A large-size non-layered two-dimensional cadmium sulfide thin film, its preparation method and application

Abstract

The present invention belongs to the technical field of the preparation of two-dimensional nanometer thin film materials, and particularly relates to a large-size non-layered two-dimensional cadmium sulfide thin film, a preparation method thereof and an application thereof. In the present invention, a cadmium source is dissolved in glycerol to prepare a cadmium precursor solution; the cadmium precursor solution and a gaseous sulfur source undergo a chemical reaction at a gas-liquid interface to form a non-layered two-dimensional cadmium sulfide thin film. The present invention adopts a heterogeneous reaction, uses the gas-liquid interface to inhibit the diffusion of the precursor, promotes the two-dimensional growth of the cadmium sulfide product, and uses the interface as a template to induce the formation of a non-layered cadmium sulfide thin film. The cadmium sulfide thin film prepared by the method of the present invention has a typical non-layered crystal structure, the thickness is nanoscale, while the lateral size of the thin film can reach centimeter scale or even larger size, providing a material basis for the large-scale application of integrated circuits and flexible optoelectronic devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of two-dimensional nanometer thin film materials, and particularly relates to a large-size non-layered two-dimensional cadmium sulfide thin film, a preparation method thereof, and an application thereof. Background Art

[0002] Since the successful exfoliation of ultrathin graphene materials from the surface of graphite using transparent tape by the group of A.K. Geim at the University of Manchester, UK in 2004, two-dimensional materials have experienced rapid development. The successive emergence of new two-dimensional nanomaterials such as hexagonal boron nitride (hBN), transition metal chalcogenides (TMDs), transition metal carbonitrides (MXenes), graphitic carbon nitride (g-C3N4), metal-organic frameworks (MOFs), metal oxides, black phosphorus (BP), and elemental metals not only enriches the types of two-dimensional materials but also exhibits many physicochemical properties different from those of bulk materials. Due to the ultrathin atomic layer thickness and unique quantum confinement effect of two-dimensional materials, they have broad application prospects in the fields of microelectronics, photonics, energy storage, biomedicine, and environmental science.

[0003] Existing methods for preparing two-dimensional materials are divided into top-down methods and bottom-up methods. Top-down methods include mechanical exfoliation, liquid-phase exfoliation, ion intercalation exfoliation, etc., to achieve the preparation of two-dimensional materials by breaking the van der Waals forces between layers of layered materials. However, due to the typical non-layered crystal structure of cadmium sulfide and the large number of surface active sites, it is difficult for top-down methods to break the strong chemical bonds between cadmium sulfide layers and cannot be used to prepare two-dimensional cadmium sulfide thin films.

[0004] Bottom-up methods include wet chemical methods and chemical vapor deposition (CVD) methods, etc., which directly synthesize two-dimensional materials through chemical reactions between precursors. The lateral size of two-dimensional non-layered materials synthesized by bottom-up methods is often less than 100 μm, which is not conducive to the integrated and device applications of two-dimensional materials. Therefore, developing a preparation method capable of forming large-size cadmium sulfide thin films is of great significance for the integrated and device applications of cadmium sulfide thin films. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a new method for preparing large-size non-layered two-dimensional cadmium sulfide thin films. The present invention adopts a heterogeneous reaction, uses the gas-liquid interface to inhibit the diffusion of precursors, promotes the two-dimensional growth of cadmium sulfide products, and uses the interface as a template to induce the formation of cadmium sulfide thin films. Since the lateral size of the thin film prepared by the method of the present invention for preparing cadmium sulfide thin films depends on the surface size of the precursor solution, the preparation method of the present invention is suitable for preparing large-size cadmium sulfide thin films; the cadmium sulfide polycrystalline thin film prepared by the method of the present invention has a non-layered crystal structure, the film thickness is nanoscale, while the lateral size of the film can reach centimeter scale or even larger size, providing a material basis for the large-scale application of integrated circuits and flexible optoelectronic devices.

[0006] Based on the above purpose, the technical solution adopted by the present invention is as follows:

[0007] In the first aspect, the present invention provides a method for preparing a large-size non-layered two-dimensional cadmium sulfide thin film, comprising the following steps:

[0008] S1: Dissolve a cadmium source in glycerol to prepare a cadmium precursor solution;

[0009] S2: React the cadmium precursor solution with a gaseous sulfur source at the gas-liquid interface to form a non-layered two-dimensional cadmium sulfide thin film.

