A method for growing a multilayer two-dimensional material van der waals heterojunction by layer-by-layer

Abstract

The application discloses a method for growing a multilayer two-dimensional material van der Waals heterojunction by layering, which realizes layer-by-layer growth by precisely controlling reaction temperature and reaction products of each step, and prepares a wafer-level, multilayer, multi-type high-quality van der Waals heterojunction film.In addition, the application prepares a metal film by physical vapor deposition, and obtains a target product by chemical vapor deposition, which not only controls the amount of raw materials involved in the reaction, but also almost has no waste of raw materials.Compared with the traditional method, the raw material utilization rate is greatly improved, the crystal quality of the product is greatly improved, and the product has strong atmospheric environmental stability.The size of the van der Waals heterojunction film prepared by the application can reach wafer level, and the patterned growth can be realized, which has important significance for large-scale production and application.The successful preparation of the multi-type van der Waals heterojunction film material provides technical support for the development of the fields of optoelectronic devices, spin quantum devices and the like.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional material preparation technology and relates to a method for growing multilayer two-dimensional van der Waals heterostructures. Specifically, it is a method that combines physical vapor deposition and chemical vapor deposition, and achieves layer-by-layer growth by precisely controlling the reaction temperature and the reaction products at each step. Finally, it prepares high-quality van der Waals heterostructure films with wafer-level, controllable number of layers and various types, which are suitable for large-size preparation and property research of van der Waals heterostructures. Background Technology

[0002] In recent years, two-dimensional materials have exhibited a wealth of physical and chemical properties, including semiconductor, metallic, magnetic, and superconducting properties. Therefore, combining two-dimensional materials into van der Waals heterostructures has become a promising research hotspot in recent years, aiming to explore novel materials and improve the performance of functional devices. Although this direction has received widespread attention, most van der Waals heterostructure materials are still obtained by vertically stacking exfoliated two-dimensional materials using a multiple-transfer method. However, this method, based on mechanical exfoliation and manual re-stacking, is difficult to apply to large-scale device production, and may even introduce interface impurities during the transfer process. Therefore, exploring a method to prepare clean van der Waals heterostructure interfaces by directly epitaxially growing and stacking different layered materials is crucial.

[0003] Currently, almost all research focuses on semiconductor van der Waals heterostructures, and is limited to the simplest bilayer heterostructures achieved by selecting specific material combinations. This is mainly because previous van der Waals heterostructure fabrication methods could not obtain two-dimensional superconducting materials with good stability, and growing complex heterostructures with three or more different materials also requires that each layer be sufficiently stable and intact to be preserved intact during subsequent growth. Such multifunctional multilayer van der Waals heterostructures, which combine semiconductor and superconducting materials with different properties, can achieve functions that other currently fabricated semiconductor heterostructures cannot. However, to date, such multifunctional multilayer heterostructures have not been realized, and current technologies are even less capable of achieving the free growth of van der Waals heterostructures. Summary of the Invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for growing multilayer two-dimensional van der Waals heterojunctions. This method combines physical vapor deposition and chemical vapor deposition, and achieves layer-by-layer growth by precisely controlling the growth temperature, so as to prepare high-quality van der Waals heterojunction films at the wafer level. It can be used as an ideal method for nanodevice assembly and basic research.

[0005] Technical Solution: To solve the above-mentioned technical problems, the present invention provides a method for growing multilayer two-dimensional van der Waals heterostructures, the method comprising the following steps:

[0006] (1) Deposition and preparation of metal precursor thin film: A metal thin film with high flatness and high crystallinity is deposited on a flat substrate (the flat substrate includes C-side sapphire or SiO2 / Si substrate) as a precursor using physical vapor deposition.

[0007] (2) Preparation of the first layer of transition metal compound film: The precursor obtained in step (1) is placed in a heating furnace, the carrier gas flow, temperature and pressure are adjusted, and the non-metallic precursor is heated to sublimate into gaseous state. The constant temperature heating position is moved to the location of the metal precursor to promote the gas phase deposition reaction. After the reaction is completed, the heating of the non-metallic precursor is turned off, and the reactants are cooled naturally. When the temperature drops to room temperature, the preparation of the first layer of transition metal compound is completed.

