A method for preparing an ultrathin transition metal oxide and a carbide heterostructure thereof

Abstract

The present application relates to the field of two-dimensional materials, in particular to a preparation method of ultrathin transition metal oxide and its heterostructure with carbide. A copper foil is covered on the top of a transition metal foil after ultrasonic cleaning and high-temperature carbonization pretreatment, forming a double-metal growth substrate structure for two-step normal pressure chemical vapor deposition growth. First, the temperature is raised above the melting point of copper, and the liquid copper acts as a channel for the lower transition metal atoms and accelerates their diffusion. Then the temperature is lowered below the melting point of copper for the growth of oxide thin film. Then the transition metal carbide crystal structure with a specific growth orientation is epitaxially grown below the transition metal oxide thin film, thereby preparing an ultrathin two-dimensional transition metal oxide crystal and a two-dimensional transition metal oxide / carbide vertical heterostructure. The preparation process of the present application is simple, and can realize controllable preparation of large-area and high-quality two-dimensional transition metal oxide and its heterostructure with carbide.

Description

Technical fields:

[0001] This invention relates to the field of novel materials of two-dimensional transition metal oxides and two-dimensional transition metal oxide / carbide heterostructures and their preparation by chemical vapor deposition (CVD), specifically a method for preparing high-quality two-dimensional transition metal oxides or two-dimensional transition metal oxide / carbide heterostructures, suitable for the preparation of large-area, high-quality two-dimensional transition metal oxides and their carbide heterostructures. Background technology:

[0002] Transition metal oxides (TMOs) have a longer history than other atomic-layer-thick materials. Two-dimensional (2D) TMOs, in particular, exhibit a large number of stable structures due to the different charge states and configurations of their cations. Furthermore, their cations exhibit numerous novel properties in different oxidation states, leading to their widespread application in optics, electronics, catalysis, energy units, sensors, and biological systems. Currently, the main method for preparing 2D TMOs is the chemical liquid-phase exfoliation method, which introduces intercalating agents to increase the degree of swelling between layers and weaken interlayer interactions, thereby achieving layer exfoliation. However, this method suffers from low preparation efficiency, random sample preparation, and small nanosheet sizes (ranging from hundreds of nanometers to several micrometers), significantly limiting the exploration of the fundamental properties and applications of 2D TMOs.

[0003] Meanwhile, the construction and performance study of vertical heterostructures of two-dimensional materials is also a current hot topic in two-dimensional materials research. Currently, the main method for preparing vertical heterostructures is through mechanical exfoliation of two-dimensional materials, followed by directional transfer and stacking. This method suffers from problems such as interface contamination, material damage, and the inability to precisely control the torsion angle between the two-dimensional materials during the transfer process, significantly reducing the performance of the heterostructure. Alternatively, vertical heterostructures can be prepared using a single-step chemical vapor deposition (CVD) method, but elemental doping easily occurs during this growth process, making it impossible to obtain intrinsic vertical heterostructures. Therefore, developing a simple and feasible two-step CVD method for preparing two-dimensional transition metal vertical heterostructures is of great significance for studying the intrinsic properties of these structures and exploring their applications. Summary of the Invention:

[0004] The purpose of this invention is to provide a method for preparing high-quality ultrathin two-dimensional transition metal oxides or two-dimensional transition metal oxide / carbide heterostructures. The method uses chemical vapor deposition to prepare ultrathin transition metal oxides and their carbide heterostructures, which solves the problems of impurity, poor quality, small size, and inability to achieve the growth of high-quality two-dimensional transition metal heterostructures with clean interfaces obtained in current research. This lays the foundation for studying the intrinsic properties of two-dimensional transition metal oxides and their carbide heterostructures and exploring their applications.

[0005] The technical solution of this invention is:

[0006] A method for preparing an ultrathin transition metal oxide and its carbide heterostructure involves subjecting a transition metal foil to high-temperature carbonization pretreatment to obtain a pre-carbonized transition metal foil. A bimetallic stack consisting of an upper copper foil and a lower pre-carbonized transition metal foil is used as a growth substrate. The temperature is raised above the melting point of copper, and liquid copper serves as a channel for the lower transition metal atoms, accelerating their diffusion. An ultrathin two-dimensional transition metal oxide film is grown using chemical vapor deposition. As needed, this is used as a growth template to epitaxially grow a transition metal carbide crystal structure with a specific growth orientation beneath the two-dimensional transition metal oxide film. Subsequently, the copper foil substrate is etched away, and the ultrathin two-dimensional transition metal oxide film or the ultrathin two-dimensional transition metal oxide film / carbide heterostructure is transferred to any substrate.

[0007] The method for preparing the ultrathin transition metal oxide and its heterostructure with carbides involves an ultrathin two-dimensional transition metal oxide film with a thickness of approximately 1 nm and a single crystal size of 5 μm to 50 μm. By extending the growth time, the crystal domain size is increased, thereby obtaining a complete and continuous film. The film size depends on the substrate size used during the growth process. The transition metal carbide crystal epitaxially grown below the two-dimensional transition metal oxide film has a thickness of 1 to 5 nm, and its bottom edge is always parallel to the edge of the two-dimensional transition metal oxide, exhibiting a specific epitaxial orientation and high crystallinity.

[0008] The method for preparing the ultrathin transition metal oxide and its heterostructure with carbides uses niobium, tantalum, tungsten, titanium, chromium or vanadium foil as the bottom layer, and copper foil with a thickness of 100 nm to 100 μm and a purity of 98 wt% to 99.9999 wt% as the top layer.

[0009] In the preparation method of the ultrathin transition metal oxide and its heterostructure with carbides, during the chemical vapor deposition reaction, the carbon source is a hydrocarbon: one or more of methane, ethane, ethylene, acetylene, benzene, toluene, cyclohexane, ethanol, methanol, acetone, or carbon monoxide; or, the carbon source is a solid carbon source: amorphous carbon, paraffin, or one or more of the polymer high molecular weight polymethyl methacrylate, polycarbonate, polystyrene, polyethylene, or polypropylene.

