Method for mass production of h-phase vanadium diselenide film and application thereof

Abstract

This invention relates to a method for large-scale preparation of H-phase vanadium diselenide thin films and their applications, comprising the following steps: S1, growing H-phase MoSe2 nanoislands with a coverage of 30%~50% on a substrate using molecular beam epitaxy; S2, continuing with molecular beam epitaxy, using the H-phase MoSe2 nanoislands as seed crystals, to epitaxially grow H-phase VSe2 thin films. This method effectively promotes the growth of H-phase VSe2 thin films and obtains MoSe2-VSe2 lateral heterojunctions with atomically flat interfaces. The H-phase VSe2 thin films exhibit extremely high purity, filling the gap in the growth of high-quality monolayer H-phase VSe2 thin films, opening up new possibilities for the development and application of two-dimensional materials, especially in the synthesis of functional two-dimensional materials and the development of two-dimensional spintronic devices.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional transition metal chalcogenide (2D-TMDs) synthesis technology, and in particular to a method for large-scale preparation of H-phase vanadium diselenide thin films and their applications. Background Technology

[0002] Since the successful exfoliation of single-layer graphene, two-dimensional materials have attracted much attention due to their excellent properties, especially transition metal chalcogenides (TMDs). Their thin or single layers exhibit rich electrical properties (including metal, semiconductor, and insulator properties) and a variety of novel physical properties under the quantum size effect, which can be widely used in energy conversion and harvesting, and have broad application prospects in future electronic and optoelectronic devices.

[0003] Monolayer VSe2 is a type of intrinsically ferromagnetic telemeter (TMD). Regulated by the intrinsic exchange interaction between V 3d electrons, 2H-VSe2 exhibits spontaneous valley polarization behavior, thus being classified as a ferro-valley material. Due to its unique physical properties, VSe2 shows great application potential and significant research value in fields such as electronics, optics, optoelectronics, strain control, flexible devices, and energy storage. However, current research on the fundamental properties of VSe2 and the fabrication and application of its functional devices is still in its early stages, with a lack of research focused on practical production and industrial applications. TMD materials exist in various crystal phases, including 2H, 1T, and 1T', and different phases of the same material often exhibit drastically different physical and chemical properties. Among them, the H-phase VSe2, due to its excellent semiconductor properties combined with ferromagnetism, shows great promise for applications in two-dimensional spintronic devices.

[0004] Common methods for synthesizing large-area two-dimensional materials include chemical vapor deposition (CVD), atomic layer deposition (ALD), and molecular beam epitaxy (MBE). Among these, MBE offers several advantages over other methods: growth occurs in an ultra-high vacuum environment, avoiding the involvement of impurities; the precursor is deposited onto the substrate surface via an evaporation source, allowing for precise control of the deposition flux; and epitaxial growth occurs on specific substrate surfaces, enabling the growth of materials with specific structures through interfacial interactions. Taking MBE as an example, it typically grows VSe2 directly on a substrate, specifically involving the following steps: selenium atoms are deposited onto the HOPG substrate surface using a K-cell evaporation source, while vanadium atoms are simultaneously deposited onto the graphene substrate surface using an electron beam thermal evaporation source; the substrate is maintained at 180–220°C to allow for sufficient bonding between selenium and vanadium atoms, with the growth time lasting 10–20 minutes, ultimately forming a two-dimensional ordered monolayer of VSe2 on the substrate surface.

[0005] However, the aforementioned common synthesis methods typically only yield 1T phase structures, making it difficult to prepare high-quality H-phase VSe2 thin films, which hinders their application in two-dimensional spintronic devices. Therefore, the stable preparation of large-area, high-quality H-phase VSe2 thin films is crucial for their device applications. Summary of the Invention

[0006] Based on this, the purpose of this invention is to fill the gap in the growth of high-quality H-phase VSe2 monolayer thin films, and to propose a method for large-scale preparation of H-phase vanadium diselenide thin films and its applications. This H-phase VSe2 thin film growth method uses MoSe2 as a seed crystal in ultra-high vacuum, and induces the growth of H-phase VSe2 through molecular beam epitaxy via lattice-matched MoSe2 nanoislands. This method not only significantly improves the quality of the VSe2 film, but also achieves highly precise interlayer control, resulting in MoSe2-VSe2 lateral heterojunctions.

