A morphology-controllable single-layer hexagonal boron nitride growth method

Abstract

A method for growing a single layer of hexagonal boron nitride with controllable morphology relates to the field of two-dimensional material synthesis. The method comprises the following steps: S1, placing a metal foil as a growth substrate on a support material, and then placing the support material with the metal foil into the reaction zone of a chemical vapor deposition apparatus; S2, placing a precursor containing a nitrogen source and a boron source in the upstream zone of the chemical vapor deposition apparatus, the upstream zone being upstream of the reaction zone along the direction of carrier gas flow; S3, introducing a carrier gas and heating the reaction zone until the metal foil is completely molten, then heating the upstream zone to a temperature of 75-90°C, performing a chemical vapor deposition reaction for 5-40 minutes, and cooling to obtain a two-dimensional hexagonal boron nitride material. Using a molten metal surface as the growth substrate for the two-dimensional hexagonal boron nitride has the advantages of uniform nucleation and rapid growth. By controlling the heating temperature of the precursor, high-quality, shape-controllable hexagonal boron nitride domains are obtained on the molten copper surface.

Description

Technical Field

[0001] The present invention belongs to the field of two-dimensional material synthesis, and in particular relates to a method for growing a single-layer hexagonal boron nitride with controllable morphology. Background Art

[0002] Hexagonal boron nitride is also called "white graphene" because it has a honeycomb structure similar to graphene. It is composed of boron atoms and nitrogen atoms alternately arranged in sp 2 Different from the zero band gap of single-layer graphene, single-layer hexagonal boron nitride has a wide band gap of up to 5.9eV. Due to the strong sp 2 Hexagonal boron nitride (HBN) possesses high mechanical strength, excellent chemical properties, and thermal stability. These unique properties make HBN a promising material for a wide range of applications, such as as a deep ultraviolet emitter, a growth substrate for other two-dimensional materials with similar hexagonal crystal structures, and enhancing the performance of graphene-based field-effect transistors. Recently, numerous studies have also demonstrated that point defects in HBN can act as single-photon emission sites at room temperature, making HBN promising for applications in quantum technology. Therefore, the controllable preparation of HBN is an important research direction in the field of two-dimensional material synthesis.

[0003] The main methods for growing two-dimensional materials include mechanical exfoliation, liquid phase exfoliation, physical vapor deposition and chemical vapor deposition. Among them, chemical vapor deposition (CVD) is considered to be the most likely method for mass production of hexagonal boron nitride and other two-dimensional materials. Currently, pilot-scale graphene production has been successfully achieved through chemical vapor deposition. Factors affecting the growth of hexagonal boron nitride include the type of precursor, growth temperature and pressure, growth time, growth substrate, etc., among which the growth substrate determines the growth direction and morphology. Researchers have made many attempts to obtain a suitable hexagonal boron nitride growth substrate, such as using polycrystalline metal foil, silicon (111) surface, platinum foil and copper-nickel alloy. Recently, researchers have achieved metal step-induced seamless splicing of hexagonal boron nitride on Cu (111) and Cu (110) surfaces to obtain large-area single-crystalline hexagonal boron nitride films.

[0004] During the growth process on solid metal surfaces, obtaining a growth substrate requires expensive sapphire substrates or lengthy annealing of metal foils to produce single-crystal copper films with specific metal steps, significantly increasing production costs. For example, patent application number CN201910298770.1, entitled "A Method for Preparing Wafer-Scale Uniform Hexagonal Boron Nitride Thin Films," uses a single-crystal copper film as a substrate and requires an annealing time of 30-180 minutes. Compared to solid metal, molten metal surfaces offer advantages such as uniform nucleation and rapid growth as growth substrates for two-dimensional hexagonal boron nitride, making them ideal substrates for hexagonal boron nitride growth. However, hexagonal boron nitride currently grown on liquid metal surfaces exhibits shape uncertainty. For example, hexagonal boron nitride grown on liquid gold is uniformly circular, while hexagonal boron nitride grown on liquid copper exhibits circular or hexagonal shapes. The morphology of hexagonal boron nitride can affect its intrinsic properties. For example, the boundaries of hexagonal boron nitride crystals have a higher density of single-photon emission sites. Therefore, effectively controlling the growth morphology of hexagonal boron nitride is of great significance for its large-scale industrial application. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the present invention aims to provide a method for growing a single-layer hexagonal boron nitride with controllable morphology, so as to solve the problem of uncertain crystal morphology in the current growth of two-dimensional hexagonal boron nitride.

