Transfer method for two-dimensional material

Abstract

The present invention relates to the technical field of two-dimensional materials, and provided thereby is a transfer method for a two-dimensional material. In the present invention, a metal substrate / two-dimensional material device and a target substrate are stacked, and the two-dimensional material is in contact with the target substrate for bonding to obtain a metal substrate / two-dimensional material / target substrate device. The target substrate is a semiconductor substrate. A cooling treatment and a thermal annealing treatment are sequentially carried out on the metal substrate / two-dimensional material / target substrate device, and the metal substrate in the obtained device is stripped to obtain a target substrate / two-dimensional material device, thereby achieving the transfer of the two-dimensional material. In the present invention, the two-dimensional material is tightly combined with the target substrate by means of a bonding technique, and then, by utilizing the difference between the thermal expansion coefficient of the metal substrate and the thermal expansion coefficient of the two-dimensional material, a temperature difference is achieved on the basis of performing the cooling treatment and the thermal annealing treatment, thereby separating the two-dimensional material from the metal substrate. The entire process does not require the use of an organic thin film as a transfer carrier, and impurities are not introduced into the two-dimensional material.

Description

A method for transferring two-dimensional materials

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on June 30, 2023, with application number CN202310792288X and invention name “A method for transferring two-dimensional materials”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of two-dimensional materials, and in particular to a method for transferring two-dimensional materials. Background Art

[0003] Two-dimensional materials, or 2D atomic crystal materials, refer to materials in which electrons can move freely (in-plane) only in two dimensions, on the nanoscale (1 to 100 nm). Examples include nanofilms, superlattices, and quantum wells. Because carrier migration and heat diffusion are confined within a two-dimensional plane, these materials exhibit many unique properties and are widely used in fields such as field-effect transistors, optoelectronic devices, and thermoelectric devices.

[0004] Two-dimensional materials were proposed in 2004 when the Geim group at the University of Manchester successfully separated a single atomic layer of graphite material - graphene. Subsequently, some other two-dimensional materials were separated, such as boron nitride (BN), molybdenum disulfide (MoS2), tungsten disulfide (WS2) and MXene materials.

[0005] Take graphene as an example, which is a sp 2 Materials in which hybrid-connected carbon atoms are tightly packed into a single-layer two-dimensional honeycomb lattice structure have excellent optical, electrical and mechanical properties and have broad application prospects in the fields of materials science, energy, biomedicine and drug delivery. In order to prepare graphene-based devices, the primary issue is to prepare large-scale, high-quality graphene films. Chemical vapor deposition (CVD) is a common method for preparing large-scale, high-quality graphene films. When using this method to prepare graphene films, a copper substrate is required, and then the prepared graphene film needs to be transferred from the copper substrate to a suitable target substrate. For example, in the fields of electronics and optoelectronics, it is necessary to obtain inch-level, high-quality graphene films on insulating substrates. In the prior art, when transferring graphene films from a copper substrate to a target substrate, it is usually necessary to use an organic compound (such as polymethyl methacrylate, abbreviated as PMMA) film as a transfer carrier, which is very easy to introduce organic impurities, and the organic impurities are not easy to remove, affecting the quality of the graphene film.

[0006] Summary of the Invention

[0007] The purpose of the present invention is to provide a method for transferring two-dimensional materials. The method provided by the present invention can realize the transfer of large-area, high-quality two-dimensional materials without introducing impurities.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0009] The present invention provides a method for transferring a two-dimensional material, comprising the following steps:

[0010] Providing a metal substrate / two-dimensional material device, wherein the metal substrate / two-dimensional material device comprises a metal substrate and a two-dimensional material on a surface of the metal substrate;

[0011] Laying the metal substrate / two-dimensional material device on a target substrate, and bringing the two-dimensional material into contact with the target substrate for bonding, to obtain a metal substrate / two-dimensional material / target substrate device; the target substrate is a semiconductor substrate;

[0012] The metal substrate / two-dimensional material / target substrate device is subjected to cooling treatment and thermal annealing treatment in sequence, and then the metal substrate in the obtained device is peeled off, and the two-dimensional material is transferred from the metal substrate to the target substrate to obtain a target substrate / two-dimensional material device.

