Two-dimensional beta-CUI crystal and manufacturing method thereof

Abstract

The invention discloses a two-dimensional beta-CUI crystal and a manufacturing method thereof, the manufacturing method comprises the following steps: a substrate and a reaction base solution are provided, the substrate is a graphene copper foil sheet with a single-layer graphene film with the coverage rate of 98% or more, and the surface of the graphene copper foil sheet is an atomic level flat surface; the reaction base solution is prepared by dissolving elemental iodine in absolute ethyl alcohol; and placing the reaction base solution on the surface of a substrate for a set time so as to grow a two-dimensional beta-CUI crystal on the surface of the substrate. The manufacturing method is simple and feasible, easy to operate and implement and low in implementation cost, the obtained two-dimensional beta-CUI crystal is high in purity, large in area and easy to transfer, and multi-layer crystal growth and performance testing are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of two-dimensional materials, and in particular to a two-dimensional β-CUI crystal and a method for making the same. Background Art

[0002] Since the advent of graphene in 2004, two-dimensional materials have continued to attract attention due to their special physical properties. Among them, the two-dimensional semiconductor family materials have shown new possibilities beyond traditional silicon-based technology due to their ultra-thin layers, diverse energy band structures and unique electronic properties.

[0003] Cuprous iodide (CuI) is a binary compound with important physical and chemical properties, such as high ionic conductivity (~0.1S / cm), wide bandgap (~3.1eV) and large exciton binding energy (~62meV). Moreover, as the first semiconductor reported to be completely transparent in the visible spectrum, this unique property makes it not only important in the development of optical materials, but also in the application of semiconductor technology. In addition, the phase transition characteristics of cuprous iodide are also very significant. As a non-layered halogen compound, bulk cuprous iodide crystals have three different phase structures: α phase, β phase and γ phase; and the above three phase structures can be transformed into each other with temperature changes, such as: it can be transformed from zinc blende cubic γ phase to hexagonal β phase at temperatures above 643K, and further transformed from hexagonal β phase to rock salt cubic α phase at temperatures above 673K. In the early days, the judgment on the phase structure was mainly based on the results of X-ray diffraction and neutron diffraction, and there was no intuitive atomic-level crystal structure proof, which led to the fact that the specific structure of the hexagonal β phase was still controversial due to the constraints of instrument conditions. In the past few decades, several possible structural characterizations of β-phase cuprous iodide (β-CUI) have been proposed through experimental and theoretical research, such as: wurtzite (WZ) structure, space group P-6m2 structure, space group P3m1 structure, space group P-3m1 structure, or space group R-3m structure, etc., but the clear structural characterization of β-CUI has not been finalized.

[0004] In the above structural characterization of β-CUI material, the space group P3m1 structure and the space group P-3m1 structure show a van der Waals layered structure, which makes the concept of two-dimensional CuI material possible to realize, but because this phase is only stable in a narrow temperature range of 645 to 675K, it is quite difficult to obtain two-dimensional CuI material by exfoliation. At present, some researchers have used graphene oxide as a template material at room temperature to directly grow two-dimensional β-CUI crystals in graphene interlayers, and subsequent related promotion work believes that the two-dimensional β-CUI crystals in the rGO film (reduced graphene oxide film) obtained by this method have unexpected piezoresistive effect and room temperature ferromagnetism. However, due to the growth mode of two-dimensional β-CUI crystals, various performance tests are difficult to confirm, resulting in the structural characterization of the two-dimensional β-CUI crystals is still vague. In view of this, the present invention is specially proposed. Summary of the invention

[0005] In order to overcome the above-mentioned defects, the present invention provides a two-dimensional β-CUI crystal and a method for making the same. The method is simple and feasible, easy to operate and implement, and has low implementation cost. The obtained two-dimensional β-CUI crystal has high purity and large area, is easy to transfer, and realizes multi-layer crystal growth and performance testing.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a method for preparing a two-dimensional β-CUI crystal, comprising:

[0007] A substrate and a reaction base liquid are provided, wherein the substrate is a graphene copper foil having a single-layer graphene film with a coverage rate of more than 98%, and the surface of the graphene copper foil is an atomic-level flat surface; and the reaction base liquid is prepared by dissolving iodine in anhydrous ethanol;

[0008] The reaction base liquid is placed on the substrate surface for a set time to grow a two-dimensional β-CUI crystal on the substrate surface.

