Preparation method and application of ultrathin two-dimensional In2O3-In2S3 heterojunction

Abstract

The invention discloses a preparation method and application of an ultrathin two-dimensional In2O3-In2S3 heterojunction. The preparation method comprises the following steps: S1, preparing flower-shaped In2S3 by adopting a hydrothermal method; s2, dispersing the flower-shaped In2S3 by using water as a solvent, and preparing an In2S3 nanosheet by using an ultrasonic stripping method; s3, taking the flower-shaped In2S3 prepared in the step S1, and carrying out annealing treatment at the temperature of 450-550 DEG C to obtain In2O3; the preparation method comprises the following steps: dispersing In2O3 by using water as a solvent, and preparing In2O3 nanosheets by using an ultrasonic stripping method; s4, ethylene glycol and ethyl alcohol are added into the In2S3 nanosheet solution, and an In2S3 solution is obtained; formamide and ethyl alcohol are added into the In2O3 nanosheet solution, and an In2O3 solution is obtained; the In2S3 solution is dropwise added to a silicon wafer preheated to 45 DEG C, after the solution is volatilized, the temperature of the silicon wafer is increased to 200 DEG C, the temperature is kept constant for 1 h, then the temperature is decreased to 45 DEG C, the In2O3 solution is dropwise added, and after the solution is volatilized, the two-dimensional In2O3-In2S3 heterojunction is formed on the silicon wafer. According to the invention, the problem that the two-dimensional ultrathin In2O3-In2S3 heterojunction material is difficult to prepare is solved, and a novel heterojunction preparation method is created.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor gas-sensitive materials, and in particular to the preparation of two-dimensional transition metal sulfides and transition metal oxides, the preparation of heterojunctions and their applications in the field of gas sensing. Background Art

[0002] With the continuous development of nanotechnology, two-dimensional materials have emerged. Compared with bulk materials, two-dimensional materials not only have two-dimensional quantum confinement effects, but also have specific surface areas close to theoretical extremes and unique gas adsorption capabilities. They can generate charge exchange with gas molecules adsorbed on the surface at room temperature or lower temperatures and form interface dipoles, thereby significantly changing the conductivity properties of the material. Therefore, two-dimensional materials have unique advantages in low-power gas sensing. However, a single type of two-dimensional material often has certain limitations when applied to devices. For example, h-BN is difficult to be used alone in devices due to its wide band gap (about 5.97eV), and exposed BP is easily oxidized in the air, resulting in performance degradation. Constructing heterojunctions is an effective method to improve the overall gas-sensing performance of sensitive materials. The two-dimensional vertical heterojunction constructed by van der Waals interactions can not only retain the excellent intrinsic properties of two-dimensional materials, but also its interlayer quantum coupling effect will show novel physical properties, thus bringing new possibilities for the acquisition of high-performance gas sensors.

[0003] However, the traditional preparation methods of two-dimensional material heterojunctions mainly include artificial fixed-point transfer method and chemical vapor deposition (CVD) method, which are usually used to prepare two-dimensional layered material heterojunctions and have certain defects. For example, the artificial fixed-point transfer method is difficult to avoid the introduction of impurities and defects; the CVD method has strict requirements on reaction conditions, and the types of materials prepared are limited. Therefore, the development of simple and controllable new heterojunction preparation methods can controllably obtain more high-quality two-dimensional material heterojunctions, thereby expanding the range of choices for gas-sensitive materials.

[0004] Indium sulfide (In2S3) and indium oxide (In2O3) are typical n-type non-layered semiconductor materials with certain applications in gas sensing, photocatalysis and electrochemistry. However, due to their intrinsic non-layered structure, the preparation of ultrathin two-dimensional In2S3 and In2O3 as well as two-dimensional heterojunctions is very difficult. Summary of the invention

[0005] In view of the difficulty in preparing the current two-dimensional In2O3-In2S3 heterojunction, the present invention provides a method for preparing an ultra-thin two-dimensional In2O3-In2S3 heterojunction.

