A method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction

Abstract

The present invention discloses a method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction. SnS powder is directly heated by a single molecular beam evaporation source. SnS molecules are directly deposited on an Au substrate in an ultra-high vacuum environment. The interaction between the SnS molecules and the Au substrate is utilized to directly prepare a two-dimensional planar vertical SnS / SnS2 heterojunction in one step. This technology uses an ultra-high vacuum molecular beam epitaxy method to deposit SnS molecules on the Au substrate. The growth environment of the SnS / SnS2 heterojunction is clean and free of impurity sources. The prepared SnS / SnS2 heterojunction has high purity and a simple growth mechanism. The present invention discloses a method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction. The prepared SnS / SnS2 heterojunction is a two-dimensional planar vertical SnS / SnS2 heterojunction, which is different from the nanocrystalline SnS / SnS2 heterojunction prepared by a one-step solvothermal method and a one-step phase-controlled synthesis. At the same time, the ultra-high vacuum molecular beam epitaxy method can also accurately control the morphology, number of layers and thickness of the two-dimensional planar vertical SnS / SnS2 heterojunction.

Description

Technical Field

[0001] The present invention relates to the technical field of heterojunctions, and in particular to a method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction. Background Art

[0002] In recent years, two-dimensional layered ferroelectric thin films have attracted extensive research attention due to their inherent ferroelectric polarization properties and potential applications in sensors, transistors, and memristors. Group IV monochalcogenides (SnS, GeS, SnSe, and SnSe) have garnered particular attention as a new family of ferroelectric materials. These compounds possess novel lattice structures, optical and electronic properties, and atomic structures similar to black phosphorus. Although numerous theoretical calculations have predicted their potential as two-dimensional ferroelectric materials, the preparation of single-layer or multilayer thin films and their heterojunction structures remains challenging due to strong interlayer interactions and relatively high exfoliation energies compared to other two-dimensional materials.

[0003] At present, the preparation methods of SnS / SnS2 heterojunction mainly include: one-step solvent thermal method and one-step phase-controlled synthesis of SnS / SnS2 heterojunction nanocrystals. Among them, the patent with publication number CN106006720A: A method for preparing SnS / SnS2 heterojunction materials and their application discloses a method for preparing SnS / SnS2 heterojunction materials using a solvent thermal method. The method uses SnCl2·2H2O and SnCl4·5H2O as tin sources, and is combined with a sulfur source and a surfactant to chemically react and control Sn 2+ With Sn 4+ The raw material ratio is adjusted to achieve the control of the ratio of SnS to SnS2 in the product, obtaining a SnS / SnS2 heterojunction material with a flower-like morphology. However, since the solution thermal method requires preparation in a specific solution, an unclean solution environment will result in poor single crystallinity of the prepared flower-shaped non-two-dimensional heterojunction. At the same time, since the chemical reaction occurs in the solution environment, it will cause the surface of the film to adsorb many substances in the solvent, resulting in the flower-shaped non-two-dimensional heterojunction itself and the surface being unclean, thereby affecting the two-dimensional ferroelectricity and physicochemical properties of SnS and causing changes in the performance of the corresponding device. At the same time, the heterojunction prepared by this method is a flower-shaped heterojunction.

[0004] Patent publication number CN102897827A: One-step phase-controlled synthesis of SnS, SnS2 or SnS / SnS2 heterojunction nanocrystalline materials, discloses a one-step phase-controlled synthesis of SnS / SnS2 heterojunction nanocrystals. This method utilizes a chemical reaction with tin diethyldithiocarbamate as an organic precursor of S, and changes the amount of CS2 added to the precursor to phase-control the synthesis of SnS, SnS2 or SnS / SnS2 nanocrystals. This method is still prepared in solution and has similar problems to the solvothermal method for preparing heterojunctions. At the same time, the phase-controlled method prepares non-two-dimensional planar nanocrystals, and its configuration diagram is shown as follows: Figure 2 As shown in a.

[0005] Therefore, the prior art of preparing SnS / SnS2 heterojunctions by a one-step solvothermal method and a one-step phase-controlled synthesis method has the technical defect that it is difficult to prepare a two-dimensional planar vertical SnS / SnS2 heterojunction. Summary of the Invention

[0006] The purpose of the present invention is to propose a method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction, which aims to solve the technical defects of the existing technology of preparing SnS / SnS2 heterojunction by a one-step solvothermal method and a one-step phase-controlled synthesis method, which is difficult to prepare a two-dimensional planar vertical SnS / SnS2 heterojunction.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] The present invention discloses a method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction, comprising:

[0009] S1. Raw material preparation: installing a molecular beam evaporation source containing SnS powder in a molecular beam epitaxial growth chamber, degassing the SnS powder, and adjusting the temperature of the molecular beam evaporation source to a first preset temperature;