[0013] Preferably, the two-dimensional material includes graphene or boron nitride.

[0014] Preferably, the size of the two-dimensional material is 1 cm×1 cm to 4 cm×4 cm; and the two-dimensional material is a wafer-level two-dimensional material.

[0015] Preferably, the metal substrate includes a copper substrate, a nickel substrate or an alloy substrate.

[0016] Preferably, the preparation method of the metal substrate / two-dimensional material device is chemical vapor deposition.

[0017] Preferably, the method for preparing the metal substrate / two-dimensional material device comprises the following steps:

[0018] annealing the metal substrate to obtain an annealed metal substrate;

[0019] In the presence of monomers required for growing two-dimensional materials, chemical vapor deposition is used to grow two-dimensional materials on the surface of the annealed metal substrate to obtain a metal substrate / two-dimensional material device.

[0020] Preferably, the annealing process is performed in a hydrogen atmosphere; the flow rate of the hydrogen is 5 to 20 sccm; and the pressure provided by the hydrogen is 20 to 100 mTorr.

[0021] Preferably, when the two-dimensional material is graphene, the annealing treatment includes sequentially performing a first annealing and a second annealing; the temperature of the first annealing is 100-200° C., and the holding time is 5-15 minutes; the temperature of the second annealing is 1030-1040° C., and the holding time is 25-35 minutes;

[0022] When the two-dimensional material is boron nitride, the annealing treatment includes: heating to 1030-1040° C. over 15-25 minutes and keeping the temperature for 25-35 minutes.

[0023] Preferably, when the two-dimensional material is graphene, the monomer is methane; when the two-dimensional material is boron nitride, the monomer is borane.

[0024] Preferably, when the two-dimensional material is graphene, growing the two-dimensional material on the surface of the annealed metal substrate includes sequentially performing a first growth stage and a second growth stage; in the first growth stage, the monomer flow rate is 5 to 20 sccm, the gas pressure is preferably 50 to 150 mTorr, and the holding time is 2 to 10 min; in the second growth stage, the monomer flow rate is 5 to 15 sccm, the gas pressure is 800 to 1000 mTorr, and the holding time is 1 to 5 min. During the second growth stage, H2 and Ar are introduced to maintain the required gas pressure; the flow rate of H2 is 10 to 50 sccm, and the flow rate of Ar is 10 to 50 sccm;

[0025] When the two-dimensional material is boron nitride, H2 and Ar are introduced during the growth of the two-dimensional material on the surface of the annealed metal substrate to maintain a gas pressure of 700-900 mTorr, the flow rate of H2 is 10-50 sccm, and the flow rate of Ar is 10-50 sccm.

[0026] Preferably, the target substrate includes a SiO2 substrate or an Al2O3 substrate.

[0027] Preferably, the bonding comprises sequentially performing a first bonding process and a second bonding process;

[0028] The temperature of the first bonding treatment is 400-500°C, the pressure is 2500-3500N, and the heat and pressure holding time is 25-35s;

[0029] The temperature of the second bonding treatment is 400-500° C., the pressure is 14000-16000 N, and the heat and pressure holding time is 20-40 minutes.

[0030] Preferably, the bonding is performed in the presence of a protective gas; the pressure provided by the protective gas is 800-1000 mbar.

[0031] Preferably, the temperature of the thermal annealing treatment is 690-700K higher than the temperature of the cooling treatment.

[0032] Preferably, the cooling treatment temperature is 75-80K and the holding time is 25-35min;

[0033] The temperature of the thermal annealing treatment is 770-780K, and the holding time is 25-35 minutes.

