Preparation method of suspended patterned two-dimensional material

Abstract

The invention provides a preparation method of a suspended patterned two-dimensional material. Through the strategy of first transferring and then patterning, the positioning precision is remarkably improved, the risks of material wrinkles, residual stress and damage are reduced, meanwhile, the technological process is simplified, tedious etching steps are avoided, material pollution and the failure rate are reduced, and the overall success rate and the sample cleanliness are improved. According to the method, fixed-point transfer of the two-dimensional material on the complex suspended structure is achieved, the sample preparation quality and success rate are greatly improved, transfer and patterning are completed through one-time photoresist coating, the technological process is shortened, and the influence of multiple times of spin coating on the sample cleanliness is avoided. The method has wide applicability, can be popularized to various suspended structures such as porous metal films, carbon films, grooves, pore plates and the like, is suitable for various tests of thermotics, electrics, optics and the like, and has good applicability to preparation of two-dimensional materials such as transition metal sulfides and boron nitride and preparation of suspended two-dimensional materials from a single layer to multiple layers.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional materials technology, and specifically relates to a method for preparing suspended patterned two-dimensional materials. Background Technology

[0002] The novel physical properties of two-dimensional materials have attracted widespread attention from the scientific and industrial communities, especially since graphene won the 2010 Nobel Prize in Physics, making two-dimensional materials increasingly star materials in the fields of materials science and physics. Compared with the extensive research on the mechanical, electrical, and optical properties of two-dimensional materials, research on their thermal properties is relatively limited, especially the measurement of the thermal conductivity of suspended two-dimensional materials, represented by graphene, which remains a challenging task.

[0003] Suspended two-dimensional materials are a class of materials with a two-dimensional structure (usually composed of only a single layer of atoms or molecules) that do not rely on conventional solid substrates for their applications. Unlike traditional two-dimensional materials (such as graphene and black phosphorus), these materials are "suspended," meaning they are not in direct contact with a three-dimensional substrate but exist in air or a vacuum, or interact with the external environment through some indirect contact method. They can also refer to two-dimensional materials with internal pores or grooves. The unique properties of suspended two-dimensional materials make them highly promising in fields such as electronics, optics, catalysis, and energy storage. For example, suspended graphene or transition metal dichalcogenides have extremely high electron mobility, making them suitable for ultrafast electronic devices and novel sensors. To expand the applications of suspended two-dimensional materials, it is necessary to measure their electrical and thermal properties. The thermal properties of suspended two-dimensional materials are highly sensitive to the substrate. For example, the thermal conductivity of graphene with a substrate differs from that of suspended graphene by several times, limiting the measurement of the thermal conductivity of suspended two-dimensional materials. Furthermore, experiments involving the physical properties of two-dimensional materials involve complex suspended structures, making the precise transfer of patterned suspended two-dimensional materials with clean surfaces and a high success rate a technical challenge.

[0004] Existing methods for preparing patterned suspended two-dimensional material samples involve first patterning the two-dimensional material on a substrate, and then transferring the patterned two-dimensional material to the surface of a suspended structure to form a patterned suspended two-dimensional material. This method suffers from difficulties in material positioning during patterning, low transfer accuracy, and a tendency for the two-dimensional material to develop wrinkles, residual stress, and breakage.

[0005] Therefore, there is a need to develop a new method for preparing suspended patterned two-dimensional materials. Summary of the Invention

[0006] The present application aims to at least solve one of the above technical problems in the prior art. To this end, the present application provides a method for preparing a suspended patterned two-dimensional material. In view of the problems of the existing method for preparing a patterned two-dimensional material sample on a suspended substrate, such as multiple sample wrinkles, poor patterning effect, long preparation period, and extremely low success rate, the method provided by the present application is simple and efficient, has high sample quality, good reliability, and can be compatible with various two-dimensional materials prepared by mechanical exfoliation and chemical vapor deposition (CVD) method.

[0007] The first aspect of the present application provides a method for preparing a suspended patterned two-dimensional material, comprising the following steps:

[0008] S1: coating photoresist on the surface of the two-dimensional material;

[0009] S2: using a transfer film to lift the photoresist adhered with the two-dimensional material by a water-assisted method, and transferring it to a glass slide, wherein the transfer film is attached to the glass slide;

[0010] S3: moving the glass slide to align the two-dimensional material on the glass slide with a suspended device, so that the two-dimensional material contacts the contact surface of the suspended device;

[0011] S4: by heating, the photoresist is adhered to the contact surface, the glass slide is lifted, the transfer film is separated from the photoresist, and the photoresist remains on the contact surface;

[0012] S5: exposing the photoresist on the surface of the two-dimensional material to form a mask, developing and fixing, removing the two-dimensional material not covered by the mask by etching, leaving the patterned two-dimensional material, and obtaining the suspended patterned two-dimensional material.

