Low-melting metal assisted two-dimensional material non-destructive transfer method

Abstract

The present application relates to the field of two-dimensional material lossless transfer, in particular to a two-dimensional material lossless transfer method assisted by low melting point metal. An organic transfer medium is spin-coated on a two-dimensional material synthesized on the surface of a metal substrate, and a transfer medium / two-dimensional material / metal substrate composite is obtained after heating and curing. The composite is placed on the surface of a liquid metal, and heated with a hot stage. The metal substrate is dissolved by alloying with the liquid metal, and separated from the transfer medium / two-dimensional material. The liquid metal and the transfer medium / two-dimensional material composite are separated, the transfer medium / two-dimensional material composite is transferred to the surface of a target substrate, the transfer medium is removed by organic solvent cleaning, and the two-dimensional material is transferred without damage. The method breaks the dilemma of having to use an oxidizing chemical etchant, and makes the transferred two-dimensional material have a more complete surface and a crystal structure that is not oxidized by chemical reagents, laying a foundation for the intrinsic property research and practical application of two-dimensional materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of two-dimensional material non-destructive transfer, in particular to a two-dimensional material non-destructive transfer method assisted by low melting point metal, which does not involve any oxidizing chemical reagent, and is suitable for the clean, non-damaged and non-doped transfer of two-dimensional material grown on a metal substrate. BACKGROUND

[0002] The integrated circuit industry has been advancing by reducing the size of individual transistors and increasing their integration density, but the complexity of traditional silicon-based device doping process and the aggravation of short channel effect make it difficult to continue Moore's law. Since 2004, the discovery of emerging two-dimensional materials such as graphene, hexagonal boron nitride and molybdenum disulfide has opened a new chapter for the scientific and industrial communities. The recently reported MoSi2N4 family of two-dimensional materials has potential applications in electronic / optoelectronic devices, spin devices, solar cells, sensing, and detection, etc. due to its high theoretical carrier mobility, suitable band gap, excellent mechanical properties and thermal transport characteristics, providing a new way to continue Moore's law. Chemical vapor deposition is a common method for efficient preparation of two-dimensional materials such as MoSi2N4, and metal substrates are the preferred substrates in the preparation process due to their good catalytic activity. However, in practical applications, it is often necessary to transfer two-dimensional materials grown on metal substrates to other target substrates. Currently, the most widely used methods are oxidizing chemical reagent etching and electrochemical bubbling. The electrochemical bubbling method has strict requirements for the matching of the binding force between the sample and the growth substrate, and is usually only suitable for a small number of samples and substrates. Oxidizing chemical reagents are widely used in etching metal substrates, but they can also etch and dope the sample, causing damage and modification of the sample, which makes it difficult to realize its intrinsic high performance and seriously hinders its application in the field of optoelectronic devices.

[0003] According to the phase diagram, low melting point metals represented by gallium and their alloys can alloy with metal substrates on which two-dimensional materials are grown at a relatively low temperature. Since the growth substrate is generally thin (for example, the copper substrate for growing graphene, hexagonal boron nitride and MoSi2N4 is 12.5 μm to 25 μm), it is relatively easy to completely dissolve in low melting point metals such as gallium or alloys, thereby achieving complete "dissolution". In addition, such low melting point metals or alloys have reducing and stabilizing properties, and will not cause oxidation and doping of two-dimensional materials, and are not easy to cause damage and vacancy defects. Therefore, low melting point metals such as gallium or alloys can replace oxidizing chemical reagents such as ammonium persulfate to "etch" metal substrates, and then achieve non-destructive transfer of two-dimensional materials, thereby improving the measured performance of two-dimensional materials after transfer, which is of great significance for the intrinsic property research and practical application of two-dimensional materials. SUMMARY

[0004] The application aims to provide a low-melting-point metal-assisted two-dimensional material nondestructive transfer method, which uses low-melting-point metal to replace oxidizing chemical reagents to "dissolve" the metal substrate, and is suitable for clean and nondestructive transfer of the two-dimensional material grown on the metal substrate.

[0005] The technical scheme of the application is:

[0006] A low-melting-point metal-assisted two-dimensional material nondestructive transfer method, in which low-melting-point metal replaces oxidizing chemical etching reagents to remove the metal substrate by alloying, and the method comprises the following steps:

[0007] Step 1: spin coating an organic transfer medium on the surface of the metal substrate on which the two-dimensional material is grown, and then heating and drying to obtain a transfer medium / two-dimensional material / metal substrate composite;

[0008] Step 2: placing the composite on the surface of low-melting-point metal, preheating and melting the low-melting-point metal, so that the metal substrate in the composite tightly adheres to the liquid metal and alloying occurs, thereby dissolving the metal substrate;

[0009] Step 3: separating the liquid alloy substrate from the two-dimensional material by using electrochemical hydrogen production bubbling or polyethylene terephthalate flexible substrate direct assisted peeling and reverse fishing to obtain a transfer medium / two-dimensional material composite;

[0010] Step 4: transferring the transfer medium / two-dimensional material composite to deionized water, washing, and then transferring to a target substrate and drying;

[0011] Step 5: cleaning and removing the organic transfer medium by using an organic solvent, thereby realizing nondestructive transfer of the two-dimensional material.

