A method for preparing a hexagonal boron nitride single crystal

Abstract

The application discloses a preparation method of hexagonal boron nitride single crystal material and belongs to the technical field of hexagonal boron nitride single crystal. The preparation method of the hexagonal boron nitride single crystal material comprises the steps of raw material deoxidization, high-temperature growth, annealing treatment and single crystal peeling, wherein the stainless steel alloy sheet is used as a fluxing agent, and more preferably, the 316 stainless steel alloy sheet is used, which contains rich element composition components, can improve the growth quality of the hexagonal boron nitride single crystal material from various aspects, is helpful to obtain single crystal material with high quality and large size, and in the process of high-temperature growth, the sample is placed in the form of a hexagonal boron nitride powder layer-stainless steel alloy sheet layer-hexagonal boron nitride powder layer, so that the contact area between the powder and the stainless steel alloy can be improved, and the effect of the stainless steel alloy sheet fluxing agent can be maximally exerted.

Description

Technical Field

[0001] This invention belongs to the field of hexagonal boron nitride single crystal technology, and specifically relates to a method for preparing hexagonal boron nitride single crystals. Background Technology

[0002] Hexagonal boron nitride is a semiconductor material that possesses isotopic properties. 10 B, isotopes 10 Boron nitride (BN) can undergo nuclear reactions with neutrons, producing secondary charged particles with a certain kinetic energy. These secondary charged particles then propagate within the hexagonal boron nitride (HBN) crystal and collide with lattice atoms, generating a large number of electron-hole pairs. These electron-hole pairs can be separated by an electric field and collected by electrodes. The collected signal can then be characterized as a thermal neutron detection signal. Utilizing this property of hexagonal boron nitride crystals, many researchers have focused on the study of h-BN neutron detectors. In h-BN neutron detectors, neutron capture, charge collection, and electrical signal generation can all occur within the same layer, thus enabling direct neutron detection.

[0003] As a crucial component of the h-BN neutron detector, the quality of hexagonal boron nitride single crystals directly impacts the accuracy and quality of the resulting neutron detector. Currently, the primary method for preparing hexagonal boron nitride single crystals is chemical vapor deposition (CVD). This method typically uses precursors such as boronamidine or trimethylamine boron, or borane or boron chloride as the boron source and ammonia or nitrogen as the nitrogen source, obtaining the hexagonal boron nitride single crystal under high temperature or high pressure conditions. However, most of the raw materials used in this method are highly toxic, posing risks to safe production and control over the reaction process.

[0004] Another method for preparing hexagonal boron nitride single crystals is the metal flux method. Compared to chemical vapor deposition (CVD), the metal flux method uses hexagonal boron nitride powder as the raw material, which is safe and non-toxic, and is easier to control than gaseous raw materials. However, the hexagonal boron nitride single crystals obtained by the metal flux method are small in size, and the quality of single crystal growth is poor, with cracks present. Therefore, there is an urgent need for a safe, easily controllable method to prepare high-quality, large-size hexagonal boron nitride single crystals. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing hexagonal boron nitride single crystal materials, so as to solve the problems of poor quality, poor performance and small size of hexagonal boron nitride single crystal materials obtained by existing preparation methods.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] This invention provides a method for preparing hexagonal boron nitride single crystal material, comprising the following steps:

[0008] S1. Clean and dry the stainless steel alloy sheet for later use;

[0009] S2. Deoxidize the hexagonal boron nitride powder and the boron nitride crucible boat together to obtain pretreated hexagonal boron nitride powder;

[0010] S3. Spread the pretreated hexagonal boron nitride powder evenly in the boron nitride crucible boat, cover it with a stainless steel alloy sheet, then spread a layer of pretreated hexagonal boron nitride powder evenly on the stainless steel alloy sheet, and finally cover the boron nitride crucible boat with the lid to obtain the sample to be processed.

[0011] S4. Place the sample obtained in step S3 in a tube furnace, first evacuate the furnace to remove air, then introduce nitrogen to atmospheric pressure, grow at high temperature for 10-12 hours under nitrogen flow, then cool down to 900-1000℃ and stop heating, and let it cool naturally to room temperature to obtain a crude hexagonal boron nitride single crystal grown on the surface of stainless steel alloy.