[0008] (3) Secondary deposition preparation of metal precursor thin film: A second metal precursor layer is deposited on the first compound thin film that has been grown using physical vapor deposition.

[0009] (4) Preparation of the second layer of transition metal compound film: The second layer of metal precursor in step (3) is placed in a chemical vapor deposition apparatus. The temperature, carrier gas flow and pressure are adjusted. The growth temperature is set not higher than the growth temperature of the first layer of transition metal compound film. At the same time, the non-metallic precursor is heated to sublimate into a gaseous state. The isothermal heating position is moved to the location of the metal precursor to promote the vapor deposition reaction. The reaction time is set. After the reaction is completed, the heating of the non-metallic precursor is turned off. At the same time, the reactants are allowed to cool naturally. When the temperature drops to room temperature, the preparation of the second layer of transition metal compound is completed.

[0010] (5) Stacked growth of multilayer two-dimensional van der Waals heterostructures: By changing the type of deposited metal film and the precursor, the preparation process of steps (1) to (2) is repeated.

[0011] In step (1), the physical vapor deposition method includes one or more of the following: magnetron sputtering, thermal evaporation, electron beam evaporation, or pulsed laser deposition.

[0012] In step (1), the substrate includes, but is not limited to, silicon wafers or sapphire.

[0013] In step (1), high flatness and high crystallinity refer to the average flatness per 100 μm. 2 Metal thin films with undulations within ±0.5 nm and grain sizes between 10 and 50 μm, including one or more of Mo, W, Nb, Ti, V, Ta, and Pt.

[0014] In step (1), when the physical vapor deposition method is magnetron sputtering, the parameters are: pressure of 0.1 to 500 Pa, carrier gas of one or more of nitrogen, argon, oxygen or hydrogen, thin film deposition rate of 0.01 to 10 nm / s, substrate temperature of 20 to 800 °C, and metal thin film thickness of 0.5 to 100 nm.

[0015] In step (1), when the physical vapor deposition method is thermal evaporation, electron beam evaporation, or pulsed laser deposition, the parameter is a pressure of <10. -4 Pa, thin film deposition rate of 0.01–10 nm / s, substrate heating of 20–800 °C, and metal thin film thickness of 0.5–100 nm.

[0016] In step (2), the non-metallic precursor is one of S, Se, Te, I2 or Br2.

[0017] In step (2), the vapor deposition reaction includes one or more of the following reactions: sulfidation, selenization, tellurization, iodization, or bromination.

[0018] In step (2) or (4), the vapor deposition reaction temperature is 50–800°C, preferably 400–800°C; the pressure is 10... -5 ~10 5 Pa, preferably in the range of 10 -2 ~10 5 Pa; the carrier gas is nitrogen, argon, hydrogen or an inert gas; the gas flow rate is 5 to 200 sccm, preferably 20 to 100 sccm; the thickness of the product film is 0.5 to 100 nm.

[0019] The annealing treatment of the sample after reaction in this invention specifically involves: a temperature of 50–800°C, preferably 200–700°C; and a pressure of 10... -5 ~10 5 Pa, preferably in the range of 10 -5 ~0.1 Pa; the carrier gas can be a reducing or inert gas such as nitrogen, argon, or hydrogen; the gas flow rate is 5 to 200 sccm, preferably 20 to 200 sccm.

[0020] The metal films include one or more of the following: Mo, W, Nb, Ti, V, Ta, and Pt.

[0021] The size of the sample in this invention ranges from 1 μm to 1000 cm, and preferably from -1 to 20 cm.

[0022] In this invention, the sample shape can be customized and complexly patterned. When the steps involve physical vapor deposition, it is necessary to pattern the deposited metal thin film.

[0023] In this invention, the ambient temperature is between 20 and 50°C, preferably between 20 and 30°C.