[0006] The method for preparing an ultrathin two-dimensional In2O3-In2S3 heterojunction provided by the present invention comprises the following steps:

[0007] S1, preparation of flower-like In2S3 by hydrothermal method;

[0008] S2, dispersing the flower-shaped In2S3 obtained in step S1 with water as solvent, preparing In2S3 nanosheets by ultrasonic exfoliation, and obtaining an In2S3 nanosheet solution with water as solvent;

[0009] S3, taking the flower-shaped In2S3 obtained in step S1 and annealing it at 450-550°C to obtain In2O3; dispersing the In2O3 with water as solvent, preparing In2O3 nanosheets by ultrasonic exfoliation, and obtaining an In2O3 nanosheet solution with water as solvent;

[0010] S4. Prepare a two-dimensional In2O3-In2S3 heterojunction, as follows:

[0011] S41. Add ethylene glycol and ethanol to the In2S3 nanosheet solution to obtain an In2S3 solution; the volume ratio of ethylene glycol: ethanol: water in the In2S3 solution is controlled to be 2:1:1.

[0012] S42. Add formamide and ethanol to the In2O3 nanosheet solution to obtain an In2O3 solution; the volume ratio of formamide:ethanol:water in the In2O3 solution is controlled to be 1:1:1.

[0013] S43. Add the In2S3 solution dropwise onto the silicon wafer preheated to 40-45°C. After the solution evaporates, heat the silicon wafer to 180-220°C and keep the temperature constant for 0.5-1h. Then cool it down to 45°C and add the In2O3 solution dropwise. After the solution evaporates, a two-dimensional In2O3-In2S3 heterojunction is formed on the silicon wafer.

[0014] Preferably, step S1 is specifically: adding indium chloride tetrahydrate and thioacetamide to water, stirring for 20 minutes, transferring the solution to a reactor, performing a hydrothermal reaction at 150-180°C for 10-16 hours, and then centrifuging to obtain a precipitate, which is flower-shaped In2S3. Further preferably, the hydrothermal reaction conditions are: hydrothermal reaction at 160°C for 16 hours.

[0015] Preferably, in step S2, the power of ultrasonic stripping is 200 W, the stripping time is 3 h, and then the solution is centrifuged to obtain a supernatant that is an In2S3 nanosheet solution with water as solvent.

[0016] Preferably, in step S3, In2S3 is placed in a muffle furnace for sintering at 450-550°C for 2h to obtain In2O3; In2O3 is dispersed in water, the ultrasonic stripping power is 200W, the stripping time is 3h, and then the solution is centrifuged to obtain a supernatant, which is an In2O3 nanosheet solution with water as the solvent. Further preferably, the sintering condition is sintering at 500°C for 2h.

[0017] Compared with the prior art, the present invention is beneficial in that:

[0018] (1) The present invention combines hydrothermal and liquid phase exfoliation methods to prepare ultrathin two-dimensional In2O3 nanosheets and In2S3 nanosheets respectively, and then changes the surface potential and activity of the two-dimensional material dispersion by adding a specific solvent, so that it self-assembles into a two-dimensional heterojunction on a silicon wafer. This method solves the problem of difficulty in preparing two-dimensional ultrathin In2O3-In2S3 heterojunction materials and creates a new heterojunction preparation method. This method is simple, controllable, and has low equipment requirements, providing a new idea for the preparation of non-layered two-dimensional heterojunctions.

[0019] (2) The two-dimensional ultrathin In2O3-In2S3 heterojunction prepared by the present invention can improve the gas sensing performance of In2O3 and In2S3 at room temperature and under visible light excitation.

[0020] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the preparation process of the two-dimensional In2O3-In2S3 heterojunction of the present invention.

[0022] Figure 2 The result diagram of step S4 of the preparation method of the present invention when different dropping conditions are used. Among them, (a) is the drop of In2O3 under pure water; (b) is the drop of In2S3 under pure water; (c) is the drop of In2O3 under ethanol: water = 1:1 solvent; (d) is the drop of In2S3 under ethanol: water = 1:1 solvent; (e) is the drop of In2O3 under formamide: ethanol: water = 1:2:2 solvent; (f) is the drop of In2O3 under formamide: ethanol: water = 2:1:1 solvent; (g) is the drop of In2O3 under formamide: ethanol: water = 1:1:1 solvent; (h) is the drop of In2S3 under ethylene glycol: ethanol: water = 1:1:1 solvent; (i) is the drop of In2S3 under ethylene glycol: ethanol: water = 2:1:1 solvent. The proportions of the above solvents are all volume ratios.