[0012] S5. Anneal the crude hexagonal boron nitride single crystal to obtain hexagonal boron nitride single crystal;

[0013] S6. Use heat-release adhesive tape to peel off the hexagonal boron nitride single crystal from the surface of the stainless steel alloy to obtain the hexagonal boron nitride single crystal material.

[0014] Preferably, the stainless steel alloy sheet is a 316 stainless steel alloy sheet; the 316 stainless steel alloy sheet comprises the following components: carbon 0.08-0.1%, manganese 1.5-2.0%, silicon 1-1.5%, phosphorus 0.04-0.045%, sulfur 0.03-0.04%, chromium 16.0-21.0%, nickel 9.0-12.0%, and molybdenum 2.0-3.0%.

[0015] Preferably, the hexagonal boron nitride powder has a purity of ≥99.9% and a particle size of 1–3 μm.

[0016] Preferably, the deoxygenation treatment is carried out under a nitrogen flow of 100–120 sccm; the deoxygenation treatment temperature is 1350–1450℃; and the deoxygenation treatment time is 10–12 h.

[0017] Preferably, the mass ratio of pretreated hexagonal boron nitride powder to stainless steel alloy sheet is 1:(10-14).

[0018] More preferably, the mass ratio of pretreated hexagonal boron nitride powder to stainless steel alloy sheet is 1:12.

[0019] Preferably, the mass ratio of the two layers of pretreated hexagonal boron nitride powder located above and below the stainless steel alloy sheet is (0.5-0.6):(0.4-0.5).

[0020] More preferably, the mass ratio of the two layers of pretreated hexagonal boron nitride powder located above and below the stainless steel alloy sheet is 0.5:0.5.

[0021] Preferably, the nitrogen flow rate in step S4 is 100–200 sccm.

[0022] Preferably, the heating rate for high-temperature growth is 10–15 °C / min; and the high-temperature growth temperature is 1300–1400 °C.

[0023] Preferably, the cooling rate in step S4 is 5–10 °C / min.

[0024] Preferably, the annealing temperature is 1100-1200℃ and the annealing time is 2-3 hours.

[0025] Preferably, the heat release temperature of the heat release tape is 90–100°C.

[0026] The beneficial effects of this invention are:

[0027] 1. The hexagonal boron nitride single crystal material of this invention undergoes deoxidation treatment before preparation. Since conventionally purchased hexagonal boron nitride powder inevitably contains oxygen, these oxygen atoms can react with boron or nitrogen during subsequent high-temperature growth, affecting the formation of the single crystal structure and leading to byproducts. Deoxidation treatment prevents the carried oxygen and moisture from affecting single crystal growth, thereby reducing unnecessary phase transitions or byproduct generation and contributing to obtaining a hexagonal boron nitride single crystal material with higher purity and better quality. Furthermore, during the deoxidation process, the loading tool for subsequent high-temperature growth, namely the boron nitride crucible boat, is also deoxidized. This improves the mechanical strength and thermal stability of the boron nitride crucible boat to some extent and effectively prevents trace amounts of oxygen and impurity elements from being incorporated into the sample, thus avoiding contamination of the obtained hexagonal boron nitride single crystal or alteration of its chemical composition, reducing interference from the tool on single crystal formation.

[0028] 2. In this invention, 316 stainless steel alloy sheets are used as flux for the formation of hexagonal boron nitride single crystals. Compared with general elemental metal fluxes or some alloy fluxes, the flux raw materials of this invention are readily available, and the 316 stainless steel alloy sheets contain abundant metallic components, which can improve the growth quality of single crystals at different levels. In particular, compared with other alloy materials, 316 stainless steel alloy contains a relatively high proportion of chromium. The high proportion of nickel-chromium components can increase the solubility of nitrogen in the alloy. Furthermore, this invention has found that molybdenum can also increase the solubility of nitrogen. As nitrogen is an essential element for the growth of hexagonal boron nitride single crystals, increased solubility of nitrogen will significantly promote single crystal growth. Nickel also has a certain catalytic effect, which can guide the growth of hexagonal boron nitride single crystals. Moreover, although the high-temperature growth of this invention is carried out under conditions of removing air and nitrogen gas flow, it is difficult to achieve an absolute vacuum and absolute deoxidation of the material. However, 316 stainless steel alloy contains a small amount of carbon, and these carbon atoms can help absorb oxygen and moisture during the high-temperature growth process, which is beneficial to the growth of single crystals. Furthermore, compared to directly doping with carbon powder, this invention does not require the addition of additional substances, which facilitates material separation and improves the purity and quality of the single crystal.

