A method for synthesizing and screening Bi2O2Se twisted molar superlattices

Abstract

The present invention relates to a method for synthesizing and screening Bi2O2Se twisted molar superlattices, belonging to the technical field of material synthesis. In the present invention, under an ice-water bath and stirring conditions, ammonium bismuth citrate and sodium selenite are successively added to a KOH solution, mixed evenly and stirred for 0.8 - 1.2 h to obtain a precursor solution A; the precursor solution A is hydrothermally reacted at a temperature of 180 - 185 °C for 24 - 36 h to obtain a mixed solution B; the mixed solution B is successively washed with deionized water and ethanol, and centrifuged to remove the bottom solid impurities to obtain a supernatant; the supernatant is evenly dispersed on a silicon substrate and dried to obtain a sample, and the sample is observed with a visible light microscope, and the sample showing a color different from that of the intrinsic Bi2O2Se sample under the visible light microscope is located; the located sample is placed under a scanning electron microscope for observation, and the sample with orange wrinkles is selected, then the sample showing a color different from that of the intrinsic Bi2O2Se sample under the visible light microscope and having orange wrinkles under the scanning electron microscope is the Bi2O2Se twisted molar superlattice.

Description

Technical Field

[0001] The present invention relates to a method for synthesizing and screening a Bi2O2Se twisted moiré superlattice, belonging to the technical field of material synthesis. Background Art

[0002] Bi2O2Se is an emerging two-dimensional material with a medium bandgap (about 0.8 eV), excellent air stability, extremely high carrier mobility (Hall mobility at 2 K is ~2.8*10 5 cm 2 / Vs), and good mechanical properties. These characteristics make it show great potential in microelectronic processes, wearable devices, and photodetectors. In addition, Bi2O2Se also has properties such as strong spin-orbit coupling, piezoelectricity, and ferroelectricity.

[0003] Bi2O2Se has a unique layered structure. Microscopically, it is composed of positively charged [Bi2O2] n 2n+ layers and negatively charged [Se] n 2n- layers that are alternately stacked along the c-axis and maintain its layered structure by electrostatic force rather than van der Waals force.

[0004] In recent years, in the field of two-dimensional materials, twisted moiré superlattices have attracted great attention. Novel physical phenomena such as the quantum anomalous Hall effect, correlated insulating state, and superconducting state have been successively discovered in twisted two-dimensional materials. Various homo / hetero twisted two-dimensional materials have become an important platform for condensed matter physicists to explore new phenomena, such as twisted graphene, twisted TMD, twisted MoO3, etc. The construction methods of their twisted systems are generally the exfoliation-stacking method and the epitaxial growth method. However, the twisted moiré superlattice of Bi2O2Se has not been prepared and discovered yet.

[0005] In the process of constructing moiré superlattices, the ordinary exfoliation-stacking method has disadvantages such as being prone to damage / contamination of samples and difficult transfer; epitaxial growth is also difficult to control, and fewer systems have been reported. Therefore, it is of great value to develop a growth / construction method for two-dimensional twisted materials that is stable, controllable, pollution-free, and easy to transfer. Summary of the Invention

[0006] In view of the blank problem in the preparation and screening of the twisted molar superlattice of Bi2O2Se in the Bi2O2Se material system, the present invention proposes a method for synthesizing and screening the twisted molar superlattice of Bi2O2Se, that is, under the condition of an ice-water bath, ammonium bismuth citrate and sodium selenite react in a potassium hydroxide alkaline solution to generate a precursor, and then through a hydrothermal reaction, centrifugation to remove impurities, and the twisted molar superlattice of Bi2O2Se is screened out by a visible light microscope and a scanning electron microscope; the method of the present invention is simple and inexpensive, and the twisted molar superlattice of Bi2O2Se can be obtained relatively easily.

[0007] A method for synthesizing and screening the twisted molar superlattice of Bi2O2Se, the specific steps are as follows:

[0008] (1) Under the conditions of an ice-water bath and stirring, ammonium bismuth citrate and sodium selenite are successively added to the KOH solution, mixed evenly and stirred for 0.8 - 1.2 h to obtain a precursor solution A;

[0009] (2) The precursor solution A is subjected to a hydrothermal reaction at a temperature of 180 - 185 °C and under stirring conditions for 24 - 36 h to obtain a mixed solution B;

[0010] (3) The mixed solution B is successively washed with deionized water and ethanol, centrifuged to separate and remove the bottom solid impurities to obtain a supernatant, and the supernatant is an ethanol dispersion of Bi2O2Se nanosheets;

[0011] (4) The ethanol dispersion of Bi2O2Se nanosheets is evenly dispersed on a silicon substrate and dried to obtain a sample. The sample is observed by a visible light microscope, and the samples that show different colors from the intrinsic Bi2O2Se sample under the visible light microscope are located;

[0012] (5) The located samples are placed under a scanning electron microscope for observation. Samples with orange wrinkles are selected. Then, the samples that show different colors from the intrinsic Bi2O2Se sample under the visible light microscope and have orange wrinkles under the scanning electron microscope are the twisted molar superlattice of Bi2O2Se.

