Preparation method of large-size ternary compound MA2Z4 film with controllable layer number

Abstract

The application relates to the field of chemical vapor deposition preparation of two-dimensional layered MA2Z4 thin film materials, in particular to a preparation method of large-size ternary compound MA2Z4 thin films with controllable layer number. A chemical vapor deposition method is adopted, a gold-eighth group transition metal alloy foil is used as a growth substrate, a thin film containing a transition group metal M is deposited, pre-storage of M-A or M-Z sources in the alloy foil substrate is realized through annealing treatment in an environment with an A source or a Z source, a third element Z or A is introduced, and the stored elements precipitated to the surface of the alloy foil are reacted at high temperature not higher than the alloy melting point, the MA2Z4 thin film with controllable layer number is grown by regulating the thickness of the M source and the content of the eighth group transition metal in the growth substrate, and the electrochemical bubbling method is used to transfer the thin film to any substrate. The preparation process is simple, the film forming rate is fast, the thin film size is easy to enlarge, and the method is suitable for the preparation of large-area high-quality MA2Z4 thin films with controllable layer number.

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 large-size ternary compound MA2Z4 thin films with controllable layer number, suitable for the preparation of large-area, high-quality MA2Z4 thin films with controllable layer number. Background technology:

[0002] Two-dimensional (2D) materials, represented by graphene, are a class of atomically thin materials that have attracted widespread attention due to their unique and novel physical properties within the two-dimensional limit, and have shown broad application prospects in fields such as flexible displays, nanoelectronic devices, and energy storage devices. Examples include graphene, a zero-bandgap semiconductor with extremely high carrier mobility, ultra-high fracture strength, massless Dirac fermions, and an anomalous quantum Hall effect; h-BN, an insulator with an atomically smooth surface and excellent chemical and thermal stability; and MoS2 and WS2, semiconductors with spin-orbit coupling and valley polarization effects. Currently, the property control of single-layer 2D materials usually relies on surface modification or heteroatom doping, while the number of layers adds new degrees of freedom to the property control of 2D materials. However, current research on multilayer 2D materials is mainly limited to common material systems. Exploring the layer number control of novel 2D materials is expected to reveal more interesting new properties and further enrich the research on 2D materials.

[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. Chinese Invention Patent Publication No. CN113718227A proposes a type of two-dimensional layered ternary compound and its preparation method. The molecular formula of the two-dimensional layered ternary compound is MX2Y4 (equivalent to MA2Z4 in this invention, where A corresponds to X and Z corresponds to Y), wherein: M is a transition metal element, X is a Group IV element, and Y is a Group V element. Each layer consists of seven atomic layers: YXYMYXY, and the layers are bonded together by van der Waals forces.

[0004] Theoretical calculations show that the fundamental electrical and optical properties of MA2Z4 are highly dependent on its layer number. Therefore, precisely controlling the layer number of MA2Z4 is crucial for regulating its electrical and nonlinear optical properties and exploring its applications in nanoelectronic devices and on-chip lasers. However, current growth techniques can only produce uniform monolayer films. While increasing the Z source concentration can grow multilayer MA2Z4 islands, the domain sizes are small, the stacking is random, and the thickness is non-uniform, making the controlled fabrication of multilayer films a significant challenge. Therefore, there is an urgent need to develop a layer-number-controllable fabrication method to lay the foundation for large-area uniform layer growth of two-dimensional MA2Z4 materials and for exploring its related properties and applications. Summary of the Invention:

[0005] The purpose of this invention is to provide a method for preparing large-size ternary compound MA2Z4 thin films with controllable number of layers, solving the problems of small island domain size, random stacking, and uneven thickness of multilayer MA2Z4 obtained in current research, and laying the foundation for achieving efficient and rapid growth of MA2Z4 thin films with controllable number of layers and exploring related properties and applications.