[0010] The present invention dissolves the cadmium source in the liquid phase, and the sulfur source participates in the reaction in the gas phase state. The two reactants are in different phases. The cadmium precursor solution and the gaseous sulfur source carry out a gas-liquid heterogeneous reaction. The gas-liquid interface effectively inhibits the diffusion of the reaction precursor cadmium source, so that the cadmium source and the sulfur source react at the interface and use the interface as a template to induce the growth of non-layered cadmium sulfide along the gas-liquid interface to form an ultra-thin two-dimensional structure. The film thickness is nanoscale, 10-50 nm, with uniform thickness. The lateral size of the film can reach centimeter scale or even larger size. When the precursor is sufficient, the film will grow as large as the liquid phase area theoretically. The method of the present invention provides the possibility for the preparation of ultra-large-size two-dimensional cadmium sulfide thin films.

[0011] Preferably, in step S1, a viscosity regulator is further added to the cadmium precursor solution to adjust the viscosity of the cadmium precursor solution. The viscosity range of the cadmium precursor solution at 40 °C to 120 °C is 11-8.9×10 4 mpa·s.

[0012] By adding a viscosity regulator, the present invention adjusts the viscosity of the cadmium precursor solution. Through experiments, it is found that the viscosity of the cadmium precursor solution has a great influence on the film morphology. When the viscosity is low, the diffusion rate of cadmium sulfide at the gas-liquid interface is greater than the synthesis rate of cadmium sulfide, and the film growth is insufficient, resulting in the appearance of holes. When the viscosity of the liquid-phase cadmium sulfide precursor solution is in the range of 11-8.9×10 at 40 °C to 120 °C4 When it is mpa·s, the diffusion rate of cadmium sulfide at the gas-liquid interface further slows down. At this time, the reaction rate of synthesizing cadmium sulfide is greater than its diffusion rate, and the film growth is more complete. A complete cadmium sulfide film will appear at the gas-liquid interface.

[0013] Preferably, the concentration of the cadmium source in the cadmium precursor solution is 1-10 mg / mL.

[0014] It is found through experiments that when the concentration of the cadmium source in the cadmium precursor solution is too low, it is not conducive to the formation of a complete cadmium sulfide film. When the concentration of the cadmium source in the cadmium precursor solution is too high, excess particles will be generated on the film surface. When the concentration of the cadmium source in the cadmium precursor solution is 1-10 mg / mL, a complete and uniform cadmium sulfide film can be formed.

[0015] Preferably, in step S2, the reaction temperature of the cadmium precursor solution and the gaseous sulfur source is 40-120 °C.

[0016] It is found through experiments that the reaction temperature of the cadmium precursor solution and the gaseous sulfur source has a great influence on the film morphology. A complete cadmium sulfide film will be formed when the reaction temperature is between 40 °C and 120 °C. When the reaction temperature is relatively low, the reaction rate is slow and the film growth is insufficient. When the reaction temperature is too high, the diffusion rate of the precursor accelerates, resulting in the formation of aggregated particulate products.

[0017] Preferably, the cadmium source is cadmium chloride or cadmium acetate; the sulfur source is thiourea, thioacetamide or thioformamide.

[0018] Preferably, the viscosity regulator is soluble starch, and the addition amount of soluble starch in the cadmium precursor solution is 0-0.3 g / mL.

[0019] In the present invention, soluble starch is used as the viscosity regulator. By controlling the addition amount of soluble starch, the viscosity of the cadmium precursor solution is regulated. The viscosity of the cadmium precursor solution has a great influence on the film morphology. When the viscosity is relatively low, the diffusion rate of cadmium sulfide at the gas-liquid interface is greater than the synthesis rate of cadmium sulfide, and the film growth is insufficient, resulting in the appearance of holes. The viscosity of the cadmium precursor solution is also related to the thickness of the cadmium sulfide film, and the thickness of the cadmium sulfide film can be controlled by adjusting the viscosity of the cadmium precursor solution.

[0020] Preferably, the reaction atmosphere of the cadmium precursor solution and the gaseous sulfur source is an inert atmosphere, and the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0021] In the present invention, an inert gas such as nitrogen or argon is introduced during the reaction. On the one hand, it effectively isolates oxygen and avoids the oxidation of reactants such as cadmium source and sulfur source. On the other hand, the introduced inert gas serves as a carrier for the gaseous sulfur source, transporting the sulfur source to the gas-liquid interface for chemical reaction to synthesize cadmium sulfide.

