A method for preparing highly oriented molybdenum disulfide thin films

Abstract

The present invention relates to the technical field of molybdenum disulfide thin film preparation, in particular to a method for preparing highly oriented molybdenum disulfide thin films, comprising the following steps: cleaning the substrate; buckling the polished surface of the substrate downward on a quartz boat; weighing molybdenum oxide and sulfur powder and placing them in the quartz boat, respectively placing the three quartz boats containing sulfur powder, molybdenum oxide, and the substrate in the first temperature zone, the second temperature zone, and the third temperature zone arranged in sequence in a tube furnace, repeating the cleaning three times with argon and then setting the growth parameters, the flow direction of argon is from the first temperature zone to the third temperature zone, and finally obtaining highly oriented molybdenum disulfide thin films. The method for preparing highly oriented molybdenum disulfide thin films proposed by the present invention has advantages such as simple operation and few defects in the prepared samples, laying a foundation for the application of molybdenum disulfide thin films.

Description

Technical Field

[0001] The present invention relates to the technical field of molybdenum disulfide thin film preparation, especially a method for preparing highly oriented molybdenum disulfide thin films. Background Art

[0002] Molybdenum disulfide (MoS2) has attracted extensive attention in the family of two-dimensional materials due to its excellent mechanical, electrical, and optoelectronic properties, and is widely used in various fields such as photovoltaic devices, optoelectronic sensors, photodetectors, and photocatalytic hydrogen evolution. Currently, the preparation of MoS2 thin films mainly involves growing individual MoS2 grains on a substrate and growing them into large-sized thin films. However, this method will introduce a large number of grain boundaries in the MoS2 thin film, restricting the application of the MoS2 thin film.

[0003] To solve the problem of excessive grain boundaries in MoS2 thin films, researchers have optimized polycrystalline MoS2 thin films through three strategies: (1) By expanding the size of individual MoS2 grains, growing a thin film with a small number of large-sized MoS2 grains, thereby reducing the generation of grain boundaries (Nature communications, 2018, 9(1): 979.); (2) Through the single-core growth method, allowing only one crystal nucleus to grow on the substrate and increasing the size of the crystal nucleus to form a wafer-scale MoS2 thin film. Currently, this method has only been successful on graphene (Chemical Society Reviews, 2023, 52(5): 1650-1671.); (3) By controlling the orientation of MoS2 grains, enabling MoS2 to grow into a thin film along the same orientation. The MoS2 thin film prepared in this way basically does not generate grain boundaries (Nature, 2022, 605(7908): 69-75.). Compared with the first two strategies, the third one can significantly reduce grain boundaries and has higher feasibility.

[0004] In order to enable MoS2 to grow along the same orientation, usually the substrate needs to be annealed for 1-4 hours before preparation, halogen salts need to be added to molybdenum oxide during the preparation process to reduce the evaporation temperature of molybdenum oxide, and hydrogen or oxygen needs to be introduced to etch the substrate, etc. This method has a long preparation time, high operation difficulty, and high preparation cost. Summary of the Invention

[0005] Common methods for preparing highly oriented molybdenum disulfide films often cannot take into account the characteristics of short time, simple operation, low cost and high film quality at the same time. The present invention proposes a method for preparing highly oriented molybdenum disulfide films, in which the substrate is annealed for a short time in the third temperature zone of a tubular furnace with three temperature zones, and the substrate does not need to be taken out and cooled after annealing. The raw materials in the first and second temperature zones are directly transported to the third temperature zone for deposition by carrier gas, which reduces the substrate annealing time, and no halogen salts need to be added to the molybdenum oxide. The preparation environment does not require the assistance of hydrogen or oxygen, which effectively reduces the preparation cost and shortens the preparation time.

[0006] In order to prepare a highly oriented molybdenum disulfide film, the present invention is implemented according to the following technical scheme: a substrate is ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 10 minutes and then put into use; 1-2 mg of molybdenum oxide and 60-100 mg of sulfur powder are weighed and added into two quartz boats respectively; the surface of the ultrasonically cleaned substrate is blown dry with nitrogen and the polished surface is placed on a third quartz boat with the polished surface facing downward; the three quartz boats containing sulfur powder, molybdenum oxide, and the substrate are placed in the first temperature zone, the second temperature zone, and the third temperature zone of a tube furnace respectively, the tube furnace is evacuated to near vacuum, and then filled with argon gas at a flow rate of 600 sccm. , after repeating the operation three times, the furnace was filled with argon and maintained at normal pressure; first set the temperature of the first temperature zone of the tubular furnace to 100°C, the heating rate to 10°C / min, and keep warm for 140 minutes; then increase to 300°C in 20 minutes and keep warm for 5 minutes; set the temperature of the second temperature zone to 500°C, the heating rate to 10°C / min, and keep warm for 80 minutes; then increase to 900°C in 40 minutes and keep warm for 5 minutes; set the temperature of the third temperature zone of the tubular furnace to 1000°C, the heating rate to 10°C / min and keep warm for 75 minutes. After the operation of the tubular furnace is completed, a highly oriented molybdenum disulfide film is obtained.