[0013] The present application relates to a method for preparing a suspended patterned two-dimensional material, which has at least the following beneficial effects:

[0014] The method simplifies the sample preparation steps and shortens the sample preparation period, while ensuring the sample quality, having high reliability and success rate. At the same time, the steps are simple and the materials are not contaminated. Specifically:

[0015] Firstly, the method of the present application, the suspended structure surface is transferred first and then patterned, which is beneficial to: (1) improving positioning accuracy: transferring first and then patterning avoids the difficulty of positioning after direct patterning on the substrate, reduces the risk of material wrinkles, residual stress and damage; (2) simplifying the process flow: without etching the bottom substrate after patterning, the cumbersome steps are reduced, and the material pollution and failure rate are reduced; (3) improving success rate: directly transferring two-dimensional materials to the suspended device surface reduces the intermediate steps and improves the overall success rate; (3) keeping the material clean: reducing the substrate etching step reduces material pollution and maintains the cleanliness of two-dimensional materials; (4) enhancing experimental controllability: transferring first and then patterning makes the experimental process more controllable, which is convenient for accurate regulation of the position and morphology of two-dimensional materials.

[0016] Secondly, the present application realizes the fixed-point transfer of two-dimensional materials on complex suspended structures, greatly improving the quality and success rate of two-dimensional material sample preparation on suspended structure surfaces.

[0017] Thirdly, through the ingenious process optimization of the present application, the transfer and patterning of two-dimensional materials can be completed only once by coating photoresist in the whole process, greatly reducing the process flow and avoiding the influence of multiple spin-on photoresist on sample cleanliness.

[0018] Fourthly, the method provided by the present application has wide applicability and can be popularized to two-dimensional material sample preparation on suspended structure surfaces such as porous metal membranes, various carbon membranes, grooves and hole plates.

[0019] Fifthly, the suspended structure two-dimensional material such as graphene suspended membrane prepared by the method of the present application can be used for various tests such as thermal, electrical and optical tests.

[0020] Sixthly, the preparation method provided by the present application is also applicable to two-dimensional materials such as transition metal sulfides and boron nitride.

[0021] Seventhly, the present application is applicable to the preparation of suspended two-dimensional materials with different layers, from single layer to double layer and multiple layers.

[0022] According to some embodiments of the present application, the two-dimensional material includes one of graphene, molybdenum disulfide and boron nitride.

[0023] According to some embodiments of the present application, the method of coating photoresist on the surface of the two-dimensional material in step S1 includes spin coating.

[0024] According to some embodiments of the present application, the photoresist is coated on the surface of the silicon wafer to which the two-dimensional material is adhered in step S1.

[0025] According to some embodiments of the present application, the spin-coating method comprises: first spin-coating at a speed of 500-1000 rpm for 10-30 s, and then spin-coating at a speed of 3000-6000 rpm for 60-120 s.

[0026] According to some embodiments of the present application, the spin-coating method comprises: first spin-coating at a speed of 500-1000 rpm for 10-30 s, and then spin-coating at a speed of 3000-6000 rpm for 60-120 s.

[0027] The speed of the low-speed spin-coating can be 500-1000 rpm, or any one of 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, or a range formed by any two of them, such as 700 rpm-900 rpm.

[0028] The time of the low-speed spin-coating can be 10-30 s, or any one of 10 s, 15 s, 20 s, 25 s, 30 s, or a range formed by any two of them, such as 20 s-25 s.

[0029] According to some embodiments of the present application, the spin-coating method comprises: spin-coating at a speed of 3000-6000 rpm for high-speed spin-coating.

[0030] The speed of the high-speed spin-coating can be 3000-6000 rpm, or any one of 3000 rpm, 3500 rpm, 4000 rpm, 4500 rpm, 5000 rpm, 5500 rpm, 6000 rpm, or a range formed by any two of them, such as 4000 rpm-5000 rpm.

[0031] The time of the low-speed spin-coating can be 60-120 s, or any one of 60 s, 65 s, 70 s, 75 s, 80 s, 85 s, 90 s, 95 s, 100 s, 105 s, 110 s, 115 s, 120 s, or a range formed by any two of them, such as 70 s-90 s.

[0032] According to some embodiments of the present application, the photoresist comprises at least one of an electron beam photoresist (such as PMMA), an ultraviolet exposure photoresist, a laser direct writing photoresist, and a nanoimprint photoresist.

[0033] According to some embodiments of the present application, the transfer film comprises one of a PDMS film, a PPC film, and a PP film.

