CN114920239B - Two-dimensional material transferring or stacking method based on water vapor - Google Patents

Abstract

Embodiments of the present invention disclose a water vapor-based two-dimensional material transfer or stacking method, which includes: treating a substrate with oxygen plasma, generating layered two-dimensional materials on the surface of the pre-treated substrate, and obtaining a prefabricated material. Composite substrate; spin-coat the transfer medium on the surface of the prefabricated composite substrate and then dry it, and cover the surface with support gel to obtain the prefabricated transfer substrate; fumigate the prefabricated transfer substrate in a water vapor environment to obtain the transfer substrate; The pretreated substrate on the transfer substrate is peeled off to obtain the transfer substrate; the transfer substrate is transferred to the target substrate, and after baking, the transfer medium is eluted to complete the transfer of the two-dimensional material. Through the above method, it is possible to transfer multiple types of two-dimensional materials prepared by mechanical cleavage or CVD growth in a simple, efficient and low-pollution manner, and reduce sample contamination caused by wet transfer in scientific research and shield the dangers caused by the use of strong acid/alkaline solutions. sex, thereby reducing scientific research costs and improving scientific research efficiency.

Description

A water vapor-based method for transferring or stacking two-dimensional materials

Technical field

Embodiments of the present invention relate to the technical field of layered material preparation, and specifically relate to a two-dimensional material transfer or stacking method based on water vapor.

Background technique

The field of two-dimensional materials inspired by graphene has become a hot topic today. Two-dimensional materials with nanometer scale show extraordinary physical and chemical properties, show great potential in the research of sensors, detectors, optoelectronic devices, etc., and are of great significance to important frontier technology fields such as circuit electronics and energy storage.

In particular, the stacking and assembly of different two-dimensional materials will produce more novel structures and physical properties. Van der Waals heterojunctions have demonstrated amazing properties in research on superconductivity, topological insulation, and energy valleys. These special structures also have absolute advantages in the fields of electrical, optics, energy harvesting and storage. In recent years, researchers have opened up the research field of corner double-layer two-dimensional materials and found that Moiré fringes can be prepared by changing the rotation angle when stacking two-dimensional materials, thereby affecting the electrical or optoelectronic properties of the materials. Research shows that there is a rare superconducting phenomenon in the "magic angle" three-layer graphene material, which can effectively prove that superconducting behavior originates from the strong interaction between electrons. In addition, properties such as many-body correlation spectral signals and three-quarter filled state ferromagnetism have also been gradually discovered in various "magic angle" structures.

The preparation of two-dimensional van der Waals heterojunctions is often inseparable from the sample transfer and stacking process. Through the transfer of two-dimensional materials, experimental purposes such as the integration of multiple functional substrates, passivation of air-sensitive materials, preparation of corner structures, and multi-dimensional hybrid devices can be achieved. Therefore, from the perspective of basic research, transfer technology is a necessary process for preparing special structures. It plays an irreplaceable role in the study of basic material properties and can help people discover new functional devices by constructing multiple types of structures. Therefore, transfer is an important technical method to study the properties of two-dimensional materials and their hetero/homogeneous structures. The transfer methods of two-dimensional materials can be roughly divided into two methods: wet transfer and dry transfer:

Wet transfer:

(1) Take the wet transfer technology of graphene grown by chemical vapor deposition (CVD) as an example. The process includes spin coating polymethyl methacrylate (PMMA), using ferric chloride (FeCl ₃ ) or ammonium disulfate ((NH ₄ ) ₂ S ₂ O ₈ ) solution to remove copper, baking, acetone removal, and cleaning. Wait for steps. Since the transfer process is long, operational proficiency has a certain impact on the quality of graphene after transfer. In addition, the introduction of FeCl ₃ and other solutions and the incomplete removal of the copper metal substrate have a greater impact on the quality of the transferred graphene film.

(2) Electrochemical transfer of graphene. The graphene/copper foil spin-coated with PMMA is used as the cathode, and the carbon rod is used as the anode. In the electrolytic cell, direct current is used to decompose water, and the bubbles between the graphene and the copper foil are used to separate the PMMA/graphene layer. Finally clean off the PMMA with acetone. During the experiment, the bubbles generated by the cathode of the electrolytic cell will destroy the integrity of the graphene film, and placing carbon rods in the solution and applying electricity will easily introduce impurities into the solution, thereby contaminating the graphene sample.

Dry transfer:

(3) Taking hexagonal boron nitride (h-BN)-assisted dry transfer of graphene as an example. You need to first spin-coat polypropylene carbonate (PPC) on the spare silicon wafer, peel h-BN and graphene on the PPC and silicon wafer, and stick the PPC with Scotch tape. At this time, you need to align the h-BN sample position. , and then adhered to the PDMS on the glass slide to form a transfer frame. Then align and stick the h-BN and the graphene sample below again, heat the sample stage to above the PCC glass transition temperature, and then cool it back to room temperature. At this time, the h-BN will stick to the graphene sample. And based on this premise, it is transferred to the target substrate. If a heterostructure is constructed, it needs to be aligned again. Finally, the PPC film was released by heating and placed in acetone. The secondary transfer process requires high proficiency of the operator and requires multiple target alignments.

