A large bandgap topological insulator material Bi4Br4 nanostructure and its preparation method

Abstract

This invention relates to a large-bandgap topological insulator material, Bi4Br4, and its preparation method, belonging to the field of crystal materials technology. The nanostructure is prepared using a physical vapor transport method. The method uses Bi4Br4 single crystals as raw materials, and directly prepares high-quality two-dimensional Bi4Br4 nanostructures on a silicon substrate coated with an Au film by vacuum heating the raw material end at 320-400℃ and holding it at that temperature for 30-90 minutes. The Bi4Br4 nanostructures exhibit uniform phase formation and low impurity content.

Description

Technical Field

[0001] This invention relates to a large bandgap topological insulator material Bi4Br4 nanostructure and its preparation method, belonging to the field of crystal material technology. Background Technology

[0002] Topological insulators are a novel quantum state of matter. Simply put, they possess a bulk bandgap similar to that of ordinary insulators, but exhibit gapless conductive channels on their surfaces. They also display a linear energy-momentum dispersion relation, with spin and momentum locked surface electrons protected by time-reversal symmetry. Moreover, these three-dimensional surface-state materials or two-dimensional edge-state materials are more stable than ordinary metals and are unaffected by scattering from defects or impurities. Therefore, topological insulators are considered to have enormous application potential in low-power transmission, sensing, and quantum detection.

[0003] Bi4Br4 is predicted to be a large-bandgap topological insulator, with its nanostructures possessing single Dirac cone edge states spanning the bulk bandgap, making it an ideal carrier for dissipative transport. However, current research primarily focuses on three-dimensional bulk materials. As research progresses, it has become increasingly difficult to directly extract single-layer or few-layer structures from three-dimensional bulk materials, significantly hindering subsequent device development and future applications. Therefore, directly fabricating high-quality two-dimensional Bi4Br4 nanostructures is of paramount importance.

[0004] Chinese patent CN113445124B discloses a Bi4Br4 thin film and its preparation method. The method employs molecular beam epitaxy (MBE) to grow a Bi thin film on a substrate. The substrate is either a (001) cleavage plane of a transition metal chalcogenide single crystal or a HOPG (0001) cleavage plane. BiBr3 is deposited onto the surface of the Bi thin film using high-temperature pyrolysis. Deposition ends when the thickness of the film deposited on the Bi film surface is 4-5 times the thickness of the Bi film. When the substrate is a HOPG (0001) cleavage plane, the film on the substrate is a Bi4Br4 thin film; when the substrate is a (0001) cleavage plane of a transition metal chalcogenide single crystal, the film on the substrate is a BiBr thin film. Annealing is then performed to obtain the Bi4Br4 thin film. This method is complex, energy-intensive, cannot achieve precise control of the Bi4Br4 nanostructure, and is difficult to obtain uniform nanomaterials. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a large bandgap topological insulator material Bi4B. r4The nanostructure and its preparation method are disclosed. The nanostructure is grown directly on the substrate using Bi4Br4 single crystal as raw material and silicon wafer as substrate through a novel physical vapor transport method. This method is of great value for the subsequent device research and future applications of Bi4Br4.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] A method for preparing Bi4Br4 nanostructures, a large bandgap topological insulator material, comprising the following steps:

[0008] (1) In an environment where the water and oxygen content is less than 0.1 ppm, the Bi4Br4 single crystal and the silicon wafer are placed at both ends of a quartz tube, and the quartz tube is vacuum sealed with a vacuum degree less than or equal to 1×10⁻⁶. -4 Pa;

[0009] (2) The end where the silicon wafer is placed in the quartz tube sealed in step (1) is the growth end, and the end where the Bi4Br4 single crystal is placed is the raw material end. The raw material end is heated from room temperature to 320~400℃, kept at a constant temperature for 30~100min and then cooled to room temperature. The growth end is not heated.

[0010] (3) Open the quartz tube and generate a large bandgap topological insulator material Bi4Br4 nanostructure on the surface of the silicon wafer.

[0011] Preferably, in step (1), the silicon wafer surface is uniformly coated with an Au film of 10-20 nm thickness. The gold film can control the type of nanostructure; for example, the thicker the gold film, the more the nanostructure tends to be a thin film structure.

[0012] Preferably, in step (1), the vacuum degree in the sealed quartz tube is less than or equal to 1×10⁻⁶. -4 Pa.