[0012] The low-melting-point metal-assisted two-dimensional material nondestructive transfer method, the low-melting-point metal includes but is not limited to gallium, rubidium, cesium, indium, bismuth, tin, and alloys of two or more thereof.

[0013] The low-melting-point metal-assisted two-dimensional material nondestructive transfer method, the organic transfer medium includes but is not limited to high polymer or small molecule material, the high polymer is polymethyl methacrylate or polyvinyl formal, and the small molecule material is paraffin or rosin.

[0014] The low-melting-point metal-assisted two-dimensional material nondestructive transfer method, in step 1, the transferred two-dimensional material is a two-dimensional material single crystal or film grown on the metal substrate, and the metal substrate includes but is not limited to gold, silver, copper, iron, nickel, cobalt, platinum or palladium; the two-dimensional material includes but is not limited to MoSi2N4, WSi2N4, graphene, hexagonal boron nitride, tungsten disulfide, tungsten diselenide, molybdenum disulfide, molybdenum diselenide, rhenium disulfide, rhenium diselenide, or a heterostructure material composed of one or two or more thereof.

[0015] The low-melting-point metal-assisted two-dimensional material nondestructive transfer method, in step 1, the organic transfer medium is heated to above its melting point and spin-coated onto the surface of the metal substrate on which the two-dimensional material is grown at a rotation speed of 1000-5000 rpm.

[0016] The low-melting-point metal-assisted two-dimensional material nondestructive transfer method, step 2 is completed in an oxygen-free environment, in a nitrogen-protected glove box or with liquid sealing of the organic solvent on the surface of the low-melting-point metal to avoid oxidation of the surface of the low-melting-point metal.

[0017] The low-melting-point metal-assisted two-dimensional material nondestructive transfer method, in step 2, the preheating and melting temperature of the low-melting-point metal or alloy is between 25℃ and 300℃ above the melting point.

[0018] The low-melting-point metal-assisted two-dimensional material nondestructive transfer method, in step 3, when the two-dimensional material is peeled off from the metal substrate by the electrochemical hydrogen bubbling method, the liquid metal is first solidified on a cold stage with a temperature controlled at -18℃, the electrochemical bubbling is carried out in a 0.5-2M NaOH aqueous solution, a direct current source is used in a constant current mode, and the current is controlled at 100-200 mA; when the flexible polyethylene terephthalate substrate is used to assist in direct peeling, the temperature of the hot stage is first lowered to below 90℃, the polyethylene terephthalate film is pasted and lightly pressed to the transfer medium side to completely adhere to each other, and then the temperature of the hot stage is increased by 20-40℃, so that the polyethylene terephthalate film can completely peel off the transfer medium / two-dimensional material composite from the liquid metal, and the composite is placed in deionized water and a new polyethylene terephthalate film is used for re-fishing.

[0019] The low-melting-point metal-assisted two-dimensional material nondestructive transfer method, in step 5, the transfer medium is removed by dissolving in an organic solvent, and the organic solvent includes but is not limited to one or more of acetone, dichloroethane, petroleum ether, n-hexane, chloroform, carbon disulfide, dimethylbenzene, and ethanol.

[0020] The design principle of the present application is:

[0021] The low-melting-point metal or alloy is in liquid state at room temperature or slightly higher temperature, and can be alloyed with the metal substrate on which the two-dimensional material is grown at a lower temperature according to a phase diagram, so that the metal substrate is removed and the organic transfer medium / two-dimensional material composite is completely retained.

[0022] The present application has the following advantages and beneficial effects:

[0023] 1. The low-melting-point metal or alloy is in liquid state at room temperature or slightly higher temperature, and can be alloyed with the metal substrate on which the two-dimensional material is grown at a lower temperature, so that the metal substrate is removed and the organic transfer medium / two-dimensional material composite is completely retained.

[0024] 2. The low-melting-point metal or alloy has reducing property and will not cause oxidation and doping of the two-dimensional material during the transfer process.

[0025] 3. The alloying process is carried out in a glove box or a glycol liquid sealed environment to avoid oxidation or doping of the two-dimensional material by oxygen.

[0026] 4. The present application can realize lossless transfer of the two-dimensional material, and the obtained two-dimensional material can maintain high light transmittance, integrity and cleanliness, and break through the previous difficulty of using oxidizing chemical etchant, so that the transferred two-dimensional material has a more complete surface and a crystal structure that is not oxidized or doped by chemical reagents, which is of great significance for the study of intrinsic physical properties of the two-dimensional material and the promotion of practical application. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Figure 1 is a flowchart of the process of transferring two-dimensional material assisted by the low-melting-point metal of the present application.

[0028] Figure 2 Figure 3 is an optical microscope photo of MoSi2N4 film transferred to a SiO2 / Si substrate assisted by gallium.

