Transition metal chalcogenide vertical heterojunction and method of making the same

Abstract

The application discloses a transition metal chalcogen compound vertical heterojunction and a preparation method thereof, and belongs to the technical field of semiconductor materials and two-dimensional film heterojunction preparation. The method utilizes the characteristic that a water-soluble ion residual layer exists at the bottom of a TMD material grown by a salt-assisted CVD method, adopts a step-by-step transfer strategy, removes the ion layer at the bottom of a second TMD component in water first, stacks the second TMD component with a first TMD component in a non-water liquid to avoid the ion layer at the bottom of the first component from being dissolved and falling off in advance, and finally transfers the whole to a new substrate in water and removes the residual ion layer and a support layer. The application realizes an atom-level clean heterojunction interface, is safe and simple in process, and is highly compatible with existing semiconductor processes.

Description

Technical Field

[0001] This invention relates to the field of semiconductor materials and two-dimensional thin film heterojunction preparation technology, and particularly to a transition metal chalcogenide vertical heterojunction and its preparation method. Background Technology

[0002] Transition metal chalcogenides (TMDs) have shown great promise for applications in next-generation electronic devices, optoelectronic devices, and energy catalysis due to their excellent and tunable semiconductor, optoelectronic, and mechanical properties. The heterojunction formed by vertically stacking different types of two-dimensional TMD materials through van der Waals forces not only retains the intrinsic properties of each component but also generates new physical phenomena through interfacial coupling, representing an important approach to expanding the functionality of two-dimensional materials.

[0003] Currently, one of the effective strategies for preparing high-quality TMD thin films is salt-assisted chemical vapor deposition (CVD). This method, by introducing additives such as sodium salts during the growth process, can significantly reduce the reaction energy barrier and promote the growth of highly crystalline TMD thin films. However, TMD thin films grown using this method usually inevitably have a layer of water-soluble ionic salts (such as Na2SO4, Na2SeO4, etc.) remaining at the interface with the growth substrate (such as SiO2 / Si). This residual salt layer deteriorates the electrical properties of the TMD material; on the other hand, its water solubility also facilitates the transfer of the film, meaning that strong corrosive etching solutions such as hydrofluoric acid are not required, and the film can be separated from the substrate simply by water bath treatment.

[0004] When constructing vertical heterojunctions using TMD materials grown via the aforementioned salt-assisted CVD method, existing technologies commonly employ a polymethyl methacrylate (PMMA)-assisted wet transfer strategy. This method typically requires transferring and stacking different types of TMD films layer by layer. However, this process presents a key technical challenge: when using a "PMMA + water transfer" method to process the two TMD components separately, organic contaminants such as PMMA easily remain on the surface of the first TMD layer during the transfer process. When the second TMD layer is stacked with it, these contaminants become trapped at the heterojunction interface, hindering the formation of atomically clean contact between the two materials, thereby severely degrading the interface quality of the heterojunction and the overall performance of the device.

[0005] Therefore, how to effectively avoid the dual pollution problem of ionic and organic residues at the heterojunction interface while taking advantage of the ease of water transfer of materials grown by salt-assisted CVD, and thus achieve the construction of vertical heterojunctions with atomically clean interfaces, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The main objective of this invention is to provide a method for preparing vertical heterojunctions of transition metal chalcogenides, aiming to solve the technical problem of reduced heterojunction quality caused by interfacial ion residues and organic residues in the prior art.

[0007] To achieve the above objectives, the present invention provides a method for preparing a vertical heterojunction of a transition metal chalcogenide, comprising the following steps: S1. Preparation of the first layered structure: A first TMD thin film is prepared on the surface of a first substrate by salt-assisted CVD, and a first water-soluble ion residual layer is formed between the first substrate and the first TMD thin film to obtain a first stacked structure. The first stacked structure includes the first TMD thin film, the first water-soluble ion residual layer and the first substrate stacked sequentially. S2. Preparation of the second layered structure: A second TMD film is prepared on the surface of a second substrate by salt-assisted CVD. A second water-soluble ion residue layer is formed between the second substrate and the second TMD film. Then, a support layer is prepared on the surface of the second TMD film away from the second substrate. Next, the film is placed in deionized water for a first water bath transfer to remove the second water-soluble ion residue layer, thereby separating the second TMD film from the second substrate and obtaining a second stacked structure. The second stacked structure includes the support layer and the second TMD film stacked in sequence. S3. Preparation of the third layered structure: The first stacked structure and the second stacked structure are stacked in the same non-aqueous liquid, and the non-aqueous liquid is removed to obtain a third stacked structure. The third stacked structure includes the support layer, the second TMD film, the first TMD film, the first water-soluble ion residue layer, and the first substrate stacked in sequence. S4. Preparation of the fourth layered structure: The third stacked structure is placed in deionized water for a second water bath transfer to remove the first water-soluble ion residue layer, thereby separating the first TMD film from the first substrate to obtain a stacked structure. The stacked structure includes the support layer, the second TMD film, and the first TMD film stacked sequentially. The stacked structure is then transferred to the surface of the third substrate to obtain a fourth stacked structure. The fourth stacked structure includes the support layer, the second TMD film, the first TMD film, and the third substrate stacked sequentially. S5. Preparation of the fifth layered structure: Removing the support layer from the fourth stacked structure yields a fifth stacked structure, which includes a second TMD film, a first TMD film, and a third substrate stacked sequentially.