[0029] 3. In the sample preparation of this invention, a layer of pretreated hexagonal boron nitride powder is first laid down, then a stainless steel alloy sheet is covered, and finally another layer of pretreated hexagonal boron nitride powder is laid down. This special material placement arrangement can maximize the contact area between the hexagonal boron nitride powder and the stainless steel alloy sheet, and can also better improve the heat transfer efficiency, so that the material can be heated evenly. At the same time, it can also grow evenly on the surface of the stainless steel alloy, increase the size of the formed single crystal, and better reduce the occurrence of cracks.

[0030] 4. After high-temperature growth, hexagonal boron nitride single crystals are prone to thermal stress accumulation at the interface due to the mismatch in thermal expansion coefficients between boron nitride and stainless steel alloys. After cooling, this stress can easily lead to cracks or other defects in the single crystal, affecting its quality. Therefore, this invention performs annealing treatment on the hexagonal boron nitride single crystals after growth. This not only eliminates stress and reduces stress-induced defects and damage, but also helps promote atomic rearrangement, making the obtained single crystal structure more ordered and perfect. This improves the ductility, crystallinity, and stability of the obtained single crystal material, and facilitates the separation between the boron nitride and stainless steel alloys.

[0031] 5. This invention uses heat-release adhesive tape to peel off hexagonal boron nitride single crystal material grown on the surface of stainless steel alloy, which can obtain larger and higher quality single crystal material more completely and reduce single crystal damage and loss caused during the peeling process. Attached Figure Description

[0032] The invention will now be further described with reference to the accompanying drawings.

[0033] Figure 1 This is a flowchart illustrating Embodiment 1 of the present invention;

[0034] Figure 2 This is a schematic diagram of the raw material placement structure in Embodiment 1 of the present invention; wherein 1 is a boron nitride crucible boat, 2 is a pretreated hexagonal boron nitride powder layer, and 3 is a 316 stainless steel alloy sheet;

[0035] Figure 3 This is the Fourier transform infrared spectrum of Embodiment 1 of the present invention. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] Example

[0038] Example 1: A hexagonal boron nitride single crystal material was prepared according to the following method:

[0039] S1. Take a 316 stainless steel alloy sheet with a mass of 180g, clean it with deionized water and ethanol in sequence, and then dry it for later use.

[0040] S2. Place the hexagonal boron nitride powder in a boron nitride crucible boat, then place it in a tube furnace. Use a vacuum pump to evacuate the furnace tube to a vacuum state, then introduce nitrogen gas until the furnace is at atmospheric pressure. Then, under a nitrogen flow of 100 sccm, raise the temperature to 1400℃ at a heating rate of 10℃ / min, hold for 12 hours, and then allow it to cool naturally to room temperature for deoxidation treatment to obtain pretreated hexagonal boron nitride powder.

[0041] S3. Take 15g of pretreated hexagonal boron nitride powder, spread the pretreated hexagonal boron nitride powder evenly in the boron nitride crucible boat, cover it with the 316 stainless steel alloy sheet that was dried and prepared in step S1, and then spread a layer of pretreated hexagonal boron nitride powder evenly on the 316 stainless steel alloy sheet. The mass ratio of the two layers of pretreated hexagonal boron nitride powder above and below the 316 stainless steel alloy sheet is 0.5:0.5. Finally, cover the boron nitride crucible boat with the lid to obtain the sample to be processed.

[0042] S4. Place the sample obtained in step S3 in a tube furnace. First, evacuate the furnace to remove air, then introduce nitrogen to atmospheric pressure. Under a nitrogen flow of 100 sccm, raise the temperature to 1300℃ at a heating rate of 10℃ / min, hold at the temperature for high-temperature growth for 10 hours, then lower the temperature to 1000℃ at a cooling rate of 5℃ / min and stop heating. Allow it to cool naturally to room temperature to obtain a crude hexagonal boron nitride single crystal grown on the surface of a stainless steel alloy.

[0043] S5. The crude hexagonal boron nitride single crystal obtained above is annealed by heating to 1200°C at a rate of 10°C / min, holding for 2 hours and then naturally cooling to room temperature to obtain hexagonal boron nitride single crystal.

