A method for preparing an ultraflat nanofilm

Abstract

The application provides a method for preparing an ultra-flat nanometer film, which comprises the following steps: applying a transfer adhesive layer to the upper surface of nanometer material; placing the nanometer material on the smooth surface of a target substrate so that the lower surface of the nanometer material is attached to the smooth surface of the target substrate; removing the transfer adhesive layer; applying a medium layer to the upper surface of the nanometer material; and etching the target substrate to obtain an ultra-flat nanometer film. The material of the transfer adhesive layer comprises vaseline, paraffin or rosin; the nanometer material comprises graphene or boron nitride; and the material of the medium layer comprises epoxy resin or polyester resin. The graphene or boron nitride film is ultra-flat after the nanometer material is conformally contacted with the target substrate having a smooth surface, and the target substrate is removed after conformal contact.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro-nano material film, and particularly relates to a method for preparing an ultra-flat nano film. BACKGROUND

[0002] At present, nano films have wide applications in semiconductor device preparation, electronic devices and equipment, such as graphene films. In the existing technology, the methods commonly used for preparing graphene films with high flatness include CVD direct growth method or transfer method. However, the above two methods have the following disadvantages:

[0003] The direct growth method is limited to target substrates (such as single-crystal copper substrates, sapphire substrates, silicon wafers, etc.), and can only realize growth of graphene with high flatness on fixed substrates, and has high energy consumption.

[0004] The transfer method always forms wrinkles during growth due to strong coupling between the transferred target substrate and the graphene, which not only causes line defects and affects the continuity of the graphene, but also causes the adhesive on the surface to be difficult to clean completely, thereby limiting the uniformity of graphene device preparation. In addition, the graphene transferred by directly coating a layer (film) on the surface of the graphene / growth substrate can reproduce the surface morphology of the copper foil, and the surface roughness is difficult to control.

[0005] Therefore, there is an urgent need for a method for preparing an ultra-flat nano film. SUMMARY

[0006] In view of the deficiencies in the prior art, the present application provides a method for preparing an ultra-flat nano film, and the technical scheme adopted is as follows:

[0007] In a first aspect, a method for preparing an ultra-flat nano film is provided.

[0008] In a first implementation, the method comprises the following steps:

[0009] applying a transfer adhesive layer to the upper surface of the nano material;

[0010] placing the nano material on the smooth surface of the target substrate so that the lower surface of the nano material is attached to the smooth surface of the target substrate;

[0011] removing the transfer adhesive layer;

[0012] applying a medium layer to the upper surface of the nano material;

[0013] etching the target substrate to obtain an ultra-flat nano film.

[0014] In a second implementation, in combination with the first implementation, the material of the transfer adhesive layer comprises vaseline, paraffin or rosin.

[0015] The transfer adhesive layer is coated on the upper surface of the nanomaterial, including: heating the transfer adhesive layer material to melt, and then uniformly coating the melted transfer adhesive layer material on the surface of the nanomaterial by using a spin coater, and cooling;

[0016] Or, the melted transfer adhesive layer material liquid is uniformly dropped on the surface of the nanomaterial until the liquid covers the surface of the nanomaterial and is about to overflow, and then cooled.

[0017] In combination with the first implementation manner, in the third implementation manner, after the transfer adhesive layer is coated on the upper surface of the nanomaterial, a support skeleton is added on the surface of the transfer adhesive layer, and the support skeleton includes a screen window net, a polytetrafluoroethylene plate, and a PET film.

[0018] In combination with the first implementation manner, in the fourth implementation manner, the nanomaterial includes graphene or boron nitride.

[0019] In combination with the first implementation manner, in the fifth implementation manner, the target substrate is a rigid planar structure, and at least one of the upper and lower surfaces of the target substrate is a smooth surface; and the target substrate includes a silicon wafer and glass.

[0020] In combination with the first implementation manner, in the sixth implementation manner, before the nanomaterial is placed on the smooth surface of the target substrate, a solvent is applied to the smooth surface of the target substrate; and the solvent includes deionized water, anhydrous ethanol solution diluted with deionized water, anhydrous ethanol, or acetone.

[0021] The manner of applying the solvent includes immersing the target substrate in the solvent.

[0022] In combination with the first implementation manner, in the seventh implementation manner, the transfer adhesive layer is removed, including:

[0023] The transfer adhesive layer is melted by heating, and then is placed in a n-hexane solution for water bath heating, and then is placed in a preheated petroleum ether solution for heating, and finally is dried by using a nitrogen gun.