(4) Liquid embedding method as an example. This method mainly covers the surface of the sample and substrate with a hydrophobic layer of levorotatory polylactic acid (PLLA), transfers it through the hydrophobicity of PLLA and melts PLLA onto the desired substrate, and finally uses dichloromethane (DCM) to remove PLLA. Although this method is easy to operate, the use of PLLA and DCM solvents increases the experimental cost.

All the above solutions can realize the transfer of two-dimensional materials, but it is undeniable that unnecessary solutions will be introduced during the wet transfer process, which increases the difficulty of transfer and sample contamination, and may even involve strong acids that may cause serious harm to the human body. Strong alkali solution; dry transfer technology often requires the use of new adhesive materials (PPC, PLLA, h-BN, etc.). Although it greatly improves the cleanliness during the sample transfer process, it increases experimental costs and cumbersome operating steps. The wet and dry transfer technologies currently involved need to be improved in terms of cleanliness and operating procedures, and the processing is difficult.

Contents of the invention

To this end, embodiments of the present invention provide a water vapor-based two-dimensional material transfer or stacking method. The transfer process of existing layered materials (such as graphene, MoS ₂ , WSe _{2 ,} etc.) is difficult and dangerous. , serious pollution, low success rate and other shortcomings, realize simple, efficient, low pollution, positionable transfer of various types of two-dimensional materials prepared by mechanical cleavage or CVD growth, and reduce sample contamination and shielding caused by wet transfer in scientific research The dangers brought by strong acid/alkaline solutions can reduce the cost of scientific research and improve the efficiency of scientific research.

In order to achieve the above objects, embodiments of the present invention provide the following technical solutions:

In one aspect of the embodiment of the present invention, a water vapor-based two-dimensional material transfer or stacking method is provided, including:

S100. Treat the substrate with oxygen plasma to obtain a pre-treated substrate;

S200. Generate layered two-dimensional materials on the surface of the pretreated substrate to obtain a prefabricated composite substrate;

S300. Spin-coat transfer medium on the surface of the prefabricated composite substrate and then dry it, and cover the surface of the dried transfer medium with support gel to obtain a prefabricated transfer substrate;

S400. After fumigating the prefabricated transfer base material in a water vapor environment, the transfer base material is obtained;

S500. Peel off the pretreated substrate on the transfer substrate to obtain the transfer substrate;

S600. Transfer the transfer substrate to the target substrate, and after baking, elute the transfer medium to complete the transfer or stacking of the two-dimensional material.

As a preferred embodiment of the present invention, the material of the substrate is selected from one or more of silicon, sapphire and mica.

As a preferred embodiment of the present invention, the layered two-dimensional material is provided by graphite or metal chalcogenide;

Preferably, the chemical formula of the metal chalcogen compound is MX ₂ , wherein M is selected from Mo, W, Sn, Ta, Nb, Pt or Ga, and X is selected from S, Se or Te.

As a preferred embodiment of the present invention, the graphite is highly oriented pyrolytic graphite crystals or natural graphite crystals.

As a preferred embodiment of the present invention, mechanical cleavage or chemical vapor deposition can be used to generate the layered two-dimensional material in step S200.

As a preferred embodiment of the present invention, the transfer medium in step S300 is selected from one or more of polymethyl methacrylate, polystyrene and rosin;

Preferably, the thickness of the spin-coated transfer medium after drying is 200 nm-10 μm.

As a preferred embodiment of the present invention, the temperature of the drying process in step S300 is 100-140°C, and the time is 2-10 minutes.

As a preferred embodiment of the present invention, the transfer medium is selected from polymethyl methacrylate and rosin, and the spin coating process specifically includes:

S301. After spin-coating rosin on the surface of the prefabricated composite substrate, lightly touch the rosin surface with a rough surface, and then dry it under the first temperature condition for 1-2 minutes to obtain the base material prototype;

S302. On the obtained base material embryo, further spin-coat polymethyl methacrylate on the surface of the rosin layer, and then place it in a second temperature condition to dry for 1-9 minutes; wherein,

The temperature value of the first temperature is less than the temperature value of the second temperature;

Preferably, the surface area of the spin-coated rosin in step S301 is smaller than the area of the spin-coated polymethyl methacrylate in step S302, and the spin-coated polymethyl methacrylate forms a circle around the outer edge of the spin-coated rosin. Surround the perimeter.

As a preferred embodiment of the present invention, the supporting gel is polydimethylsiloxane and/or silica gel;

Preferably, the thickness of the support gel is 200 μm-2 mm.

As a preferred version of the present invention, the fumigation time in step S400 is 10-30 minutes;

Preferably, the temperature of the baking process in step S600 is 120-150°C and the time is 1-3 minutes.

The embodiments of the present invention have the following advantages:

1) Based on the use of oxygen plasma to pretreat the substrate surface, it avoids the corrosion operation of the substrate during the conventional transfer process, effectively avoids damage to the surface of the two-dimensional material, and greatly reduces the resulting defects; at the same time, the above Interfacial strain occurs on the surface of the substrate after pretreatment, forming an oxygen-loving interface. On this basis, through the introduction of water vapor, the overall transfer or stacking can be completed more simply, quickly and effectively. And this method can be widely suitable for the transfer of two-dimensional layered materials formed by mechanical cleavage or CVD growth, greatly increasing the scope of application.