[0022] Second aspect, the present invention provides a large-sized non-layered two-dimensional cadmium sulfide thin film prepared by the above method.

[0023] Preferably, the cadmium sulfide thin film prepared by the method of the present invention has three-dimensional co-directional chemical bonds, showing a typical non-layered crystal structure. The thickness of the thin film is 10 - 50 nm, and the thickness distribution is uniform. The lateral size of the thin film depends on the interface size and can reach centimeter level or even larger size.

[0024] Third aspect, the present invention provides the application of the above large-sized non-layered two-dimensional cadmium sulfide thin film in integrated circuits and flexible optoelectronic devices.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) Cadmium sulfide has a typical non-layered crystal structure and has many surface active sites. The present invention uses a cadmium precursor solution and a gaseous sulfur source for a gas-liquid heterogeneous reaction. The gas-liquid interface effectively inhibits the diffusion of the reaction precursor cadmium source, induces the growth of non-layered cadmium sulfide along the gas-liquid interface, forms an ultra-thin two-dimensional structure, and the process for preparing the cadmium sulfide thin film is simple and controllable, and can be mass-produced.

[0027] (2) The cadmium sulfide thin film prepared by the preparation method of the present invention is connected by covalent bonds in three dimensions, showing a typical non-layered crystal structure. The thickness of the thin film is at the nanometer level, the thickness distribution is uniform, and the lateral size of the thin film depends on the interface size and can reach centimeter level or even larger size, providing a material basis for the large-scale application of integrated circuits and flexible optoelectronic devices. Description of the Drawings

[0028] Figure 1 TEM image and element distribution pattern of the cadmium sulfide thin film prepared in Example 1;

[0029] Figure 2 Bright field image of the cadmium sulfide thin film prepared in Example 1;

[0030] Figure 3 Ultra-depth-of-field microscope image and SEM image of the cadmium sulfide thin film prepared in Example 1;

[0031] Figure 4 Crystal structure diagram of cadmium sulfide;

[0032] Figure 5 Ultra-depth-of-field microscope image of the cadmium sulfide thin film prepared in Example 2;

[0033] Figure 6 Ultra-depth-of-field microscope image of the cadmium sulfide thin film prepared in Example 3;

[0034] Figure 7 AFM images of the cadmium sulfide thin films prepared in Examples 1 - 3;

[0035] Figure 8 Ultra-depth-of-field microscope image of the cadmium sulfide thin film prepared in Example 4;

[0036] Figure 9 Ultra-depth-of-field microscope image of the cadmium sulfide thin film prepared in Example 5;

[0037] Figure 10 Ultra-depth-of-field microscope image of the cadmium sulfide thin film prepared in Example 6;

[0038] Figure 11 Ultra-depth-of-field microscope image of the cadmium sulfide thin film prepared in Example 7;

[0039] Figure 12 Ultra-depth-of-field microscope image of the cadmium sulfide thin film prepared in Example 8;

[0040] Figure 13 Ultra-depth-of-field microscope image of the cadmium sulfide thin film prepared in Example 9;

[0041] Figure 14 Ultra-depth-of-field microscope image of the cadmium sulfide thin film prepared in Example 10;

[0042] Figure 15 Ultra-depth-of-field microscope image of the product obtained in Comparative Example 1;

[0043] Figure 16 Ultra-depth-of-field microscope image of the product obtained in Comparative Example 2;

[0044] Figure 17 Ultra-depth-of-field microscope image of the product obtained in Comparative Example 3;

[0045] Figure 18 Homogeneous reaction mechanism diagram of cadmium sulfide and SEM image of cadmium sulfide particles in Comparative Example 4. Detailed implementation manners

[0046] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. The test methods used in the examples are all conventional methods unless otherwise specified; the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0047] Example 1

[0048] This example provides a method for preparing a large-size non-layered two-dimensional cadmium sulfide thin film, including the following steps:

[0049] Take 100 mg of thiourea as the sulfur source and place it in the middle of the tube furnace. Set the temperature of the tube furnace to 180 °C to ensure the gasification of thiourea at this temperature.

[0050] Add 50 mg of cadmium chloride and 3 g of soluble starch to 10 mL of glycerol in sequence to form a cadmium precursor solution. Take 200 μL of the cadmium precursor solution and drop it on a sterile coverslip, and place it at the downstream of the tube furnace. The temperature of the tube furnace here is 80 °C, which is also the reaction temperature of the cadmium precursor solution and gaseous thiourea. The viscosity of the cadmium precursor solution at this temperature is 8.9×10 4 mpa·s.

