A two-dimensional material heterojunction device and a preparation method thereof

Abstract

The application relates to a two-dimensional material heterojunction device and a preparation method thereof, and belongs to the field of two-dimensional materials. The preparation method processes an embedding electrode after etching a substrate by a reactive ion etching machine, guarantees that the electrode is basically consistent with the substrate in height, effectively improves surface flatness, is favorable for avoiding rupture of a heterojunction structure when a multilayer heterojunction structure is prepared, is favorable for forming a heterojunction structure with more layers, and greatly improves the success rate and device quality of the multilayer heterojunction device. The preparation method also controls a fitting speed in a dry transfer process by thermal expansion and cold contraction to reduce damage to materials in the fitting process, and greatly improves the success rate and device quality of the multilayer heterojunction device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of two-dimensional materials, in particular to a method for preparing a high-quality two-dimensional material heterojunction device based on electrode embedding. BACKGROUND

[0002] Two-dimensional materials can be easily cleaved into monolayers due to the van der Waals force between layers, and van der Waals heterojunction devices can be prepared by stacking different materials. Such devices have excellent physical and chemical properties and have great application prospects in new field effect transistors, optoelectronics, energy storage, and flexible electronic devices. The preparation of such devices requires special transfer methods, generally wet transfer and dry transfer. Since wet transfer contaminates two-dimensional materials and is not suitable for water and oxygen sensitive materials such as transition metal dichalcogenides (TMDS), black phosphorus, and cadmium iodide, device preparation techniques based on dry transfer are being developed.

[0003] For van der Waals heterojunction devices, traditional electrode preparation methods have many drawbacks. If the electrode is prepared after dry transfer, the two-dimensional material will be exposed to air during the process, which will oxidize and deteriorate, affecting the quality of the device. Even if special means are used to isolate water and oxygen, the electrode deposited by evaporation will destroy the contact interface, which will greatly affect the performance of thin film two-dimensional materials. At the same time, due to the electrode above the two-dimensional material, this structure cannot be prepared with a top gate, and a field effect transistor based on a van der Waals heterojunction device cannot be prepared. On the other hand, if the electrode is prepared on the silicon substrate (substrate or base) in advance before transferring the two-dimensional material, the thickness of the electrode generally needs to be greater than 30 nm due to the mechanical strength requirement. For the target device, the thickness of the two-dimensional material used is generally less than 5 nm, so there is a relatively large height difference between the electrode and the substrate (base). After transfer, the material on the surface of the electrode will be uneven and even broken. On the one hand, this situation will greatly affect the success rate of van der Waals heterojunction device preparation, on the other hand, it will also reduce the interlayer bonding quality of van der Waals heterojunction, and further affect the device performance in electrical testing.

[0004] Therefore, it is urgent to find a method for preparing a two-dimensional material heterojunction device with good integrity, high success rate, and multiple layers. SUMMARY

[0005] To solve the above problems, the present application provides a two-dimensional material heterojunction device and a preparation method thereof.

[0006] In a first aspect, the present application provides a method for preparing a two-dimensional material heterojunction device.

[0007] A method for preparing a two-dimensional material heterojunction device, comprising:

[0008] (I) dissociating a two-dimensional material;

[0009] (II) embedding an electrode into a substrate: spin-coating an electron beam resist on the substrate, baking, exposing a pre-designed electrode shape using electron beam lithography, developing, etching the substrate in a reactive ion etching machine, and finally, evaporating the electrode and removing the resist to obtain a substrate embedded with an electrode;

[0010] (III) transferring the dissociated two-dimensional material onto the substrate embedded with the electrode;

[0011] (IV) repeating steps (I) and (III) with at least one same or different two-dimensional material to form a multi-layer heterojunction structure, and obtaining a two-dimensional material heterojunction device;

[0012] The steps (I) and (II) can be performed in any order.

[0013] The present application embeds the evaporated electrode into the substrate etched by the reactive ion etching machine, ensures that the electrode and the substrate are substantially the same in height, effectively improves the surface flatness, forms a super-flat ohmic contact interface between the electrode and the two-dimensional material, is conducive to avoiding the breakage of the two-dimensional material, greatly improves the integrity of the heterojunction structure, and greatly improves the success rate and device quality of the multi-layer van der Waals heterojunction device prepared by using water-oxygen sensitive materials.

[0014] The etching depth can be 20-100 nm below the substrate surface; the thickness of the electrode can be 21-125 nm; and the electrode is 1-25 nm higher than the substrate surface.