[0008] In some embodiments of the present invention, the materials used to prepare the first TMD film and the second TMD film include chalcogenide precursors and metal precursors.

[0009] In some embodiments of the present invention, the metal element precursor includes at least one of Na2MoO4, Na2WO4, a mixture of MoO3 and NaCl, and a mixture of WO3 and NaCl.

[0010] In some embodiments of the present invention, the chalcogen element precursor includes at least one of S, Se, ZnS, and ZnSe.

[0011] In some embodiments of the present invention, the support layer comprises PMMA.

[0012] In some embodiments of the present invention, the preparation process of the support layer is as follows: dissolving the material for preparing the support layer in a solvent to obtain a support layer precursor solution, spin-coating the support layer precursor solution onto the surface of the second TMD film away from the second substrate, and then heating to remove the solvent.

[0013] In some embodiments of the present invention, the non-aqueous liquid includes at least one of isopropanol, n-hexane, and n-heptane.

[0014] In some embodiments of the present invention, the support layer is removed by steam fumigation. Alternatively, the support layer can be removed by immersion in an organic solvent, wherein the organic solvent includes one or more of acetone and anisole.

[0015] In some embodiments of the present invention, the substrate includes at least one of SiO2 / Si, sapphire, mica, and quartz.

[0016] The present invention also provides a transition metal chalcogenide vertical heterojunction, which is prepared by the preparation method of transition metal chalcogenide vertical heterojunction as described above.

[0017] The beneficial effects that this invention can achieve are: (1) Achieving atomic-level clean contact at the heterojunction interface: In this invention, the first TMD film is never coated with a support layer material before stacking, and its surface remains in its original clean state. After the first water transfer, the second water-soluble ion residue layer on the lower surface of the second TMD film has been completely removed. When the two are bonded in a non-aqueous liquid, a direct physical contact is formed between the clean lower surface of the second TMD film and the clean upper surface of the first TMD film. There is no residue of any support layer material at the heterojunction interface, which effectively ensures the atomic-level tight coupling between the two TMD materials and achieves atomic-level clean contact at the heterojunction interface, which is beneficial to improving the interface quality and device performance of the heterojunction.

[0018] (2) Resolves the temporal contradiction in ion residue control: This invention cleverly utilizes a step-by-step combination strategy of "non-aqueous liquid" and "water". First, a first water bath transfer is performed to remove the second water-soluble ion residue layer at the bottom of the second TMD film. Then, the second TMD film and the first TMD film are vertically stacked in a non-aqueous liquid. The non-aqueous liquid protects the first water-soluble ion residue layer at the bottom of the first TMD film from premature dissolution, preventing it from detaching from its own growth substrate. Then, a second water transfer is performed to directionally remove the first water-soluble ion residue layer of the first TMD film. In this way, this invention breaks through the technical bottleneck of the traditional single water transfer process where "stacking" and "desalination" cannot be simultaneously achieved. It retains the convenience of easy transfer in water in salt-assisted CVD and completely eliminates all undesirable residues at the interfaces in the final product through step-by-step operation, thus resolving the temporal contradiction in ion residue control.

