Preparation method of single-layer tungsten diselenide single-crystal thin film

Abstract

The invention relates to a preparation method of a single-layer tungsten diselenide single-crystal thin film, which comprises the following steps: taking a tungsten source, ferrous chloride and a selenium source as raw materials, taking inert gas as carrier gas, adopting a chemical vapor deposition method, and carrying out three-temperature-zone heating growth to obtain the tungsten diselenide single-crystal thin film. According to the method, the growth process is simple and easy to operate, the preparation process is accurate and controllable, the domain orientation of the obtained single-layer tungsten diselenide crystal is consistent, no domain grain boundary exists, and the thickness uniformity and the crystal quality are excellent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new material preparation, in particular, the present application relates to a preparation method of single-layer tungsten diselenide monocrystal thin film. BACKGROUND

[0002] With the transistor size entering the quantum limit category, the short channel effect is becoming more and more significant, which seriously affects the running speed and storage density of electronic devices, so it is particularly important to develop new semiconductor materials and electronic devices. The new two-dimensional semiconductor material represented by n-type molybdenum disulfide and p-type tungsten diselenide can reduce the working voltage and energy consumption due to its atomic layer thickness and excellent static control ability; the surface without dangling bond can reduce the reduction of carrier mobility caused by scattering; the rich energy band structure facilitates the design of diversified logic and memory devices.

[0003] It should be noted that the development of high-performance / multifunctional field effect transistors and integrated circuits must be based on large-size two-dimensional monocrystal materials. However, due to the lower dimension of two-dimensional materials, the growth technology of traditional three-dimensional semiconductor monocrystals cannot be directly applied to the synthesis of two-dimensional materials.

[0004] Developing new preparation technology to realize the synthesis of wafer-size two-dimensional semiconductor monocrystals has become the most core scientific and technical problem in the field of new materials. SUMMARY

[0005] The inventors found that the preparation of two-inch monocrystal molybdenum disulfide and tungsten disulfide can be realized by using a specially designed sapphire substrate step control mechanism. However, compared with n-type molybdenum disulfide and tungsten disulfide, the material growth and device preparation of p-type tungsten diselenide are seriously lagging behind, which restricts the application of two-dimensional semiconductors in advanced process integrated circuits. In addition, the growth substrate selected by the above preparation method is mostly specially designed sapphire, which needs to be specially processed. The sapphire substrate has a cutting angle of 0.5° or less relative to its crystal axis, which increases the cost of sapphire processing and material preparation. In addition, the sapphire substrate needs to be pre-annealed at a high temperature of 1000℃ or above for a long time before the growth of two-dimensional semiconductor materials, which makes the material preparation process more complex. Therefore, the present application proposes a mild / low-cost method to control the preparation of high-quality wafer-size single-layer tungsten diselenide monocrystal thin film to solve the problem of small size of tungsten diselenide monocrystal in related technologies. The single-layer tungsten diselenide monocrystal thin film can be used in high-performance electronic devices and integrated circuits.

[0006] In an aspect of the present disclosure, a method for preparing a single-layer tungsten diselenide monocrystal thin film is provided. According to an embodiment of the present disclosure, the method comprises: using a tungsten source, ferrous chloride, and a selenium source as raw materials, an inert gas as a carrier gas, and using a chemical vapor deposition method and a three-temperature-zone heating to grow a tungsten diselenide monocrystal thin film. The inventors first use ferrous chloride as a raw material, which can solve the problems of small size and random distribution of crystal domains of tungsten diselenide monocrystals in the related art, and obtain a two-inch tungsten diselenide monocrystal thin film. The single-layer tungsten diselenide crystal obtained by the method has consistent domain orientation, no domain grain boundaries, excellent thickness uniformity, and excellent crystal quality.