[0029] Figure 3 Figure 4 is a Raman spectrum of MoSi2N4 film transferred to a SiO2 / Si substrate assisted by gallium; in the figure, the horizontal coordinate Raman Shift represents Raman shift cm-1, and the vertical coordinate Intensity represents relative intensity a.u. -1 ​

[0030] Figure 4 Raman spectra of MoSi2N4 thin films transferred by ammonium persulfate solution etching and gallium-assisted on SiO2 / Si substrates; in the figure, the horizontal coordinate Raman Shift represents the Raman shift cm -1 , the vertical coordinate Intensity represents the relative intensity a.u.; (NH4)2S2O8 etching transferred is ammonium persulfate solution etching transferred, and Ga assisting transferred is gallium-assisted transferred. DETAILED DESCRIPTION

[0031] In the implementation process, the two-dimensional material synthesized on the surface of a type of metal substrate is spin-coated with an organic transfer medium, and after heating and curing, a transfer medium / two-dimensional material / metal substrate composite is obtained; the composite is placed on the surface of a low-melting-point liquid metal (such as gallium, rubidium, cesium, indium, bismuth, tin, and an alloy of two or more thereof), and is heated with a hot stage; after a period of time, the lowest layer of the composite, i.e., the metal substrate, is alloyed with the liquid metal and is dissolved, thereby separating from the transfer medium / two-dimensional material; the liquid metal and the transfer medium / two-dimensional material composite are separated by methods such as electrochemical hydrogen production bubbling, polyethylene terephthalate (PET) direct assistance peeling, and reverse fishing; the transfer medium / two-dimensional material composite is transferred to the surface of a target substrate, and the transfer medium is removed by organic solvent cleaning, thereby realizing lossless transfer of the two-dimensional material.

[0032] As shown in Figure 1 , the present application proposes a method for transferring two-dimensional materials using low-melting-point metals, and the specific steps are as follows:

[0033] (1) spin-coat an organic transfer medium on the surface of a metal substrate with a two-dimensional material grown thereon, and then heat and dry to obtain a transfer medium / two-dimensional material / metal substrate composite;

[0034] (2) place the composite on the surface of a low-melting-point metal, preheat and melt the low-melting-point metal, make the metal substrate in the composite tightly adhere to the liquid metal and alloy, and thereby dissolve the metal substrate;

[0035] Step 2 is completed in an oxygen-free environment, such as in a nitrogen-protected glove box or by liquid sealing with an organic solvent such as ethylene glycol on the surface of the low-melting-point metal to avoid oxidation of the low-melting-point metal surface.

[0036] (3) separate the liquid metal and the two-dimensional material by methods such as electrochemical hydrogen production bubbling, polyethylene terephthalate (PET) and other flexible substrates directly assisting peeling, and reverse fishing, to obtain a transfer medium / two-dimensional material composite;

[0037] Wherein, when the two-dimensional material is peeled off from the metal substrate by electrochemical hydrogen bubbling method, the liquid metal is first solidified on a cold stage with the temperature controlled at -18℃, the electrochemical bubbling is carried out in 1M NaOH aqueous solution, a direct current power supply is used in constant current mode, and the current is controlled at 100-200 mA; when the two-dimensional material is directly peeled off with the aid of a flexible substrate such as polyethylene terephthalate (PET), the temperature of a hot stage is first lowered to below 90℃, and the PET film is pasted and lightly pressed to the two from the transfer medium side until they are completely attached, then the temperature of the hot stage is increased by about 30℃, and finally the PET film completely peels off the liquid metal from the two-dimensional material / transfer medium composite, and the composite is quickly placed in deionized water for re-fishing with a new PET film.

[0038] (4) The two-dimensional material / transfer medium composite is transferred to deionized water, washed, and then transferred to a target substrate and dried;

[0039] (5) The two-dimensional material is transferred to a target substrate after cleaning and drying with acetone and deionized water, thereby realizing the damage-free and undoped transfer of the two-dimensional material.

[0040] Hereinafter, the present application will be further described in detail by examples and drawings.

[0041] Example 1

[0042] As shown in the figure, this embodiment uses gallium to transfer graphene grown on a copper foil, including the following steps: Figure 1

[0043] (1) First, a 4% by mass poly(methyl methacrylate) (PMMA) ethyl lactate solution is dropped onto the surface of the graphene-grown copper foil, and a spin coater is used to uniformly spin coat at a speed of 3000 rpm for 60 s, and then sequentially dried and cured at 60℃, 90℃, and 120℃ for 10 min each time, to obtain a PMMA / graphene / copper foil composite. The thickness of the PMMA film is 140-200 nm, the thickness of the graphene layer is 0.34 nm, and the thickness of the copper foil is 25 μm.

