Low-dimensional mixed-dimensional heterojunctions, methods of making and uses thereof

Abstract

The application discloses a low-dimensional mixed-dimension heterojunction and a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing a transition metal oxide and an alkaline solution to obtain a precursor solution; (2) coating the precursor solution on a substrate surface, and supplying the obtained substrate and a sulfur family element to a protective reducing atmosphere for heating treatment, so as to form a transition metal sulfur family compound layer on the substrate surface; and (3) performing oxygen plasma treatment on the transition metal sulfur family compound layer, so as to form transition metal oxide nanowires on the surface of the transition metal sulfur family compound layer, and obtain the low-dimensional mixed-dimension heterojunction. The method is simple in preparation process, time-saving and efficient, and the prepared low-dimensional mixed-dimension heterojunction has high molecular detection sensitivity and good environmental stability.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology, specifically relating to low-dimensional mixed-dimensional heterostructures, their preparation methods, and applications. Background Technology

[0002] Surface-enhanced Raman scattering (SERS) is a rapid, sensitive, and non-destructive detection technique that has attracted widespread attention in numerous fields, such as environmental monitoring, chemical catalysis, and bio / medical sensing. One of the most important metrics for evaluating the sensitivity of SERS substrates is the detection limit, i.e., the lowest detectable concentration of molecules. In some fields (such as clinical diagnostics, DNA sequencing, and chemical analysis), the sensitivity of molecular detection needs to reach the femtomolar or even atmolar levels. Noble metal-based nanomaterials and nanostructures offer extensive research possibilities in this field; however, limited noble metal resources and the low surface uniformity of their nanomaterials severely hinder the practical application of such materials. In recent years, two-dimensional transition metal dichalcogenides (TMDCs) have been widely used in SERS substrate research due to their atomically flat surfaces and good chemical stability. Unlike the electromagnetic enhancement mechanism of traditional noble metal-based nanomaterials, the enhancement mechanism of TMDCs as SERS substrates is mainly chemical, attributed to charge transport between the detection substrate and the target molecule. However, achieving ultrasensitive molecular detection on two-dimensional material SERS substrates remains a significant challenge. Summary of the Invention

[0003] This invention is primarily based on the following problems and findings:

[0004] Two-dimensional transition metal chalcogenides (TMCs) offer unique integrated tunability for enhancing performance, but the synthesis of TMC-based low-dimensional mixed-dimensional heterojunctions is challenging, hindering their practical application. Currently, various methods for preparing low-dimensional mixed-dimensional heterojunctions have been disclosed, but these typically require complex and precise procedures and stringent reaction conditions. For example, some methods use mechanical exfoliation and transfer to stack one-dimensional materials and two-dimensional TMCs in a specific order and angle to form vertical heterojunctions, but large-scale production is difficult. Other methods use chemical vapor deposition to synthesize large-area TMC-based low-dimensional mixed-dimensional heterojunctions, but these methods have low controllability and reproducibility. Therefore, a simple and efficient method for preparing low-dimensional mixed-dimensional heterojunctions is urgently needed.

[0005] This invention aims to at least partially address one of the technical problems in related technologies. Therefore, one objective of this invention is to propose a low-dimensional hybrid heterojunction, its preparation method, and its applications. This method is not only simple, time-saving, and efficient in its preparation process, but also yields a low-dimensional hybrid heterojunction with high molecular detection sensitivity and good environmental stability.

[0006] In one aspect of the invention, a method for preparing low-dimensional mixed-dimensional heterojunctions is provided. According to an embodiment of the invention, the method includes:

[0007] (1) The transition metal oxide and alkaline solution are mixed to obtain a precursor solution;

[0008] (2) The precursor solution is coated on the substrate surface, and the obtained substrate and chalcogenide are supplied to a protective reducing atmosphere for heating treatment so as to form a transition metal chalcogenide layer on the substrate surface.

[0009] (3) The transition metal chalcogenide layer is subjected to oxygen plasma treatment to form transition metal oxide nanowires on the surface of the transition metal chalcogenide layer, thereby obtaining a low-dimensional mixed-dimensional heterojunction.

[0010] The method for preparing low-dimensional hybrid heterojunctions according to the above embodiments of the present invention selectively converts the target region of two-dimensional transition metal sulfides into one-dimensional transition metal oxide nanowires through an oxygen plasma post-processing technique, resulting in a low-dimensional hybrid heterojunction structure. This method is not only simple and efficient, enabling mass production, but also offers good controllability and high reproducibility in heterojunction preparation. Furthermore, the one-dimensional / two-dimensional heterojunction obtained by this method exhibits strain at the interface of the one-dimensional transition metal oxide nanowires, and strong interlayer coupling between the one-dimensional transition metal oxide and the two-dimensional transition metal sulfide, promoting effective charge transport between the surface-enhanced Raman scattering substrate and the detector molecules. This endows it with highly sensitive molecular detection performance and good environmental stability. Moreover, the low-dimensional hybrid heterojunction obtained by this method shows promising applications in DNA sequencing, lasers, semiconductor devices, clean energy, and energy storage devices.

