A method for preparing monolayer single-crystal rhenium disulfide by chemical vapor deposition

Abstract

This invention discloses a method for preparing monolayer single-crystal rhenium disulfide by chemical vapor deposition, relating to the field of two-dimensional material preparation. Its key technical points include: raw material preparation, raw material loading, temperature-controlled reaction, and final sampling. This invention utilizes face-to-face stacked substrates to construct a spatially confined growth space, and employs a dual-temperature zone tubular furnace quartz tube to prepare monolayer single-crystal ReS2. The preparation process is simple, easy to operate, and controllable. It not only obtains monolayer ReS2 with uniform thickness and high crystallinity on various substrate surfaces, but also achieves controllable preparation of monolayer single-crystal ReS2 on the magnesium oxide (001) surface.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional material preparation, specifically to a method for preparing monolayer single-crystal rhenium disulfide by chemical vapor deposition. Background Technology

[0002] Two-dimensional transition metal dichalcogenides (TMDCs) possess atomic-level thickness, high specific surface area, absence of dangling bonds, and strong interlayer van der Waals forces, making them widely applicable in optics, electronics, catalysis, and energy fields. Low-symmetry two-dimensional rhenium disulfide (ReS2) is a typical representative of two-dimensional TMDs, exhibiting anisotropic in-plane physicochemical properties and semiconductor characteristics, thus showing great promise for applications in electronic devices, photodetectors, and electrocatalysis. Single-crystal preparation is a prerequisite for realizing its anisotropic applications such as polarization photodetectors and anisotropic logic devices.

[0003] Currently, commonly used preparation methods include mechanical exfoliation, liquid phase exfoliation, chemical vapor transport, and chemical vapor deposition (CVD). Compared with other methods, CVD has advantages such as high yield and high quality.

[0004] In existing CVD methods, due to weak interface coupling, easy formation of out-of-plane chemical bonds, and low grain boundary formation energy, the following problems exist in the preparation of ReS2 by CVD: (1) poor experimental repeatability; (2) difficulty in growing monolayers; (3) difficulty in preparing single crystals.

[0005] Therefore, the present invention aims to provide a method for preparing monolayer single-crystal rhenium disulfide by chemical vapor deposition to solve the above-mentioned problems. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned problems and provide a method for preparing monolayer single-crystal rhenium disulfide by chemical vapor deposition. By employing a spin-coating precursor salt combined with a spatially confined reaction chamber construction method, the reaction concentrations and concentration gradients of the precursor sulfur and precursor sodium perrhenate are effectively controlled, effectively avoiding the uneven spatial distribution of the product caused by uneven precursor concentration distribution. Simultaneously, a relatively wide growth parameter window is obtained, improving the stability and reproducibility of the experiment.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] This invention provides a method for preparing monolayer single-crystal rhenium disulfide by chemical vapor deposition, comprising the following steps:

[0009] S1. Substrate preparation: Prepare a spin-coating substrate and a target substrate. Spin-coat a sodium perrhenate (NaReO4) solution onto the spin-coating substrate. Place the target substrate above the spin-coating substrate, with the polished surface of the spin-coating substrate facing the polished surface of the target substrate to form a slit, thus constituting a spatially confined reaction chamber.

[0010] S2. Precursor pretreatment and loading: Sulfur powder is loaded into a corundum crucible, melted, and recrystallized as a sulfur source; a dual-temperature zone tubular furnace quartz tube is prepared, the sulfur source is placed at the end of the quartz tube near the inlet, the spatially confined reaction chamber is placed at the end of the quartz tube near the outlet, the inlet and outlet flanges are sealed, and then a predetermined flow rate of inert gas is introduced to completely replace the air in the quartz tube.

[0011] S3. Controlling the reaction: Inert gas is introduced, and the center temperature of the high-temperature zone and the center temperature of the low-temperature zone of the tube furnace are set respectively. After heating to the set temperature, the relative position of the quartz tube and the furnace body is adjusted so that the spatially confined reaction chamber is aligned with the center of the high-temperature zone of the tube furnace and the sulfur source container is aligned with the center of the low-temperature zone of the tube furnace. The reaction time is 15-30 minutes.