[0015] In some embodiments, the step (IV) can be repeating step (III) with at least one different two-dimensional material to form a multi-layer heterojunction structure, and obtaining a two-dimensional material heterojunction device. In some embodiments, the step (IV) is repeating step (III) with one or two different two-dimensional materials to form a multi-layer heterojunction structure, and obtaining a two-dimensional material heterojunction device.

[0016] The step (III) can include transferring the dissociated two-dimensional material to a PDMS surface, placing the PDMS with the two-dimensional material close to the electrode, heating to expand the PDMS and contact the substrate, turning off the heating, cooling the PDMS, and removing the PDMS. The two-dimensional material is transferred by heating to expand the PDMS, and the PDMS loses adhesion under high temperature conditions, which is conducive to transferring the two-dimensional material to the substrate. Then, by cooling, the PDMS shrinks away from the substrate, realizing complete transfer of the two-dimensional material, and greatly improving the success rate and device quality of the multi-layer van der Waals heterojunction device prepared by using water-oxygen sensitive materials.

[0017] The multilayer heterojunction structure in step (IV) can include a 2-4 layer heterojunction structure. In some embodiments, the multilayer heterojunction structure in step (IV) includes a 2, 3, or 4 layer heterojunction structure.

[0018] The bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 10-500 μm between the two-dimensional material and the electrode. In some embodiments, the bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 50-400 μm between the two-dimensional material and the electrode. In some embodiments, the bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 50-300 μm between the two-dimensional material and the electrode. In some embodiments, the bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 50-200 μm between the two-dimensional material and the electrode. In some embodiments, the bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 50-200 μm between the two-dimensional material and the electrode. In some embodiments, the bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 100-200 μm between the two-dimensional material and the electrode. In some embodiments, the bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 100-200 μm between the two-dimensional material and the electrode.

[0019] The bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 10-500 μm between the two-dimensional material and the electrode. In some embodiments, the bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 50-400 μm between the two-dimensional material and the electrode. In some embodiments, the bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 50-300 μm between the two-dimensional material and the electrode. In some embodiments, the bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 50-200 μm between the two-dimensional material and the electrode. In some embodiments, the bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 50-200 μm between the two-dimensional material and the electrode. In some embodiments, the bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 100-200 μm between the two-dimensional material and the electrode. In some embodiments, the bringing the PDMS with the two-dimensional material close to the electrode can be bringing the PDMS with the two-dimensional material close to the electrode to a distance of 100-200 μm between the two-dimensional material and the electrode.

[0020] The thickness of the PDMS can be 500-2000 μm. In some embodiments, the thickness of the PDMS is 800-1500 μm. In some embodiments, the thickness of the PDMS is 800-1200 μm. In some embodiments, the thickness of the PDMS is 900-1100 μm.

[0021] The heating can be heating to 130-150°C. Based on PDMS with a thickness of 1000 pm, the expansion rate of the PDMS gradually decreases from 20 pm / °C to 1-2 pm / °C during gradual heating of the PDMS from 90°C to 150°C. After a certain distance between the PDMS and the electrode, the PDMS is heated to 130-150°C for expansion and bonding. The certain distance consumes the higher expansion of the PDMS at 90-130°C, and fully utilizes the low expansion of the PDMS at 130-150°C, so that the sample can be bonded very slowly, which is beneficial to improve the integrity of the two-dimensional material heterojunction.

[0022] The heating can be heating at a rate of 1-4°C / s. In some embodiments, the heating is at a rate of 1-3°C / s. In some embodiments, the heating is at a rate of 2-4°C / s. In some embodiments, the heating is at a rate of 1°C / s, 2°C / s, 3°C / s or 4°C / s.

[0023] The cooling is cooling to a temperature at which the PDMS detaches from the substrate or cooling to 50-70°C.

[0024] The two-dimensional material can include at least one selected from transition metal chalcogenide, graphene, boron nitride, black phosphorus and chromium triiodide.

[0025] The transition metal chalcogenide includes at least one selected from molybdenum disulfide, molybdenum ditelluride, tungsten ditelluride, tungsten diselenide, niobium diselenide and indium selenide.

[0026] The substrate can include at least one selected from silicon dioxide, silicon wafer with a surface layer containing silicon dioxide, silicon wafer, mica, sapphire or flexible material. In some embodiments, the substrate is silicon dioxide, silicon wafer with a surface layer containing silicon dioxide, silicon wafer, mica, sapphire or flexible material.

[0027] The flexible material includes at least one selected from polyimide, polyvinyl alcohol, polyester and polyethylene terephthalate.