[0024] The van der Waals heterojunction thin films prepared by this invention can reach wafer-level size and can achieve patterned growth, which is of great significance for large-scale production and application. The successful preparation of various types of van der Waals heterojunction thin film materials provides material preparation technology support for the development of optoelectronic devices, spin quantum devices and other fields.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0026] 1. This invention employs physical vapor deposition to deposit metal thin films, followed by chemical vapor deposition to obtain the target product. This method not only controls the amount of raw materials involved in the reaction and minimizes material waste, but also allows for the stacking and preparation of van der Waals heterostructures with different configurations according to application research needs by changing different metal deposited films and growth precursors. This provides high designability and flexibility. The final deposited film is flat, ensuring sample quality. Compared with traditional methods, the raw material utilization rate is greatly improved, the crystal quality of the product is greatly improved, and the product exhibits extremely strong atmospheric environmental stability.

[0027] 2. This invention effectively controls the thickness and crystallinity of the metal thin film by adjusting the rate of physical vapor deposition and the temperature of the substrate.

[0028] 3. This invention uses chemical vapor deposition to combine metal films with other non-metallic elements, ensuring the cleanliness and quality of the samples.

[0029] 4. The present invention includes a post-processing step to effectively remove excess material from the sample surface.

[0030] 5. This invention is a universal method that can overcome existing technical difficulties and achieve free stacking growth of various types of van der Waals heterojunction thin films. It can prepare high-quality two-dimensional van der Waals heterojunction materials at the wafer level, with multiple layers and various types, and can achieve patterned growth. It is not limited to materials with specific properties or lattice structures, which is of great significance for large-scale production applications. The successful preparation of various types of functional van der Waals heterojunction thin film materials provides material preparation technology support for the development of optoelectronic devices, spin quantum devices and other fields. Attached Figure Description

[0031] Figure 1The two-layer WS2 / MoS2 van der Waals heterojunction films prepared: a) Optical microscope image of the two-layer WS2 / MoS2 van der Waals heterojunction films on a sapphire substrate; b) Atomic force microscope image of the two-layer WS2 / MoS2 van der Waals heterojunction films on a silicon wafer substrate; c) Atomic force microscope corresponding height cross-sectional view.

[0032] Figure 2 The prepared three-layer WS2 / MoS2 / MoSe2 van der Waals heterojunction thin film: a, a four-inch photograph of the film grown on a sapphire substrate; b, an atomic force microscope photograph; c, a height cross-sectional view corresponding to the atomic force microscope.

[0033] Figure 3 The prepared four-layer WS2 / MoS2 / MoSe2 / NbSe2 and five-layer WS2 / MoS2 / MoSe2 / NbSe2 / PtTe2 van der Waals heterojunction films are shown in the following images: a) Photograph of the four-layer film grown on a four-inch sapphire substrate; b) Photograph of the four-layer film grown on a four-inch silicon wafer substrate; c) Photograph of the five-layer film grown on a four-inch sapphire substrate; d) Photograph of the five-layer film grown on a four-inch sapphire substrate.

[0034] Figure 4 The general process of growing two-dimensional van der Waals heterostructures by stacking layers. Detailed Implementation

[0035] Example 1: Preparation of WS2 / MoS2 bilayer van der Waals heterojunction film on sapphire substrate

[0036] The method of growing a double-layer two-dimensional van der Waals heterostructure on a sapphire substrate involves, specifically: placing the sapphire substrate on a tray in a magnetron sputtering reaction chamber using high-purity tungsten metal as the target material, and waiting until the pressure in the reaction chamber is <10. - 4 The tungsten metal film was heated to 200℃, with a coating pressure of 5 Pa, a coating rate of 0.05 nm / s, and a deposition time of 20 s. The film was placed in the quartz tube of a tube furnace, and the sulfur source was placed upstream of the metal film. During the chemical reaction, the sulfur source was heated to 160℃, the metal film temperature was 800℃, and the carrier gases were argon (100 sccm) and hydrogen (100 sccm). The reaction ended after 30 minutes. The sulfur source temperature was rapidly reduced, and the sample was annealed in situ at 350℃. After 60 minutes, the quartz tube was rapidly cooled to obtain the first thin film of tungsten sulfide. The first thin film product was placed on a tray in the magnetron sputtering reaction chamber, and the reaction chamber pressure was lowered to <10 Pa. - 4The temperature was set at 200℃, the coating pressure at 5 Pa, the coating rate at 0.05 nm / s, and the evaporation time at 20 s. The molybdenum metal film was placed in the quartz tube of a tube furnace, and the sulfur source was placed upstream of the metal film. During the combination reaction, the sulfur source was heated to 160℃, the metal film temperature was 700℃, and the carrier gas was argon at 100 sccm and hydrogen at 150 sccm. The reaction ended after 30 minutes. The temperature of the sulfur source was rapidly reduced, and the sample was annealed in situ at 350℃. After 60 minutes, the quartz tube was rapidly cooled to obtain the product, a tungsten sulfide / molybdenum sulfide bilayer van der Waals heterojunction film. Figure 1 a.