[0009] As a further improvement of the present invention, the two-dimensional β-CUI crystal is grown on the surface of the substrate by completely immersing the substrate in the reaction base liquid for a set time, or by dropping a set amount of the reaction base liquid on the surface of the substrate.

[0010] As a further improvement of the present invention, the substrate is completely immersed in the reaction base liquid at a temperature of 20°C to 30°C for 0.5 to 2s and then taken out, and then the residual liquid on the surface of the substrate is blown away with a nitrogen spray gun to obtain the two-dimensional β-CUI crystal.

[0011] As a further improvement of the present invention, the substrate is completely immersed in the reaction base liquid at a temperature of 25° C. for 1 second and then taken out, and then the residual liquid on the surface of the substrate is blown off with a nitrogen spray gun to obtain the two-dimensional β-CUI crystal.

[0012] As a further improvement of the present invention, the reaction base liquid with a temperature of 20°C to 30°C is picked up by a pipette and dropped onto the surface of the substrate in a drop volume of 5 to 15 μL. After 8 to 20 seconds, the two-dimensional β-CUI crystal can be obtained on the surface of the substrate and away from the dropping location.

[0013] As a further improvement of the present invention, the reaction base liquid at a temperature of 25°C is picked up by a pipette and dropped onto the surface of the substrate in a drop volume of 10 μL. After 10 seconds, the two-dimensional β-CUI crystal can be obtained on the surface of the substrate and outside the diffusion reaction interface.

[0014] As a further improvement of the present invention, the surface roughness Ra of the graphene copper foil is less than 5 nm.

[0015] As a further improvement of the present invention, the molar concentration of the reaction base liquid is 0.05-0.15 mol / L.

[0016] The present invention also provides a two-dimensional β-CUI crystal, which is prepared by the method for preparing the two-dimensional β-CUI crystal of the present invention.

[0017] The beneficial effects of the present invention are as follows: ① Compared with the prior art, the present invention creatively provides a method for producing high-purity, large-area two-dimensional β-CUI crystals, and the production method is simple, feasible, easy to operate and implement, and has low implementation costs. ② Compared with the prior art in which two-dimensional β-CUI crystals are grown in graphene interlayers, the two-dimensional β-CUI crystals produced by the present invention are in a naked state, which is not only easy to be peeled off / transferred, but also easy to achieve multi-layer crystal growth and performance testing, thereby promoting the technical development of two-dimensional β-CUI crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of the method for making a two-dimensional β-CUI crystal according to Example 1 of the present invention;

[0019] Figure 2 This is a flow chart of the method for making a two-dimensional β-CUI crystal according to Example 2 of the present invention;

[0020] Figure 3 Schematic diagram of the cross-sectional structure of the graphene copper foil of the present invention;

[0021] Figure 4A scanning electron microscope image of the substrate on which crystal growth is completed in Example 1 of the present invention;

[0022] Figure 5 A scanning electron microscope image of the substrate on which crystal growth is completed in Example 2 of the present invention;

[0023] Figure 6 The electron microscope image of the cross-sectional atomic structure distribution characterization analysis of the two-dimensional β-CUI crystal obtained by the present invention;

[0024] Figure 7 A schematic diagram of the crystal structure of the two-dimensional β-CUI crystal obtained in the present invention under the 100 band axis;

[0025] Figure 8 This is the CL spectrum of the two-dimensional β-CUI crystal obtained in the present invention.

[0026] Combined with the accompanying drawings, the following description is given:

[0027] 10. Copper foil base layer; 11. Single-layer graphene film. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0029] The present invention provides a two-dimensional β-CUI crystal and a method for making the same. The method is simple and feasible, easy to operate and implement, and has low implementation cost. The obtained two-dimensional β-CUI crystal has high purity and large area, and is easy to transfer, realize multi-layer crystal growth and performance testing. The reason for this is that the present invention optimizes and innovates the method for making the two-dimensional β-CUI crystal, which is specifically described as follows:

[0030] 1. Preparation of the two-dimensional β-CUI crystal described in this application:

[0031] Embodiment 1:

[0032] This embodiment 1 provides a method for manufacturing a two-dimensional β-CUI crystal, by which a two-dimensional β-CUI crystal in a bare state with high purity and large area can be obtained.