[0024] In combination with the first implementation manner, in the eighth implementation manner, the material of the medium layer includes epoxy resin or polyester resin.

[0025] The medium layer is coated on the upper surface of the nanomaterial, including: coating liquid epoxy resin or polyester resin on the upper surface of the graphene by using a spin coating / drop coating / blade coating / roller pressing manner, and standing to completely solidify.

[0026] In combination with the first implementation manner, in the ninth implementation manner, after the medium layer is coated on the upper surface of the nanomaterial, an additional support film is placed on the upper surface of the medium layer; and the material of the additional support film includes polytetrafluoroethylene, PET, or sapphire.

[0027] In a second aspect, there is provided an ultra-flat nanometer film, prepared by any one of the first to ninth possible implementation manners of the first aspect, comprising an ultra-flat graphene film and an ultra-flat boron nitride film.

[0028] From the above technical solution, the beneficial technical effects of the present application are as follows:

[0029] By conformally contacting the nanometer material with the target substrate having a smooth surface, and then removing the target substrate after conformal contact, an ultra-flat graphene and boron nitride film can be obtained. The factors affecting the device performance such as residual glue and wrinkles on the surface of graphene and boron nitride are avoided, and the surface of the film is smooth and clean. The process steps are less, simple and easy to operate. The nanometer film with a smooth surface is obtained by a macroscopic method, which is more magnified and operable compared with micro-growth. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the present application, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale.

[0031] Figure 1 Flow chart for preparing an ultra-flat nanometer film according to an embodiment of the present application;

[0032] Figure 2 Process schematic diagram for preparing an ultra-flat graphene film according to an embodiment of the present application;

[0033] Reference numerals:

[0034] 1 - transfer adhesive layer, 2 - graphene, 3 - target substrate, 4 - medium layer, 5 - additional support film. DETAILED DESCRIPTION

[0035] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, but cannot limit the protection scope of the present application.

[0036] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in the present application should be understood as the usual meanings understood by the skilled person in the field to which the present application belongs.

[0037] EMBODIMENT

[0038] The present embodiment provides a method for preparing an ultra-flat nanometer film, and the materials needed for the preparation method include: prepared nanometer material, transfer adhesive layer, target substrate, and additional support film and medium layer.

[0039] In the present embodiment, the material of the prepared nanomaterial includes graphene and boron nitride, and the morphology and size of the nanomaterial are not limited. For example, single-layer or multi-layer graphene can be used. The nanomaterial can be a self-supporting film or a nanomaterial prepared on a copper foil.

[0040] The transfer adhesive layer can be implemented in various forms, and can be made of vaseline, paraffin, rosin or other substances that release stress of the nanofilm by using the difference in thermal expansion coefficient. In the specific embodiment, when the transfer adhesive layer is a solid, it needs to be pretreated. The pretreatment method is as follows: a part of the transfer adhesive layer is placed in a container, heated in a water bath, and the adhesive layer is melted after the pretreatment.

[0041] The target substrate is a rigid plane with a smooth surface, and the material and size of the target substrate are not limited. For example, the material can be a silicon wafer or glass, and the size is determined according to the super-flat nanofilm to be prepared. Preferably, at least one of the upper and lower surfaces of the target substrate is a smooth surface, and the surface roughness is less than 10 nanometers.

[0042] The medium layer can be made of acid-resistant epoxy resin or highly corrosion-resistant polyester resin, such as epoxy resin and an unsaturated monobasic acid addition reactant containing a double bond. The medium layer is used to fix the graphene structure and provide support for the graphene film during preparation. Epoxy resin, as a commonly used resin matrix, has excellent bonding properties, mechanical strength, heat resistance and dielectric properties, and can be cured under ultraviolet light. It is inert in strong acid and strong corrosive solution, and is a good medium layer material.

[0043] As shown in FIG. 1, the super-flat nanofilm is prepared according to the following steps: Figure 1

[0044] S1, coating the transfer adhesive layer on the upper surface of the nanomaterial

[0045] The transfer adhesive layer is solid vaseline, and the nanomaterial is graphene. An appropriate amount of solid vaseline is taken into a beaker and heated in a 60-70°C water bath until it melts. Then the melted vaseline is uniformly coated on the surface of the graphene by using a spin coater, or the melted vaseline liquid is directly and uniformly dropped on the surface of the graphene until the vaseline liquid covers the surface of the graphene and is about to overflow. After cooling, the transfer adhesive layer / graphene composite structure is obtained.