[0037] Example 2: Preparation of tungsten sulfide / molybdenum sulfide bilayer van der Waals heterojunction thin films on SiO2 / Si substrates

[0038] A method for growing a bilayer two-dimensional van der Waals heterostructure on a SiO2 / Si substrate. Specifically, a SiO2 / Si substrate is placed on a tray in a magnetron sputtering reaction chamber using high-purity tungsten metal as the target material, and the reaction chamber pressure is kept below 10... - 4 The tungsten metal film was heated to 200℃, with a coating pressure of 5 Pa, a coating rate of 0.05 nm / s, and a deposition time of 20 s. The film was placed in the quartz tube of a tube furnace, and the sulfur source was placed upstream of the metal film. During the chemical reaction, the sulfur source was heated to 160℃, the metal film temperature was 800℃, and the carrier gases were argon (100 sccm) and hydrogen (100 sccm). The reaction ended after 30 minutes. The sulfur source temperature was rapidly reduced, and the sample was annealed in situ at 350℃. After 60 minutes, the quartz tube was rapidly cooled to obtain the first thin film of tungsten sulfide. The first thin film product was placed on a tray in the magnetron sputtering reaction chamber, and the reaction chamber pressure was lowered to <10 Pa. - 4 The temperature was set at 200℃, the coating pressure at 5 Pa, the coating rate at 0.05 nm / s, and the evaporation time at 20 s. The molybdenum metal film was placed in the quartz tube of a tube furnace, and the sulfur source was placed upstream of the metal film. During the combination reaction, the sulfur source was heated to 160℃, the metal film temperature was 700℃, and the carrier gas was argon at 100 sccm and hydrogen at 150 sccm. The reaction ended after 30 minutes. The temperature of the sulfur source was rapidly reduced, and the sample was annealed in situ at 350℃. After 60 minutes, the quartz tube was rapidly cooled to obtain the product, a tungsten sulfide / molybdenum sulfide bilayer van der Waals heterojunction film. Figure 1 b and 1c.

[0039] Example 3

[0040] A double-layer van der Waals heterostructure with controllable thickness was prepared by a layer-by-layer growth method (in this embodiment, the thickness of each sample layer can be 1nm to 10nm). Specifically, a high-purity metal, such as titanium, molybdenum, niobium, or tantalum, was used as the target material. The SiO2 / Si substrate was placed on a tray in the magnetron sputtering reaction chamber, and the reaction chamber pressure was lowered to <10 nm. -4 The film was heated to 200℃, with a deposition pressure of 5 Pa and a deposition rate of 0.05 nm / s. The film thickness was controlled by changing the deposition time, which was adjusted between 20 s and 200 s. The metal film was placed in the quartz tube of a tube furnace, and the sulfur source was placed upstream of the metal film. During the chemical reaction, the sulfur source was heated to 160℃, the metal film temperature was 800℃, and the carrier gas was argon at 100 sccm and hydrogen at 100 sccm. The reaction ended after 30 minutes. The temperature of the sulfur source was rapidly reduced, and the sample was annealed in situ at 350℃. After 60 minutes, the quartz tube was rapidly cooled to obtain the first thin film. The first thin film product was placed on a tray in the magnetron sputtering reaction chamber, and the reaction chamber pressure was lowered to <10 Pa. -4 The metal film was heated to 200℃, with a deposition pressure of 5 Pa and a deposition rate of 0.05 nm / s. The film thickness was controlled by changing the deposition time, which was adjusted between 20 s and 200 s. The metal film was placed in the quartz tube of a tube furnace, and the selenium source was placed upstream of the metal film. During the chemical reaction, the selenium source was heated to 350℃, the metal film temperature was 700℃, and the carrier gas was argon at 100 sccm and hydrogen at 150 sccm. The reaction ended after 30 minutes. The temperature of the selenium source was rapidly reduced, and the sample was annealed in situ at 350℃. After 60 minutes, the quartz tube was rapidly cooled to obtain the product, a two-layer van der Waals heterojunction film.