[0006] The technical solution of this invention is:

[0007] A method for preparing a large-size ternary compound MA2Z4 thin film with controllable number of layers involves depositing a group VIII transition metal on the surface of a gold foil using physical vapor deposition (PVD) to obtain a gold-group VIII transition metal alloy foil as a growth substrate. Then, a thin film containing the transition metal M is deposited. The MA source or MZ source is pre-stored in the alloy foil substrate by annealing in an environment with an A source or a Z source through chemical vapor deposition (CVD). A third element, Z or A, is then introduced and reacts with the stored element precipitated on the surface of the alloy foil at a reaction temperature not exceeding the melting point of the alloy. By controlling the thickness of the M film and the content of the group VIII element, a MA2Z4 thin film with controllable number of layers is grown. Subsequently, it is transferred to any substrate using an electrochemical bubbling method.

[0008] 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; and group VIII transition metals include but not limited to iron, cobalt or nickel.

[0009] The method for preparing large-size ternary compound MA2Z4 thin films with controllable layer number describes that the size of the two-dimensional layered MA2Z4 thin film is controlled by changing the size of the alloy foil substrate or the deposition area of ​​the transition metal M thin film, ultimately achieving the growth of high-quality thin films with controllable layer number.

[0010] The method for preparing large-size ternary compound MA2Z4 thin films with controllable layer number involves using a smooth gold foil with a purity greater than 98 wt% and a thickness of 1 μm to 2 mm. A group VIII transition metal layer is physically vapor-deposited on the gold foil to obtain a gold-group VIII transition metal alloy foil. Then, a thin film containing a transition metal M is deposited to obtain a transition metal / group VIII transition metal / gold alloy metal growth substrate. The physical vapor deposition method includes magnetron sputtering, electron beam evaporation, or ion beam sputtering. The deposition conditions are: a group VIII transition metal deposition rate of 0.01–1 nm / s, and a group VIII transition metal layer thickness of 0 nm to 500 nm on the gold foil surface; a transition metal M deposition rate of 0.01–1 nm / s, and a transition metal M layer thickness of 0.2–1000 nm on the gold foil surface. The target material used includes, but is not limited to, a pure transition metal target, a transition metal and gold alloy target, or a transition metal and a group IV or V element alloy target.

[0011] The method for preparing large-size ternary compound MA2Z4 thin films with controllable number of layers introduces 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 is introduced by coating in the form of MA alloy or MZ alloy.

[0012] The method for preparing large-size ternary compound MA2Z4 thin films with controllable number of layers, wherein A is a Group IV 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 V 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.

[0013] The method for preparing large-size ternary compound MA2Z4 thin films with controllable number of layers 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 large-area, high-quality MA2Z4 thin films with controllable number of layers is 800℃~1063℃, and the growth time is 1 minute~360 minutes.

[0014] The method for preparing large-size ternary compound MA2Z4 thin films with controllable number of layers involves uniformly coating a layer of polymer on the surface of the MA2Z4 thin film for protection before transfer. Then, the protective layer / two-dimensional layered MA2Z4 thin film is separated from the alloy substrate by an electrochemical bubbling method. The resulting protective layer / MA2Z4 thin film is transferred to other substrates, and the protective layer is dissolved and removed.

[0015] The method for preparing large-size ternary compound MA2Z4 thin films with controllable number of layers uses a polymer of one or more of polymethyl methacrylate, polyethylene, polystyrene, and polypropylene, and the organic solvent used to remove the polymer protective layer is one or more of ketones, chlorinated hydrocarbons, halogenated hydrocarbons, and aromatic hydrocarbons.

[0016] The design concept of this invention is:

[0017] This invention employs physical vapor deposition (PVD) to deposit a group VIII transition metal on the surface of a gold foil, obtaining a gold-group VIII transition metal alloy foil as a growth substrate. Then, a thin film containing a transition metal M is deposited. By annealing in an environment with an A or Z source, the MA or MZ source is pre-stored in the gold foil substrate. Then, a third element Z or A is introduced and reacts with the stored element precipitated on the surface of the alloy foil at a high temperature not exceeding the alloy melting point, thereby achieving efficient and rapid growth of MA2Z4 thin films with controllable layer number.

