Preparation method of large-size high-quality antimony selenide single crystal

Abstract

This invention discloses a method for preparing large-size, high-quality antimony selenide single crystals, including large-size, high-quality single crystal growth, rapid orientation of bulk single crystals, and micron-level ultrathin sheet-like single crystal exfoliation steps. The single crystal growth employs the Bridgman crystal growth technique. First, high-purity Se and Sb powders in stoichiometric ratios are thoroughly ground and pressed into tablets, then loaded into a cleaned and dried single-end sealed high-purity quartz tube. The tube is then evacuated to 10⁻¹⁰ using a mechanical pump and a molecular pump. ‑3 Pa is used to seal the quartz tube. Next, within a vertical Bridgman crystal growth furnace with a known temperature distribution, the aforementioned device is pulled through a controlled temperature gradient region at a certain rate to perform single crystal growth. Then, utilizing the unique cleavage plane morphology resulting from the one-dimensional crystal structure of Sb₂Se₃, the high-quality Sb₂Se₃ single crystal grown by this method is rapidly oriented, and after grinding and polishing, two more orthogonal crystal planes perpendicular to each other are obtained. Finally, through a special exfoliation process, complete thin slices with a thickness of tens of micrometers and a size of over 10 mm are obtained. The thin slices of this invention can be used for ultrafast spectroscopy studies such as THz to study information such as photogenerated carriers.

Description

Technical Field

[0001] This invention relates to single crystal growth, orientation, and exfoliation techniques, and particularly to a method for growing large-size, high-quality antimony selenide single crystals, rapidly orienting bulk single crystals, and exfoliating micron-scale ultrathin sheet-like single crystals. Background Technology

[0002] Antimony selenide (Sb₂Se₃), a group V-VI binary inorganic compound, is a novel, inexpensive, and non-toxic light-absorbing layer material for thin-film photovoltaic cells. It possesses a suitable bandgap (approximately 1.1–1.2 eV) and a high absorption coefficient (over 10 in the short-wavelength band). 5 cm -1 With its advantages of simple phase structure (only one phase) and low crystal growth temperature (phase can be formed at around 300℃), antimony selenide is expected to become a high-efficiency and low-cost optoelectronic material, applicable to photovoltaic power generation and photoelectrochemical water splitting for hydrogen production, in order to solve the serious problems of energy crisis, environmental pollution and climate warming brought about by rapid global economic development. Current research on antimony selenide is based on nanowires or nanocrystalline thin films. However, due to its unique crystal structure, such as... Figure 1 As shown, nanowire or nanopolycrystalline thin film structures have many defects, leading to significant errors in revealing the properties of the material itself. Therefore, it is necessary to prepare high-quality Sb₂Se₃ single crystals and conduct optical and electrical studies on the (100), (010), and (001) orthorhombic crystal planes of Sb₂Se₃ single crystals to obtain the fundamental anisotropic properties of Sb₂Se₃. Ultrafast spectroscopy can be used to obtain information such as the photogenerated carrier mobility and lifetime of the material; however, the THz (terahertz) light spot size is approximately 3 mm, thus requiring the preparation of single crystals with a size greater than 3 mm. Furthermore, due to the absorption of mid-infrared light, the single crystal thickness must be on the order of micrometers. Therefore, developing a method for preparing large-size, high-quality antimony selenide single crystals has significant academic value. Summary of the Invention

[0003] This invention provides a method for preparing large-size, high-quality antimony selenide single crystals, which overcomes the shortcomings of conventional single crystals, such as small particle size and low quality.