[0010] S2. Preliminary degassing of the substrate: an Au substrate is placed in an ultra-high vacuum molecular beam epitaxy system and heated under a first preset condition;

[0011] S3. Further processing of the substrate: in an ultra-high vacuum molecular beam epitaxy system, bombarding the surface of the Au substrate with an Ar ion gun for a first preset time, and performing a high-temperature annealing treatment on the Au substrate under a second preset condition, and the processing flow is repeated multiple times;

[0012] S4. Heterojunction deposition: Preheat the Au substrate, heat the temperature of the molecular beam evaporation source to 450 ° C, and keep it for a second preset time. Open the mask and expose the Au substrate to the front end of the molecular beam evaporation source to facilitate SnS deposition on the surface of the Au substrate to form a two-dimensional planar vertical SnS / SnS2 heterojunction.

[0013] Wherein, in step S1, the first preset temperature is 300-600°C.

[0014] Wherein, before step S2, the method further includes: cleaning the Au substrate with a solvent and deionized water in sequence.

[0015] Preferably, the solvent includes: one or more combinations of hydrochloric acid, sulfuric acid, acetone, and alcohol.

[0016] In step S2, the first preset conditions include: heating temperature of 200°C, vacuum degree of 1×10 -9 mbar.

[0017] Wherein, in step S3, the first preset time is 8-20 min; the second preset conditions include: the processing time is 8-20 min, and the processing temperature is 300-500°C.

[0018] In step S4, the Au substrate is preheated, including: performing a first heating treatment on the Au substrate in an ultra-high vacuum molecular beam epitaxy system to ensure that the Au substrate is heated evenly.

[0019] Preferably, the conditions of the first heat treatment include: a heating temperature of 150-300° C. and a heating time of 20-40 min.

[0020] Wherein, in step S4, the second preset time is 15-30 minutes.

[0021] The present technical solution discloses a method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction, which directly prepares a two-dimensional planar vertical SnS / SnS2 heterojunction on a specific metal substrate in one step by directly heating SnS powder through ultra-high vacuum molecular beam epitaxy combined with a single molecular beam evaporation source. The preparation method prepares the SnS / SnS2 heterojunction in an ultra-high vacuum environment without the problem of solution contamination. At the same time, only a single SnS powder is used as the growth material. During the preparation process, SnS and SnS2 layered films grow layer by layer to form a two-dimensional planar vertical SnS / SnS2 heterojunction. The prepared SnS / SnS2 heterojunction has a completely planar structure. The schematic diagram of the structure of the SnS / SnS2 heterojunction prepared in this application is shown in FIG. Figure 2 As shown in b. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 A flow chart of a method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction disclosed in an embodiment of the present invention;

[0024] Figure 2 Schematic diagrams of the structures of SnS / SnS2 heterojunctions in different forms disclosed in the embodiments of the present invention, wherein (a) is a nanocrystalline SnS / SnS2 heterostructure type, and (b) is a two-dimensional planar vertical SnS / SnS2 heterostructure type;

[0025] Figure 3 This is an STM scanning result diagram of the Au substrate after treatment disclosed in an embodiment of the present invention;

[0026] Figure 4 This is the STM scanning result of the first SnS2 thin film disclosed in the embodiment of the present invention;

[0027] Figure 5 This is an STM scanning result diagram of the second SnS2 thin film disclosed in an embodiment of the present invention;

[0028] Figure 6 This is an STM scanning result diagram of the third SnS film disclosed in an embodiment of the present invention;

[0029] Figure 7 High-resolution X-ray photoelectron spectroscopy (XPS) images of the first SnS2 thin film, the second SnS2 thin film, and the third SnS thin film disclosed in the embodiment of the present invention; DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0031] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0033] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] The present invention discloses a method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction, such as Figure 1 Shown, including:

[0035] S1. Raw material preparation: Install a molecular beam evaporation source containing SnS powder in a molecular beam epitaxial growth chamber, degas the SnS powder, and adjust the temperature of the molecular beam evaporation source to a first preset temperature to remove moisture and impurities whose evaporation temperature is lower than the SnS growth temperature; wherein the first preset temperature is 300-600°C;

[0036] S2. Preliminary degassing of substrate: Place the Au substrate in the ultra-high vacuum molecular beam epitaxy system and heat the Au substrate under the first preset conditions to remove gas molecules and impurities adsorbed on the surface of the Au substrate; wherein the first preset conditions include: heating temperature of 200 °C, vacuum degree of 1×10 -9 mbar;