[0028] The step (I) can include using a mechanical exfoliation method for exfoliation.

[0029] The step (I) can include: using a tape to stick the two-dimensional material, then using a new tape to stick with the tape with the two-dimensional material and tear off, and repeating 3-4 times of using a new tape to stick with the tape with the two-dimensional material and tear off, to obtain a tape containing single-layer or few-layer two-dimensional material.

[0030] The transferring of the exfoliated two-dimensional material to the surface of the PDMS can include using the tape containing single-layer or few-layer two-dimensional material to stick with the PDMS and tear off.

[0031] The electron beam photoresist may include a material selected from polymethyl methacrylate (PMMA).

[0032] The developer may include a mixed solution selected from methyl isobutyl ketone and isopropyl alcohol.

[0033] The volume ratio of the methyl isobutyl ketone and isopropyl alcohol can be 9:1-1:9. In some embodiments, the volume ratio of the methyl isobutyl ketone and isopropyl alcohol is 6:1-1:6. In some embodiments, the volume ratio of the methyl isobutyl ketone and isopropyl alcohol is 3:1-1:6. In some embodiments, the volume ratio of the methyl isobutyl ketone and isopropyl alcohol is 1:1-1:6. In some embodiments, the volume ratio of the methyl isobutyl ketone and isopropyl alcohol is 1:1-1:4. In some embodiments, the volume ratio of the methyl isobutyl ketone and isopropyl alcohol is 1:1-1:3. In some embodiments, the volume ratio of the methyl isobutyl ketone and isopropyl alcohol is 1:3.

[0034] The etching may be performed using trifluoromethane gas.

[0035] The step (II) may include, after etching the substrate in a reactive ion etcher and before evaporating the electrode, cleaning with at least one solvent selected from water, acetone, and isopropanol. In some embodiments, the step (II) may include, after etching the substrate in a reactive ion etcher and before evaporating the electrode, ultrasonic cleaning with at least one solvent selected from water, acetone, and isopropanol. In some embodiments, the step (II) may include, after etching the substrate in a reactive ion etcher and before evaporating the electrode, ultrasonic cleaning with at least one solvent selected from water, acetone, and isopropanol for 1 minute to 15 minutes respectively. In some embodiments, the step (II) may include, after etching the substrate in a reactive ion etcher and before evaporating the electrode, ultrasonic cleaning with water, acetone, and isopropanol for 1 minute to 15 minutes respectively.

[0036] The degumming may include degumming by soaking in acetone; or the degumming may include degumming by soaking in acetone and then cleaning with isopropyl alcohol.

[0037] The method may further include performing plasma cleaning with hydrogen, argon or a mixture thereof after step (III).

[0038] In the mixed gas of hydrogen and argon, the volume ratio of hydrogen to argon is 100:1-1:100. In some embodiments, in the mixed gas of hydrogen and argon, the volume ratio of hydrogen to argon is 50:1-1:50. In some embodiments, in the mixed gas of hydrogen and argon, the volume ratio of hydrogen to argon is 20:1-1:20. In some embodiments, in the mixed gas of hydrogen and argon, the volume ratio of hydrogen to argon is 10:1-1:10. In some embodiments, in the mixed gas of hydrogen and argon, the volume ratio of hydrogen to argon is 5:1-1:5.

[0039] The plasma cleaning time may be 20s-120s. In some embodiments, the plasma cleaning time may be 30s-100s. In some embodiments, the plasma cleaning time may be 30s-60s.

[0040] After step (IV), the two-dimensional material heterojunction device can be placed in a vacuum to remove air from the interlayer. Placing the two-dimensional material heterojunction device in a vacuum facilitates the removal of air from the interlayer between the two-dimensional material and the electrode and substrate, and from the interlayer between the two-dimensional materials themselves. This helps prevent oxidation of the two-dimensional material by the interlayer air, improves their bonding strength, and enhances electrical test performance.

[0041] The time of being placed under vacuum condition can be 1-3 hours.In certain embodiments, the time of being placed under vacuum condition is 1 hour, 2 hours or 3 hours.

[0042] Spin coating the substrate with the electron beam photoresist may include evenly spreading the electron beam photoresist on the substrate using a desktop spin coater at a rotation speed of 3000 rpm-6000 rpm for 1 minute-2 minutes.

[0043] The baking temperature may be 120°C-180°C.

[0044] The baking time can be 1 minute to 2 minutes.

[0045] The steps (I) and / or (III) are carried out in a glove box.