[0044] (2) The metal gallium is preheated and melted in a glove box, and a glass syringe is used to draw gallium liquid drops onto a glass culture dish placed on a hot stage. The PMMA / graphene / copper foil composite is placed on the gallium liquid drops in the glass culture dish, and the copper foil substrate is tightly attached to the liquid gallium. The temperature of the hot stage is adjusted to 150℃, and the copper foil is alloyed with the liquid gallium, thereby dissolving the copper foil substrate, to obtain a PMMA / graphene / alloy substrate;

[0045] ​(3) using electrochemical hydrogen bubbling or polyethylene terephthalate (PET) and other flexible substrates to directly assist in stripping and reverse fishing, etc. to separate the liquid gallium copper alloy substrate from graphene, to obtain PMMA / graphene composite;

[0046] (4) transferring the PMMA / graphene composite to deionized water, washing and transferring to the target substrate (SiO2 / Si substrate, i.e. a uniform silicon dioxide SiO2 film on the surface of a silicon wafer Si) and drying;

[0047] (5) using acetone at 70°C to clean and remove PMMA transfer medium, thereby achieving lossless transfer of graphene.

[0048] Using an optical microscope and a Raman spectrometer to characterize the morphology and quality of the graphene film, it is shown that the transferred graphene film has a complete structure, a clean surface and very high quality.

[0049] Example 2

[0050] As shown in Figure 1 , this embodiment uses gallium to transfer hexagonal boron nitride (h-BN) grown on a copper foil, including the following steps:

[0051] (1) First, drop a 4% by mass poly(methyl methacrylate) (PMMA) ethyl lactate solution onto the surface of the copper foil on which h-BN is grown, and use a spin coater to spin coat uniformly at a speed of 3000 revolutions per minute for 60 seconds. Then, sequentially dry and cure on hot plates at 60°C, 90°C and 120°C for 10 minutes each, to obtain a PMMA / h-BN / copper foil composite. The thickness of the PMMA film is 140-200 nm, the thickness of the h-BN layer is 0.33 nm, and the thickness of the copper foil is 25 μm.

[0052] (2) Preheat and melt the metal gallium in a glove box, and use a glass syringe to draw gallium droplets onto a glass culture dish, with the glass culture dish placed on a hot plate. Place the PMMA / h-BN / copper foil composite on the gallium droplets in the glass culture dish, with the copper foil substrate tightly attached to the liquid gallium. Adjust the temperature of the hot plate to 150°C and allow the copper foil to alloy with the liquid gallium, thereby dissolving away the copper foil substrate to obtain a PMMA / h-BN / alloy substrate;

[0053] (3) using electrochemical hydrogen bubbling or polyethylene terephthalate (PET) and other flexible substrates to directly assist in stripping and reverse fishing, etc. to separate the liquid gallium copper alloy substrate from graphene, to obtain PMMA / graphene composite;

[0054] (4) transferring the PMMA / h-BN composite to deionized water, washing and transferring to the target substrate (SiO2 / Si substrate) and drying;

[0055] (5) The PMMA transfer medium is removed by cleaning with acetone at 70°C, thereby achieving non-destructive transfer of h-BN.

[0056] The morphology and quality of the h-BN thin film were characterized using optical microscopy and Raman spectroscopy, showing that the transferred h-BN thin film has a complete structure, a clean surface, and high quality.

[0057] Example 3

[0058] like Figure 1 As shown, the MoSi2N4 grown on gallium-transfer copper foil in this embodiment includes the following steps:

[0059] (1) First, a 4% (w / w) polymethyl methacrylate (PMMA) ethyl lactate solution was dropped onto the surface of a copper foil on which MoSi2N4 was grown. The solution was then uniformly spin-coated at 3000 rpm for 60 seconds using a spin coater. Afterward, the solution was dried and cured sequentially on hot plates at 60℃, 90℃, and 120℃ for 10 minutes each, resulting in a PMMA / MoSi2N4 / copper foil composite. The PMMA film thickness was 140 nm–200 nm, the MoSi2N4 layer thickness was 1.07 nm, and the copper foil thickness was 25 μm.

[0060] (2) Preheat and melt metallic gallium in a glove box, and use a glass syringe to draw gallium droplets into a glass culture dish, which is then placed on a hot plate. Place the PMMA / MoSi2N4 / copper foil composite on the gallium droplets in the glass culture dish, with the copper foil substrate in close contact with the liquid gallium. Adjust the temperature of the hot plate to 150°C and alloy the copper foil with the liquid gallium, thereby dissolving the copper foil substrate to obtain the PMMA / MoSi2N4 / alloy substrate.

[0061] (3) The liquid gallium copper alloy substrate is separated from MoSi2N4 by methods such as electrochemical hydrogen generation bubbling or direct assisted peeling and reverse retrieval of flexible substrates such as polyethylene terephthalate (PET) to obtain PMMA / MoSi2N4 composite.

[0062] (4) Transfer the PMMA / MoSi2N4 composite to deionized water, rinse it, transfer it to the target substrate (SiO2 / Si substrate) and dry it;

[0063] (5) The PMMA transfer medium is removed by cleaning with acetone at 70°C, thereby achieving non-destructive transfer of MoSi2N4.

[0064] The morphology and quality of the MoSi2N4 thin film were characterized by optical microscopy and Raman spectroscopy, showing that the transferred MoSi2N4 thin film has a complete structure, clean surface, and high quality.