[0051] Introduce nitrogen into the tube furnace to remove the oxygen in the furnace. In a nitrogen atmosphere, after a 2-hour reaction, a cadmium sulfide thin film is formed on the surface of the cadmium precursor solution.

[0052] Gently stick a silicon wafer or any other substrate on the surface of the cadmium precursor solution to transfer the prepared cadmium sulfide thin film to the substrate. Then, put the cadmium sulfide thin film sample transferred to the substrate into petri dishes containing hot glycerol and DMF in sequence to remove the residual soluble starch and glycerol, and obtain a pure cadmium sulfide thin film.

[0053] Perform transmission electron microscopy analysis on the cadmium sulfide thin film sample prepared in this example. The obtained results are as Figure 1 shown. It can be seen from the figure that cadmium and sulfur elements are evenly distributed in the thin film sample, confirming that the prepared thin film is a cadmium sulfide thin film.

[0054] The bright-field photograph of the thin film sample is as Figure 2 shown, indicating that the lateral size of the prepared cadmium sulfide thin film reaches the centimeter level.

[0055] Characterize the cadmium sulfide thin film prepared in this example using a super-depth-of-field microscope. As Figure 3 shown. It can be seen from the figure that the prepared cadmium sulfide thin film has a continuous structure and consistent contrast at the micron scale, and has large-size two-dimensional characteristics.

[0056] The crystal structure of cadmium sulfide is as Figure 4 shown, indicating that cadmium sulfide is connected by covalent bonds in three dimensions, showing a typical non-layered crystal structure.

[0057] Example 2

[0058] This example provides a method for preparing a large-size non-layered two-dimensional cadmium sulfide thin film, including the following steps:

[0059] Take 100 mg of thiourea as the sulfur source and place it in the middle of the tube furnace. Set the temperature of the tube furnace to 180 °C.

[0060] 50 mg of cadmium chloride and 2 g of soluble starch were successively added to 10 mL of glycerol to form a cadmium precursor solution. 200 μL of the cadmium precursor solution was dropped onto a clean coverslip and placed downstream of a tube furnace at a temperature of 80 °C. At this temperature, the viscosity of the cadmium precursor solution was 4.6×10 4 mpa·s.

[0061] Nitrogen was introduced into the tube furnace. In a nitrogen atmosphere, after a 2-hour reaction, a cadmium sulfide thin film was formed on the surface of the cadmium precursor solution.

[0062] The cadmium sulfide thin film prepared was transferred to a substrate and cleaned using the method described in Example 1 to obtain a pure cadmium sulfide thin film.

[0063] A super-depth-of-field microscope was used to characterize the cadmium sulfide thin film sample prepared in this example. As Figure 5 shown, it can be seen from the figure that the prepared cadmium sulfide thin film has a continuous structure and uniform contrast at the micron scale, and has large-size two-dimensional characteristics, indicating that the preparation method of this example successfully prepared a non-layered two-dimensional cadmium sulfide thin film.

[0064] Example 3

[0065] This example provides a method for preparing a large-size non-layered two-dimensional cadmium sulfide thin film, including the following steps:

[0066] 100 mg of thiourea was taken as the sulfur source and placed in the middle of the tube furnace. The temperature of the tube furnace was set to 180 °C.

[0067] 50 mg of cadmium chloride and 1 g of soluble starch were added to 10 mL of glycerol to form a cadmium precursor solution. 200 μL of the cadmium precursor solution was dropped onto a clean coverslip and placed downstream of a tube furnace at a temperature of 80 °C. At this temperature, the viscosity of the cadmium precursor solution was 5×10 3 mpa·s.

[0068] Nitrogen was introduced into the tube furnace. In a nitrogen atmosphere, after a 2-hour reaction, a cadmium sulfide thin film was formed on the surface of the cadmium precursor solution. The cadmium sulfide thin film prepared was transferred to a substrate and cleaned using the method described in Example 1 to obtain a pure cadmium sulfide thin film.

[0069] A super-depth-of-field microscope was used to characterize the cadmium sulfide thin film sample prepared in this example. As Figure 6 shown, it can be seen from the figure that the prepared cadmium sulfide thin film has a continuous structure and uniform contrast at the micron scale, and has large-size two-dimensional characteristics, indicating that the preparation method of this example successfully prepared a non-layered two-dimensional cadmium sulfide thin film.