[0006] The purpose of the present invention is achieved by adopting the following technical solutions:

[0007] A method for growing a single layer of hexagonal boron nitride with controllable morphology is provided, comprising the following steps:

[0008] S1, placing a metal foil as a growth substrate on a support material, and then placing the support material carrying the metal foil into a reaction zone of a chemical vapor deposition device;

[0009] S2, placing a precursor containing a nitrogen source and a boron source in an upstream area of ​​a chemical vapor deposition apparatus, wherein the upstream area is located upstream of the reaction zone along a flow direction of the carrier gas;

[0010] S3, introducing a carrier gas and heating the reaction zone until the metal foil is completely molten, then heating the upstream zone to a temperature of 75 to 90° C., performing a chemical vapor deposition reaction for 5 to 40 minutes, and cooling to obtain a hexagonal boron nitride two-dimensional material.

[0011] Furthermore, the metal foil is copper foil, gold foil or nickel foil, and the thickness of the metal foil is 20-30 μm.

[0012] Furthermore, the supporting material is tungsten foil with a thickness of 40-60 μm.

[0013] Furthermore, the precursor is ammonia borane.

[0014] Furthermore, step S1 also includes a pretreatment step, which is to soak the metal foil in a chemical solution to remove impurities from the surface of the metal foil, then rinse it with deionized water, and blow dry it with a nitrogen gun to obtain a clean metal foil.

[0015] Furthermore, the chemical solution is glacial acetic acid, and the soaking time is 3-10 minutes.

[0016] Furthermore, in step S1, 2-4 clean metal foils are stacked on a support material, and the support material is placed horizontally in the reaction area.

[0017] Furthermore, the specific operation in step S2 is to place the precursor in a quartz boat, and place the quartz boat containing the precursor in the upstream area, where the upstream area is 30-40 cm away from the center of the metal foil.

[0018] Furthermore, in step S3, the carrier gas is a mixed gas consisting of argon and hydrogen, the flow rate of the argon is 180-220 sccm, and the flow rate of the hydrogen is 18-22 sccm.

[0019] Furthermore, in step S3, the metal foil is copper foil, and the specific operation of heating the reaction zone is: raising the temperature in the reaction zone to 1085° C. within 40 minutes, and maintaining the constant temperature for 10-15 minutes to ensure that the copper foil is completely melted.

[0020] Furthermore, the hexagonal boron nitride two-dimensional material is a triangular, angled triangle or circular crystal with a width of 5 to 20 μm. Compared with the prior art, the present invention has the following advantages:

[0021] The present invention grows two-dimensional hexagonal boron nitride material by chemical vapor deposition, using a molten metal surface as the growth substrate for the two-dimensional hexagonal boron nitride. Compared with common sapphire substrates and solid metal substrates, the present invention has the advantages of uniform nucleation and rapid growth. By controlling the heating temperature of the precursor, the sublimation rate of the precursor is effectively controlled, and then the concentration of ammonia borane in the carrier gas is controlled, so that high-quality, shape-controllable hexagonal boron nitride domains are obtained on the molten metal surface. Compared with the currently available chemical vapor deposition growth methods for hexagonal boron nitride, the method of the present invention is simple to operate, highly repeatable, and highly controllable, laying the foundation for the industrial application of hexagonal boron nitride in shape specificity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the principle of hexagonal boron nitride growth in the present invention;

[0023] Figure 2is a typical optical microscope image of hexagonal boron nitride of Example 1;

[0024] Figure 3 This is the Raman spectrum of the hexagonal boron nitride after transfer to silicon wafer in Example 1;

[0025] Figure 4 is an atomic force microscope image of the hexagonal boron nitride of Example 1 after transfer to a silicon wafer;

[0026] Figure 5 This is a scanning electron microscope image of the hexagonal boron nitride of Example 1; the right image is a partial enlarged view of the left image;

[0027] Figure 6 This is a scanning electron microscope image of the hexagonal boron nitride of Example 2; the image on the right is a partial enlarged view of the image on the left;

[0028] Figure 7 This is a scanning electron microscope image of the hexagonal boron nitride of Example 3; the right image is a partial enlarged view of the left image;

[0029] Figure 8 This is a scanning electron microscope image of the hexagonal boron nitride of Example 4; the right image is a partial enlarged image of the left image. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0031] Example 1

[0032] A method for growing a single layer of hexagonal boron nitride with controllable morphology comprises the following steps:

[0033] 1) Pre-treat the copper foil substrate. Select a copper foil with a thickness of 25 μm and use glacial acetic acid immersion to remove impurities on the surface. Organic matter, oxides and other impurities on the surface of the copper foil can be removed. The immersion time is 5 minutes. After the immersion is completed, rinse with deionized water and blow dry with a nitrogen gun to obtain a clean copper foil with surface pre-treatment.