[0010] In the preparation method of the ultrathin transition metal oxide and its heterostructure with carbides, the carrier gas in the chemical vapor deposition reaction is hydrogen or a mixture of hydrogen and an inert gas.

[0011] The method for preparing ultrathin transition metal oxides and their heterostructures with carbides involves chemical vapor deposition at a temperature of 1085℃ to 1300℃ and a growth time of 1 minute to 480 minutes.

[0012] The method for preparing ultrathin transition metal oxides and their heterostructures with carbides involves controlling the size of the ultrathin two-dimensional transition metal oxide thin film crystals by extending the growth time, thereby obtaining a complete continuous film; the thickness of the transition metal carbide crystals epitaxially grown beneath the transition metal oxide thin film is controlled by changing the degree of substrate carbonization pretreatment and the growth time.

[0013] The method for preparing the ultrathin transition metal oxide and its heterostructure with carbides involves uniformly coating a layer of polymer as a protective layer on the surface of the ultrathin two-dimensional transition metal carbide or transition metal oxide / carbide heterostructure before the transfer process. The polymer is one or a mixture of two or more of polymethyl methacrylate, polyethylene, polystyrene, and polypropylene. The copper foil substrate is etched away, the resulting composite film is transferred to another substrate, and the polymer protective layer is dissolved and removed.

[0014] The method for preparing the ultrathin transition metal oxide and its heterostructure with carbides uses copper etching solutions such as ammonium persulfate aqueous solution, tin tetrachloride aqueous solution, ferric chloride aqueous solution, concentrated ammonia or dilute hydrochloric acid.

[0015] The method for preparing the ultrathin transition metal oxide and its heterostructure with carbides uses an organic solvent, one or a mixture of two or more of ketones, chlorinated hydrocarbons, halogenated hydrocarbons, and aromatic hydrocarbons, to remove the polymer protective layer.

[0016] The design concept of this invention is:

[0017] This invention employs chemical vapor deposition (CVD) to prepare ultrathin transition metal oxides and their carbide heterostructures. A copper foil is deposited on top of a cleaned and carbonized transition metal foil to form a bimetallic growth substrate. A two-step atmospheric pressure CVD growth process is then performed. First, the temperature is raised above the melting point of copper, with liquid copper acting as a channel for the lower transition metal atoms and accelerating their diffusion. Then, the temperature is lowered below the melting point of copper to grow the oxide film. This substrate is then used as a growth template to epitaxially grow transition metal carbide crystal structures with specific growth orientations beneath the transition metal oxide film, thereby preparing ultrathin two-dimensional transition metal oxide crystals and two-dimensional transition metal oxide / carbide vertical heterostructures. This method of confined growth using an epitaxial template can reduce the thickness of non-layered carbide materials to the thickness of a single cell, which is beneficial for subsequent exploration of the intrinsic properties and applications of ultrathin two-dimensional carbide materials.

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

[0019] 1. This invention proposes a carbonization pretreatment method to prepare high-quality ultrathin transition metal oxides and their heterostructure materials with carbides on a bimetallic growth substrate using chemical vapor deposition.

[0020] 2. The CVD method proposed in this invention can be carried out under normal pressure, and has the characteristics of convenient operation, easy control, and easy large-area preparation.

[0021] 3. The thickness of the transition metal oxide thin film and the transition metal carbide crystal epitaxially grown below it obtained by the present invention is about 1 to 5 nm. The size of the grown oxide thin film depends on the size of the growth substrate, and the orientation and thickness of the lower transition metal carbide depends on the confinement effect of the upper transition metal oxide film.

[0022] 4. The preparation process of this invention is simple and can achieve the controllable preparation of large-area, high-quality niobium oxide samples. Furthermore, by utilizing the confinement effect of the upper transition metal oxide film, the crystal orientation and thickness of the lower carbide can be effectively controlled, thereby enabling the exploration of the intrinsic properties and related applications of ultrathin two-dimensional transition metal oxides and their heterostructures with carbides. Attached image description:

[0023] Figure 1 This is a schematic diagram of an experimental setup for growing high-quality ultrathin transition metal carbides using the CVD method. In the diagram, 1 is the gas inlet; 2 is the bimetallic growth substrate; 21 is the copper foil; 22 is the transition metal foil after carbonization pretreatment; 3 is the gas outlet; and 4 is the heating furnace.

[0024] Figure 2 The figures show the XRD characterization results of niobium foil before and after carbonization pretreatment. The appearance of characteristic peaks in niobium carbide indicates that some transition metal niobium has been successfully converted into niobium carbide. In the figure, the horizontal axis 2θ represents the diffraction angle (degrees), and the vertical axis Intensity represents the intensity (au).

[0025] Figure 3 The figure shows the XPS characterization results of niobium foil after carbonization pretreatment, with the fine C element spectrum shown. The presence of Nb-C bonds further confirms the successful conversion of some transition metal niobium into niobium carbide. In the figure, the horizontal axis represents binding energy (eV), the vertical axis represents intensity (au), experimental data represents experimental data, fitting represents the fitted curve, background represents the baseline, CC represents CC bond, and Nb-C represents Nb-C bond.

[0026] Figure 4Optical photographs of niobium oxide, a transition metal, with different grain sizes. Image a has an average grain size of approximately 10 μm, and image b has an average grain size of approximately 50 μm.

[0027] Figure 5 Figure a shows an optical photograph of the niobium oxide crystal transferred onto the SiO2 / Si substrate, and Figure b shows the thickness characterization of the corresponding sample. The results indicate that the ultrathin transition metal niobium oxide obtained by this CVD method is approximately 1.44 nm thick and has uniform thickness.

[0028] Figure 6 The images show the secondary ion mass spectrometry characterization results of ultrathin transition metal niobium oxide obtained by CVD. Figure a shows the O element image, and figure b shows the Nb element image. These results indicate that the sample is rich in oxygen and niobium, further confirming that the prepared crystal is a niobium oxide material.

[0029] Figure 7 These are optical photographs of the ultrathin transition metal niobium oxide thin film obtained by the CVD method. In Figure a, the optical photograph is of the nearly formed niobium oxide crystal, and in Figure b, the optical photograph is of the formed niobium oxide thin film, indicating that the material is a continuous thin film with a uniform and complete surface.

