Method for preparing multilayer single-crystal rhombohedral boron nitride thin film

Abstract

A method for preparing a multilayer single-crystal rhombohedral boron nitride thin film, comprising: (1) placing a growth source and a single-crystal nickel foil in an upstream temperature zone and a downstream temperature zone of a chemical vapor deposition system, respectively; (2) introducing a carrier gas into the chemical vapor deposition system, and raising the temperature of the downstream temperature zone to 1300-1450℃, to remove an oxide layer from a surface of the nickel foil, and maintaining the temperature of the upstream temperature zone at less than 60℃; (3) cooling the downstream temperature zone to 1200-1350℃ at a constant rate and maintaining this temperature, so that parallel steps are formed on the surface of the nickel foil, the parallel steps being composed of terraces and inclined surfaces; (4) heating the upstream temperature zone so as to form single-orientation multilayer rhombohedral boron nitride crystal nuclei, and subsequently maintaining the temperature of the upstream temperature zone unchanged and fixing the carrier gas, while heating the downstream temperature zone to 1300-1450℃, so as to grow a multilayer single-crystal rhombohedral boron nitride thin film.

Description

Method for preparing multilayer single crystal rhombohedral boron nitride thin film Technical Field

[0001] The present invention belongs to the technical field of two-dimensional material growth. Specifically, the present invention relates to a method for preparing a multilayer single-crystalline rhombohedral boron nitride thin film. More specifically, the present invention relates to a method for growing a multilayer single-crystalline rhombohedral boron nitride thin film using step angle locking. Background Art

[0002] Layered boron nitride is considered an ideal two-dimensional chip-scale insulator due to its many excellent properties, including low dielectric constant and dielectric dissipation, large electrical band gap, ultra-high chemical stability, excellent thermal conductivity, and the absence of dangling bonds on the surface. While rhombohedral boron nitride possesses these properties, its parallel stacking configuration between layers endows it with a breaking of both in-plane and out-of-plane spatial inversion symmetry. This enables efficient second-order nonlinear optical frequency conversion over a wide band, while also exhibiting non-volatile interlayer slip ferroelectricity at the atomic scale. This makes it a key material for future applications in integrated photonic chips, ferroelectric field-effect transistors, and integrated computing and storage devices.

[0003] The preparation of large-scale, single-crystal, pure-phase, rhombohedral boron nitride films with controllable thickness is a prerequisite for their true application. Currently, the development of boron nitride synthesis methods focuses on controlling the lattice orientation of single-layer boron nitride and the thickness of multilayer boron nitride. This involves leveraging the rich surface structure of the substrate to control the orientation of the single-layer boron nitride, or preparing multilayer boron nitride films of varying thicknesses based on the dissolution and precipitation growth pattern of the growth source in a high-solubility metal substrate.

[0004] However, to date, there has been no reliable solution for regulating the stacking pattern of multilayer boron nitride layers. The main reason is that the Coulomb interaction between boron nitride layers causes the antiparallel stacking configuration (i.e., the hexagonal phase) to be in the lowest energy state. Although traditional high-temperature and high-pressure synthesis methods can produce rhombohedral boron nitride powder polycrystalline, the harsh conditions required by this process result in low purity of the prepared crystal phase and cannot be used to prepare thin film samples.

[0005] Therefore, there is an urgent need for a method that can simultaneously and effectively control the consistent in-plane lattice orientation and the interlayer rhombohedral stacking configuration, and achieve the preparation of large-size, thickness-controllable single-crystal rhombohedral boron nitride films.

[0006] SUMMARY OF THE INVENTION

[0007] The present invention aims to provide a method for preparing multilayer single-crystalline rhombohedral boron nitride films. This method can effectively control both the uniform in-plane lattice orientation and the rhombohedral stacking structure between layers, and can also achieve the preparation of large-scale, thickness-controllable single-crystalline rhombohedral boron nitride films.

[0008] The above-mentioned object of the present invention is achieved through the following technical solutions.