[0034] According to some embodiments of the present application, in step S2, before the photoresist adhering with the two-dimensional material is lifted by the transfer film, the edge of the photoresist is first scraped off. The purpose is to facilitate the embedding of deionized water between the photoresist and the silicon wafer, reduce the adhesion between the two-dimensional material and the silicon wafer, and make the two-dimensional material follow the photoresist to be transferred.

[0035] According to some embodiments of the present application, in step S3, the two-dimensional material on the glass slide is aligned with the suspended device, and the operation is carried out under a microscope.

[0036] The magnification of the microscope can be 5X, 10X, 20X, and 50X.

[0037] According to some embodiments of the present application, in step S3, the temperature of the heating is 50℃-80℃.

[0038] According to some embodiments of the present application, in step S3, the temperature of the heating is any one of 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃ or a range value formed by any two of them, such as 60℃-70℃.

[0039] According to some embodiments of the present application, the heating time is 5-10min.

[0040] According to some embodiments of the present application, the heating time can be any one of 5min, 6min, 7min, 8min, 9min, 10min or a range value formed by any two of them, such as 7min-8min.

[0041] According to some embodiments of the present application, in step S5, the etching includes plasma etching.

[0042] According to some embodiments of the present application, the gas for ion etching includes oxygen.

[0043] According to some embodiments of the present application, the flow rate of the gas is 1-10mL / min.

[0044] According to some embodiments of the present application, the flow rate of the gas can be any one of 1mL / min, 2mL / min, 3mL / min, 4mL / min, 5mL / min, 6mL / min, 7mL / min, 8mL / min, 9mL / min, 10mL / min or a range value formed by any two of them, such as 5min-8min.

[0045] According to some embodiments of the present application, the power of the ion etching is 50-100W.

[0046] According to some embodiments of the present application, the power of the ion etching can be any one of 50 W, 60 W, 70 W, 80 W, 90 W, 100 W or a range formed by any two of them, such as 60 W-80 W.

[0047] According to some embodiments of the present application, the time of the ion etching is 100-300 s.

[0048] According to some embodiments of the present application, the time of the ion etching can be any one of 100 s, 120 s, 130 s, 140 s, 150 s, 160 s, 170 s, 180 s, 190 s, 200 s, 210 s, 220 s, 230 s, 240 s, 250 s, 260 s, 270 s, 280 s, 290 s, 300 s or a range formed by any two of them, such as 200 s-250 s.

[0049] According to some embodiments of the present application, the preparation method further comprises, after step S5, cleaning and drying the sample with an organic solvent. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 is a schematic diagram of the transfer film adhering the photoresist film in Example 1.

[0051] Figure 2 is a diagram of the suspended patterned two-dimensional material prepared in Example 1.

[0052] Figure 3 is a diagram of the suspended patterned two-dimensional material prepared in Example 2. DETAILED DESCRIPTION

[0053] The following are specific embodiments of the present application, and the technical solutions of the present application are further described in conjunction with the embodiments, but the present application is not limited to these embodiments.

[0054] In a first aspect, some embodiments of the present application provide a preparation method of a suspended patterned two-dimensional material, comprising the following steps:

[0055] S1: coating a photoresist on the surface of a two-dimensional material;

[0056] S2: using a transfer film to lift the photoresist adhering the two-dimensional material by a water-assisted method, and transfer to a glass slide, the transfer film being attached to the glass slide;

[0057] S3: moving the glass slide to align the two-dimensional material on the glass slide with a suspended device, so that the two-dimensional material is in contact with the contact surface of the suspended device;

[0058] S4: by heating, the photoresist is adhered to the contact surface, the slide is lifted, the film is separated from the photoresist, and the photoresist remains on the contact surface;

[0059] S5: the photoresist on the surface of the two-dimensional material is exposed to form a mask, developed and fixed, and the two-dimensional material not covered by the mask is removed by etching, leaving a patterned two-dimensional material, and obtaining a suspended patterned two-dimensional material.

[0060] It can be understood that the method of the present application simplifies the sample preparation steps and shortens the sample preparation period, while ensuring the sample quality, having high reliability and success rate. At the same time, the steps are simple and the materials are not contaminated.