[0030] Figure 8 Optical photographs of the ultrathin transition metal niobium oxide and niobium carbide heterojunction obtained by this CVD method are shown. Image a shows an optical photograph of the transition metal niobium oxide single crystal and the niobium carbide heterojunction, while image b shows an optical photograph of the transition metal niobium oxide thin film and the niobium carbide heterojunction. This indicates that the underlying niobium carbide crystal has a specific orientation and consistent optical contrast.

[0031] Figure 9 The transmission electron microscopy (TEM) characterization results of the ultrathin transition metal niobium oxide-niobium carbide heterostructure obtained by this CVD method are shown in Figure a. Figure a is the STEM image of the niobium carbide crystal, Figure b is the diffraction pattern of the niobium carbide crystal, and Figure c is a high-resolution TEM image of the niobium carbide crystal. These results indicate that the niobium carbide crystal beneath the ultrathin transition metal niobium oxide obtained by this CVD method possesses a perfect crystal structure and high crystallinity.

[0032] Figure 10 Optical photographs of the ultrathin transition metal tantalum oxide film obtained by this CVD method and its heterojunction with tantalum carbide are shown. Figure a shows an optical photograph of a single tantalum oxide crystal, and Figure b shows an optical photograph of the tantalum oxide-tantalum carbide heterojunction. Detailed implementation method:

[0033] In its specific implementation, the method for preparing ultrathin transition metal oxides and their carbide heterostructures of this invention involves coating a copper foil over a pre-treated carbonized transition metal foil as a bimetallic growth substrate to prepare an ultrathin transition metal oxide film. This copper foil is then used as a growth template to epitaxially grow a transition metal carbide crystal structure with a specific growth orientation beneath the transition metal oxide film. Subsequently, the copper foil substrate is etched and transferred to obtain a two-dimensional transition metal oxide or a two-dimensional transition metal oxide / carbide heterostructure material. The specific steps are as follows:

[0034] (1) CVD growth of two-dimensional transition metal oxides and their heterostructures with carbides: A copper foil is wrapped on top of the pre-treated transition metal foil as a bimetallic growth substrate. The temperature is raised to above the melting point of copper. A liquid alloy is formed at the interface of the bimetallic growth substrate as a diffusion channel for transition metal atoms. First, a thin film of transition metal oxide is grown on the surface of the copper foil substrate. If necessary, it is used as a growth template. A transition metal carbide crystal structure with a specific growth orientation is epitaxially grown under the thin film of transition metal oxide.

[0035] The growth substrate used is copper foil and carbonized pretreated transition metal foil (including molybdenum, tungsten, tantalum, titanium, niobium, chromium, or vanadium foil, etc.), wherein: the copper foil thickness is 100nm to 100μm, preferably 1μm to 25μm; the purity is 98wt% to 99.9999wt%, preferably 99.5wt% to 99.9999wt%. The CVD pyrolysis carbon source used is a hydrocarbon, such as one or more of methane, ethane, acetylene, benzene, toluene, cyclohexane, ethanol, methanol, acetone, and carbon monoxide; or, the CVD pyrolysis carbon source is a solid carbon source, such as one or more of amorphous carbon, paraffin, and polymers (polymethyl methacrylate, polycarbonate, polystyrene, polyethylene, and polypropylene). The carrier gas used for CVD growth is hydrogen, or a mixture of hydrogen and an inert gas, with a flow rate of 10 mL / min to 2000 mL / min, preferably 500 mL / min to 1000 mL / min. The carbonization pretreatment temperature is 950℃ to 1080℃, preferably 1000℃ to 1060℃, and the treatment time is 30 min to 360 min, preferably 60 min to 240 min. The CVD growth temperature is 1085℃ to 1300℃, preferably 1085℃ to 1100℃, and the growth time is 3 min to 480 min, preferably 10 min to 240 min. After the reaction, the cooling rate is 10℃ / min to 600℃ / min, preferably 200℃ / min to 600℃ / min.

[0036] (2) Coating of a polymer protective layer: A polymer is uniformly coated on the surface of a high-quality ultrathin transition metal oxide or transition metal oxide / carbide heterostructure as a protective layer to prevent the film from being damaged during subsequent processing. These polymers are one or more of polymethyl methacrylate, polyethylene, polystyrene, and polypropylene.

[0037] (3) Dissolution of copper foil substrate: The copper foil substrate is removed by dissolving it with copper etching solution to obtain a polymer / two-dimensional transition metal oxide (or polymer / transition metal oxide and carbide heterostructure) composite film; the dissolving solution for removing the copper foil substrate is tin tetrachloride aqueous solution, ammonium persulfate aqueous solution or ferric chloride aqueous solution, etc., and the molar concentration of the dissolving solution is 0.05mol / L to 2mol / L.

[0038] (4) Removal of the polymer protective layer: The obtained polymer / two-dimensional transition metal oxide (or polymer / transition metal oxide and carbide heterostructure) is placed on the target matrix, and the polymer protective layer covering the sample surface is dissolved and removed using an organic solvent. The organic solvent used is one or more of the following: acetone, ethyl lactate, dichloroethane, trichloroethylene, chloroform, ketones, chlorinated hydrocarbons, halogenated hydrocarbons, aromatic hydrocarbons, etc.

[0039] The transition metal oxide crystal obtained by this invention has a thickness of about 1 nm and a single crystal size of 5 μm to 50 μm. By extending the growth time and increasing the crystal domain size, a complete continuous film can be obtained. The film size depends on the substrate size used in the growth process. The transition metal carbide crystal epitaxially grown under the two-dimensional transition metal oxide film has a thickness of 1 to 5 nm. Its bottom edge is always parallel to the edge of the two-dimensional transition metal oxide, and it has a specific epitaxial orientation and high crystal quality.

[0040] The present invention will now be described in further detail with reference to embodiments and accompanying drawings.