[0009] The present invention provides a method for preparing a multilayer single-crystalline rhombohedral boron nitride film, which comprises the following steps in sequence:

[0010] (1) placing a growth source and a single crystal nickel foil in the upstream and downstream temperature zones of a chemical vapor deposition system, respectively;

[0011] (2) introducing a carrier gas into the chemical vapor deposition system and heating the downstream temperature zone to 1300-1450° C. for annealing to remove the oxide layer on the surface of the nickel foil; the temperature of the upstream temperature zone is maintained at less than 60° C.;

[0012] (3) cooling the downstream temperature zone to 1200-1350° C. at a constant rate and maintaining the temperature, so that parallel steps are formed on the surface of the nickel foil, wherein the parallel steps are composed of a platform surface and an inclined surface;

[0013] (4) raising the temperature of the upstream temperature zone to form a single-oriented multi-layer rhombohedral boron nitride nucleus on the surface of the nickel foil having parallel steps; then, while maintaining the temperature of the upstream temperature zone constant and fixing the carrier gas, raising the temperature of the downstream temperature zone to 1300-1450° C. to grow a multi-layer single-crystal rhombohedral boron nitride film;

[0014] (5) Optionally, after the growth is completed, the heating power supply is turned off, the gas flow rate in the tube furnace is maintained unchanged, and the tube furnace is naturally cooled to room temperature to obtain a multi-layer single crystal rhombohedral boron nitride film.

[0015] The inventors of this application unexpectedly discovered that when a single-crystal nickel foil in the downstream temperature zone is heated (to 1300-1450°C) and then cooled at a constant rate (to 1200-1350°C), it can form parallel steps of a certain height composed of periodic terraces and inclined surfaces. This parallel step structure enables the preparation of large-area, single-crystal, pure-phase, rhombohedral boron nitride thin films with adjustable thickness.

[0016] The present invention mainly designs and constructs parallel steps on the surface of a metal substrate, where the angle between the platform surface and the inclined surface of the step is greater than 90°. At the same time, the consistent lattice orientation of each layer of boron nitride and the fixed slip vector between adjacent layers are locked, thereby achieving the preparation of large-area single-crystal pure phase and thickness-adjustable rhombohedral boron nitride films, laying a material foundation for its application in many fields such as future photonics chips, high-density non-volatile storage, and integrated storage and computing devices.

[0017] In the present invention, the parallel steps in step (3) may have a certain height, and the parallel steps of the present invention are similar to a "staircase" shape.

[0018] Preferably, in the method of the present invention, the method further comprises the following step, prior to step (1): annealing an industrial nickel foil in a carrier gas at 1300-1450° C. for 1-20 hours to obtain the single crystal nickel foil. In the present invention, if an industrial nickel foil is used, the industrial nickel foil needs to be annealed in a carrier gas (such as hydrogen) to remove impurities such as carbon.

[0019] Preferably, in the method of the present invention, the carrier gas in step (2) comprises argon with a flow rate of 10-1000 sccm and hydrogen with a flow rate of 0-100 sccm.

[0020] Preferably, in the method of the present invention, the annealing in step (2) is performed for 10-60 minutes.

[0021] Preferably, in the method of the present invention, the constant rate in step (3) is 1-20°C / min.

[0022] Preferably, in the method described in the present invention, the insulation in step (3) is carried out for 1-8 hours.

[0023] Preferably, in the method described in the present invention, the formation of a single-oriented multilayer rhombohedral boron nitride nucleus on the surface of the nickel foil having parallel steps in step (4) is carried out under the following conditions: the upstream temperature zone is heated to 60-90°C, and the volume percentage of hydrogen in the carrier gas is adjusted and the nucleation time is controlled.

[0024] Preferably, in the method of the present invention, the adjusting the volume percentage of hydrogen in the carrier gas is to adjust the volume percentage of hydrogen to be above 1%.

[0025] Preferably, in the method of the present invention, the nucleation time is 0.1-2h.

[0026] Preferably, in the method of the present invention, the growth of the multilayer single-crystalline rhombohedral boron nitride film in step (4) is carried out for 1-10 hours.