[0007] A method for preparing highly oriented molybdenum disulfide film has the following main principles: high-temperature annealing is performed on the substrate in the third temperature zone of a tubular furnace. Parallel steps will be formed on the annealed substrate, and molybdenum disulfide grains will preferentially nucleate at the edge of the step. One side of the molybdenum disulfide grain will tend to be flush with the edge of the step, thereby causing the grain to grow in a directional manner.

[0008] Preferably, the amount of molybdenum oxide is 2 mg.

[0009] Preferably, the amount of sulfur powder used is 120 mg.

[0010] Preferably, the sapphire substrate has its c-plane beveled at 1° toward the a-axis.

[0011] Preferably, the substrate is sapphire with the c-plane beveled toward the a-axis or the m-axis.

[0012] Preferably, the c-plane sapphire is obliquely cut at an angle of 1° or 2° with respect to the a-axis or m-axis. In this way, it is possible to better form steps on the substrate and improve the orientation rate of the MoS2 film.

[0013] Advantages of the present invention:

[0014] 1. A method for preparing a highly oriented molybdenum disulfide film proposed by the present invention combines substrate annealing and MoS2 growth into one step, shortening the preparation time.

[0015] 2. A method for preparing a highly oriented molybdenum disulfide film proposed by the present invention does not require introducing hydrogen or oxygen during the growth process to etch the substrate, effectively reducing the preparation cost.

[0016] 3. A method for preparing a highly oriented molybdenum disulfide film proposed by the present invention does not require adding halogen salts to molybdenum oxide, effectively reducing the introduction of impurities.

[0017] 4. A method for preparing a highly oriented molybdenum disulfide film proposed by the present invention can obtain highly oriented MoS2 with only a small amount of raw materials, effectively reducing the preparation cost.

[0018] 5. A method for preparing a highly oriented molybdenum disulfide film proposed by the present invention reduces the generation of grain boundaries in the MoS2 film, effectively improving the electrical and mechanical properties of the MoS2 film.

[0019] The present invention will be further described in detail below with reference to the accompanying drawings. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of a deposition system for preparing a highly oriented MoS2 film.

[0021] Figure 2 It is a temperature curve for preparing a highly oriented MoS2 film.

[0022] Figure 3 It is an optical microscope (OM) image of the prepared highly oriented MoS2 film.

[0023] Figure 4 It is a scanning electron microscope (SEM) image of the prepared highly oriented MoS2 film: (a) is the SEM image of the MoS2 film at low magnification; (b) is the SEM image of the MoS2 film at high magnification.

[0024] Figure 5 It is an X-ray photoelectron spectroscopy (XPS) image of the prepared highly oriented MoS2: (a) is the Mo 3d spectrum; (b) is the S2p spectrum. Detailed Embodiments

[0025] To make the objectives, technical solutions and advantages of this application more clear and understandable, the following provides examples with reference to the accompanying drawings and further elaborates on this application in detail.

[0026] A method for preparing highly oriented MoS2 thin films, the specific steps are as follows:

[0027] The sapphire substrate with the c-plane obliquely cut by 1° towards the a-axis is ultrasonically cleaned in acetone, absolute ethanol, and deionized water for 10 minutes respectively, and then dried with nitrogen on the surface. The polished surface is buckled downward above the quartz boat; the obtained MoS2 thin film is grown on the polished surface; compared with the polished surface facing upward, the samples prepared by this method have larger size and better uniformity; Weigh 2 mg of molybdenum oxide and 120 mg of sulfur powder and place them in the quartz boat respectively. The quartz boats containing sulfur powder, molybdenum oxide, and sapphire are placed in the first temperature zone, the second temperature zone, and the third temperature zone of the tube furnace respectively, as Figure 1 shown. Among them, the distance between the first temperature zone and the second temperature zone is 30 cm, and the distance between the second temperature zone and the third temperature zone is 20 cm, which can make the grain growth more evenly dispersed on the substrate and facilitate the observation of the grain orientation. Figure 2 Schematic diagram of the temperature curve of the highly oriented MoS2 thin film prepared in Example 1 of the present invention. As Figure 2 shown, the first temperature zone, the second temperature zone, and the third temperature zone are heated simultaneously and end simultaneously. The temperature of the first temperature zone of the tube furnace is set at 100 °C, the heating rate is 10 °C / min and it is kept warm for 140 minutes, then it rises to 300 °C in 20 minutes and is kept warm for 5 minutes; the temperature of the second temperature zone is set at 500 °C, the heating rate is 10 °C / min and it is kept warm for 80 minutes, then it rises to 900 °C in 40 minutes and is kept warm for 5 minutes; the temperature of the third temperature zone of the tube furnace is set at 1000 °C, the heating rate is 10 °C / min and it is kept warm for 75 minutes. The flow direction of argon is from the first temperature zone to the third temperature zone. After the operation of the tube furnace is completed, a highly oriented molybdenum disulfide thin film is obtained.