[0013] Preferably, in step (2), the quartz tube sealed in step (1) is placed in a dual-temperature zone tube furnace, with the raw material end placed at the high-temperature end and the growth end placed at the low-temperature end. Although the low-temperature end is not heated, the temperature at the low-temperature end will also change due to heat conduction from the high-temperature end. Both the high-temperature and low-temperature ends of the dual-temperature zone tube furnace are equipped with thermocouples, which can directly display the temperature reading at the low-temperature end, making it convenient to observe and record the actual working conditions at the low-temperature end.

[0014] Preferably, in step (2), when the raw material temperature is 350~365℃ and the isothermal holding time is 30~40min, the prepared Bi4Br4 nanostructure contains more than 70% nanowires and the remainder is nanosheets; when the raw material temperature is 365~385℃ and the isothermal holding time is extended to 60~80min, the prepared Bi4Br4 nanostructure contains more than 70% nanosheets and the remainder is nanowires; when the raw material temperature is 385~400℃ and the isothermal holding time is extended to 90~100min, the prepared Bi4Br4 nanostructure contains more than 70% nanofilms and the remainder is nanosheets.

[0015] Preferably, in step (2), the heating and cooling rate is 4℃ / min~5℃ / min.

[0016] A large bandgap topological insulator material Bi4Br4 nanostructure, wherein the nanostructure comprises one or more of nanosheets, nanofilms, and nanowires.

[0017] Beneficial effects

[0018] 1. This invention provides a large bandgap topological insulator material Bi4Br4 nanostructure, wherein the nanostructure includes at least one of nanosheets, nanoribbons and nanofilms; the Bi4Br4 nanostructure has uniform phase formation and low impurity content, and can be directly transferred and used to fabricate devices, and has great potential application value in the field of low power devices.

[0019] 2. This invention provides a large-bandgap topological insulator material, Bi4Br4, with a nanostructure prepared using a physical vapor transport method. The method uses Bi4Br4 single crystals as raw material, directly fabricating a high-quality two-dimensional Bi4Br4 nanostructure on a silicon substrate by vacuum heating the raw material end at 320-400℃ and holding it at that temperature for 30-90 minutes. Controlling the heating temperature and holding temperature of the raw material end during physical vapor transport allows for the adjustment of the Bi4Br4 nanostructure. Compared to materials prepared by flux methods, it exhibits more intrinsic properties of Bi4Br4, providing a material basis for its properties research. The method is simple, practical, and can be applied to the preparation of nanostructures of other materials. Attached Figure Description

[0020] Figure 1 This is the X-ray diffraction (XRD) pattern of the Bi4Br4 single crystal described in this embodiment of the invention.

[0021] Figure 2 This is a scanning electron microscope (SEM) image of the Bi4Br4 material described in Example 1.

[0022] Figure 3The image shows the XRD pattern of the Bi4Br4 material described in Example 1.

[0023] Figure 4 This is a SEM image of the Bi4Br4 material described in Example 2.

[0024] Figure 5 This is a SEM image of the Bi4Br4 material described in Example 4.

[0025] Figure 6 The image shows the X-ray energy dispersive spectroscopy (EDS) spectra of the Bi4Br4 material described in Examples 1, 2, and 4. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments.

[0027] The reagents and instruments used in the following examples are all conventional reagents and instruments in the art and can be obtained commercially.

[0028] In Examples 1-4 below, Bi4Br4 single crystals were grown using a flux method, and the specific steps are as follows:

[0029] (1) The Bi particles were encapsulated in a quartz tube filled with hydrogen at 0.8 atmospheres and annealed at 220K to remove the oxide layer on the surface.

[0030] Using Bi as a flux and BiBr3 as a raw material, the raw material and flux were weighed and placed in a quartz tube according to a stoichiometric ratio of BiBr3:Bi = 1:16. The raw material mass was 7.5g, with a weighing error of 0.1%. Quartz wool was added, and then the quartz tube was placed under a vacuum of 1×10⁻⁶. -4 The Pa sealing system is sealed;

[0031] The purity of both the flux Bi and the raw material BiBr3 is 99.99%.

[0032] (2) Place the vacuum-sealed quartz tube from step (1) into a muffle furnace, raise the temperature to 500°C after 3 hours, maintain the temperature at 500°C for 10 hours, then lower the temperature to 310°C after 15 hours, maintain the temperature at this temperature for 5 hours, and finally lower the temperature to 278°C at a rate of 1°C / h, and centrifuge at 278°C. During the centrifugation process, excess Bi is adsorbed by the quartz wool and separated from the single crystal; open the quartz tube to obtain the product.

