Method for preparing single-layer tungsten disulfide single-crystal film

Abstract

The invention relates to a method for preparing a single-layer tungsten disulfide single crystal film, which comprises the following steps of: adopting a low-pressure chemical vapor deposition method, taking a sapphire substrate with a tungsten element-containing modification layer as a substrate, and taking sulfur powder and tungsten trioxide powder as precursor sources to perform growth of a single-layer single-orientation tungsten disulfide domain region, thereby obtaining the single-layer tungsten disulfide single crystal film. And regulating and controlling the growth time of the single-layer single-orientation tungsten disulfide domain region according to the required coverage so as to prepare the single-layer tungsten disulfide single-crystal thin film on the sapphire substrate. By utilizing the low-pressure chemical vapor deposition method, batch preparation of large-area and high-quality single-layer tungsten disulfide single crystal film samples can be realized.

Description

Technical Field

[0001] This invention belongs to the field of materials, specifically, it relates to a method for preparing a single-layer tungsten disulfide single-crystal thin film. Background Technology

[0002] Two-dimensional transition metal chalcogenides (TMDCs), as important low-dimensional functional materials in the post-graphene era, have shown broad application prospects in nanoelectronic devices, optoelectronic devices, and flexible electronics due to their unique layered crystal structure and tunable electronic band structure, becoming a research hotspot in materials science and condensed matter physics. Compared with traditional three-dimensional bulk materials, TMDCs have advantages such as ultra-high specific surface area, excellent optical response characteristics, good mechanical flexibility, and functional customization through interlayer modulation. They have broken through many limitations of traditional semiconductor materials in miniaturization and integration applications, driving the development of low-dimensional optoelectronic devices towards high performance and low power consumption. It is worth noting that the unique physicochemical properties of monolayer TMDCs can only be fully demonstrated by their high-quality single-crystal thin films. Polycrystalline thin films are prone to performance degradation due to grain boundary defects. Therefore, the preparation of high-quality monolayer TMDC single-crystal thin films is a core prerequisite for their industrial application in high-end optoelectronic devices, and has important research value and practical necessity.

[0003] Tungsten disulfide, as a typical two-dimensional TMDCs material, possesses excellent physicochemical properties: its crystal structure is a hexagonal layered structure, with atoms within the layers bonded by strong covalent bonds and those between layers relying on weak van der Waals forces; in terms of electrical properties, monolayer tungsten disulfide exhibits direct bandgap semiconductor characteristics, with a bandgap of approximately 1.98 electron volts, demonstrating superior light absorption and emission performance compared to the indirect bandgap of bulk tungsten disulfide; chemically, tungsten disulfide exhibits good chemical stability, maintaining structural and performance stability even under complex environments; furthermore, it possesses excellent carrier mobility, good mechanical strength, and flexibility, making it an ideal candidate material for constructing high-performance field-effect transistors, photodetectors, and light-emitting diodes. In summary, the successful fabrication of monolayer tungsten disulfide single-crystal thin films is a crucial prerequisite for the development of this field. Summary of the Invention

[0004] The purpose of this invention is to provide a method for the large-area, high-quality batch preparation of single-layer tungsten disulfide single-crystal thin films.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing a single-layer tungsten disulfide single-crystal thin film. The method employs low-pressure chemical vapor deposition, using a sapphire substrate with a tungsten-containing modification layer as the substrate, and sulfur powder and tungsten trioxide powder as precursor sources to grow a single-layer, single-oriented tungsten disulfide domain region. The growth time of the single-layer, single-oriented tungsten disulfide domain region is controlled according to the required coverage, so as to obtain a single-layer tungsten disulfide single-crystal thin film on the sapphire substrate.

[0006] The method for preparing a single-layer tungsten disulfide single-crystal thin film of the present invention may include the following steps: 1) Clean the (0001) side of the sapphire substrate; 2) Under an argon atmosphere, the sapphire substrate and the tungsten trioxide powder placed thereunder are kept at 900-1050℃ for 1-2 hours, thereby depositing tungsten trioxide species on the surface of the sapphire substrate to obtain a sapphire substrate with tungsten trioxide deposited. 3) The sapphire substrate with deposited tungsten trioxide is heated to 1200-1300℃ in an atmospheric atmosphere and held for 2-4 hours to form a tungsten-containing modification layer on the surface of the sapphire substrate; 4) Under an argon atmosphere and at a low pressure of 60-80 Pascals, a sapphire substrate with the tungsten-containing modified layer, tungsten trioxide powder placed below it, and sulfur powder placed upstream of it are heated in sections to grow a single-layer, single-oriented tungsten disulfide domain region. 5) Adjust the growth time of the single-layer, single-oriented tungsten disulfide domain region according to the coverage; after the growth is completed, cool to room temperature to obtain a single-layer tungsten disulfide single crystal film on the sapphire substrate.