[0034] The present invention provides a method for transferring a two-dimensional material, comprising the following steps: providing a metal substrate / two-dimensional material device, wherein the metal substrate / two-dimensional material device comprises a metal substrate and a two-dimensional material on the surface of the metal substrate; stacking the metal substrate / two-dimensional material device and a target substrate, and bringing the two-dimensional material into contact with the target substrate for bonding, thereby obtaining a metal substrate / two-dimensional material / target substrate device; wherein the target substrate is a semiconductor substrate; sequentially subjecting the metal substrate / two-dimensional material / target substrate device to a cooling treatment and a thermal annealing treatment, after which the metal substrate in the obtained device is peeled off, and the two-dimensional material is transferred from the metal substrate to the target substrate, thereby obtaining a target substrate / two-dimensional material device. The present invention tightly combines the two-dimensional material and the target substrate through a bonding technique, and then utilizes the difference in thermal expansion coefficients between the metal substrate and the two-dimensional material to achieve a temperature difference based on a cooling treatment and a thermal annealing treatment, thereby separating the two-dimensional material from the metal substrate. The entire process does not require the use of an organic film as a transfer carrier, and does not introduce impurities into the two-dimensional material. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a flow chart of preparing a graphene film on a copper foil surface and transferring the graphene film to a SiO2 substrate surface in Example 1;

[0036] FIG2 is an optical effect diagram of the graphene film before and after transfer in Example 1;

[0037] FIG3 is a Raman spectrum of the copper substrate / graphene thin film device and the SiO2 substrate / graphene thin film device in Example 1;

[0038] FIG4 is a flow chart of the growth of a boron nitride film prepared on a copper foil surface in Example 2;

[0039] FIG5 is an optical effect diagram of the boron nitride film before and after transfer in Example 2;

[0040] FIG6 is a Raman spectrum of the SiO2 substrate / boron nitride thin film device in Example 2. DETAILED DESCRIPTION

[0041] The present invention provides a method for transferring a two-dimensional material, comprising the following steps:

[0042] Providing a metal substrate / two-dimensional material device, wherein the metal substrate / two-dimensional material device comprises a metal substrate and a two-dimensional material on a surface of the metal substrate;

[0043] Laying the metal substrate / two-dimensional material device on a target substrate, and bringing the two-dimensional material into contact with the target substrate for bonding, to obtain a metal substrate / two-dimensional material / target substrate device; the target substrate is a semiconductor substrate;

[0044] The metal substrate / two-dimensional material / target substrate device is subjected to cooling treatment and thermal annealing treatment in sequence, and then the metal substrate in the obtained device is peeled off, and the two-dimensional material is transferred from the metal substrate to the target substrate to obtain a target substrate / two-dimensional material device.

[0045] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known to those skilled in the art.

[0046] The present invention provides a metal substrate / two-dimensional material device, which includes a metal substrate and a two-dimensional material on the surface of the metal substrate. In the present invention, the two-dimensional material preferably includes graphene or boron nitride; the size of the two-dimensional material is preferably 1cm×1cm~4cm×4cm; the two-dimensional material is preferably a wafer-level two-dimensional material. In the present invention, the metal substrate preferably includes a copper substrate, a nickel substrate or an alloy substrate. In the present invention, the preparation method of the metal substrate / two-dimensional material device is preferably a chemical vapor deposition method. In the present invention, the method of preparing the metal substrate / two-dimensional material device by chemical vapor deposition preferably includes the following steps:

[0047] annealing the metal substrate to obtain an annealed metal substrate;

[0048] In the presence of monomers required for growing two-dimensional materials, chemical vapor deposition is used to grow two-dimensional materials on the surface of the annealed metal substrate to obtain a metal substrate / two-dimensional material device.

[0049] The present invention anneals the metal substrate to obtain an annealed metal substrate. The present invention preferably places the metal substrate in the constant temperature zone at the center of the quartz tube of a tubular furnace, evacuates the tube to remove the residual air, and then performs the annealing treatment; the evacuation is preferably performed to 10 -6Torr. In the present invention, the annealing treatment is preferably carried out in a hydrogen atmosphere; the flow rate of the hydrogen is preferably 5 to 20 sccm, more preferably 5 to 10 sccm; the pressure provided by the hydrogen is preferably 20 to 100 mTorr, more preferably 50 to 70 mTorr. The present invention preferably selects a corresponding annealing treatment method according to the type of the two-dimensional material. In the present invention, taking the two-dimensional material as a graphene film as an example, the annealing treatment preferably includes performing a first annealing and a second annealing in sequence; the temperature of the first annealing is preferably 100 to 200°C, more preferably 150°C, and the holding time is preferably 5 to 15 minutes, more preferably 10 minutes; the temperature of the second annealing is preferably 1030 to 1040°C, more preferably 1035°C, and the holding time is preferably 25 to 35 minutes, more preferably 30 minutes; the present invention mainly removes water vapor in the system during the first annealing process, and removes oxides on the surface of the metal substrate while increasing the grain size of the metal substrate during the second annealing process. In the present invention, taking the two-dimensional material as a boron nitride film as an example, the annealing treatment is preferably to heat the temperature to 1030-1040°C for 15-25 minutes and keep it warm for 25-35 minutes; more preferably, to heat the temperature to 1035°C for 20 minutes and keep it warm for 30 minutes; the present invention adopts this annealing treatment method to remove water vapor in the system, and can remove oxides on the surface of the metal substrate while increasing the grain size of the metal substrate.

