the successful transfer of single-layer or multi-layer MoSi2N4 crystals.

[0061] The composition, crystal structure, morphology and thickness of MoSi2N4 crystals were characterized by optical microscopy, transmission electron microscopy and atomic force microscopy. The results showed that the obtained MoSi2N4 was a single crystal sample with a hexagonal structure, an average single crystal size of about 50 μm and a thickness of about 1 nm, with high crystal quality and semiconductor properties.

[0062] Example 6

[0063] First, such as Figure 1 As shown, this invention employs a horizontal reactor to grow a uniform single-layer WSi2N4 thin film. The horizontal reactor has a gas inlet 1 and a gas outlet 5 at each end. A tungsten / copper bimetallic substrate foil (the tungsten is obtained through physical vapor deposition on the copper foil surface, with a thickness of 0.3 nm and a tungsten target purity of 99.95 wt%; the copper foil is 3 cm × 4 cm × 25 μm, with a purity of 99.5 wt%) is placed in the central high-temperature region of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm); under hydrogen gas... Annealing was performed by heating to 1070℃ and holding for 2 hours in an atmosphere (hydrogen flow rate of 200 ml / min and heating rate of 20℃ / min during heating). Then, a mixture of ammonia and hydrogen was introduced (gas flow rates of 4 ml / min for ammonia and 200 ml / min for hydrogen) to begin the growth of two-dimensional WSi2N4. The growth time was 30 minutes. After the growth was completed, the film was rapidly cooled at a rate of 500℃ / min to obtain a 2 square inch WSi2N4 film with a thickness of about 1 nm on the copper foil surface.

[0064] Then, molten paraffin wax heated to 150°C was dropped onto the copper foil surface on which WSi2N4 films were grown. The sample stage temperature of the spin coater was set to 40°C and the rotation speed was set to 2000 rpm to spin coat a 600 nm thick paraffin wax film. After curing at room temperature for 5 minutes, the film was placed in a 0.15 mol / L ferric chloride aqueous solution and reacted at 70°C for 20 minutes to dissolve the copper foil substrate. The paraffin / MoSi2N4 film was then repeatedly washed in deionized water and transferred to a SiO2 / Si substrate. The film was then dried at 40°C for 24 hours. The paraffin wax was dissolved in petroleum ether at 55°C, and finally, a 2 square inch WSi2N4 film was successfully transferred.

[0065] The composition, crystal structure, morphology and thickness of the WSi2N4 thin film were characterized by optical microscopy, transmission electron microscopy and atomic force microscopy. The results showed that the obtained WSi2N4 was a single-layer polycrystalline WSi2N4 thin film with a hexagonal structure. The film size was 3 cm × 4 cm and the thickness was about 1 nm. It was a strictly uniform single-layer film with high crystal quality and semiconductor properties.

[0066] Example 7

[0067] First, such as Figure 1 As shown, this invention uses a horizontal reactor to grow a uniform single-layer WSi2N4 thin film. The horizontal reactor has a gas inlet 1 and a gas outlet 5 at each end. A tungsten / copper bimetallic substrate foil (the tungsten is obtained by physical vapor deposition on the copper foil surface, with a thickness of 0.5 nm and a tungsten target purity of 99.95 wt%; the copper foil is 8 cm × 9 cm × 25 μm, with a purity of 99.5 wt%) is placed in the central high-temperature region of the horizontal reactor (furnace tube diameter 105 mm, reaction zone length 200 mm); under hydrogen... Annealing was performed by heating to 1070℃ and holding for 2 hours in an atmosphere (hydrogen flow rate of 400 mL / min and heating rate of 20℃ / min during heating). Then, a mixture of ammonia and hydrogen was introduced (gas flow rates of 8 mL / min for ammonia and 400 mL / min for hydrogen) to begin the growth of two-dimensional WSi2N4 for 4 hours. After growth, the film was rapidly cooled at a rate of 500℃ / min to obtain a 4 square inch WSi2N4 film with a thickness of approximately 1 nm on the copper foil surface.