[0007] In one specific implementation, the sapphire substrate can be commercially available.

[0008] In one specific embodiment, the cleaning of the sapphire substrate can be carried out as follows: the (0001) surface of the sapphire substrate is placed in deionized water and anhydrous ethanol for 30 minutes each for ultrasonic cleaning, and then dried with an air gun.

[0009] In one specific embodiment, the deposition of tungsten trioxide species on a sapphire substrate can be performed as follows: the cleaned sapphire substrate is placed in a high-temperature tube furnace, with 50-100 mg (preferably 70-100 mg) of tungsten trioxide powder placed underneath. Argon gas is first introduced at a flow rate of 200-500 sccm (preferably 300-500 sccm) for 30 minutes for gas cleaning. Then, the argon gas flow rate is adjusted to 100-200 sccm (preferably 150-200 sccm), and the tube furnace is heated to 900-1050℃ (preferably 950-1000℃) and held at that temperature for 1-2 hours (preferably 1-1.5 hours). After the holding period, the tube furnace is allowed to cool down naturally. Here, sccm is a unit of volumetric flow rate, which is standard cubic centimeters per minute.

[0010] In one specific embodiment, the formation of a tungsten-containing modification layer on the surface of a sapphire substrate can be carried out as follows: the sapphire substrate with deposited tungsten trioxide is placed in a high-temperature muffle furnace and heated to 1200-1300°C (preferably 1200-1250°C) in an atmospheric atmosphere and then held at that temperature for 2-4 hours (preferably 2-3 hours) to form a tungsten-containing modification layer.

[0011] In one specific embodiment, the growth of a single-layer, single-oriented tungsten disulfide domain region can be processed as follows: A sapphire substrate having the tungsten-containing modified layer is placed in a three-temperature zone high-temperature tube furnace. 1-3 mg (preferably 1 mg) of tungsten trioxide powder is placed below the sapphire substrate. 800-1200 mg (preferably 900-1200 mg, more preferably 1000 mg) of sulfur powder is placed upstream of the sapphire substrate in the tube furnace. The tube furnace is pumped to a low pressure of 1-5 Pa using a mechanical pump, and 80-150 sccm (preferably 1000 sccm) of argon gas is introduced as the growth carrier gas. The furnace pressure is adjusted to a low pressure of 60-80 Pa (preferably 65-75 Pa). The area containing the sulfur powder is heated to 100-200°C (preferably 150-200°C), and the area containing the sapphire substrate and tungsten trioxide powder is heated to 950-980°C.

[0012] In one specific embodiment, the growth time of a single-layer, single-oriented tungsten disulfide domain region can be 1-15 minutes.

[0013] The advantages of this invention are: 1) This invention utilizes low-pressure chemical vapor deposition to achieve the batch preparation of large-area, high-quality monolayer tungsten disulfide single-crystal thin film samples; 2) Sapphire substrates are commonly used in the semiconductor industry. Constructing a tungsten-containing modification layer on a sapphire substrate can efficiently and reproducibly prepare a single-layer tungsten disulfide single crystal thin film, which is compatible with actual production and is expected to promote the industrialization of two-dimensional materials. 3) By controlling the growth time, the coverage of the single-layer, single-orientation tungsten disulfide domain region can be adjusted, and a fully covered single-layer tungsten disulfide single crystal film can eventually be achieved. 4) The method of the present invention can realize the exploration of the microstructure, domain splicing behavior and future applications of single-layer tungsten disulfide single crystal thin films. Attached Figure Description