[0004] The technical solution adopted by this invention to solve its technical problem is:

[0005] A method for preparing large-size, high-quality antimony selenide single crystals, characterized by comprising the following steps:

[0006] Step 1. Large-size single crystal growth

[0007] First, prepare the raw materials by grinding them thoroughly in a mortar for 0.5–1 hour. After pressing the raw materials into tablets using a tablet press, transfer them into a thoroughly cleaned and dried single-end sealed high-purity quartz tube. Then, evacuate the tube to 100°C. -3Below Pa, the other end of the quartz tube is melted and sealed; then, in a dual-temperature zone vertical Bridgman crystal growth furnace with a temperature gradient of 4–10 °C / cm, the quartz tube is pulled through the temperature gradient zone at a rate of 0.01–0.03 mm / min to grow a single crystal; once all the liquid has solidified and the temperature at the top has dropped to 40–100 °C below the melting point, the movement of the quartz tube is stopped, and the crystal growth furnace is then cooled to 180–220 °C at a rate of 2–5 °C / min, followed by natural cooling.

[0008] Step 2. Rapid orientation of single crystal

[0009] The antimony selenide single crystal grown in step one is rapidly oriented: based on the crystal structure parameters of the orthorhombic antimony selenide system, the cleavage plane is determined to be (010); the cleavage plane is analyzed using an optical / metallurgical microscope, and a set of parallel lines is observed. The plane perpendicular to the direction of the parallel lines is (001); then the plane that is perpendicular to both (010) and (001) is (100). After cutting, grinding and polishing, three orthorhombic crystal planes that are perpendicular to each other are obtained.

[0010] Step 3. Micron-scale large-size sheet-like single crystal exfoliation

[0011] Using paraffin wax with a melting point of 40–80°C, a suitable amount is placed on a quartz plate and melted by heating on a hot plate. The cleavage planes of the single crystal block are then completely adhered to the quartz plate. The wax is then cooled to solidify and cooled to room temperature. Rapid separation of the quartz plate and the single crystal block yields large, intact plate-like single crystals. The large plate-like single crystals are then peeled off using acetone to remove the paraffin wax, resulting in plate-like single crystals with a diameter of over 10 mm and a thickness of tens of micrometers. Paraffin wax with a melting point of 40–80°C is used because it does not melt when the crystal is peeled off by hand. Furthermore, the paraffin wax is easily dissolved and cleaned when heated with acetone. Preferably, the melting point of the paraffin wax is 40–60°C.

[0012] In a preferred embodiment of the present invention, in step one, the raw materials are prepared in a glove box under a 5N high-purity argon atmosphere; vacuuming is performed using a mechanical pump and a molecular pump.

[0013] In a preferred embodiment of the present invention, in step one, the inner diameter of the quartz tube is 40-100 mm.

[0014] In a preferred embodiment of the present invention, in step three, the peeled sheet-like single crystal is placed in acetone and heated for washing to remove the paraffin wax from the surface of the single crystal.

[0015] In a preferred embodiment of the present invention, the acetone heating and washing are repeated 3-5 times.

[0016] In a preferred embodiment of the present invention, in step three, the diameter "more than 10 mm" refers to 10 to 50 mm.

[0017] In step three, the "tens of micrometers" refers to 10-100 μm. Preferably, it is 20-80 μm.

[0018] In this invention, high quality refers to a full width at half maximum (FWHM) of less than or equal to 0.1 for each diffraction peak on the cleavage plane XRD. An FWHM value below 0.1 indicates that the crystal is suitable for commercial use.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. This invention uses a metallographic microscope or scanning electron microscope commonly used in laboratories to observe the dissociation surface, and then combines it with the crystal structure to quickly determine the crystal plane and perform single crystal orientation.

[0021] 2. It can produce ultrathin sheets with large diameters and high quality, with an FWHM value below 0.1. It can be used for various optical, electrical, and photoelectric property studies.

[0022] 3. In existing technologies, adhesive tape peeling is generally used to peel off crystal flakes. However, the applicant has found that this method is prone to fragmentation or cracking during the peeling of antimony selenide, and can only be used for peeling antimony selenide flakes with diameters at the micro-nano scale. In contrast, this invention uses paraffin peeling, resulting in ultrathin flakes that are less prone to fragmentation or cracking, of high quality, and capable of producing crystal flakes with diameters of 10 mm or more. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Figure 1 The crystal structure of Sb₂Se₃ is shown. (a) (100) crystal plane; (b) (010) crystal plane (a cleavage plane); (c) (001) crystal plane; (d) 3D diagram of the crystal structure; (e) schematic diagram of Sb₄Se₆.