[0033] Please see attached Figure 1 As shown, the method for making the two-dimensional β-CUI crystal includes the following steps:

[0034] S1: Provide a substrate and a reaction base liquid, wherein the substrate is a graphene copper foil having a single-layer graphene film with a coverage rate of more than 98%, and the surface of the graphene copper foil is an atomically flat surface; the reaction base liquid is prepared by dissolving iodine in anhydrous ethanol.

[0035] Specifically, regarding the graphene copper foil, its specific structure is as follows: Figure 3 As shown, the graphene copper foil sheet includes a copper foil base layer 10 with a crystal orientation in the

[001] direction and a single-layer graphene film 11 grown on the surface of the copper foil base layer 10 by a CVD chemical vapor deposition process, and the coverage of the single-layer graphene film 11 is more than 98% (can be further optimized to 99%), and the flatness of the surface of the graphene copper foil sheet reaches atomic level flatness (the surface roughness Ra of the graphene copper foil sheet can be further optimized to be less than 5nm). By using the graphene copper foil sheet as a substrate, the iodination reaction process of the reaction base liquid can be delayed by the single-layer graphene film 11 on the graphene copper foil sheet, while the flatness of the substrate surface is also well improved, providing solid technical support and guarantee for obtaining high-purity, large-area two-dimensional β-CUI crystals.

[0036] Supplementary explanation: It has been verified through experiments and production that the flatness of the substrate surface has a crucial influence on the growth of two-dimensional β-CUI crystals. If the substrate surface is not flat, it will make it difficult for the two-dimensional β-CUI crystals to grow continuously.

[0037] In addition, regarding the reaction base liquid, the molar concentration of the reaction base liquid is optimally controlled to 0.1 mol / L in this embodiment 1. Based on the reaction base liquid, the uniformity of the iodination reaction can be ensured while also ensuring that the purity of the two-dimensional β-CUI crystals is improved (i.e., the proportion of γ-CUI particles is reduced). Of course, this embodiment 1 does not impose any restrictions on the molar concentration of the reaction base liquid. According to experiments and production verification, when the molar concentration of the reaction base liquid is controlled to be between 0.05 and 0.15 mol / L, high-purity two-dimensional β-CUI crystals that meet production and experimental requirements can be obtained.

[0038] S2: placing the reaction base liquid on the substrate surface for a set time to grow two-dimensional β-CUI crystals on the substrate surface.

[0039] Specifically, the specific operation method of the above S2 in this embodiment 1 is: completely immerse the substrate in the reaction base liquid at a temperature of 20°C to 30°C for 0.5 to 2 seconds, then take it out, and then use a nitrogen spray gun to blow off the residual liquid on the surface of the substrate (that is, the residual reaction base liquid), so as to obtain the two-dimensional β-CUI crystal. It can be understood that the two-dimensional β-CUI crystal obtained in this embodiment 1 is in a naked state.

[0040] Furthermore, the parameters of the iodination reaction of the reaction base liquid on the substrate can be further optimized as follows: the reaction temperature (ie, the temperature of the reaction base liquid) is 25° C., and the reaction time is 1 s.

[0041] Supplementary explanation: Since the reactivity of iodine and copper is very high, this will cause the two-dimensional β-CUI crystal to be further transformed into a cubic phase structure γ-CUI particle with a space group of F-43m as the iodination reaction proceeds while growing the two-dimensional β-CUI crystal. Therefore, in addition to the preferred substrate and the reaction base liquid, this embodiment 1 also performs the above-mentioned optimization control on the iodination reaction parameters, thereby further ensuring the improvement of the purity of the two-dimensional β-CUI crystal.

[0042] Embodiment 2:

[0043] This embodiment 2 also provides a method for manufacturing a two-dimensional β-CUI crystal, and the manufacturing method can also obtain a two-dimensional β-CUI crystal in a bare state with high purity and large area.

[0044] Please refer to the attached Figure 2 As shown, the method for making the two-dimensional β-CUI crystal includes the following steps:

[0045] S1: Provide a substrate and a reaction base liquid, wherein the substrate is a graphene copper foil having a single-layer graphene film with a coverage rate of more than 98%, and the surface of the graphene copper foil is an atomically flat surface; the reaction base liquid is prepared by dissolving iodine in anhydrous ethanol.