[0061] It should be noted that, on the one hand, some existing methods for preparing patterned suspended two-dimensional material samples first pattern the two-dimensional material on a substrate, and then transfer the patterned two-dimensional material to the surface of a suspended structure to form a patterned suspended two-dimensional material. Since the precision during patterning is the precision of electron beam exposure, and the subsequent alignment of the patterned two-dimensional material with the target structure (the surface of the suspended structure) is performed under a microscope, which is optical precision. The precision of the electron beam and the optical precision are not at the same precision level, so the two-dimensional material in this method is difficult to position during patterning, and the subsequent transfer precision is low. On the other hand, when testing, the sample needs to be placed in a specific place, such as a four-electrode, and if the transfer precision is not enough, it will not be able to test. Thirdly, the force for transferring the patterned two-dimensional material to the suspended structure cannot be too large, otherwise it is easy to be damaged, and if the force is small, it is also difficult to transfer. The method of the present application solves the above problems. Specifically:

[0062] Firstly, in the method of the present application, the surface of the suspended structure is transferred first and then patterned, which is beneficial to: (1) improving the positioning precision: transferring first and then patterning avoids the positioning difficulty during direct patterning on the substrate, reducing the risk of material wrinkles, residual stress and damage; (2) simplifying the process flow: the two-dimensional material can be directly transferred to the surface of the suspended structure, without the need to etch the bottom substrate after patterning, reducing the cumbersome steps and reducing the risk of material contamination and failure; (3) improving the success rate: directly transferring the two-dimensional material to the surface of the suspended device reduces the intermediate steps and improves the overall success rate; (3) keeping the material clean: reducing the substrate etching step reduces the risk of material contamination and maintains the cleanliness of the two-dimensional material; (4) enhancing the controllability of the experiment: transferring first and then patterning makes the experimental process more controllable, facilitating accurate adjustment of the position and morphology of the two-dimensional material.

[0063] Secondly, the present application realizes the point transfer of two-dimensional materials on complex suspended structures, greatly improving the quality and success rate of the preparation of two-dimensional material samples on the surface of suspended structures.

[0064] Thirdly, the present application can realize the transfer and patterning of two-dimensional materials by only one photoresist coating in the whole process, greatly reducing the process flow and avoiding the influence of multiple spin-on photoresist on sample cleanliness.

[0065] Fourthly, the method provided by the present application has wide applicability and can be popularized to the preparation of two-dimensional material samples on the surface of suspended structures such as porous metal films, various carbon films, grooves and hole plates.

[0066] Fifthly, the suspended structure two-dimensional material such as graphene suspended film prepared by the method of the present application can be used for various tests such as thermal, electrical and optical tests.

[0067] Sixthly, the preparation method provided by the present application is also applicable to two-dimensional materials such as transition metal sulfides and boron nitride.

[0068] Seventhly, the present application is applicable to the preparation of suspended two-dimensional materials with different layers, from single layer to double layer and multi-layer.

[0069] In combination with the first aspect, in some embodiments of the present application, the two-dimensional material includes one of graphene, molybdenum disulfide and boron nitride.

[0070] In combination with the first aspect, in some embodiments of the present application, the method for coating photoresist on the surface of the two-dimensional material in step S1 includes spin coating.

[0071] In combination with the first aspect, in some embodiments of the present application, the method of spin coating includes: first spin coating at a speed of 500-1000 rpm for 10-30 s, and then spin coating at a speed of 3000-6000 rpm for 60-120 s.

[0072] In combination with the first aspect, in some embodiments of the present application, the method of spin coating includes: first spin coating at a speed of 500-1000 rpm, which is low-speed spin coating.

[0073] In combination with the first aspect, in some embodiments of the present application, the speed of low-speed spin coating can be 500-1000 rpm, and can also be any value or a range value formed by any two values in 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm and 1000 rpm, such as 700 rpm-900 rpm.

[0074] In combination with the first aspect, in some embodiments of the present application, the time of low-speed spin coating can be 10-30 s, and can also be any value or a range value formed by any two values in 10 s, 15 s, 20 s, 25 s and 30 s, such as 20 s-25 s.

[0075] With reference to the first aspect, in some embodiments of the present application, the method of spin coating comprises: spin coating at a speed of 3000-6000 rpm, which is high speed spin coating.

[0076] The speed of high speed spin coating can be 3000-6000 rpm, and can also be any one of 3000 rpm, 3500 rpm, 4000 rpm, 4500 rpm, 5000 rpm, 5500 rpm, 6000 rpm or a range value formed by any two of them, such as 4000-5000 rpm.

[0077] The time of low speed spin coating can be 60-120 s, and can also be any one of 60 s, 65 s, 70 s, 75 s, 80 s, 85 s, 90 s, 95 s, 100 s, 105 s, 110 s, 115 s, 120 s or a range value formed by any two of them, such as 70-90 s.

[0078] With reference to the first aspect, in some embodiments of the present application, the photoresist comprises one of electron beam lithography resist (PMMA), ultraviolet exposure photoresist, laser direct writing photoresist, nanoimprint photoresist, etc.