[0007] The present invention is achieved through the following technical solution: a method for large-scale preparation of H-phase vanadium diselenide thin films, comprising the following steps: S1, growing H-phase MoSe2 nano-islands with a coverage of 30%~50% on a substrate using molecular beam epitaxy; S2, continuing to use molecular beam epitaxy, using the H-phase MoSe2 nano-islands as seed crystals, to epitaxially grow H-phase VSe2 thin films.

[0008] Compared with the prior art, the present invention has at least the following beneficial effects:

[0009] This invention employs molecular beam epitaxy (MBE) to use H-phase MoSe2 nanoislands, lattice-matched with VSe2, as seed crystals for in-plane heteroepitaxial growth, promoting the growth of H-phase VSe2 films. This yields high-quality, atomically thin H-phase VSe2 films with a banded structure, and simultaneously creates a MoSe2-VSe2 lateral heterojunction. This heterojunction features an atomically flat interface and a type II band arrangement. This band arrangement typically confines electrons and holes to different material layers, making electron transitions difficult and limiting electron-hole recombination, thereby improving the electron-hole pair separation efficiency in the heterostructure. This not only extends carrier lifetime but also has broad application prospects in unipolar electronic devices and photocatalysis. This method, using MoSe2 as a seed crystal and employing in-plane and out-of-plane epitaxial growth, provides an effective and controllable strategy for preparing H-phase VSe2 materials from two-dimensional transition metal chalcogenides. It achieves precise control over the crystal phase and microstructure of H-phase VSe2, improves the structural quality of VSe2, enriches the phase structure library of two-dimensional material systems, and opens up new possibilities for the development and application of two-dimensional materials. It is particularly significant in the synthesis of electronic and optoelectronic materials and the development of electronic devices with specific phase structures.

[0010] In one embodiment, the method further includes step S0, degassing the substrate and growth source under ultra-high vacuum conditions, wherein the substrate is selected as a highly oriented pyrolytic graphite substrate, and the growth source includes a Mo source, a V source, and a Se source.

[0011] In one embodiment, step S0, the degassing process includes: heating the highly oriented pyrolytic graphite substrate under ultra-high vacuum conditions, maintaining the substrate at 480~550°C, and performing high-temperature degassing until the ambient vacuum level is less than 1×10⁻⁶. -8 mbar; the V source and Mo source are degassed separately using an electron beam evaporation source until the ambient vacuum is maintained at 1×10 mbar. -9 The Se source is degassed using a molecular evaporation source for 40-60 minutes at a temperature of 150-170°C and a constant degassed power of 5-8W.

[0012] In one embodiment, step S1 includes: evaporating high-purity Se and Mo atoms onto a substrate in a selenium-rich environment, maintaining the substrate temperature at 320~380℃ for a reaction time of 15~20 min; subsequently introducing excess Se for annealing at a temperature of 450~500℃ for a time of 10~35 min, thereby obtaining high-quality MoSe2 nanoislands on the substrate.

[0013] In one embodiment, step S2 includes: using molecular beam epitaxy to evaporate high-purity Se atoms and V atoms onto MoSe2 nanoislands or a substrate, maintaining the temperature of the substrate and MoSe2 nanoislands at 140~180℃ for a reaction time of 10~20 min; subsequently, introducing excess Se and performing high-temperature annealing at 140~180℃ for 5~10 min, thereby preparing H-phase VSe2 on H-phase MoSe2 nanoislands or a substrate.

[0014] The present invention also provides an H-phase VSe2 thin film grown epitaxially using H-phase MoSe2 nano islands as seed crystals. The film has a hexagonal symmetry structure, a band gap of 0.4~0.6eV, and the interlayer is formed by van der Waals forces.