[0025] Figure 2 In Example 1: (a) a grown Sb₂Se₃ single crystal, sealed in a quartz tube, Φ 外 =13mm, Φ 内 =11mm, H=70mm; (b) Large-size ultrathin single crystal wafer stripped; (c) Scanning electron microscope of the ultrathin single crystal wafer, magnified to 10000x, showing a set of parallel lines, with a single crystal wafer thickness of approximately 23um; (d) UV-vis transmittance curve of the large-size ultrathin single crystal wafer, with (e) direct band gap of 1.18eV and (f) indirect band gap of 1.16eV obtained through analysis. The smallest grid size in the grid ruler paper in the figure is 1mm*1mm. (g) XRD curve of the cleavage plane of the single crystal, which is the (010) crystal plane; (h) Full width at half maximum (FWHM) and intensity of each diffraction peak of the cleavage plane XRD.

[0026] Figure 3 In Example 2: (a) a large-size Sb2Se3 single crystal grown by the Bridgman method with dimensions of Φ = 30 mm and H = 50 mm; (b) polishing the top of the single crystal pillar to observe bulk crystal faces; (c) cutting and polishing to obtain two other faces perpendicular to the cleavage plane; (d) XRD curves of the cut (100), (001) and the cleaved (010) planes; (e) ultrafast spectral analysis of the three mutually perpendicular crystal faces. Detailed Implementation

[0027] A method for preparing large-size, high-quality antimony selenide single crystals includes large-size, high-quality single crystal growth, rapid orientation of bulk single crystals, and micron-level ultrathin sheet-like single crystal exfoliation. The method involves grinding and pressing high-purity Se and Sb powders in stoichiometric ratios, then loading them into a high-purity quartz tube and sealing it under vacuum. Single crystal growth is then performed in a vertical Bridgman crystal growth furnace. Utilizing the one-dimensional crystal structure of Sb₂Se₃, the single crystal is rapidly oriented, exposing two other orthorhombic crystal planes that are perpendicular to each other. Through a special exfoliation process, complete sheets with a thickness of tens of micrometers and a size of over 10 mm are obtained for use in ultrafast spectroscopy studies such as THz to investigate information such as photogenerated carriers.

[0028] Example 1

[0029] First, Φ 外 =13mm, Φ 内 One end of an 11mm high-purity quartz tube is sealed into a conical bottom in a high-temperature flame. After cooling to room temperature, it is cleaned sequentially with acetone and ethanol for 15 minutes, and then placed in a 150℃ oven for 6 hours. Using Se powder (Alfa, 99.999% purity) and Sb powder (Alfa, 99.999% purity) as raw materials, 30 grams of the drug are accurately weighed according to the Sb2Se3 stoichiometric ratio (accuracy 0.0001 grams), and ground in an agate mortar for 1 hour. The thoroughly ground powder is placed into a one-inch infrared tablet press mold and pressed to 15MPa to obtain a dense, sheet-like raw material. The sheet-like raw material is broken into small pieces with a diameter of less than 11mm and placed into the quartz tube. A vacuum of 10 MPa is created using a mechanical pump and a molecular pump. -3 When Pa, seal the other end of the quartz tube, such as Figure 2a. The above apparatus was then placed in a Bridgman single crystal growth furnace (the quartz tube used had dimensions of Φ outer = 50 mm and Φ inner = 44 mm). The furnace was heated to 680°C at a rate of 10°C / min, held for 24 hours, and then cooled to 620°C (slightly higher than the melting point of Sb₂Se₃, 612°C). In a vertical Bridgman crystal growth furnace with a dual-temperature zone of 5°C / cm, the quartz tube was pulled through the temperature gradient zone at a rate of 0.015 mm / min to grow the single crystal. Once all the liquid had solidified and the temperature at the top had dropped to 50°C below the melting point, the movement of the quartz tube was stopped. The crystal growth furnace was then cooled to 200°C (upper temperature zone) at a rate of 5°C / min, and then allowed to cool naturally. Once the furnace temperature had dropped to room temperature (25°C), the furnace power was turned off, the vacuum-sealed tube was removed, and the Sb₂Se₃ single crystal was obtained.