[0019] (3) The process is safe and highly compatible: The entire transfer process does not require the use of highly corrosive or toxic etching solutions such as hydrofluoric acid (HF) and potassium hydroxide (KOH), making it environmentally friendly and highly safe to operate. At the same time, the materials used, such as the material of the support layer and the grade of the non-aqueous liquid, are optional. Standard reagents in the field of semiconductor micro-nano processing can be selected, which is highly compatible with existing CMOS processes and laboratory research conditions, making it easy to promote and apply. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 This is a schematic flowchart of a method for preparing a vertical heterojunction of transition metal chalcogenides according to an embodiment of the present invention. Figure 2This is an optical microscope image of the first TMD thin film MoSe2 in Embodiment 1 of the present invention; Figure 3 This is the Raman spectrum of the first TMD thin film MoSe2 in Example 1 of the present invention; Figure 4 This is the photoluminescence (PL) spectrum of the first TMD thin film MoSe2 in Embodiment 1 of the present invention; Figure 5 This is an optical microscope image of the second TMD thin film MoS2 in Embodiment 1 of the present invention; Figure 6 This is the Raman spectrum of the second TMD thin film MoS2 in Embodiment 1 of the present invention; Figure 7 This is the photoluminescence (PL) spectrum of the second TMD thin film MoS2 in Embodiment 1 of the present invention; Figure 8 The above are XPS spectra of the second TMD thin film MoS2 in Embodiment 1 of the present invention, where (a) is the S 2p spectrum and (b) is the Na 1s spectrum. Figure 9 The above are XPS spectra of the second TMD thin film MoS2 in Embodiment 1 of the present invention after the first water bath transfer, where (a) is the S 2p spectrum and (b) is the Na 1s spectrum. Figure 10 This is an optical microscope image of the MoS2 / MoSe2 vertical heterojunction of Embodiment 1 of the present invention; Figure 11 This is the Raman spectrum of the MoS2 / MoSe2 vertical heterojunction of Embodiment 1 of the present invention, where curves (i), (ii), and (iii) correspond to Figure 10 Test areas (i), (ii), and (iii) in the text. Figure 12 This is a surface potential distribution diagram of the MoS2 / MoSe2 vertical heterojunction in Embodiment 1 of the present invention; Figure 13 The surface potential curves of the MoS2 / MoSe2 vertical heterojunction in Embodiment 1 of the present invention are shown, where curves (i), (ii), and (iii) correspond to... Figure 12 The dashed lines (i), (ii), and (iii) in the text. Figure 14 This is an optical microscope image of the MoS2 / WS2 vertical heterojunction of Embodiment 2 of the present invention; Figure 15 This is the Raman spectrum of the MoS2 / WS2 vertical heterojunction in Embodiment 2 of the present invention, where curves (i), (ii), and (iii) correspond to Figure 14 The test areas (i), (ii), and (iii) are shown in the figure.

[0022] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0023] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] In this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Furthermore, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. If the combination of technical solutions is contradictory or impossible to implement, such a combination should be considered non-existent and not within the scope of protection claimed by this invention.

[0026] This invention provides a transition metal chalcogenide vertical heterojunction and its preparation method, referring to... Figure 1 The preparation method includes the following steps: S1. Preparation of the first layered structure: A first TMD thin film is prepared on the surface of a first substrate by salt-assisted CVD, and a first water-soluble ion residual layer is formed between the first substrate and the first TMD thin film to obtain a first stacked structure. The first stacked structure includes the first TMD thin film, the first water-soluble ion residual layer and the first substrate stacked sequentially. S2. Preparation of the second layered structure: A second TMD film is prepared on the surface of a second substrate by salt-assisted CVD. A second water-soluble ion residue layer is formed between the second substrate and the second TMD film. Then, a support layer is prepared on the surface of the second TMD film away from the second substrate. Next, the film is placed in deionized water for a first water bath transfer to remove the second water-soluble ion residue layer, thereby separating the second TMD film from the second substrate and obtaining a second stacked structure. The second stacked structure includes the support layer and the second TMD film stacked in sequence. S3. Preparation of the third layered structure: The first stacked structure and the second stacked structure are stacked in the same non-aqueous liquid, and the non-aqueous liquid is removed to obtain a third stacked structure. The third stacked structure includes the support layer, the second TMD film, the first TMD film, the first water-soluble ion residue layer, and the first substrate stacked in sequence. S4. Preparation of the fourth layered structure: The third stacked structure is placed in deionized water for a second water bath transfer to remove the first water-soluble ion residue layer, thereby separating the first TMD film from the first substrate to obtain a stacked structure. The stacked structure includes the support layer, the second TMD film, and the first TMD film stacked sequentially. The stacked structure is then transferred to the surface of the third substrate to obtain a fourth stacked structure. The fourth stacked structure includes the support layer, the second TMD film, the first TMD film, and the third substrate stacked sequentially. S5. Preparation of the fifth layered structure: Removing the support layer from the fourth stacked structure yields a fifth stacked structure, which includes a second TMD film, a first TMD film, and a third substrate stacked sequentially.