[0046] Specifically, regarding the substrate and the reaction base liquid, this embodiment 2 adopts the same technical means as that of embodiment 1, so it will not be described here in detail.

[0047] S2: placing the reaction base liquid on the surface of the substrate for a set time to grow two-dimensional β-CUI crystals on the surface of the substrate.

[0048] Specifically, the specific operation method of the above S2 in this embodiment 2 is: pick up the reaction base liquid at a temperature of 20℃~30℃ with a pipette gun, and drop it on the surface of the substrate in a drop amount of 5~15μL. After 8~20s, the solution diffuses and reacts completely, and the two-dimensional β-CUI crystal can be obtained on the surface of the substrate and away from the drop location. It can be understood that based on the effect of the single-layer graphene film 11, the reaction base liquid can be promoted to diffuse rapidly to the entire surface of the substrate, ensuring that a large area of ​​the two-dimensional β-CUI crystal can be obtained.

[0049] Furthermore, the parameters of the iodination reaction of the reaction base liquid on the substrate can be further optimized as follows: the reaction temperature (temperature of the reaction base liquid) is 25° C., the dripping volume is 10 μL, and the reaction time is 10 s.

[0050] It can be understood that, similar to the above-mentioned embodiment 1, the present embodiment 2 can further ensure the improvement of the purity of the two-dimensional β-CUI crystal by performing the above-mentioned optimization control on the iodination reaction parameters.

[0051] After the iodination reaction is completed, the two-dimensional β-CUI crystal is obtained on the surface of the substrate and outside the diffusion reaction interface in Example 2. Note: The reason for choosing to obtain the two-dimensional β-CUI crystal at "outside the diffusion reaction interface" is that the two-dimensional β-CUI crystal grown at the above preferred position has a higher proportion, high purity, and contains a lower proportion of γ-CUI particles.

[0052] 2. Structural characterization and luminescence performance test of the two-dimensional β-CUI crystal described in this application:

[0053] The two-dimensional β-CUI crystals prepared in Examples 1 to 2 of the present application were subjected to a number of performance analyses and / or tests, as specifically described below:

[0054] 2.1) The morphology analysis method and results of the two-dimensional β-CUI crystal:

[0055] The morphology of the substrate on which the crystal growth was completed in Examples 1 to 2 of the present application was tested using a high-performance thermal field scanning electron microscope (SEM). The test results are shown in the attached Figure 4 and attached Figure 5 shown.

[0056] Attached Figure 4 and attached Figure 5 The scanning electron microscope images (also called SEM images) of the substrates in Examples 1 and 2 of the present application are shown respectively. It can be seen from the SEM images that there are a large number of two-dimensional lamellar structures on the surface of the substrate (specifically, the gray lamellar structures in the red circles can be seen), and the two-dimensional lamellar structures are the grown two-dimensional β-CUI crystals.

[0057] It can be understood that, by means of the manufacturing method provided in the present application, the two-dimensional β-CUI crystal with a two-dimensional sheet structure is successfully grown.

[0058] 2.2) Crystal structure characterization of the two-dimensional β-CUI crystal:

[0059] After completing the morphological analysis of the substrate surface in 2.1) above, a field emission focused ion beam electron microscope is used to complete the transmission electron microscope sample preparation of the specified area of ​​the substrate surface, and then an atomic resolution spherical aberration corrected transmission electron microscope is used to characterize and analyze the cross-sectional atomic structure distribution of the sample, and then combined with the industry standard crystal structure database comparison, the crystal structure of the two-dimensional β-CUI crystal described in this application is obtained, as shown in the attached Figure 6 and attached Figure 7 shown.

[0060] By the attached Figure 6 and attached Figure 7 It can be seen that the crystal structure of the two-dimensional β-CUI crystal described in the present application is a hexagonal phase structure of the space group P-3m1, which is a true two-dimensional layered structure.

[0061] 2.3) Test method and results of the luminescence performance of the two-dimensional β-CUI crystal:

[0062] The luminescence performance of the two-dimensional β-CUI crystals prepared in Examples 1 to 2 of the present application was tested using a cathode fluorescence spectrometer (CL). The test results are shown in the attached Figure 8 shown.