2) Based on the selection of the substrate, it can be combined with the supporting gel to achieve overall transparent visibility, making it easier to prepare and accurately position and transfer functional structures such as heterojunctions.

3) This invention is mainly based on the interface changes on the surface of the substrate after oxygen plasma treatment, which has a low impact on the sample itself. Therefore, the obtained crystal quality is higher, which is helpful for studying high-quality two-dimensional material films and their heterostructures. nature.

4) The present invention will provide a more convenient, clean, rapid and pollution-free transfer or stacking method for research on the preparation of special structures from two-dimensional layered materials. It is beneficial to obtain heterojunction structures with high-quality performance and facilitate the research and future development of next-generation multi-functional devices and integrated circuits based on two-dimensional materials.

Description of the drawings

In order to more clearly explain the embodiments of the present invention or the technical solutions in the prior art, the drawings that need to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only exemplary. For those of ordinary skill in the art, other implementation drawings can be obtained based on the extension of the provided drawings without exerting creative efforts.

The structures, proportions, sizes, etc. shown in this specification are only used to coordinate with the contents disclosed in the specification for the understanding and reading of people familiar with this technology. They are not used to limit the conditions under which the invention can be implemented, and therefore do not have any technical Any structural modification, change in proportion or size adjustment shall still fall within the scope of the technical content disclosed in the present invention without affecting the effectiveness and purpose achieved by the present invention. within the scope that can be covered.

Figure 1 is a flow chart of a two-dimensional material transfer or stacking method provided by an embodiment of the present invention;

Figure 2(a) is an optical photograph of the substrate before oxygen plasma treatment provided by the embodiment of the present invention;

Figure 2(b) is an optical photograph of the substrate after oxygen plasma treatment provided by the embodiment of the present invention;

Figure 3(a) is a physical diagram of a substrate for obtaining a large-area single-layer graphene obtained in step (2) in Example 2 of the present invention;

Figure 3(b) is a physical diagram of the graphene-PMMA-PDMS sample obtained in step (3) in Example 2 of the present invention;

Figure 3(c) is a partial enlarged view of PMMA on the graphene-PMMA-PDMS sample obtained in step (3) in Example 2 of the present invention;

Figure 3(d) shows the structure of a single-layer MoS ₂ -single-layer graphene film prepared in Example 2 of the present invention;

Figure 4(a) shows the silver pattern structure covered with graphene film prepared in Example 1 of the present invention;

Figure 4(b) shows the heterostructure of a stack of large-area single-layer Bi2212 and single-layer graphene prepared in Example 3 of the invention;

Figure 4(c) shows the heterostructure of multi-layer WSe ₂ and single-layer graphene stacks prepared in Example 4 of the invention;

Figure 4(d) is a substrate structure with a suspended graphene film prepared in Example 5 of the invention;

Figure 4(e) shows the heterostructure of a thin layer of MoTe ₂ and a single layer of graphene stacked in Example 6 of the invention.

Figure 4(f) shows the heterostructure of thin-layer WSe ₂ -Bi ₂ O ₂ Se stacks prepared in Example 7 of the invention.

Detailed ways

The following specific embodiments are used to illustrate the implementation of the present invention. Persons familiar with this technology can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only part of the embodiments of the present invention. , not all examples. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

The present invention provides a two-dimensional material transfer or stacking method based on water vapor, specifically including:

1. Treat the substrate (i.e. substrate) with oxygen plasma, mechanically cleave or grow the two-dimensional layered material onto the surface of the substrate through CVD to obtain the substrate-layered material;

2. Spin-coat the organic solution on the surface of the substrate-layered material obtained above, and then place it in a constant temperature oven or a hot stage to dry for 2-10 minutes to obtain a substrate-layered material-organic film;

3. Cover the base-layered material-organic film obtained above with the supporting gel, put it into a water container without contacting water, heat it up until steam is generated, and fumigate for 10-30 minutes;

4. Peel off the self-supporting gel layer of the base-layered material-organic film covered with the supporting gel, so that the base and the layered material-organic film are separated to obtain the layered material-organic film-supporting gel;

5. Transfer the layered material-organic film-support gel obtained above to the required substrate (i.e., the target substrate) and bake it again for 1-3 minutes so that the new substrate adheres closely to the sample;

6. Use acetone or acetone vapor to desorb the organic film layer in the new base-layered material-organic film-support gel to obtain the transferred functional structure, which is the new base-layered material.

The type of substrate here can be selected from any material type that can be routinely understood and used by those skilled in the art. For example, in preferred embodiments, silicon, sapphire, mica, etc. can be specifically selected.

In another preferred embodiment, the two-dimensional layered material here can be taken from graphite or metal chalcogenide. Preferably, the graphite here can be selected from highly oriented pyrolytic graphite crystals or natural graphite crystals. Further, when graphite is selected here, the obtained base-layered material is a base-graphene film material. At the same time, the metal chalcogen compound here is further selected as MX ₂ , where M is Mo, W, Sn, Ta, Nb, Pt or Ga, and X is S, Se or Te.

