A method for preparing a two-dimensional heterojunction structure

Abstract

The present invention discloses a method for preparing a two-dimensional heterojunction structure, and belongs to the technical field of two-dimensional materials. The present invention utilizes the difference in the optimal viscosity temperature of PC and PPC, and drops the two-dimensional heterojunction structure including the upper and lower supporting layers on the PPC film that loses viscosity onto the PC film with strong viscosity in the temperature range of 90°C-110°C, thereby realizing the transfer of the two-dimensional heterojunction structure, and thus completing the preparation of the two-dimensional heterojunction structure. The present invention can avoid the pollution and damage to the two-dimensional material and the supporting layer by the organic matter extraction soaking or high-temperature annealing process existing in the prior art; at the same time, PC and PPC are flexible organic film materials, which can effectively reduce the stress on the two-dimensional material, thereby making the two-dimensional material more uniform.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional materials, and specifically relates to a method for preparing a two-dimensional heterojunction structure. Background Art

[0002] With the success of tape-assisted exfoliation of single-layer graphene, more and more two-dimensional layered materials can be obtained on silicon wafers, such as hexagonal boron nitride (hBN), transition metal dichalcogenides (TMD) and other two-dimensional materials. Experimentally, their quality can be verified by optical microscopy, Raman characterization, atomic force microscopy and other methods.

[0003] Thanks to the ubiquitous van der Waals forces between two-dimensional materials, the technology of dry transfer has flourished. Its main operation is to gradually pick up the two-dimensional material through the PPC or PC film, and finally place it on the silicon wafer for subsequent electrical or optical characterization. Especially for electrical characterization, two graphite gates are often required to control the carrier concentration and electric displacement field strength of the sample. Therefore, it is necessary to perform multi-step transfer operations on the sample to obtain a two-dimensional heterojunction structure with double graphite gates.

[0004] With the continuous enrichment of research systems, there are many specific systems that require the least number of transfer steps to ensure the stability of the system, such as the corner graphene system, rhombohedral graphene system, corner TMD system, etc. Therefore, researchers have invented various methods for preparing substrates, with the aim of obtaining a clean substrate, and then directly transferring the sample two-dimensional material to the substrate after turning it up, reducing the number of transfers of the sample two-dimensional material, thereby reducing the stress on the sample system. The existing methods for preparing substrates require that the substrate be soaked in a solution or annealed at high temperature after the substrate is transferred, and the surface is characterized and cleaned with AFM to remove the PC or PPC film used for transfer, but these methods cause the surface of the substrate in contact with the sample to be damaged by high temperature or chemical reagents, rather than the thin layer of two-dimensional material obtained by fresh cleavage, which affects the interaction between the two-dimensional heterojunction layers. Summary of the invention

[0005] In order to solve the above problems existing in the art, the present invention aims to provide a method for preparing a two-dimensional heterojunction structure.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a two-dimensional heterojunction structure, characterized in that the specific steps include the following:

[0008] 1) A polydimethylsiloxane (PDMS) semi-spherical structure is prepared on a glass slide and covered with a layer of polycarbonate (PC) film;

[0009] 2) In the temperature range of 90°C-120°C, a PDMS semi-spherical structure covered with a PC film is used to sequentially pick up and cleave from a silicon wafer to obtain a support layer and a sample two-dimensional material to form a stack;

[0010] 3) making a polydimethylsiloxane PDMS semi-spherical structure on a glass slide, sticking a layer of highly transparent tape on the PDMS semi-spherical structure, and sticking a polypropylene carbonate PPC film on a silicon wafer to the highest point of the PDMS semi-spherical structure to form a PPC film / highly transparent tape / PDMS semi-spherical structure;

[0011] 4) In a temperature range of 40° C. to 60° C., the PPC film / highly transparent tape / PDMS semi-spherical structure obtained in step 3) is picked up and cleaved from a silicon wafer to obtain a support layer as a substrate;

[0012] 5) placing the substrate obtained in step 4) on the stack obtained in step 2) in a temperature range of 90° C. to 110° C., and obtaining a two-dimensional heterojunction structure including upper and lower support layers on the PC film;

[0013] 6) In a temperature range of 130° C. to 150° C., the two-dimensional heterojunction structure on the PC film obtained in step 5) is transferred to a silicon wafer to complete the preparation of the two-dimensional heterojunction structure.