[0013] In the step (2), the concentration of the KOH solution is 0.8 - 1.2 mol / L, the concentration of ammonium bismuth citrate in the mixed solution A is 0.08 - 0.12 mol / L, and the concentration of sodium selenite is 0.16 - 0.24 mol / L.

[0014] In the step (5), the color of the intrinsic Bi2O2Se sample is silver-gray.

[0015] The beneficial effects of the present invention are:

[0016] (1) The present invention generates a precursor through an ice-water bath reaction. The precursor then undergoes a hydrothermal reaction to construct a Bi2O2Se twisted moiré superlattice. The Bi2O2Se twisted moiré superlattice is screened out by a visible light microscope and a scanning electron microscope. Compared with the intrinsic Bi2O2Se, the Bi2O2Se twisted moiré superlattice exhibits stronger light absorption in the red light band, especially near 685 nm, and has great potential in the field of optoelectronics;

[0017] (2) The method of the present invention is simple and inexpensive, and the Bi2O2Se twisted moiré superlattice can be obtained relatively easily. Description of the Drawings

[0018] Figure 1 XRD pattern of Bi2O2Se synthesized in Example 1;

[0019] Figure 2 Transmission electron microscope image of the Bi2O2Se twisted moiré superlattice synthesized in Example 1;

[0020] Figure 3 Cross-sectional HAADF-STEM image and structural model of the Bi2O2Se twisted moiré superlattice in Example 1;

[0021] Figure 4 Optical microscope-scanning electron microscope image of Bi2O2Se synthesized in Example 1;

[0022] Figure 5 Raman spectra of the Bi2O2Se twisted moiré superlattice and the intrinsic Bi2O2Se sample synthesized in Example 1;

[0023] Figure 6 Micro-area absorption spectra of the Bi2O2Se twisted moiré superlattice and the intrinsic Bi2O2Se sample synthesized in Example 1;

[0024] Figure 7 Optical microscope-scanning electron microscope image of the Bi2O2Se twisted moiré superlattice synthesized in Example 2;

[0025] Figure 8 Raman spectrum of the Bi2O2Se twisted moiré superlattice synthesized in Example 2;

[0026] Figure 9 Optical microscope-scanning electron microscope image of the Bi2O2Se twisted moiré superlattice synthesized in Example 3;

[0027] Figure 10 Raman spectrum of the Bi2O2Se twisted moiré superlattice synthesized in Example 3. Detailed Embodiments

[0028] The present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the content described above.

[0029] Example 1: A method for synthesizing and screening Bi2O2Se twisted molar superlattice, the specific steps are as follows:

[0030] (1) Under ice-water bath and stirring conditions, ammonium bismuth citrate and sodium selenite are successively added to the KOH solution and mixed evenly and reacted for 1.0 h to obtain precursor solution A; the concentration of the KOH solution is 1 mol / L, the concentration of ammonium bismuth citrate in the mixed solution A is 0.1 mol / L, and the concentration of sodium selenite is 0.2 mol / L;

[0031] (2) The precursor solution A is placed in a constant-temperature forced-air drying oven and hydrothermally reacted for 34 h at a temperature of 180 °C under stirring conditions to obtain a mixed solution B;

[0032] (3) The mixed solution B is washed successively with deionized water and ethanol, and centrifuged to remove the bottom solid impurities (the solid impurities are yellowish-green) to obtain a supernatant, and the supernatant is an ethanol dispersion of Bi2O2Se nanosheets;

[0033] (4) The ethanol dispersion of Bi2O2Se nanosheets is evenly dispersed on a golden Si / SiO2 substrate and dried to obtain a sample. The sample is observed with a visible light microscope, and the flaky samples that show a color different from the color of the intrinsic Bi2O2Se sample (silver-gray) under the visible light microscope are located. The optical microscope-scanning electron microscope images of the synthesized Bi2O2Se are shown in Figure 4 , and the green or pink area points are the area points with a color different from the color of the intrinsic Bi2O2Se sample (silver-gray);

[0034] (5) The located sample is observed under a scanning electron microscope, and the sample with orange-like wrinkles is selected (see Figure 4 ), then the sample that shows a color different from the color of the intrinsic Bi2O2Se sample under the visible light microscope and has orange-like wrinkles under the scanning electron microscope is the Bi2O2Se twisted molar superlattice;