[0065] Example 4

[0066] As shown in Figure 1 , the embodiment of transferring graphene grown on copper foil by indium includes the following steps:

[0067] (1) First, drop a 4% by mass ethyl lactate solution of polymethyl methacrylate (PMMA) onto the surface of the copper foil on which graphene is grown, uniformly spin coat for 60 s at a speed of 3000 rpm using a spin coater, and then sequentially dry and cure for 10 min at 60°C, 90°C, and 120°C on a hot plate, to obtain a PMMA / graphene / copper foil composite. The thickness of the PMMA film is 140-200 nm, the thickness of the graphene layer is 0.34 nm, and the thickness of the copper foil is 25 μm.

[0068] (2) Preheat and melt the metal indium in a glove box, and use a glass syringe to draw indium droplets into a glass culture dish, with the glass culture dish placed on a hot plate. Place the PMMA / graphene / copper foil composite on the indium droplets in the glass culture dish, with the copper foil base tightly attached to the liquid indium, adjust the temperature of the hot plate to 180°C, and allow the copper foil to alloy with the liquid indium, thereby dissolving away the copper foil base, to obtain a PMMA / graphene / alloy base;

[0069] (3) Use electrochemical hydrogen generation bubbling or a flexible substrate such as polyethylene terephthalate (PET) to directly assist in peeling and reverse fishing, and separate the liquid indium copper alloy base from the graphene, to obtain a PMMA / graphene composite;

[0070] (4) Transfer the PMMA / graphene composite to deionized water, rinse, and then transfer to a target substrate (SiO2 / Si base) and dry;

[0071] (5) Use acetone at 70°C to clean and remove the PMMA transfer medium, thereby achieving non-destructive transfer of the graphene.

[0072] Use an optical microscope and a Raman spectrometer to characterize the morphology and quality of the graphene film, which shows that the transferred graphene film has an intact structure, a clean surface, and very high quality.

[0073] Example 5

[0074] As shown in Figure 1 , the embodiment of transferring graphene grown on copper foil by tin includes the following steps:

[0075] (1) First, a 4% by mass ethyl lactate solution of polymethyl methacrylate (PMMA) is dropped onto the surface of a copper foil on which graphene is grown, and is uniformly spin-coated at a speed of 3000 rpm for 60 s using a spin coater, and then is dried and cured on a hot stage at 60°C, 90°C and 120°C for 10 min each, to obtain a PMMA / graphene / copper foil composite. The thickness of the PMMA film is 140-200 nm, the thickness of the graphene layer is 0.34 nm, and the thickness of the copper foil is 25 μm.

[0076] (2) In a glove box, tin is preheated and melted, and a drop of the tin liquid is extracted using a glass syringe and dropped into a glass culture dish placed on a hot stage. The PMMA / graphene / copper foil composite is placed on the drop of tin liquid in the glass culture dish, and the copper foil substrate is tightly attached to the liquid tin. The temperature of the hot stage is adjusted to 240°C, and the copper foil is alloyed with the liquid tin, so that the copper foil substrate is dissolved, to obtain a PMMA / graphene / alloy substrate.

[0077] (3) The liquid tin-copper alloy substrate is separated from the graphene by using electrochemical hydrogen production bubbling or a flexible substrate such as polyethylene terephthalate (PET) to directly assist peeling and reverse fishing, to obtain a PMMA / graphene composite.

[0078] (4) The PMMA / graphene composite is transferred to deionized water, washed, and then transferred to a target substrate (SiO2 / Si substrate) and dried.

[0079] (5) The PMMA transfer medium is removed by washing with acetone at 70°C, to realize non-destructive transfer of the graphene.

[0080] The morphology and quality of the graphene film are characterized by optical microscopy and Raman spectroscopy, and it is shown that the graphene film obtained by transfer has a complete structure, a clean surface and high quality.

[0081] Example 6

[0082] As shown in Figure 1 , this embodiment uses gallium to transfer graphene grown on a nickel foil, including the following steps:

[0083] (1) First, a 4% by mass ethyl lactate solution of polymethyl methacrylate (PMMA) is dropped onto the surface of a copper foil on which graphene is grown, and is uniformly spin-coated at a speed of 3000 rpm for 60 s using a spin coater, and then is dried and cured on a hot stage at 60°C, 90°C and 120°C for 10 min each, to obtain a PMMA / graphene / copper foil composite. The thickness of the PMMA film is 140-200 nm, the thickness of the graphene layer is 0.34 nm, and the thickness of the copper foil is 25 μm.

[0084] (2) Preheat and melt metallic gallium in a glove box, and use a glass syringe to draw gallium droplets into a glass culture dish, which is then placed on a hot plate. Place the PMMA / graphene / nickel foil composite on the gallium droplets in the glass culture dish, with the nickel foil substrate in close contact with the liquid gallium. Adjust the temperature of the hot plate to 150°C and alloy the nickel foil with the liquid gallium, thereby dissolving the nickel foil substrate to obtain the PMMA / graphene / alloy substrate.