[0050] After obtaining the annealed metal substrate, the present invention uses chemical vapor deposition to grow the two-dimensional material on the surface of the annealed metal substrate in the presence of the monomer required for growing the two-dimensional material, thereby obtaining a metal substrate / two-dimensional material device. The present invention does not specifically limit the type of the monomer. Taking the two-dimensional material as a graphene film as an example, the monomer is preferably methane; taking the two-dimensional material as a boron nitride film as an example, the monomer is preferably borane. In the embodiment of the present invention, specifically under the condition of 80°C, ammonia borane powder is simultaneously decomposed into hydrogen, monomer amino borane BH2NH2 and borane (HBNH)3, wherein borane is an effective decomposition product for generating boron nitride film, and catalyzes dehydrogenation on the surface of the metal substrate to form a boron nitride film. In the present invention, taking the two-dimensional material as a graphene film as an example, growing the two-dimensional material on the surface of the annealed metal substrate preferably includes sequentially performing a first growth stage and a second growth stage. In the present invention, the flow rate of the monomer in the first growth stage is preferably 5-20 sccm, more preferably 10 sccm; the gas pressure is preferably 50-150 mTorr, more preferably 100 mTorr; and the holding time is preferably 2-10 min, more preferably 5 min. In the present invention, the flow rate of the monomer in the second growth stage is preferably 5-15 sccm, more preferably 10 sccm; the gas pressure is preferably 800-1000 mTorr, more preferably 900 mTorr; and the holding time is preferably 1-5 min, more preferably 3 min. In the present invention, H2 and Ar are preferably introduced during the second growth stage to maintain the required gas pressure; the flow rate of H2 is preferably 10-50 sccm, more preferably 20 sccm; and the flow rate of Ar is preferably 10-50 sccm, more preferably 30 sccm. In the present invention, taking the two-dimensional material as a boron nitride film as an example, during the process of growing the two-dimensional material on the surface of the annealed metal substrate, H2 and Ar are preferably introduced to maintain a gas pressure of 700-900 mTorr, preferably 800 mTorr; the flow rate of the H2 is preferably 10-50 sccm, more preferably 20 sccm; the flow rate of the Ar is preferably 10-50 sccm, more preferably 30 sccm. During the process of growing the two-dimensional material on the surface of the annealed metal substrate, the ammonia borane powder is thermally decomposed into hydrogen, monomeric amino borane BH2NH2, and borane oxazine (HBNH)3. Driven by the concentration gradient diffusion effect, the powder reaches the surface of the metal substrate via the carrier gas (Ar) flow, and dehydrogenates and cracks under high temperature conditions to form a thin film, that is, a boron nitride thin film is obtained on the surface of the metal substrate. After the two-dimensional material is grown on the surface of the annealed metal substrate, the present invention preferably cools the tube furnace naturally to room temperature to obtain a metal substrate / two-dimensional material device.