[0027] In this invention, the first TMD film is never coated with a support layer material before stacking, and its surface remains in its original clean state. After the first water transfer, the second water-soluble ion residue layer on the lower surface of the second TMD film has been completely removed. When the two are bonded in a non-aqueous liquid, a direct physical contact is formed between the clean lower surface of the second TMD film and the clean upper surface of the first TMD film. There is no residue of any support layer material at the heterojunction interface, which effectively ensures the atomic-level tight coupling between the two TMD materials and achieves atomic-level clean contact at the heterojunction interface, which is beneficial to improving the interface quality and device performance of the heterojunction.

[0028] Furthermore, this invention cleverly utilizes a step-by-step combination strategy of "non-aqueous liquid" and "water". First, a first water bath transfer removes the second water-soluble ion residue layer at the bottom of the second TMD film. Then, in a non-aqueous liquid, the second TMD film and the first TMD film are vertically stacked. The non-aqueous liquid protects the first water-soluble ion residue layer at the bottom of the first TMD film from premature dissolution, preventing it from detaching from its growth substrate. A second water transfer is then performed to directionally remove the first water-soluble ion residue layer from the first TMD film. Thus, this invention overcomes the technical bottleneck of the traditional single water transfer process where "stacking" and "desalination" cannot be simultaneously achieved. It retains the convenience of easy transfer in water in salt-assisted CVD while completely eliminating all undesirable residues at the interfaces in the final product through step-by-step operations, resolving the timing contradiction in ion residue control.

[0029] Furthermore, the entire transfer process eliminates the need for highly corrosive or toxic etching solutions such as hydrofluoric acid (HF) and potassium hydroxide (KOH), making it environmentally friendly and highly safe to operate. Simultaneously, the materials used, such as the support layer material and the grade of the non-aqueous liquid, are selectable, allowing for the selection of standard reagents from the semiconductor micro / nano fabrication field. This ensures high compatibility with existing CMOS processes and laboratory research conditions, facilitating widespread adoption and application.

[0030] In some embodiments, the materials used to prepare the first TMD thin film include chalcogenide precursors and metal precursors.

[0031] In some embodiments, the chalcogen element precursor includes at least one of S, Se, ZnS, and ZnSe.

[0032] In some embodiments, the metal element precursor includes at least one of Na2MoO4, Na2WO4, a mixture of MoO3 and NaCl, and a mixture of WO3 and NaCl.

[0033] Both the first and second TMD films are TMD films. The formation principle of TMD films is as follows: using metal element precursors and chalcogen element precursors as raw materials, TMD films are prepared by salt-assisted CVD. S-containing chalcogen element precursors, such as S and ZnS, will volatilize or decompose into gaseous S upon heating; Se-containing chalcogen element precursors, such as Se and ZnSe, will volatilize or decompose into gaseous Se upon heating. The metal element precursors will also volatilize. The volatilized metal element precursors react chemically with gaseous S and / or gaseous Se on the substrate surface to form a TMD film, creating a water-soluble ion residue layer between the TMD film and the substrate. However, Zn in ZnS and ZnSe will not volatilize under these conditions, will not come into contact with the substrate, and will remain in the chalcogen element precursors, not participating in the preparation of the TMD film.

[0034] After the first TMD film is grown using salt-assisted CVD, a first water-soluble ionic residue layer naturally forms between the first TMD film and the first substrate. In some embodiments, the first water-soluble ionic residue layer includes a sodium salt, which includes at least one of Na₂SO₄ and Na₂SeO₄. During this step, the upper surface of the first TMD film remains clean and uncoated by any polymers (such as support layer materials), which facilitates the subsequent formation of an atomically clean interface.

[0035] In some embodiments, the materials used to prepare the second TMD film include chalcogenide precursors and metal precursors.

[0036] In some embodiments, the chalcogen element precursor includes at least one of S, Se, ZnS, and ZnSe.

[0037] In some embodiments, the metal element precursor includes at least one of Na2MoO4, Na2WO4, a mixture of MoO3 and NaCl, and a mixture of WO3 and NaCl.

[0038] After the second TMD film is grown by salt-assisted CVD, a second water-soluble ionic residue layer will naturally form between the second TMD film and the second substrate. In some embodiments, the second water-soluble ionic residue layer includes a sodium salt, which includes at least one of Na2SO4 and Na2SeO4.