[0037] S3. Further substrate processing: In an ultra-high vacuum molecular beam epitaxy system, bombarding the surface of the Au substrate with an Ar ion gun for a first preset time, and performing a high-temperature annealing treatment on the Au substrate under second preset conditions. The processing process is repeated multiple times, and the surface of the Au substrate becomes a single crystal surface. The substrate is further processed until the surface of the Au substrate is clean and suitable for growing the target thin film; wherein the first preset time is 8-20 minutes; the second preset conditions include: a processing time of 8-20 minutes and a processing temperature of 300-500°C;

[0038] S4. Heterojunction deposition: In an ultra-high vacuum molecular beam epitaxy system, preheat the Au substrate and heat the molecular beam evaporation source to 450°C to reach the SnS molecular evaporation temperature for 15-30 minutes. Then, open the mask and expose the Au substrate to the front end of the molecular beam evaporation source. As the temperature of the molecular beam evaporation source increases and reaches the SnS molecular evaporation temperature, the SnS raw material in the molecular beam evaporation source evaporates and is deposited on the surface of the Au substrate, forming a two-dimensional planar vertical SnS / SnS2 heterojunction.

[0039] Before step S2, the process further includes: cleaning the Au substrate with a solvent and deionized water in sequence. In this embodiment, the solvent includes one or more combinations of hydrochloric acid, sulfuric acid, acetone, alcohol, etc., but is not limited thereto.

[0040] In step S4, preheating the Au substrate includes performing a first heat treatment on the Au substrate in an ultra-high vacuum molecular beam epitaxy system to uniformly heat the Au substrate and facilitate the diffusion, bonding, and film growth of SnS molecules on its surface. Specifically, the first heat treatment conditions are: a heating temperature of 150-300°C and a heating time of 20-40 minutes. Specific embodiments

[0042] The steps for preparing the SnS / SnS2 heterojunction in this embodiment are as follows:

[0043] S1. Raw material preparation: Install a molecular beam evaporation source filled with SnS powder in the molecular beam epitaxial growth chamber, degas the SnS powder in the molecular beam evaporation source, and adjust the temperature of the molecular beam evaporation source to 450°C to remove moisture and impurities whose evaporation temperature is lower than the SnS growth temperature;

[0044] S2. Preliminary degassing of the substrate: Use hydrochloric acid, sulfuric acid, acetone, alcohol, and deionized water to clean the Au substrate in sequence. Place the cleaned Au substrate into the ultra-high vacuum molecular beam epitaxy system and adjust the vacuum degree in the system to 1×10 -9 mbar, and heated the Au substrate at 200 °C to remove gas molecules and impurities adsorbed on the surface of the Au substrate;

[0045] S3. Further processing of the substrate: In an ultra-high vacuum molecular beam epitaxy system, the surface of the Au substrate was bombarded with an Ar ion gun for 10 minutes, and then the Au substrate was subjected to a high-temperature annealing treatment at 400°C for 15 minutes. The treatment process was repeated many times, and the surface of the Au substrate became a single crystal surface. The Au substrate was further processed until the surface of the Au substrate was clean and suitable for growing the target film. The STM scanning results of the Au substrate after further processing are as follows: Figure 3 As shown;

[0046] S4. Heterojunction deposition: In an ultra-high vacuum molecular beam epitaxy system, preheat the Au substrate and heat the molecular beam evaporation source to 450°C to reach the SnS molecular evaporation temperature for 20 minutes. Then, open the mask and expose the Au substrate to the front end of the molecular beam evaporation source to facilitate SnS deposition on the substrate surface to form a thin film. As the temperature of the molecular beam evaporation source increases, the SnS raw material in the molecular beam evaporation source evaporates and is deposited on the surface of the Au substrate.

[0047] Specifically, the growth mechanism of SnS film is as follows: Since the orthorhombic lattice structure of SnS is inconsistent with the lattice structure of Au substrate, and S and Au have a strong interaction, stress is introduced at the interface. Under the action of this interface stress and S-Au bond, the first layer is formed as a buffer layer with defects: the first layer of SnS2 film, the STM scanning results of the first layer of SnS2 film are as follows Figure 4 As shown in the figure, as the reaction proceeds, SnS molecules continue to deposit on the surface of the first SnS2 film to form a second SnS2 film. Due to the basic release of stress and the isolation of the interface layer, the S-Au bond effect is weakened, and a large area SnS2 film without defects is formed in the second layer. The STM scanning results of the second SnS2 film are shown in the figure. Figure 5 As shown; as the reaction continues, SnS molecules are deposited on the surface of the second SnS2 film to form a third SnS film. Due to the epitaxial effect of the van der Waals force, the third SnS film has a large area and no defects. Figure 6 As shown, the first SnS2 film layer, the second SnS2 film layer, and the third SnS film layer are stacked to construct a two-dimensional planar vertical SnS / SnS2 heterojunction with a multi-layer thin film structure.