[0046] In a second aspect, the present invention provides a two-dimensional material heterojunction device prepared according to the method described in the first aspect.

[0047] A two-dimensional material heterojunction device prepared according to the method described in the first aspect.

[0048] Beneficial effects

[0049] Compared with the prior art, the present invention has at least one of the following beneficial technical effects:

[0050] (1) The application embeds the evaporated electrode into the substrate after etching by a reactive ion etching machine (trifluoromethane), ensures that the electrode and the substrate are basically consistent in height, thereby effectively improving the surface flatness, forming a super-flat ohmic contact interface between the electrode and the two-dimensional material, which is conducive to avoiding the rupture of the heterojunction structure when preparing a multi-layer heterojunction structure, conducive to forming a heterojunction structure with more layers, and can form a morphologically complete heterojunction structure with at least 2 layers, thereby greatly improving the success rate and device quality of the multi-layer van der Waals heterojunction device.

[0051] (2) The application also improves the dry transfer technology of two-dimensional materials. The fitting speed in the dry transfer process is controlled by thermal expansion and cold contraction to reduce the damage to the material during the fitting process. The PDMS is expanded to transfer the two-dimensional material by heating, and the PDMS loses adhesion under high temperature conditions, which is conducive to transferring the two-dimensional material to the substrate. Then, the PDMS is cooled to shrink away from the substrate, realizing the complete transfer of the two-dimensional material, and greatly improving the success rate and device quality of the multi-layer van der Waals heterojunction device prepared by using water-oxygen sensitive materials.

[0052] (3) When transferring the two-dimensional material to the substrate, the heating speed is 1-4℃ / s, which is conducive to improving the integrity of the two-dimensional material heterojunction structure and avoiding the rupture of the two-dimensional material. When the heating speed is ≥5℃ / s, the heating speed is too fast, which is easy to cause the rupture of the two-dimensional material.

[0053] (4) When transferring the two-dimensional material to the substrate, the temperature is heated to 130-150℃ for transfer. Based on the PDMS with a thickness of 1000μm, the expansion rate of the PDMS gradually decreases from 20μm / ℃ to 1-2μm / ℃ in the process of gradually heating from 90℃ to 150℃. After a certain distance between the PDMS and the electrode, the temperature is heated to 130-150℃ for expansion and fitting. The certain distance consumes the high expansion property of the PDMS at 90-130℃, and fully utilizes the low expansion property of the PDMS at 130-150℃, so that the sample can be very slowly fitted, which is conducive to improving the integrity of the two-dimensional material heterojunction structure and avoiding the rupture of the two-dimensional material.

[0054] (5) The two-dimensional material heterojunction device is placed in a vacuum condition to remove the air in the interlayer. Placing the two-dimensional material heterojunction device in a vacuum condition is conducive to removing the air in the interlayer between the two-dimensional material and the electrode and the substrate, and between the two-dimensional materials, which is conducive to avoiding the oxidation of the two-dimensional material by the air in the interlayer, improving their bonding force, and improving the electrical test performance. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 The microscope magnified image of the heterojunction structure obtained in Example 1.

[0056] Figure 2 This is a magnified microscope image of the heterojunction structure obtained in Example 2.

[0057] Figure 3 This is a magnified microscope image of the heterojunction structure obtained in Example 3.

[0058] Figure 4 This is a magnified microscope image of the heterojunction structure obtained in Example 4.

[0059] Figure 5 This is a magnified microscope image of the heterojunction structure obtained in Example 5.

[0060] Figure 6 This is a magnified microscope image of the heterojunction structure obtained in Example 6.

[0061] Definition of terms:

[0062] In the foregoing text of the present invention, all numerical values ​​disclosed herein are approximate, regardless of whether the word "about" or "approximately" is used. Based on the disclosed numbers, the value of each numerical value may vary by less than ±10% or by a reasonable difference deemed by a person skilled in the art, such as ±1%, ±2%, ±3%, ±4%, or ±5%.

[0063] The term "PDMS" means polydimethylsiloxane.

[0064] The term "PMMA" means polymethyl methacrylate.

[0065] The term "and / or" should be understood to mean any one of the options or a combination of any two or more of the options.

[0066] The term "multi-layer" means at least two layers or more.

[0067] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction. DETAILED DESCRIPTION

[0068] In order to enable those skilled in the art to better understand the technical solutions of the present invention, some non-limiting embodiments are further disclosed below to further illustrate the present invention in detail.

[0069] The reagents used in the present invention can be purchased from the market or prepared by the method described in the present invention.