[0035] The XRD pattern of the Bi2O2Se synthesized in this example is shown in Figure 1 , from Figure 1 it can be seen that the Bi2O2Se sample synthesized in this example has good crystallinity, can well match with the PDF, and the preferred orientation is the (001) plane;

[0036] The transmission electron microscope image of the synthesized Bi2O2Se twisted molar superlattice is shown in Figure 2 , from Figure 2It can be seen that the sample is relatively thin (electron beam transparent) and has orange-like wrinkles; the SAED (selected area electron diffraction) of the sample shows obvious secondary diffraction characteristics, indicating that interlayer torsion has occurred in the sample; the HAADF-STEM atomic images at four different rotation angles (5°, 10°, 20°, 40°) show different rotation angle situations of the Bi2O2Se twist-angle molar superlattice sample;

[0037] The cross-sectional HAADF-STEM image and structural model of the Bi2O2Se twist-angle molar superlattice synthesized in this example are shown in Figure 3 , from Figure 3 it can be seen that the Bi2O2Se twist-angle molar superlattice sample was successfully synthesized and screened in this example, and its cross-sectional model shows that the twist angle of the sample is close to 45°;

[0038] The corresponding light microscopy-scanning electron microscopy images of the Bi2O2Se intrinsic sample and the Bi2O2Se twist-angle molar superlattice synthesized in this example are shown in Figure 4 , from Figure 4 it can be seen that orange-like wrinkles (at the yellow circle) can be observed in the pink and green samples under the scanning electron microscope;

[0039] The Raman spectra of the Bi2O2Se twist-angle molar superlattice and the Bi2O2Se intrinsic sample synthesized in this example are shown in Figure 5 , from Figure 5 it can be seen that the silver-gray sample (intrinsic) and the green sample (non-intrinsic, i.e., Bi2O2Se twist-angle molar superlattice) have the same Raman characteristic peaks, which are 159.2 cm -1 , attributed to the A 1g mode of Bi2O2Se;

[0040] The micro-area absorption spectra of the Bi2O2Se twist-angle molar superlattice and the Bi2O2Se intrinsic sample synthesized in this example are shown in Figure 6 , from Figure 6 it can be seen that the green sample (i.e., Bi2O2Se twist-angle molar superlattice) shows stronger light absorption in the red light band, especially near 685 nm.

[0041] Example 2: A method for synthesizing and screening a Bi2O2Se twist-angle molar superlattice, the specific steps are as follows:

[0042] (1) Under ice-water bath and stirring conditions, ammonium bismuth citrate and sodium selenite are successively added to the KOH solution, mixed evenly and stirred for reaction for 1.2 h to obtain the precursor solution A; the concentration of the KOH solution is 1.2 mol / L, the concentration of ammonium bismuth citrate in the mixed solution A is 0.08 mol / L, and the concentration of sodium selenite is 0.16 mol / L;

[0043] (2) Place the precursor solution A in a constant-temperature air-circulating drying oven, and carry out hydrothermal reaction for 28 h at a temperature of 182 °C under stirring conditions to obtain a mixed solution B;

[0044] (3) Wash the mixed solution B successively with deionized water and ethanol, and centrifuge to remove the bottom solid impurities (the solid impurities are yellowish green) to obtain a supernatant, and the supernatant is an ethanol dispersion of Bi2O2Se nanosheets;

[0045] (4) Uniformly disperse the ethanol dispersion of Bi2O2Se nanosheets on a golden Si / SiO2 substrate and dry it to obtain a sample. Observe the sample with a visible light microscope, and locate the flaky samples that present a color different from that of the intrinsic Bi2O2Se sample (silver gray) under the visible light microscope. The optical microscope-scanning electron microscope images of the synthesized Bi2O2Se are shown in Figure 7 , and the pink area points are the area points with a color different from that of the intrinsic Bi2O2Se sample (silver gray);

[0046] (5) Place the located sample under a scanning electron microscope for observation, and select the sample with orange folds (see Figure 7 ), then the sample that presents a color different from that of the intrinsic Bi2O2Se sample under the visible light microscope and has orange folds under the scanning electron microscope is the Bi2O2Se twist moiré superlattice;

[0047] The corresponding optical microscope-scanning electron microscope images of the synthesized Bi2O2Se intrinsic sample and Bi2O2Se twist moiré superlattice in this example are shown in Figure 7 , from Figure 7 it can be seen that orange folds (at the yellow circle) can be observed in the pink sample under the scanning electron microscope;

[0048] The Raman spectrum of the synthesized Bi2O2Se twist moiré superlattice sample in this example is shown in Figure 8 , from Figure 8 it can be seen that the Raman characteristic peak of this pink sample is 159.2 cm -1 , which belongs to the A 1g mode of Bi2O2Se.