[0039] In some embodiments, the support layer is made of polymethyl methacrylate (PMMA).

[0040] In some embodiments, the process for preparing the support layer is as follows: spin-coating a support layer precursor solution onto the surface of the second TMD film away from the second substrate, followed by heating to remove the solvent.

[0041] In some embodiments, the spin coating speed is 2500-5000 rpm, the spin coating time is 30-90 s, the heating temperature is 110-130°C, and the heating time is 3-10 min, which is beneficial for solvent removal.

[0042] In some embodiments, the spin coating speed is 3000 rpm, the spin coating time is 60 s, the heating temperature is 120°C, and the heating time is 5 min.

[0043] In some embodiments, the material of the support layer is dissolved in an organic solvent to obtain a support layer precursor solution, the organic solvent including anisole, and the mass concentration of the support layer precursor solution is 3% to 5%, which can be 4%.

[0044] After the support layer was prepared, the sample with the support layer was placed in deionized water for the first water bath transfer. Because the second water-soluble ion residue layer dissolves in water, the second TMD film supported by the support layer naturally separates from the second substrate. Therefore, the first water bath transfer not only achieved the transfer of the second TMD film, but more importantly, it simultaneously removed the ion residues at the bottom of the second TMD film, improving the cleanliness of its lower surface. This ensures atomically clean contact between the second and first TMD films at the heterojunction interface.

[0045] In the step of preparing the third stacked structure, the second stacked structure with a support layer is placed in a non-aqueous liquid. Then, the non-aqueous liquid is slowly removed, causing the liquid level to drop, thereby guiding the second TMD film to slowly and completely adhere to the upper surface of the first TMD film. Since the entire stacking process takes place in a non-aqueous environment, the first water-soluble ion residue layer at the bottom of the first TMD film does not come into contact with water and therefore will not dissolve. This ensures that the first TMD film remains firmly attached to the first substrate throughout the stacking process, preventing film breakage or wrinkling and guaranteeing the success rate of the stacking operation. At this point, a physical contact is formed between the second and first TMD films, and there is no intermediate dielectric layer at the interface, thus obtaining the third stacked structure: support layer, second TMD film, first TMD film, first water-soluble ion residue layer, and first substrate.

[0046] In some embodiments, the non-aqueous liquid includes, but is not limited to, at least one of isopropanol, n-hexane, and n-heptane.

[0047] In the step of preparing the fourth stacked structure, the third stacked structure is placed in deionized water for a second water bath transfer. The goal of this water bath is to separate the first substrate from the first TMD film by dissolving the first water-soluble ionic residue layer. Specifically, water molecules permeate between the first TMD film and the first substrate, dissolving the first water-soluble ionic residue layer and thereby separating the first TMD film from the first substrate, resulting in the following stacked structure: a support layer, a second TMD film, and a first TMD film stacked sequentially. Subsequently, the stacked structure floating on the water surface is retrieved using the third substrate, thus realizing the overall transfer of the heterojunction to the new substrate, and completely removing the ionic residue at the bottom of the first TMD film in the process.

[0048] In the step of preparing the fifth stacked structure, an organic solvent is used to remove the uppermost support layer. The organic solvent includes, but is not limited to, one or more of acetone and anisole. The removal method can be immersion in the organic solvent or steam fumigation. For example, the sample is immersed in an acetone solution for several hours to dissolve the PMMA layer, then rinsed with isopropanol and dried with nitrogen to obtain the final target product: a second TMD film / first TMD film vertical heterojunction.

[0049] In some embodiments, the first substrate, the second substrate, and the third substrate include at least one of SiO2 / Si, sapphire, mica, and quartz.

[0050] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following specific embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0051] Example 1 This embodiment provides a method for preparing a vertical heterojunction of a transition metal chalcogenide, specifically including the following steps: S1. Preparation of the first layered structure: Using Na₂MoO₄ as the metal precursor and ZnSe powder as the chalcogenide precursor, a salt-assisted CVD method was employed. Under conditions of 100 sccm Ar, 760℃, 120 Pa, and 15 min, ZnSe powder decomposed to release gaseous Se, while Na₂MoO₄ volatilized. The volatilized Na₂MoO₄ and gaseous Se met and reacted on the surface of the first substrate (SiO₂ / Si, with a thermal oxide layer thickness of 285 nm), growing a first TMD film mainly composed of MoSe₂. Furthermore, after natural cooling to room temperature, a first water-soluble ionic residue layer (mainly composed of Na₂SeO₄) was formed between the first substrate and the first TMD film. The Zn in the ZnSe powder, under the salt-assisted CVD conditions, does not volatilize and does not come into contact with the first substrate; it remains in the ZnSe powder and does not participate in the preparation of the first TMD film. This yielded a first stacked structure, labeled as: MoSe₂ / Na₂SeO₄ / SiO₂ / Si.