[0034] 2) Using a tubular heating furnace as a chemical vapor deposition apparatus, stack three clean copper foils obtained on a tungsten foil with a thickness of 50 μm and place them in the reaction zone of the heating tube of the tubular heating furnace, ensuring that the tungsten foil is placed horizontally. Take 2 mg of borane ammonia solid and place it in a quartz boat. Place the quartz boat containing the borane ammonia solid in the upstream area of ​​the heating tube, where the upstream area is 35 cm away from the center of the copper foil. Put a heating tape on the corresponding position of the upstream area so that its center is aligned with the center of the quartz boat. Open the argon valve and adjust its flow rate to 200 sccm. Keep it for 5 minutes to remove the residual oxygen in the tubular furnace.

[0035] 3) Opening the hydrogen valve and adjusting its flow rate to 20 sccm, turning on the heating switch of the tubular heating furnace to raise the temperature in the reaction zone to 1085°C within 40 minutes; maintaining this temperature for 10 minutes to ensure complete melting of the copper sheet; then turning on the heating belt and adjusting the temperature to 75°C, subliming the ammonia borane solid into the reaction zone to begin chemical vapor deposition of hexagonal boron nitride for 30 minutes, so that the hexagonal boron nitride two-dimensional material is grown at a constant temperature on the molten copper substrate.

[0036] 4) After the reaction is completed, turn off the heating tape switch and move the heating tape away from the upstream zone to prevent further sublimation of the borane solid; turn off the heating device of the tubular furnace and move the heating tube horizontally to expose the copper foil outside the heating zone for rapid cooling; close the hydrogen valve; after the heating tube cools to room temperature, remove the sample and perform the required characterization operations on the grown hexagonal boron nitride.

[0037] The growth process of hexagonal boron nitride on molten copper sheet is as follows: Figure 1 Using a molten metal surface as a growth substrate for two-dimensional hexagonal boron nitride (HBN) offers advantages such as uniform nucleation and rapid growth. By controlling the sublimation heating temperature of the precursor, effectively controlling the sublimation rate of the precursor and, in turn, the concentration of ammonia borane in the carrier gas, high-quality, shape-controllable HBN crystal domains are obtained on the molten copper surface.

[0038] Performance testing

[0039] Crystal domain characterization:

[0040] The hexagonal boron nitride was transferred to a SiO2 / Si substrate. The sample was transferred using a traditional substrate etching method. First, a layer of PMMA glue was spin-coated on the copper foil with the hexagonal boron nitride at 4000 rpm. The copper was then etched away using a 1M ferric chloride solution. The PMMA / hBN was then removed with a glass slide and placed in clean water for one hour. The sample was then removed with the target substrate and evaporated to dryness. Finally, the PMMA was dissolved with acetone to obtain the hexagonal boron nitride transferred to the target substrate for further characterization.

[0041] The copper foil was placed on a heating table and heated to 200°C for 10 seconds, so that the copper foil portion not covered by hexagonal boron nitride was oxidized to red copper oxide. The hexagonal boron nitride crystal domains can be observed by using the color difference. The results are as follows: Figure 2 As shown in the figure, hexagonal boron nitride mostly presents a triangle shape. After the borane ammonia sublimates and enters the reactor, it is decomposed by heat and deposited on the surface of the molten copper, forming nuclei uniformly.

[0042] like Figure 5 As shown, at the precursor heating temperature, the grown hexagonal boron nitride crystal domains are triangular.

[0043] like Figure 3 As shown, after the obtained hexagonal boron nitride was transferred to a silicon wafer, a characteristic peak at about 1370 cm-1 was observed under a Raman microscope, confirming that the crystal domain was a hexagonal boron nitride crystal domain.

[0044] like Figure 4 As shown, the atomic force microscope image shows that its thickness is about 0.65nm, confirming that it is a single-layer hexagonal boron nitride crystal domain.