[0085] (3) The liquid gallium nickel alloy substrate is separated from the graphene by methods such as electrochemical hydrogen generation bubbling or direct assisted peeling and back-fishing of flexible substrates such as polyethylene terephthalate (PET) to obtain PMMA / graphene composite.

[0086] (4) Transfer the PMMA / graphene composite to deionized water, rinse it, transfer it to the target substrate (SiO2 / Si substrate) and dry it;

[0087] (5) Use acetone to clean and remove the PMMA transfer medium at 70°C to achieve non-destructive transfer of graphene.

[0088] The morphology and quality of the graphene film were characterized using optical microscopy and Raman spectroscopy, showing that the transferred graphene film has a complete structure, a clean surface, and high quality.

[0089] Example 7

[0090] like Figure 1 As shown, this embodiment uses molybdenum disulfide (MoS2) grown on gallium-transfer gold foil, and includes the following steps:

[0091] (1) First, a 4% (w / w) polymethyl methacrylate (PMMA) ethyl lactate solution was dropped onto the surface of a gold foil on which MoS2 was grown. The solution was then uniformly spin-coated at 3000 rpm for 60 seconds using a spin coater. Afterward, the composite was dried and cured sequentially at 60℃, 90℃, and 120℃ for 10 minutes each, yielding a PMMA / MoS2 / gold foil composite. The PMMA film thickness was 140–200 nm, the MoS2 layer thickness was 0.68 nm, and the gold foil thickness was 10 μm.

[0092] (2) Preheat and melt metallic gallium in a glove box, and use a glass syringe to draw gallium droplets into a glass culture dish, which is then placed on a hot plate. Place the PMMA / MoS2 / gold foil composite on the gallium droplets in the glass culture dish, with the gold foil substrate in close contact with the liquid gallium. Adjust the temperature of the hot plate to 150°C and alloy the gold foil with the liquid gallium, thereby dissolving the gold foil substrate to obtain the PMMA / MoS2 / alloy substrate.

[0093] (3) Using electrochemical hydrogen bubbling or polyethylene terephthalate (PET) and other flexible substrates to directly assist in stripping and reverse fishing, etc. to separate the liquid gallium gold alloy substrate from MoS2, and obtain PMMA / MoS2 composite;

[0094] (4) Transfer the PMMA / MoS2 composite to deionized water, rinse and transfer to the target substrate (SiO2 / Si substrate) and dry;

[0095] (5) Using acetone at 70°C to clean and remove PMMA transfer medium, so as to realize the lossless transfer of MoS2.

[0096] Using optical microscope and Raman spectrometer to characterize the morphology and quality of MoS2 film, it is shown that the MoS2 film obtained by transfer has complete structure, clean surface and high quality.

[0097] Example 8

[0098] As shown in the following figure, the present embodiment uses gallium-indium alloy to transfer graphene grown on copper foil, including the following steps: Figure 1

[0099] (1) First, drop a 4% mass fraction of polymethyl methacrylate (PMMA) ethyl lactate solution onto the surface of the copper foil on which graphene is grown, use a spin coater to spin at a speed of 3000 rpm for 60 s, and then sequentially dry and solidify on a hot stage at 60°C, 90°C and 120°C for 10 min each, to obtain a PMMA / graphene / copper foil composite. The thickness of the PMMA film is 140-200 nm, the thickness of the graphene layer is 0.34 nm, and the thickness of the copper foil is 25 μm.

[0100] (2) Preheat and melt the metal gallium and the metal indium in the glove box, and use a glass syringe to draw a certain mass of gallium and indium droplets into a glass culture dish to obtain a gallium-indium alloy with a mass fraction of indium of 20.5%, and the glass culture dish is placed on a hot stage. Place the PMMA / graphene / copper foil composite on the gallium-indium alloy droplet in the glass culture dish, with the copper foil substrate tightly attached to the liquid gallium-indium alloy, adjust the temperature of the hot stage to 120°C, and make the copper foil alloy with the liquid gallium-indium alloy, so as to dissolve the copper foil substrate, and obtain a PMMA / graphene / alloy substrate;

[0101] (3) Using electrochemical hydrogen bubbling or polyethylene terephthalate (PET) and other flexible substrates to directly assist in stripping and reverse fishing, etc. to separate the liquid gallium gold alloy substrate from MoS2, and obtain PMMA / MoS2 composite;

[0102] (4) Transfer the PMMA / MoS2 composite to deionized water, rinse and transfer to the target substrate (SiO2 / Si substrate) and dry; ​

[0103] (5) Use acetone to clean and remove the PMMA transfer medium at 70°C to achieve non-destructive transfer of graphene.

[0104] The morphology and quality of the graphene film were characterized using optical microscopy and Raman spectroscopy, showing that the transferred graphene film has a complete structure, a clean surface, and high quality.