[0018] The advantages and beneficial effects of this invention are:

[0019] 1. This invention proposes a method for preparing large-size ternary compound MA2Z4 thin films with controllable layer number. By adjusting the thickness of the M source and the content of Group VIII transition metal in the growth substrate, the layer number of the MA2Z4 thin film can be controlled. 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. It is suitable for preparing large-area, high-quality thin films with controllable layer number.

[0020] 2. In the preparation process of this invention, the transition metal M source can be pre-stored together with the A source on the surface and inside of the alloy foil after the annealing process, and can be grown directly on the surface of the highly catalytically active alloy foil, which greatly improves the growth rate of MA2Z4 film.

[0021] 3. The MA2Z4 material prepared by this invention can be transferred non-destructively by electrochemical bubbling, providing a material basis for the study of the physical properties of high-quality MA2Z4 material.

[0022] 4. The MA2Z4 thin film with controllable number of layers prepared by this invention is grown on a flexible substrate, which is expected to realize large-area roll-to-roll transfer. Attached image description:

[0023] Figure 1 This is a schematic diagram of an experimental setup for growing large-size MA2Z4 thin films with controllable layer number using CVD. In the diagram, 1 is the gas inlet; 2 is the metal substrate; 21 is the gold foil; 22 is the Group VIII transition metal thin film; 23 is the transition metal M thin film; 3 is the heating furnace; 4 is the quartz tube; and 5 is the gas outlet.

[0024] Figure 2 A photograph of a 5mm × 5mm WSi2N4 thin film grown by CVD on a W / Au substrate.

[0025] Figure 3 A photograph of a WSi2N4 thin film grown on a W / Au substrate by CVD transferred onto a SiO2 (300 nm thick) / Si substrate.

[0026] Figure 4 The figure shows the photoluminescence spectrum of a monolayer WSi2N4 thin film grown by CVD. In the figure, the horizontal axis represents wavelength (nm) and the vertical axis represents intensity (au).

[0027] Figure 5 The image shows an atomic force microscope (AFM) image of a monolayer WSi2N4 film grown on a W / Au substrate by CVD transferred to a SiO2 (300 nm thick) / Si substrate. The curve in the image represents the thickness of the monolayer sample as measured by AFM.

[0028] Figure 6 This is a photograph of a 1cm × 1cm multilayer WSi2N4 thin film grown by CVD on a W / Fe / Au substrate.

[0029] Figure 7 Raman spectra of monolayer and multilayer WSi2N4 films grown by CVD on W / Fe / Au substrates are shown. In the figure, the horizontal axis represents the Raman shift (cm). -1 The vertical axis Intensity represents the relative intensity (au).

[0030] Figure 8 The image shows an atomic force microscope (AFM) image of a multilayer WSi2N4 thin film grown on a W / Fe / Au substrate by CVD transferred to a SiO2 (300 nm thick) / Si substrate. The curve in the image represents the thickness curve of the multilayer sample as measured by AFM. Detailed implementation method:

[0031] In its specific implementation, this invention proposes a method for preparing a large-size ternary compound MA2Z4 thin film with controllable layer number. A layer of Group VIII transition metal is deposited on the surface of a gold foil using physical vapor deposition (PVD) to obtain a gold-Group VIII transition metal alloy foil as a growth substrate. Then, a thin film containing transition metal M is deposited. The MA or MZ source is pre-stored in the alloy foil substrate through annealing in an environment with an A or Z source. A third element, Z or A, is then introduced and reacts with the stored element precipitated on the alloy foil surface at a high temperature not exceeding the alloy's melting point. By controlling the thickness of the M source and the content of Group VIII transition metal in the growth substrate, a MA2Z4 thin film with controllable layer number is grown. Subsequently, it is transferred to any substrate using an electrochemical bubbling method. The specific steps are as follows:

[0032] (1) CVD growth of MA2Z4 thin films with controllable number of layers, taking the two-dimensional layered transition metal silicon-nitrogen ternary compound MSi2N4 as an example: A layer of Group VIII transition metal is deposited on the surface of gold foil using physical vapor deposition technology to obtain a gold-Group VIII transition metal alloy foil as a growth substrate. Then, a thin film containing transition metal M is deposited to obtain an alloy metal growth substrate of transition metal / Group VIII transition metal / gold. A silicon wafer or quartz wafer is placed above or in front of the growth substrate as a silicon source, and ammonia is used 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 gold foil substrate. Subsequently, N element is introduced. At a reaction temperature not higher than the melting point of the alloy, M atoms and Si atoms that diffuse uniformly to the surface of the catalytically active alloy foil substrate react with the introduced N atoms to grow a layer-controllable MSi2N4 thin film. When there is no Group VIII transition metal, it is a single-layer MSi2N4 thin film. By controlling the thickness of the M source and the content of Group VIII transition metal in the growth substrate, MA2Z4 thin films with different numbers of layers can be grown.

[0033] The growth substrate used is a metal alloy containing transition metal M / group VIII / gold. The thickness of the transition metal M layer deposited by physical vapor deposition is 0.2–1000 nm, preferably 0.2–1 nm, with a deposition rate of 0.01–1 nm / s, preferably 0.01–0.03 nm / s. The thickness of the group VIII transition metal layer is 0–500 nm, preferably 0–10 nm (0 nm corresponds to a single-layer MSi₂N₄ film, and different thicknesses of group VIII transition metal correspond to different numbers of MSi₂N₄ films), with a deposition rate of 0.01–1 nm / s, preferably 0.01–0.03 nm / s. The thickness of the gold foil used is 1 μm–2 mm, preferably 5 μm–25 μm, and 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 a silicon wafer, a quartz wafer, or silane. When growing other two-dimensional MA2Z4 crystals, the germanium source is a germanium wafer or germanane, the phosphorus source is elemental phosphorus, and the arsenic source is elemental arsenic. The carrier gas used in CVD growth is hydrogen or a mixture of hydrogen and an inert gas (carrier gas flow rate of 20 mL / min to 1000 mL / min). The CVD growth temperature is 800℃ to 1063℃, preferably 950℃ to 1058℃; the growth time is 1 minute to 360 minutes, preferably 20 minutes to 240 minutes; the cooling rate after the reaction is 10℃ / min to 600℃ / min, preferably 200℃ / min to 600℃ / min.

[0034] (2) Coating of a polymer protective layer: A polymer layer is uniformly coated on the surface of the two-dimensional layered MA2Z4 film to prevent it from being damaged during subsequent processing; these polymers are one or more of polymethyl methacrylate, polyethylene, polystyrene, and polypropylene.

[0035] (3) Separation of the polymer / two-dimensional layered MA2Z4 composite film from the gold substrate: The polymer / two-dimensional layered MA2Z4 composite film is separated from the alloy substrate by an electrochemical bubbling method, and then the composite film is placed on the target substrate. The polymer / two-dimensional layered MA2Z4 composite film / metal substrate is connected to the cathode of a constant current power supply, with a platinum sheet as the anode. The electrolyte aqueous solution includes one or more of sodium hydroxide, potassium hydroxide, sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, sodium nitrate, and potassium nitrate.

[0036] (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 with an organic solvent. The organic solvent used to remove the protective layer is one or more of the following: acetone, ethyl lactate, dichloroethane, trichloroethylene, chloroform, etc., ketones, chlorinated hydrocarbons, halogenated hydrocarbons, aromatic hydrocarbons, etc.

[0037] The MA2Z4 thin film obtained by this invention can achieve control over at least several layers, with the film size depending on the size of the transition metal M film obtained by physical vapor deposition. The prepared MA2Z4 film has uniform composition and high crystallinity. It grows rapidly, forming multilayer films in 60 minutes, and can be transferred non-destructively using an electrochemical bubbling method.