[0007] In another aspect of the present disclosure, a method for preparing a single-layer tungsten diselenide monocrystal thin film is provided. According to an embodiment of the present disclosure, the method comprises the following steps: 1) placing a selenium source in a first temperature zone, mixing a tungsten source and ferrous chloride and placing the mixture in a second temperature zone, and placing a substrate in a third temperature zone; 2) passing argon / hydrogen mixed carrier gas through the first temperature zone, the second temperature zone, and the third temperature zone in sequence; 3) program heating the first temperature zone, the second temperature zone, and the third temperature zone to respective predetermined temperatures, and growing a single-layer tungsten diselenide monocrystal thin film on the substrate based on the principle of chemical vapor deposition. The inventors first use ferrous chloride as a raw material, which can solve the problems of small size and random distribution of crystal domains of tungsten diselenide monocrystals in the related art, and obtain a two-inch tungsten diselenide monocrystal thin film. The single-layer tungsten diselenide crystal obtained by the method has consistent domain orientation, no domain grain boundaries, excellent thickness uniformity, and excellent crystal quality.

[0008] According to an embodiment of the present disclosure, the above method can further comprise at least one of the following technical features: According to an embodiment of the present disclosure, the mass ratio between the selenium source, the tungsten source, and the ferrous chloride powder is (500-650 mg):(80-120 mg):(5-10 mg). The inventors find that if the mass ratio between the selenium source and the tungsten source is too low, the tungsten source is not fully selenized, intermediate products are easily generated, the tungsten diselenide thin film is discontinuous, the size is small, and the thickness is not uniform. If the mass ratio between the selenium source and the tungsten source is too high, excess selenium vapor is easily deposited on the surface of the single-layer tungsten diselenide thin film in the form of tungsten diselenide particles, resulting in an uneven product surface. The introduction of ferrous chloride during the growth process promotes the reconstruction of the substrate surface and induces the formation of a periodic parallel step on the substrate surface, which is helpful for the nucleation and growth of the single-layer tungsten diselenide with consistent domain orientation. If the content of ferrous chloride is too low, the prepared tungsten diselenide is randomly oriented, and the tungsten diselenide thin film obtained by splicing is a polycrystalline thin film. If the content of ferrous chloride is too high, the prepared tungsten diselenide is a multilayer nanosheet.

[0009] According to an embodiment of the present disclosure, the mass ratio between the selenium source, the tungsten source and the ferrous chloride powder is 600 mg: 100 mg: 8 mg.

[0010] According to an embodiment of the present disclosure, the predetermined temperature of the first temperature zone is 300-350°C. If the predetermined temperature is too low, the volatilization amount of the selenium source, the tungsten source and the ferrous chloride is too small, so that there are too few nucleation points on the substrate to form a large-area thin film. If the predetermined temperature is too high, the reactant gas phase concentration is too high, thereby causing too many nucleation points to form on the substrate, and causing the tungsten diselenide to tend to grow vertically, which is easy to prepare dispersed and multi-layer tungsten diselenide nanosheets.

[0011] According to an embodiment of the present disclosure, the predetermined temperature of the first temperature zone is 330°C.

[0012] According to an embodiment of the present disclosure, the predetermined temperature of the second temperature zone is 900-950°C. If the predetermined temperature is too low, the volatilization amount of the selenium source, the tungsten source and the ferrous chloride is too small, so that there are too few nucleation points on the substrate to form a large-area thin film. If the predetermined temperature is too high, the reactant gas phase concentration is too high, thereby causing too many nucleation points to form on the substrate, and causing the tungsten diselenide to tend to grow vertically, which is easy to prepare dispersed and multi-layer tungsten diselenide nanosheets.

[0013] According to an embodiment of the present disclosure, the predetermined temperature of the second temperature zone is 930°C.

[0014] According to an embodiment of the present disclosure, the predetermined temperature of the third temperature zone is 900-950°C. If the predetermined temperature is too low, the volatilization amount of the selenium source, the tungsten source and the ferrous chloride is too small, so that there are too few nucleation points on the substrate to form a large-area thin film. If the predetermined temperature is too high, the reactant gas phase concentration is too high, thereby causing too many nucleation points to form on the substrate, and causing the tungsten diselenide to tend to grow vertically, which is easy to prepare dispersed and multi-layer tungsten diselenide nanosheets.

[0015] According to an embodiment of the present disclosure, the predetermined temperature of the third temperature zone is 930°C.

[0016] According to an embodiment of the present disclosure, the growth time of the single-layer tungsten diselenide is 5-30 min.

[0017] According to an embodiment of the present disclosure, the flow rate ratio between the argon gas and the hydrogen gas is (50-80 seem): (5-10 seem).