[0105] Example 9

[0106] like Figure 1 As shown, this embodiment uses graphene grown on a copper-nickel alloy foil with a gallium-transfer copper atomic fraction of 50%, and includes the following steps:

[0107] (1) First, a 4% (w / w) polymethyl methacrylate (PMMA) ethyl lactate solution was dropped onto the surface of a copper-nickel alloy foil with graphene grown on it. The solution was then uniformly spin-coated at 3000 rpm for 60 seconds using a spin coater. Afterward, it was dried and cured sequentially on hot plates at 60℃, 90℃, and 120℃ for 10 minutes each, resulting in a PMMA / graphene / copper-nickel alloy foil composite. The PMMA film thickness was 140–200 nm, the graphene layer thickness was 0.34 nm, and the copper-nickel alloy foil thickness was 25 μm.

[0108] (2) Preheat and melt metallic gallium in a glove box, and use a glass syringe to draw gallium droplets into a glass culture dish, which is then placed on a hot plate. Place the PMMA / graphene / copper-nickel alloy foil composite on the gallium droplets in the glass culture dish, with the copper-nickel alloy foil substrate in close contact with the liquid gallium. Adjust the temperature of the hot plate to 150°C and alloy the copper-nickel alloy foil with the liquid gallium, thereby dissolving the copper-nickel alloy foil substrate to obtain the PMMA / graphene / alloy substrate.

[0109] (3) The liquid gallium copper nickel alloy substrate is separated from the graphene by methods such as electrochemical hydrogen generation bubbling or direct assisted peeling and back-fishing of flexible substrates such as polyethylene terephthalate (PET) to obtain PMMA / graphene composite.

[0110] (4) Transfer the PMMA / graphene composite to deionized water, rinse it, transfer it to the target substrate (SiO2 / Si substrate) and dry it;

[0111] (5) Use acetone to clean and remove the PMMA transfer medium at 70°C to achieve non-destructive transfer of graphene.

[0112] The morphology and quality of the graphene film were characterized using optical microscopy and Raman spectroscopy, showing that the transferred graphene film has a complete structure, a clean surface, and high quality.

[0113] Example 10

[0114] As Figure 1 shown, the embodiment adopts gallium-transferred graphene / h-BN vertical heterojunction grown on copper foil, including the following steps:

[0115] (1) First, a 4% by mass poly(methyl methacrylate) (PMMA) ethyl lactate solution is dropped onto the surface of the copper foil on which the graphene / h-BN vertical heterojunction is grown, and a spin coater is used to uniformly spin coat at a speed of 3000 rpm for 60 s, and then the PMMA is cured by drying on a hot stage at 60°C, 90°C and 120°C for 10 min each time, to obtain a PMMA / graphene / h-BN vertical heterojunction / copper foil composite. The thickness of the PMMA film is 140-200 nm, the thickness of the graphene / h-BN vertical heterojunction is about 1.2 nm, and the thickness of the copper foil is 25 μm.

[0116] (2) The metal gallium is preheated and melted in a glove box, and a glass syringe is used to draw gallium liquid drops into a glass culture dish, and the glass culture dish is placed on a hot stage. The PMMA / graphene / h-BN vertical heterojunction / copper foil composite is placed on the gallium liquid drops in the glass culture dish, the copper foil substrate is tightly attached to the liquid gallium, the temperature of the hot stage is adjusted to 150°C, and the copper foil is alloyed with the liquid gallium, so that the copper foil substrate is dissolved away, and a PMMA / graphene / h-BN vertical heterojunction / alloy substrate is obtained.

[0117] (3) The liquid gallium copper alloy substrate is separated from the graphene by using methods such as electrochemical hydrogen production bubbling, flexible substrates such as polyethylene terephthalate (PET), direct auxiliary peeling, and reverse fishing, to obtain a PMMA / graphene / h-BN vertical heterojunction composite;

[0118] (4) The PMMA / graphene / h-BN vertical heterojunction composite is transferred to deionized water, washed, and then transferred to a target substrate (SiO2 / Si substrate) and dried;

[0119] (5) The PMMA transfer medium is removed by washing with acetone at 70°C, so that the graphene / h-BN vertical heterojunction is transferred without damage.

[0120] The morphology and quality of the graphene / h-BN vertical heterojunction film are characterized by optical microscopy and Raman spectroscopy, and it is shown that the graphene / h-BN vertical heterojunction film obtained by transfer has an intact structure, a clean surface and high quality.

[0121] As Figure 2 shown, the MoSi2N4 film obtained in Example 3 is completely transferred.

[0122] As Figure 3 shown, the MoSi2N4 obtained in Example 3 has high quality.

[0123] As shown in Figure 4 Compared with the traditional ammonium persulfate etching method for copper substrate, the MoSi2N4 obtained by the gallium-assisted transfer method in Example 3 has higher quality.