[0014] Figure 1 The optical microscope results are for the monolayer tungsten disulfide single-crystal domain region prepared in Example 1 with a growth time of 5 minutes. Figure 2 The optical microscope results are for the monolayer tungsten disulfide single-crystal domain region prepared in Example 1 with a growth time of 10 minutes. Figure 3 The optical microscope results show the growth time of the monolayer tungsten disulfide single crystal thin film prepared in Example 1 for 15 minutes. Figure 4 The X-ray photoelectron spectroscopy results of tungsten in the monolayer tungsten disulfide single crystal thin film prepared in Example 1 with a growth time of 15 minutes; Figure 5 The X-ray photoelectron spectroscopy results are for sulfur in the monolayer tungsten disulfide single crystal thin film prepared in Example 1 with a growth time of 15 minutes. Figure 6 The results are Raman spectra of the monolayer tungsten disulfide single-crystal thin film prepared in Example 1 with a growth time of 15 minutes. Figure 7 , 8 The results are optical microscope and second harmonic generation surface scan of the monolayer tungsten disulfide single-crystal domain region prepared in Example 2 with a growth time of 10 minutes, respectively. Figure 9 , 10 The results are obtained by optical microscopy and second harmonic generation surface scanning of the monolayer tungsten disulfide single crystal thin film prepared in Example 2 with a growth time of 15 minutes. Detailed Implementation

[0015] Any feature disclosed in this specification, unless specifically stated otherwise, may be replaced by other equivalent or similar features. Unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features. The descriptions are merely illustrative and should not be construed as limiting the scope of the invention.

[0016] The method for preparing a single-layer tungsten disulfide single-crystal thin film of the present invention employs low-pressure chemical vapor deposition, using a sapphire substrate with a tungsten-containing modified layer as the substrate, and sulfur powder and tungsten trioxide powder as precursor sources to grow a single-layer, single-oriented tungsten disulfide domain region. The growth time of the single-layer, single-oriented tungsten disulfide domain region is controlled according to the required coverage, so as to obtain a single-layer tungsten disulfide single-crystal thin film on the sapphire substrate.

[0017] According to a preferred embodiment of the present invention, the method for preparing a single-layer tungsten disulfide single-crystal thin film on a sapphire substrate with a tungsten-containing element modification layer provided by the present invention includes the following steps: 1) Clean the commercial (0001) surface sapphire substrate, and place it in a high-temperature tube furnace with 80 mg of tungsten trioxide powder underneath; 2) A high-temperature tube furnace was purged with 300 sccm of argon gas. Then the flow rate of argon gas was adjusted to 200 sccm and the tube furnace was heated to 1000℃ and held for 1 hour to deposit tungsten trioxide species on the surface of the sapphire substrate. 3) Place the sapphire substrate with tungsten trioxide deposited in a high-temperature muffle furnace, heat it to 1200℃ in an atmospheric atmosphere and hold it for 2 hours to form a tungsten-containing modification layer on the surface of the sapphire substrate. 4) The obtained sapphire substrate with a tungsten-containing modified layer was placed in a three-temperature zone high-temperature tube furnace, with 1 mg of tungsten trioxide powder placed below and 1000 mg of sulfur powder placed upstream of the sapphire substrate. 4) Use a mechanical pump to pump the tubular furnace to a low pressure state (below 3 Pascals), and introduce 100 sccm of argon gas as the growth carrier gas. Adjust the gas pressure inside the furnace to a low pressure state of about 68 Pascals, and raise the temperature of the areas where sulfur powder, sapphire and tungsten trioxide powder are located to 180℃ and 950℃ respectively to grow a single-layer single-oriented tungsten disulfide domain region. 5) After growth is complete, turn off the temperature control program and allow the high-temperature tube furnace to cool down to room temperature naturally. Turn off the argon gas to obtain a single-layer, single-oriented tungsten disulfide domain region on the sapphire substrate. By adjusting the growth time, a single-layer tungsten disulfide single crystal film can be finally obtained.

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0019] Example 1 The commercial (0001) sapphire substrate (purchased from Jiangyin Lanke Crystal Materials Co., Ltd., 2 inches in diameter) was placed in deionized water and anhydrous ethanol in sequence for 30 minutes each for ultrasonic cleaning, and then dried with an air gun to complete the cleaning of the sapphire substrate.

[0020] The cleaned sapphire substrate was placed in a high-temperature tube furnace, with 80 mg of tungsten trioxide powder placed underneath. Argon gas was first purged at 300 sccm for 30 minutes to purge the gas. Then, the argon flow rate was adjusted to 200 sccm, and the furnace was heated to 1000°C and held at that temperature for 1 hour, thus depositing tungsten trioxide species on the surface of the sapphire substrate. After the holding period, the furnace was allowed to cool naturally, resulting in a sapphire substrate with tungsten trioxide deposits.

[0021] A sapphire substrate with tungsten trioxide deposited on it was placed in a high-temperature muffle furnace and heated to 1200°C in an atmospheric atmosphere and held for 2 hours to form a tungsten-containing modification layer on the surface of the sapphire substrate.