[0018] According to an embodiment of the present disclosure, the flow rate ratio between the argon gas and the hydrogen gas is 80 seem: 10 seem.

[0019] According to an embodiment of the present disclosure, the flow rate of the argon / hydrogen mixed carrier gas is 50-90 seem.

[0020] According to an embodiment of the present disclosure, the distance between the selenium source and the tungsten source is 5-8 cm.

[0021] According to an embodiment of the present disclosure, the distance between the selenium source and the tungsten source is 7 cm.

[0022] According to an embodiment of the present disclosure, the distance between the tungsten source and the substrate is 3-5 cm.

[0023] According to an embodiment of the present disclosure, the distance between the tungsten source and the substrate is 4 cm.

[0024] According to an embodiment of the present disclosure, the substrate is a sapphire substrate.

[0025] According to an embodiment of the present disclosure, the sapphire substrate is a sapphire substrate with impurities removed from the surface.

[0026] According to an embodiment of the present disclosure, the selenium source comprises selenium powder.

[0027] According to an embodiment of the present disclosure, the tungsten source comprises tungsten trioxide powder.

[0028] According to an embodiment of the present disclosure, before the argon / hydrogen mixed carrier gas is passed through the first temperature zone, the second temperature zone and the third temperature zone, the method comprises The first temperature zone, the second temperature zone and the third temperature zone are vacuumed to below 5 Pa.

[0029] According to an embodiment of the present disclosure, after the growth of the tungsten diselenide single crystal thin film is completed, the argon / hydrogen mixed carrier gas is continuously introduced, and the carrier gas is turned off when the first temperature zone, the second temperature zone and the third temperature zone are reduced to room temperature, thereby obtaining the single-layer tungsten diselenide single crystal thin film.

[0030] According to an embodiment of the present disclosure, the size of the single-layer tungsten diselenide single crystal thin film is two inches.

[0031] In still another aspect of the present disclosure, the present disclosure also provides an application of the single-layer tungsten diselenide single crystal thin film prepared by the preparation method of the single-layer tungsten diselenide single crystal thin film as described above in high-performance electronic devices and integrated circuits.

[0032] According to an embodiment of the present disclosure, the technical solution provided by the present disclosure comprises at least one of the following beneficial effects: 1) The ferrous chloride assisted chemical vapor deposition method can be used to prepare a two-inch single-layer tungsten diselenide single crystal thin film on a common non-cut-angle sapphire substrate; 2) The method of the present disclosure is simple and easy to operate, the preparation process is controllable, the obtained single-layer tungsten diselenide crystal has consistent domain orientation and no domain grain boundary, and has excellent thickness uniformity and crystal quality. Attached Figure Description

[0033] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0034] Figure 1 Optical photographs and corresponding optical micrographs of the two-inch monolayer tungsten diselenide single crystal thin film provided in Embodiment 1 of this application; Figure 2 An optical micrograph of a single-layer tungsten diselenide nanosheet provided in Example 2 of this application; Figure 3 An optical micrograph of a single-layer tungsten diselenide nanosheet provided in Example 3 of this application; Figure 4 An optical micrograph of a single-layer tungsten diselenide nanosheet provided in Example 4 of this application; Figure 5 An optical micrograph of a single-layer tungsten diselenide single-crystal thin film provided in Embodiment 5 of this application; Figure 6 An optical micrograph of a single-layer tungsten diselenide single-crystal thin film provided in Embodiment 6 of this application; Figure 7 An atomic force microscopy image of a single-layer tungsten diselenide nanosheet provided in Example 2 of this application; Figure 8 The Raman spectrum of the single-layer tungsten diselenide single-crystal thin film provided in Example 1 of this application; Figure 9 Transmission electron microscopy image of a single-layer tungsten diselenide nanosheet provided in Example 2 of this application; Figure 10 The electron diffraction pattern of the monolayer tungsten diselenide nanosheets provided in Example 2 of this application; Figure 11 This is a double aberration-corrected scanning transmission electron microscopy image of a single-layer tungsten diselenide nanosheet provided in Example 2 of this application; Figure 12 This is a low-energy electron diffraction pattern of the single-layer tungsten diselenide single-crystal thin film provided in Example 1 of this application; Figure 13 Optical micrographs comparing the single-layer tungsten diselenide single-crystal thin film sample provided in Example 1 of this application before and after oxygen etching; Figure 14An optical micrograph of a monolayer tungsten diselenide nanosheet provided in Comparative Example 1 of this application; Figure 15 An optical micrograph of a monolayer tungsten diselenide nanosheet provided in Comparative Example 2 of this application; Figure 16 Optical micrograph of the multilayer tungsten diselenide nanosheets provided in Comparative Example 3 of this application; Figure 17 An optical micrograph of a single-layer tungsten diselenide nanosheet provided in Comparative Example 4 of this application; Figure 18 An optical micrograph of a monolayer tungsten diselenide nanosheet provided in Comparative Example 5 of this application; Figure 19 An optical micrograph of a single-layer tungsten diselenide nanosheet provided in Comparative Example 6 of this application; Figure 20 An optical micrograph of the multilayer tungsten diselenide nanosheets provided in Comparative Example 7 of this application. Detailed Implementation