[0045] Example 2:

[0046] The difference between this embodiment and embodiment 1 is that the heating temperature of the precursor ammonia borane is increased to 80° C., the reaction time is shortened to 20 min, and the other process parameters are exactly the same as those in embodiment 1.

[0047] The results of this embodiment: Figure 6 As shown, the grown hexagonal boron nitride is a folded triangle.

[0048] Example 3:

[0049] The difference between this embodiment and embodiment 1 is that the heating temperature of the precursor ammonia borane is increased to 85° C., the reaction time is shortened to 10 min, and the other process parameters are exactly the same as those in embodiment 1.

[0050] The results of this embodiment: Figure 7 As shown, the grown hexagonal boron nitride is nearly circular with many inward angles, and a second layer or even multiple layers of nucleation points begin to appear in the crystal domain.

[0051] Example 4:

[0052] The difference between this embodiment and embodiment 1 is that the heating temperature of the precursor ammonia borane is increased to 90° C., the reaction time is shortened to 8 min, and the other process parameters are exactly the same as those in embodiment 1.

[0053] The results of this embodiment: Figure 8 As shown, the grown hexagonal boron nitride is basically circular, has a high nucleation density and has many multi-layer nucleation points in the crystal domain.

[0054] In combination with Examples 1 to 4, by changing the heating temperature of the precursor sublimation, the sublimation rate of the precursor can be effectively regulated, thereby controlling the morphology of the hexagonal boron nitride growth. The resulting hexagonal boron nitride has a uniform nucleation density, and its morphology can therefore be changed from a triangle to a folded triangle and finally to a circle with a width of 5 to 20 μm. The method of the present invention is simple to operate and highly repeatable, filling the current technical gap in the uncontrollable growth morphology of two-dimensional hexagonal boron nitride and is of significant significance.

[0055] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A method for growing a single layer of hexagonal boron nitride with controllable morphology, characterized in that: The following steps are involved: S1, placing a metal foil as a growth substrate on a support material, and then placing the support material carrying the metal foil into a reaction zone of a chemical vapor deposition device; S2, placing a precursor containing a nitrogen source and a boron source in an upstream area of ​​a chemical vapor deposition apparatus, wherein the upstream area is located upstream of the reaction zone along a flow direction of the carrier gas; The specific operation in step S2 is to place the precursor in a quartz boat, and place the quartz boat containing the precursor in the upstream area, where the upstream area is 30-40 cm away from the center of the metal foil; S3, introducing a carrier gas and heating the reaction zone until the metal foil is completely molten, then heating the upstream zone to a temperature of 75-90° C., performing a chemical vapor deposition reaction for 5-20 minutes, and cooling to obtain a hexagonal boron nitride two-dimensional material; In step S3, the carrier gas is a mixed gas consisting of argon and hydrogen, the flow rate of the argon is 180-220 sccm, and the flow rate of the hydrogen is 18-22 sccm.

2. The method for growing a single-layer hexagonal boron nitride with controllable morphology according to claim 1, wherein: The metal foil is copper foil, gold foil or nickel foil, and the thickness of the metal foil is 20-30 μm.

3. The method for growing a single-layer hexagonal boron nitride with controllable morphology according to claim 1, wherein: The supporting material is tungsten foil with a thickness of 40-60 μm.

4. The method for growing a single-layer hexagonal boron nitride with controllable morphology according to claim 1, wherein: The precursor is ammonia borane.

5. A method for growing a single layer of hexagonal boron nitride with controllable morphology according to any one of claims 1 to 4, characterized in that: Step S1 also includes a pretreatment step, which includes soaking the metal foil in a chemical solution to remove impurities from the surface of the metal foil, then rinsing it with deionized water and drying it with a nitrogen gun to obtain a clean metal foil.

6. A method for growing a single layer of hexagonal boron nitride with controllable morphology as claimed in claim 5, characterized in that: The chemical solution is glacial acetic acid, and the soaking time is 3-10 minutes.

7. The method for growing a single-layer hexagonal boron nitride with controllable morphology according to claim 5, wherein: In step S1 , 2-4 clean metal foils are stacked on a support material, and the support material is placed horizontally in a reaction area.

8. The method for growing a single-layer hexagonal boron nitride with controllable morphology according to claim 1, wherein: In step S3, the metal foil is copper foil, and the specific operation of heating the reaction zone is: raising the temperature in the reaction zone to 1085° C. within 40 minutes, and maintaining the constant temperature for 10-15 minutes to ensure that the copper foil is completely melted.

Images