Monocrystal AgCrSe2 nanosheet as well as preparation and application thereof

Abstract

The invention discloses a single crystal AgCrSe2 nanosheet and preparation and application thereof.The preparation method comprises the following steps that Ag powder, Cr powder and Se powder are mixed and subjected to dry ball milling, and mixed powder is obtained; the mixed powder is pressed and then sealed, a solid-phase reaction is carried out again, and an AgCrSe2-based compound ingot body is obtained; the AgCrSe2-based compound ingot body is sequentially subjected to grinding and pressing treatment, and a pre-compact block body is obtained; and under the vacuum condition, carrying out secondary solid-phase reaction on the pre-compact block to obtain the single crystal AgCrSe2 nanosheet. According to the preparation method, the surface single crystal AgCrSe2 nanosheet with specific orientation is obtained by carrying out pre-densification and two-step solid-phase reaction in a specific temperature and pressure interval, the (00l) crystal face of the AgCrSe2 single crystal nanosheet presents preferred orientation in the growth process, and the AgCrSe2 single crystal nanosheet has obvious single crystal orientation, good crystal quality and high stability.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and in particular to a single crystal AgCrSe2 nanosheet and preparation and application thereof. Background Art

[0002] As the core material in the field of nanotechnology, the preparation technology of single-crystal nanosheets plays a decisive role in the development of electronic, optical and energy devices. With highly ordered lattice structure and significant size effect, single-crystal nanosheets can significantly optimize the electrical, optical and mechanical properties of materials, providing a key material basis for high-frequency devices, flexible optoelectronic devices and efficient energy conversion systems. Among them, AgCrSe2 has become an ideal candidate material for the next generation of semiconductor devices due to its unique layered crystal structure and excellent electrical (such as high carrier mobility) and optical (such as adjustable band gap) properties, especially in the fields of light detection, thermoelectric conversion and flexible electronics, showing broad application prospects.

[0003] At present, the synthesis of AgCrSe2 single crystal nanosheets mainly relies on thermal evaporation and chemical vapor deposition (CVD), but the existing process has significant technical bottlenecks: the material is easily decomposed by heat during the reaction, resulting in poor crystal integrity and difficulty in obtaining a single crystal structure; the inherent ion migration tendency of AgCrSe2 aggravates the formation of grain boundary defects and is easy to decompose during the reaction, resulting in insufficient product stability, limiting its actual device application. The above problems have led to the lack of efficient and controllable technical solutions for the large-scale preparation of AgCrSe2 single crystal nanosheets, which seriously restricts its industrialization process.

[0004] Therefore, a technical solution is continued to prepare AgCrSe2 single crystal nanosheets with high single crystallinity and high stability. Summary of the invention

[0005] In view of this, the present application provides a single-crystalline AgCrSe2 nanosheet and its preparation and application, which are used to solve the problem of how to ensure the single crystallinity and stability of the AgCrSe2 nanosheet.

[0006] In order to achieve the above technical objectives, this application adopts the following technical solutions: In a first aspect, the present application provides a method for preparing a single-crystalline AgCrSe2 nanosheet, comprising the following steps: Ag powder, Cr powder and Se powder are mixed and dry-milled to obtain a mixed powder; The mixed powder is compressed and sealed, and then subjected to a solid phase reaction to obtain an AgCrSe2-based compound ingot; The AgCrSe2-based compound ingot is subjected to grinding and pressing treatment in sequence to obtain a pre-densified block; Under vacuum conditions, the pre-densified block is subjected to a secondary solid-phase reaction to obtain single-crystalline AgCrSe2 nanosheets.

[0007] Preferably, the molar ratio of Ag powder, Cr powder, and Se powder is 1:1:(1 - 2).

[0008] Preferably, the temperature of the first solid-phase reaction is 1300 - 1400K, and the reaction time is 12 - 36h.

[0009] Preferably, the particle size of the ground AgCrSe2-based compound ingot is ≤10μm, the pressing pressure is 5 - 20Mpa, and the thickness of the pre-densified block is 1 - 5mm.