[0079] With reference to the first aspect, in some embodiments of the present application, the transfer film comprises one of PDMS film, PPC film, and PP film.

[0080] With reference to the first aspect, in some embodiments of the present application, in step S2, before the photoresist adhering to the two-dimensional material is lifted using the transfer film, the edges of the photoresist are first scraped off. The purpose is to: (1) improve the success rate of transfer: after scraping off the edges, the contact between the photoresist and the transfer film is more uniform, reducing bubbles or unevenness and improving the success rate of transfer; (2) enhance adhesion: after removing the edges, the contact area between the photoresist and the transfer film is more closely, enhancing the adhesion and preventing falling off during the transfer process; (3) reduce pollution: the edge photoresist may contain impurities, scraping off reduces the risk of pollution and keeps the material clean; (4) facilitate operation: scraping off the edges makes the boundary of the photoresist clear, facilitating subsequent alignment and transfer operation.

[0081] With reference to the first aspect, in some embodiments of the present application, in step S3, the two-dimensional material on the glass slide is aligned with the suspended device under a microscope.

[0082] With reference to the first aspect, in some embodiments of the present application, the magnification of the microscope can be 5X, 10X, 20X, 50X.

[0083] With reference to the first aspect, in some embodiments of the present application, in step S3, the temperature of heating is 50-80°C.

[0084] With reference to the first aspect, in some embodiments of the present application, the temperature of the heating in step S3 is any one or a range formed by any two of 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, such as 60°C-70°C.

[0085] With reference to the first aspect, in some embodiments of the present application, the time of the heating is 5-10 min.

[0086] With reference to the first aspect, in some embodiments of the present application, the time of the heating can be any one or a range formed by any two of 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, such as 7 min-8 min.

[0087] With reference to the first aspect, in some embodiments of the present application, the etching in step S5 includes plasma etching.

[0088] With reference to the first aspect, in some embodiments of the present application, the gas for the ion etching includes oxygen.

[0089] With reference to the first aspect, in some embodiments of the present application, the flow rate of the gas is 1-10 mL / min.

[0090] With reference to the first aspect, in some embodiments of the present application, the flow rate of the gas can be any one or a range formed by any two of 1 mL / min, 2 mL / min, 3 mL / min, 4 mL / min, 5 mL / min, 6 mL / min, 7 mL / min, 8 mL / min, 9 mL / min, 10 mL / min, such as 5 min-8 min.

[0091] With reference to the first aspect, in some embodiments of the present application, the power of the ion etching is 50-100 W.

[0092] With reference to the first aspect, in some embodiments of the present application, the power of the ion etching can be any one or a range formed by any two of 50 W, 60 W, 70 W, 80 W, 90 W, 100 W, such as 60 W-80 W.

[0093] With reference to the first aspect, in some embodiments of the present application, the time of the ion etching is 10-60 s.

[0094] With reference to the first aspect, in some embodiments of the present application, the time of the ion etching can be any one or a range formed by any two of 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, such as 30 s-50 s.

[0095] With reference to the first aspect, in some embodiments of the present application, further comprising, after step S5, cleaning and drying the sample with an organic solvent.

[0096] In some embodiments of the first aspect, the preparation method can be:

[0097] (1) spin a layer of PMMA photoresist on the surface of the two-dimensional material sample by a spin coater;

[0098] (2) scrape off the PMMA photoresist on the four edges of the above-mentioned silicon wafer surface, and paste the PDMS on the surface of the PMMA photoresist on the scraped edges, and use the PDMS to lift the PMMA photoresist with the two-dimensional material adhered thereto by the water-assisted method;

[0099] (3) paste the above-mentioned PDMS film on a clean glass slide;

[0100] (4) fix the above-mentioned glass slide on a two-dimensional material transfer clamp, fix the transferred target device on the sample stage of the transfer stage, and adjust the sample position under the microscope to align the two-dimensional material with the target position;

[0101] (5) slowly lower the two-dimensional material sample to make it fully contact with the surface of the target position;

[0102] (6) turn on the heating device to make the PMMA film tightly contact with the substrate;

[0103] (7) when the PMMA film is in full contact with the substrate, slowly lift the glass slide to separate the PDMS film from the PMMA film, and at this time the PMMA film with the two-dimensional material adhered thereto is transferred to the surface of the suspended device;

[0104] (8) without re-spinning the glue, use an electron beam exposure machine to expose at the specified position to form a mask on the surface of the two-dimensional material by means of the PMMA photoresist on the surface of the two-dimensional material, and then develop and fix;

[0105] (9) confirm the effect of exposure and development under the microscope, and take the device with better effect for subsequent etching;

[0106] (10) put the above-mentioned device with better effect into a plasma etching machine for etching, and the two-dimensional material not covered by the mask is etched away, leaving only the two-dimensional material of the mask part;

[0107] (11) there is still a layer of PMMA on the surface of the two-dimensional material after patterning, and organic solvent is used for cleaning;

[0108] (12) the cleaned device is dried by a critical point drying instrument.