[0048] In order to verify the elemental composition and element ratio of the constructed film, high-resolution X-ray photoelectron spectroscopy (XPS) characterization was performed on the first layer of SnS2 film, the second layer of SnS2 film, and the third layer of SnS film. The characterization results are shown in Figure 2. Figure 7As shown in the figure, the XPS spectrum shows that only S and Sn elements are present in the film, indicating that the film was successfully prepared. Using CasaXPS software, a Gaussian / Lorentzian mixed function was used to fit the data while simultaneously fixing the spacing between the two spin-orbit splitting peaks and the area ratio of the two peaks. The fitting results show that the first SnS2 film layer, the second SnS2 film layer, and the third SnS film layer are defective SnS2 film, defect-free SnS2 film, and SnS film, respectively.

[0049] The technical solution discloses a method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction, which uses a molecular beam evaporation source to directly heat SnS powder, and directly deposits SnS molecules on an Au substrate in an ultra-high vacuum environment. The interaction between the SnS molecules and the Au substrate is used to directly prepare a two-dimensional planar vertical SnS / SnS2 heterojunction in one step. This technology adopts a physical preparation method: ultra-high vacuum molecular beam epitaxy to prepare a two-dimensional planar vertical SnS / SnS2 heterojunction. The growth environment of the SnS / SnS2 heterojunction is clean and free of impurity sources. The prepared SnS / SnS2 heterojunction has high purity and a simple growth mechanism. The present invention discloses a method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction. The prepared SnS / SnS2 heterojunction is a two-dimensional planar vertical SnS / SnS2 heterojunction, which is different from the nanocrystalline SnS / SnS2 heterojunction prepared by a one-step solvothermal method and a one-step phase-controlled synthesis. At the same time, the ultra-high vacuum molecular beam epitaxy method can also accurately control the morphology, number of layers and thickness of the two-dimensional planar vertical SnS / SnS2 heterojunction.

[0050] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are intended solely to illustrate the principles of the present invention and are not to be construed in any way as limiting the scope of protection of the present invention. Based on the explanations herein, those skilled in the art will readily conceive of other specific embodiments of the present invention without inventive effort, and such embodiments will fall within the scope of protection of the present invention.

Claims

1. A method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction, characterized in that: include: S1. Raw material preparation: installing a molecular beam evaporation source containing SnS powder in a molecular beam epitaxial growth chamber, degassing the SnS powder, and adjusting the temperature of the molecular beam evaporation source to a first preset temperature; S2. Preliminary degassing of the substrate: an Au substrate is placed in an ultra-high vacuum molecular beam epitaxy system and heated under a first preset condition; S3. Further processing of the substrate: in an ultra-high vacuum molecular beam epitaxy system, bombarding the surface of the Au substrate with an Ar ion gun for a first preset time, and performing a high-temperature annealing treatment on the Au substrate under a second preset condition, and the processing flow is repeated multiple times; S4. Heterojunction deposition: Preheat the Au substrate, heat the temperature of the molecular beam evaporation source to 450°C and maintain it for a second preset time, open the mask, and expose the Au substrate to the front end of the molecular beam evaporation source to facilitate SnS deposition on the surface of the Au substrate to form a two-dimensional planar vertical SnS / SnS2 heterojunction.

2. The method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction according to claim 1, characterized in that: In step S1, the first preset temperature is 300-600°C.

3. The method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction according to claim 1, characterized in that: Before step S2, the method further includes: cleaning the Au substrate using a solvent and deionized water in sequence.

4. The method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction according to claim 3, characterized in that: The solvent includes: one or more combinations of hydrochloric acid, sulfuric acid, acetone, and alcohol.

5. The method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction according to claim 1, characterized in that: In step S2, the first preset conditions include: heating temperature of 200°C, vacuum degree of 1×10 -9 mbar.

6. The method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction according to claim 1, characterized in that: In step S3, the first preset time is 8-20 minutes; The second preset conditions include: a processing time of 8-20 minutes and a processing temperature of 300-500°C.

7. The method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction according to claim 1, characterized in that: In step S4, the Au substrate is preheated, including: performing a first heating treatment on the Au substrate in an ultra-high vacuum molecular beam epitaxy system to ensure that the Au substrate is heated evenly.

8. The method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction according to claim 7, characterized in that: The conditions of the first heat treatment include: a heating temperature of 150-300° C. and a heating time of 20-40 minutes.

9. The method for preparing a two-dimensional planar vertical SnS / SnS2 heterojunction according to claim 1, characterized in that: In step S4, the second preset time is 15-30 minutes.

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