[0010] Preferably, the final temperature of the second solid-phase reaction is 1123 - 1223K.

[0011] Preferably, the temperature control program for the second solid-phase reaction is: heating to 873K at a rate of 3 - 5K / min; heating to the final temperature at a rate of 1 - 2K / min; holding for 12 hours; cooling to 900 - 1000K at a rate of 1 - 2K / min, holding for 12h, and then cooling to room temperature.

[0012] Preferably, the specific steps for subjecting the pre-densified block to the second solid-phase reaction are: exposing the largest surface area of the pre-densified block and placing it flat in a quartz tube. After evacuating, carry out the reaction according to the temperature control program of the two solid-phase reactions.

[0013] Preferably, the vacuum degree of the vacuum condition is ≤10 -4 Pa.

[0014] In a second aspect, the present application provides a single-crystal AgCrSe2 nanosheet.

[0015] In a third aspect, the present application provides an application of the single-crystal AgCrSe2 nanosheet in the field of semiconductor materials.

[0016] The beneficial effects of the present application are as follows: By performing pre-densification and two-step solid-phase reactions within specific temperature and pressure ranges, the present application obtains surface single-crystal AgCrSe2 nanosheets with a specific orientation. The (00l) crystal plane of the AgCrSe2 single-crystal nanosheets shows a preferred orientation during the growth process, with obvious single-crystal orientation, good crystallization quality, and high stability. Description of the Drawings

[0017] Figure 1 It is the surface test diagram of different nanosheets; Figure 2 It is the SEM morphology diagram of different nanosheets; Figure 3 It is the HRTEM and SAED pattern of different nanosheets. Detailed Embodiments

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] This application provides a method for preparing single-crystal AgCrSe2 nanosheets, comprising the following steps: S1. Mix Ag powder, Cr powder, and Se powder, and after dry ball milling, obtain a mixed powder; S2. Press and seal the mixed powder, and then perform a primary solid-phase reaction to obtain an AgCrSe2-based compound ingot; S3. Grind and press the AgCrSe2-based compound ingot in sequence to obtain a pre-dense block; S4. Under vacuum conditions, perform a secondary solid-phase reaction on the pre-dense block to obtain single-crystal AgCrSe2 nanosheets.

[0020] In this application, the (00l) crystal plane of the AgCrSe2 single-crystal nanosheets shows preferred orientation during the growth process, which is achieved through the following settings: during the preparation process, the raw materials are accurately proportioned and fully mixed, and the mixed powder is subjected to a primary solid-phase reaction to obtain a matrix, and then the matrix is ground and pre-densified to form lattice distortion. Subsequently, the block is placed in a specific vacuum environment for a secondary solid-phase reaction, and a suitable temperature range and heating and cooling procedures are set; during the secondary solid-phase reaction, the largest surface of the block is exposed to minimize the surface energy; throughout the process, the ultra-low oxygen environment inhibits oxidation and ensures the smooth progress of the reaction.

[0021] In some embodiments, the molar ratio of Ag powder, Cr powder, and Se powder is 1:1:(1 - 2).

[0022] In some embodiments, the temperature of the primary solid-phase reaction is 1300 - 1400K, and the reaction time is 12 - 36h.

[0023] In some embodiments, the particle size of the ground AgCrSe2-based compound ingot is ≤10μm, the pressing pressure is 5 - 20Mpa, and the thickness of the pre-dense block is 1 - 5mm.

[0024] In this application, the lattice distortion formed by high-pressure pre-densification provides the nucleation driving force for the nanosheets; preferably, the pressing pressure is 10 - 15MPa, and more preferably, the pressing pressure is fixed at 10MPa to ensure sufficient contact between the powders and form a suitable lattice distortion.

[0025] In some embodiments, the final temperature of the secondary solid-phase reaction is 1123 - 1223K.

[0026] In some embodiments, the temperature control program for the secondary solid-phase reaction is as follows: heating up to 873K at a rate of 3-5K / min; heating up to the final temperature at a rate of 1-2K / min; keeping the temperature for 12 hours; cooling down to 900-1000K at a rate of 1-2K / min, keeping the temperature for 12h, and then cooling to room temperature.