The organic film here is preferably a polymethyl methacrylate film or a polystyrene film, and has a thickness of 200 nanometers to 10 micrometers. In a preferred embodiment, the supporting gel is a polydimethylsiloxane film or a silicone film with a thickness of 200 microns to 2 millimeters.

The specific method for preparing folds of layered materials will be further elaborated below with reference to the accompanying drawings.

A. As shown in Figure 1(a), oxygen plasma treated single polished silicon/silicon oxide (thickness 300nm) is used as the substrate; as shown in Figure 1(b), 3M tape is used to mechanically cleave graphite (graphite here Highly oriented pyrolytic graphite crystals or natural graphite crystals can be selected to be added to the treated substrate surface to obtain a substrate-graphene film material as shown in Figure 1(c);

B. As shown in Figure 1(d), spin-coat PMMA (polymethyl methacrylate) solution on the surface of the substrate-graphene film material obtained in step A, and then place it in a constant temperature oven or a hot stage to dry for 2 -10min, obtain the substrate-graphene film material-PMMA film (the thickness of the PMMA film is no more than 2 μm);

C. Cover the substrate-graphene film material-PMMA film obtained in step B with PDMS (polydimethylsiloxane, and the thickness of the PDMS film is not greater than 500 μm), put it into a water container, without contacting water, and heat it to Steam is generated and fumigation takes 10-30 minutes. Figure 1(e) is a schematic diagram of the fumigation process;

D. Peel off the PDMS layer in step C. As can be seen from Figure 1(f), the substrate is separated from the graphene film material-PMMA film to obtain the graphene film material-PMMA film-PDMS film;

E. Transfer the graphene film material-PMMA film-PDMS film obtained in step D to a new substrate with a pre-prepared silver pattern (BIT letters, silver layer thickness 10nm) and bake it again for 1-3 minutes, Figure 1 (g ) display process diagram;

F. Use acetone or acetone vapor to remove the PMMA film layer in the new substrate-graphene film material-PMMA film-PDMS film in step E. The structural schematic diagram and physical diagram of the transferred material obtained are shown in Figure 1(h). ) and shown in Figure 4(a).

The above operation method uses single polished silicon/silicon oxide after oxygen plasma treatment as the substrate, and uses 3M tape to cleave highly oriented pyrolytic graphite (HOPG) crystals or natural graphite crystals on the surface of the substrate, which can effectively prepare large-area thin films. layer of graphene. The PMMA solution was spin-coated on the surface of the prepared sample, and the PMMA layer was dried on a hot stage or in an oven. In order to support the extremely soft PMMA film layer, we use PDMS as the support layer, which is pasted on top of the PMMA film layer, and then placed in a container filled with water (there is a cushion in the container), so that the sample does not touch the water. , raise the temperature until steam is generated, and fumigate for 10 to 30 minutes to allow the steam to fully enter between the substrate and the graphene film-PMMA. This is because oxygen ions are on the surface of the substrate, causing the substrate and graphene to be non-closely attached, and the presence of oxygen ions makes the substrate very hydrophilic, allowing water molecules to enter between graphene and the substrate to form a separated graphene film - PMMA and the main driving force at the substrate interface. Due to the weakening of the interaction force between the graphene film-PMMA and the substrate, peeling off the PMMA film that is tightly adhered to the support layer PDMS at this time can effectively peel off the graphene film from the substrate surface. The power, oxygen flow, and time of oxygen plasma treatment of the substrate have no obvious impact on the transfer of two-dimensional materials from the substrate. However, it is easier to achieve water molecule insertion and transfer when the oxygen plasma is used for a long time, with high power and a stable amount of oxygen. . At a power range of 40-100mW and a time of 30-360 seconds, the amount of oxygen is stable and the plasma white light is visible. Transfer can be achieved if the above conditions are met, and the substrate after oxygen plasma treatment is easier to achieve large-area cleavage of the sample. PDMS is a thin film layer that plays a supporting and adhesive role. PDMS with a thickness ranging from 200 microns to 2 mm can be used. Other rigid organic films with adhesive properties can also produce similar effects, such as silicone, plastic, etc.