[0027] Preferably, in the method described in the present invention, the angle between the platform surface and the inclined surface of the parallel step is 90°<θ<180°. In the present invention, the angle between the platform surface and the inclined surface of the parallel step is shown as θ in Figure 1.

[0028] Preferably, in the method described in the present invention, the crystal plane index of the single crystal nickel foil is Ni(hk0).

[0029] Preferably, in the method described in the present invention, the size of the single crystal nickel foil is above the centimeter level.

[0030] Preferably, in the method of the present invention, the growth source is ammonia borane and / or cycloborazine.

[0031] The present invention has the following beneficial effects:

[0032] 1. In the present invention, the multilayer single-crystal rhombohedral boron nitride prepared has a uniformly oriented nucleus ratio greater than 99%, an area exceeding the centimeter level, and a thickness of 1-15 nm. The multilayer single-crystal rhombohedral boron nitride prepared by the present invention has adjustable thickness, high quality, and promising application prospects.

[0033] 2. The present invention can use commercially available polycrystalline nickel foil, and only requires simple surface pretreatment (high temperature annealing) to obtain a corresponding large-sized single crystal substrate, with low production cost.

[0034] 3. The surface crystal plane index of the single crystal nickel foil selected in the present invention includes but is not limited to (hk0), which reduces the cost of crystal plane selection and has strong universality.

[0035] 4. The step angle locking mode proposed in this invention has broad reference value for the growth of other rhombohedral two-dimensional materials (such as graphene, transition metal chalcogenides, etc.).

[0036] 5. Compared with the extreme environments (such as ultra-high temperature and pressure) required for traditional boron nitride crystal preparation, the preparation temperature and pressure used in the present invention can be achieved in an ordinary tube furnace, reducing energy consumption and preparation costs, and has the prospect of large-scale industrial production.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which:

[0039] FIG1 is a schematic diagram showing the principle of growing a multilayer single crystal rhombohedral boron nitride film by using step angle locking in the present invention (left) and the difference in binding energy between different stacking nuclei and step edges (right).

[0040] Figure 2 is a physical picture of the single crystal nickel substrate used in Example 1 of the present invention (left), X-ray diffraction data for characterizing the crystal plane index (center), and an atomic force microscope image of the surface step morphology and the corresponding angle statistics (right).

[0041] Figure 3 is a scanning electron microscope image (left) of the rhombohedral boron nitride multilayer domains growing along the steps on the surface of single-crystalline nickel in Example 1 of the present invention, as well as atomically resolved scanning projection electron microscope images of the plane (middle) and cross-section (right) of the prepared sample.

[0042] FIG4 is an electron microscope image of single-oriented multilayer domains of rhombohedral boron nitride obtained at different positions on the surface of single-crystalline nickel in Example 1 of the present invention.

[0043] FIG5 is an atomic force microscope characterization image of the single-crystalline rhombohedral boron nitride film prepared in Example 1 of the present invention.

[0044] 6 is a scanning electron microscope image (left), a cross-sectional scanning transmission electron microscope image (center), and a photograph (right) of the 6 nm thick single-crystalline rhombohedral boron nitride continuous film prepared in Example 2 of the present invention.

[0045] FIG. 7 is an atomic force microscope characterization image of single-crystalline rhombohedral boron nitride films of different thicknesses obtained by using different growth times in Example 3 of the present invention.

[0046] FIG8 is a scanning electron microscope photograph, a low-energy electron diffraction pattern, and a transmission electron microscope photograph of hexagonal boron nitride prepared in Comparative Example 1 of the present invention.

[0047] Best Mode for Carrying Out the Invention

[0048] The present invention will be further described in detail below in conjunction with specific embodiments. The examples given are only for illustrating the present invention, not for limiting the scope of the present invention.

[0049] In the following embodiments, the methods are conventional methods unless otherwise specified; the raw materials can be obtained from public commercial channels unless otherwise specified.