[0030] The quartz tube was broken open, and a low-speed diamond cutter was used to cut the single crystal perpendicular to the crystal axis, cutting off small pieces of the single crystal to expose the cleavage planes. XRD analysis was performed as follows. Figure 2 g, corresponding to a diffraction peak with a full width at half maximum (FWHM) reaching the level of commercially available single-crystal materials, such as Figure 2 h. Observing the cleavage surface under a ZEISS SIGMA scanning electron microscope, a set of parallel lines was observed, such as... Figure 2 c. If this direction is

[001] , then the plane perpendicular to the parallel line is (001). Since Sb2Se3 is an orthorhombic crystal system, the plane parallel to the parallel line and perpendicular to the plane of the paper is (100).

[0031] Using paraffin wax with a melting point of 50℃, a suitable amount is placed on a 20mm*20mm quartz sheet. After melting it on a hot plate, the cleavage planes of the single crystal block are completely adhered to the quartz sheet. The mixture is then cooled and solidified to room temperature. Rapid separation of the quartz sheet from the single crystal block yields results such as... Figure 2 Figure b shows an 8mm*7mm sheet-like single crystal. The detached sheet-like single crystal was heated and washed in acetone to remove the paraffin wax from the surface. This process was repeated five times to obtain a pure sheet-like single crystal. Scanning electron microscopy analysis showed that the thickness of the sheet was approximately 23µm. This sheet was used for UV-vis transmittance mode analysis, yielding the following results: Figure 2 The transmittance curve shown in figure d (it should be noted that this transmittance curve can only be obtained for single crystals with a size of 3 mm or larger) can be processed to obtain its optical bandgap. The results show that Sb₂Se₃ possesses both a direct optical bandgap of 1.18 eV and an indirect optical bandgap of 1.16 eV, as shown in figure d. Figure 2 As shown in e and 2f. Figure 2 As shown in h, the FWHM value is less than 0.1.

[0032] Example 2

[0033] First, Φ 内One end of a 30mm high-purity quartz tube is sealed into a conical bottom in a high-temperature flame. After cooling to room temperature, it is cleaned sequentially with acetone and ethanol for 30 minutes, and then placed in a 120℃ oven for 12 hours. Using Se powder (Alfa, 99.999% purity) and Sb powder (Alfa, 99.999% purity) as raw materials, 200 grams of the drug are accurately weighed according to the Sb2Se3 stoichiometric ratio (accuracy 0.0001 grams), and ground in batches in an agate mortar for 0.5 hours. The thoroughly ground powder is placed into a one-inch infrared tablet press mold and pressurized to 20MPa to obtain a dense, sheet-like raw material. The sheet-like raw material is broken into small pieces with a diameter of less than 15mm and placed into the quartz tube. A vacuum of 10 MPa is created using a mechanical pump and a molecular pump. -3 When Pa, seal the other end of the quartz tube. Then, place the above apparatus into a Bridgeman single crystal growth furnace tube furnace and raise the temperature to 800°C at a rate of 10°C / min, hold for 24 hours, and then cool down to 620°C at a rate of 2°C / min. Then, in a vertical Bridgeman crystal growth furnace with a dual-temperature zone and a temperature gradient of 4°C / cm, pull the quartz tube through the temperature gradient zone at a rate of 0.01 mm / min to perform single crystal growth. Once all the liquid has solidified and the temperature at the top has dropped to 50°C below the melting point, stop moving the quartz tube, and cool the crystal growth furnace to 200°C at a rate of 2°C / min, then allow it to cool naturally. Once the tube furnace temperature has dropped to room temperature (25°C), turn off the power to the tube furnace, remove the vacuum-sealed tube, and obtain the desired result. Figure 3 Figure a shows a single Sb₂Se₃ crystal with Φ = 30 mm and H = 50 mm.