[0023] Figure 3These are atomic force microscopy characterization images, where (a) and (b) are atomic force microscopy images and height maps of In2O3; (c) and (d) are atomic force microscopy images and height maps of In2S3; (e) and (f) are atomic force microscopy images and height maps of In2O3-In2S3 heterojunction.

[0024] Figure 4 The figures are X-ray photoelectron spectroscopy characterization diagrams, where (a) is the total X-ray diffraction spectrum of In2O3; (b) is the In 3d high-resolution spectrum of In2O3; (c) is the O1s high-resolution spectrum of In2O3; (d) is the total X-ray diffraction spectrum of In 3d of In2S3; (e) is the In 3d high-resolution spectrum of In2S3; (f) is the S2p high-resolution spectrum of In2S3.

[0025] Figure 5 The test results of the gas-sensing performance of two-dimensional materials to NO2 target gas at room temperature, where (a) is the gas-sensitive response of In2S3 under different light excitation; (b) is the gas-sensitive repeatability of In2S3 at a NO2 concentration of 10ppm; (c) is the gas-sensitive dynamic response of In2S3; (d) is the gas-sensitive response of In2O3 under different light excitation; (e) is the gas-sensitive repeatability of In2O3 at a NO2 concentration of 10ppm; (f) is the gas-sensitive dynamic response of In2O3; (g) is the gas-sensitive response of In2O3-In2S3 heterojunction under different light excitation; (h) is the gas-sensitive repeatability of In2O3-In2S3 heterojunction at a NO2 concentration of 10ppm; (i) is the gas-sensitive dynamic response of In2O3-In2S3 heterojunction. DETAILED DESCRIPTION

[0026] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0027] Example 1

[0028] like Figure 1 As shown, the preparation method of the ultrathin two-dimensional In2O3-In2S3 heterojunction provided by the present invention comprises the following steps:

[0029] S1. The raw materials used are indium chloride tetrahydrate (InCl3·4H2O, 99%) and thioacetamide (CH3CSNH2, 99%). All materials do not need further purification. First, use a high-precision electronic balance to weigh 0.22g of indium chloride tetrahydrate and 0.15g of thioacetamide, add the two raw materials, magnet and 40ml of deionized water into a 100ml glass, seal the glass with a sealing film to avoid the solution from splashing during stirring, place the glass on a magnetic stirrer for stirring, the stirring speed is 500r / min, and the stirring time is 30min; then add the fully mixed solution into the inner tank of a 50ml reactor, place the reactor in a muffle furnace for heating, and set Muffle furnace procedure: initial temperature 25°C, heating time 60min, heating to 160°C and keeping warm for 16h, cooling with the furnace after the reaction; finally, pour the reaction mixture into a 50ml centrifuge tube, centrifuge at 4000r / min for 30min to obtain the precipitate supernatant layer, remove the supernatant, add 40ml deionized water to the centrifuge tube, centrifuge at 4000r / min for 30min, take out the supernatant again, and the final precipitate is pure flower-like In2S3.

[0030] S2. Put the flower-shaped In2S3 prepared in step S1 into a clean 100ml glass cup, add 40ml deionized water and seal it with tin foil to avoid solution splashing, and peel the flower-shaped In2S3 by cell ultrasonic crusher. The crusher power is set to 200W and the crushing time is 3h. Finally, the crushed mixed solution is centrifuged at 4000r / min for 30min to separate the precipitate from the supernatant, and the supernatant is taken to obtain an In2S3 nanosheet solution with water as the solvent.