[0052] S2. Preparation of the second layered structure: Using Na₂MoO₄ as the metal precursor and ZnS powder as the chalcogenide precursor, a salt-assisted CVD method was employed. Under conditions of 100 sccm Ar, 760℃, 120 Pa, and 15 min, ZnS powder decomposed to release gaseous S, and Na₂MoO₄ volatilized. The volatilized Na₂MoO₄ and gaseous S met and reacted on the surface of a second substrate (SiO₂ / Si, with a thermal oxide layer thickness of 285 nm), growing a second TMD film mainly composed of MoS₂. Furthermore, after natural cooling to room temperature, a second water-soluble ionic residue layer (composed of Na₂SO₄) was formed between the second substrate and the second TMD film. The Zn in the ZnS powder, under the salt-assisted CVD conditions, does not volatilize and does not come into contact with the second substrate; it remains in the ZnS powder and does not participate in the preparation of the second TMD film. The resulting structure is labeled as MoS₂ / Na₂SO₄ / SiO₂ / Si.

[0053] Next, PMMA A4 (molecular weight 500K, concentration 4 wt% anisole solution) was selected as the precursor solution for the support layer. The precursor solution was spin-coated at 3000 rpm on the surface of the second TMD film away from the second water-soluble ion residual layer for 60 s to obtain the PMMA layer. Then, it was baked on a hot stage at 120℃ for 5 min to cure the PMMA layer, which was labeled as PMMA / MoS2 / Na2SO4 / SiO2 / Si.

[0054] Then, PMMA / MoS2 / Na2SO4 / SiO2 / Si was placed in deionized water for the first water bath transfer, with a soaking time of 10 min. Taking advantage of the water solubility of the second water-soluble ion residual layer Na2SO4, the PMMA / MoS2 portion naturally separated from its own SiO2 / Si growth substrate, thus obtaining a MoS2 film independently supported by PMMA, i.e., the second stacked structure, labeled as PMMA / MoS2.

[0055] S3. Preparation of the third layered structure: The first stacked structure MoSe2 / Na2SeO4 / SiO2 / Si from step S1 was immersed in a petri dish containing non-aqueous liquid isopropanol (IPA) and spread evenly on the bottom of the petri dish. The second stacked structure PMMA / MoS2 obtained in step S2 was transferred into the IPA, at least partially floating on the surface of the IPA and at least partially suspended inside the IPA. The IPA was slowly removed, and as the liquid level dropped, PMMA / MoS2 slowly adhered to the surface of the MoSe2 film of the first stacked structure MoSe2 / Na2SeO4 / SiO2 / Si. After natural drying in air, a third stacked structure was obtained, labeled PMMA / MoS2 / MoSe2 / Na2SeO4 / SiO2 / Si.

[0056] In this step, since the entire process is carried out in an IPA (non-aqueous) environment, the contact between water and the first water-soluble ionic residual layer Na2SeO4 in the first stacked structure is avoided, thereby effectively preventing the first TMD thin film MoSe2 from prematurely detaching from the first substrate (SiO2 / Si) due to ionic salt dissolution during the stacking process.

[0057] S4. Preparation of the fourth layered structure: The third-layer structure, PMMA / MoS2 / MoSe2 / Na2SeO4 / SiO2 / Si, was placed in deionized water for a second water bath transfer, with a soaking time of 10 min. This allowed the first water-soluble ion-residual layer, Na2SeO4, to dissolve in the water, separating the PMMA / MoS2 / MoSe2 thin film from the original SiO2 / Si growth substrate. Subsequently, the PMMA / MoS2 / MoSe2 floating on the water surface was retrieved using the third substrate (SiO2 / Si) and transferred to its surface. After natural drying, the fourth-layer structure, labeled PMMA / MoS2 / MoSe2 / SiO2 / Si, was obtained.