[0034] The ends of single crystals exhibit a distinct layered structure. Wet grinding and polishing with appropriately gritted sandpaper yields the following results: Figure 3 The polished surface shown in b. Using a low-speed diamond cutter, a crystal of approximately 10mm thickness was polished to obtain two additional perpendicular crystal planes based on the morphology of the layered cleavage planes and the parallel lines observed under an optical microscope, as shown in b. Figure 3 As shown in c. XRD analysis was performed on the three crystal planes, as follows. Figure 3 d, and it was determined that there are three crystal planes: (100), (010), and (100). Sb2Se3 in the orthorhombic crystal system has significant anisotropic properties. Obtaining the three crystal planes perpendicular to the axial crystal direction is of great research value for the study of material properties. Figure 3 e is an ultrafast spectroscopy technique used to study the properties of photogenerated carriers on three crystal planes, which can obtain information such as photogenerated carrier lifetime and mobility.

[0035] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing large-size, high-quality antimony selenide single crystals, characterized in that... Includes the following steps: Step 1. Large-size single crystal growth First, prepare the raw materials Se powder and Sb powder, and grind them thoroughly in a mortar for 0.5–1 hour. After pressing the Se powder and Sb powder into tablets using a tablet press, transfer them into a thoroughly cleaned and dried single-end sealed high-purity quartz tube. Then, evacuate to 100°C. -3 Below Pa, the other end of the quartz tube is melted and sealed; then, in a vertical Bridgman crystal growth furnace with a temperature gradient of 4–10 °C / cm, the quartz tube is pulled through the temperature gradient region at a rate of 0.01–0.03 mm / min to grow a single crystal; once all the liquid has solidified and the temperature at the top has dropped to 40–100 °C below the melting point of antimony selenide, the movement of the quartz tube is stopped, and the crystal growth furnace is then cooled to 180–220 °C at a rate of 2–5 °C / min, followed by natural cooling. Step 2. Rapid orientation of single crystal The antimony selenide single crystal grown in step one is rapidly oriented: based on the crystal structure parameters of the antimony selenide orthorhombic crystal system, the cleavage plane is determined to be (010); the cleavage plane is analyzed using an optical / metallurgical microscope, and a set of parallel lines is observed. The plane perpendicular to the direction of the parallel lines is (001); then the plane that is perpendicular to both (010) and (001) is (100). After cutting, grinding and polishing, three orthorhombic crystal planes that are perpendicular to each other are obtained. Step 3. Micron-scale large-size sheet-like single crystal exfoliation Using paraffin wax with a melting point of 40–80°C, take an appropriate amount and place it on a quartz plate. After heating and melting it on a hot plate, completely adhere the cleavage plane of the single crystal block to the quartz plate. Cool down to allow the paraffin wax to solidify, and then cool to room temperature. Quickly separate the quartz plate from the single crystal block to obtain a large-sized, complete sheet-like single crystal. Remove the paraffin wax from the large-sized sheet-like single crystal with heated acetone to obtain sheet-like single crystals with a diameter of 10–50 mm and a thickness of 10–100 μm.

2. The method for preparing large-size, high-quality antimony selenide single crystals according to claim 1, characterized in that, In step one, the raw materials are prepared in a glove box under a 5N high-purity argon atmosphere; vacuuming is performed using a mechanical pump and a molecular pump.

3. The method for preparing large-size, high-quality antimony selenide single crystals according to claim 1, characterized in that: In step one, the inner diameter of the quartz tube is 40-100mm.

4. The method for preparing large-size, high-quality antimony selenide single crystals according to claim 1, characterized in that: In step three, the melting point of paraffin is between 40 and 60°C.

5. The method for preparing large-size, high-quality antimony selenide single crystals according to claim 1, characterized in that: In step three, the acetone heating and washing process is repeated 3-5 times.

6. The method for preparing large-size, high-quality antimony selenide single crystals according to claim 1, characterized in that, In step three, the thickness of the sheet-like single crystal is 20–80 μm.

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