[0033] The structure of the obtained product was analyzed using X-ray diffraction (XRD), and the results are as follows: Figure 1 As shown, a comparison with the standard card (ICSD number: 98-000-1560) reveals that the product is a Bi4Br4 single crystal.

[0034] In the following Examples 1 to 4: the silicon wafer used is 4 to 5 cm long and 6 to 7 mm wide, and the silicon wafer is uniformly electroplated with an Au film with a thickness of 10 to 20 nm; the quartz tube used has an inner diameter of 8 mm and an outer diameter of 12 mm.

[0035] Example 1

[0036] A large bandgap topological insulator material, Bi4Br4, nanostructures, primarily consisting of nanosheets, were prepared using a physical vapor transport method. The specific steps are as follows:

[0037] (1) Weigh 0.02g of Bi4Br4 single crystal in a glove box with water and oxygen content less than 0.1ppm and argon atmosphere. Place the single crystal and a silicon wafer with a uniform Au film on the surface at both ends of a quartz tube. Perform gas purging with argon in a vacuum tube sealing system. After purging, use a mechanical pump to evacuate the argon in the tube. Place the quartz tube under a vacuum of 1×10 -4 The Pa sealing system is sealed;

[0038] (2) Place the sealed quartz tube in a dual-temperature zone tube furnace with a temperature zone of 10cm. Use the end of the quartz tube where the Bi4Br4 single crystal is placed as the raw material end and the end where the silicon wafer is placed as the growth end. Place the raw material end at the high temperature end of the dual-temperature zone tube furnace and the growth end at the low temperature end of the dual-temperature zone tube furnace. After 80 minutes, the high temperature end is heated from room temperature to 320°C and kept at 320°C for 90 minutes. The growth end is not heated. Then, after 80 minutes, the temperature is lowered to room temperature and the tube furnace is turned off.

[0039] (3) When the quartz tube is opened, Bi4Br4, a large bandgap topological insulator material, is generated on the surface of the silicon wafer.

[0040] After opening the quartz tube, the blackening of the silicon wafer surface was clearly visible to the naked eye; the morphology of the Bi4Br4 material formed on the silicon wafer surface of Example 1 was observed using a scanning electron microscope (SEM), and the results are as follows. Figure 2 As shown, the Bi4Br4 material is mainly in the form of sheets, with the length and width of the nanosheets in the micrometer range and the thickness in the nanometer range. The content of nanosheets in the prepared Bi4Br4 nanostructure is more than 70%.

[0041] The elemental composition of the Bi4Br4 material prepared in Example 1 was determined using X-ray energy dispersive spectroscopy (EDS), and the results are as follows: Figure 6 As shown in (a), characteristic peaks of Bi and Br appear, and the ratio of each element is very close to 1:1. At the same time, the EDS results between each selected region are very similar, indicating that the Bi4Br4 material has high purity and good uniformity.

[0042] The structure of the Bi4Br4 material prepared in Example 1 was determined using X-ray diffraction (XRD), and the results are as follows: Figure 3 As shown, compared with the standard card (ICSD number: 98-000-1560), it can be seen that all the spectral peaks of the Bi4Br4 material prepared in Example 1 are close to the diffraction peaks of Bi4Br4 single crystal. Among them, the peak near 2θ=70° originates from the substrate, indicating that the Bi4Br4 material prepared in Example 1 has a single crystal structure.

[0043] Example 2

[0044] A large bandgap topological insulator material, Bi4Br4, nanostructure, mainly consisting of a nanofilm, is prepared using a physical vapor transport method. The specific steps are as follows:

[0045] (1) Weigh 0.02g of Bi4Br4 single crystal in a glove box with water and oxygen content less than 0.1ppm and argon atmosphere. Place the single crystal and a silicon wafer with a uniform Au film on the surface at both ends of a quartz tube. Perform gas purging with argon in a vacuum tube sealing system. After purging, use a mechanical pump to evacuate the argon in the tube. Place the quartz tube under a vacuum of 1×10 -4 The Pa sealing system is sealed;

[0046] (2) Place the sealed quartz tube in a dual-temperature zone tube furnace with a temperature zone of 10cm. Use the end of the quartz tube where the Bi4Br4 single crystal is placed as the raw material end and the end where the silicon wafer is placed as the growth end. Place the raw material end at the high temperature end of the dual-temperature zone tube furnace and the growth end at the low temperature end of the dual-temperature zone tube furnace. After 80 minutes, the high temperature end is heated from room temperature to 320°C and kept at 320°C for 60 minutes. The growth end is not heated. Then, after 80 minutes, the temperature is lowered to room temperature and the tube furnace is turned off.