[0015] In one embodiment, the H-phase VSe2 film generally exhibits an irregular banded morphological structure.

[0016] In one embodiment, the H-phase VSe2 thin film has 1 to 3 layers.

[0017] The present invention also provides a MoSe2-VSe2 heterojunction, wherein the heterojunction is an in-plane lateral heterojunction with an atomically flat interface and a type II band arrangement, wherein the MoSe2 is an H-phase MoSe2 nanoisland and the VSe2 is an H-phase VSe2 thin film, wherein the H-phase VSe2 thin film is distributed along the flat edge of the MoSe2 nanoisland to form a lateral heterojunction with lattice continuity and a flat interface.

[0018] In one embodiment, the heterojunction generally exhibits an irregular island-like morphological structure.

[0019] In one embodiment, the width of the island-like morphology of the heterojunction is 10 nm to 100 nm.

[0020] The present invention also provides the application of the H-phase VSe2 thin film and / or the MoSe2-VSe2 heterojunction in optoelectronic devices.

[0021] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0022] Figure 1 This is a large-scale STM topography image of MoSe2-VSe2 according to an embodiment of the present invention.

[0023] Figure 2 This is a small-scale STM topography image of MoSe2-VSe2 according to an embodiment of the present invention.

[0024] Figure 3 This is a morphological diagram of MoSe2-VSe2 according to an embodiment of the present invention.

[0025] Figure 4 This is an atomic resolution diagram of H-phase VSe2 according to an embodiment of the present invention.

[0026] Figure 5 This is the Fourier transform diagram corresponding to the atomic resolution diagram of the H phase VSe2 of an embodiment of the present invention.

[0027] Figure 6 This is an atomic resolution diagram of T-phase VSe2 according to an embodiment of the present invention.

[0028] Figure 7 This is the Fourier transform diagram corresponding to the atomic resolution diagram of the T phase VSe2 of an embodiment of the present invention.

[0029] Figure 8 It is a mirror twin grain boundary in H-phase VSe2 according to an embodiment of the present invention.

[0030] Figure 9 This is a constant height image of the MoSe2-VSe2 interface obtained using nc-AFM in an embodiment of the present invention.

[0031] Figure 10 This is a dI / dV spectrum of H-phase VSe2 according to an embodiment of the present invention.

[0032] Figure 11 This is the electronic density of states distribution diagram obtained from theoretical calculations of H-phase VSe2.

[0033] Figure 12 This is the band structure diagram obtained from the H-phase VSe2 experiment.

[0034] Figure 13 This is a large-scale STM topography image of the T-phase VSe2 of Comparative Example 1, with a scan size of 150 nm.

[0035] Figure 14 This is a small-scale STM topography image of the T-phase VSe2 in Comparative Example 1, with a scan size of 6 nm. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. The described embodiments are merely some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from publicly available commercial channels.

[0037] This specification uses spatially relative terms such as “below,” “under,” “down,” “above,” “above,” and “upper” to explain the positioning of one element relative to a second element. These terms are intended to cover different orientations of the device, except for those different from those shown in the figures.

[0038] Furthermore, the use of terms such as "having," "containing," "including," and "comprise" are open-ended terms, indicating the presence of the stated elements or features, but not excluding additional elements or features, unless the context clearly indicates otherwise.

[0039] This invention analyzes the reasons why existing technologies struggle to synthesize H-phase VSe2 thin films. It reveals that when synthesizing large-area two-dimensional materials using molecular beam epitaxy, the synthesized material often requires lattice matching with the substrate, and its physical properties are influenced by the substrate. However, current conventional substrates do not exhibit better lattice matching with T-phase VSe2 thin films than with H-phase VSe2 thin films, making it difficult to synthesize H-phase VSe2 thin films.

[0040] Therefore, the present invention considers first growing a transition layer on the substrate using molecular beam epitaxy (MBE), and then using the transition layer as a seed crystal to epitaxially grow an H-phase VSe2 thin film.