[0109] The concept and the technical effects of the present application will be described clearly and completely in combination with the embodiments, so that the purpose, features and effects of the present application can be fully understood. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0110] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are contained in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0111] Unless otherwise specified, "room temperature" in the present application means 25℃±5℃.

[0112] Unless otherwise specified, "about" in the present application means that the allowable error is within ±2%.

[0113] Unless otherwise specified, the specific conditions in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not marked with the manufacturer, which are all conventional products that can be purchased on the market.

[0114] Example 1

[0115] This embodiment is a preparation method of a suspended patterned two-dimensional material, which utilizes mechanical exfoliation of graphene to prepare high-quality patterned suspended graphene samples. The specific steps are as follows:

[0116] (1) Graphene is mechanically exfoliated from a single crystal graphite block and then transferred to a silicon wafer with a silicon oxide surface, wherein the thickness of the silicon oxide layer is 200-300nm. The mechanical exfoliation uses a commonly used exfoliation tape;

[0117] (2) A layer of PMMA photoresist is spin-coated on the surface of the silicon wafer by a spin coater, wherein the PMMA photoresist is 950K, A4, and positive photoresist. In the spin coating step, first keep at a low speed of 750rpm for 20s, and then keep at a high speed of 4500rpm for 90s;

[0118] (3) The silicon wafer with suitable size graphene is observed and selected in a microscope. The "suitable size" here is determined according to the experimental requirements and the size of the suspended device;

[0119] (4) Use a blade to scrape off 1-2 mm of the four edges of the PMMA on the surface of the silicon wafer, and then attach the PDMS to the PMMA surface from which the edges have been scraped off. Use the PDMS to lift the PMMA with graphene adhered thereto by means of the water-assisted method (see Fig. 2). Figure 1

[0120] It should be noted that how to take down the PMMA flatly is a difficulty in the prior art, and the present application can achieve the flat taking down of the PMMA by means of the water-assisted method, i.e. using the wetting effect of water to take down the PMMA flatly by means of the PDMS.

[0121] The thickness of the PDMS film is between 2-5 mm, and the size is slightly larger than that of the silicon wafer by 2-4 mm.

[0122] The water used for wetting is deionized water.

[0123] (5) Attach the above-mentioned PDMS film to a clean glass slide, and the specific attachment manner is that the PDMS faces the glass slide.

[0124] (6) Fix the above-mentioned glass slide on the clamp of the two-dimensional material transfer platform, fix the target device on the sample stage of the two-dimensional material transfer platform, and adjust the sample position under the assistance of a microscope so that the graphene is aligned with the target position of the substrate. The target position is a suspended silicon nitride film connected to the substrate by a cantilever.

[0125] The target position can also be a circular hole, a groove or a more complex suspended device surface.

[0126] (7) Slowly lower the two-dimensional material sample so that it is in full contact with the surface of the target position.

[0127] (8) Turn on the heating device, and the heating temperature is 65°C. The heating time is 7 minutes. During the heating process, the interaction force between the two-dimensional material and the substrate will increase due to thermal expansion, and the position of the two-dimensional material sample needs to be dynamically adjusted to reduce the interaction force between the two-dimensional material and the substrate.

[0128] (9) After 7 minutes of heating, observe under the microscope to confirm that the PMMA film is in full contact with the substrate without bubbles. At this time, slowly lift the glass slide upwards so that the PDMS film is separated from the PMMA film. At this time, the PMMA film with graphene adhered thereto is transferred to the surface of the suspended device.

[0129] (10) In order to meet the special size and shape requirements of the two-dimensional material in some experiments, the two-dimensional material needs to be patterned on the basis of the above-mentioned operation. By means of the PMMA photoresist on the surface of the two-dimensional material, it is not necessary to re-coat the photoresist. An electron beam exposure machine is used to expose at the specified position, and then development and fixing are performed. At this time, a PMMA mask with a specific size and shape is left on the surface of the two-dimensional material. ​

[0130] The developing solution used in the developing operation is a mixture of methyl isobutyl ketone (MIBK) and isopropyl alcohol (IPA), and the volume fraction of MIBK is 25%;

[0131] The fixing solution used in the fixing operation is IPA;

[0132] (11) The exposed and developed device is observed under a microscope to confirm the effect, and a device with better effect is used for subsequent etching (see FIG. 5). Figure 2 "better effect" here refers to clear and neat lines after exposure. Figure 2 In the figure, 1 is a cantilever, 2 is a thermometer, 3 is a target device, and 4 is a photoresist, i.e., a PMMA film (to be disposed of later). The device is used to measure the thermal properties of the cantilevered graphene. As can be seen from FIG. 6, Figure 2 It can be seen that the graphene is successfully transferred to the cantilevered structure to form a complex structure of the cantilevered two-dimensional material.