[0047] (3) When the quartz tube is opened, Bi4Br4, a large bandgap topological insulator material, is generated on the surface of the silicon wafer.

[0048] After opening the quartz tube, the blackening of the silicon wafer surface was clearly visible to the naked eye; the morphology of the Bi4Br4 material formed on the silicon wafer surface in Example 2 was observed using a scanning electron microscope (SEM), and the results are as follows. Figure 4 As shown, the Bi4Br4 material is mainly a nanofilm grown on a silicon wafer coated with an Au film; the content of the nanofilm in the prepared Bi4Br4 nanostructure is more than 70%.

[0049] The elemental composition of the Bi4Br4 material prepared in Example 2 was determined using X-ray energy dispersive spectroscopy (EDS), and the results are as follows: Figure 6As shown in (b), characteristic peaks of Bi and Br appear, and the ratio of each element is very close to 1:1. At the same time, the EDS results between each selected region are very similar, indicating that the Bi4Br4 material has high purity and good uniformity.

[0050] The structure of the Bi4Br4 material prepared in Example 2 was determined by X-ray diffraction (XRD), and the results showed that the Bi4Br4 material prepared in Example 2 has a polycrystalline structure.

[0051] The film prepared in this embodiment is denser than the film in CN113445124B, and the equipment used is simpler to operate and has a lower cost.

[0052] Example 3

[0053] A large bandgap topological insulator material, Bi4Br4, nanostructure, mainly consisting of a nanofilm, is prepared using a physical vapor transport method. The specific steps are as follows:

[0054] (1) Weigh 0.02g of Bi4Br4 single crystal in a glove box with water and oxygen content less than 0.1ppm and argon atmosphere. Place the single crystal and a silicon wafer with a uniform Au film on the surface at both ends of a quartz tube. Perform gas purging with argon in a vacuum tube sealing system. After purging, use a mechanical pump to evacuate the argon in the tube. Place the quartz tube under a vacuum of 1×10 -4 The Pa sealing system is sealed;

[0055] (2) Place the sealed quartz tube in a dual-temperature zone tube furnace with a temperature zone of 10cm. Use the end of the quartz tube where the Bi4Br4 single crystal is placed as the raw material end and the end where the silicon wafer is placed as the growth end. Place the raw material end at the high temperature end of the dual-temperature zone tube furnace and the growth end at the low temperature end of the dual-temperature zone tube furnace. After 80 minutes, the high temperature end is heated from room temperature to 400℃ and kept at 400℃ for 60 minutes. The growth end is not heated. Then, after 80 minutes, the temperature is reduced to room temperature and the tube furnace is turned off.

[0056] (3) When the quartz tube is opened, Bi4Br4, a large bandgap topological insulator material, is generated on the surface of the silicon wafer.

[0057] After opening the quartz tube, the blackening of the silicon wafer surface can be clearly seen with the naked eye. The morphology of the Bi4Br4 material generated on the silicon wafer surface in Example 3 was observed using a scanning electron microscope (SEM). The results were similar to those in Example 2. The Bi4Br4 material was mainly a nanofilm grown on a silicon wafer coated with an Au film. The content of the nanofilm in the prepared Bi4Br4 nanostructure was more than 70%.

[0058] The elemental ratio of the Bi4Br4 material prepared in Example 3 was determined by X-ray energy dispersive spectroscopy (EDS). The results were similar to those in Example 2, with characteristic peaks of Bi and Br appearing and the ratio of each element being very close to 1:1. At the same time, the EDS results between different selected regions were very similar, indicating that the Bi4Br4 material has high purity and good uniformity.

[0059] The structure of the Bi4Br4 material prepared in Example 3 was determined by X-ray diffraction (XRD). The results were similar to those in Example 2, indicating that the Bi4Br4 material prepared in Example 3 has a polycrystalline structure.