The integrity of the sample during the transfer process is extremely high, and the area is related to the size of the two-dimensional material prepared by the original cleavage. The realization of transfer has no correlation with the number of sample layers. From single-layer graphene to thick-layer graphite, water vapor-assisted quasi-dry transfer can be used, and the device structure prepared by the transfer is of high quality. During the entire process, the sample only contacts PMMA. Organic solvents. At the same time, in order to better facilitate the removal of PMMA, reduce the roughness of the structure surface after transfer or stacking, and further reduce the impact of impurities introduced during the transfer or stacking process, a layer of PMMA can be further spin-coated before spin-coating PMMA. layer of rosin, and perform a drying operation after spin-coating the rosin. Of course, the temperature and time of the drying operation here are smaller than the drying temperature and drying time after spin-coating PMMA, so as to make the subsequent interface here easier. Elute and improve overall cleanliness. For example, in a specific embodiment, the drying temperature after spin-coating rosin can be 95-105°C and the time can be selected to be 1-2 minutes, while the drying temperature after spin-coating PMMA can be 100-140°C and the time can be selected to be 100-140°C. It can be selected to be 2-10 min. Of course, the present invention is not limited to this specific example. Any suitable time and temperature range can be selected, as long as the temperature and time of the rosin drying process are smaller than the temperature and time of the PMMA drying process. Time is enough. Such an arrangement can further effectively achieve the overall drying effect, and at the same time, it can perform a layer-by-layer drying process on the above two spin coatings, thereby achieving targeted segmented adhesion of the two to the substrate, which is better. to facilitate subsequent elution. At the same time, it can be further provided that the surface area of the rosin spin-coated in step S301 is smaller than the area of the polymethylmethacrylate spin-coated in step S302, and the polymethylmethacrylate after spin-coating is on the surface of the spin-coated rosin. The outer edge is formed with a surrounding edge. That is, the polymethyl methacrylate in the center is overlapped on the surface of the rosin, and the polymethyl methacrylate in the periphery is coated on the substrate. This arrangement can avoid the relatively high temperature during the second step of drying. Causes overflow problems such as softening of the rosin layer, and better improves the temperature resistance of the entire preparation process.

The method of the present invention has the following advantages:

(1) It can be seen from the preparation principle that the transfer process is easier and cleaner than other transfer or stacking methods, and the materials involved are all required for the transfer and preparation of traditional two-dimensional materials. This experiment only used conventional transfer solvent, PMMA solvent. Although PMMA solvent can be quickly removed with solvents such as acetone, in the past, using PMMA to transfer samples from silicon oxide substrates required the use of strong acid/alkaline solutions to etch away the silicon oxide layer, which inevitably caused damage to the sample surface and destroyed the two-dimensional Defects occur on the surface of the material. We can solve this problem very well by treating the substrate interface with oxygen plasma. First, oxygen plasma-treated substrates facilitate the cleavage of two-dimensional materials such as graphene. Secondly, as can be seen from Figure 2(a) and (b), the substrate that becomes an oxygen-philic interface will attract water molecules. The introduction of a large number of water molecules can quickly reduce the effect of the two-dimensional material and the substrate, making it easier for conventional organic materials such as PMMA to The transfer solvent carries the 2D material away from the substrate. Using steam transfer is significantly different from wet transfer. In wet transfer, the solution often contains many micro-nano particles that are invisible to the naked eye, which is a fatal problem for high-cleanliness transfer processes. However, the water molecules in the steam contain almost no particulate matter, which can reduce the amount of contaminants at the transfer interface. In general, the entire preparation process of the water vapor-assisted transfer method is simple, rapid, and effective, and the graphene obtained is low-cost and high-quality. It is an environmentally friendly, safe and reliable preparation method. This method has been proven to be widely suitable for the transfer of cleaved or CVD-grown layered materials on oxygen plasma-treated substrates.

(2) This transfer method can obtain a pure transparent medium-two-dimensional material sample and is protected by a supporting gel, which is more convenient for the positioning and transfer of functional structures such as heterojunctions. In the past, when PMMA was used as the transfer medium, most methods relied on wet transfer technology. PMMA and two-dimensional materials were soaked into the solution together and picked up. It was difficult to grasp the transfer position of the sample, making it difficult to obtain heterogeneous samples. structure. Compared with dry transfer technology, our transfer does not require more steps. For example, it is necessary to prepare a boron nitride (h-BN) film and find the position of the transferred sample multiple times (the sample is attached to the boron nitride surface and Transfer the sample to the corresponding location). Based on the above two points, our transfer technology does not require the influence of any solution and does not require multiple alignments to achieve positioning transfer. Overall, through our quasi-dry transfer technology, large areas of 2D materials can be efficiently transferred to achieve clean heterojunction stacking.

(3) The preparation of high-quality heterostructures and functional devices has become the primary prerequisite for high-performance devices. Since defects will have many performance effects on sample testing, high-quality films are of great significance for studying the physical and chemical properties of the material itself. The two-dimensional materials obtained by mechanical cleavage have fewer defects and higher crystal quality. Our technology mainly relies on the substrate after oxygen plasma treatment, which has minimal impact on the sample itself, so the crystal quality obtained is higher, which is helpful for studying the properties of high-quality two-dimensional material films and their heterostructures.

(4) Layered materials grown by CVD often have regular structural characteristics, which is essential for studying the structural characteristics of two-dimensional materials. This method is also suitable for the transfer of CVD-grown two-dimensional materials. It only needs to be grown on the substrate after oxygen plasma treatment, and this technical method can be used.

(5) The present invention will provide a more convenient, clean, rapid and pollution-free transfer method for research on the preparation of special structures from layered materials. It is beneficial to obtain heterojunction structures with high-quality performance and facilitate the research and future development of next-generation multi-functional devices and integrated circuits based on two-dimensional materials.

The preparation method of the present invention will be described below with reference to several specific examples.