[0041] First, the present invention screened the raw materials for the transition layer and found that H-phase MoSe2 and H-phase VSe2 have a high lattice matching degree and can be used as seed crystals for epitaxial growth of H-phase VSe2 thin films, which laid a key foundation for subsequent preparation work.

[0042] Furthermore, this invention explores the preparation method of H-phase MoSe2 and the influence of growth coverage on the performance of H-phase VSe2 thin films, and finds that growing high-quality H-phase MoSe2 nanoisland thin films with a coverage of 30%~50% on the substrate is beneficial to achieving the preparation of high-quality large-area H-phase VSe2 thin films.

[0043] Based on this, the present invention provides a method for large-scale preparation of H-phase vanadium diselenide thin films. The method first uses molecular beam epitaxy to grow high-quality H-phase MoSe2 nanoisland thin films with a coverage of 30% to 50% on a substrate. Then, the H-phase MoSe2 nanoisland thin films are used as seed crystals to epitaxially grow H-phase VSe2 thin films, thereby achieving the goal of preparing high-quality, large-area H-phase VSe2 thin films.

[0044] Based on this, the present invention also investigated the preparation conditions of VSe2 thin films. The choice of substrate temperature is crucial when growing H-phase VSe2 thin films. Experiments showed that the optimal substrate temperature is 320–380 °C. If the temperature is too low, atomic clusters will form on the substrate surface, resulting in poor film quality; while if the temperature is too high, VSe2 will undergo a phase transition, changing from the H phase to the T phase. Furthermore, through repeated experiments, it was found that controlling the growth temperature between 140 and 180 °C can effectively regulate the crystal quality and structure of the VSe2 thin film.

[0045] Meanwhile, creating a selenium-rich atmosphere during the growth process helps to meet the stoichiometric ratio requirements of MoSe2 and VSe2. It can also dynamically control the surface Se concentration through physical adsorption and desorption mechanisms, promoting the migration and orderly arrangement of atoms on the substrate surface, thereby achieving high-quality growth. Therefore, before growing MoSe2 or VSe2, this invention first evaporates the Se source to create a selenium-rich atmosphere during the growth process. Then, by co-evaporating the Se source and the Mo source, or the Se source and the V source, Se atoms and Mo atoms or V atoms are deposited on the substrate for growth. After co-evaporation, the Se source is evaporated again, so that the Se atoms and Mo atoms or V atoms deposited on the substrate surface still maintain a selenium-rich atmosphere during the reaction and bonding process.

[0046] Besides temperature, the magnitude of the V-beam current also directly affects the growth rate and coverage of the VSe2 film. When the V-beam current is too low, it is not easy to obtain a VSe2 film; when the V-beam current is too high, the prepared sample is too thick, making it difficult to observe the VSe2 film and MoSe2-VSe2 lateral heterostructure in STM.

[0047] Furthermore, by adjusting the deposition time, the film coverage can be further controlled to obtain thin VSe2 films, enabling precise control over film properties. Specifically, increasing the deposition time increases the film thickness and alters its electronic properties; conversely, decreasing the deposition time helps obtain thinner films with lower coverage, and even forms monolayer structures in the two-dimensional limit, thereby inducing quantum confinement effects and electronic state changes that are distinctly different from those of thick films.

[0048] Based on the above research, the present invention provides a method for large-scale preparation of H-phase vanadium diselenide thin films, specifically comprising the following steps: S0. Under ultra-high vacuum conditions, the substrate and growth source are degassed.

[0049] S1. H-phase MoSe2 nanoislands with a coverage of 30%~50% are grown on the substrate using molecular beam epitaxy.

[0050] S2. Continue to use molecular beam epitaxy process, using the H-phase MoSe2 nano islands as seed crystals, to epitaxially grow H-phase VSe2 thin films, to obtain H-phase vanadium diselenide thin films or MoSe2-VSe2 lateral heterojunctions.