[0012] S4. End sampling: Continue to introduce inert gas, adjust the quartz tube away from the furnace heating position to cool the quartz tube quickly, adjust the flow rate of inert gas during the cooling process, and after the quartz tube cools to room temperature, remove the spatially confined reaction chamber to obtain a monolayer of ReS2 on the target substrate surface.

[0013] Furthermore, in S1, the spin-coating substrate is c-plane sapphire, and the material of the target substrate is one of c-plane sapphire, a-plane sapphire, strontium titanate (001), and magnesium oxide (001).

[0014] Furthermore, in S1, the spin-coated substrate is subjected to oxygen plasma treatment for 50 s before spin-coating with NaReO4 solution, with the power set to 50 W.

[0015] Furthermore, in S1, the concentration of the NaReO4 solution is 0.0025–0.05 mol / L.

[0016] Furthermore, in S1, the amount of NaReO4 solution added during spin coating is 20–50 μL / cm².

[0017] Furthermore, in S1, the spin-coating substrate is placed on a spin coater, and the NaReO4 solution is drawn up with a pipette and dropped onto the surface of the spin-coating substrate; the spin coater rotates at 500-5000 rpm, and the spin coating time is 30-50 s.

[0018] Furthermore, in S2, after sulfur powder is placed in a corundum crucible, it is heated to 120°C–140°C using a hot plate to melt it, and then cooled to room temperature for recrystallization.

[0019] Furthermore, in S2, the sulfur source is in excess during the reaction; the predetermined flow rate of the inert gas is 100-200 sccm, and the introduction time is 15-30 min; the inert gas is argon.

[0020] Furthermore, in S3, the flow rate of the inert gas is 40-60 sccm, the introduction time is 15-30 min, and the inert gas is argon.

[0021] Furthermore, in S3, the center temperature of the high-temperature zone of the tubular furnace is 800-880℃, and the heating rate is 20-40℃ / min; the center temperature of the low-temperature zone of the tubular furnace is 140-180℃, and the heating rate is 10-20℃ / min.

[0022] Furthermore, in S4, the flow rate of the inert gas during the quartz tube cooling process is adjusted to 200 sccm.

[0023] Furthermore, in S4, the resulting monolayer ReS2 grain size is 7–20 μm.

[0024] Furthermore, in S4, when magnesium oxide (001) is used as the target substrate, the resulting monolayer ReS2 grains are single crystals.

[0025] Compared with existing technologies, the beneficial effects of this solution are:

[0026] 1. This invention employs a spin-coating precursor salt combined with a spatially confined reaction chamber method to effectively control the reaction concentration and concentration gradient of precursor sulfur and precursor sodium perrhenate, effectively avoiding the uneven spatial distribution of products caused by uneven precursor concentration distribution; at the same time, it also obtains a relatively wide growth parameter window, improving the stability and repeatability of the experiment.

[0027] 2. In this invention, oxygen plasma pretreatment of the spin-coated substrate makes the spin-coated substrate hydrophilic, which allows the sodium perrhenate precursor to be uniformly dispersed on the substrate surface, which is beneficial to the uniform growth of rhenium disulfide.

[0028] 3. In this invention, the precursor sulfur undergoes melting and recrystallization before the reaction, which makes the surface area of ​​the sulfur precursor fixed during the reaction, and can effectively control the amount of sulfur precursor volatilization;

[0029] 4. In this invention, the dual-temperature zone tubular furnace quartz tube is moved away from the precursor and substrate. After preheating to the set temperature, the furnace body is moved to the center of the sulfur precursor and the spatially confined reaction chamber, which are respectively located in the low-temperature zone and the high-temperature zone. This effectively reduces the reaction time and temperature variables during the reaction process. After the reaction is completed, the dual-temperature zone tubular furnace quartz tube is moved away from the precursor and substrate, and the inert gas flow is adjusted to 200 sccm to quickly reduce the temperature of the spatially confined reaction chamber and quickly terminate the reaction, effectively reducing the generation of by-products.