Example 1

(1) Use 1×1cm ² silicon/silicon oxide as the substrate, treat the substrate surface with oxygen plasma, the power is 80mW, and the time is 3 minutes.

(2) Use tweezers to pick up the highly oriented pyrolytic graphite (HOPG) crystal purchased from Nanjing Xianfeng Nano Company, adhere it to the surface of the 3M tape, repeatedly cleave it and then attach it to the silicon/oxidation medium in (1) The surface of the silicon substrate is pressed on a hot stage at 110 degrees Celsius, and the graphite is mechanically dissociated during the cooling process, and a large-area single-layer graphene is obtained on the substrate.

(3) Spin-coat PMMA solvent on the surface of the substrate with graphene, dry it and attach PDMS as a support layer, put it into a container with water vapor at 80 degrees Celsius, stay for 20 minutes, take out and uncover the PDMS support layer. The graphene-PMMA-PDMS sample can be obtained.

(4) Attach the graphene-PMMA-PDMS sample obtained in (3) to a pre-prepared substrate with a silver pattern (10nm thick), and heat it at a high temperature of 100 degrees Celsius to facilitate the close adhesion of the graphene to the functional substrate. . Afterwards, place it in acetone vapor for a period of time and peel off the PDMS support layer. Figure 4(a) shows the single-layer graphene film-silver pattern structure prepared in Example 1. As can be seen from Figure 4(a), when PMMA is completely removed by acetone vapor, a silver pattern structure covered with graphene film can be obtained.

Example 2

(1) Use 1×1cm ² silicon/silicon oxide as the substrate, treat the substrate surface with oxygen plasma, the power is 60mW, and the time is 1 minute.

(2) Use tweezers to pick up the highly oriented pyrolytic graphite (HOPG) crystal purchased from Nanjing Xianfeng Nano Company, adhere it to the surface of the 3M tape, repeatedly cleave it and then attach it to the silicon/oxidation medium in (1) The surface of the silicon substrate is pressed on a hot stage at 110 degrees Celsius, and the graphite is mechanically dissociated during the cooling process. As can be seen from Figure 3(a), a large area of single-layer graphene is obtained on the substrate.

(3) Spin-coat PMMA solvent on the surface of the substrate with graphene, dry it and attach PDMS as a support layer, put it into a container with water vapor at 90 degrees Celsius, stay for 30 minutes, take out and uncover the PDMS support layer. As can be seen from Figure 3(b), a graphene-PMMA-PDMS sample is obtained. As can be seen from Figure 3(c), graphene is minimally deformed on the surface of PMMA.

(4) Attach the graphene-PMMA-PDMS sample obtained in (3) to a substrate with a pre-mechanically cleaved MoS ₂ monolayer and heat it at 100 degrees Celsius. As can be seen from Figure 1(i), the graphene closely adhere to the MoS ₂ -substrate. Afterwards, place it in acetone vapor for a period of time and peel off the PDMS support layer. Figure 3(d) shows the structure of a single-layer MoS ₂ -single-layer graphene film prepared in Example 2. As can be seen from Figure 1(j) and Figure 3(d), when PMMA is completely removed by acetone vapor, a heterostructure of single-layer _MoS2 and single-layer graphene stacks can be obtained.

Example 3

(1) Use 1×1cm ² silicon/silicon oxide as the substrate, treat the substrate surface with oxygen plasma, the power is 60mW, and the time is 1 minute.

(2) Use tweezers to pick up the highly oriented pyrolytic graphite (HOPG) crystal purchased from Nanjing Xianfeng Nano Company, adhere it to the surface of the 3M tape, repeatedly cleave it and then attach it to the silicon/oxidation medium in (1) The surface of the silicon substrate is pressed on a hot stage at 110 degrees Celsius, and the graphite is mechanically dissociated during the cooling process, and a large-area single-layer graphene is obtained on the substrate.

(3) Spin-coat PMMA solvent on the surface of the substrate with graphene, dry it and attach PDMS as a support layer, put it into a container with water vapor at 90 degrees Celsius, stay for 30 minutes, take out and uncover the PDMS support layer. The graphene-PMMA-PDMS sample can be obtained.

(4) Attach the graphene-PMMA-PDMS sample obtained in (3) to a substrate with a pre-mechanically cleaved Bi2212 monolayer, and heat it at 60 degrees Celsius to facilitate the close adhesion of graphene to the substrate. Afterwards, place it in acetone vapor for a period of time and peel off the PDMS support layer. Figure 4(b) shows the structure of a single-layer Bi2212-single-layer graphene film prepared in Example 3. As can be seen from Figure 4(b), after the PMMA is completely removed by acetone vapor, a large-area heterostructure of single-layer Bi2212 and single-layer graphene stacks can be obtained.

Example 4

(1) Use 1×1cm2 silicon/silicon oxide as the substrate, treat the substrate surface with oxygen plasma, the power is 80mW, and the time is 3 minutes.

(2) Use tweezers to pick up the highly oriented pyrolytic graphite (HOPG) crystal purchased from Nanjing Xianfeng Nano Company, adhere it to the surface of the 3M tape, repeatedly cleave it and then attach it to the silicon/oxidation medium in (1) The surface of the silicon substrate is pressed on a hot stage at 115 degrees Celsius, and the graphite is mechanically dissociated during the cooling process, and a large-area single-layer graphene is obtained on the substrate.