[0049] Example 3: A method for synthesizing and screening Bi2O2Se twist moiré superlattice, the specific steps are as follows:

[0050] (1) Under ice-water bath and stirring conditions, add ammonium bismuth citrate and sodium selenite to the KOH solution in sequence, mix evenly and stir for 0.9 h to obtain a precursor solution A; the concentration of the KOH solution is 0.8 mol / L, the concentration of ammonium bismuth citrate in the mixed solution A is 0.12 mol / L, and the concentration of sodium selenite is 0.24 mol / L;

[0051] (2) Place the precursor solution A in a constant-temperature forced-air drying oven and perform a hydrothermal reaction at a temperature of 185 °C under stirring conditions for 24 h to obtain a mixed solution B;

[0052] (3) Wash the mixed solution B successively with deionized water and ethanol, and centrifuge to separate and remove the bottom solid impurities (the solid impurities are yellowish-green) to obtain a supernatant, which is an ethanol dispersion of Bi2O2Se nanosheets;

[0053] (4) Uniformly disperse the ethanol dispersion of Bi2O2Se nanosheets on a golden Si / SiO2 substrate and dry it to obtain a sample. Observe the sample with a visible light microscope, and locate the flaky samples that exhibit a color different from that of the intrinsic Bi2O2Se sample (silver-gray) under the visible light microscope. The optical microscope-scanning electron microscope images of the synthesized Bi2O2Se are shown in Figure 9 , and the green area points are the area points with a color different from that of the intrinsic Bi2O2Se sample (silver-gray);

[0054] (5) Place the located sample under a scanning electron microscope for observation, and select the sample with orange-like wrinkles (see Figure 9 ). Then, the sample that exhibits a color different from that of the intrinsic Bi2O2Se sample under the visible light microscope and has orange-like wrinkles under the scanning electron microscope is the Bi2O2Se twist moiré superlattice;

[0055] The corresponding optical microscope-scanning electron microscope images of the synthesized Bi2O2Se intrinsic sample and Bi2O2Se twist moiré superlattice in this example are shown in Figure 9 , and from Figure 9 it can be seen that orange-like wrinkles (at the yellow circle) can be observed in the green sample under the scanning electron microscope;

[0056] The Raman spectrum of the synthesized Bi2O2Se twist moiré superlattice sample in this example is shown in Figure 10 , and from Figure 10 it can be seen that the Raman characteristic peak of this green sample is 159.2 cm -1 , which belongs to the A 1g mode of Bi2O2Se.

[0057] The specific embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for synthesizing and screening Bi2O2Se twisted molar superlattices, characterized in that, The specific steps are as follows: (1) Under the conditions of ice-water bath and stirring, ammonium bismuth citrate and sodium selenite are successively added to the KOH solution, mixed evenly and stirred for reaction for 0.8 - 1.2 h to obtain the precursor solution A; (2) The precursor solution A is subjected to hydrothermal reaction at a temperature of 180 - 185 °C and under stirring conditions for 24 - 36 h to obtain the mixed solution B; (3) The mixed solution B is washed successively with deionized water and ethanol, and centrifuged to remove the bottom solid impurities to obtain the supernatant, and the supernatant is the ethanol dispersion of Bi2O2Se nanosheets; (4) The ethanol dispersion of Bi2O2Se nanosheets is evenly dispersed on the silicon substrate and dried to obtain the sample. The sample is observed with a visible light microscope, and the sample showing a color different from that of the intrinsic Bi2O2Se sample under the visible light microscope is located; (5) The located sample is observed under a scanning electron microscope, and the sample with orange-like wrinkles is selected. Then, the sample showing a color different from that of the intrinsic Bi2O2Se sample under the visible light microscope and having orange-like wrinkles under the scanning electron microscope is the Bi2O2Se twist molar superlattice.

2. The method for synthesizing and screening the Bi2O2Se angular molar superlattice according to claim 1, characterized in that: In step (2), the concentration of the KOH solution is 0.8 - 1.2 mol / L, the concentration of ammonium bismuth citrate in the mixed solution A is 0.08 - 0.12 mol / L, and the concentration of sodium selenite is 0.16 - 0.24 mol / L.

3. The method for synthesizing and screening the Bi2O2Se angular molar superlattice according to claim 1 or 2, characterized in that: In step (5), the color of the intrinsic Bi2O2Se sample is silver-gray.

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