[0068] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the surface of a copper foil on which a MoSi2N4 film was grown. A PMMA film with a thickness of 200 nm was coated by spin coating at 5000 rpm. After baking at 120°C for 10 minutes, the film was placed in a 0.15 mol / L ferric chloride aqueous solution and reacted at 70°C for 20 minutes to dissolve the copper foil substrate, thus transferring the PMMA / MoSi2N4 film onto a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55°C, finally achieving a successful transfer of a 4 square inch WSi2N4 film.

[0069] The composition, crystal structure, morphology and thickness of the WSi2N4 thin film were characterized by optical microscopy, transmission electron microscopy and atomic force microscopy. The results showed that the obtained WSi2N4 was a single-layer polycrystalline WSi2N4 thin film with a hexagonal structure. The film size was 8 cm × 9 cm and the thickness was about 1 nm. It was a strictly uniform single-layer film with high crystal quality and semiconductor properties.

[0070] Example 8

[0071] First, such as Figure 1 As shown, this invention uses a horizontal reactor to grow a uniform single-layer WSi2N4 thin film. The horizontal reactor has a gas inlet 1 and a gas outlet 5 at each end. A tungsten / copper bimetallic substrate foil (the tungsten is obtained by physical vapor deposition on the copper foil surface, with a thickness of 0.5 nm and a tungsten target purity of 99.95 wt%; the copper foil is 3 cm × 4 cm × 25 μm, with a purity of 99.5 wt%) is placed in the central high-temperature region of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm); under hydrogen gas... Annealing was performed by heating to 1030℃ and holding for 2 hours in an atmosphere (hydrogen flow rate of 200 ml / min and heating rate of 20℃ / min during heating). Then, a mixture of ammonia and hydrogen was introduced (gas flow rates of 4 ml / min for ammonia and 200 ml / min for hydrogen) to begin the growth of two-dimensional WSi2N4. The growth time was 4 hours. After the growth was completed, the film was rapidly cooled at a rate of 500℃ / min to obtain a 2 square inch WSi2N4 film with a thickness of about 1 nm on the copper foil surface.

[0072] Then, molten paraffin wax heated to 150°C was dropped onto the copper foil surface on which WSi2N4 films were grown. The sample stage temperature of the spin coater was set to 40°C and the rotation speed was set to 2000 rpm to spin coat a 600 nm thick paraffin wax film. After curing at room temperature for 5 minutes, the film was placed in a 0.15 mol / L ferric chloride aqueous solution and reacted at 70°C for 20 minutes to dissolve the copper foil substrate. The paraffin / MoSi2N4 film was then repeatedly washed in deionized water and transferred to a SiO2 / Si substrate. The film was then dried at 40°C for 24 hours. The paraffin wax was dissolved in petroleum ether at 55°C, and finally, a 2 square inch WSi2N4 film was successfully transferred.

[0073] The composition, crystal structure, morphology and thickness of the WSi2N4 thin film were characterized by optical microscopy, transmission electron microscopy and atomic force microscopy. The results showed that the obtained WSi2N4 was a single-layer polycrystalline WSi2N4 thin film with a hexagonal structure. The film size was 3 cm × 4 cm and the thickness was about 1 nm. It was a strictly uniform single-layer film with high crystal quality and semiconductor properties.

[0074] Example 9

[0075] First, such as Figure 1 As shown, this invention employs a horizontal reactor to grow a uniform single-layer WSi2N4 thin film. The horizontal reactor has a gas inlet 1 and a gas outlet 5 at each end. A copper-tungsten alloy / copper bimetallic substrate foil (tungsten obtained through physical vapor deposition on the copper foil surface, with a thickness of 10 nm; the copper-tungsten alloy target material purity is 99.95 wt%; the copper-tungsten ratio is 9:1; the copper foil is 3 cm × 4 cm × 25 μm, with a purity of 99.5 wt%) is placed in the center of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm) at a high temperature. The area was annealed by heating to 1070°C in a hydrogen atmosphere and holding for 2 hours (the hydrogen flow rate during heating was 200 mL / min, and the heating rate was 20°C / min). Then, a mixture of ammonia and hydrogen was introduced (the gas flow rates were 4 mL / min for ammonia and 200 mL / min for hydrogen) to begin the growth of two-dimensional WSi2N4. The growth time was 4 hours. After the growth was completed, the area was rapidly cooled at a rate of 500°C / min to obtain a 2 square inch WSi2N4 film with a thickness of approximately 1 nm on the copper foil surface.