[0014] Furthermore, the support layer in step 2) and step 4) includes 35-45 nm thick boron nitride, 3-5 nm thick gate graphite and 10-20 nm thick gate boron nitride.

[0015] Further, the steps of preparing the PDMS hemispherical structure in step 1) and step 3) include:

[0016] 1-1) Prepare PDMS solution: Mix PDMS and AB solution in a mass fraction ratio of 9:1, stir thoroughly with a syringe, and then put it into a vacuum tank to evacuate the air bubbles in the PDMS mixture;

[0017] 1-2) Drop the prepared PDMS solution on a glass slide, place it flat and then invert it, place it on a heating table and heat it to obtain a PDMS hemispherical structure.

[0018] Furthermore, the preparation method of the polycarbonate PC film in step 1) is to prepare a PC solution with a mass fraction of 5% to 8% using PC particles and chloroform solution, and flatten and unfold it between two glass slides to obtain a PC film, and then use a puncher to punch a hole in the tape, and stick the tape on the PC film to obtain the PC film in the hole.

[0019] Furthermore, the preparation method of the polypropylene carbonate PPC film in step 3) is to prepare a PPC solution with a mass fraction of 15%-18% using PPC particles and anisole solution, spin-coat it on a clean silicon wafer, and bake it at 85-95°C to obtain a PPC film, then use a puncher to punch a hole in the tape, stick the tape on the PPC film, and obtain the PPC film in the hole.

[0020] Furthermore, in step 5), the PC film is melted in a temperature range of 180°C-200°C.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] 1) The present invention utilizes the difference in the optimal viscosity temperature of PC and PPC, and drops the two-dimensional heterojunction structure on the PPC film that has lost its viscosity onto the PC film with strong viscosity in the temperature range of 90°C-110°C, thereby realizing the transfer of the two-dimensional heterojunction structure and completing the preparation of the two-dimensional heterojunction structure. The present invention avoids the need for organic extraction soaking or high-temperature annealing in the existing substrate manufacturing method, and reduces the contamination and damage to the gate boron nitride in contact with the sample two-dimensional material;

[0023] 2) The present invention avoids the multiple pressurization of the sample two-dimensional material in the traditional transfer method, and instead can encapsulate it between the gate boron nitride with the assistance of high temperature and two softer PC and PPC organic films, which can effectively reduce the stress on the sample and make the sample more uniform. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flow chart of a specific embodiment of the present invention;

[0025] Figure 2 for Figure 1 Legend for the figure;

[0026] Figure 3 Schematic diagram of the operation of an embodiment of the present invention. Specific embodiments

[0027] The present invention will be further described below by way of implementation examples in conjunction with the accompanying drawings, but the scope of the present invention is not limited in any way.

[0028] The method for preparing the two-dimensional heterojunction structure of the present invention is as follows: Figure 1 As shown, the steps include the following:

[0029] 1) A hemispherical structure of polydimethylsiloxane (PDMS) is fabricated on a glass slide and covered with a layer of polycarbonate (PC) film; Fabrication of a hemispherical structure of polydimethylsiloxane (PDMS):

[0030] 1-1) Prepare PDMS solution: Mix PDMS and AB solution in a mass fraction ratio of 9:1, stir thoroughly with a syringe, and place in a vacuum tank for one hour to remove bubbles in the PDMS mixture;

[0031] 1-2) Drop a drop of freshly prepared PDMS solution on a glass slide, place it flat for 1 minute, then invert it on a heating table and heat it for 30 minutes at 120°C to fix the hemispherical PDMS structure;

[0032] 1-3) Preparation of polycarbonate (PC) film: PC solution with a mass fraction of 6% was prepared by using PC particles and chloroform solution, and the solution was flattened and spread between two glass slides to obtain a PC film;