[0051] In a preferred embodiment, a highly oriented pyrolytic graphite substrate is selected as the substrate. After the H-phase VSe2 thin film is grown, the H-phase VSe2 thin film is characterized using a scanning tunneling microscope (STM), and the grown MoSe2-VSe2 lateral heterojunction is characterized using a non-contact atomic force microscope (nc-AFM).

[0052] The present invention also provides an H-phase VSe2 thin film, which is obtained by the above method, such as... Figure 2 As shown, the thin film exhibits an irregular island-like morphology overall, with an atomic-level thickness. In one embodiment, the H-phase VSe2 thin film is a single layer; in another embodiment, the H-phase VSe2 thin film has two layers. The thickness of the single-layer VSe2 thin film is approximately 0.7 nm.

[0053] Another aspect of the present invention provides a MoSe2-VSe2 heterojunction, which is an in-plane lateral heterojunction, wherein MoSe2 is an H-phase MoSe2 nanoislands and VSe2 is an H-phase VSe2 thin film, as shown below. Figure 1As shown, the heterojunction exhibits an irregular island-like morphology overall, with an atomic-level thickness and a width of 10 nm to 100 nm. The H-phase VSe2 film is distributed along the edges of the MoSe2 nanoislands, forming a clear and smooth interface at the atomic scale, as shown. Figure 8 As shown.

[0054] The following describes a method for large-scale preparation of H-phase vanadium diselenide thin films provided by the present invention, in conjunction with specific embodiments and accompanying drawings.

[0055] Example 1 This embodiment provides a method for large-scale preparation of H-phase vanadium diselenide thin films, specifically including the following steps: S1. Substrate and Growth Source Pretreatment: Under ultra-high vacuum conditions, a highly oriented pyrolytic graphite (HOPG) substrate is heated by direct current with a tungsten filament and maintained at 500°C for high-temperature degassing until the ambient vacuum level is less than 1×10⁻⁶. -8 mbar; degas the V source and Mo source separately for 10 minutes using an electron beam evaporation source until the ambient vacuum is maintained at 1×10 mbar. -9 The parameters are in the mbar range, where the constant degassing power of the V source is 13W, the constant degassing power of the Mo source is 42W, and the Se source is degassed for 60 minutes by a molecular evaporation source, where the degassing temperature of the Se source is 160℃.

[0056] S2. Growth of H-phase MoSe2 nanoislands with a coverage of 30%–50% on a substrate using molecular beam epitaxy: Selenium source was evaporated at 148°C. In a selenium-rich environment, molybdenum source was evaporated using an electron beam evaporation source at a constant power of 39.6 W. The temperature of the highly oriented pyrolytic graphite substrate was maintained at 370°C for 16 minutes. After the reaction, selenium was continuously introduced for 15 minutes to ensure an excess of selenium. Finally, the substrate was annealed at 490°C for 20 minutes to obtain H-phase MoSe2 nanoislands on the substrate. Figure 2 As shown.

[0057] S3. Continuing with molecular beam epitaxy, using the aforementioned H-phase MoSe2 nanoislands as seed crystals, an H-phase VSe2 thin film is epitaxially grown: the selenium source is evaporated at 148°C, and the vanadium source is evaporated at a constant power of 11.1W in a selenium-rich environment using an electron beam evaporation source. The substrate temperature is maintained at 160°C, and the reaction is carried out for 16 minutes. After the reaction, the film is annealed at 160°C for 5 minutes to obtain H-phase VSe2 along the edge of the H-phase MoSe2 nanoislands. Figures 1-3 As shown, this embodiment successfully fabricated a large-area H-phase VSe2 thin film, and also fabricated a MoSe2-VSe2 heterojunction, wherein the heterojunction width is 50-100nm and the H-VSe2 width is 10-50nm.