[0046] In some embodiments, when large-area graphene is transferred, a support skeleton such as a screen window net, a polytetrafluoroethylene plate, PET (polyethylene terephthalate) or the like can be added to the surface of the transfer adhesive layer, and the screen window net is preferred. The addition of the support skeleton can provide a certain mechanical force as support, which is more conducive to the preparation of large-area thin films. ​

[0047] For graphene with a back substrate, such as a copper foil, the graphene coated with the transfer adhesive layer is placed in a ferric chloride etching solution for etching for 1 h, and the copper foil surface is rinsed with clean water for 2-3 min repeatedly for 3 times to remove the copper foil back substrate. In a specific embodiment, the ferric chloride etching solution has a concentration of 1 mol / L of FeCl3 and a mass fraction of 5% of HCL.

[0048] In some embodiments, to more completely remove the back substrate, the graphene / copper foil can be sealed with a tape on the back side before the transfer adhesive layer is coated, and the back side of the graphene / copper foil is etched by a reactive ion etching machine. After the etching is completed, the graphene surface is continuously rinsed with clean water to remove the residual etching solution, and then the subsequent steps are performed. The step of coating the transfer adhesive layer is to release the stress of the graphene in the subsequent operation, so that the prepared graphene film is more flat and the warping caused by internal attraction is reduced.

[0049] In this step, the thickness of the transfer adhesive layer is in the order of millimeters, generally 1-2 mm.

[0050] S2, placing the nanomaterial on the smooth surface of the target substrate so that the lower surface of the nanomaterial is attached to the smooth surface of the target substrate

[0051] The graphene coated with the transfer adhesive layer is placed on the smooth surface of the target substrate so that the graphene is attached to the smooth surface of the target substrate, and a transfer adhesive layer / graphene / target substrate composite structure is obtained.

[0052] In some embodiments, to more closely attach the graphene to the smooth surface of the target substrate, a solvent can be applied to the smooth surface of the target substrate before the graphene is placed on the smooth surface of the target substrate. The solvent is selected from a liquid with a certain volatility and a low surface tension, such as deionized water, anhydrous ethanol solution diluted with deionized water (volume ratio of water to anhydrous ethanol is 1:1), anhydrous ethanol, and acetone; and the diluted anhydrous ethanol is preferably used as the solvent.

[0053] S3, removing the transfer adhesive layer

[0054] In a specific embodiment, the transfer adhesive layer is vaseline and the target substrate is a silicon wafer, and the transfer adhesive layer / graphene / target substrate is heated by a heating table to melt the vaseline. After the residual liquid between the graphene and the silicon wafer is dried, the graphene / target substrate composite structure is obtained by placing it in n-hexane and petroleum ether for 1 h and then blowing dry with a nitrogen gun.

[0055] After the treatment in this step, the upper surface of the graphene is not smooth, and in general, the upper surface of the graphene at this time has wrinkles, residual impurity particles, etc.

[0056] S4, coating a medium layer on the upper surface of the nanomaterial

[0057] In a specific embodiment, the medium layer is exemplified by an epoxy resin: an acid-resistant and corrosion-resistant liquid epoxy resin is coated on the upper surface of graphene by a spin coater (or by using a drop coating / blade coating / roll coating method), and is left to completely solidify, thereby obtaining a medium layer / graphene / target substrate composite structure.

[0058] In some embodiments, a certain pressure can be applied downward to the solidified medium layer, so that the lower surface of the graphene is more closely attached to the smooth surface of the target substrate; the pressure application method is not limited, and a heavy weight or a tablet press can be selected for pressure application.

[0059] In this step, the thickness of the medium layer is generally less than 2 mm.

[0060] S5, etching the target substrate to obtain an ultra-flat nanometer thin film

[0061] The etching method for the target substrate is not limited, and the target substrate is exemplified by a silicon wafer: the medium layer / graphene / target substrate composite structure is placed in hydrofluoric acid, and the target substrate is etched; after the target substrate is completely etched, an ultra-flat graphene thin film with a medium layer / graphene composite structure (the thickness of single-layer graphene is only about 0.3 nm, and it is difficult to realize self-supporting without the action of the medium layer) is obtained, and the lower surface of the graphene in the medium layer / graphene composite structure is smooth.