[0041] Example 1

[0042] First, such as Figure 1As shown, this invention uses a horizontal reactor to grow ultrathin transition metal oxide single crystals. The horizontal reactor has a gas inlet 1 and a gas outlet 3 at both ends. Niobium foil is cut into strips of 100 mm × 5 mm and placed in the high-temperature zone of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm) for carbonization pretreatment. It is heated to 1050°C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30°C / min). After the furnace temperature reaches 1050°C, a mixture of methane and hydrogen is introduced (gas flow rates of 3 mL / min for methane and 200 mL / min for hydrogen). The carbonization pretreatment time is 1 hour. After the carbonization pretreatment, it is rapidly cooled at a rate of 500°C / min, and the niobium foil is removed and coated with a layer of copper foil. The copper foil / niobium foil pretreated with carbonization was placed in the central high-temperature zone of a horizontal reactor (copper foil 5 mm × 5 mm × 5 μm, purity 99.5 wt%, niobium foil 5 mm × 5 mm × 100 μm, purity 99.95 wt%), and heated to 1085 °C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30 °C / min). After the furnace temperature reached 1085 °C, hydrogen was introduced (gas flow rate 200 mL / min), and the growth time was 30 minutes. After the growth was completed, it was rapidly cooled at a rate of 500 °C / min to obtain an ultrathin niobium oxide single crystal with a thickness of approximately 1 nm on the surface of the copper foil.

[0043] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the surface of a copper foil on which niobium oxide single crystals were grown. A PMMA film with a thickness of 200 nm was formed by spin coating at 5000 rpm. After baking at 150 °C for 30 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70 °C for 10 minutes to dissolve the copper foil substrate. The PMMA / niobium oxide film was then transferred to a SiO2 / Si substrate (a uniform silicon dioxide SiO2 film was formed on the surface of the silicon wafer Si). The PMMA was then dissolved with acetone at 55 °C, thus achieving the successful transfer of the niobium oxide single crystal.

[0044] The composition, crystal structure, morphology, and thickness of niobium oxide were characterized using optical microscopy, transmission electron microscopy, and atomic force microscopy. The prepared niobium oxide single crystals had an average size of 20 μm, were hexagonal in shape, and had a thickness of approximately 1 nm, exhibiting high crystallinity.

[0045] Example 2

[0046] First, such as Figure 1As shown, this invention uses a horizontal reactor to grow ultrathin transition metal oxide single crystals. The horizontal reactor has a gas inlet 1 and a gas outlet 3 at both ends. Niobium foil is cut into strips of 100 mm × 5 mm and placed in the high-temperature zone of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm) for carbonization pretreatment. It is heated to 1050°C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30°C / min). After the furnace temperature reaches 1050°C, a mixture of methane and hydrogen is introduced (gas flow rates of 3 mL / min for methane and 200 mL / min for hydrogen). The carbonization pretreatment time is 1 hour. After the carbonization pretreatment, it is rapidly cooled at a rate of 500°C / min, and the niobium foil is removed and coated with a layer of copper foil. The copper foil / niobium foil pretreated by carbonization was placed in the central high-temperature zone of a horizontal reactor (copper foil 5 mm × 5 mm × 5 μm, purity 99.5 wt%, niobium foil 5 mm × 5 mm × 100 μm, purity 99.95 wt%), and heated to 1085 °C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30 °C / min). After the furnace temperature reached 1085 °C, hydrogen was introduced (gas flow rate 200 mL / min), and the growth time was 1 hour. After the growth was completed, it was rapidly cooled at a rate of 500 °C / min to obtain an ultrathin niobium oxide single crystal with a thickness of approximately 1 nm on the surface of the copper foil.

[0047] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the surface of a copper foil on which niobium oxide single crystals were grown. A PMMA film with a thickness of 200 nm was coated by spin coating at 5000 rpm. After baking at 150 °C for 30 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70 °C for 10 minutes to dissolve the copper foil substrate, transferring the PMMA / niobium oxide film to a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55 °C, finally achieving the successful transfer of the niobium oxide single crystal.

[0048] The composition, crystal structure, morphology, and thickness of niobium oxide were characterized using optical microscopy, transmission electron microscopy, and atomic force microscopy. The prepared niobium oxide single crystals had an average size of 50 μm, were hexagonal in shape, and had a thickness of approximately 1 nm, exhibiting high crystallinity.

[0049] Example 3

[0050] First, such as Figure 1As shown, this invention uses a horizontal reactor to grow ultrathin transition metal oxide films. The horizontal reactor has a gas inlet 1 and a gas outlet 3 at both ends. Niobium foil is cut into strips of 100 mm × 5 mm and placed in the high-temperature zone of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm) for carbonization pretreatment. It is heated to 1050°C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30°C / min). After the furnace temperature reaches 1050°C, a mixture of methane and hydrogen is introduced (gas flow rates of 3 mL / min for methane and 200 mL / min for hydrogen). The carbonization pretreatment time is 1 hour. After the carbonization pretreatment, it is rapidly cooled at a rate of 500°C / min, and the niobium foil is removed and coated with a layer of copper foil. The copper foil / niobium foil pretreated with carbonization was placed in the central high-temperature zone of a horizontal reactor (copper foil 5 mm × 5 mm × 5 μm, purity 99.5 wt%, niobium foil 5 mm × 5 mm × 100 μm, purity 99.95 wt%), and heated to 1085 °C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30 °C / min). After the furnace temperature reached 1085 °C, hydrogen was introduced (gas flow rate 200 mL / min), and the growth time was 3 hours. After the growth was completed, it was rapidly cooled at a rate of 500 °C / min to obtain an ultrathin niobium oxide film with a thickness of approximately 1 nm on the surface of the copper foil.

[0051] 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 niobium oxide film was grown. A PMMA film with a thickness of 200 nm was coated by spin coating at 5000 rpm. After baking at 150 °C for 30 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70 °C for 10 minutes to dissolve the copper foil substrate, thus transferring the PMMA / niobium oxide film onto a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55 °C, finally achieving the successful transfer of the niobium oxide film.

[0052] The composition, crystal structure, morphology, and thickness of niobium oxide were characterized using optical microscopy, transmission electron microscopy, and atomic force microscopy. The prepared niobium oxide film had a thickness of approximately 1 nm and exhibited high crystallinity.