[0035] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0037] This application provides a method for preparing a two-inch monolayer tungsten diselenide single-crystal thin film, comprising the following steps: The selenium source is placed in the first temperature zone, the tungsten source and ferrous chloride powder are mixed and placed in the second temperature zone, and the ordinary uncut sapphire substrate is placed in the third temperature zone. The argon / hydrogen mixed carrier gas is passed sequentially through the first temperature zone, the second temperature zone, and the third temperature zone; The first, second, and third temperature zones are programmed to be heated to their respective predetermined temperatures to grow a two-inch monolayer tungsten diselenide single crystal thin film.

[0038] The preparation method described in this application employs a three-zone tubular furnace vapor deposition system with independently controlled temperatures. The three zones have different heating temperatures to meet the reaction requirements. The selenium source is located in the upstream first zone; after heating and volatilization, it enters the third zone with the carrier gas. The tungsten source and ferrous chloride, located in the middle, also volatilize after heating and enter the third zone with the carrier gas. This avoids the problems of excessively high nucleation density and uncontrollable layer count caused by the inability to independently control the tungsten source evaporation and growth temperatures in traditional chemical vapor deposition. The third zone is the main reaction zone, where the selenium, tungsten, and iron vapor phases from the upstream are transported to the sapphire substrate surface to begin pre-nucleation. The selenium source reacts with the tungsten source to generate tungsten diselenide.

[0039] Specifically, the first temperature zone, the second temperature zone, and the third temperature zone are arranged sequentially along the horizontal direction.

[0040] In some embodiments, the mass ratio of the selenium source, the tungsten source and the ferrous chloride powder is (500-650 mg): (80-120 mg): (5-10 mg).

[0041] When the mass ratio of the selenium source to the tungsten source is too low, the tungsten source selenization is incomplete, and intermediate products are easily formed, resulting in discontinuous, small-sized, and unevenly thick tungsten diselenide films. If the mass ratio of the selenium source to the tungsten source is too high, excess selenium vapor easily forms tungsten diselenide particles that deposit on the surface of a single-layer tungsten diselenide film, resulting in an uneven product surface.

[0042] The introduction of ferrous chloride during growth promotes sapphire surface reconstruction and induces the formation of periodic parallel steps on the sapphire substrate surface, which is conducive to the nucleation and growth of monolayer tungsten diselenide with consistent domain orientation. When the ferrous chloride content is too low, the prepared tungsten diselenide is randomly oriented, and the tungsten diselenide film obtained by splicing is a polycrystalline film. When the ferrous chloride content is too high, the prepared tungsten diselenide is a multilayer nanosheet.

[0043] Furthermore, it is preferred that the weight of the selenium source is 500-650 mg, the weight of the tungsten source is 80-120 mg, and the weight of the ferrous chloride powder is 5-10 mg.

[0044] In some embodiments, the predetermined temperature of the first temperature zone is 300-350°C, the predetermined temperature of the second temperature zone is 900-950°C, and the predetermined temperature of the third temperature zone is 900-950°C.