[0062] In some embodiments, for the purpose of industrial application, such as the preparation of a large-area ultra-flat graphene thin film, after the step S4 of coating the medium layer on the upper surface of the nanomaterial is implemented, an additional support film can be placed on the upper surface of the medium layer and left to solidify, and then a certain pressure is applied downward to the additional support film, so that the lower surface of the nanomaterial is more closely attached to the smooth surface of the target substrate; the pressure application method is not limited, and a heavy weight or a tablet press can be selected for pressure application. The additional support film can be highly corrosion-resistant polyester, which is usually an adduct of an epoxy resin and an unsaturated monobasic acid containing a double bond, such as polytetrafluoroethylene, PET, sapphire, etc.; in some embodiments, the polytetrafluoroethylene support film can be packaged in a roll or a sheet. For example, the medium layer is exemplified by an epoxy resin, and the additional support film is exemplified by PET: the prepared ultra-flat graphene thin film is a graphene / epoxy resin / PET composite structure, and can be directly applied as a transparent conductive film for application testing.

[0063] The following is the actual preparation process of the ultra-flat nanometer thin film:

[0064] Example 1, preparation of an ultra-flat graphene thin film

[0065] The vaseline with purity of 99% is heated in water bath at 70℃ for 20 min to melt. The graphene / copper foil is placed on the heating stage with temperature set at 50℃. The melted vaseline solution is slowly coated on the surface of graphene grown copper foil until the surface of graphene / copper foil is covered with vaseline liquid and is about to overflow. No more vaseline is added. The heating stage is turned off. The vaseline is solidified after cooling for tens of seconds at room temperature.

[0066] The cut screen window net (with area slightly larger than the sample area to be transferred) is pasted on the surface of the solidified vaseline and put into 1 mol / L FeCl3 etching solution for etching for 1 h. The background is removed for 2-3 times. The time interval for each time of removing the background and the time for rinsing with water can be maintained at about 2-3 min. The screen window net is rinsed with deionized water. The ethanol solution (volume ratio of water to ethanol is 1:1) is prepared and the screen window net is put into the ultrasonic cleaner for cleaning for 15-30 min to remove the bubbles in the solution. At the same time, the silicon wafer is immersed in the prepared ethanol solution and waits for pasting.

[0067] After etching, the graphene / vaseline composite structure is lifted from the etching solution by holding one corner of the screen window net. The etching solution remaining on the surface of graphene is continuously rinsed with water. Then the graphene is pasted on the smooth surface of the silicon wafer. The vaseline / graphene / silicon wafer composite structure after pasting is vertically placed for 1 h to allow the liquid remaining between the pasting interfaces to fully leave. Then the composite structure is put into the oven at 30℃ for heating for 24 h.

[0068] The vaseline / graphene / silicon wafer composite structure is taken out and the screen window net is removed. The vaseline / graphene / silicon wafer composite structure after removing the screen window net is placed on the heating stage at 50℃ until the vaseline becomes liquid again. The silicon wafer is vertically placed to allow the excess vaseline to remain due to gravity. Then the silicon wafer is put into n-hexane solution and heated in water bath at 60℃ for 1 h. Then the silicon wafer is put into preheated petroleum ether solution and heated at 90℃ for 1 h. The silicon wafer after removing the vaseline is taken out from the petroleum ether. The surface of the silicon wafer is rinsed with clean petroleum ether and anhydrous ethanol respectively. Finally, the silicon wafer is dried with nitrogen gun to obtain the graphene / silicon wafer composite structure.

[0069] The transparent epoxy resin is coated on the graphene surface of the graphene / silicon wafer composite structure. A layer of PET film is further coated on the surface of the epoxy resin. The PET side is irradiated with ultraviolet lamp for 30 min or more to ensure that the epoxy resin is fully cured.

[0070] The PET / epoxy resin / graphene / silicon wafer composite structure is put into hydrofluoric acid solution with concentration of 10%-50% and etched at 50℃ for about 3 h until the silicon wafer is completely etched and disappears. The PET / epoxy resin / graphene composite structure is taken out and immersed in deionized water. The silicon wafer is rinsed and dried to obtain a smooth and ultra-flat graphene film.

[0071] Example 2, Preparation of ultra-smooth boron nitride film

[0072] Paraffin wax with a purity of 99% is used, and heated in a 90°C water bath for 20 min to melt it. At the same time, the glass sheet is immersed in the prepared ethanol solution, and waits for bonding.

[0073] The melted paraffin wax is coated on the surface of the boron nitride film using a spin coater, and then the boron nitride is bonded to the smooth surface of the glass sheet. The paraffin wax / boron nitride / glass sheet composite structure after bonding is placed vertically for 1 h, so that the residual liquid between the bonding interfaces is fully left, and then placed in an oven at 30°C for 24 h.