[0070] Examples 1 to 3 only differ in the viscosity of the cadmium precursor solution. The thickness of the cadmium sulfide thin films prepared in Examples 1 to 3 was analyzed using an atomic force microscope, and the results are as Figure 7 shown. The thickness of the cadmium sulfide thin film prepared in Example 1 was 10.7 nm to 11.3 nm ( Figure 7 a); the thickness of the cadmium sulfide thin film prepared in Example 2 was 32.3 to 33.1 nm ( Figure 7 b); the thickness of the cadmium sulfide thin film prepared in Example 3 was 47.9 to 49.8 nm ( Figure 7 c). From the Figure 7 detection results, it can be seen that as the viscosity of the system increases, the film thickness decreases from about 49.6 nm to about 10.9 nm, indicating that the thickness of the cadmium sulfide thin film can be controlled by regulating the viscosity of the system.

[0071] Example 4

[0072] This example provides a method for preparing a large-size non-layered two-dimensional cadmium sulfide thin film, which includes the following steps:

[0073] Take 100 mg of thiourea as the sulfur source and place it in the middle of the tube furnace. The temperature of the tube furnace is set to 180 °C.

[0074] Add 50 mg of cadmium chloride to 10 mL of glycerol as the cadmium precursor solution. Take 200 μL of the cadmium precursor solution and drop it on a clean cover glass and place it at the downstream of the tube furnace. The temperature of the tube furnace here is 40 °C, and the viscosity of the cadmium precursor solution at this temperature is 259 mPa·s.

[0075] Introduce nitrogen into the tube furnace. In a nitrogen atmosphere, after 2 h of reaction, a layer of cadmium sulfide thin film is formed on the surface of the cadmium precursor solution. The cadmium sulfide thin film prepared is transferred to a substrate and cleaned using the method described in Example 1 to obtain a pure cadmium sulfide thin film.

[0076] The cadmium sulfide thin film sample prepared in this example was characterized using a super-depth-of-field microscope, as Figure 8 shown. It can be seen from the figure that the prepared cadmium sulfide thin film has a continuous structure and uniform contrast at the micron scale and has large-size two-dimensional characteristics. This indicates that the preparation method in this example has successfully prepared a non-layered two-dimensional cadmium sulfide thin film.

[0077] Example 5

[0078] This example provides a method for preparing a large-size non-layered two-dimensional cadmium sulfide thin film, which includes the following steps:

[0079] Take 100 mg of thiourea as the sulfur source and place it in the middle of the tube furnace. The temperature of the tube furnace is set to 180 °C.

[0080] Add 10 mg of cadmium chloride to 10 mL of glycerol to obtain a cadmium precursor solution. Take 200 μL of the solution and drop it on a clean cover glass placed downstream of a tube furnace, where the temperature of the tube furnace is 60 °C. At this temperature, the viscosity of the cadmium precursor solution is 84 mPa·s.

[0081] Introduce nitrogen into the tube furnace. In a nitrogen atmosphere, after a 2-hour reaction, a cadmium sulfide thin film is formed on the surface of the cadmium precursor solution. Transfer the obtained cadmium sulfide thin film to a substrate and clean it using the method described in Example 1 to obtain a pure cadmium sulfide thin film.

[0082] Characterize the cadmium sulfide thin film sample prepared in this example using a super-depth-of-field microscope, as Figure 9 shown. It can be seen from the figure that the prepared cadmium sulfide thin film has a continuous structure and consistent contrast at the micron scale, and has large-size two-dimensional characteristics, indicating that the preparation method in this example successfully prepares a non-layered two-dimensional cadmium sulfide thin film.

[0083] Example 6

[0084] This example provides a method for preparing a large-size non-layered two-dimensional CdS thin film, including the following steps:

[0085] Take 100 mg of thiourea as a sulfur source and place it in the middle of the tube furnace. Set the temperature of the tube furnace to 180 °C.

[0086] Add only 10 mg of cadmium chloride to 10 mL of glycerol to obtain a cadmium precursor solution. Take 200 μL of the solution and drop it on a clean cover glass placed downstream of the tube furnace, where the temperature of the tube furnace is 40 °C. At this temperature, the viscosity of the cadmium precursor solution is 259 mPa·s.

[0087] Introduce nitrogen into the tube furnace. In a nitrogen atmosphere, after a 2-hour reaction, a cadmium sulfide thin film is formed on the surface of the solution. Transfer the obtained cadmium sulfide thin film to a substrate and clean it using the method described in Example 1 to obtain a pure cadmium sulfide thin film.