[0030] 5. This invention is applicable to a variety of target substrates, including a-side sapphire, c-side sapphire, strontium titanate (001), and magnesium oxide (001), and has a certain degree of universality. Attached Figure Description

[0031] Figure 1 This is a flowchart of the method for preparing single-layer single-crystal rhenium disulfide in an embodiment of the present invention;

[0032] Figure 2 This is a physical diagram of the spatially confined reaction chamber in an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram of the dual-temperature zone tube furnace and its quartz tube structure used in the embodiments of the present invention;

[0034] Figure 4 This is a physical diagram of the dual-temperature zone tube furnace and its quartz tube structure used in the embodiments of the present invention;

[0035] Figure 5 These are two-dimensional ReS2 scanning electron microscope images from embodiments of the present invention;

[0036] Figure 6 These are atomic force microscope images and dimensional statistics of two-dimensional ReS2 in embodiments of the present invention;

[0037] Figure 7 These are scanning transmission electron microscope images and selected area electron diffraction patterns of two-dimensional ReS2 in embodiments of the present invention;

[0038] Figure 8 These are optical microscope images of two-dimensional ReS2 prepared at different reaction temperatures in the embodiments of the present invention;

[0039] Figure 9 This is an optical microscope image of two-dimensional ReS2 prepared under different concentrations of sodium perrhenate solution in the embodiments of the present invention. Detailed Implementation

[0040] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be described in further detail below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0041] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0042] Example:

[0043] Prepare a 10mm×10mm×0.5mm single-sided polished c-side sapphire as a spin-coating substrate and a 5mm×5mm×0.5mm single-sided polished magnesium oxide (001) as a target substrate;

[0044] The spin-coated substrate was placed in an oxygen plasma treatment device with a power of 50W; the device was started to expose the substrate to oxygen plasma for 50 seconds; the treated spin-coated substrate will be used as a substrate for loading Re source precursors.

[0045] Prepare a 0.005 mol / L sodium perrhenate solution; place the spin-coating substrate on the spin coater, turn on the vacuum mechanical pump connected to the spin coater, and use negative pressure to fix the substrate on the spin coater; set the spin coating parameters, spin coat at 500 rpm for 10 seconds, then spin coat at 3000 rpm for 30 seconds; use a pipette to draw 30 μL of sodium perrhenate solution and drop it onto the center of the spin-coating substrate, run the spin coater, and spin coat according to the above-mentioned parameters; after spin coating is completed, turn off the vacuum mechanical pump and remove the spin-coated substrate;

[0046] The target substrate and the spin-coated substrate loaded with sodium perrhenate are placed face-to-face with the polished surfaces facing each other, with the target substrate on top and the spin-coated substrate on the bottom, to form a spatially confined reaction chamber.

[0047] S2: Weigh 150mg of sulfur powder using an analytical balance and place it into an alumina crucible with a diameter of 10mm and a height of 5mm. Place the alumina crucible containing the sulfur powder on a hot plate. Set the temperature of the hot plate to 140℃. After the sulfur powder has completely melted into liquid, remove the alumina crucible containing liquid sulfur from the hot plate. After the alumina crucible containing liquid sulfur cools to room temperature, the liquid sulfur will recrystallize.

[0048] Use a corundum crucible containing recrystallized sulfur as the sulfur source; set the gas inlet end of a quartz tube with a diameter of 1 inch as the upstream end, mark the position coinciding with the insulation ring of the tube furnace as 0cm, place the sulfur source at 16.5cm marked on the quartz tube, place the space-confined reaction chamber on the frosted surface of a single-sided polished c-faced sapphire with dimensions of 20mm×15mm×0.5mm, and place this whole assembly at 39.5cm marked on the quartz tube;

[0049] Install the inlet and outlet flanges at both ends of the quartz tube and ensure a seal. Introduce argon gas at a flow rate of 200 sccm for 10 minutes to expel as much air as possible from the quartz tube.