(3) Spin-coat PMMA solvent on the surface of the substrate with graphene, dry it and attach PDMS as a support layer, put it into a container with water vapor at 90 degrees Celsius, stay for 10 minutes, take out and uncover the PDMS support layer. The graphene-PMMA-PDMS sample can be obtained.

(4) Attach the graphene-PMMA-PDMS sample obtained in (3) to a substrate with pre-mechanically cleaved WSe ₂ multilayers, and heat it at 100 degrees Celsius to facilitate the close attachment of graphene to the substrate. Afterwards, place it in acetone vapor for a period of time and peel off the PDMS support layer. Figure 4(c) shows the structure of the multi-layer WSe ₂ -single-layer graphene film prepared in Example 4. As can be seen from Figure 4(c), when PMMA is completely removed by acetone vapor, a heterostructure of multi-layer _WSe2 and single-layer graphene stacks can be obtained.

Example 5

(1) Use 1×1cm ² silicon/silicon oxide as the substrate, treat the substrate surface with oxygen plasma, the power is 100mW, and the time is 2 minutes.

(2) Use tweezers to pick up the highly oriented pyrolytic graphite (HOPG) crystal purchased from Nanjing Xianfeng Nano Company, adhere it to the surface of the 3M tape, repeatedly cleave it and then attach it to the silicon/oxidation medium in (1) The surface of the silicon substrate is pressed on a hot stage at 110 degrees Celsius, and the graphite is mechanically dissociated during the cooling process, and a large-area thin layer of graphene is obtained on the substrate.

(3) Spin-coat PMMA solvent on the surface of the substrate with a thin layer of graphene, dry it and attach PDMS as a support layer, put it into a container with water vapor at 90 degrees Celsius, stay for 10 minutes, take out and uncover the PDMS support layer, the graphene-PMMA-PDMS sample can be obtained.

(4) Attach the graphene-PMMA-PDMS sample obtained in (3) to the partially etched grooved substrate prepared in advance, and heat it at a high temperature of 70 degrees Celsius to facilitate the close attachment of the graphene to the substrate. Afterwards, place it in acetone vapor for a period of time and peel off the PDMS support layer. Figure 4(d) shows the suspended thin-layer graphene film structure prepared in Example 5. As can be seen from Figure 4(d), after the PMMA is completely removed by acetone vapor, a base structure with a suspended graphene film can be obtained.

Example 6

(1) Use 1×1cm ² silicon/silicon oxide as the substrate, treat the substrate surface with oxygen plasma, the power is 100mW, and the time is 30 seconds.

(2) Use tweezers to pick up the MoTe ₂ crystal purchased from hq-graphene company, adhere it to the surface of the silica gel film, and use multiple PDMS films of the same size to repeatedly cleave and attach it to the silicon/oxidation interface in (1) The surface of the silicon substrate was pressed on a hot stage at 110 degrees Celsius, and the graphite was mechanically dissociated during the cooling process, that is, a thin layer of MoTe ₂ was obtained on the substrate.

(3) Spin-coat PMMA solvent on the surface of the substrate with a thin layer of MoTe ₂ , dry it and attach PDMS as a support layer, put it into a container with water vapor at 90 degrees Celsius, stay for 20 minutes, take out and uncover the PDMS support layer, a thin-layer MoTe ₂ -PMMA-PDMS sample can be obtained.

(4) Attach the thin-layer MoTe ₂ -PMMA-PDMS sample obtained in (3) to a substrate pre-mechanically cleaved with single graphene and evaporated with gold electrodes, and heat it at 100 degrees Celsius to facilitate the thin-layer MoTe ₂ and The substrate - a single layer of graphene adheres closely. Afterwards, place it in acetone vapor for a period of time and peel off the PDMS support layer. Figure 4(e) shows the thin-layer MoTe ₂ -single-layer graphene heterostructure prepared in Example 6. As can be seen from Figure 4(e), after the PMMA is completely removed by acetone vapor, a heterostructure of a thin layer of MoTe ₂ and a single layer of graphene stack can be obtained.

Example 7

(1) Use 3×5cm ² silicon/silicon oxide as the substrate, and treat the substrate surface with oxygen plasma with a power of 50mW and a time of 200 seconds.

(2) Place a quartz boat upstream of the tube furnace, and place weighed high-purity sulfur powder in the boat. Use a ceramic boat to place WO _2.9 powder as the precursor in the high-temperature area, and place it upside down above the boat (1) In the substrate, the flow rate is controlled at 80 sccm, the growth temperature is 850 degrees, and the high temperature is maintained for 40 minutes. Finally, CVD-grown _WSe2 triangular crystals were obtained on the substrate.

(3) Spin-coat PMMA solvent on the surface of the substrate with a thin layer of CVD-grown _WSe2 , dry it and attach PDMS as a support layer, put it into a container with water vapor at 90 degrees Celsius, stay for 15 minutes, take it out and uncover it By opening the PDMS support layer, a thin layer WSe ₂ -PMMA-PDMS sample can be obtained.