[0088] Characterize the cadmium sulfide thin film sample prepared in this example using a super-depth-of-field microscope, as Figure 10 shown. It can be seen from the figure that the prepared cadmium sulfide thin film has a continuous structure and consistent contrast at the micron scale and has large-size two-dimensional characteristics.

[0089] Example 7

[0090] This example provides a method for preparing a large-size non-layered two-dimensional cadmium sulfide thin film, including the following steps:

[0091] Take 100 mg of thiourea as a sulfur source and place it in the middle of the tube furnace. Set the temperature of the tube furnace to 180 °C.

[0092] 10 mg of cadmium chloride was added to 10 mL of glycerol to form a cadmium precursor solution. 200 μL of the solution was dropped onto a clean cover glass and placed downstream of a tube furnace, where the temperature of the tube furnace was 120 °C. The viscosity of the cadmium precursor solution at this temperature was 11 mPa·s.

[0093] Nitrogen was introduced into the tube furnace. In a nitrogen atmosphere, after a reaction of 2 h, a cadmium sulfide thin film was formed on the surface of the cadmium precursor solution. The cadmium sulfide thin film prepared was transferred to a substrate and cleaned using the method described in Example 1 to obtain a pure cadmium sulfide thin film.

[0094] The CdS prepared in this example was characterized using a super-depth-of-field microscope, as Figure 11 shown. It can be seen from the figure that the prepared cadmium sulfide thin film has a continuous structure and uniform contrast at the micron scale and has large-size two-dimensional characteristics, indicating that the preparation method in this example successfully prepared a non-layered two-dimensional cadmium sulfide thin film.

[0095] Example 8

[0096] This example provides a method for preparing a large-size non-layered two-dimensional CdS thin film, which includes the following steps:

[0097] 100 mg of thiourea was taken as the sulfur source and placed in the middle of a tube furnace, and the temperature of the tube furnace was set to 180 °C.

[0098] 50 mg of cadmium chloride was added to 10 mL of glycerol to form a cadmium precursor solution. 200 μL of the solution was dropped onto a clean cover glass and placed downstream of a tube furnace, where the temperature of the tube furnace was 80 °C. The viscosity of the cadmium precursor solution at this temperature was 35 mPa·s.

[0099] Nitrogen was introduced into the tube furnace. In a nitrogen atmosphere, after a reaction of 2 h, a cadmium sulfide thin film was formed on the surface of the cadmium precursor solution. The cadmium sulfide thin film prepared was transferred to a substrate and cleaned using the method described in Example 1 to obtain a pure cadmium sulfide thin film.

[0100] The cadmium sulfide thin film sample prepared in this example was characterized using a super-depth-of-field microscope, as Figure 12 shown. It can be seen from the figure that the prepared cadmium sulfide thin film has a continuous structure and uniform contrast at the micron scale and has large-size two-dimensional characteristics, indicating that the preparation method in this example successfully prepared a non-layered two-dimensional cadmium sulfide thin film.

[0101] Example 9

[0102] This example provides a method for preparing a large-size non-layered two-dimensional CdS thin film, which includes the following steps:

[0103] Take 100 mg of thiourea as the sulfur source and place it in the middle of the tubular furnace. The temperature of the tubular furnace is set at 180 °C.

[0104] Add 100 mg of cadmium chloride to 10 ml of glycerol to form a cadmium precursor solution. Take 200 μL of the solution and drop it on a clean coverslip placed downstream of the tubular furnace, where the temperature of the tubular furnace is 60 °C. The viscosity of the cadmium precursor solution at this temperature is 84 mPa·s.

[0105] Introduce nitrogen gas into the tubular furnace. In a nitrogen atmosphere, after a 2-hour reaction, a cadmium sulfide thin film is formed on the surface of the cadmium precursor solution. Transfer the obtained cadmium sulfide thin film to a substrate and clean it using the method described in Example 1 to obtain a pure cadmium sulfide thin film.

[0106] Characterize the cadmium sulfide thin film sample prepared in this example using a super-depth-of-field microscope, as Figure 13 shown. It can be seen from the figure that the prepared cadmium sulfide thin film has a continuous structure and uniform contrast at the micron scale, and has large-size two-dimensional characteristics, indicating that the preparation method of this example has successfully prepared a non-layered two-dimensional cadmium sulfide thin film.