[0050] S3: When setting the reaction parameters, push the tubular furnace away from the reaction zone under an argon flow rate of 200 sccm. Set the low-temperature zone to 150℃ with a heating rate of 10℃ / min; set the high-temperature zone to 840℃ with a heating rate of 20℃ / s. At the start of the reaction, once the high and low temperature zones reach their target temperatures, reduce the argon flow rate to 40 sccm and push the tubular furnace back into the reaction zone, aligning the sulfur source and the confined reaction chamber with the center positions of the low-temperature and high-temperature zones respectively. Maintain the low-temperature zone at 150℃, the high-temperature zone at 840℃, and the argon flow rate at 40 sccm for 20 minutes.

[0051] S4: After the reaction is complete, adjust the argon flow rate to 200 sccm. After 30 seconds, push the tube furnace away from the reaction area and stop heating in the high and low temperature zones. After the tube furnace and the confined reaction chamber have cooled to room temperature, turn off the argon flow, remove the confined reaction chamber, and obtain a monolayer of ReS2 grains on the target substrate surface.

[0052] The scanning electron microscope images and Raman spectroscopy results of this embodiment are attached. Figure 5 As shown in a and 5d, the grains are spindle-shaped, and Raman spectroscopy confirms that the prepared sample is ReS2. The atomic force microscopy images and dimensional statistics of the grains in this embodiment are attached. Figure 6 As shown in a and 6b, the grain thickness is 0.9 nm, and the average size is approximately 18 μm. (Scanning transmission electron microscopy images) Figure 7 a) Shows no grain boundaries within the grains, selected electron diffraction pattern ( Figure 7 b) The absence of diffraction pattern splitting indicates that the crystal is a single crystal, which means that the ReS2 crystal prepared in Example 1 is a single crystal.

[0053] The only difference between Examples 2 to 4 and Example 1 is the spin-coating substrate. In Example 2, the spin-coating substrate is sapphire on the a-side; in Example 3, it is sapphire on the c-side; and in Example 4, it is strontium titanate (001).

[0054] Examples 5 to 15 are compared with Example 1, using different growth temperatures and sodium perrhenate solution concentrations, while other implementation processes are the same as in Example 1.

[0055] Table 1 shows the main parameters for preparing ReS2 in the examples.

[0056]

[0057]

[0058] In Table 1, numbers 1 to 15 represent Examples 1 to 15, respectively. The effects of Examples 1 to 4 are shown in the appendix. Figure 5 As shown in the attached examples 5 to 15 Figure 8 and attached Figure 9 As shown.

[0059] The method for preparing ReS2 provided by this invention is applicable to a-plane sapphire, c-plane sapphire, strontium titanate (001), and magnesium oxide (001), and has a certain degree of universality. See Examples 1 to 4 (attached). Figure 5 ).

[0060] By controlling the reaction temperature and precursor concentration using the controlled variable method, the product size, thickness, and nucleation density can be affected. At lower temperatures in the low-temperature region and suitable temperatures in the high-temperature region, the nucleation density is lower, the product thickness is thinner, and the product size is larger. Figure 8 a) As the temperature in the low-temperature region increases, the sulfur concentration increases, the nucleation density increases, and thick nuclei begin to appear at the grain centers, resulting in smaller grain sizes. Figure 8 (bd). When the temperature in the low-temperature region is suitable and the temperature in the high-temperature region is relatively low, the nucleation density is low, the thickness is thin, and the size is small. Figure 8 e); As the temperature in the high-temperature region rises, the nucleation density does not change significantly, the size first increases and then decreases, and thick nuclei begin to appear at the grain centers. Figure 8 fh). When both the low-temperature and high-temperature regions are at suitable temperatures, and the sodium perrhenate solution concentration is low, the nucleation density is low, the thickness is thin, and the size is small. Figure 9 a) As the concentration of sodium perrhenate solution increases, the nucleation density increases, the size increases, and thick nuclei begin to appear at the grain centers. Figure 9 (b, c). The experimental results show that when the temperature is 150-170℃ in the low-temperature region, 820-850℃ in the high-temperature region, and the sodium perrhenate solution concentration is 0.005-0.01mol / L, a good balance can be achieved in terms of product size, thickness, and nucleation density.