[0044] S6. Hexagonal boron nitride single crystals were peeled off from the surface of a stainless steel alloy using heat-release tape to obtain hexagonal boron nitride single crystal material. The heat release temperature of the heat-release tape was 100℃, and the tape area was 20mm×20mm.

[0045] pass Figure 3 It can be seen that at 780.2cm -1 and 1375cm -1 The two main spectral bands nearby are primarily BNB bending vibrations and BN stretching vibrations, which are typical characteristics of hexagonal boron nitride. Furthermore, the peaks are clear and free of impurities, indicating that the material prepared in this invention is high-purity hexagonal h-BN. Observation also shows that the obtained single-crystal material maintains good morphology, exhibits good crystallinity, is crack-free, and has a large size, with single-crystal edge lengths reaching hundreds of micrometers.

[0046] Example 2 presents a hexagonal boron nitride single crystal material, differing from Example 1 only in that the amount of pretreated hexagonal boron nitride powder added is 13g. Finally, a large-size hexagonal boron nitride single crystal material with good crystallinity and no cracks is obtained.

[0047] Example 3 presents a hexagonal boron nitride single crystal material, differing from Example 1 only in that the amount of pretreated hexagonal boron nitride powder added is 18g. Finally, a large-size hexagonal boron nitride single crystal material with good crystallinity and no cracks is obtained.

[0048] Example 4 presents a hexagonal boron nitride single crystal material, differing from Example 1 only in that the amount of pretreated hexagonal boron nitride powder added is 10g. Finally, a large-size hexagonal boron nitride single crystal material with good crystallinity and no cracks is obtained.

[0049] Example 5 presents a hexagonal boron nitride single crystal material, differing from Example 1 only in that the mass ratio of the two layers of pretreated hexagonal boron nitride powder located above and below the 316 stainless steel alloy sheet is 0.6:0.4. Finally, a large-size hexagonal boron nitride single crystal material with good crystallinity and no cracks is obtained.

[0050] Example 6, a hexagonal boron nitride single crystal material, differs from Example 1 only in that the mass ratio of the two layers of pretreated hexagonal boron nitride powder located above and below the 316 stainless steel alloy sheet is 0.4:0.6.

[0051] Compared to the single-crystal material obtained in Example 1, fine cracks appeared, and after the single crystals grew on the stainless steel surface, due to their small size and thinness, they were difficult to peel off using heat-release tape, resulting in a decrease in the proportion of perfectly shaped single-crystal material removed. Furthermore, some powder beneath the stainless steel alloy sheet failed to crystallize on the stainless steel alloy surface, leading to a decrease in crystallinity.

[0052] Comparative Example

[0053] Comparative Example 1 presents a hexagonal boron nitride single crystal material, differing from Example 1 only in that an equal amount of elemental nickel sheet is used instead of the 316 stainless steel alloy sheet. The resulting hexagonal boron nitride single crystal material is small in size, difficult to peel off, and contains micro-cracks.

[0054] Comparative Example 2 presents a hexagonal boron nitride single crystal material. The only difference from Example 1 is that the rough hexagonal boron nitride single crystal grown on a stainless steel alloy surface after high-temperature growth is not annealed; instead, the single crystal material is directly peeled off using heat-release tape. The resulting hexagonal boron nitride single crystal material exhibits poor crystallinity, with cracks appearing on both the surface and inside the material.

[0055] Comparative Example 3 presents a hexagonal boron nitride single crystal material, differing from Example 1 only in that the hexagonal boron nitride powder and the boron nitride crucible boat are not deoxidized. Ultimately, only a small amount of hexagonal boron nitride single crystal material is grown on the stainless steel alloy surface, and the resulting single crystal material contains numerous small cracks.

[0056] Comparative Example 4, a hexagonal boron nitride single crystal material, differs from Example 1 only in that S3 is performed according to the following steps:

[0057] Take 15g of pretreated hexagonal boron nitride powder and spread it evenly in a boron nitride crucible boat. Cover it with the dried 316 stainless steel alloy sheet prepared in step S1, and finally cover the boron nitride crucible boat with its lid to obtain the sample to be processed. Ultimately, only a portion of hexagonal boron nitride single crystal material forms on the surface of the stainless steel alloy, and the formed single crystal material has poor crystallinity, cracks, and uneven single crystal size with variations in size.