[0051] After obtaining the metal substrate / two-dimensional material device, the present invention places the metal substrate / two-dimensional material device and the target substrate in a stacked manner, and brings the two-dimensional material into contact with the target substrate for bonding to obtain a metal substrate / two-dimensional material / target substrate device. In the present invention, the target substrate is a semiconductor substrate, and the semiconductor substrate preferably includes a SiO2 substrate or an Al2O3 substrate. In the present invention, specifically, the metal substrate / two-dimensional material device and the target substrate are stacked horizontally, and the two-dimensional material is brought into contact with the target substrate for bonding in the vertical direction. The present invention preferably places the metal substrate / two-dimensional material device and the target substrate in a stacked manner horizontally, and then places them horizontally in a high vacuum chamber, and pumps the air pressure in the chamber to ≤1×10 -2 mbar, heating from room temperature to 250-350°C (preferably 300°C) at a rate of 25-35°C / min (preferably 30°C / min), then applying vertical pressure and heating to the required bonding temperature at a rate of 95-105°C / min (preferably 100°C / min) to perform bonding. In the present invention, the bonding is preferably performed in the presence of a protective gas, preferably nitrogen; the pressure provided by the protective gas is preferably 800-1000 mbar, more preferably 900 mbar. In the present invention, the bonding preferably includes performing a first bonding treatment and a second bonding treatment in sequence; the temperature of the first bonding treatment is preferably 400-500°C, more preferably 450°C, the pressure is preferably 2500-3500N, more preferably 3000N, and the heat preservation and pressure holding time is preferably 25-35s, more preferably 30s; the temperature of the second bonding treatment is preferably 400-500°C, more preferably 450°C, the pressure is preferably 14000-16000N, more preferably 15000N, and the heat preservation and pressure holding time is preferably 20-40min, more preferably 25-35min, and further preferably 30min. After the second bonding treatment, the present invention preferably cools down to 30-40°C (preferably 35°C) at a rate of 25-35°C / min (preferably 30°C / min), breaks the vacuum, and cools down to room temperature to obtain a metal substrate / two-dimensional material / target substrate device. In the present invention, after bonding, a strong van der Waals force is formed between the two-dimensional material and the target substrate, thereby achieving a close bond between the two.

[0052] After obtaining the metal substrate / two-dimensional material / target substrate device, the present invention sequentially performs a cooling treatment and a thermal annealing treatment on the metal substrate / two-dimensional material / target substrate device, and then peels off the metal substrate in the obtained device, and the two-dimensional material is transferred from the metal substrate to the target substrate to obtain the target substrate / two-dimensional material device. In the present invention, the temperature of the thermal annealing treatment is preferably 690-700K higher than the temperature of the cooling treatment, and more preferably 696K. In the present invention, the temperature of the cooling treatment is preferably 75-80K, and more preferably 77K; the holding time is preferably 25-35min, and more preferably 30min. In an embodiment of the present invention, the metal substrate / two-dimensional material / target substrate device is specifically placed in a liquid nitrogen cooling chamber for cooling treatment. After the cooling treatment, the present invention preferably performs a thermal annealing treatment on the cooled device within 3s. In the present invention, the temperature of the thermal annealing treatment is preferably 770-780K, and more preferably 773K (500°C); the holding time is preferably 25-35min, and more preferably 30min. After the thermal annealing treatment, the present invention preferably cools the device after the thermal annealing treatment to room temperature at a rate of 10 to 30°C / min, so that at least a portion of the metal substrate in the resulting device is raised, thereby separating from the target substrate / two-dimensional material device, and then the metal substrate is peeled off with tweezers to obtain the target substrate / two-dimensional material device, that is, an uncontaminated two-dimensional material is obtained on the surface of the target substrate, completing the transfer of the two-dimensional material. The present invention utilizes the cooling treatment and the thermal annealing treatment to form a strong temperature difference. Since the thermal expansion coefficients of the two-dimensional material and the metal substrate are different, two-dimensional materials such as graphene are not sensitive to temperature (the thermal expansion coefficient of graphene is almost 0), and the metal substrate is transferred from low temperature to high temperature. Due to thermal expansion, at least a portion of the metal substrate is raised and separated from the target substrate / two-dimensional material device, but it does not affect the interaction between the target substrate and the two-dimensional material, thereby ensuring that the target substrate / two-dimensional material device is finally obtained and the transfer of the two-dimensional material is achieved.