[0124] The above results show that the low-melting-point metal or alloy thereof and the metal substrate with the two-dimensional material grown on the surface are alloyed at a lower temperature, thereby removing the metal substrate and obtaining the two-dimensional material by complete transfer. The low-melting-point metal has a reducing property rather than an oxidizing property, which not only replaces the oxidizing chemical etchant, but also does not cause the oxidizing etching effect and the doping modification effect on the two-dimensional material. In the alloying process at a certain temperature, the organic transfer medium / two-dimensional material is always in an oxygen-free environment, and oxygen cannot cause oxidative damage and doping to the transfer process of the sample. Therefore, the low-melting-point metal or alloy thereof can realize the lossless transfer of the two-dimensional material grown on the metal substrate, which is of great significance to the intrinsic property research of the two-dimensional material and the practical application of the thin film.

Claims

1. A method for non-destructive transfer of two-dimensional materials assisted by a low-melting-point metal, characterized in that, Removing a metal substrate by alloying with a low-melting-point metal instead of an oxidizing chemical etchant, the method includes the following steps: Step 1: Spin-coat an organic transfer medium onto the surface of a metal substrate on which two-dimensional materials have been grown, and then heat and dry to obtain a transfer medium / two-dimensional material / metal substrate composite. Step 2: Place the composite on the surface of a low-melting-point metal, preheat and melt the low-melting-point metal, so that the metal substrate in the composite adheres tightly to the liquid metal and alloys, thereby dissolving the metal substrate; Step 3: Separate the liquid alloy substrate from the two-dimensional material using electrochemical hydrogen generation bubbling or direct assisted peeling and back-fishing method with polyethylene terephthalate flexible substrate to obtain a transfer medium / two-dimensional material composite. Step 4: Transfer the transfer medium / two-dimensional material composite to deionized water, rinse, transfer it to the target substrate, and dry it. Step 5: Use organic solvents to clean and remove the organic transfer medium, thereby achieving non-destructive transfer of two-dimensional materials.

2. The method for non-destructive transfer of two-dimensional materials assisted by low-melting-point metals according to claim 1, characterized in that, Low-melting-point metals include, but are not limited to, elemental gallium, rubidium, cesium, indium, bismuth, tin, and alloys of two or more of them.

3. The method for non-destructive transfer of two-dimensional materials assisted by low-melting-point metals according to claim 1, characterized in that, Organic transfer media include, but are not limited to, polymers or small molecule materials. The polymers are polymethyl methacrylate or polyvinyl alcohol formaldehyde, and the small molecule materials are paraffin or rosin.

4. The method for non-destructive transfer of two-dimensional materials assisted by low-melting-point metals according to claim 1, characterized in that, In step 1, the transferred two-dimensional material is a single crystal or thin film of a two-dimensional material grown on a metal substrate. The metal substrate includes, but is not limited to, gold, silver, copper, iron, nickel, cobalt, platinum, or palladium. The two-dimensional material includes, but is not limited to, one or more of the following heterostructure materials: MoSi2N4, WSi2N4, graphene, hexagonal boron nitride, tungsten disulfide, tungsten diselenide, molybdenum disulfide, molybdenum diselenide, rhenium disulfide, and rhenium diselenide.

5. The method for non-destructive transfer of two-dimensional materials assisted by low-melting-point metals according to claim 1, characterized in that, In step 1, the organic transfer medium is heated above its melting point and spin-coated onto the surface of the metal substrate on which the two-dimensional material is grown at a speed of 1000 to 5000 rpm.

6. The method for non-destructive transfer of two-dimensional materials assisted by low-melting-point metals according to claim 1, characterized in that, Step 2 is performed in an oxygen-free environment, either in a nitrogen-protected glove box or by adding an organic solvent to the surface of the low-melting-point metal for liquid sealing to prevent oxidation of the low-melting-point metal surface.

7. The method for non-destructive transfer of two-dimensional materials assisted by low-melting-point metals according to claim 1, characterized in that, In step 2, the temperature at which the low-melting-point metal or alloy is preheated and melted is above its melting point, between 25°C and 300°C.

8. The method for non-destructive transfer of two-dimensional materials assisted by low-melting-point metals according to claim 1, characterized in that, In step 3, when using the electrochemical hydrogen-generating bubbling method to peel the two-dimensional material from the metal substrate, the liquid metal is first placed on a cold stage to solidify, with the cold stage temperature controlled at -18℃. Electrochemical bubbling is carried out in a NaOH aqueous solution with a molar concentration of 0.5–2M, using a DC power supply in constant current mode, with the current controlled at 100–200mA. When using a flexible polyethylene terephthalate (PET) substrate to assist in direct peeling, the hot stage temperature is first lowered to below 90℃, and the PET film is pasted from the transfer medium side and gently pressed until the two are completely adhered. The hot stage temperature is then increased by 20–40℃, ultimately achieving complete peeling of the transfer medium / two-dimensional material composite from the liquid metal using the PET film. The composite is then placed in deionized water and retrieved using a new PET film.

9. The method for non-destructive transfer of two-dimensional materials assisted by low-melting-point metals according to claim 1, characterized in that, In step 5, an organic solvent is used to dissolve and remove the transfer medium. The organic solvent includes, but is not limited to, one or more of the following: acetone, dichloroethane, petroleum ether, n-hexane, chloroform, carbon disulfide, xylene, and ethanol.

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