[0133] (12) The exposed device is placed in a plasma etching machine for etching. Oxygen is used as the gas source, the flow rate is 5 mL / min, the power is 75 W, and the processing time is 30 s. The flow rate, power, and processing time for etching need to be set according to the type and thickness of the two-dimensional material;

[0134] (13) The surface of the two-dimensional material after patterning still has a layer of PMMA, which needs to be cleaned with an organic solvent. Specifically, first, acetone is used to remove the residual PMMA photoresist, and then isopropyl alcohol is used to remove the acetone. The acetone cleaning needs to be heated to 50-55°C with a water bath or a hot plate, and the device is soaked in the acetone for 5-10 minutes. This process can be repeated 1-3 times to achieve better degreasing effect. The isopropyl alcohol removal of acetone process can be carried out at room temperature, and the cleaning time is 3-5 minutes;

[0135] (14) The cleaned device is dried using a critical point drying instrument. Liquid carbon dioxide is used as the displacement solution in the supercritical drying machine, and carbon dioxide is used to displace isopropyl alcohol. After the isopropyl alcohol is completely displaced, heating is performed to make the liquid carbon dioxide reach a supercritical state. After all the carbon dioxide is discharged, the device is taken out.

[0136] Example 2

[0137] This embodiment is a method for preparing a cantilevered patterned two-dimensional material, which uses CVD graphene to prepare a high-quality patterned cantilevered graphene sample. The specific steps are as follows:

[0138] (1) Graphene is grown on both sides of a metal substrate by a CVD method, and the graphene film on one side is marked for use in the experiment, and the other side is removed by a plasma etching method. The metal substrate is copper, and the plasma etching uses oxygen as the gas source, the flow rate is 5 mL / min, the power is 75 W, and the time is 30 s;

[0139] (2) Spin a layer of PMMA photoresist on the CVD graphene surface by spin coater. The PMMA photoresist is 950K, A4, positive resist, compatible with e-beam exposure process; in the spin coating step, first at a low speed of 750 rpm for 20 seconds, then at a high speed of 4000 rpm for 90 seconds;

[0140] (3) Etch the copper metal substrate of the CVD graphene by ferric chloride solution;

[0141] (4) Use a glass slide with a PDMS film attached to the surface to fish the PMMA film with graphene from the etching solution, the thickness of the PDMS film is between 2-5 mm;

[0142] (5) Wash the above sample in acetone, isopropyl alcohol and water for 1-3 minutes, then dry with nitrogen;

[0143] (6) Observe the surface state of graphene using an optical microscope and a Raman spectrometer, select a clean and defect-free area and mark it;

[0144] (7) Fix the above glass slide on the clamp of the two-dimensional material transfer platform (Zhuo Jie Technology 2DEV-03), fix the target device on the sample stage of the two-dimensional material transfer platform, adjust the sample position under the microscope, align the selected clean and defect-free graphene area with the target position on the substrate, which is a suspended silicon nitride film connected to the substrate by a cantilever. The target position can also be a circular hole, a groove or a more complex suspended device surface;

[0145] (8) Slowly lower the two-dimensional material sample to make it fully contact with the surface of the target position;

[0146] (9) Turn on the heating device, the heating temperature is 65°C, and the heating time is 7 minutes. During the heating process, the interaction force between the two-dimensional material and the substrate will increase due to thermal expansion, so the position of the two-dimensional material sample needs to be adjusted dynamically to reduce the interaction force between the two-dimensional material and the substrate;

[0147] (10) After heating, observe under the microscope to confirm that the PMMA film is in full contact with the substrate without bubbles. At this time, slowly lift the glass slide to separate the PDMS film from the PMMA film. At this time, the PMMA film with graphene is transferred to the surface of the suspended device;

[0148] (11) In order to meet the requirements of special size and shape of two-dimensional materials in some experiments, the two-dimensional materials are patterned on the basis of the above operation, with the aid of PMMA photoresist on the surface of the two-dimensional materials, without re-coating, exposure is performed at the specified position by using an electron beam exposure machine, and then development and fixing are performed, at this time, a PMMA mask with a specific size and shape is left on the surface of the two-dimensional materials; the developing solution used in the development operation is a mixture of methyl isobutyl ketone (MIBK) and isopropyl alcohol (IPA), and the volume fraction of MIBK is 25%; the fixing solution used in the fixing operation is IPA;

[0149] (12) The effect of exposure and development is confirmed under a microscope, and the device with better effect is taken for subsequent etching (refer to Figure 3 ), wherein "better effect" refers to clear and neat lines after exposure; Figure 3 In the figure, 1 is a cantilever, 2 is a thermometer, 3 is a target device, and 4 is photoresist, i.e. a PMMA film (which will be processed later). The device is used to measure the thermal performance of the suspended graphene. As can be seen from Figure 2 , the graphene is successfully transferred to the suspended structure to form a suspended two-dimensional material with a complex structure.