[0070] In the present invention, "sccm" means standard milliliter per minute; "s" means second; "nm" means nanometer; "μm" means micrometer; "mm" means millimeter; "rpm" means revolutions per minute; and "°C / s" means degree Celsius per second.

[0071] Reagents and consumables:

[0072] PDMS polydimethylsiloxane film (MKNANO, approximately 1000 μm thick), blue tape (USI, ULTRONSYSTEMS, INC.), acetone, methanol, and isopropyl alcohol (purchased from Alfa Group), silicon wafer. PMMA 950A4 adhesive, a mixture of methyl isobutyl ketone and isopropyl alcohol (volume ratio 1:3) (purchased from MicroChem);

[0073] instrument:

[0074] Glove box, optical microscope, two-dimensional material transfer platform, plasma cleaner, desktop coater, electron beam exposure system, electron beam evaporator.

[0075] Example 1: Preparation of a Two-Dimensional Material Heterojunction Device (Three-Layer Boron Nitride-NbSe2-Tungsten Ditelluride Heterojunction)

[0076] (1) Cut a silicon wafer (Si) with 300nm of silicon dioxide (SiO2) on the surface into 5mm × 5mm pieces. Use PMMA950A4 glue and evenly spread the glue on the silicon wafer using a desktop glue spreader at 4000rpm for 1 minute. Then bake on a hot plate at 120℃ for 1 minute.

[0077] (2) Expose the pre-designed electrode pattern on an electron beam exposure system and develop it for 1 minute using a mixture of methyl isobutyl ketone and isopropyl alcohol (volume ratio of 1:3). Then, use a reactive ion etcher (RIE) to etch 60nm of silicon dioxide using trifluoromethane (CHF3) gas. Next, clean the processed silicon wafer by ultrasonication in water, acetone, and isopropyl alcohol for 10 minutes each. Then, use an electron beam coating machine to coat a 65nm gold film as an electrode. After removal, soak in acetone for half an hour to remove the glue, and finally rinse with isopropyl alcohol.

[0078] (3) In the glove box, the two-dimensional material is dissociated from the self-grown WTe2 (tungsten telluride) crystal, which is uniformly laid on the blue tape. Then, another piece of blue tape is attached to the two-dimensional material, and the tape is torn to thin the two-dimensional material. Repeat 3-4 times with new tape and the tape with two-dimensional material. Finally, tear the tape to obtain a tape containing single-layer or few-layer two-dimensional material.

[0079] (4) After cutting the PDMS to the appropriate size, remove the outer protective film, and attach the soft film to the two-dimensional material area of the tape containing single-layer or few-layer two-dimensional material. Then, gently attach the PDMS to the tape to exclude the gas in the middle. After about 5 minutes, use tweezers to quickly tear the PMDS from the tape. Place it on a glass slide and use an optical microscope to find the appropriate thin layer and mark it. Meanwhile, cut the PDMS block with the two-dimensional material area to the appropriate size.

[0080] (5) Place the treated PDMS block on a specially designed transfer glass slide. The raised area in the middle of the glass slide is used to lift the two-dimensional material part of the PDMS, making it easier to contact the substrate. Then, assemble the transfer glass slide with the two-dimensional material transfer platform and adjust it so that the two-dimensional material is in the center of the optical microscope field.

[0081] (6) Place the electrode on the transfer platform so that the center of the electrode is aligned with the two-dimensional material. Slowly control the cantilever to approach the electrode. Just before the fit (after the interference fringes appear), turn on the heating and use the thermal expansion of the PDMS to slowly attach the two-dimensional material to the electrode. The slow rate of thermal expansion method will reduce the damage to the two-dimensional material.

[0082] (7) First, stabilize the heating stage to 80°C and start heating. During the transfer of the two-dimensional material, stop the stepper motor and switch to the heating transfer platform. Control the heating rate at about 3.6°C / s (the heating rate will change as the temperature rises, and the average value is taken). Slowly heat the PDMS to 150°C. In this process, the PDMS will slowly and gradually expand and attach to the silicon surface, achieving a tight fit with our flat electrode. After the fit is complete, stop heating and allow it to cool and shrink. Gently move the stage to detach the two-dimensional material from the PDMS, and then slowly lift the cantilever. At this point, the two-dimensional material will remain on the electrode surface.

[0083] (8) Place the electrode in the plasma cleaning machine and use hydrogen-argon mixed gas (hydrogen 5 sccm, argon 25 sccm) to treat the two-dimensional material for 30 seconds to remove surface impurities and organic matter and facilitate the subsequent operation steps.