[0053] Example 4

[0054] First, such as Figure 1As shown, this invention uses a horizontal reactor to grow ultrathin transition metal oxide films. The horizontal reactor has a gas inlet 1 and a gas outlet 3 at both ends. Niobium foil is cut into strips of 100 mm × 5 mm and placed in the high-temperature zone of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm) for carbonization pretreatment. It is heated to 1050°C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30°C / min). After the furnace temperature reaches 1050°C, a mixture of methane and hydrogen is introduced (gas flow rates of 3 mL / min for methane and 200 mL / min for hydrogen). The carbonization pretreatment time is 1 hour. After the carbonization pretreatment, it is rapidly cooled at a rate of 500°C / min, and the niobium foil is removed and coated with a layer of copper foil. The copper foil / niobium foil pretreated with carbonization was placed in the central high-temperature zone of a horizontal reactor (copper foil 5 mm × 5 mm × 5 μm, purity 99.5 wt%, niobium foil 5 mm × 5 mm × 100 μm, purity 99.95 wt%), and heated to 1100 °C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30 °C / min). After the furnace temperature reached 1100 °C, hydrogen was introduced (gas flow rate 200 mL / min), and the growth time was 1 hour. After the growth was completed, it was rapidly cooled at a rate of 500 °C / min to obtain an ultrathin niobium oxide film with a thickness of approximately 1 nm on the surface of the copper foil.

[0055] 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 niobium oxide film was grown. A PMMA film with a thickness of 200 nm was coated by spin coating at 5000 rpm. After baking at 150 °C for 30 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70 °C for 10 minutes to dissolve the copper foil substrate, thus transferring the PMMA / niobium oxide film onto a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55 °C, finally achieving the successful transfer of the niobium oxide film.

[0056] The composition, crystal structure, morphology, and thickness of niobium oxide were characterized using optical microscopy, transmission electron microscopy, and atomic force microscopy. The prepared niobium oxide film had a thickness of 1 nm and exhibited high crystallinity.

[0057] Example 5

[0058] First, such as Figure 1As shown, this invention uses a horizontal reactor to grow ultrathin transition metal oxide single crystals. The horizontal reactor has a gas inlet 1 and a gas outlet 3 at both ends. Niobium foil is cut into strips of 100 mm × 5 mm and placed in the high-temperature zone of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm) for carbonization pretreatment. It is heated to 1050°C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30°C / min). After the furnace temperature reaches 1050°C, a mixture of methane and hydrogen is introduced (gas flow rates of 3 mL / min for methane and 200 mL / min for hydrogen). The carbonization pretreatment time is 2 hours. After the carbonization pretreatment, it is rapidly cooled at a rate of 500°C / min, and the niobium foil is removed and coated with a layer of copper foil. The copper foil / niobium foil pretreated with carbonization was placed in the central high-temperature zone of a horizontal reactor (copper foil 5 mm × 5 mm × 5 μm, purity 99.5 wt%, niobium foil 5 mm × 5 mm × 100 μm, purity 99.95 wt%), and heated to 1085 °C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30 °C / min). After the furnace temperature reached 1085 °C, hydrogen was introduced (gas flow rate 200 mL / min), and the growth time was 30 minutes. After the growth was completed, it was rapidly cooled at a rate of 500 °C / min to obtain an ultrathin niobium oxide single crystal with a thickness of approximately 1 nm on the surface of the copper foil.

[0059] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the surface of a copper foil on which niobium oxide single crystals were grown. A PMMA film with a thickness of 200 nm was coated by spin coating at 5000 rpm. After baking at 150 °C for 30 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70 °C for 10 minutes to dissolve the copper foil substrate, transferring the PMMA / niobium oxide film to a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55 °C, finally achieving the successful transfer of the niobium oxide single crystal.

[0060] The composition, crystal structure, morphology, and thickness of niobium oxide were characterized using optical microscopy, transmission electron microscopy, and atomic force microscopy. The prepared niobium oxide single crystals had an average size of approximately 50 μm, were hexagonal in shape, and had a thickness of 1 nm, exhibiting high crystallinity.

[0061] Example 6

[0062] First, such as Figure 1As shown, this invention uses a horizontal reactor to grow ultrathin transition metal oxide films. The horizontal reactor has a gas inlet 1 and a gas outlet 3 at both ends. Niobium foil is cut into strips of 100 mm × 5 mm and placed in the high-temperature zone of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm) for carbonization pretreatment. It is heated to 1050°C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30°C / min). After the furnace temperature reaches 1050°C, a mixture of methane and hydrogen is introduced (gas flow rates of 3 mL / min for methane and 200 mL / min for hydrogen). The carbonization pretreatment time is 2 hours. After the carbonization pretreatment, it is rapidly cooled at a rate of 500°C / min, and the niobium foil is removed and coated with a layer of copper foil. The copper foil / niobium foil pretreated with carbonization was placed in the central high-temperature zone of a horizontal reactor (copper foil 5 mm × 5 mm × 5 μm, purity 99.5 wt%, niobium foil 5 mm × 5 mm × 100 μm, purity 99.95 wt%), and heated to 1085 °C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30 °C / min). After the furnace temperature reached 1085 °C, hydrogen was introduced (gas flow rate 200 mL / min), and the growth time was 1 hour. After the growth was completed, it was rapidly cooled at a rate of 500 °C / min to obtain an ultrathin niobium oxide film with a thickness of approximately 1 nm on the surface of the copper foil.

[0063] 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 niobium oxide film was grown. A PMMA film with a thickness of 200 nm was coated by spin coating at 5000 rpm. After baking at 150 °C for 30 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70 °C for 10 minutes to dissolve the copper foil substrate, thus transferring the PMMA / niobium oxide film onto a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55 °C, finally achieving the successful transfer of the niobium oxide film.

[0064] The composition, crystal structure, morphology, and thickness of niobium oxide were characterized using optical microscopy, transmission electron microscopy, and atomic force microscopy. The prepared niobium oxide film had a thickness of approximately 1 nm and exhibited high crystallinity.