[0050] Example 1:

[0051] (1) placing 30 mg of ammonia borane in the upstream temperature zone of a chemical vapor deposition system and placing single crystal nickel (520) in the downstream temperature zone of the system;

[0052] (2) introducing 500 sccm of argon and 50 sccm of hydrogen into the system, raising the temperature of the downstream temperature zone to 1450°C, and annealing the single crystal nickel foil for 1 hour; then lowering the temperature of the downstream temperature zone to 1350°C at a constant rate of 20°C / min and maintaining it for 5 hours; at this time, the temperature of the upstream temperature zone is maintained below 60°C;

[0053] (3) The upstream temperature zone was rapidly heated to 65°C, the argon gas was adjusted to 50 sccm, the hydrogen gas was adjusted to 30 sccm, and the pressure in the corundum tube was reduced to 200 Pa using a mechanical pump. The nucleation time was 2 h. Subsequently, the temperature of the upstream temperature zone was kept constant, the carrier gas was fixed, and the downstream temperature zone was rapidly heated to 1450°C to grow a multilayer single crystal rhombohedral boron nitride film. The growth time was 10 h.

[0054] (4) After the growth is completed, the heating power supply is turned off, the gas flow in the tube furnace is maintained unchanged, and the tube furnace is naturally cooled to room temperature to obtain a multi-layer single crystal rhombohedral boron nitride.

[0055] FIG2 shows a physical image of the single crystal nickel substrate used in this embodiment (left), X-ray diffraction data for characterizing the crystal plane index (center), and an atomic force microscope image of the surface step morphology and the corresponding angle statistics (right).

[0056] Figure 3 shows a scanning electron microscope image (left) of the growth of rhombic boron nitride multilayer domains along the steps of the single crystal nickel surface in this embodiment, as well as the plane (center) and cross-sectional (right) atomic resolution scanning projection electron microscope images of the prepared sample. In step (3), the multilayer rhombic boron nitride domains will nucleate and grow along the parallel steps of the nickel surface (as shown in Figure 3 (left)), and lock their in-plane orientation and interlayer stacking by the step angle. The plane (center) and cross-sectional (right) atomic resolution scanning projection electron microscope images in Figure 3 confirm that the obtained boron nitride domains have a perfect rhombic stacking configuration.

[0057] Figure 4 is an electron microscope image of rhombohedral boron nitride single-orientation multilayer crystal domains obtained at different locations on the surface of single-crystal nickel in this embodiment. Figure 4 shows that the proportion of the prepared multilayer rhombohedral boron nitride crystal cores with uniform orientation is greater than 99%.

[0058] Figure 5 is an atomic force microscope image of the single-crystalline rhombohedral boron nitride film prepared in this embodiment. Figure 5 shows that the thickness of the single-crystalline rhombohedral boron nitride film is 12 nm.

[0059] Example 2:

[0060] (1) placing 15 mg of borazine in the upstream temperature zone of a chemical vapor deposition system and placing single crystal nickel (520) in the downstream temperature zone of the system;

[0061] (2) introducing 100 sccm of argon and 30 sccm of hydrogen into the system, raising the temperature of the downstream temperature zone to 1350°C, and annealing the single crystal nickel foil for 10 minutes; then lowering the temperature of the downstream temperature zone to 1250°C at a constant rate of 5°C / min and maintaining it for 2 hours; at this time, the temperature of the upstream temperature zone is maintained below 60°C;

[0062] (3) The upstream temperature zone was rapidly heated to 75°C, the argon gas was adjusted to 20 sccm, the hydrogen gas was adjusted to 80 sccm, and the pressure in the corundum tube was reduced to 200 Pa using a mechanical pump. The nucleation time was 30 min. Subsequently, the temperature of the upstream temperature zone was kept constant, the carrier gas was fixed, and the downstream temperature zone was rapidly heated to 1350°C to grow a multilayer single crystal rhombohedral boron nitride film. The growth time was 2 h.

[0063] (4) After the growth is completed, the heating power supply is turned off, the gas flow in the tube furnace is maintained unchanged, and the tube furnace is naturally cooled to room temperature to obtain a multi-layer single crystal rhombohedral boron nitride.