[0053] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0054] Example 1

[0055] FIG1 is a flow chart of preparing a graphene film on a copper foil surface and transferring the graphene film to a SiO2 substrate surface in this embodiment, which will be described in detail below in conjunction with FIG1 :

[0056] (1) Preparation of graphene film

[0057] a) Preparation of copper substrate: Place the copper substrate (specifically copper foil, 4 cm × 4 cm in size) in the constant temperature zone at the center of the quartz tube in the tube furnace and evacuate to 10 -6 Torr, to remove residual air in the tube;

[0058] b) Hydrogen annealing stage: Hydrogen is introduced at a flow rate of 5 sccm and the pressure is controlled to be maintained at 20 mTorr. The temperature is then raised to 150°C and held for 10 minutes to remove water vapor. The temperature is then raised to 1035°C and held for 30 minutes to remove oxides on the surface of the copper substrate and increase the grain size of the copper substrate.

[0059] c) Graphene growth stage: methane was introduced at a flow rate of 10 sccm, the pressure was controlled at 100 mTorr and maintained for 5 minutes, the methane flow rate was maintained at 10 sccm, H2 was introduced at a flow rate of 20 sccm, and Ar was introduced at a flow rate of 30 sccm, the pressure was controlled at 900 mTorr and maintained for 3 minutes, and a graphene film was obtained on the surface of the copper substrate, which was recorded as a copper substrate / graphene film device;

[0060] d) Cooling stage: After the graphene growth is completed, the tube furnace is naturally cooled to room temperature.

[0061] (2) Bonding of copper substrate / graphene film device to target substrate

[0062] The copper substrate / graphene film device and the target substrate (specifically SiO2 substrate) are stacked horizontally, and the graphene film is in contact with the target substrate. Then, the device is placed horizontally in a high vacuum chamber, and the pressure in the chamber is pumped down to ≤1×10 -2 mbar, then heated from room temperature to 300°C at a rate of 30°C / min, controlled the pressure plate to apply pressure in the vertical direction at a pressure of 3000N, and at the same time heated to 450°C at a rate of 100°C / min, and performed the first bonding treatment for 30s under the conditions of a pressure of 3000N and a temperature of 450°C; then controlled the pressure plate to apply pressure in the vertical direction at a pressure of 15000N, and performed the second bonding treatment for 30min under the conditions of a pressure of 15000N and a temperature of 450°C; the first bonding treatment and the second bonding treatment were carried out under nitrogen flow, and the gas pressure was maintained at 900mbar; after the second bonding treatment was completed, cooled to 35°C at a rate of 30°C / min, broke the vacuum, lifted the pressure plate, and cooled to room temperature to obtain a copper substrate / graphene film / SiO2 substrate device.

[0063] (3) Transfer of graphene film

[0064] The copper substrate / graphene film / SiO2 substrate device was placed in a liquid nitrogen cooling chamber and maintained at 77K for 30 minutes to achieve thermal stability; then the cooled device was transferred to a high-temperature chamber at 773K (500℃) within 3 seconds and maintained for 30 minutes to achieve thermal stability; thereafter, the heated device was cooled to room temperature at a rate of 10℃ / min, and part of the copper substrate was raised and separated from the SiO2 substrate / graphene film device. The copper substrate was peeled off with tweezers to obtain a SiO2 substrate / graphene film device, that is, an uncontaminated graphene film was obtained on the surface of the SiO2 substrate, thereby realizing the transfer of the graphene film.

[0065] Figure 2 shows the optical effects of the graphene film before and after transfer in this embodiment. The left side shows the optical effect of the copper substrate / graphene film / SiO2 substrate device, and the right side shows the optical effect of the SiO2 substrate / graphene film device. As shown in Figure 2, the present invention uses bonding technology and a transfer method combining liquid nitrogen treatment and high-temperature thermal annealing to successfully transfer the graphene film from the copper substrate surface to the target substrate surface.

[0066] Figure 3 shows the Raman spectra of the copper substrate / graphene thin film device and the SiO2 substrate / graphene thin film device in this embodiment. As can be seen from Figure 3, the Raman spectrum of the SiO2 substrate / graphene thin film device obtained after transfer and the Raman spectrum of the copper substrate / graphene thin film device before transfer both show G and 2D peaks, and the 2D / G intensity ratio is about 1.7, which is a typical Raman spectral feature of single-layer graphene, indicating that the graphene film was successfully transferred to the SiO2 substrate.