[0058] After the H-phase VSe2 thin film was grown, the H-phase VSe2 thin film was characterized by scanning tunneling microscopy (STM), and the grown MoSe2-VSe2 lateral heterojunction was characterized by non-contact atomic force microscopy (nc-AFM). Figure 1 This is a large-scale STM topography image of a preferred example. Figure 2 These are small-scale STM morphology images. Both the grown MoSe2 and VSe2 films formed high-quality, single-atom-layer thin films. Figure 4 The image shows the atomic resolution of H-phase VSe2 obtained using STM scanning. Figure 5 The figure shows its Fourier transform, and... Figure 6 The T-phase VSe2 and obtained by the scan shown Figure 7 The Fourier transforms shown are significantly different, indicating that the VSe2 and T phases grown using this method are not the same phase structure. Figure 8 The mirrored twin grain boundaries characteristic of the H phase shown indicate that a high-quality H-phase VSe2 thin film was grown using this method. Images were taken at the Se and Mo edges of the MoSe2 nanoislands using nc-AFM, as shown... Figure 9 As shown, the precise interface between MoSe2 and VSe2 is displayed, demonstrating the structural docking between the two materials at the atomic scale. It shows that the interface of the MoSe2-VSe2 lateral heterojunction is very clear and smooth at the atomic scale, and the H-phase VSe2 film exhibits a hexagonal symmetry structure.

[0059] The scanning tunneling spectrum (STS) of H-phase VSe2 was measured using STM, and the dI / dV curve was plotted. The dI / dV spectrum is a method for measuring the electronic density of states of a sample. The electronic density of states of H-phase VSe2 grown by this method is as follows: Figure 10 As shown, it exhibits a band gap of 0.5 ± 0.05 eV, indicating that the H-phase VSe2 displays semiconductor characteristics. In the figure, the increased peak intensity indicates changes in local electronic states. Theoretical calculations were performed on the H-phase VSe2, as follows... Figure 11 As shown, combined with the spin state, the H-phase VSe2 has a band gap of approximately 0.5 eV, indicating that the H-phase VSe2 is semiconductor, which is consistent with the experiment.

[0060] In this embodiment, while preparing the H-phase VSe2 thin film, a MoSe2-VSe2 heterojunction was also obtained. This heterojunction is an in-plane lateral heterojunction, in which MoSe2 consists of H-phase MoSe2 nanoislands and VSe2 consists of an H-phase VSe2 thin film. Figure 1As shown, the heterojunction exhibits an irregular island-like morphology overall, with an atomic-level thickness and a width of 10 nm to 100 nm. The H-phase VSe2 film is distributed along the edges of the MoSe2 nanoislands, forming a clear and smooth interface at the atomic scale, as shown. Figure 9 As shown. Further investigation into the electronic structure of the heterojunction, such as... Figure 12 As shown, the MoSe2-VSe2 heterojunction exhibits a type II band structure, with a significant upward band bend in the MoSe2 band at the interface. This band arrangement confines electrons and holes within different material layers, suppressing electron transitions and reducing the electron-hole recombination probability, thus effectively improving the electron-hole pair separation efficiency in the heterostructure. This not only extends carrier lifetime but also shows broad application prospects in unipolar electronic devices and photocatalysis.

[0061] Comparative Example 1 Under ultra-high vacuum conditions, V and Se atoms were co-deposited on a HOPG substrate using molecular beam epitaxy. The substrate was kept at 200°C during the process to allow the selenium and vanadium atoms to fully combine. The growth time lasted for 15 minutes.

[0062] After the VSe2 film growth was completed, the VSe2 film was characterized using a scanning tunneling microscope (STM). Figure 13 These are large-scale STM morphology images of the VSe2 thin film. Figure 14 The image shows a small-scale STM morphology, indicating that the VSe2 film formed in Comparative Example 1 is a T-phase VSe2 film. Therefore, directly preparing VSe2 films can only yield T-phase VSe2 films.

[0063] In summary, the method for large-scale preparation of H-phase vanadium diselenide thin films provided by this invention has the following advantages: (1) It fills the gap in the growth of high-quality monolayer H phase VSe2 thin films, opening up new possibilities for the development and application of two-dimensional materials, especially in the synthesis of functional two-dimensional materials and the research and development of electronic devices with specific phase structures.