[0084] (9) Take two-dimensional materials niobium diselenide and boron nitride respectively, repeat steps (1)-(8), and stack them in sequence to form a three-layer heterojunction. Since PDMS loses its viscosity when heated, the previously placed two-dimensional material will not be lifted during extraction.

[0085] (10) After stacking is completed, the substrate stacked with the two-dimensional material is placed in a vacuum environment for 1 hour to exhaust the gas in the interlayer to obtain a two-dimensional material heterojunction device.

[0086] (11) The heterojunction morphology of the obtained two-dimensional material heterojunction device was observed under an optical microscope. The results are shown in Figure 1 .Depend on Figure 1 It can be seen that by adopting the technical solution of this embodiment, a three-layer two-dimensional material heterojunction with a complete structure and no damage can be obtained.

[0087] Example 2: Preparation of a Two-Dimensional Material Heterojunction Device (Three-Layer Boron Nitride-Molybdenum Ditelluride-Tungsten Ditelluride Heterojunction)

[0088] Steps (1) to (8) are the same as in Example 1.

[0089] (9) Take two-dimensional materials boron nitride and molybdenum ditelluride respectively, repeat steps (1)-(8), and stack them in sequence to form a special heterojunction. Since PDMS loses its viscosity when heated, the previously placed two-dimensional material will not be lifted during extraction.

[0090] Step (10) is the same as in Example 1.

[0091] (11) The heterojunction morphology of the obtained two-dimensional material heterojunction device was observed under an optical microscope. The results are shown in Figure 2 .Depend on Figure 2 It can be seen that by adopting the technical solution of this embodiment, a three-layer two-dimensional material heterojunction with a complete structure and no damage can be obtained.

[0092] Example 3: Preparation of a Two-Dimensional Material Heterojunction Device (without Reactive Ion Etching)

[0093] Step (1) is the same as in Example 1.

[0094] (2) Expose the pre-designed electrode pattern on an electron beam exposure system and develop it for 1 minute using a mixture of methyl isobutyl ketone and isopropyl alcohol (volume ratio of 1:3). Next, clean the processed silicon wafer by ultrasonication in water, acetone, and isopropyl alcohol for 10 minutes each. Then, use an electron beam coating machine to coat a 65nm gold film. After removal, soak in acetone for half an hour to remove the glue, and finally rinse with isopropyl alcohol.

[0095] Steps (3) to (10) are the same as in Example 1.

[0096] (11) The morphology of the obtained two-dimensional material device was observed by optical microscope. The results are shown in Figure 3. By Figure 3 It can be seen that if the substrate after etching the embedded electrode is used to transfer the two-dimensional material, the obtained two-dimensional material device will be damaged and uneven. Since the bottom layer material is damaged, the subsequent stacking of the top layer material is not performed.

[0097] Example 4: Preparation of two-dimensional material heterojunction device (without using thermal expansion and cold contraction to transfer two-dimensional material)

[0098] Steps (1)-(5) are the same as in Example 1.

[0099] (6) Place the electrode on the transfer platform, align the center of the electrode with the two-dimensional material, slowly control the cantilever to approach the electrode, continue to lower the PDMS carrying the two-dimensional material to adhere to the substrate, slowly lift it, and the two-dimensional material remains on the substrate.

[0100] (7) Put the electrode into the plasma cleaning machine, use hydrogen argon mixed gas (hydrogen 5 sccm, argon 25 sccm) to treat the two-dimensional material for 30 seconds to remove surface impurities and organic matter.

[0101] (8) Observe the morphology of the obtained two-dimensional material device under an optical microscope, and the results are shown in Figure 4 , and Figure 4 It can be seen that by directly transferring the two-dimensional material, the obtained two-dimensional material will be damaged and uneven. Since the bottom layer material is damaged, the subsequent stacking of the top layer material is not performed.

[0102] Example 5: Preparation of two-dimensional material heterojunction device (heating speed investigation)

[0103] Steps (1)-(6) are the same as in Example 1.

[0104] (7) First, stabilize the heating stage to 80°C, then start heating. During the transfer of the two-dimensional material, it is found that a part of the PDMS in the microscope window adheres to the silicon wafer, stop the operation of the stepper motor, and switch to the heating transfer platform, control the heating rate to about 5°C / s (the heating rate will change as the temperature rises, and the average value is taken), slowly heat the PDMS to 150°C, in this process, the PDMS expands slowly and gradually adheres to the surface of the silicon wafer, and cooperates with our flat electrode to achieve close adhesion. After the adhesion is completed, stop heating, allow it to cool and shrink, and gently move the stage to separate the two-dimensional material from the PDMS, then slowly lift the cantilever, at this time the two-dimensional material will remain on the electrode surface.