[0058] S5. Preparation of the fifth layered structure: The fourth stacked structure PMMA / MoS2 / MoSe2 / SiO2 / Si obtained in step S4 was immersed in acetone solution for 12 hours to dissolve and remove the uppermost PMMA support layer. After removal, it was rinsed three times with isopropanol and dried with nitrogen to finally obtain the fifth stacked structure: a vertical heterojunction structure, labeled MoS2 / MoSe2 / SiO2 / Si.

[0059] Example 1 Performance Characterization and Result Analysis 1. The first TMD thin film MoSe2 grown in step S1 was characterized, and the results are shown in [the table below]. Figures 2 to 4 .

[0060] Optical microscope image ( Figure 2 The film surface appears uniform and continuous. Raman spectroscopy ( Figure 3 The characteristic peak E of in-plane vibration is displayed. 2g 1 Located at 298 cm -1 Out-of-plane vibration characteristic peak A 1g Located at 242 cm -1 ; PL spectrum ( Figure 4 The emission peak of the light source was located at 1.57 eV, which is consistent with the characteristics of MoSe2, proving that a high-quality MoSe2 film was successfully prepared.

[0061] 2. The second TMD thin film MoS2 grown in step S2 was characterized, and the results are shown in [the table below]. Figures 5 to 7 .

[0062] Optical microscope image ( Figure 5 The film quality is good; Raman spectroscopy ( Figure 6 E is displayed. 2g 1 The peak is located at 382 cm. -1 A 1g The peak is located at 404 cm. -1 ; PL spectrum ( Figure 7 The emission peak was found to be at 1.83 eV, which is consistent with the characteristics of MoS2, proving that a high-quality MoS2 film was successfully prepared.

[0063] X-ray photoelectron spectroscopy (XPS) analysis Figure 8 This confirmed the presence of Na2SO4 ions at the bottom of the grown MoS2 film. (See reference [link to relevant documentation] for details.) Figure 8 The Na 1s peak in (b). After the first water bath transfer, the XPS spectrum ( Figure 9 The complete disappearance of the Na 1s peak in the sample proves that water bath treatment can effectively and thoroughly remove residual ions.

[0064] 3. The MoS2 / MoSe2 vertical heterojunction in the fifth stacked structure MoS2 / MoSe2 / SiO2 / Si was characterized, and the results are shown in [Figure number missing]. Figures 10 to 13 .

[0065] Optical microscope image ( Figure 10 The Raman spectrum clearly shows the boundary between the heterojunction region (darker area) and the independent MoS2 and MoSe2 regions. Figure 11 The characteristic peak of MoS2 (E) was simultaneously detected in the heterojunction region spectrum (ii). 2g 1 382cm -1 and A 1g 404 cm -1 The characteristic peaks of MoSe2 (A) and MoSe2 1g 242 cm -1 and E 2g 1 298 cm -1 Furthermore, no other impurity peaks were observed, strongly demonstrating that the present invention successfully prepared a high-quality MoS2 / MoSe2 vertical heterojunction.

[0066] Figure 12 and Figure 13 This is a Kelvin probe force microscope (KPFM) scan of the surface potential of the heterojunction region. Multiple heterojunction regions exhibit significant color contrast compared to individual regions. Figure 12 Surface potential curve ( Figure 13 The results show that the surface potential of the heterojunction region is significantly lower than that of the independent MoS2 region, with a reduction of approximately 18–35 mV. This indicates that effective charge transfer (electrons transfer from MoS2 to MoSe2) occurs between the upper MoS2 and lower MoSe2 layers, confirming that the heterojunction interface has high-quality atomic-level coupling, laying the structural foundation for achieving excellent optoelectronic performance.

[0067] Example 2 Example 2 is a vertical heterojunction of transition metal chalcogenides prepared according to the process of Example 1, except that: in Example 2, Na2WO4 is used as the metal element precursor and ZnS is used as the chalcogen element precursor to prepare a first TMD film with WS2 as the main component, which is different from the first TMD film with MoSe2 as the main component in Example 1. In addition, the non-aqueous liquid isopropanol in step S3 for preparing the third stacked structure is replaced with n-hexane, and the final vertical heterojunction structure is labeled as MoS2 / WS2.

[0068] Example 2 Performance Characterization and Result Analysis 1. The vertical heterojunction structure MoS2 / WS2 was characterized, and the results are shown in the optical microscope images. Figure 14 ) and Raman spectroscopy ( Figure 15 ).