[0045] If the predetermined temperature is too low, the volatilization of selenium source, tungsten source, and ferrous chloride will be insufficient, resulting in fewer nucleation sites on the substrate and making it impossible to form a large-area thin film. If the predetermined temperature is too high, the concentration of reactants in the gas phase will be too high, leading to the formation of too many nucleation sites on the substrate. This will cause tungsten diselenide to tend to grow vertically, making it easier to prepare dispersed and multilayered tungsten diselenide nanosheets.

[0046] In some embodiments, the distance between the selenium source and the tungsten source is 5-8 cm; the distance between the tungsten source and the sapphire substrate is 3-5 cm; and the tungsten source and the ferrous chloride powder are mixed and placed together.

[0047] In a preferred embodiment, the selenium source is placed in a first open container, and the mixture of the tungsten source and ferrous chloride powder is placed in a second open container. The distance between the first and second open containers is 5–8 cm, and the distance between the second open container and the sapphire substrate is 3–5 cm. Within the above distance range, high-quality single-layer tungsten diselenide single-crystal thin films can be rapidly prepared.

[0048] In some embodiments, the selenium source comprises selenium powder; the tungsten source comprises tungsten trioxide powder.

[0049] In some embodiments, the growth time of the monolayer tungsten diselenide is 5 to 30 minutes.

[0050] If the growth time is too short, the resulting tungsten diselenide will be too small, which is not conducive to the formation of continuous films. As the growth time increases, the number of nucleation sites increases, the grain boundaries decrease, and the film area increases. However, if the growth time is too long, the tungsten diselenide may deposit along the vertical direction, resulting in an excessively thick film.

[0051] In some embodiments, the flow rate of the argon / hydrogen mixed carrier gas is 50–90 sccm.

[0052] The flow rate of the mixed carrier gas affects the quality of the monolayer tungsten diselenide film. If the flow rate of the mixed carrier gas is too low, the deposition process is too slow. If the flow rate of the mixed carrier gas is too high, the selenium vapor concentration in the third temperature zone is too high. When it reaches a certain level, it will inhibit the volatilization of the tungsten source, thereby reducing the density of nucleation sites on the substrate, which is not conducive to the formation of a large-area monolayer tungsten diselenide film.

[0053] In some embodiments, the method further includes the following steps before placing the sapphire substrate: Remove impurities from the surface of the sapphire substrate.

[0054] This helps reduce the number of nucleation sites on the surface of monolayer tungsten diselenide.

[0055] Specifically, impurities on the surface of a sapphire substrate can be removed by ultrasonic cleaning, which may include the following steps: The sapphire substrate was ultrasonically cleaned in deionized water, ethanol, and acetone for 5 minutes each, and then dried with nitrogen gas to complete the cleaning of the sapphire substrate.

[0056] In some embodiments, the preparation method further includes, prior to passing the argon / hydrogen mixed carrier gas through the first temperature zone, the second temperature zone, and the third temperature zone: The first temperature zone, the second temperature zone, and the third temperature zone are evacuated to below 5 Pa.

[0057] Furthermore, the preparation of a single-layer tungsten diselenide also includes: The reaction chamber of the three-temperature zone tubular furnace vapor deposition system is cleaned: the reaction chamber is evacuated to below 5 Pa, carrier gas is introduced, and the reaction chamber is cleaned for 30 minutes to remove residual air in the reaction chamber and avoid affecting the quality of the single-layer tungsten diselenide film.

[0058] Furthermore, the carrier gas is a protective atmosphere, such as argon.

[0059] In some embodiments, after the growth of the monolayer tungsten diselenide single crystal film is completed, an argon / hydrogen mixed carrier gas is continuously introduced. The carrier gas is turned off when the first temperature zone, the second temperature zone, and the third temperature zone drop to room temperature, thereby obtaining the two-inch monolayer tungsten diselenide single crystal film.

[0060] This application utilizes ferrous chloride doping and a sapphire substrate to efficiently prepare a two-inch monolayer tungsten diselenide single crystal thin film.

[0061] The present invention will be further illustrated by the following examples.

[0062] Example 1 101: Place a two-inch commercial uncut C-side sapphire substrate in deionized water, ethanol, and acetone in sequence, and perform ultrasonic cleaning for 5 minutes each. After cleaning, dry it with nitrogen gas.