[0022] A sapphire substrate with a tungsten-modified layer was placed in a three-zone high-temperature tube furnace. One milligram of tungsten trioxide powder was placed below the sapphire substrate, and 1000 milligrams of sulfur powder was placed upstream of the sapphire substrate within the tube furnace. The furnace pressure was first evacuated to below 3 Pa using a mechanical pump. Then, 100 sccm of argon gas was introduced as both the growth carrier gas and the protective gas, adjusting the furnace pressure to approximately 68 Pa. The area containing the sulfur powder was heated to 180°C, and the area containing the sapphire substrate and tungsten trioxide powder was heated to 950°C to grow a single-layer, single-oriented tungsten disulfide domain.

[0023] The growth time was adjusted to 5, 10, and 15 minutes. After growth, the high-temperature tube furnace was allowed to cool naturally to room temperature, and the argon gas was turned off, resulting in monolayer tungsten disulfide single crystal samples with different coverage on the sapphire substrate.

[0024] The obtained samples were characterized by optical microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The results are as follows: Figures 1 to 6 As shown.

[0025] Figure 1 Optical microscopy results of a single-crystal domain region of tungsten disulfide prepared with a growth time of 5 minutes; Figure 2 Optical microscopy results of a single-crystal domain region of tungsten disulfide prepared with a growth time of 10 minutes; Figure 3 Optical microscopy results of a single-layer tungsten disulfide single-crystal thin film prepared with a growth time of 15 minutes. (Example:) Figures 1 to 3 The optical microscope results show that the monolayer tungsten disulfide domains are arranged in a large area with a single orientation on the sapphire substrate, and the coverage of the monolayer tungsten disulfide gradually increases as the growth time increases from 5 minutes to 15 minutes; when the growth time is 15 minutes, the sample obtained has 100% coverage, that is, a complete single crystal film.

[0026] Figure 4 , Figure 5The X-ray photoelectron spectroscopy (XPS) results are shown for tungsten and sulfur elements in a single-layer tungsten disulfide single-crystal film prepared with a growth time of 15 minutes. The binding energies of 32.7 eV and 34.9 eV correspond to W0.05 and W0.05, respectively. 4+ 4f 7 / 2 and 4f 5 / 2 The orbitals, with binding energies of 162.3 eV and 163.4 eV, correspond to S, respectively. 2- 2p 3 / 2 and 2p 1 / 2 The orbital pattern demonstrates the formation of tungsten disulfide on the surface of the sapphire substrate. Furthermore, Figure 4 The binding energy of 36.2 electron volts corresponds to W 6+ 4f 7 / 2 The orbital pattern indicates the presence of a tungsten-containing modification layer on the sapphire surface, with tungsten having a +6 valence state.

[0027] Figure 6 The results of the Raman spectrum of a single-layer tungsten disulfide single-crystal thin film prepared with a growth time of 15 minutes. (Example:) Figure 6 As shown, Raman spectral characterization reveals a position at 356 cm⁻¹. -1 and 418 cm -1 The two characteristic peaks correspond to the in-plane and out-of-plane vibrations of tungsten disulfide, respectively, and their peak position difference is approximately 62 cm. -1 This indicates that tungsten disulfide is a single layer.

[0028] Example 2 The monolayer tungsten disulfide single crystal samples obtained in Example 1 by growing on a sapphire substrate with a tungsten-modified layer for 10 minutes and 15 minutes were directly subjected to second harmonic generation surface scan characterization. The results are as follows: Figures 7 to 10 As shown.

[0029] Figure 7 , 8 The images show the results of optical microscopy and second harmonic generation surface scanning of a single-crystal domain region of tungsten disulfide prepared with a growth time of 10 minutes. Figure 7 , Figure 8 As shown, for the sample formed by splicing single-layer, single-oriented tungsten disulfide domain regions, the contrast in the second harmonic generation surface scan is uniform, and no obvious intensity reduction is observed at the splicing point, indicating that single-layer, single-oriented tungsten disulfide domain regions can be seamlessly spliced ​​without the formation of grain boundaries at the splicing point.