[0065] Example 7

[0066] First, such as Figure 1As shown, this invention employs a horizontal reactor to grow ultrathin transition metal oxide / carbide heterostructures. The horizontal reactor has a gas inlet 1 and a gas outlet 3 at each end. Niobium foil is cut into strips of 100 mm × 5 mm and placed in the high-temperature zone of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm) for carbonization pretreatment. It is heated to 1050°C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30°C / min). After the furnace temperature reaches 1050°C, a mixture of methane and hydrogen is introduced (gas flow rates of 3 mL / min for methane and 200 mL / min for hydrogen). The carbonization pretreatment time is 1 hour. After the carbonization pretreatment, it is rapidly cooled at a rate of 500°C / min, and the niobium foil is removed and coated with a layer of copper foil. The copper foil / niobium foil pretreated with carbide was placed in the central high-temperature zone of a horizontal reactor (copper foil 5 mm × 5 mm × 5 μm, purity 99.5 wt%, niobium foil 5 mm × 5 mm × 100 μm, purity 99.95 wt%), and heated to 1085 °C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30 °C / min). After the furnace temperature reached 1085 °C, hydrogen gas was introduced (gas flow rate 200 mL / min) and held at this temperature for 1 hour. Then, methane was introduced at this temperature (gas flow rate 0.35 mL / min) and growth continued for another hour. After growth, the material was rapidly cooled at a rate of 500 °C / min, resulting in an ultrathin niobium oxide and niobium carbide heterostructure on the copper foil surface, with a thickness of approximately 2–6 nm.

[0067] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the surface of a copper foil with a niobium oxide and niobium carbide heterostructure grown on it. A PMMA film with a thickness of 200 nm was formed by spin coating at 5000 rpm. After baking at 150 °C for 30 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70 °C for 10 minutes to dissolve the copper foil substrate, thus transferring the PMMA / niobium oxide and niobium carbide heterostructure film onto a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55 °C, finally achieving the successful transfer of the ultrathin niobium oxide and niobium carbide heterostructure.

[0068] The composition, crystal structure, morphology, and thickness of the ultrathin niobium oxide and niobium carbide heterostructures were characterized using optical microscopy, transmission electron microscopy, and atomic force microscopy. The prepared ultrathin niobium oxide and niobium carbide heterostructures exhibited an average niobium oxide crystal size of approximately 40 μm and a thickness of approximately 1 nm, while the underlying niobium carbide crystals had an average size of approximately 2 μm and a thickness of approximately 1–5 nm, demonstrating high crystallinity.

[0069] Example 8

[0070] First, such as Figure 1 As shown, this invention employs a horizontal reactor to grow ultrathin transition metal oxide / carbide heterostructures. The horizontal reactor has a gas inlet 1 and a gas outlet 3 at each end. Niobium foil is cut into strips of 100 mm × 5 mm and placed in the high-temperature zone of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm) for carbonization pretreatment. It is heated to 1050°C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30°C / min). After the furnace temperature reaches 1050°C, a mixture of methane and hydrogen is introduced (gas flow rates of 3 mL / min for methane and 200 mL / min for hydrogen). The carbonization pretreatment time is 1 hour. After the carbonization pretreatment, it is rapidly cooled at a rate of 500°C / min, and the niobium foil is removed and coated with a layer of copper foil. The copper foil / niobium foil pretreated with carbide was placed in the central high-temperature zone of a horizontal reactor (copper foil 5 mm × 5 mm × 5 μm, purity 99.5 wt%, niobium foil 5 mm × 5 mm × 100 μm, purity 99.95 wt%), and heated to 1085 °C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30 °C / min). After the furnace temperature reached 1085 °C, hydrogen was introduced (gas flow rate 200 mL / min) and held at this temperature for 1 hour. Then, methane was introduced at this temperature (gas flow rate 0.5 mL / min) and growth continued for 1 hour. After growth, the material was rapidly cooled at a rate of 500 °C / min, resulting in an ultrathin niobium oxide and niobium carbide heterostructure on the copper foil surface, with a thickness of approximately 2–6 nm.

[0071] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the surface of a copper foil with a niobium oxide and niobium carbide heterostructure grown on it. A PMMA film with a thickness of 200 nm was formed by spin coating at 5000 rpm. After baking at 150 °C for 30 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70 °C for 10 minutes to dissolve the copper foil substrate, thus transferring the PMMA / niobium oxide and niobium carbide heterostructure film onto a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55 °C, finally achieving the successful transfer of the ultrathin niobium oxide and niobium carbide heterostructure.

[0072] The composition, crystal structure, morphology, and thickness of the ultrathin niobium oxide and niobium carbide heterostructures were characterized using optical microscopy, transmission electron microscopy, and atomic force microscopy. The prepared ultrathin niobium oxide and niobium carbide heterostructures exhibited an average niobium oxide crystal size of approximately 40 μm and a thickness of approximately 1 nm, while the underlying niobium carbide crystals had an average size of approximately 2 μm and a thickness of approximately 1–5 nm, demonstrating high crystallinity.

[0073] Example 9

[0074] First, such as Figure 1 As shown, this invention employs a horizontal reactor to grow ultrathin transition metal oxide / carbide heterostructures. The horizontal reactor has a gas inlet 1 and a gas outlet 3 at each end. Niobium foil is cut into strips of 100 mm × 5 mm and placed in the high-temperature zone of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm) for carbonization pretreatment. It is heated to 1050°C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30°C / min). After the furnace temperature reaches 1050°C, a mixture of methane and hydrogen is introduced (gas flow rates of 3 mL / min for methane and 200 mL / min for hydrogen). The carbonization pretreatment time is 1 hour. After the carbonization pretreatment, it is rapidly cooled at a rate of 500°C / min, and the niobium foil is removed and coated with a layer of copper foil. The copper foil / niobium foil pretreated with carbide was placed in the central high-temperature zone of a horizontal reactor (copper foil 5 mm × 5 mm × 5 μm, purity 99.5 wt%, niobium foil 5 mm × 5 mm × 100 μm, purity 99.95 wt%), and heated to 1085 °C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30 °C / min). After the furnace temperature reached 1085 °C, hydrogen gas was introduced (gas flow rate 200 mL / min) and held at this temperature for 1 hour. Then, methane was introduced at this temperature (gas flow rate 0.35 mL / min) and growth continued for 2 hours. After growth, the material was rapidly cooled at a rate of 500 °C / min, resulting in an ultrathin niobium oxide and niobium carbide heterostructure on the copper foil surface, with a thickness of approximately 2–6 nm.