[0041] Example 4: Growth of a three-layer van der Waals heterojunction thin film on a sapphire substrate

[0042] A three-layer van der Waals heterostructure was fabricated on a sapphire substrate using a stacked growth method (in this embodiment, the first metal layer is deposited on the sapphire substrate). Specifically, high-purity tungsten metal was used as the target material, and the sapphire substrate was placed on a tray in the magnetron sputtering reaction chamber. The reaction chamber pressure was lower than 10... -4The metal film was heated to 400℃, with a deposition pressure of 10 Pa, a deposition rate of 0.02 nm / s, and a deposition time of 20 s. The metal film was placed in the quartz tube of a tube furnace, and the sulfur source was placed upstream of the metal film. During the chemical reaction, the sulfur source was heated to 160℃, the metal film temperature was 800℃, and the carrier gas consisted of argon at 100 sccm and hydrogen at 100 sccm. The reaction ended after 30 minutes. The temperature of the sulfur source was rapidly reduced, and the sample was annealed in situ at 350℃. After 60 minutes, the quartz tube was rapidly cooled to obtain the first thin film of tungsten sulfide. The first thin film product was placed on a tray in a magnetron sputtering reaction chamber, and molybdenum metal was deposited by vapor deposition. The deposition was carried out when the reaction chamber pressure was <10 Pa. -4 The metal film was heated to 200℃, with a coating pressure of 5 Pa, a coating rate of 0.05 nm / s, and a deposition time of 20 s. The metal film was placed in the quartz tube of a tube furnace, and the sulfur source was placed upstream of the metal film. During the chemical reaction, the sulfur source was heated to 160℃, the metal film temperature was 700℃, and the carrier gas was argon at 100 sccm and hydrogen at 150 sccm. The reaction ended after 30 minutes. The temperature of the sulfur source was rapidly reduced, and the sample was annealed in situ at 350℃. Molybdenum metal was then deposited again until the reaction chamber pressure was <10 Pa. -4 The metal film was heated to 200℃, with a coating pressure of 5 Pa, a coating rate of 0.05 nm / s, and a deposition time of 20 s. The metal film was placed in the quartz tube of a tube furnace, and the selenium source was placed upstream of the metal film. During the chemical reaction, the selenium source was heated to 350℃, the metal film temperature was 700℃, and the carrier gas was argon at 100 sccm and hydrogen at 150 sccm. The reaction ended after 30 minutes. The temperature of the selenium source was rapidly reduced, and the sample was annealed in situ at 350℃. After 60 minutes, the quartz tube was rapidly cooled to obtain the product, a three-layer van der Waals heterojunction film. Figure 2 As shown.

[0043] Example 5

[0044] The method in this embodiment, based on Embodiment 1 or 2, prepares a multilayer van der Waals heterostructure of transition metal chalcogenides using a stacked growth method. Specifically, a high-purity metal is used as the target material. In this embodiment, the high-purity metal includes tungsten, molybdenum, niobium, and platinum. A sapphire or SiO2 / Si substrate with the C-side is placed on a tray in the magnetron sputtering reaction chamber. The reaction chamber pressure is then lowered to <10 ppm. -4The coating process involves heating to 200°C, applying a coating pressure of 5 Pa, a coating rate of 0.05 nm / s, and a coating time of 20 s. Multiple sulfidation, selenization, and tellurization processes are performed (in this embodiment, the precursor used for chemical vapor deposition includes telluride; for "telluride growth and preparation," please refer to the literature: Zhou, Z., Xu, T., Zhang, C. et al. Enhancing stability by tuning element ratio in 2D transition metal chalcogenides. Nano Res. 2021, 14, 1704-1710). In this embodiment, the reaction temperature of the successively grown two-dimensional material is not higher than the reaction temperature of the previous growth product, thus obtaining a multilayer van der Waals heterojunction film. Figure 3 As shown in a-3d, van der Waals four-layer and five-layer films grown on sapphire and silicon substrates are presented.