[0061] The above specific embodiments are merely explanations of the present invention and are not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to these embodiments without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for preparing monolayer single-crystal rhenium disulfide by chemical vapor deposition, characterized in that: The method includes the following steps: S1. Substrate preparation: Prepare a spin-coating substrate and a target substrate. Spin-coat sodium perrhenate solution onto the spin-coating substrate. Place the target substrate above the spin-coating substrate, with the polished surface of the spin-coating substrate and the polished surface of the target substrate facing each other to form a slit, thus constituting a spatially confined reaction chamber. S2. Precursor pretreatment and loading: Sulfur powder is loaded into a corundum crucible, melted, and recrystallized as a sulfur source; the sulfur source is placed at the end of the quartz tube of the dual-temperature zone tubular furnace near the gas inlet, and the spatially confined reaction chamber is placed at the end of the quartz tube of the dual-temperature zone tubular furnace near the gas outlet. After sealing the gas inlet and gas outlet flanges, a predetermined flow rate of inert gas is introduced to completely replace the air in the quartz tube. S3. Controlling the reaction: Inert gas is introduced into the quartz tube of the dual-temperature zone tubular furnace, and the center temperature of the high-temperature zone and the center temperature of the low-temperature zone of the dual-temperature zone tubular furnace quartz tube are heated to the set temperature respectively. Then, the relative position of the quartz tube and the furnace body is adjusted so that the space-confined reaction chamber reacts with the sulfur source container for 15 to 30 minutes. S4. End of sampling: After the reaction is completed, adjust the flow rate of the inert gas and cool the dual-temperature zone tubular furnace quartz tube. After the dual-temperature zone tubular furnace quartz tube has cooled to room temperature, remove the spatially confined reaction chamber and obtain a monolayer of ReS2 on the surface of the target substrate. The spin-coating substrate is c-plane sapphire, and the target substrate is made of c-plane sapphire, a-plane sapphire, strontium titanate, or magnesium oxide. The spin-coated substrate is subjected to oxygen plasma treatment for 50 seconds before spin-coating with sodium perrhenate solution, with the power set to 50W. The concentration of the sodium perrhenate solution is 0.0025–0.05 mol / L. In step S1, when magnesium oxide is used as the target substrate, the monolayer ReS2 grains obtained in S4 are single crystals.

2. The method for preparing monolayer single-crystal rhenium disulfide by chemical vapor deposition as described in claim 1, characterized in that: The method of spin coating sodium perrhenate solution on spin-coating substrate is to place the spin-coating substrate on a spin coater and use a pipette to draw sodium perrhenate solution and drop it onto the surface of the spin-coating substrate; the spin coater speed is 500-5000 rpm and the spin coating time is 30-50 s; The amount of sodium perrhenate solution added during spin coating is 20–50 μL / cm. 2 .

3. The method for preparing monolayer single-crystal rhenium disulfide by chemical vapor deposition as described in claim 1, characterized in that: in In step S2, sulfur powder is placed in a corundum crucible for melting and heated to 120°C to 140°C using a hot plate to melt the sulfur powder. Then, it is cooled to room temperature and recrystallized to obtain the sulfur source. The predetermined flow rate of the inert gas is 40-80 sccm, and the introduction time is 15-30 min. The inert gas is argon or nitrogen. In step S3, after the center temperatures of the high-temperature zone and the low-temperature zone of the dual-temperature zone tubular furnace quartz tube reach the set temperature, the space-confined reaction chamber is aligned with the center of the high-temperature zone of the dual-temperature zone tubular furnace quartz tube, and the sulfur source container is aligned with the center of the low-temperature zone of the dual-temperature zone tubular furnace quartz tube. In step S4, the flow rate of the inert gas is adjusted to 200 sccm.

4. The method for preparing monolayer single-crystal rhenium disulfide by chemical vapor deposition as described in claim 1, characterized in that: The set temperature of the center of the high-temperature zone of the dual-temperature zone tubular furnace quartz tube is 800-880℃, and the heating rate is 20-40℃ / min; the set temperature of the center of the low-temperature zone of the dual-temperature zone tubular furnace quartz tube is 140-180℃, and the heating rate is 10-20℃ / min.

5. The method for preparing monolayer single-crystal rhenium disulfide by chemical vapor deposition as described in claim 1, characterized in that: The single-layer grain size of the ReS2 is 7–20 μm.

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