[0063] 102: In a three-zone high-temperature tube furnace, following the gas path from upstream to downstream, 600 mg of selenium powder is placed in the first zone; 100 mg of tungsten trioxide powder and 8 mg of ferrous chloride powder are mixed evenly and placed together in the second zone; the cleaned sapphire substrate is placed in the third zone. The distance between the tungsten trioxide / ferrous chloride mixture and the selenium powder is 7 cm, and the distance between the tungsten trioxide / ferrous chloride mixture and the sapphire substrate is 4 cm. 103: First, evacuate the reaction chamber of the tubular furnace to below 5 Pa, then introduce 500 sccm of argon gas into the reaction chamber to clean it and remove any residual air inside. The cleaning time is 30 minutes. 104: The temperature of the first temperature zone was raised to 330℃, the temperature of the second temperature zone to 930℃, and the temperature of the third temperature zone to 930℃. An argon / hydrogen mixture (flow rate ratio of 80:10 sccm) was introduced, with a flow rate of 90 sccm. The reaction was maintained at these temperatures for 30 minutes. After the reaction was completed, the mixture was allowed to cool naturally to obtain a two-inch monolayer tungsten diselenide single crystal film.

[0064] Example 2 It includes most of the operational steps of Example 1, with the only difference being: The heat preservation reaction time is 5 minutes.

[0065] Example 3 It includes most of the operational steps of Example 1, with the only difference being: The heat preservation reaction time is 15 minutes.

[0066] Example 4 It includes most of the operational steps of Example 1, with the only difference being: The heat preservation reaction time is 25 minutes.

[0067] Example 5 It includes most of the operational steps of Example 1, with the only difference being: The amount of ferrous chloride powder is 5 mg.

[0068] Example 6 It includes most of the operational steps of Example 1, with the only difference being: The amount of ferrous chloride powder is 10 mg.

[0069] See Figures 1-6 As shown, Figures 1-6 Optical micrographs of the monolayer tungsten diselenide prepared in Examples 1-6 are shown. As can be seen from the figures, the domain orientations of the tungsten diselenide nanosheets obtained at different growth times in Examples 1-6 are consistent, and the tungsten diselenide coverage increases with increasing growth time. Figure 1 As shown, when the growth time is extended to 30 minutes, a two-inch single-layer tungsten diselenide single crystal thin film can be obtained.

[0070] See Figure 7 As shown, Figure 7 Atomic force microscopy images of the tungsten diselenide nanosheets prepared in Example 2 are shown. According to... Figure 7 It can be seen that the thickness of the tungsten diselenide nanosheets prepared in Example 2 is 0.8 nm, indicating that the prepared tungsten diselenide is a single-layer sample.

[0071] See Figure 8 As shown, Figure 8The Raman spectrum of the monolayer tungsten diselenide thin film prepared in Example 1 is shown. According to... Figure 8 As can be seen from the Raman spectroscopy characterization results, the positions of the Raman characteristic peaks obtained along different directions of the large-area monolayer tungsten diselenide film do not change, indicating that the prepared two-inch monolayer tungsten diselenide has very high thickness uniformity.

[0072] See Figures 9-10 As shown, Figures 9-10 The transmission electron microscopy (TEM) characterization results of two examples of monolayer tungsten diselenide nanosheets on copper mesh are presented. The preparation process of the tungsten diselenide / copper mesh samples included the following steps: a 300 nm thick polystyrene polymer support film was spin-coated onto the surface of a sapphire substrate on which tungsten diselenide was grown, and then dried at 150 °C for 15 min. Subsequently, the substrate was etched in a sodium hydroxide etching solution for 15 min. The polystyrene polymer film / tungsten diselenide sample was then retrieved using a copper mesh and dried at 100 °C for 15 min to ensure sufficient contact between the sample and the copper mesh. Finally, the polystyrene polymer film / tungsten diselenide / copper mesh was immersed in toluene to remove the polymer support film (for 30 min), yielding the tungsten diselenide / copper mesh sample.