[0033] 1-4) Preparation of transfer template (stamp) combining PC and PDMS:

[0034] Use a 5 mm diameter hole puncher to punch a hole of a specific size on the tape, stick the tape to the PC film on the glass slide, get the PC film in the hole, and stick the PC film to the highest point of the PDMS hemisphere to form a PC / PDMS bond;

[0035] 2) In the temperature range of 90℃-120℃, the PDMS semi-spherical structure covered with PC film is picked up and cleaved from the silicon wafer in sequence to obtain the support layer and the sample two-dimensional material to form a stack:

[0036] In the temperature range of 90°C-120°C, the support layer boron nitride 1 (about 35-45 nm), gate graphite 1 (about 3-5 nm), gate boron nitride 1 (about 10-20 nm), and sample two-dimensional material obtained by cleavage are picked up from the silicon wafer in sequence using PDMS covered with a PC film, and used as a stack (i.e., support layer boron nitride 1-gate graphite 1-gate boron nitride 1-sample two-dimensional material multilayer heterojunction) for standby use;

[0037] 3) A polydimethylsiloxane PDMS semi-spherical structure is made on a glass slide, a layer of highly transparent tape is attached to the PDMS semi-spherical structure, and a polypropylene carbonate PPC film on a silicon wafer is attached to the highest point of the PDMS semi-spherical structure to form a combination of PPC film / highly transparent tape / PDMS semi-spherical structure:

[0038] 3-1) Prepare PDMS solution: Mix PDMS and AB solution in a mass fraction ratio of 9:1, stir thoroughly with a syringe, and place in a vacuum tank for one hour to remove bubbles in the PDMS mixture;

[0039] 3-2) Drop a drop of freshly prepared PDMS solution on a glass slide, place it flat for 1 minute, then invert it on a heating table and heat it for 30 minutes at a temperature of 110-120°C to fix the hemispherical PDMS structure;

[0040] 3-3) Preparation of polypropylene carbonate (PPC) film: PPC particles and anisole solution were used to prepare a 15% PPC solution, which was spin-coated on a clean silicon wafer at 2000 rpm and baked at 90°C for 2 min to obtain a PPC film;

[0041] 3-4) Preparation of transfer template (stamp) combining PPC and PDMS: stick a layer of highly transparent tape on the hemispherical structure of PDMS, and then use a 5 mm diameter puncher to punch holes in the tape, stick the tape to the PPC film on the silicon wafer, obtain the PPC film in the hole, and stick it to the highest point of the hemispherical structure combined with PDMS / highly transparent tape to form a combination of PC / highly transparent tape / PDMS;

[0042] 4) In the temperature range of 40°C-60°C, the PPC film / high transparent tape / PDMS semi-spherical structure obtained in step 3) is picked up and cleaved from the silicon wafer to obtain a support layer as a substrate:

[0043] In a temperature range of 40°C-60°C, the support layer boron nitride 2 (about 35-45 nm), gate graphite 2 (about 3-5 nm), and gate boron nitride 2 (about 10-20 nm) obtained by cleavage are picked up from the silicon wafer using PDMS covered with a PPC film and a high-transparent tape as a substrate (i.e., a support layer boron nitride 2-gate graphite 2-gate boron nitride 2 multilayer heterojunction);

[0044] 5) In a temperature range of 90°C to 110°C, place the substrate obtained in step 4) on the laminate obtained in step 2) as follows: Figure 3 As shown, a two-dimensional heterojunction structure including upper and lower support layers is obtained on the PC film:

[0045] In the temperature range of 90°C-110°C, the substrate on the PPC is dropped onto the stack on the PC to obtain a two-dimensional heterojunction structure of the upper and lower support layers (i.e., a double-layer heterojunction of support layer boron nitride 1-gate graphite 1-gate boron nitride 1-sample two-dimensional material-gate boron nitride 2-gate graphite 2-support layer boron nitride 2);

[0046] 6) In the temperature range of 130°C-150°C, the two-dimensional heterojunction structure on the PC film obtained in step 5) is transferred to the silicon wafer:

[0047] In the temperature range of 130℃-150℃, the two-dimensional heterojunction structure including the upper and lower supporting layers on the PC is transferred to an empty silicon wafer, and the PC film is melted in the temperature range of 180℃-200℃. If a small part of the PC film residue is left on the top, the silicon wafer with the PC film residue and the final two-dimensional heterojunction structure is placed in chloroform and rinsed for 10 minutes to remove the PC residue, thereby realizing the dry transfer of the two-dimensional heterojunction structure of supporting layer boron nitride 1-gate graphite 1-gate boron nitride 1-sample two-dimensional material-gate boron nitride 2-gate graphite 2-support layer boron nitride 2 onto the silicon wafer, and the interfaces of each layer of two-dimensional material are not contaminated by organic matter.

[0048] Finally, it should be noted that the purpose of publishing the embodiments is to help further understand the present invention, but those skilled in the art can understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments, and the scope of protection claimed by the present invention shall be subject to the scope defined in the claims.

Claims

1. A method for preparing a two-dimensional heterojunction structure, characterized in that: The specific steps include the following: 1) Make a polydimethylsiloxane (PDMS) semi-spherical structure on a glass slide and cover it with a layer of polycarbonate (PC) film; 2) In the temperature range of 90℃-120℃, a PDMS semi-spherical structure covered with a PC film is used to pick up and cleave from the silicon wafer in sequence to obtain a support layer and a sample two-dimensional material to form a stack; 3) A polydimethylsiloxane (PDMS) semi-spherical structure is made on a glass slide, a layer of transparent tape is attached to the PDMS semi-spherical structure, and a polypropylene carbonate (PPC) film on a silicon wafer is attached to the highest point of the PDMS semi-spherical structure to form a PPC film / transparent tape / PDMS semi-spherical structure; 4) In a temperature range of 40°C to 60°C, the PPC film / scotch tape / PDMS semi-spherical structure obtained in step 3) is picked up and cleaved from the silicon wafer to obtain a support layer as a substrate; 5) placing the substrate obtained in step 4) on the stack obtained in step 2) in a temperature range of 90°C-110°C, and obtaining a two-dimensional heterojunction structure including upper and lower support layers on the PC film; 6) In the temperature range of 130° C. to 150° C., the two-dimensional heterojunction structure on the PC film obtained in step 5) is transferred to a silicon wafer to complete the preparation of the two-dimensional heterojunction structure.

2. The preparation method according to claim 1, characterized in that The support layer in step 2) and step 4) includes 35-45 nm thick boron nitride, 3-5 nm thick gate graphite and 10-20 nm thick gate boron nitride.

3. The preparation method according to claim 1, characterized in that: The steps for preparing the PDMS hemispherical structure in step 1) and step 3) include: 1-1) Prepare PDMS solution: Mix PDMS and AB solution in a mass fraction ratio of 9:1, stir thoroughly with a syringe, and then put it into a vacuum tank to evacuate the air bubbles in the PDMS mixture; 1-2) Drop the prepared PDMS solution on a glass slide, place it flat and then invert it, place it on a heating table and heat it to obtain a PDMS hemispherical structure.

4. The preparation method according to claim 1, characterized in that: The preparation method of the polycarbonate PC film in step 1) is to prepare a PC solution with a mass fraction of 5% to 8% using PC particles and chloroform solution, and flatten and unfold it between two glass slides to obtain a PC film, and then use a puncher to punch a hole in the tape, and stick the tape on the PC film to obtain the PC film in the hole.

5. The preparation method according to claim 1, characterized in that: In step 3), the preparation method of the polypropylene carbonate PPC film is to prepare a PPC solution with a mass fraction of 15%-18% using PPC particles and anisole solution, spin-coat it on a clean silicon wafer, and bake it at 85-95°C to obtain a PPC film, then use a hole puncher to punch a hole in the tape, stick the tape on the PPC film, and obtain the PPC film in the hole.

6. The preparation method according to claim 1, characterized in that: In step 6), the PC film is melted in a temperature range of 180°C-200°C.

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