[0027] In this application, the final temperature is 1173±50K; preferably, during the secondary solid-phase reaction, after heating up to 873K at a rate of 5K / min, then heating up to 1173±50K at a rate of 1K / min; more preferably, precisely controlling the heating to 1173K to ensure a stable reaction environment; after the reaction is completed, cooling down to 973K at a rate of 1K / min and keeping the temperature for 12h, and then slowly cooling to room temperature at a rate of 1K / min; to pursue better crystal quality, the time for slow cooling to room temperature can be appropriately extended, such as slowly cooling to room temperature (20-25℃) within 24 hours.

[0028] In some embodiments, the specific steps for performing the secondary solid-phase reaction on the pre-densified block are as follows: exposing the largest surface area of the pre-densified block and placing it flat in a quartz tube. After evacuating the air, perform the reaction according to the temperature control program of the two solid-phase reactions.

[0029] In this embodiment, the largest surface of the block is exposed to minimize the surface energy and promote the preferential epitaxial growth of the (00l) crystal plane.

[0030] In some embodiments, the vacuum degree of the vacuum condition is ≤10 -4 Pa.

[0031] Specifically, the steps for preparing single-crystal AgCrSe2 nanosheets in this application are as follows: S1. Raw material mixing: Weigh Ag powder, Cr powder, and Se powder with a purity ≥99.99% according to a molar ratio of 1:1:(1-2), and perform dry ball milling in a mortar for 15-20 minutes to obtain a mixed powder; S2. Press the mixed powder into a columnar sample with a certain diameter and height. After sealing, perform a primary solid-phase reaction in a vacuum furnace at a reaction temperature of 1300-1400K, with a reaction process time of 12-36h, keep the temperature for two days, and slowly cool down by 24 h to obtain an AgCrSe2-based compound ingot; S3. Grind the AgCrSe2-based compound ingot to a particle size ≤10μm. Take part of the powder and place it in a steel mold, and press it into a block with a thickness of 1-5mm under a pressure of 5-20MPa to obtain a pre-densified block; S4. Expose the largest surface of the obtained pre-densified block, place it flat in a quartz tube, evacuate the air, and the vacuum degree is ≤10 -4Pa, and perform a secondary solid-phase reaction according to the following temperature control program: heat up to 873 K at a rate of 3 - 5 K / min; heat up to 1123 - 1223 K at a rate of 1 - 2 K / min; keep the temperature for 12 hours; cool down to 900 - 1000 K at a rate of 1 - 2 K / min, keep the temperature for 12 h, and then cool to room temperature to obtain the AgCrSe2 material with single-crystal nanosheets grown on the surface.

[0032] This application provides a single-crystal AgCrSe2 nanosheet.

[0033] This application provides an application of the single-crystal AgCrSe2 nanosheet in the field of semiconductor materials.

[0034] The following further illustrates the present solution through specific examples.

[0035] Example 1 A single-crystal AgCrSe2 nanosheet, and its preparation method is as follows: S1. Weigh Ag powder, Cr powder, and Se powder with a purity ≥ 99.99% according to a molar ratio of 1:1:2, and perform dry ball milling in a mortar for 15 minutes to obtain a mixed powder; S2. Press the mixed powder into a Φ10×5 mm cylinder, react in a vacuum furnace at 1323 K for 12 hours, slowly cool after keeping the temperature for 48 hours to obtain an AgCrSe2-based compound ingot; S3. Grind the AgCrSe2-based compound ingot to a particle size ≤ 10 μm, take 3 g of the powder and press it into a 3 mm thick block under a pressure of 10 MPa to obtain a pre-densified block; S4. Place the obtained pre-densified block in a quartz tube with a vacuum degree of 10 ⁻4 Pa, place the quartz tube horizontally in a muffle furnace, ensure that the largest surface of the ingot is parallel to the ground, heat up to 873 K at a rate of 5 K / min, then heat up to 1173 K at a rate of 1 K / min, and keep the temperature for 12 h; set the cooling rate to 1 K / min to cool down to 973 K, keep the temperature for 12 h, and slowly cool to 20 °C at a rate of 1 K / min to obtain a single-crystal AgCrSe2 nanosheet.