[0060] Example 4

[0061] A large bandgap topological insulator material, Bi4Br4, nanostructures, primarily composed of nanowires, were prepared using a physical vapor transport method. The specific steps are as follows:

[0062] (1) Weigh 0.02g of Bi4Br4 single crystal in a glove box with water and oxygen content less than 0.1ppm and argon atmosphere. Place the single crystal and a silicon wafer with a uniform Au film on the surface at both ends of a quartz tube. Perform gas purging with argon in a vacuum tube sealing system. After purging, use a mechanical pump to evacuate the argon in the tube. Place the quartz tube under a vacuum of 1×10 -4 The Pa sealing system is sealed;

[0063] (2) Place the sealed quartz tube in step (1) into a dual-temperature zone tube furnace with a temperature zone of 10cm. Use the end of the quartz tube where the Bi4Br4 single crystal is placed as the raw material end and the end where the silicon wafer is placed as the growth end. Place the raw material end at the high temperature end of the dual-temperature zone tube furnace and the growth end at the low temperature end of the dual-temperature zone tube furnace. After 80 minutes, the high temperature end is heated from room temperature to 400℃ and kept at 400℃ for 30 minutes. The growth end is not heated. Then, after 80 minutes, the temperature is lowered to room temperature and the tube furnace is turned off.

[0064] (3) When the quartz tube is opened, Bi4Br4, a large bandgap topological insulator material, is generated on the surface of the silicon wafer.

[0065] After opening the quartz tube, the blackening of the silicon wafer surface was clearly visible to the naked eye; the morphology of the Bi4Br4 material formed on the silicon wafer surface in Example 4 was observed using a scanning electron microscope (SEM), and the results are as follows. Figure 5 As shown, the Bi4Br4 material is mainly in the form of strips; the content of nanowires in the prepared Bi4Br4 nanostructure is more than 70%.

[0066] The elemental composition of the Bi4Br4 material prepared in Example 4 was determined using X-ray energy dispersive spectroscopy (EDS), and the results are as follows: Figure 6As shown in (c), characteristic peaks of Bi and Br appear, and the composition ratio of each element is very close to 1:1. At the same time, the EDS results between each selected region are very similar, indicating that the Bi4Br4 material has high purity and good uniformity.

[0067] The structure of the Bi4Br4 material prepared in Example 4 was determined by X-ray diffraction (XRD). The results were similar to those in Example 1, indicating that the Bi4Br4 material prepared in Example 4 has a single crystal structure.

[0068] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A method for preparing a large band gap topological insulator material Bi4Br4 nanostructure, characterized by comprising the following steps: The method steps include: ​ (1) In an environment where the water and oxygen content is less than 0.1 ppm, place the Bi4Br4 single crystal and the silicon wafer at both ends of a quartz tube and vacuum seal the quartz tube. (2) The end where the silicon wafer is placed in the quartz tube sealed in step (1) is the growth end, and the end where the Bi4Br4 single crystal is placed is the raw material end. The raw material end is heated from room temperature to 320~400℃, kept at a constant temperature for 30~100min and then cooled to room temperature. The growth end is not heated. (3) Open the quartz tube to generate a large bandgap topological insulator material Bi4Br4 nanostructure on the surface of the silicon wafer.

2. The method for preparing a large bandgap topological insulator material Bi4Br4 nanostructure as described in claim 1, characterized in that: In step (1), the vacuum degree in the sealed quartz tube is less than or equal to 1 x 10 -4 Pa.

3. The method for preparing a large bandgap topological insulator material Bi4Br4 nanostructure as described in claim 1, characterized in that: In step (1), the silicon wafer surface is uniformly coated with a 10~20nm thick Au film.

4. The method for preparing a large bandgap topological insulator material Bi4Br4 nanostructure as described in claim 1, characterized in that: In step (2), the quartz tube sealed in step (1) is placed in a dual-temperature zone tube furnace, with the raw material end placed at the high-temperature end of the dual-temperature zone tube furnace and the growth end placed at the low-temperature end of the dual-temperature zone tube furnace.

5. The method for preparing a large bandgap topological insulator material Bi4Br4 nanostructure as described in claim 1, characterized in that: In step (2), when the raw material temperature is 350~365℃ and the isothermal holding time is 30~40min, the prepared Bi4Br4 nanostructure contains more than 70% nanowires and the remainder is nanosheets; when the raw material temperature is 365~385℃ and the isothermal holding time is extended to 60~80min, the prepared Bi4Br4 nanostructure contains more than 70% nanosheets and the remainder is nanowires; when the raw material temperature is 385~400℃ and the isothermal holding time is extended to 90~100min, the prepared Bi4Br4 nanostructure contains more than 70% nanofilms and the remainder is nanosheets.

6. The method for preparing a large bandgap topological insulator material Bi4Br4 nanostructure as described in claim 1, characterized in that: In step (2), the heating and cooling rate is 4~5℃ / min.

Images