[0076] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the surface of a copper foil on which a WSi2N4 film was grown. A PMMA film with a thickness of 200 nm was coated by spin coating at 5000 rpm. After baking at 120°C for 10 minutes, the film was placed in a 0.15 mol / L ferric chloride aqueous solution and reacted at 70°C for 20 minutes to dissolve the copper foil substrate, thus transferring the PMMA / WSi2N4 film onto a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55°C, finally achieving a successful transfer of a 2 square inch WSi2N4 film.

[0077] The composition, crystal structure, morphology and thickness of the WSi2N4 thin film were characterized by optical microscopy, transmission electron microscopy and atomic force microscopy. The results showed that the obtained WSi2N4 was a single-layer polycrystalline WSi2N4 thin film with a hexagonal structure. The film size was 3 cm × 4 cm and the thickness was about 1 nm. It was a strictly uniform single-layer film with high crystal quality and semiconductor properties.

[0078] Example 10

[0079] First, such as Figure 1 As shown, this invention employs a horizontal reactor to grow a uniform single-layer WSi2N4 thin film. The horizontal reactor has a gas inlet 1 and a gas outlet 5 at each end. A copper-tungsten alloy / copper bimetallic substrate foil (tungsten obtained through physical vapor deposition on the copper foil surface, with a thickness of 15 nm, a copper-tungsten target purity of 99.95 wt%, and a copper-tungsten ratio of 9:1; the copper foil is 8 cm × 9 cm × 25 μm, with a purity of 99.5 wt%) is placed in the center of the horizontal reactor (furnace tube diameter 105 mm, reaction zone length 200 mm) at a high temperature. The area was annealed by heating to 1070°C in a hydrogen atmosphere and holding for 2 hours (hydrogen flow rate was 400 mL / min, and heating rate was 20°C / min). Then, a mixture of ammonia and hydrogen was introduced (gas flow rates of 8 mL / min for ammonia and 400 mL / min for hydrogen) to begin the growth of two-dimensional WSi2N4. The growth time was 6 hours. After the growth was completed, the area was rapidly cooled at a rate of 500°C / min to obtain a 4 square inch WSi2N4 film with a thickness of approximately 1 nm on the copper foil surface.

[0080] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the copper foil surface on which a WSi2N4 film was grown. A PMMA film with a thickness of 200 nm was coated by spin coating at 5000 rpm. After baking at 120°C for 10 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70°C for 20 minutes to dissolve the copper foil substrate, thus transferring the PMMA / WSi2N4 film to a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55°C, finally achieving a successful transfer of a 4 square inch WSi2N4 film.

[0081] The composition, crystal structure, morphology and thickness of the WSi2N4 thin film were characterized by optical microscopy, transmission electron microscopy and atomic force microscopy. The results showed that the obtained WSi2N4 was a single-layer polycrystalline WSi2N4 thin film with a hexagonal structure. The film size was 8 cm × 9 cm and the thickness was about 1 nm. It was a strictly uniform single-layer film with high crystal quality and semiconductor properties.

[0082] like Figure 1 The diagram shows an experimental setup for growing high-quality, uniform monolayer MA2Z4 thin films using the CVD method of this invention. Taking the two-dimensional layered transition metal silicon-nitrogen ternary compound MSi2N4 as an example, the setup mainly includes a gas inlet 1, a metal substrate 2 (copper foil 21 and transition metal thin film 22), a heating furnace 3, a quartz tube 4, and a gas outlet 5. The carrier gas enters the quartz tube 4 of the heating furnace 3 from the gas inlet 1 and exits from the gas outlet 5. The metal substrate 2 is composed of copper foil 21 and an upper transition metal thin film 22.