[0038] The present invention will now be described in further detail with reference to embodiments and accompanying drawings.

[0039] Example 1

[0040] First, such as Figure 1 As shown, this embodiment uses a horizontal heating furnace to grow a uniform single-layer WSi2N4 thin film. The horizontal heating furnace 3 has a gas inlet 1 and a gas outlet 5 at both ends. A tungsten / gold bimetallic substrate foil (the tungsten is obtained by physical vapor deposition on the gold foil surface, with a thickness of 0.4 nm and a tungsten target purity of 99.95 wt%; the gold foil size is 5 mm × 5 mm × 10 μm, with a purity of 99.99 wt%) is placed in the central area of ​​a quartz tube 4 (inner diameter 20 mm, length 100 cm). Then, the tungsten / gold bimetallic substrate foil and the quartz tube 4 are placed together in the horizontal heating furnace 3 (furnace tube diameter...). The central high-temperature region (22 mm long, reaction zone 20 mm long) was heated to 1050 °C in a hydrogen atmosphere and held for 40 minutes for annealing (hydrogen flow rate was 300 mL / min, heating rate was 30 °C / min). Then, a mixture of ammonia and hydrogen was introduced (gas flow rates were 6 mL / min for ammonia and 300 mL / min for hydrogen) to begin the growth of two-dimensional WSi2N4 for 80 minutes. After growth, the mixture was rapidly cooled at a rate of 500 °C / min to obtain a 5 mm × 5 mm WSi2N4 film with a thickness of approximately 1 nm on the gold foil surface.

[0041] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the gold surface on which WSi2N4 crystals were grown. A PMMA film was coated by spin coating at 2000 rpm. After baking at 120°C for 10 minutes, WSi2N4 grown on the tungsten / gold bimetallic substrate was transferred to the SiO2 / Si substrate by bubble transfer. Then, the PMMA was dissolved with acetone at 55°C, and the WSi2N4 film was successfully transferred.

[0042] The morphology, crystal structure, and thickness of the WSi2N4 thin film were characterized using optical microscopy, Raman spectroscopy, photoluminescence spectroscopy, and atomic force microscopy. The results showed that the obtained WSi2N4 was a single-layer polycrystalline WSi2N4 thin film with a hexagonal structure, a film size of 4 mm × 4 mm, a thickness of about 1 nm, high crystal quality, and semiconductor properties.

[0043] Example 2

[0044] First, such as Figure 1 As shown, this embodiment uses a horizontal heating furnace to grow a controllable number of WSi2N4 thin films. The horizontal heating furnace 3 has a gas inlet 1 and a gas outlet 5 at both ends. A tungsten / iron / gold substrate foil (tungsten obtained by physical vapor deposition on a gold surface, with a thickness of 0.4 nm and a tungsten target purity of 99.95 wt%; iron obtained by physical vapor deposition on a gold surface, with a thickness of 1 nm and a tungsten target purity of 99.95 wt%; gold foil with dimensions of 1 cm × 1 cm × 10 μm and a purity of 99.99 wt%) is placed in the central area of ​​a quartz tube 4 (inner diameter 20 mm, length 100 cm). Then, the tungsten / iron / gold substrate foil and the quartz tube... The tube 4 was placed together in the central high-temperature area of ​​the horizontal heating furnace 3 (furnace tube diameter 22 mm, reaction zone length 20 mm); it was heated to 1050℃ in a hydrogen atmosphere and held for 40 minutes for annealing (hydrogen flow rate was 300 ml / min and heating rate was 30℃ / min during heating). Then, a mixture of ammonia and hydrogen was introduced (gas flow rates were 6 ml / min for ammonia and 300 ml / min for hydrogen) to start the growth of two-dimensional WSi2N4. The growth time was 80 minutes. After the growth was completed, it was rapidly cooled at a rate of 500℃ / min to obtain a 1 square centimeter WSi2N4 film with a thickness of about 4 nm on the alloy surface.