[0069] Specifically, optical microscope images ( Figure 14 The image shows the vertical heterojunction structure of MoS2 / WS2 prepared in Example 2, and its Raman spectrum ( Figure 15 The characteristic peak of MoS2 (E) was simultaneously detected in the heterojunction region. 2g 1 382 cm -1 and A 1g 404cm -1 ) and the characteristic peaks of WS2 (E) 2g 1 352 cm -1 and A 1g 420 cm -1 Furthermore, no other impurity peaks were observed, strongly demonstrating that the present invention successfully prepared a high-quality MoS2 / WS2 vertical heterojunction.

[0070] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for preparing a vertical heterojunction of a transition metal chalcogenide, characterized in that, Includes the following steps: S1. Preparation of the first layered structure: A first TMD thin film is prepared on the surface of a first substrate by salt-assisted CVD, and a first water-soluble ion residual layer is formed between the first substrate and the first TMD thin film to obtain a first stacked structure. The first stacked structure includes the first TMD thin film, the first water-soluble ion residual layer and the first substrate stacked sequentially. S2. Preparation of the second layered structure: A second TMD film is prepared on the surface of a second substrate by salt-assisted CVD. A second water-soluble ion residue layer is formed between the second substrate and the second TMD film. Then, a support layer is prepared on the surface of the second TMD film away from the second substrate. Next, the film is placed in deionized water for a first water bath transfer to remove the second water-soluble ion residue layer, thereby separating the second TMD film from the second substrate and obtaining a second stacked structure. The second stacked structure includes the support layer and the second TMD film stacked in sequence. S3. Preparation of the third layered structure: The first stacked structure and the second stacked structure are stacked in the same non-aqueous liquid, and the non-aqueous liquid is removed to obtain a third stacked structure. The third stacked structure includes the support layer, the second TMD film, the first TMD film, the first water-soluble ion residue layer, and the first substrate stacked in sequence. S4. Preparation of the fourth layered structure: The third stacked structure is placed in deionized water for a second water bath transfer to remove the first water-soluble ion residue layer, thereby separating the first TMD film from the first substrate to obtain a stacked structure. The stacked structure includes the support layer, the second TMD film, and the first TMD film stacked sequentially. The stacked structure is then transferred to the surface of the third substrate to obtain a fourth stacked structure. The fourth stacked structure includes the support layer, the second TMD film, the first TMD film, and the third substrate stacked sequentially. S5. Preparation of the fifth layered structure: Removing the support layer from the fourth stacked structure yields a fifth stacked structure, which includes a second TMD film, a first TMD film, and a third substrate stacked sequentially.

2. The method for preparing a vertical heterojunction of a transition metal chalcogenide according to claim 1, characterized in that, The materials used to prepare the first TMD film and the second TMD film include chalcogenide precursors and metal precursors.

3. The method for preparing a vertical heterojunction of transition metal chalcogenides according to claim 2, characterized in that, The metal element precursor includes at least one of Na2MoO4, Na2WO4, a mixture of MoO3 and NaCl, and a mixture of WO3 and NaCl.

4. The method for preparing a vertical heterojunction of transition metal chalcogenides according to claim 2, characterized in that, The chalcogen element precursors include at least one of S, Se, ZnS, and ZnSe.

5. The method for preparing a vertical heterojunction of a transition metal chalcogenide according to claim 1, characterized in that, The support layer includes PMMA.

6. The method for preparing a vertical heterojunction of a transition metal chalcogenide according to claim 1, characterized in that, The preparation process of the support layer is as follows: dissolve the material for preparing the support layer in a solvent to obtain a support layer precursor solution, spin coat the support layer precursor solution onto the surface of the second TMD film away from the second substrate, and then heat to remove the solvent.

7. The method for preparing a vertical heterojunction of a transition metal chalcogenide according to claim 1, characterized in that, The non-aqueous liquid includes at least one of isopropanol, n-hexane, and n-heptane.

8. The method for preparing a vertical heterojunction of a transition metal chalcogenide according to claim 1, characterized in that, The support layer was removed by steam fumigation. Alternatively, the support layer can be removed by immersion in an organic solvent, wherein the organic solvent includes one or more of acetone and anisole.

9. The method for preparing a vertical heterojunction of a transition metal chalcogenide according to claim 1, characterized in that, The substrate includes at least one of SiO2 / Si, sapphire, mica, and quartz.

10. A transition metal chalcogenide vertical heterojunction, characterized in that, The transition metal chalcogenide vertical heterojunction is prepared by the method for preparing a transition metal chalcogenide vertical heterojunction as described in any one of claims 1 to 9.

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