[0083] like Figure 2 As shown, the CVD method yielded a 2-square-inch MoSi2N4 thin film on copper. The photograph shows that the material is a uniform, complete, and continuous film.

[0084] like Figure 3 As shown, the 2-square-inch uniform monolayer MoSi2N4 film obtained by this CVD method can be completely transferred to SiO2 / Si and PET substrates. The transferred film maintains the same optical contrast as the SiO2 / Si substrate, indicating that the MoSi2N4 film has a uniform thickness.

[0085] like Figure 4 As shown, transmission electron microscopy characterization results indicate that the MoSi2N4 thin film prepared by this CVD method has high crystallinity and is free of defects and vacancies.

[0086] like Figure 5 As shown, the uniform monolayer MoSi2N4 film obtained by this CVD method has certain light absorption characteristics in the visible light range, with a band gap of 1.91 eV.

[0087] like Figure 6 As shown, the CVD method yielded a 2-square-inch WSi2N4 thin film on copper. The photograph shows that the material is a uniform, complete, and continuous thin film.

[0088] like Figure 7 As shown, the 2-square-inch uniform monolayer WSi2N4 film obtained by this CVD method can be completely transferred to SiO2 / Si and PET substrates. The transferred film maintains the same optical contrast as the SiO2 / Si substrate, indicating that the WSi2N4 film has a uniform thickness.

[0089] like Figure 8 As shown, a 4-square-inch WSi2N4 thin film on copper obtained by this CVD method was subjected to oxidative treatment at 180°C in air for 30 minutes. The photograph shows that the sample is a uniform, complete and continuous thin film.

[0090] like Figure 9 As shown, transmission electron microscopy characterization results indicate that the WSi2N4 thin film prepared by this CVD method has high crystallinity and is free of defects and vacancies.

[0091] like Figure 10 As shown, the uniform monolayer WSi2N4 thin film obtained by this CVD method has certain light absorption characteristics in the visible light range, and its band gap is 2.02 eV.

[0092] The above results demonstrate that this invention uses copper foil as the growth substrate and employs physical vapor deposition (PVD) technology to deposit a thin film containing transition metal M on the copper foil surface. By annealing in an environment with an A or Z source, the MA or MZ source is pre-stored in the copper foil substrate. Then, a third element, Z or A, is introduced, reacting with the stored element precipitated on the copper foil surface at a temperature not exceeding the melting point of copper, thereby achieving efficient and rapid growth of a uniform monolayer MA2Z4 thin film. The low-melting-point metal layer can be removed by etching, allowing for the clean and non-destructive transfer of the MA2Z4 thin film to any substrate. This method can also prepare large-size monolayer or multilayer single-crystal samples. This invention features a simple preparation process, efficient and rapid preparation flow, easily controllable product thickness and size, and ease of large-area thin film preparation. Furthermore, the two-dimensional layered MA2Z4 thin film obtained by this PVD and CVD combined preparation method is strictly controlled to be a monolayer with a uniform structure, high crystallinity, and excellent environmental, chemical, thermal stability, and mechanical properties. This efficient and rapid preparation method makes it possible for the industrial application of high-quality, uniform monolayer MA2Z4 thin films in fields such as electronic devices, optoelectronic devices, valley electronics devices, high-strength thin films, high-transmittance thin films, proton / ion exchange membranes, and separation membranes.