[0107] Example 10

[0108] A method for preparing a large-size non-layered two-dimensional cadmium sulfide thin film in this example includes the following steps:

[0109] Take 100 mg of thiourea as the sulfur source and place it in the middle of the tubular furnace. The temperature of the tubular furnace is set at 200 °C.

[0110] Add 100 mg of cadmium chloride to 10 ml of glycerol to form a cadmium precursor solution. Take 200 μL of the solution and drop it on a clean coverslip placed downstream of the tubular furnace, where the temperature of the tubular furnace is 60 °C. The viscosity of the cadmium precursor solution at this temperature is 84 mPa·s.

[0111] Introduce nitrogen gas into the tubular furnace. In a nitrogen atmosphere, after a 2-hour reaction, a cadmium sulfide thin film is formed on the surface of the solution. Transfer the obtained cadmium sulfide thin film to a substrate and clean it using the method described in Example 1 to obtain a pure cadmium sulfide thin film.

[0112] Characterize the cadmium sulfide thin film sample prepared in this example using a super-depth-of-field microscope, as Figure 14 shown. It can be seen from the figure that the prepared cadmium sulfide thin film has a continuous structure and uniform contrast at the micron scale, and has large-size two-dimensional characteristics, indicating that the preparation method of this example has successfully prepared a non-layered two-dimensional cadmium sulfide thin film.

[0113] Comparative Example 1

[0114] Take 100 mg of thiourea as the sulfur source and place it in the middle of the tube furnace. The temperature of the tube furnace is set at 180 °C.

[0115] Dissolve 50 mg of cadmium chloride in 10 mL of deionized water to obtain a cadmium precursor solution. Take 200 μL of the cadmium precursor solution and drop it on a super-clean cover glass, which is placed at the downstream of the tube furnace. The temperature of the tube furnace here is 80 °C. The viscosity of the cadmium precursor solution at this temperature is 0.64 mPa·s.

[0116] Introduce nitrogen into the tube furnace. In a nitrogen atmosphere, after 2 h of reaction, solid aggregates are formed on the surface of the cadmium precursor solution.

[0117] Use a super-depth-of-field microscope to characterize the solid aggregates of this comparative example, as Figure 15 shown. Scattered micron-sized flakes are formed on the solution surface, and no large-sized cadmium sulfide film is formed.

[0118] From the experimental results of Example 1, Example 2, Example 3, Example 7, Example 8 and Comparative Example 1, it can be seen that the viscosity of the liquid-phase cadmium precursor solution has a great influence on the film morphology. When the viscosity is low, the diffusion rate of cadmium sulfide at the gas-liquid interface is greater than the synthesis rate of cadmium sulfide, and the film growth is insufficient, resulting in the appearance of holes. It has been found through experiments that when the viscosity of the liquid-phase cadmium sulfide precursor solution is in the range of 11 mPa·s to 8.9×10 4 mPa·s, the diffusion rate of cadmium sulfide at the gas-liquid interface is further slowed down. At this time, the reaction synthesis rate of cadmium sulfide is greater than its diffusion rate, and the film growth is more complete. A complete cadmium sulfide film will appear at the gas-liquid interface.

[0119] Comparative Example 2

[0120] Take 100 mg of thiourea as the sulfur source and place it in the middle of the tube furnace. The temperature of the tube furnace is set at 180 °C.

[0121] Add 10 mg of cadmium chloride to 10 mL of glycerol to obtain a cadmium precursor solution. Take 200 μL of the cadmium precursor solution and drop it on a super-clean cover glass, which is placed at the downstream of the tube furnace. The temperature of the tube furnace here is 30 °C. The viscosity of the cadmium precursor solution at this temperature is 600 mPa·s.

[0122] Introduce nitrogen into the tube furnace. In a nitrogen atmosphere, after 2 h of reaction, solid aggregates are formed on the solution surface.

[0123] Use a super-depth-of-field microscope to characterize the solid aggregates of this comparative example, as Figure 16 shown. Scattered micron-sized flakes are formed on the solution surface, and no large-sized CdS film is formed.

[0124] Comparative Example 3

[0125] 100 mg of thiourea was taken as a sulfur source and placed in the middle of a tube furnace, and the temperature of the tube furnace was set to 180°C.

[0126] Add 10 mg of cadmium chloride to 10 mL of glycerol as a cadmium precursor solution, take 200 μL of the cadmium precursor solution and drop it on an ultra-clean cover glass and place it downstream of the tube furnace, where the temperature of the tube furnace is 140° C. The viscosity of the cadmium precursor solution at this temperature is 9 mPa.s.