[0064] (2) High-quality monolayer H-phase VSe2 thin films provide an important material basis for further research on the physical properties of H-phase VSe2, such as ferromagnetism and valley electrons, as well as the fabrication of two-dimensional spintronic devices.

[0065] (3) The MoSe2-VSe2 transverse heterojunction has a type II band distribution, which shows broad application prospects in the fields of unipolar electronic devices and photocatalysis.

[0066] (4) The two-step growth process using seed crystal surface epitaxy has a relatively simple process flow. The process parameters for preparing thin films can be adjusted arbitrarily. The reaction temperature is low and the substrate can be quickly heated to the specified temperature, which solves the complexity problem of two-dimensional material preparation and enables large-scale preparation in the laboratory.

[0067] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for large-scale preparation of H-phase vanadium diselenide thin films, characterized in that, Includes the following steps: S1. Using molecular beam epitaxy, H-phase MoSe2 nanoislands with a coverage of 30%~50% are grown on the substrate; S2. Using the H-phase MoSe2 nanoislands as seed crystals, H-phase VSe2 thin films are epitaxially grown using molecular beam epitaxy.

2. The method according to claim 1, characterized in that, It also includes step S0, which involves degassing the substrate and growth source under ultra-high vacuum conditions. The substrate is a highly oriented pyrolytic graphite substrate, and the growth source includes a Mo source, a V source, and a Se source.

3. The method according to claim 2, characterized in that, In step S0, the degassing process includes: heating the highly oriented pyrolytic graphite substrate under ultra-high vacuum conditions, maintaining the substrate at 480~550℃, and performing high-temperature degassing until the ambient vacuum level is less than 1×10⁻⁶. -8 mbar; the V source and Mo source are degassed separately using an electron beam evaporation source until the ambient vacuum is maintained at 1×10 mbar. -9 The Se source is degassed using a molecular evaporation source for 40-60 minutes at a temperature of 150-170°C and a constant degassed power of 5-8W.

4. The method according to any one of claims 1 to 3, characterized in that, Step S1 includes: evaporating high-purity Se and Mo atoms onto a substrate in a selenium-rich environment, maintaining the substrate temperature at 320~380℃ for a reaction time of 15~20 min; subsequently introducing excess Se for annealing at a temperature of 450~500℃ for a time of 10~35 min, thereby obtaining high-quality MoSe2 nanoislands on the substrate.

5. The method according to claim 4, characterized in that, Step S2 includes: using molecular beam epitaxy, evaporating high-purity Se atoms and V atoms onto MoSe2 nanoislands or a substrate, maintaining the temperature of the substrate and MoSe2 nanoislands at 140~180℃ for a reaction time of 10~20 min; then introducing excess Se for high-temperature annealing at 140~180℃ for 5~10 min, thereby preparing H-phase VSe2 on H-phase MoSe2 nanoislands or a substrate.

6. An H-phase VSe2 thin film, characterized in that, The H-phase VSe2 thin film has a hexagonal symmetry structure with a band gap of 0.4~0.6eV and is characterized by van der Waals forces between the layers.

7. The H-phase VSe2 thin film according to claim 6, characterized in that, The H-phase VSe2 film has an irregular island-like morphological structure; the H-phase VSe2 film has 1 to 3 layers.

8. A MoSe2-VSe2 heterojunction, characterized in that, The heterojunction is an in-plane lateral heterojunction with an atomically flat interface and a type II band arrangement. The MoSe2 is an H-phase MoSe2 nanoisland, and the VSe2 is an H-phase VSe2 thin film. The H-phase VSe2 thin film is distributed along the flat edges of the MoSe2 nanoisland, forming a lateral heterojunction with lattice continuity and a flat interface.

9. The MoSe2-VSe2 heterojunction according to claim 8, characterized in that, The heterojunction has an overall irregular island-like morphological structure; the width of the island-like morphological structure of the heterojunction is 10 nm to 100 nm.

10. The application of the H-phase VSe2 thin film according to claim 6 or 7 or the MoSe2-VSe2 heterojunction according to claim 8 or 9 in optoelectronic devices.

Images