[0045] Example 6

[0046] The method in this embodiment can refer to Embodiment 1 or 5, which is the general process for preparing multilayer van der Waals heterostructures containing various types of transition metal chalcogenides by a stacked growth method. Specifically, a high-purity metal is used as the target material, including but not limited to titanium, molybdenum, niobium, tantalum, platinum, etc. The substrate (C-side sapphire or SiO2 / Si substrate) is placed on the tray of the magnetron sputtering reaction chamber, and the reaction chamber pressure is lower than 10. -4 The film is heated to 200℃, with a deposition pressure of 5 Pa and a deposition rate of 0.05 nm / s. The film thickness is controlled between 1-10 nm by changing the deposition time. The metal film is placed in the quartz tube of a tube furnace and reacted at a certain temperature. The first layer of film is placed on a tray in a magnetron sputtering reaction chamber, and a second layer of metal is deposited. The thickness of the second layer is also controlled by changing the deposition time. The metal film is then placed in the quartz tube of a tube furnace for another chemical reaction. By repeating the above operations multiple times, the reaction temperature of the successively grown two-dimensional material is not higher than the reaction temperature of the previous growth product, thus obtaining a multilayer van der Waals heterostructure film, such as... Figure 4 As shown.

Claims

1. A method for growing multilayer two-dimensional van der Waals heterostructures in layers, characterized in that, The method includes the following steps: (1) Deposition and preparation of metal precursor thin film: A metal thin film with high flatness and high crystallinity is deposited on a flat substrate using physical vapor deposition as a precursor; (2) Preparation of the first layer of transition metal compound film: The precursor obtained in step (1) is placed in a heating furnace, the carrier gas flow, temperature and pressure are adjusted, and the non-metallic precursor is heated to sublimate into gaseous state. The constant temperature heating position is moved to the location of the metal precursor to promote the gas phase deposition reaction. After the reaction is completed, the heating of the non-metallic precursor is turned off, and the reactants are cooled naturally. When the temperature drops to room temperature, the preparation of the first layer of transition metal compound is completed. (3) Secondary deposition preparation of metal precursor thin film: A second metal precursor layer is deposited on the first compound thin film that has been grown using physical vapor deposition; (4) Preparation of the second layer of transition metal compound film: Place the second layer of metal precursor in step (3) in a chemical vapor deposition apparatus, adjust the temperature, carrier gas flow and pressure, set the growth temperature not higher than the growth temperature of the first layer of transition metal compound film, and heat the non-metallic precursor to sublimate it into a gaseous state. Move the constant temperature heating position to the location of the metal precursor to promote the vapor deposition reaction, and set the reaction time. After the reaction is completed, turn off the heating of the non-metallic precursor, and let the reactants cool naturally. When the temperature drops to room temperature, the preparation of the second layer of transition metal compound is completed. (5) Stacked growth of multilayer two-dimensional van der Waals heterostructures: By changing the type of deposited metal film and the precursor, the preparation process of steps (1) to (2) is repeated; In step (1), the physical vapor deposition method adopts magnetron sputtering process with the following parameters: pressure of 0.1 ~ 500 Pa, carrier gas of one or more of nitrogen, argon, oxygen or hydrogen, thin film deposition rate of 0.01 ~ 10 nm / s, substrate temperature of 20 ~ 800℃, and metal thin film thickness of 0.5 ~ 100 nm. In step (1), the substrate includes a silicon wafer or sapphire; in step (1), the metal thin film with high flatness and high crystallinity includes one or more of Mo, W, Nb, Ti, V, Ta, and Pt. In step (2), the non-metallic precursor is one of S, Se, Te, I2 or Br2; In step (2), the vapor deposition reaction includes one or more of the following: sulfidation, selenization, tellurization, iodization, or bromination. In step (2) or (4), the vapor deposition reaction temperature is 50~800℃; the pressure is 10... -5 ~ 10 5 Pa; the carrier gas is nitrogen, argon, hydrogen or an inert gas; the gas flow rate is 5 ~ 200 sccm; the thickness of the product film is 0.5 ~ 100 nm, and the metal film type includes one or more of Mo, W, Nb, Ti, V, Ta and Pt.

Images