[0127] Nitrogen was introduced into the tubular furnace. After 2 hours of reaction in the nitrogen atmosphere, discontinuous particles were generated on the surface of the solution.

[0128] The samples of this comparative example were characterized using an ultra-depth of field microscope. Figure 17 As shown, a sample with aggregated particles was formed on the substrate surface, and no large-sized CdS film was formed.

[0129] It can be seen from the experimental results of Example 5, Example 6, Example 7 and Comparative Example 2 and Comparative Example 3 that the reaction temperature has a great influence on the film morphology. A complete cadmium sulfide film will be generated when the reaction temperature is between 40°C and 120°C. When the reaction temperature is low, the reaction rate is slow and the film growth is insufficient. When the reaction temperature is too high, the diffusion rate of the precursor is accelerated, resulting in the production of aggregated granular products.

[0130] Comparative Example 4

[0131] Weigh 50 mg of cadmium chloride and 100 mg of thiourea, dissolve them in 10 g of glycerol, then transfer the mixed homogeneous solution to a hydrothermal autoclave and react in an oven at 180°C for 4 hours. The product is washed four times by centrifugation with DMF, and the precipitated material obtained by centrifugation is collected and transferred to a silicon wafer for morphological characterization.

[0132] The results are as follows Figure 18 As shown, the product obtained by homogeneous reaction in Comparative Example 4 presents aggregated particles. This is because in the homogeneous reaction system, the precursors cadmium chloride and thiourea can diffuse freely in three-dimensional space, and the growth of the crystal will continue to develop along the high-energy crystal plane on the surface, eventually forming a three-dimensional granular structure. Due to the small size of the crystal particles and the high interface energy, they are inevitably piled together, and finally form aggregated three-dimensional nanoparticles. This comparative example shows that the gas-liquid interface is a key factor in the formation of cadmium sulfide film.

[0133] In summary, the present invention uses a cadmium precursor solution and a gaseous sulfur source to carry out a gas-liquid heterogeneous reaction. The gas-liquid interface effectively inhibits the diffusion of the reaction precursor cadmium source and the sulfur source, induces the growth of non-layered cadmium sulfide along the gas-liquid interface, and forms an ultra-thin two-dimensional structure. The viscosity of the cadmium precursor solution ranges from 11 to 8.9×10 4Under the conditions such as the cadmium concentration in the cadmium precursor solution being 1-10 mg / mL and the reaction temperature at the gas-liquid interface being 40-120 °C in mpa.s, large-size non-layered two-dimensional cadmium sulfide thin films can be prepared.

Claims

1. A method for preparing a large-sized non-layered two-dimensional cadmium sulfide thin film, characterized in that, It includes the following steps: S1: Dissolve the cadmium source in glycerol to prepare a cadmium precursor solution; S2: React the cadmium precursor solution with the gaseous sulfur source at the gas-liquid interface to form a non-layered two-dimensional cadmium sulfide thin film; In step S1, a viscosity regulator is further added to the cadmium precursor solution to adjust the viscosity of the cadmium precursor solution, and the viscosity range of the cadmium precursor solution at 40 °C to 120 °C is 11 to 8.9×10 4 mpa·s; the viscosity regulator is soluble starch; The concentration of the cadmium source in the cadmium precursor solution is 1-10 mg / mL; In step S2, the reaction temperature of the cadmium precursor solution and the gaseous sulfur source is 40-120 °C.

2. The preparation method according to claim 1, characterized in that, The cadmium source is cadmium chloride or cadmium acetate; the sulfur source is thiourea, thioacetamide or thioformamide.

3. The preparation method according to claim 1, characterized in that, The addition amount of soluble starch in the cadmium precursor solution is 0-0.3 g / mL.

4. The preparation method according to claim 1, characterized in that, The reaction atmosphere of the cadmium precursor solution and the gaseous sulfur source is an inert atmosphere.

5. A large-sized non-layered two-dimensional cadmium sulfide thin film, characterized in that, The cadmium sulfide thin film is prepared by the preparation method according to any one of claims 1-4.

6. The large-sized non-layered two-dimensional cadmium sulfide thin film according to claim 5, characterized in that, The cadmium sulfide thin film has a non-layered two-dimensional structure, the thickness of the cadmium sulfide thin film is 10-50 nm, and the lateral dimension reaches the centimeter level.

7. Application of the large-sized non-layered two-dimensional cadmium sulfide thin film according to claim 5 in integrated circuits and flexible optoelectronic devices.

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