[0105] (8) Observe the heterojunction morphology of the obtained two-dimensional material device under an optical microscope, and the results are shown in Figure 5 , and Figure 5It can be seen that the two-dimensional material obtained by heating PDMS at a heating rate of 5°C / s for transfer will be damaged and uneven. Since the bottom layer material has been damaged, the top layer material will not be stacked.

[0106] Example 6: Preparation of two-dimensional material heterojunction device (heating speed investigation)

[0107] Steps (1)-(6) are the same as in Example 1.

[0108] (7) First, the heating stage is stabilized at 80°C, and then the temperature is raised. During the transfer of the two-dimensional material, it is found that a part of the PDMS in the microscope window is attached to the silicon wafer. Stop the stepper motor and switch to the heating transfer platform, control the heating rate at about 2°C / s (the heating rate will change as the temperature rises, and the average value is taken), and slowly heat the PDMS to 150°C. In this process, the PDMS expands slowly and gradually tightens the surface of the silicon wafer, and cooperates with our flat electrode to achieve tight attachment. After the attachment is completed, stop heating, allow it to cool and shrink, and gently move the stage to detach the two-dimensional material from the PDMS, and then slowly raise the cantilever beam. At this time, the two-dimensional material will remain on the electrode surface.

[0109] Step (8) is the same as in Example 1.

[0110] (9) Place the substrate containing the two-dimensional material in a vacuum environment for 1 hour to evacuate the gas in the interlayer and obtain the two-dimensional material device.

[0111] (10) Observe the morphology of the obtained two-dimensional material device under an optical microscope, and the results are shown in Figure 6 , Figure 6 For the transferred single-layer tungsten ditelluride, the transfer of single-layer requires extremely high attachment rate and is extremely easy to damage, and Figure 6 It can be seen that the two-dimensional material obtained by heating PDMS at a heating rate of 2°C / s for transfer will be flat and will not be damaged.

[0112] Conclusion: From the results of the above examples, it can be concluded that:

[0113] (1) By etching the substrate with a reactive ion etching machine to embed the electrode, it is beneficial to improve the integrity of the two-dimensional material heterojunction structure, avoid the rupture of the two-dimensional material, and also increase the number of layers of the two-dimensional material heterojunction structure.

[0114] (2) By transferring the two-dimensional material to the substrate through thermal expansion and contraction, it is beneficial to improve the integrity of the two-dimensional material heterojunction structure, avoid the rupture of the two-dimensional material, and also increase the number of layers of the two-dimensional material heterojunction structure.

[0115] (3) When transferring the two-dimensional material to the substrate, the heating rate is 1°C / s-4°C / s, which is beneficial to improving the integrity of the heterojunction structure of the two-dimensional material and avoiding the cracking of the two-dimensional material. When the heating rate is ≥5°C / s, the heating rate is too fast and it is easy to cause the cracking of the two-dimensional material.

[0116] (4) When transferring the two-dimensional material to the substrate, heating it to a temperature of 130°C-150°C is used for transfer, which is beneficial to improving the integrity of the heterojunction structure of the two-dimensional material and avoiding the cracking of the two-dimensional material.

[0117] The methods of the present invention have been described through preferred embodiments. It is apparent that those skilled in the art will be able to modify or appropriately alter and combine the methods and applications described herein within the scope, spirit, and spirit of the present invention to implement and apply the technology of the present invention. Those skilled in the art may refer to the disclosure herein and appropriately modify the process parameters to achieve the desired effect. It is particularly important to note that all similar substitutions and modifications apparent to those skilled in the art are considered encompassed by the present invention.