[0074] The paraffin wax / boron nitride / glass sheet composite structure is taken out and placed on a 90°C heating table, and the paraffin wax is re-melted. The glass sheet is placed vertically so that the excess paraffin wax is left due to gravity, and then placed in a n-hexane solution and heated in a 60°C water bath for 1 h. The glass sheet after removing the paraffin wax is taken out from the n-hexane solution, and the surface of the glass sheet is rinsed with clean n-hexane and anhydrous ethanol, respectively, and finally dried with a nitrogen gun to obtain a boron nitride / glass sheet composite structure.

[0075] The polyester resin is coated on the surface of the boron nitride of the boron nitride / glass sheet composite structure, and then the polyester resin / boron nitride / glass sheet composite structure is placed in a hydrofluoric acid solution with a concentration of 10% to 50% and etched at a temperature of 50°C for about 3 h until the glass sheet is completely etched and disappears. The polyester resin / boron nitride composite structure is taken out and soaked in deionized water, rinsed and dried to obtain a smooth ultra-smooth boron nitride film.

[0076] By using the above technical solutions of the embodiment, the nanomaterial is conformally contacted with the target substrate having a smooth surface, and after conformal bonding, the target substrate is removed, so that an ultra-smooth graphene or boron nitride film is obtained. The factors affecting the device performance such as residual glue and wrinkles on the surface of the graphene or boron nitride are avoided, and the surface of the film is smooth and clean. The process steps are few, simple and easy to operate, and the nanometer film with a smooth surface is obtained by a macroscopic method, which is more magnified and operable compared with micro-growth.

[0077] The preparation method can be applied to the preparation of devices for various transparent material films, such as transparent graphene films which can be widely used in transparent conductive films, light-emitting OLED devices, flexible display screens and various scenes.

[0078] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application.

Claims

1. A method for preparing an ultraflat nanofilm, characterized in that, The method comprises the following steps: applying a transfer adhesive layer to the upper surface of the nanomaterial; placing the nanomaterial on the smooth surface of the target substrate so that the lower surface of the nanomaterial is attached to the smooth surface of the target substrate; removing the transfer adhesive layer; applying a medium layer to the upper surface of the nanomaterial, and allowing the medium layer to completely solidify after application; and applying pressure to the solidified medium layer downward until the lower surface of the nanomaterial is tightly attached to the smooth surface of the target substrate; the medium layer comprises epoxy resin or polyester resin; etching the target substrate to obtain an ultra-flat nanomaterial film.

2. The production method according to claim 1, characterized by, The transfer adhesive layer comprises vaseline, paraffin or rosin; applying a transfer adhesive layer to the upper surface of the nanomaterial, which comprises the following steps: heating the transfer adhesive layer material to melt, and then uniformly applying the molten transfer adhesive layer material to the surface of the nanomaterial by using a spin coater, and cooling; or, uniformly dripping the molten transfer adhesive layer material liquid onto the surface of the nanomaterial until the liquid covers the surface of the nanomaterial and is about to overflow, and cooling.

3. The production method according to claim 1, characterized by, After applying the transfer adhesive layer to the upper surface of the nanomaterial, a support skeleton is added to the surface of the transfer adhesive layer, and the support skeleton comprises a screen window mesh, a polytetrafluoroethylene plate or a PET film.

4. The method of claim 1, wherein, The nanomaterial comprises graphene or boron nitride.

5. The preparation method according to claim 1, characterized in that, The target substrate is a rigid planar structure, and at least one of the upper and lower surfaces of the target substrate is a smooth surface; the target substrate comprises a silicon wafer and glass.

6. The method of claim 1, wherein, Before placing the nanomaterial on the smooth surface of the target substrate, a solvent is applied to the smooth surface of the target substrate; the solvent comprises deionized water, anhydrous ethanol solution diluted with deionized water, anhydrous ethanol or acetone; The solvent is applied by immersing the target substrate in the solvent.

7. The preparation method according to claim 1, characterized in that, The transfer adhesive layer is removed by the following steps: melting the transfer adhesive layer by heating, and then placing it in a n-hexane solution for water bath heating, and then placing it in a preheated petroleum ether solution for heating, and finally blowing it dry with a nitrogen gun.

8. The preparation method according to claim 1, wherein applying a medium layer to the upper surface of the nanomaterial comprises applying by using a spin coating / drop coating / blade coating / roller pressing method.

9. The method of claim 1, wherein, After applying the medium layer to the upper surface of the nanomaterial, an additional support film is placed on the upper surface of the medium layer; the additional support film comprises polytetrafluoroethylene, PET or sapphire.

10. An ultraflat nanofilm, comprising: The method according to any one of claims 1-9 is used to prepare an ultra-flat graphene film or an ultra-flat boron nitride film.

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