[0073] Transmission electron microscopy was used to characterize the tungsten diselenide / copper mesh sample, such as... Figure 9 As shown, the tungsten diselenide nanosheets provided in this application have a uniform thickness. Figure 10 The electron diffraction pattern at the splicing position of the two tungsten diselenide nanosheets is shown. The results show only one set of six-fold symmetrical diffraction spots, indicating that the two tungsten diselenide nanosheets have consistent domain orientation.

[0074] See Figure 11 As shown, Figure 11 The image shows a double aberration-corrected scanning transmission electron microscope (STEM) image of the monolayer tungsten diselenide nanosheets on a copper mesh provided in Example 2. The preparation of the tungsten diselenide / copper mesh sample is as described above and will not be repeated here.

[0075] The tungsten diselenide / copper mesh samples were characterized by double aberration-corrected scanning transmission electron microscopy, such as... Figure 11 As shown in the figure. The results indicate that no domain boundaries are generated at the splicing sites of tungsten diselenide nanosheets, suggesting that tungsten diselenide nanosheets with consistent domain orientation can be seamlessly spliced ​​to form single-crystal thin films.

[0076] See Figure 12 As shown, Figure 12 The following are low-energy electron diffraction patterns at nine randomly selected locations on the surface of the monolayer tungsten diselenide single-crystal thin film provided in Example 1. It can be seen that the characterization results show only one set of diffraction spots, indicating that the monolayer tungsten diselenide nanosheets were spliced ​​together to form a single-crystal thin film.

[0077] See Figure 13 As shown, Figure 13 The optical microscopy characterization results of the monolayer tungsten diselenide single-crystal thin film sample provided in Example 1 before and after oxygen etching are shown. As can be seen from the figures, there are no significant changes on the sample surface before and after oxygen etching, indicating that the monolayer tungsten diselenide thin film has good crystal quality.

[0078] In summary, the method described in this application can prepare a two-inch monolayer tungsten diselenide single crystal thin film without domain boundaries, which lays a material foundation for further research and development of integrated circuits and chip applications.

[0079] Comparative Example 1 It includes most of the operations of Example 1, except that: No ferrous chloride powder is added.

[0080] Figure 14 Optical micrographs of the tungsten diselenide sample prepared in Comparative Example 1 are shown. As can be seen from the figures, the domain orientations of the tungsten diselenide nanosheets obtained without the addition of ferrous chloride powder are randomly distributed.

[0081] Comparative Example 2 It includes most of the operations of Example 1, except that: Instead of adding ferrous chloride powder, sodium chloride powder is added.

[0082] Figure 15 Optical micrographs of the tungsten diselenide sample prepared in Comparative Example 2 are shown. As can be seen from the figures, when sodium chloride powder is added but ferrous chloride powder is not, the domain orientation of the resulting tungsten diselenide nanosheets is randomly distributed.

[0083] Comparative Example 3 It includes most of the operations of Example 1, except that: The temperature of the first temperature zone is increased to 330℃, the temperature of the second temperature zone is increased to 930℃, and the temperature of the third temperature zone is increased to 1000℃.

[0084] Figure 16 Optical micrographs of the tungsten diselenide sample prepared in Comparative Example 3 are shown. As can be seen from the figures, when the growth temperature is too high, the resulting tungsten diselenide is a multilayer nanosheet with randomly distributed domain orientations.

[0085] Comparative Example 4 It includes most of the operations of Example 1, except that: The temperature of the first temperature zone is raised to 330℃, the temperature of the second temperature zone is raised to 800℃, and the temperature of the third temperature zone is raised to 800℃.

[0086] Figure 17 Optical micrographs of the tungsten diselenide sample prepared in Comparative Example 4 are shown. As can be seen from the figures, when the growth temperature is too low, the resulting tungsten diselenide domains are small in size and randomly oriented.

[0087] Comparative Example 5 It includes most of the operations of Example 1, except that: Replace ferrous chloride powder with ferrous oxide.

[0088] Figure 18 Optical micrographs of the tungsten diselenide sample prepared in Comparative Example 5 are shown. As can be seen from the figures, the domain orientations of the tungsten diselenide nanosheets obtained by replacing ferrous chloride with ferrous oxide are randomly distributed.

[0089] Comparative Example 6 It includes most of the operations of Example 1, except that: The amount of ferrous chloride powder added is 0.5 mg.