[0063] By the attached Figure 8 It can be seen from the CL spectrum shown that the luminescence wavelength of the two-dimensional β-CUI crystal described in the present application is distributed in the range of 350 to 750 nm, which is broadband white light luminescence.

[0064] Note: Since the two-dimensional β-CUI crystals obtained in Examples 1 to 2 of the present application are single-layer products, their luminescence is weak, but since the two-dimensional β-CUI crystals obtained in the present application are in a naked state, cathode fluorescence spectrum testing (i.e., luminescence signal collection testing) can be easily performed. However, the prior art is to grow two-dimensional β-CUI crystals in a graphene interlayer, and thus it is impossible to perform luminescence signal collection testing.

[0065] In addition, it is understandable that since the two-dimensional β-CUI crystal prepared in the present application is in an exposed state, it is very easy to peel / transfer the two-dimensional β-CUI crystal from the substrate by conventional peeling means, and to control the number of layers of the two-dimensional β-CUI crystal by adjusting the iodination reaction parameters (that is, to achieve multi-layer crystal growth).

[0066] In summary, the method for preparing the two-dimensional β-CUI crystal provided by the present invention is simple and feasible, easy to operate and implement, and has low implementation cost. The obtained two-dimensional β-CUI crystal has high purity and large area, and is easy to transfer, realize multi-layer crystal growth and performance testing.

[0067] Many specific details are described in the above description to facilitate a full understanding of the present invention. However, the above description is only a preferred embodiment of the present invention. The present invention can be implemented in many other ways different from those described herein, so the present invention is not limited to the specific implementation disclosed above. At the same time, any person familiar with the art can make many possible changes and modifications to the technical solution of the present invention using the methods and technical contents disclosed above without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a two-dimensional β-CUI crystal, characterized in that: include: A substrate and a reaction base liquid are provided, wherein the substrate is a graphene copper foil having a single-layer graphene film with a coverage rate of more than 98%, and the surface of the graphene copper foil is an atomic-level flat surface; and the reaction base liquid is prepared by dissolving iodine in anhydrous ethanol; The reaction base liquid is placed on the substrate surface for a set time to grow a two-dimensional β-CUI crystal on the substrate surface.

2. The method for preparing a two-dimensional β-CUI crystal according to claim 1, characterized in that: The two-dimensional β-CUI crystal is grown on the surface of the substrate by completely immersing the substrate in the reaction base liquid for a set time, or by dropping a set amount of the reaction base liquid on the surface of the substrate.

3. The method for preparing a two-dimensional β-CUI crystal according to claim 2, characterized in that: The substrate is completely immersed in the reaction base liquid at a temperature of 20° C. to 30° C. for 0.5 to 2 seconds, then taken out, and then the residual liquid on the surface of the substrate is blown off with a nitrogen spray gun to obtain the two-dimensional β-CUI crystal.

4. The method for preparing a two-dimensional β-CUI crystal according to claim 3, characterized in that: The substrate is completely immersed in the reaction base liquid at a temperature of 25° C. for 1 second and then taken out. Then, the residual liquid on the surface of the substrate is blown off with a nitrogen spray gun to obtain the two-dimensional β-CUI crystal.

5. The method for preparing a two-dimensional β-CUI crystal according to claim 2, characterized in that: The reaction base liquid at a temperature of 20°C to 30°C is picked up with a pipette and dropped onto the substrate surface in a drop volume of 5 to 15 μL for 8 to 20 seconds, and then the two-dimensional β-CUI crystal is obtained on the substrate surface away from the drop location.

6. The method for preparing a two-dimensional β-CUI crystal according to claim 5, characterized in that: The reaction base liquid at a temperature of 25° C. is picked up with a pipette and dropped onto the substrate surface in a drop volume of 10 μL. After 10 seconds, the two-dimensional β-CUI crystal is obtained on the substrate surface and outside the diffusion reaction interface.

7. The method for preparing a two-dimensional β-CUI crystal according to claim 1, characterized in that: The surface roughness Ra of the graphene copper foil is less than 5 nm.

8. The method for preparing a two-dimensional β-CUI crystal according to claim 1, characterized in that: The molar concentration of the reaction base liquid is 0.05-0.15 mol / L.

9. A two-dimensional β-CUI crystal, characterized in that: The two-dimensional β-CUI crystal is prepared by the method for preparing the two-dimensional β-CUI crystal according to any one of claims 1 to 8.

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