[0031] S3, prepare pure flower-shaped In2S3 according to the method of step S1; put the dried flower-shaped In2S3 into a muffle furnace for sintering, set the muffle furnace program: initial temperature 25°C, heating time 60min, heating to 500°C and keeping warm for 2h, and cool with the furnace after the insulation. Put the In2O3 powder obtained after sintering in a glass cup, add 40ml deionized water, seal with tin foil to prevent the solution from sputtering, put it under a cell ultrasonic crusher to peel the In2O3 powder, set the power to 200W, the ultrasonic time to 3h, put the ultrasonic solution in a 50ml capacity centrifuge tube and centrifuge at 4000r / min for 30min to obtain a supernatant-precipitate mixture, extract the supernatant to obtain an In2O3 nanosheet solution with water as the solvent.

[0032] S4. Preheat a clean silicon wafer on a 45°C heating table for 5 minutes, add formamide and ethanol to the aqueous solution of In2O3 nanosheets to obtain an In2O3 solution, in which the volume ratio of formamide: ethanol: water is controlled to be 1:1:1. Use a pipette to take 4μl of the In2O3 solution and drop it on the silicon wafer. After the solvent evaporates, raise the temperature of the heating table to 200°C and heat at high temperature for 1h. After heating, cool it down to 45°C. Add ethylene glycol and ethanol to the aqueous solution of In2S3 nanosheets to obtain an In2S3 solution drop, in which the volume ratio of ethylene glycol: ethanol: water is controlled to be 2:1:1. Use a pipette to take 4μl of the In2S3 solution and drop it on the silicon wafer with the In2O3 drop. After the solvent evaporates completely, a two-dimensional In2O3-In2S3 heterojunction is obtained.

[0033] In the preparation method of the present invention, a two-dimensional ultrathin In2O3-In2S3 heterojunction is constructed by adding a specific ratio of solvent formamide and ethanol, ethylene glycol and ethanol in step S4. In order to demonstrate the important role of adding solvent in this step, the following comparative experimental example was conducted.

[0034] On the basis of Example 1, steps S1-S3 remain unchanged, and the preparation conditions of step S4 are changed. Specifically, when pure water is used as the solvent in step S4, that is, formamide and ethanol, ethylene glycol and ethanol are not used in step S4, the In2S3 nanosheet solution and the In2O3 nanosheet solution obtained in steps S2 and S3 are directly added dropwise to the silicon wafer, and the results are as follows: Figure 2 As shown in (a) and (b), the In2S3 nanosheet solution is very easy to agglomerate after being dropped on the silicon wafer, and it is impossible to form a two-dimensional material. When the solvent in step S4 is deionized water and ethanol, that is, in step S4, only ethanol is added to the In2S3 nanosheet solution and the In2O3 nanosheet solution, the In2O3 solution and the In2S3 solution have different degrees of dispersion. As the proportion of ethanol increases, the two solutions are more evenly dispersed after drying, but they will still agglomerate in a smaller area, making it difficult to self-assemble into a two-dimensional thin sheet material; if the proportion of ethanol continues to increase, the solution will first evaporate the ethanol during the volatilization process, and then the deionized water will evaporate, and the material will agglomerate again. Studies have found that Figure 2 As shown in (c) and (d), the best effect is achieved when ethanol: deionized water = 1:1 (volume ratio). For the In2O3 solution, after adding formamide, the edge activity of the In2O3 nanosheets is suppressed. When only a small amount of formamide is added, as shown in Figure 2 As shown in (e), the In2O3 solution still cannot form two-dimensional nanosheets. When the formamide content gradually increases and the ratio approaches the ratio of formamide: ethanol: deionized water = 1:1:1, as shown in Figure 2 As shown in (g), the probability of self-assembly to form a two-dimensional large sheet of material after the solution evaporates is greatly increased. Figure 2 As shown in (f), the material cannot form a large film. Therefore, in the In2O3 solution, the optimal volume ratio of formamide, ethanol, and deionized water is 1:1:1. After the In2O3 nanolayer is formed on the surface of the silicon wafer, if an In2S3 solution with ethanol and deionized water as solvent is directly added, In2S3 can be evenly dispersed in a large area, but agglomeration will also occur in a small area. When ethylene glycol is added to the In2S3 solution, a small amount of ethylene glycol, such as Figure 2 As shown in (h), In2S3 still cannot form a uniform large film on the surface of In2O3. When the ratio of ethylene glycol: ethanol: water in the In2S3 solution is 2:1:1 (volume ratio), as shown in Figure 2 As shown in (i), In2S3 can adhere to In2O3 and form a two-dimensional uniform film; when the amount of ethylene glycol is excessive, the formed two-dimensional uniform film will gradually become smaller until it agglomerates and disappears.