[0045] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the gold surface on which WSi2N4 crystals were grown. A PMMA film was coated by spin coating at 2000 rpm. After baking at 120°C for 10 minutes, WSi2N4 grown on the tungsten / iron / gold alloy substrate was transferred to the SiO2 / Si substrate by bubbling transfer. Then, the PMMA was dissolved with acetone at 55°C, and the WSi2N4 film was successfully transferred.

[0046] The morphology and crystal structure of the WSi2N4 thin film were characterized by optical microscopy, Raman spectroscopy, and atomic force microscopy. The results showed that the obtained WSi2N4 thin film had a size of 1 cm × 1 cm and a thickness of about 4 nm, with high crystal quality and semiconductor properties.

[0047] like Figure 1The diagram shows an experimental setup for growing large-size MA2Z4 thin films with controllable layer number using the CVD method of the present invention. Taking the two-dimensional layered transition metal silicon-nitrogen ternary compound MSi2N4 as an example, it mainly includes: a gas inlet 1, a metal substrate 2 (gold foil 21, group VIII transition metal thin film 22, and transition metal M thin film 23), a heating furnace 3, a quartz tube 4, and a gas outlet 5. The quartz tube 4 is horizontally arranged in the heating furnace 3, with the gas inlet 1 and the gas outlet 5 at its two ends, respectively. The metal substrate 2 is placed in the quartz tube 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 a lower gold foil 21, a middle group VIII transition metal thin film 22, and an upper transition metal M thin film 23 stacked together.

[0048] like Figure 2 As shown in the image, a 5 mm × 5 mm WSi2N4 thin film on gold obtained by this CVD method is presented. The image shows that the material is a uniform, complete, and continuous thin film.

[0049] like Figure 3 As shown, the 5 mm × 5 mm uniform monolayer WSi2N4 film obtained by this CVD method can be completely transferred to the SiO2 / Si substrate. The transferred film maintains the same optical contrast as the SiO2 / Si substrate, indicating that the WSi2N4 film has a uniform thickness.

[0050] like Figure 4 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 2.30 eV.

[0051] like Figure 5 As shown in the atomic force microscope image, the material has a smooth and flat surface, an intact structure, and the thickness of WSi2N4 remains at about 1 nm, indicating that it is a single-layer WSi2N4 thin film.

[0052] like Figure 6 As shown, the CVD method yields a 1 square centimeter multilayer WSi2N4 thin film on gold. The photograph shows that the material is a uniform, complete, and continuous thin film.

[0053] like Figure 7 As shown, the 1 square centimeter multilayer WSi2N4 thin film on gold obtained by this CVD method can be clearly distinguished from the single layer WSi2N4 on gold by the Raman vibration peak.

[0054] like Figure 8 As shown, the atomic force microscope image reveals that the material has a smooth and flat surface, an intact structure, and the thickness of WSi2N4 remains at around 4 nm, consisting of four layers of WSi2N4 thin film.

[0055] The above results demonstrate that a gold-group VIII transition metal alloy foil is obtained by depositing a layer of group VIII transition metal on the surface of a gold foil using physical vapor deposition (PVD) as a growth substrate. A thin film containing transition metal M is then deposited. Pre-storage of the MA or MZ source in the alloy foil substrate is achieved through annealing in an environment with either an A or Z source. A third element, Z or A, is then introduced, reacting with the stored element precipitated on the alloy foil surface at a temperature not exceeding the alloy's melting point. By controlling the thickness of the M source and the content of group VIII transition metal in the growth substrate, a MA2Z4 thin film with a controllable number of layers can be grown. Subsequently, it is transferred to any substrate using an electrochemical bubbling method. This invention features a simple preparation process, fast film formation rate, easily controllable film thickness and size, and suitability for large-area, high-quality, uniform film preparation. The obtained two-dimensional layered MA2Z4 thin film exhibits uniform thickness, high crystallinity, and excellent environmental, chemical, thermal stability, and mechanical properties. This efficient and rapid preparation method lays the foundation for exploring the application of high-quality MA2Z4 thin films with controllable layer number in electronic devices, optoelectronic devices, memory, and on-chip lasers by controlling their ferroelectric, nonlinear optical, and strongly correlated electron properties.