[0058] Comparative Example 5, a hexagonal boron nitride single crystal material, differs from Example 1 only in that S3 is performed according to the following steps:

[0059] The dried 316 stainless steel alloy sheet from step S1 was placed in a boron nitride crucible boat. Then, 15g of pretreated hexagonal boron nitride powder was spread evenly on the 316 stainless steel alloy sheet. Finally, the lid of the boron nitride crucible boat was placed on top to obtain the sample to be processed. The final hexagonal boron nitride single crystal material showed a decrease in crystallinity and crystallization performance, and cracks were present in some of the single crystal materials.

[0060] Comparative Example 6, a hexagonal boron nitride single crystal material, differs from Example 1 only in that S3 is performed according to the following steps:

[0061] 15g of pretreated hexagonal boron nitride powder was added to a boron nitride crucible boat along with 316 stainless steel alloy particles (average particle size 50μm). The crucible boat was then covered to obtain the sample to be processed. The resulting hexagonal boron nitride single crystal material was small in size, with edge lengths ranging from a few micrometers to tens of micrometers, exhibiting non-uniformity and poor crystallinity. The obtained single crystal material also contained some cracks.

[0062] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method of producing a hexagonal boron nitride single crystal material, characterized by, Includes the following steps: S1. Clean and dry the stainless steel alloy sheet for later use; S2. Deoxidize the hexagonal boron nitride powder and the boron nitride crucible boat together to obtain pretreated hexagonal boron nitride powder; S3. Spread the pretreated hexagonal boron nitride powder evenly in the boron nitride crucible boat, cover it with a stainless steel alloy sheet, then spread a layer of pretreated hexagonal boron nitride powder evenly on the stainless steel alloy sheet, and finally cover the boron nitride crucible boat with the lid to obtain the sample to be processed. The mass ratio of the two layers of pretreated hexagonal boron nitride powder located above and below the stainless steel alloy sheet is (0.5~0.6):(0.4~0.5). S4. Place the sample obtained in step S3 in a tube furnace, first evacuate the furnace to remove air, then introduce nitrogen to atmospheric pressure, grow at high temperature for 10-12 hours under nitrogen flow, then cool down to 900-1000℃ and stop heating, and let it cool naturally to room temperature to obtain a crude hexagonal boron nitride single crystal grown on the surface of stainless steel alloy. S5. Anneal the crude hexagonal boron nitride single crystal to obtain hexagonal boron nitride single crystal; S6. Use heat-release adhesive tape to peel off the hexagonal boron nitride single crystal from the surface of the stainless steel alloy to obtain the hexagonal boron nitride single crystal material.

2. The method of claim 1, wherein the hexagonal boron nitride single crystal material is prepared by a method comprising: The stainless steel alloy sheet is a 316 stainless steel alloy sheet; the 316 stainless steel alloy sheet comprises the following components: carbon 0.08-0.1%, manganese 1.5-2.0%, silicon 1-1.5%, phosphorus 0.04-0.045%, sulfur 0.03-0.04%, chromium 16.0-21.0%, nickel 9.0-12.0%, and molybdenum 2.0-3.0%.

3. The method of claim 1, wherein the hexagonal boron nitride single crystal material is prepared by a method comprising: The hexagonal boron nitride powder has a purity of ≥99.9% and a particle size of 1–3 μm.

4. The method for preparing hexagonal boron nitride single crystal material according to claim 1, characterized in that, The deoxygenation treatment is carried out under a nitrogen flow of 100–120 sccm; the deoxygenation treatment temperature is 1350–1450℃, and the deoxygenation treatment time is 10–12 h.

5. The method for preparing hexagonal boron nitride single crystal material according to claim 1, characterized in that, The mass ratio of the pretreated hexagonal boron nitride powder to the stainless steel alloy sheet is 1:(10-14).

6. The method for preparing hexagonal boron nitride single crystal material according to claim 1, characterized in that, The nitrogen flow rate in step S4 is 100–200 sccm.

7. The method for preparing hexagonal boron nitride single crystal material according to claim 1, characterized in that, The heating rate for the high-temperature growth is 10–15 °C / min; the high-temperature growth temperature is 1300–1400 °C.

8. The method for preparing hexagonal boron nitride single crystal material according to claim 1, characterized in that, The annealing temperature is 1100–1200℃, and the annealing time is 2–3 hours.

9. The method for preparing hexagonal boron nitride single crystal material according to claim 1, characterized in that, The heat release temperature of the heat release tape is 90-100℃.

Images