(4) Attach the thin-layer WSe ₂ -PMMA-PDMS sample obtained in (3) to the substrate to which Bi ₂ O ₂ Se has been transferred in advance, and heat it at 80 degrees Celsius to facilitate the connection between the thin layer WSe ₂ and the substrate-Bi ₂ O ₂ Se adheres closely. Afterwards, place it in acetone vapor for a period of time and peel off the PDMS support layer. Figure 4(f) shows the thin-layer WSe ₂ -Bi ₂ O ₂ Se heterostructure prepared in Example 7. As can be seen from Figure 4(f), when PMMA is completely removed by acetone vapor, a heterostructure of thin-layer WSe ₂ -Bi ₂ O ₂ Se stacks can be obtained.

Example 8

Prepare according to the preparation method of Example 1. The difference is that in step (3), the spin-coating PMMA solvent is adjusted to spin-coating rosin and PMMA solvent in sequence, and drying for 1 minute after spin-coating the rosin to obtain a graphene film. silver graphic structure. Compared with Example 1, the surface roughness of the transferred sample is lower.

Although the present invention has been described in detail with general descriptions and specific examples above, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims (15)

1. A two-dimensional material transfer or stacking method based on water vapor, characterized by including: S100. Treat the substrate with oxygen plasma to obtain a pre-treated substrate; S200. Generate layered two-dimensional materials on the surface of the pretreated substrate to obtain a prefabricated composite substrate; S300. Spin-coat transfer medium on the surface of the prefabricated composite substrate and then dry it, and cover the surface of the dried transfer medium with support gel to obtain a prefabricated transfer substrate; S400. After fumigating the prefabricated transfer base material in a water vapor environment, the transfer base material is obtained; S500. Peel off the pretreated substrate on the transfer substrate to obtain the transfer substrate; S600. Transfer the transfer substrate to the target substrate, and after baking, elute the transfer medium to complete the transfer or stacking of the two-dimensional material. 2. A two-dimensional material transfer or stacking method based on water vapor according to claim 1, characterized in that the material of the substrate is selected from one or more of silicon, sapphire and mica. 3. A water vapor-based two-dimensional material transfer or stacking method according to claim 1 or 2, characterized in that the layered two-dimensional material is provided by graphite or metal chalcogenide. 4. A two-dimensional material transfer or stacking method based on water vapor according to claim 3, characterized in that the chemical formula of the metal chalcogenide is MX ₂ , wherein M is selected from Mo, W, Sn , Ta, Nb, Pt or Ga, X is selected from S, Se or Te. 5. A two-dimensional material transfer or stacking method based on water vapor according to claim 3, characterized in that the graphite is a highly oriented pyrolytic graphite crystal or a natural graphite crystal. 6. A water vapor-based two-dimensional material transfer or stacking method according to claim 1 or 2, characterized in that the method of generating layered two-dimensional materials in step S200 can adopt mechanical cleavage or chemical vapor deposition. . 7. A two-dimensional material transfer or stacking method based on water vapor according to claim 1 or 2, characterized in that the transfer medium in step S300 is selected from polymethylmethacrylate, polystyrene and one or more of rosin. 8. A two-dimensional material transfer or stacking method based on water vapor according to claim 7, characterized in that the thickness of the spin-coated transfer medium after drying is 200 nm-10 μm. 9. A two-dimensional material transfer or stacking method based on water vapor according to claim 7, characterized in that the temperature of the drying process in step S300 is 100-140°C and the time is 2-10 minutes. 10. A two-dimensional material transfer or stacking method based on water vapor according to claim 9, characterized in that the transfer medium is selected from polymethyl methacrylate and rosin, and the spin coating process specifically includes: S301. After spin-coating rosin on the surface of the prefabricated composite substrate, lightly touch the rosin surface with a rough surface, and then dry it under the first temperature condition for 1-2 minutes to obtain the base material prototype; S302. On the obtained base material embryo, further spin-coat polymethyl methacrylate on the surface of the rosin layer, and then place it in a second temperature condition to dry for 1-9 minutes; wherein, The temperature value of the first temperature is smaller than the temperature value of the second temperature. 11. A two-dimensional material transfer or stacking method based on water vapor according to claim 10, characterized in that the surface area of the rosin spin-coated in step S301 is smaller than the polymethylmethacrylate spin-coated in step S302. area, and the spin-coated polymethylmethacrylate forms a circle around the outer edge of the spin-coated rosin. 12. A two-dimensional material transfer or stacking method based on water vapor according to claim 1 or 2, characterized in that the supporting gel is polydimethylsiloxane and/or silica gel. 13. A two-dimensional material transfer or stacking method based on water vapor according to claim 12, characterized in that the thickness of the support gel is 200 μm-2mm. 14. A water vapor-based two-dimensional material transfer or stacking method according to claim 1 or 2, characterized in that the fumigation time in step S400 is 10-30 minutes. 15. A two-dimensional material transfer or stacking method based on water vapor according to claim 14, characterized in that the temperature of the baking process in step S600 is 120-150°C and the time is 1-3 minutes.