Claims

1. A method for preparing large-size ternary compound MA2Z4 thin films with controllable layer number, characterized in that, A group VIII transition metal layer was deposited on the surface of a gold foil using physical vapor deposition (PVD) to obtain a gold-group VIII transition metal alloy foil as a growth substrate. Then, a thin film containing transition metal M was deposited. The MA source or MZ source was pre-stored in the alloy foil substrate by chemical vapor deposition and annealing in an environment with an A source or Z source. Then, a third element Z or A was introduced and reacted with the stored element precipitated on the surface of the alloy foil at a reaction temperature not higher than the melting point of the alloy. By controlling the thickness of the M film and the content of group VIII element, a MA2Z4 thin film with a controllable number of layers was grown. Subsequently, it was transferred to any substrate by electrochemical bubbling. 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; and group VIII transition metals include but not limited to iron, cobalt or nickel.

2. The method for preparing large-size ternary compound MA2Z4 thin films with controllable layer number according to claim 1, characterized in that, The size of the two-dimensional layered MA2Z4 thin film can be controlled by changing the size of the alloy foil substrate or the deposition area of ​​the transition metal M film, ultimately achieving high-quality, layer-controllable thin film growth.

3. The method for preparing large-size ternary compound MA2Z4 thin films with controllable layer number according to claim 1, characterized in that, A smooth gold foil with a purity greater than 98 wt% and a thickness of 1 μm to 2 mm is used. A layer of Group VIII transition metal is deposited on the gold foil using physical vapor deposition to obtain a gold-Group VIII transition metal alloy foil. Then, a thin film containing transition metal M is deposited to obtain an alloy metal growth substrate of transition metal / Group VIII transition metal / gold. The physical vapor deposition method includes magnetron sputtering, electron beam evaporation, or ion beam sputtering. The deposition conditions are as follows: the deposition rate of Group VIII transition metal is 0.01 to 1 nm / s, and the thickness of the Group VIII transition metal layer on the gold foil surface is 0 nm to 500 nm; the deposition rate of transition metal M is 0.01 to 1 nm / s, and the thickness of the transition metal M layer on the gold foil surface is 0.2 to 1000 nm. The target material used includes, but is not limited to, a pure transition metal target, an alloy target of transition metal and gold, or an alloy target of transition metal and a Group IV or Group V element.

4. The method for preparing large-size ternary compound MA2Z4 thin films with controllable layer number according to claim 1, characterized in that, 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.

5. The method for preparing large-size ternary compound MA2Z4 thin films with controllable layer number according to claim 4, characterized in that, 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.

6. The method for preparing large-size ternary compound MA2Z4 thin films with controllable layer number according to claim 1, characterized in that, 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 MA2Z4 thin films with controllable number of layers is 800℃~1063℃, and the growth time is 1 minute~360 minutes.

7. The method for preparing large-size ternary compound MA2Z4 thin films with controllable layer number according to claim 1, characterized in that, Before transfer, a layer of polymer is uniformly coated on the surface of the MA2Z4 film for protection. Then, the protective layer / two-dimensional layered MA2Z4 film is separated from the alloy substrate by electrochemical bubbling method. The resulting protective layer / MA2Z4 film is transferred to other substrates and the protective layer is dissolved and removed.

8. The method for preparing large-size ternary compound MA2Z4 thin films with controllable layer number according to claim 7, characterized in that, The polymer used is one or more of polymethyl methacrylate, polyethylene, polystyrene, and polypropylene, and the organic solvent used to remove the protective layer of the polymer is one or more of ketones, chlorinated hydrocarbons, halogenated hydrocarbons, and aromatic hydrocarbons.

Images