[0036] Comparative Example 1 An AgCrSe2 nanosheet, and its preparation method is as follows: S1. Weigh Ag powder, Cr powder, and Se powder with a purity ≥ 99.99% according to a molar ratio of 1:1:2, and perform dry ball milling in a mortar for 15 minutes to obtain a mixed powder; S2. Press the mixed powder into a Φ10×5 mm cylinder, react in a vacuum furnace at 1323 K for 12 hours, slowly cool after keeping the temperature for 48 hours to allow the cylinder to fully react and crystallize to obtain an AgCrSe2-based compound ingot; S3. Grind the AgCrSe2-based compound ingot to a particle size of ≤10 μm, take 3 g of the powder and press it into a 3-mm thick block under a pressure of 1 MPa to obtain a pre-densified block; S4. Place the obtained pre-densified block in a quartz tube with a vacuum of 10 ⁻4 Pa, place the quartz tube horizontally in a muffle furnace, ensure that the largest surface of the ingot is parallel to the ground, heat it to 873 K at a rate of 5 K / min, and then heat it to 1173 K at a rate of 1 K / min, and keep it warm for 12 h; Set the cooling rate to 1 K / min to cool to 973 K, keep it warm for 12 h, and slowly cool to 20 °C at a rate of 1 K / min to obtain AgCrSe2 nanosheets.

[0037] Comparative Example 2 A kind of AgCrSe2 nanosheets, and its preparation method is as follows: S1. Weigh Ag powder, Cr powder, and Se powder with a purity of ≥99.99% in a molar ratio of 1:1:2, and dry ball mill them in a mortar for 15 minutes to obtain a mixed powder; S2. Press the mixed powder into a Φ10×5 mm cylinder, react it in a vacuum furnace at 1323 K for 12 hours, and slowly cool it after keeping it warm for 48 hours to make the cylinder fully react and crystallize to obtain an AgCrSe2-based compound ingot; S3. Grind the AgCrSe2-based compound ingot to a particle size of ≤10 μm, take 3 g of the powder and press it into a 3-mm thick block under a pressure of 1 MPa to obtain a pre-densified block; S4. Place the obtained pre-densified block in a quartz tube with a vacuum of 10 ⁻4 Pa, place the quartz tube horizontally in a muffle furnace, ensure that the largest surface of the ingot is parallel to the ground, first heat the temperature to 873 K at a heating rate of 5 K / min, then continue to heat it to 1473 K at a rate of 1 K / min, and then heat it to 973 K at a rate of 1 K / min again, and keep it warm at this temperature for 12 hours, and slowly cool it to 20 °C at a rate of 1 K / min to obtain AgCrSe2 nanosheets.

[0038] Testing and Evaluation Test the surfaces of different materials, and the results are as Figure 1 shown, Figure 1 a is the surface of the material in Example 1, Figure 1 b is the surface of the material in Comparative Example 1, Figure 1 c is the surface of the material in Comparative Example 2.

[0039] The SEM micrographs of the surfaces of the materials obtained in Example 1 and Comparative Examples 1 and 2 are as Figure 2 shown; Figure 2 a is the SEM image of the nanosheets in Example 1, Figure 2 b is the partial enlarged view of the nanosheets in Example 1; Figure 2c is the surface SEM image of Comparative Example 1; Figure 2 d is the SEM image of Comparative Example 2.

[0040] The HRTEM and SAED patterns of the single nanosheets of Example 1 are as Figure 3 shown, where Figure 3 a is the FIB sample preparation image of the nanosheets of Example 1; Figure 3 b is the partial enlarged view of the FIB sample preparation of the nanosheets of Example 1; Figure 3 c is the SETM image of Example 1; Figure 3 d is the STEM atomic image and SAED pattern of Example 1.