[0075] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the surface of a copper foil with a niobium oxide and niobium carbide heterostructure grown on it. A PMMA film with a thickness of 200 nm was formed by spin coating at 5000 rpm. After baking at 150 °C for 30 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70 °C for 10 minutes to dissolve the copper foil substrate, thus transferring the PMMA / niobium oxide and niobium carbide heterostructure film onto a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55 °C, finally achieving the successful transfer of the ultrathin niobium oxide and niobium carbide heterostructure.

[0076] The composition, crystal structure, morphology, and thickness of the ultrathin niobium oxide and niobium carbide heterostructures were characterized using optical microscopy, transmission electron microscopy, and atomic force microscopy. The prepared ultrathin niobium oxide and niobium carbide heterostructures exhibited an average niobium oxide crystal size of approximately 40 μm and a thickness of approximately 1 nm, while the underlying niobium carbide crystals had an average size of approximately 2 μm and a thickness of approximately 1–5 nm, demonstrating high crystallinity.

[0077] Example 10

[0078] First, such as Figure 1 As shown, this invention employs a horizontal reactor to grow ultrathin transition metal oxide / carbide heterostructures. The horizontal reactor has a gas inlet 1 and a gas outlet 3 at each end. Niobium foil is cut into strips of 100 mm × 5 mm and placed in the high-temperature zone of the horizontal reactor (furnace tube diameter 22 mm, reaction zone length 20 mm) for carbonization pretreatment. It is heated to 1050°C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30°C / min). After the furnace temperature reaches 1050°C, a mixture of methane and hydrogen is introduced (gas flow rates of 3 mL / min for methane and 200 mL / min for hydrogen). The carbonization pretreatment time is 1 hour. After the carbonization pretreatment, it is rapidly cooled at a rate of 500°C / min, and the niobium foil is removed and coated with a layer of copper foil. The copper foil / niobium foil pretreated with carbide was placed in the central high-temperature zone of a horizontal reactor (copper foil 5 mm × 5 mm × 5 μm, purity 99.5 wt%, niobium foil 5 mm × 5 mm × 100 μm, purity 99.95 wt%), and heated to 1085 °C in a hydrogen atmosphere (hydrogen flow rate 200 mL / min, heating rate 30 °C / min). After the furnace temperature reached 1085 °C, hydrogen was introduced (gas flow rate 200 mL / min) and held at this temperature for 3 hours. Then, methane was introduced at this temperature (gas flow rate 0.35 mL / min) and growth continued for 1 hour. After growth, the material was rapidly cooled at a rate of 500 °C / min, resulting in an ultrathin niobium oxide and niobium carbide heterostructure on the copper foil surface, with a thickness of approximately 2–6 nm.

[0079] Then, a polymethyl methacrylate (PMMA) ethyl lactate solution (PMMA accounting for 4 wt%) was dropped onto the surface of a copper foil with a niobium oxide and niobium carbide heterostructure grown on it. A PMMA film with a thickness of 200 nm was formed by spin coating at 5000 rpm. After baking at 150 °C for 30 minutes, the film was placed in a 0.2 mol / L ammonium persulfate aqueous solution and reacted at 70 °C for 10 minutes to dissolve the copper foil substrate, thus transferring the PMMA / niobium oxide and niobium carbide heterostructure film onto a SiO2 / Si substrate. The PMMA was then dissolved with acetone at 55 °C, finally achieving the successful transfer of the ultrathin niobium oxide and niobium carbide heterostructure.

[0080] The composition, crystal structure, morphology, and thickness of the ultrathin niobium oxide and niobium carbide heterostructures were characterized using optical microscopy, transmission electron microscopy, and atomic force microscopy. In the prepared ultrathin niobium oxide and niobium carbide heterostructures, niobium oxide had formed a film, and the underlying niobium carbide crystals had an average size of approximately 2 μm and a thickness of approximately 1–5 nm, exhibiting high crystallinity.

[0081] like Figure 1As shown, the experimental apparatus for growing ultrathin transition metal oxides and their heterostructures with carbides by CVD method of the present invention mainly includes: gas inlet 1, bimetallic growth substrate 2, gas outlet 3, and heating furnace 4. Gaseous carbon source and carrier gas enter the furnace tube of heating furnace 4 from gas inlet 1 (solid carbon source can be directly coated or deposited on the upper surface of copper foil 21) and exit from gas outlet 3. Bimetallic growth substrate 2 is composed of copper foil 21 stacked in heating zone and transition metal foil 22 after carbonization pretreatment.

[0082] like Figure 2 As shown, the XRD characterization results of the niobium foil after carbonization pretreatment show the characteristic peak of niobium carbide, indicating that some transition metal niobium has been successfully converted into niobium carbide.

[0083] like Figure 3 As shown, XPS characterization results of the carbonized niobium foil indicate the presence of Nb-C bonds, further confirming that some transition metal niobium was successfully converted into niobium carbide.

[0084] like Figure 4 As shown, the CVD method yields ultrathin transition metal oxide crystals with regular geometric shapes and crystal sizes ranging from 10 to 50 μm.

[0085] like Figure 5 As shown, the ultrathin transition metal oxide crystals obtained by this CVD method were transferred to a SiO2 / Si substrate. Atomic force characterization results showed that the ultrathin transition metal oxides obtained by this CVD method were approximately 1.44 nm thick and had uniform thickness.

[0086] like Figure 6 As shown, the secondary ion mass spectrometry characterization results indicate that the ultrathin transition metal oxide obtained by this CVD method is oxygen-rich and niobium-rich, further confirming that the prepared crystal is a niobium oxide material.

[0087] like Figure 7 As shown, the ultrathin transition metal oxide film obtained by this CVD method is an optical photograph showing that the material is a continuous film with a uniform and complete surface.

[0088] like Figure 8 As shown, the ultrathin transition metal oxide and carbide heterojunction obtained by this CVD method has optical images showing that the bottom edge of the two-dimensional transition metal carbide always remains parallel to the edge of the two-dimensional transition metal oxide, exhibiting a specific epitaxial orientation and consistent optical contrast.