[0035] The two-dimensional In2O3, In2S3 and In2O3-In2S3 heterojunction prepared in Example 1 were characterized by atomic force microscopy (AFM, Park-NX 10). The results are shown in Figure 3. Figure 3 Atomic force microscope images of two-dimensional In2O3, In2S3, and In2O3-In2S3 heterojunction, as well as the height map of the red line part, can be seen from the figure that the thickness of two-dimensional In2O3 is about 2.416nm, the thickness of two-dimensional In2S3 is about 3.1nm, and the thickness of the heterojunction is 2.675nm for the lower layer and 3.096nm for the upper layer, which corresponds to two-dimensional In2O3 and two-dimensional In2S3.

[0036] The composition, content, valence state and chemical structure of In2O3 and In2S3 prepared in Example 1 were characterized by X-ray photoelectron spectroscopy (XPS, ESCALAB Xi+). Figure 4 .like Figure 4 As shown in (b) and (c), the two characteristic peaks of In are attributed to In 3+ In 3d valence 5 / 2 With In 3D 3 / 2 orbital, the peak centered at 529.6 eV corresponds to the lattice oxygen (O L ), the peak centered at 530.2 eV corresponds to oxygen vacancies (O V ), the peak centered at 531.8 eV corresponds to chemically adsorbed oxygen, that is, In2O3 is synthesized. Figure 4 As shown in (e) and (f), the two characteristic peaks of In are also In 3+ In 3d valence 5 / 2With In 3d 3 / 2 orbit. 161.6eV(S2P 3 / 2 ) and 162.8eV(S2P 1 / 2 ) proved the negative divalent state of sulfur, and the XPS test results proved the synthesis of In2S3.

[0037] The two-dimensional material was dropped onto the IDE and the gas sensing experiment was tested. The sensor response is defined as the relative change in resistance when exposed to N2 at a given gas concentration:

[0038]

[0039] in, is the resistance when exposed to N2, R g is the resistance when exposed to NO2.

[0040] Figure 5 These are the gas-sensing experimental test results of In2S3, In2O3, and In2O3-In2S3 heterojunctions prepared in Example 1. Figure 5 (a), (b), and (c) are gas-sensitive response diagrams of In2S3. As shown in Figure (a), under different light source excitations and in the same 10ppm NO2 environment, In2S3 has the best gas-sensitive response under blue light. Therefore, the tests in Figures (b) and (c) are all carried out under blue light excitation, and the subsequent tests of In2O3 and In2O3-In2S3 heterojunctions are similar. Figures (b) and (c) show the gas-sensitive repeatability and dynamic response process of In2S3. Although In2S3 shows good repeatability, its response value to gas is too low, with a response of only about 4.5 even under blue light, which cannot meet the requirements of high-performance gas sensors at all. Figure 5 (d), (e), and (f) are the gas-sensitive response diagrams of In2O3. The best excitation light source for In2O3 is also blue light, and under blue light excitation, the response value of In2O3 is only 12.5. The In2O3-In2S3 heterojunction can improve the gas-sensitive performance of In2O3 and In2S3. Figure 5 As shown in (g), (h), and (i). As shown in Figure (g), in the same gas environment, the In2O3-In2S3 heterojunction can show the best gas-sensitive response under blue light, and the response value is relatively high (about 27), while Figures (h) and (i) show that the In2O3-In2S3 heterojunction also has excellent repeatability and dynamic response performance. The successful construction of the In2O3-In2S3 heterojunction improves the gas-sensitive performance of In2O3 and In2S3, and this heterojunction can achieve high response under visible light excitation.