[0064] FIG6 is a scanning electron microscope image (left), a cross-sectional scanning transmission electron microscope image (center), and a photograph (right) of the 6 nm thick single-crystalline rhombohedral boron nitride continuous film prepared in this embodiment.

[0065] Example 3:

[0066] Preparation of multilayer single-crystalline rhombohedral boron nitride films of different thicknesses

[0067] This example adopts the same preparation method as Example 1, except that the growth time in step (3) is adjusted to 2 hours, 4 hours and 7 hours respectively.

[0068] Figure 7 shows atomic force microscope images of single-crystal rhombohedral boron nitride films of different thicknesses obtained by the present invention using different growth times. It can be seen that the thickness of the multilayer single-crystal rhombohedral boron nitride prepared by the present invention is adjustable.

[0069] Comparative Example 1:

[0070] The preparation method of this comparative example is the same as that of Example 1, except that the downstream temperature zone in step (2) is cooled to 1100°C.

[0071] Figure 8 shows that lowering the downstream temperature zone to 1100°C results in the appearance of the common hexagonal boron nitride phase. This figure shows that the lattice orientations of each layer of the grown boron nitride sample are opposite, so electron diffraction and transmission electron microscopy images can reflect the central inversion symmetry of the lattice.

Claims

1. A method for preparing a multi-layer single-crystal rhombohedral boron nitride film, which successively includes the following steps: (1) Place the growth source and the single-crystal nickel foil in the upstream temperature zone and the downstream temperature zone of the chemical vapor deposition system respectively; (2) Introduce a carrier gas into the chemical vapor deposition system, and heat the downstream temperature zone to 1300 - 1450 °C for annealing to remove the oxide layer on the surface of the nickel foil; the temperature of the upstream temperature zone is maintained at less than 60 °C; (3) Cool the downstream temperature zone to 1200 - 1350 °C at a constant rate and keep it warm, so that parallel steps are formed on the surface of the nickel foil, and the parallel steps are composed of a platform surface and an inclined surface; (4) Heat the upstream temperature zone to form single-oriented multi-layer rhombohedral boron nitride crystal nuclei on the surface of the nickel foil with parallel steps; subsequently, keep the temperature of the upstream temperature zone unchanged, and fix the carrier gas, while heating the downstream temperature zone to 1300 - 1450 °C to grow a multi-layer single-crystal rhombohedral boron nitride film.

2. The method according to claim 1, wherein, The method further includes the following step before step (1): Anneal the industrial nickel foil in a carrier gas at 1300 - 1450 °C for 1 - 20 h to obtain the single-crystal nickel foil.

3. The method according to claim 1, wherein, The carrier gas in step (2) contains argon with a flow rate of 10 - 1000 sccm and hydrogen with a flow rate of 0 - 100 sccm.

4. The method according to claim 1, wherein The annealing in step (2) is carried out for 10 - 60 min.

5. The method according to claim 1, wherein, The constant rate in step (3) is 1 - 20 °C / min.

6. The method according to claim 1, wherein The heat preservation in step (3) is carried out for 1 - 8 h.

7. The method according to claim 1, wherein The formation of single-oriented multi-layer rhombohedral boron nitride crystal nuclei on the surface of the nickel foil with parallel steps in step (4) is carried out under the following conditions: heat the upstream temperature zone to 60 - 90 °C, and adjust the volume percentage of hydrogen in the carrier gas and control the nucleation time.

8. The method according to claim 7, wherein The adjustment of the volume percentage of hydrogen in the carrier gas is to adjust the volume percentage of hydrogen to more than 1%.

9. The method according to claim 7, wherein The nucleation time is 0.1 - 2 h.

10. The method according to claim 1, wherein The growth of the multi-layer single-crystal rhombohedral boron nitride film in step (4) is carried out for 1 - 10 h; Preferably, the angle between the platform surface and the inclined surface of the parallel steps is 90° < θ < 180°. Preferably, the crystal plane index of the single-crystal nickel foil is Ni(hk0); Preferably, the size of the single-crystal nickel foil is above the centimeter scale; Preferably, the growth source is borane ammonia and / or borazine.

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