[0150] (13) The device after exposure is placed in a plasma etching machine for etching; oxygen is selected as the gas source of the plasma etching machine, the flow rate is 5 mL / min, the power is 75 W, and the processing time is 50 s. The flow rate, power and processing time selected for etching can be set according to the type and thickness of the two-dimensional material;

[0151] (14) The surface of the two-dimensional material after patterning still has a layer of PMMA, which needs to be cleaned with an organic solvent. Specifically, first, acetone is used to remove the residual PMMA photoresist, and then isopropyl alcohol is used to remove the acetone; the acetone cleaning needs to be heated to 50°C by water bath or hot plate, and the device is soaked in acetone for 7 min, and this process can be repeated 1-3 times to achieve better degreasing effect;

[0152] The isopropyl alcohol removal of acetone process can be performed at room temperature, and the cleaning time is 4 minutes;

[0153] (15) The cleaned device is dried by using a critical point drying instrument. Liquid carbon dioxide is selected as the displacement solution of the supercritical drying machine, and isopropyl alcohol is replaced by carbon dioxide. After the isopropyl alcohol is completely replaced, heating is performed to make the liquid carbon dioxide reach a supercritical state, and then the device is taken out after the carbon dioxide is completely discharged.

[0154] The above describes the present application in detail in combination with the embodiments, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge range of ordinary skill in the art without departing from the purpose of the present application.

Claims

1. A method for preparing a suspended patterned two-dimensional material, characterized in that, Includes the following steps: S1: Coating a two-dimensional material surface with photoresist; S2: Using a water-assisted method, a transfer film is used to lift the photoresist with the two-dimensional material adhering to it and transfer it onto a glass slide, wherein the transfer film is bonded to the glass slide; S3: Move the glass slide and align the two-dimensional material on the glass slide with the suspended device so that the two-dimensional material comes into contact with the contact surface of the suspended device; S4: By heating, the photoresist is bonded to the contact surface. The glass slide is then lifted, and the transfer film separates from the photoresist, leaving the photoresist on the contact surface. S5: Expose the photoresist on the surface of the two-dimensional material to form a mask, perform development and fixing, and remove the two-dimensional material not covered by the mask by etching to leave the patterned two-dimensional material, thereby obtaining the suspended patterned two-dimensional material.

2. The preparation method according to claim 1, characterized in that, The two-dimensional material includes one of graphene, molybdenum disulfide, and boron nitride.

3. The preparation method according to claim 1, characterized in that, In step S1, the method of coating photoresist on the surface of the two-dimensional material includes spin coating; and / or, the spin coating method includes: first spin coating at a speed of 500 to 1000 rpm for 10 to 30 seconds, and then spin coating at a speed of 3000 to 6000 rpm for 60 to 120 seconds.

4. The preparation method according to claim 1, characterized in that, The photoresist includes at least one of electron beam photoresist, ultraviolet exposure photoresist, laser direct writing photoresist, and nanoimprint photoresist.

5. The preparation method according to claim 1, characterized in that, The transfer membrane includes one of PDMS membrane, PPC membrane and PP membrane.

6. The preparation method according to claim 1, characterized in that, In step S2, before using the transfer film to lift the photoresist with the two-dimensional material adhering to it, the edges of the photoresist are scraped off.

7. The preparation method according to claim 1, characterized in that, In step S3, the two-dimensional material on the glass slide is aligned with the suspended device under a microscope.

8. The preparation method according to claim 1, characterized in that, In step S3, the heating temperature is 50℃~80℃; and / or the heating time is 5~10min.

9. The preparation method according to claim 1, characterized in that, In step S5, the etching includes plasma etching; and / or, the gas used for ion etching includes oxygen; and / or, the flow rate of the gas is 1 to 10 mL / min; and / or, the power of the ion etching is 50 to 100 W; and / or, the time for the ion etching is 100 to 300 s.

10. The preparation method according to claim 1, characterized in that, The preparation method further includes, after step S5, cleaning and drying the sample with an organic solvent.

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