[0089] like Figure 9 As shown, the ultrathin transition metal oxide and carbide heterojunction obtained by this CVD method has a perfect crystal structure and high crystal quality as indicated by transmission electron microscopy.

[0090] like Figure 10 As shown, using Cu / Ta bimetallic sheets as the growth substrate, two-dimensional ultrathin tantalum oxide crystals and their heterostructures with tantalum carbide can be obtained, indicating that this CVD method has good versatility and can be used to prepare other high-quality ultrathin two-dimensional transition metal oxide films and their heterostructures with carbides.

[0091] The above results demonstrate that this invention proposes a method for carbonizing and pretreating transition metal foils, which significantly limits the supply of transition metal sources during subsequent growth by using transition metal carbides. A copper foil layer is coated on top of the pretreated transition metal foil as a bimetallic growth substrate to prepare an ultrathin transition metal oxide film. This film is then used as a growth template to epitaxially grow transition metal carbide crystal structures with specific growth orientations beneath the transition metal oxide film. The two-dimensional transition metal oxides and their carbide heterostructures obtained by this method exhibit high crystallinity, thinness, and excellent chemical and thermal stability. This lays the foundation for the application of ultrathin two-dimensional transition metal oxide / carbide heterostructures in electronic devices, optoelectronic devices, electrochemical energy storage, catalysis, and other fields. Furthermore, it is of great significance for studying their fundamental physical properties, such as mechanics and optics, as well as their superconductivity and topological electronic states in the two-dimensional limit of condensed matter physics.

Claims

1. A method for preparing an ultrathin transition metal oxide and its heterostructure with a carbide, characterized in that, A high-temperature carbonization pretreatment is performed on the transition metal foil to obtain a pre-carbonized transition metal foil. A bimetallic stack consisting of an upper copper foil and a lower carbonized transition metal foil is used as the growth substrate. The lower transition metal foil can be a niobium foil, tantalum foil, tungsten foil, titanium foil, chromium foil, or vanadium foil. The temperature is raised above the melting point of copper, and liquid copper serves as a channel for the lower transition metal atoms and accelerates their diffusion. An ultrathin two-dimensional transition metal oxide film is grown using chemical vapor deposition. This film is then used as a growth template and a carbon source is introduced to epitaxially grow a transition metal carbide crystal structure with a specific growth orientation under the two-dimensional transition metal oxide film. Subsequently, the copper foil substrate is etched away, and the ultrathin two-dimensional transition metal oxide film or ultrathin two-dimensional transition metal oxide film / carbide heterostructure is transferred to any substrate. During the chemical vapor deposition reaction, the carrier gas is hydrogen or a mixture of hydrogen and an inert gas, with a flow rate of 10 mL / min to 2000 mL / min; the temperature for chemical vapor deposition growth of two-dimensional transition metal oxide films is 1085 °C to 1300 °C, and the growth time is 1 min to 480 min; using the obtained two-dimensional transition metal oxide film as a template, the temperature for epitaxial growth of transition metal carbide crystal structures is 1085 °C to 1300 °C, and the growth time is 1 min to 480 min.

2. The method for preparing the ultrathin transition metal oxide and its heterostructure with carbides according to claim 1, characterized in that, The ultrathin two-dimensional transition metal oxide film has a thickness of 1 nm and a single crystal size of 5 μm to 50 μm. By extending the growth time, the crystal domain size is increased, thereby obtaining a complete continuous film. The film size depends on the substrate size used in the growth process. The transition metal carbide crystal grown epitaxially below the two-dimensional transition metal oxide film has a thickness of 1 to 5 nm. Its bottom edge is always parallel to the edge of the two-dimensional transition metal oxide, and it has a specific epitaxial orientation and high crystal quality.

3. The method for preparing the ultrathin transition metal oxide and its heterostructure with carbides according to claim 1, characterized in that, The thickness of the upper copper foil is 100 nm to 100 μm, and the purity is 98 wt% to 99.9999 wt%.

4. The method for preparing the ultrathin transition metal oxide and its heterostructure with carbide according to claim 1, characterized in that, In the chemical vapor deposition process, the carbon source is a hydrocarbon: one or more of methane, ethane, ethylene, acetylene, benzene, toluene, cyclohexane, ethanol, methanol, acetone, or carbon monoxide; or, the carbon source is a solid carbon source: amorphous carbon, paraffin, or one or more of the polymer polymethyl methacrylate, polycarbonate, polystyrene, polyethylene, or polypropylene.

5. The method for preparing the ultrathin transition metal oxide and its heterostructure with carbides according to claim 1, characterized in that, The size of the ultrathin two-dimensional transition metal oxide thin film crystals can be controlled by extending the growth time, thereby obtaining a complete continuous film; the thickness of the transition metal carbide crystals epitaxially grown under the transition metal oxide thin film can be controlled by changing the degree of substrate carbonization pretreatment and the growth time.

6. The method for preparing the ultrathin transition metal oxide and its heterostructure with carbide according to claim 1, characterized in that, Before the transfer process, a layer of polymer is uniformly coated on the surface of the ultrathin two-dimensional transition metal oxide film or the ultrathin two-dimensional transition metal oxide film / carbide heterostructure as a protective layer. The polymer is one or a mixture of two or more of polymethyl methacrylate, polyethylene, polystyrene, and polypropylene. The copper foil substrate is etched away, the resulting composite film is transferred to other substrates, and the polymer protective layer is dissolved and removed.

7. The method for preparing the ultrathin transition metal oxide and its heterostructure with carbide according to claim 6, characterized in that, The copper etching solutions used are ammonium persulfate aqueous solution, tin tetrachloride aqueous solution, ferric chloride aqueous solution, concentrated ammonia or dilute hydrochloric acid.

8. The method for preparing the ultrathin transition metal oxide and its heterostructure with carbide according to claim 6, characterized in that, The organic solvent used to remove the protective layer of polymers is one or a mixture of two or more of the following: ketones, chlorinated hydrocarbons, halogenated hydrocarbons, and aromatic hydrocarbons.

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