[0028] The temperatures of the first stage of the rise in the first temperature zone and the second temperature zone are respectively at the critical temperatures at which the sulfur powder and molybdenum oxide powder will not evaporate, which can not only ensure that the precursors will not evaporate, but also ensure that the required growth temperature can be reached in a short time after the substrate annealing in the third temperature zone is completed; the temperature of the third temperature zone is set at the temperature required for substrate annealing; the holding time is to wait for the completion of substrate annealing. Only after the substrate completes annealing can steps be formed on the surface to achieve oriented growth.

[0029] Figure 3 Optical microscope (OM) image of the highly oriented MoS2 thin film prepared in Example 1 of the present invention. It can be seen from the figure that the edges marked by the black lines in the MoS2 grains show a parallel trend, and the grains all grow in the direction perpendicular to the black lines. The prepared sample is an oriented growth MoS2 thin film.

[0030] Figure 4This is the scanning electron microscope (SEM) image of the highly oriented MoS2 film prepared in Example 1 of the present invention. From the low-magnification SEM image ( Figure 4 a), it can be seen that the grown MoS2 grains are overall oriented in the same direction. Similarly, in the high-magnification SEM image ( Figure 4 b), it can be observed that the magnified MoS2 grains indeed show one of their edges parallel, and the growth directions are all perpendicular to this edge.

[0031] Figure 5 This is the X-ray photoelectron spectroscopy (XPS) image of the highly oriented MoS2 prepared in Example 1 of the present invention. Figure 5 (a) For the Mo 3d spectrum, two characteristic peaks can be seen at 233 eV and 229.9 eV, corresponding to Mo 3d 3 / 2 and 3d 5 / 2 orbitals respectively. The peak at 236.2 eV is caused by incomplete sulfidation of molybdenum oxide. Figure 5 (b) For the S2p spectrum, two characteristic peaks can be seen at 162.8 eV and 163.9 eV, corresponding to S2p 2 / 3 and 2p 1 / 2 orbitals respectively. No additional peaks are observed in the XPS spectrum, indicating that the MoS2 grains grow directly on the substrate and have a relatively high purity.

[0032] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for preparing a highly oriented molybdenum disulfide thin film, characterized in that: It includes the following steps: Clean the substrate; place the polished surface of the substrate downward on the quartz boat; weigh molybdenum oxide and sulfur powder and put them in the quartz boat. Place the three quartz boats containing sulfur powder, molybdenum oxide, and the substrate in the first temperature zone, the second temperature zone, and the third temperature zone arranged in sequence in the tube furnace. After repeating the purge with argon three times, set the growth parameters. The temperature of the first temperature zone is set to 100 °C and held for 140 minutes, then raised to 300 °C in 20 minutes and held for 5 minutes; the temperature of the second temperature zone is set to 500 °C and held for 80 minutes, then raised to 900 °C in 40 minutes and held for 5 minutes; the temperature of the third temperature zone is set to 1000 °C and held for 75 minutes; the flow direction of the argon is from the first temperature zone to the third temperature zone. Finally, a highly oriented molybdenum disulfide film is obtained; wherein, the substrate is sapphire with the c-plane cut obliquely towards the a-axis or m-axis, and the oblique cutting angle of the c-plane sapphire towards the a-axis or m-axis is 1° or 2°.

2. The method for preparing a highly oriented molybdenum disulfide thin film according to claim 1, wherein: The step of cleaning the substrate includes ultrasonic cleaning the substrate in acetone, absolute ethanol, and deionized water for 10 minutes respectively and drying the surface of the substrate with nitrogen.

3. The method for preparing a highly oriented molybdenum disulfide film according to claim 1, wherein: The mass ratio of molybdenum oxide to sulfur powder is between 1:50 and 1:

60.

4. The method for preparing a highly oriented molybdenum disulfide thin film according to claim 3, wherein: The distance between the first temperature zone and the second temperature zone is 30 cm, and the distance between the second temperature zone and the third temperature zone is 20 cm.

5. The method for preparing a highly oriented molybdenum disulfide film according to claim 4, wherein: The carrier gas flow rate during the cleaning stage of the tube furnace is 600 sccm, and the carrier gas flow rate during the preparation stage is 20 sccm.

Images