[0090] Figure 19 Optical micrographs of the tungsten diselenide sample prepared in Comparative Example 6 are shown. As can be seen from the figures, when the ferrous chloride content is too low, the domain orientation of the obtained tungsten diselenide nanosheets is randomly distributed.

[0091] Comparative Example 7 It includes most of the operations of Example 1, except that: The amount of ferrous chloride powder added is 50 mg.

[0092] Figure 20 Optical micrographs of the tungsten diselenide sample prepared in Comparative Example 7 are shown. As can be seen from the figures, when the ferrous chloride content is too high, the resulting tungsten diselenide is a multilayered nanosheet.

[0093] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

[0094] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0095] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a single-layer tungsten diselenide single-crystal thin film, characterized in that, This includes using tungsten source, ferrous chloride and selenium source as raw materials, inert gas as carrier gas, and chemical vapor deposition method with three-temperature zone heating to grow tungsten diselenide single crystal thin films.

2. A method for preparing a single-layer tungsten diselenide single-crystal thin film, characterized in that, Includes the following steps: 1) Place the selenium source in the first temperature zone, mix the tungsten source and ferrous chloride and place them in the second temperature zone, and place the substrate in the third temperature zone; 2) Pass the argon / hydrogen mixed carrier gas sequentially through the first temperature zone, the second temperature zone, and the third temperature zone; 3) The first temperature zone, the second temperature zone, and the third temperature zone are programmed to be heated to their respective predetermined temperatures, and a single-layer tungsten diselenide single-crystal thin film is grown on the substrate based on the principle of chemical vapor deposition.

3. The method for preparing a single-layer tungsten diselenide single-crystal thin film according to claim 1 or 2, characterized in that, The mass ratio of the selenium source, the tungsten source and the ferrous chloride powder is (500-650 mg): (80-120 mg): (5-10 mg). Optionally, the mass ratio of the selenium source, the tungsten source, and the ferrous chloride powder is 600 mg: 100 mg: 8 mg.

4. The method for preparing a single-layer tungsten diselenide single-crystal thin film according to claim 2, characterized in that, The predetermined temperature for the first temperature zone is 300–350°C; Optionally, the predetermined temperature of the second temperature zone is 900–950°C; Optionally, the predetermined temperature of the third temperature zone is 900–950°C.

5. The method for preparing a single-layer tungsten diselenide single-crystal thin film according to claim 1 or 2, characterized in that, The growth time for the single-layer tungsten diselenide is 5–30 min.

6. The method for preparing a single-layer tungsten diselenide single-crystal thin film according to claim 2, characterized in that, The flow rate ratio between the argon gas and the hydrogen gas is (50-80 sccm): (5-10 sccm). Optionally, the flow rate of the argon / hydrogen mixed carrier gas is 50–90 sccm.

7. The method for preparing a single-layer tungsten diselenide single-crystal thin film according to claim 2, characterized in that, The distance between the selenium source and the tungsten source is 5-8 cm; Optionally, the distance between the tungsten source and the substrate is 3 to 5 cm; Optionally, the substrate is a sapphire substrate; Optionally, the sapphire substrate is a sapphire substrate with surface impurities removed; Optionally, the selenium source includes selenium powder; Optionally, the tungsten source includes tungsten trioxide powder.

8. The method for preparing a single-layer tungsten diselenide single-crystal thin film according to claim 1, characterized in that, Before passing the argon / hydrogen mixed carrier gas through the first temperature zone, the second temperature zone, and the third temperature zone, including The first temperature zone, the second temperature zone, and the third temperature zone are evacuated to below 5 Pa.

9. The method for preparing a single-layer tungsten diselenide single-crystal thin film according to claim 1, characterized in that, After the growth of the tungsten diselenide single crystal thin film is completed, an argon / hydrogen mixed carrier gas is continued to be introduced. When the first temperature zone, the second temperature zone and the third temperature zone drop to room temperature, the carrier gas is turned off to obtain the single-layer tungsten diselenide single crystal thin film. Optionally, the single-layer tungsten diselenide monocrystalline thin film has a size of two inches.

10. The application of the single-layer tungsten diselenide single-crystal thin film prepared by the method according to any one of claims 1-9 in high-performance electronic devices and integrated circuits.

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