[0030] Figure 9 , 10 The images show the results of optical microscopy and second harmonic generation surface scanning of a single-layer tungsten disulfide single-crystal thin film prepared with a growth time of 15 minutes. Figure 9 , Figure 10As shown, for large-area thin film samples formed by splicing single-layer, single-oriented tungsten disulfide domain regions, the contrast of the second harmonic generation surface scan remains uniform, and no significant intensity reduction is observed. This indicates that single-layer, single-oriented tungsten disulfide domain regions can be seamlessly spliced ​​to form large-area uniform single-layer monocrystalline thin films without grain boundaries, which are expected to be applied to high-performance integrated electronic devices.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a single-layer tungsten disulfide single-crystal thin film, wherein the method employs low-pressure chemical vapor deposition, using a sapphire substrate with a tungsten-containing modified layer as the substrate, and using sulfur powder and tungsten trioxide powder as precursor sources to grow a single-layer, single-oriented tungsten disulfide domain region, and controlling the growth time of the single-layer, single-oriented tungsten disulfide domain region according to the required coverage, so as to obtain a single-layer tungsten disulfide single-crystal thin film on the sapphire substrate.

2. The method for preparing a single-layer tungsten disulfide single-crystal thin film according to claim 1, comprising the following steps: 1) Clean the (0001) side of the sapphire substrate; 2) Under an argon atmosphere, the sapphire substrate and the tungsten trioxide powder placed thereunder are kept at 900-1050℃ for 1-2 hours, thereby depositing tungsten trioxide species on the surface of the sapphire substrate to obtain a sapphire substrate with tungsten trioxide deposited. 3) The sapphire substrate with deposited tungsten trioxide is heated to 1200-1300℃ in an atmospheric atmosphere and held for 1-3 hours to form a tungsten-containing modification layer on the surface of the sapphire substrate; 4) Under an argon atmosphere and at a low pressure of 60-80 Pascals, a sapphire substrate with the tungsten-containing modified layer, tungsten trioxide powder placed below it, and sulfur powder placed upstream of it are heated in sections to grow a single-layer, single-oriented tungsten disulfide domain region. 5) The growth time of the single-layer, single-oriented tungsten disulfide domain region is adjusted to 1-15 minutes according to the coverage; after the growth is completed, the temperature is reduced to room temperature to obtain a single-layer tungsten disulfide single crystal film on the sapphire substrate.

3. The method for preparing a single-layer tungsten disulfide single crystal thin film according to claim 2, wherein in step 1), the sapphire substrate is cleaned as follows: the (0001) surface of the sapphire substrate is placed in deionized water and anhydrous ethanol for 30 minutes each for ultrasonic cleaning, and then dried with an air gun.

4. The method for preparing a single-layer tungsten disulfide single-crystal thin film according to claim 2, wherein in step 2), the deposition of tungsten trioxide species on the sapphire substrate is performed as follows: the cleaned sapphire substrate is placed in a high-temperature tube furnace, with 50-100 mg of tungsten trioxide powder placed below it. Argon gas is first introduced at a flow rate of 200-500 sccm for 30 minutes for gas cleaning. Then, the argon gas flow rate is adjusted to 100-200 sccm, and the tube furnace is heated to 900-1050°C and held for 1-2 hours. After the holding period, the tube furnace is allowed to cool down naturally. Here, sccm is a volumetric flow rate unit, which is standard cubic centimeters per minute.

5. The method for preparing a single-layer tungsten disulfide single crystal thin film according to claim 2, wherein in step 3), the tungsten-containing modification layer on the surface of the sapphire substrate is formed by treating it as follows: placing the sapphire substrate with deposited tungsten trioxide in a high-temperature muffle furnace, heating it to 1200-1300°C in an atmospheric atmosphere and holding it at that temperature for 1-3 hours to form the tungsten-containing modification layer.

6. The method for preparing a single-layer tungsten disulfide single-crystal thin film according to claim 2, wherein in step 4), the growth of the single-layer, single-oriented tungsten disulfide domain region is performed as follows: a sapphire substrate having the tungsten-containing modified layer is placed in a three-temperature zone high-temperature tube furnace, 1-3 mg of tungsten trioxide powder is placed below the sapphire substrate, 800-1200 mg of sulfur powder is placed upstream of the sapphire substrate in the tube furnace, the pressure inside the tube furnace is evacuated to a low pressure of 1-5 Pascals using a mechanical pump, and 80-150 sccm of argon gas is introduced as the growth carrier gas, adjusting the pressure inside the furnace to a low pressure of 60-80 Pascals.

7. The method for preparing a single-layer tungsten disulfide single crystal thin film according to claim 2, wherein in step 4), the regional heating includes heating the region where the sulfur powder is located to 100-200°C, and heating the region where the sapphire substrate and the tungsten trioxide powder are located to 950-980°C.

8. The method for preparing a single-layer tungsten disulfide single-crystal thin film according to claim 2, wherein in step 5), the growth time is 1-15 minutes.

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