[0041] In summary, the preparation method of the present invention changes the surface potential and activity of the two-dimensional material dispersion by adding specific solvents and controlling the dosage ratio of the solvents, so that it can self-assemble into a two-dimensional heterojunction on a silicon wafer. The prepared In2O3-In2S3 heterojunction has the advantages of high response under visible light excitation, excellent repeatability and complete recovery, etc., which provides a new perspective for the preparation of non-layered heterojunctions and promotes the process of realizing low-power and high-performance gas sensing at room temperature.

[0042] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on 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 the technical solution of the present invention.

Claims

1. A method for preparing an ultrathin two-dimensional In2O3-In2S3 heterojunction, characterized in that: The following steps are involved: S1, preparation of flower-like In2S3 by hydrothermal method; S2, dispersing the flower-shaped In2S3 obtained in step S1 with water as solvent, preparing In2S3 nanosheets by ultrasonic exfoliation, and obtaining an In2S3 nanosheet solution with water as solvent; S3, taking the flower-shaped In2S3 obtained in step S1 and annealing it at 450-550°C to obtain In2O3; dispersing the In2O3 with water as solvent, preparing In2O3 nanosheets by ultrasonic exfoliation, and obtaining an In2O3 nanosheet solution with water as solvent; S4. Prepare a two-dimensional In2O3-In2S3 heterojunction, as follows: S41, adding ethylene glycol and ethanol to the In2S3 nanosheet solution to obtain an In2S3 solution; S42, adding formamide and ethanol to the In2O3 nanosheet solution to obtain an In2O3 solution; S43. Add the In2S3 solution dropwise onto the silicon wafer preheated to 40-45°C. After the solution evaporates, heat the silicon wafer to 180-220°C and keep the temperature constant for 0.5-1h. Then cool it down to 45°C and add the In2O3 solution dropwise. After the solution evaporates, a two-dimensional In2O3-In2S3 heterojunction is formed on the silicon wafer.

2. The method for preparing an ultrathin two-dimensional In2O3-In2S3 heterojunction according to claim 1, characterized in that: In step S41, the volume ratio of ethylene glycol:ethanol:water in the In2S3 solution is controlled to be 2:1:

1.

3. The method for preparing an ultrathin two-dimensional In2O3-In2S3 heterojunction according to claim 1, characterized in that: In step S42, the volume ratio of formamide:ethanol:water in the In2O3 solution is controlled to be 1:1:

1.

4. The method for preparing an ultrathin two-dimensional In2O3-In2S3 heterojunction according to claim 1, characterized in that: Step S1 is specifically as follows: adding indium chloride tetrahydrate and thioacetamide into water, stirring for 20 minutes, transferring the solution into a reaction kettle, performing a hydrothermal reaction at 150-180° C. for 10-16 hours, and then centrifuging to obtain a precipitate, which is the flower-like In2S3.

5. The method for preparing an ultrathin two-dimensional In2O3-In2S3 heterojunction according to claim 4, characterized in that: In step S2, the power of ultrasonic stripping is 200 W, the stripping time is 3 h, and then the solution is centrifuged to obtain a supernatant that is an In2S3 nanosheet solution with water as the solvent.

6. The method for preparing an ultrathin two-dimensional In2O3-In2S3 heterojunction according to claim 4, characterized in that: In step S3, the flower-shaped In2S3 is placed in a muffle furnace for sintering at 450-550°C for 2 hours to obtain In2O3; In2O3 is dispersed in water, the ultrasonic stripping power is 200W, the stripping time is 3 hours, and then the solution is centrifuged to obtain a supernatant, which is an In2O3 nanosheet solution with water as the solvent.

7. An ultrathin two-dimensional In2O3-In2S3 heterojunction, characterized in that: Prepared by the preparation method according to any one of claims 1 to 6.

8. The use of the ultra-thin two-dimensional In2O3-In2S3 heterojunction as claimed in claim 7, characterized in that: Used as gas sensitive material.

9. The use of the ultra-thin two-dimensional In2O3-In2S3 heterojunction as claimed in claim 8, characterized in that: Used as a gas sensor for detecting NO2 concentration.

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