[0067] Example 2

[0068] In this embodiment, a boron nitride film is prepared on the surface of a copper foil and the boron nitride film is transferred to the surface of a SiO2 substrate. Specifically, a hexagonal boron nitride (h-BN) film is grown on the inner surface of a copper foil box that has been pretreated by electrolytic polishing by a CVD method, wherein ammonia borane (NH3BH3, AB) powder is used as a precursor and hydrogen (purity of 99.999%) is used as a carrier gas. The growth flow chart is shown in Figure 4. Specifically, under 80°C conditions, ammonia borane powder can be simultaneously decomposed into hydrogen, monomeric amino borane BH2NH2 and borane oxazine (HBNH)3, wherein borane oxazine is an effective decomposition product for generating h-BN, which catalyzes dehydrogenation on the surface of the copper foil to form an h-BN film. In the actual preparation process, the gas decomposed by the thermal decomposition of the ammonia borane powder escapes from the U-shaped tube under the drive of concentration gradient diffusion, reaches the surface of the copper foil through the carrier gas flow, and is dehydrogenated and cracked under high temperature conditions to form an h-BN film. The following is a detailed description:

[0069] (1) Preparation of Boron Nitride Film

[0070] a) Preparation of copper substrate: Place the copper substrate (specifically copper foil, 4 cm × 4 cm in size) in the constant temperature zone at the center of the quartz tube in the tube furnace and evacuate to 10 -6 Torr, to remove residual air in the tube;

[0071] b) Hydrogen annealing stage: hydrogen is introduced at a flow rate of 20 sccm, the pressure is controlled to be maintained at 100 mTorr, the temperature is raised to 1035°C over 20 minutes and kept at this temperature for 30 minutes to remove oxides on the surface of the copper substrate and increase the grain size of the copper substrate;

[0072] c) Boron nitride growth stage: H2 was introduced at a flow rate of 20 sccm, and Ar was introduced as a carrier gas at a flow rate of 30 sccm, and the gas pressure was maintained at 800 mTorr; ammonia borane powder was thermally decomposed into hydrogen, monomeric aminoborane BH2NH2, and borane oxazine (HBNH)3. Driven by concentration gradient diffusion, these gases escaped from the U-shaped tube and reached the copper foil surface via the carrier gas flow. Under high temperature conditions, they were dehydrogenated and cracked to form a thin film, resulting in a boron nitride thin film on the copper substrate surface, which was recorded as a copper substrate / boron nitride thin film device;

[0073] d) Cooling stage: After the boron nitride growth is completed, the tube furnace is naturally cooled to room temperature.

[0074] (2) Bonding the copper substrate / boron nitride thin film device to the target substrate (specifically, a SiO2 substrate) according to the method of Example 1 to obtain a copper substrate / boron nitride thin film / SiO2 substrate device.

[0075] (3) The graphene film is transferred according to the method of Example 1 to obtain a SiO2 substrate / boron nitride film device.

[0076] Figure 5 shows the optical effects of the boron nitride film before and after transfer in this embodiment. The left side shows the optical effect of the copper substrate / boron nitride film / SiO2 substrate device, and the right side shows the optical effect of the boron nitride film / SiO2 substrate device. As shown in Figure 5, the present invention uses bonding technology and a transfer method combining liquid nitrogen treatment and high-temperature thermal annealing to successfully transfer the boron nitride film from the copper substrate surface to the target substrate surface.

[0077] FIG6 is a Raman spectrum of the SiO2 substrate / boron nitride thin film device in this embodiment. As shown in FIG6, the Raman spectrum of the SiO2 substrate / boron nitride thin film device obtained after transfer shows that the boron nitride E 2g and 3TO peaks, which are typical Raman spectral features of two-dimensional boron nitride, indicating that the boron nitride film was successfully transferred to the SiO2 substrate.

[0078] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for transferring a two-dimensional material, comprising the following steps: Providing a metal substrate / two-dimensional material device, wherein the metal substrate / two-dimensional material device comprises a metal substrate and a two-dimensional material on a surface of the metal substrate; Laying the metal substrate / two-dimensional material device on a target substrate, and bringing the two-dimensional material into contact with the target substrate for bonding, to obtain a metal substrate / two-dimensional material / target substrate device; The target substrate is a semiconductor substrate; The metal substrate / two-dimensional material / target substrate device is subjected to cooling treatment and thermal annealing treatment in sequence, and then the metal substrate in the obtained device is peeled off, and the two-dimensional material is transferred from the metal substrate to the target substrate to obtain a target substrate / two-dimensional material device.