[0041] In Comparative Example 1, the pre-pressing pressure was small, resulting in insufficient contact between the powder particles, and the lattice distortion energy storage could not be formed. As a result, the surface diffusion driving force in the secondary reaction was insufficient, and it was difficult to initiate the orientation growth mechanism; the product finally obtained in Comparative Example 1 presented as loose black powder ( Figure 2 c). Observed by scanning electron microscope (SEM), the results showed that there was no obvious lamellar structure in the powder, thus proving that the pre-pressing densification step played a key regulatory role in the preferred growth of crystal planes.

[0042] In Comparative Example 2, the secondary reaction temperature was increased to 1473 K (exceeding the melting temperature of AgCrSe2, 1273 ± 50 K), triggering a melting reaction, which destroyed the directional diffusion channel in the (001) crystal orientation and led to the termination of single crystal growth; after the experiment in Comparative Example 2, it was found that there was an obvious melting and recrystallization phenomenon in the material in the quartz tube. Observed by scanning electron microscope (SEM) ( Figure 2 c), an irregular blocky polycrystalline structure was formed on the material surface, and the nanosheets existing in Example 1 completely disappeared. Thus, it was confirmed that when the temperature exceeded the critical value, the material would undergo melting and recrystallization and could not form a surface single crystal structure.

[0043] On the surface of the product of Example 1, uniform nanosheets were formed, with an average thickness of 30 - 60 μm and a lateral size of 50 - 150 μm. STEM and SAED characterizations showed that the nanosheets were single crystals. It shows that the process of pre-pressing at 5 - 20 MPa combined with annealing at 1173 ± 50 K plays a decisive role in the formation of single crystal nanosheets.

[0044] The above is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of single-crystal AgCrSe2 nanosheets, characterized in that, It includes the following steps: Mix Ag powder, Cr powder, and Se powder, and after dry ball milling, obtain a mixed powder; Press and seal the mixed powder, and then conduct a solid-phase reaction once to obtain an AgCrSe2-based compound ingot; Grind and press the AgCrSe2-based compound ingot in sequence to obtain a pre-dense block; Under vacuum conditions, conduct a secondary solid-phase reaction on the pre-dense block to obtain the single-crystal AgCrSe2 nanosheet.

2. The preparation method of the single-crystal AgCrSe2 nanosheet according to claim 1, characterized in that, The molar ratio of the Ag powder, Cr powder, and Se powder is 1:1:(1 - 2).

3. The preparation method of the single-crystal AgCrSe2 nanosheets according to claim 1, wherein, The temperature of the first solid-phase reaction is 1300 - 1400K, and the reaction time is 12 - 36h.

4. The preparation method of the single-crystalline AgCrSe2 nanosheets according to claim 1, wherein, The particle size of the ground AgCrSe2-based compound ingot is ≤10μm, the pressure of the pressing is 5 - 20 Mpa, and the thickness of the pre-dense block is 1 - 5mm.

5. The preparation method of the single-crystal AgCrSe2 nanosheets according to claim 1, characterized in that, The final temperature of the secondary solid-phase reaction is 1123 - 1223K.

6. The preparation method of the single-crystalline AgCrSe2 nanosheets according to claim 1, wherein, The temperature control program of the secondary solid-phase reaction is: heat up to 873K at a rate of 3 - 5K / min; heat up to the final temperature at a rate of 1 - 2K / min; keep the temperature for 12 hours; cool down to 900 - 1000K at a rate of 1 - 2K / min, keep the temperature for 12h, and then cool to room temperature.

7. The preparation method of the single crystal AgCrSe2 nanosheets according to claim 1, characterized in that, The specific steps for conducting the secondary solid-phase reaction on the pre-dense block are: expose the largest surface of the pre-dense block and place it flat in a quartz tube. After evacuating, conduct the reaction according to the temperature control program of the secondary solid-phase reaction.

8. The preparation method of the single-crystal AgCrSe2 nanosheets according to claim 1, wherein, The degree of vacuum of the said vacuum condition ≤ 10 -4 Pa.

9. A single-crystal AgCrSe2 nanosheet obtained by the preparation method according to any one of claims 1 - 8.

10. An application of the single-crystal AgCrSe2 nanosheet according to claim 9 in the field of semiconductor materials.

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