Claims

1. A method for preparing a uniform monolayer of MA2Z4 thin film, characterized in that, Using copper foil as the growth substrate, a thin film containing a transition metal M is deposited on the surface of the copper foil using physical vapor deposition. The MA source or MZ source is pre-stored in the copper foil substrate by annealing in an environment with an A source or a Z source through chemical vapor deposition. Then, a third element Z or A is introduced and reacted with the stored element precipitated on the surface of the copper foil at a reaction temperature not higher than the melting point of copper to grow a uniform monolayer MA2Z4 thin film. Subsequently, the copper foil substrate is etched to transfer it to any substrate. Where M represents transition metal elements, including molybdenum, tungsten, titanium, zirconium, hafnium, vanadium, niobium, tantalum, or chromium; A represents group IV elements, including silicon or germanium; and Z represents group V elements, including nitrogen, phosphorus, or arsenic. A smooth copper foil with a purity greater than 98 wt% and a thickness of 8 μm to 2 mm is used. A transition metal M thin film is deposited on the copper foil by physical vapor deposition to obtain a transition metal / copper bimetallic growth substrate. The physical vapor deposition method includes magnetron sputtering, electron beam evaporation, or ion beam sputtering. The deposition conditions are: deposition rate 0.01 to 1 nm / s, and the thickness of the transition metal M layer on the copper foil surface is 0.2 to 1000 nm. The target materials used include pure transition metal targets, alloy targets of transition metal and copper, and alloy targets of transition metal and Group IV or V elements. During the chemical vapor deposition reaction, the carrier gas is hydrogen or a mixture of hydrogen and an inert gas. The temperature for growing large-area, high-quality monolayer MA2Z4 films by chemical vapor deposition is 1030 ℃~1070 ℃, and the growth time is 2 hours~3 hours.

2. The method of claim 1, wherein the uniform monolayer MA2Z4 film is prepared by, The size of the two-dimensional layered MA2Z4 film can be controlled by changing the size of the copper foil substrate or the size of the deposition area of ​​the transition metal M film, ultimately achieving high-quality and uniform monolayer film growth.

3. The method of claim 1, wherein the uniform monolayer MA2Z4 film is prepared by, A and Z elements are introduced by using precursors containing A and Z, which are solids, powders, liquids, or gases that volatilize or decompose to release A or Z at high temperatures; or, they are introduced by coating in the form of MA alloys or MZ alloys.

4. The method of claim 3, wherein the MA2Z4 thin film is a uniform monolayer. A is a Group 4 element, including but not limited to silicon or germanium. Precursors of silicon include but are not limited to elemental silicon, quartz or silane. Precursors of germanium include but are not limited to elemental germanium or germanane. Z is a Group 5 element, including but not limited to nitrogen, phosphorus or arsenic. Precursors of nitrogen include but are not limited to ammonia or nitrogen. Precursors of phosphorus include but are not limited to white phosphorus or red phosphorus. Precursors of arsenic include but are not limited to elemental arsenic.

5. The method of claim 1, wherein the uniform monolayer MA2Z4 film is prepared by, Before transfer, a protective layer of polymer or organic small molecule is uniformly coated on the surface of the MA2Z4 film to protect it. The copper foil substrate is etched away, and the resulting protective layer / MA2Z4 composite film is transferred to other substrates. The protective layer is then dissolved and removed.

6. The method of claim 5, wherein the MA2Z4 thin film is a uniform monolayer. The high molecular polymer used is one or a mixture of two or more of polymethyl methacrylate, polyethylene, polystyrene, and polypropylene; the small organic molecule used is one or a mixture of two or more of paraffin, rosin, and camphor.

7. The method of claim 5, wherein the MA2Z4 thin film is a uniform monolayer. The copper foil substrate is etched using a copper etching solution, which may be an aqueous solution of ammonium persulfate, an aqueous solution of tin tetrachloride, an aqueous solution of ferric chloride, concentrated ammonia, or dilute hydrochloric acid.

8. The method of claim 7, wherein the uniform monolayer MA2Z4 film is prepared by, The organic solvents used to remove the protective layer of polymers are one or more of ketones, chlorinated hydrocarbons, halogenated hydrocarbons, and aromatic hydrocarbons; the organic solvents used to remove the protective layer of small organic molecules include, but are not limited to, one or more of ethanol, diethyl ether, chloroform, hexane, acetone, and petroleum ether.

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