Claims

1. A method for preparing a two-dimensional material heterojunction device, comprising: (I) Dissociation of 2D materials; (II) Embedding electrodes into substrates: The substrates are spin-coated with electron beam photoresist, baked, and then exposed to the pre-designed electrode shape using electron beam lithography. The substrates are developed with a developer and then etched in a reactive ion etcher. The electrodes are then evaporated and the resist is removed to obtain a substrate embedded with electrodes. (III) transferring the dissociated two-dimensional material to a substrate embedded with an electrode: the step (III) comprises transferring the dissociated two-dimensional material to a PDMS surface, bringing the PDMS with the two-dimensional material close to the electrode, heating the PDMS to expand and contact the substrate, turning off the heating, cooling the PDMS, and removing the PDMS; bringing the PDMS with the two-dimensional material close to the electrode comprises bringing the PDMS with the two-dimensional material close to the electrode until the distance between the two-dimensional material and the electrode is 10 μm-500 μm, or bringing the PDMS with the two-dimensional material close to the contact surface until interference fringes appear; the thickness of the PDMS is 500 μm-2000 μm; the heating comprises heating to 130°C-150°C; and the heating comprises heating at a rate of 1°C / second-4°C / second; (IV) taking at least one identical or different two-dimensional material and repeating steps (I) and (III) to form a multilayer heterojunction structure; obtaining a two-dimensional material heterojunction device; The steps (I) and (II) can be performed in any order; The two-dimensional material is selected from at least one of transition metal chalcogenides, graphene, boron nitride, black phosphorus and chromium triiodide; The transition metal chalcogenide is selected from at least one of molybdenum disulfide, molybdenum ditelluride, tungsten ditelluride, tungsten diselenide, niobium diselenide, and indium selenide; The substrate is selected from silicon dioxide, silicon wafer with a silicon dioxide layer on the surface, silicon wafer, mica, sapphire or flexible material; the flexible material is selected from at least one of polyimide, polyvinyl alcohol, polyester and polyethylene terephthalate.

2. The method according to claim 1, wherein the etching depth is 20 nm to 100 nm deeper than the substrate surface; the thickness of the electrode is 21 nm to 125 nm; and the electrode is 1 nm to 25 nm higher than the substrate surface.

3. The method according to any one of claims 1 to 2, The step (IV) is to repeat the steps (I) and (III) with at least one different two-dimensional material to form a multilayer heterojunction structure; thus obtaining a two-dimensional material heterojunction device. 4 . The method according to claim 1 , wherein the multi-layer heterojunction structure in step (IV) is a 2-4 layer heterojunction structure.

5. The method according to any one of claims 1 to 2, wherein step (I) comprises peeling by mechanical peeling.

6. The method according to any one of claims 1-2, wherein step (I) comprises: Use tape to stick the two-dimensional material, then use new tape to stick the tape with the two-dimensional material together and then tear it off. Repeat this 3-4 times, using new tape to stick the tape with the two-dimensional material together and then tear it off to obtain a tape containing a single layer or a few layers of two-dimensional material.

7. The method according to any one of claims 1-2, wherein transferring the dissociated two-dimensional material to the PDMS surface comprises adhering a tape containing a single layer or a few layers of the two-dimensional material to the PDMS and then tearing them apart.

8. The method according to any one of claims 1-2, wherein the electron beam photoresist comprises PMMA.

9. The method according to any one of claims 1-2, wherein the developer comprises a mixture of methyl isobutyl ketone and isopropyl alcohol.

10. The method according to claim 9, wherein the volume ratio of methyl isobutyl ketone to isopropyl alcohol is 9:1-1:

9.

11. The method according to any one of claims 1-2, wherein the etching is performed using trifluoromethane gas.

12. The method according to any one of claims 1-2, wherein the degumming comprises degumming by soaking in acetone.

13. The method according to any one of claims 1-2, wherein the degumming comprises degumming by soaking in acetone and then cleaning with isopropyl alcohol.

14. The method according to any one of claims 1 to 2, further comprising, after step (III), performing plasma cleaning with hydrogen, argon, or a mixture thereof.

15. The method according to claim 14, wherein the volume ratio of hydrogen to argon in the mixed gas of hydrogen and argon is 100:1-1:

100. The method according to claim 14 , wherein the plasma cleaning time is 20 s to 120 s.

17. The method according to any one of claims 1-2, wherein after step (IV), the two-dimensional material heterojunction device is placed in a vacuum condition to remove air from the interlayer.

18. The method according to claim 17, wherein the time of placing the mixture under vacuum conditions is 1 hour to 3 hours.

19. The method according to any one of claims 1-2, wherein spin coating the substrate with the electron beam photoresist comprises using a desktop spin coater to evenly spread the electron beam photoresist on the substrate at a rotation speed of 3000 rpm-6000 rpm for 1 minute-2 minutes.

20. The method according to any one of claims 1-2, wherein the baking temperature is 120°C-180°C.

21. The method according to any one of claims 1-2, wherein the baking time is 1 minute to 2 minutes.

22. The method according to any one of claims 1-2, wherein steps (I) and / or (III) are performed in a glove box.

23. A two-dimensional material heterojunction device prepared according to the method according to any one of claims 1 to 22.

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