2. The transfer method according to claim 1, characterized in that: The two-dimensional material includes graphene or boron nitride.

3. The transfer method according to claim 1, characterized in that: The size of the two-dimensional material is 1cm×1cm~4cm×4cm; the two-dimensional material is a wafer-level two-dimensional material.

4. The transfer method according to claim 1, characterized in that: The metal substrate includes a copper substrate, a nickel substrate or an alloy substrate.

5. The transfer method according to any one of claims 1 to 4, characterized in that: The preparation method of the metal substrate / two-dimensional material device is chemical vapor deposition.

6. The transfer method according to claim 5, characterized in that: The method for preparing the metal substrate / two-dimensional material device comprises the following steps: annealing the metal substrate to obtain an annealed metal substrate; Under the condition that monomers required for growing two-dimensional materials exist, chemical vapor deposition is used to grow two-dimensional materials on the surface of the annealed metal substrate to obtain a metal substrate / two-dimensional material device.

7. The transfer method according to claim 6, characterized in that: The annealing process is performed in a hydrogen atmosphere; the flow rate of the hydrogen is 5-20 sccm; and the pressure provided by the hydrogen is 20-100 mTorr.

8. The transfer method according to claim 7, characterized in that: When the two-dimensional material is graphene, the annealing treatment includes sequentially performing a first annealing and a second annealing; the temperature of the first annealing is 100-200° C., and the holding time is 5-15 minutes; the temperature of the second annealing is 1030-1040° C., and the holding time is 25-35 minutes; When the two-dimensional material is boron nitride, the annealing treatment includes: heating to 1030-1040° C. for 15-25 minutes and keeping the temperature for 25-35 minutes.

9. The transfer method according to claim 6, characterized in that: When the two-dimensional material is graphene, the monomer is methane; when the two-dimensional material is boron nitride, the monomer is borane.

10. The transfer method according to claim 6, characterized in that: When the two-dimensional material is graphene, growing the two-dimensional material on the surface of the annealed metal substrate includes sequentially performing a first growth stage and a second growth stage; in the first growth stage, the monomer flow rate is 5-20 sccm, the gas pressure is preferably 50-150 mTorr, and the holding time is 2-10 min; in the second growth stage, the monomer flow rate is 5-15 sccm, the gas pressure is 800-1000 mTorr, and the holding time is 1-5 min. During the second growth stage, H2 and Ar are introduced to maintain the required gas pressure; the flow rate of H2 is 10-50 sccm, and the flow rate of Ar is 10-50 sccm; When the two-dimensional material is boron nitride, H2 and Ar are introduced during the process of growing the two-dimensional material on the surface of the annealed metal substrate to maintain a gas pressure of 700-900 mTorr, the flow rate of H2 is 10-50 sccm, and the flow rate of Ar is 10-50 sccm.

11. The transfer method according to claim 1, characterized in that: The target substrate includes a SiO2 substrate or an Al2O3 substrate.

12. The transfer method according to claim 1 or 11, characterized in that: The bonding includes sequentially performing a first bonding process and a second bonding process; The temperature of the first bonding treatment is 400-500°C, the pressure is 2500-3500N, and the heat preservation and pressure holding time is 25-35s; The temperature of the second bonding treatment is 400-500° C., the pressure is 14000-16000N, and the heat preservation and pressure preservation time is 20-40 minutes.

13. The transfer method according to claim 12, characterized in that: The bonding is performed in the presence of a protective gas; the gas pressure provided by the protective gas is 800-1000 mbar.

14. The transfer method according to claim 1, characterized in that: The temperature of the thermal annealing treatment is 690-700K higher than the temperature of the cooling treatment.

15. The transfer method according to claim 1 or 14, characterized in that: The cooling treatment temperature is 75-80K, and the holding time is 25-35min; The temperature of the thermal annealing treatment is 770-780K, and the holding time is 25-35 minutes.

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