[0011] In addition, the method for preparing low-dimensional mixed-dimensional heterojunctions according to the above embodiments of the present invention may also have the following additional technical features:

[0012] In some embodiments of the present invention, the transition metal oxide, the alkaline solution, and the alkali metal salt are subjected to the mixing treatment.

[0013] In some embodiments of the present invention, in step (1), the transition metal oxide includes tungsten trioxide and / or molybdenum trioxide.

[0014] In some embodiments of the present invention, in step (1), the alkaline solution is an aqueous ammonia solution.

[0015] In some embodiments of the present invention, in step (1), the mixing process is carried out at a temperature of 60-80°C for 30-90 minutes.

[0016] In some embodiments of the present invention, in step (1), the concentration of the transition metal oxide in the precursor solution is (1-20) mg / mL.

[0017] In some embodiments of the present invention, in step (1), the mass ratio of the transition metal oxide to the metal salt is 8:(1-5).

[0018] In some embodiments of the present invention, in step (1), the alkali metal salt includes at least one of sodium chloride, sodium iodide and potassium iodide.

[0019] In some embodiments of the present invention, in step (2), the number of layers of the transition metal chalcogenide layer is a single layer and / or a few layers.

[0020] In some embodiments of the present invention, in step (2), the heat treatment is carried out in a tube furnace, the chalcogenide is placed at the upper gas flow of the substrate, and the heating temperature of the chalcogenide is controlled to be lower than the heating temperature of the substrate.

[0021] In some embodiments of the present invention, in step (2), the substrate is made of at least one of silicon wafer, Al2O3, and silicate.

[0022] In some embodiments of the present invention, in step (2), the chalcogenide is selected from selenium powder and / or sulfur powder.

[0023] In some embodiments of the present invention, in step (2), the protective reducing atmosphere includes a protective gas and a reducing gas, wherein the protective gas includes nitrogen and / or an inert gas, and the reducing gas includes hydrogen.

[0024] In some embodiments of the present invention, the heating treatment includes a heating stage and a holding stage, wherein the heating stage is performed under the protective gas atmosphere and the holding stage is performed under the protective reducing atmosphere.

[0025] In some embodiments of the present invention, the volumetric flow rate of the protective gas in the heating treatment is 80 to 240 sccm.

[0026] In some embodiments of the present invention, the volumetric flow rate of the reducing gas is 4 to 30 sccm.

[0027] In some embodiments of the present invention, during the heat preservation stage, the ratio of the volumetric flow rate of the protective gas to the volumetric flow rate of the reducing gas is (10-20):1.

[0028] In some embodiments of the present invention, in step (2), the chalcogenide is selenium powder, and the heating temperature of the selenium powder is 340-450°C.

[0029] In some embodiments of the present invention, in step (2), the chalcogenide is selenium powder, and the heat treatment of the substrate is held at a temperature of 750-850°C for 3-10 minutes.

[0030] In some embodiments of the present invention, in step (3), the oxygen plasma treatment is performed at a frequency of 40 kHz for a duration of 2 to 75 s.

[0031] In some embodiments of the present invention, the length of the transition metal oxide nanowire is 1 to 4 μm and the diameter is 0.01 to 0.3 μm.

[0032] In another aspect of the invention, a low-dimensional hybrid heterojunction prepared using the above-described method is proposed. According to an embodiment of the invention, the heterojunction comprises: a substrate, a transition metal chalcogenide layer, and transition metal oxide nanowires, wherein the transition metal chalcogenide layer is located on the surface of the substrate, and the transition metal oxide nanowires are located on the surface of the transition metal chalcogenide layer on the side away from the substrate. Compared with the prior art, this low-dimensional hybrid heterojunction not only has a simple and efficient preparation process, but also possesses better molecular detection performance and better environmental stability, significantly improving the detection sensitivity of surface-enhanced Raman scattering. Furthermore, this low-dimensional hybrid heterojunction also shows promising application prospects in fields such as DNA sequencing, lasers, semiconductor devices, clean energy, and energy storage devices.

[0033] In some embodiments of the present invention, the length of the transition metal oxide nanowire is 1 to 4 μm and the diameter is 0.01 to 0.3 μm.

[0034] In some embodiments of the present invention, the transition metal chalcogenide layer is a tungsten diselenide and / or a molybdenum diselenide layer, and the transition metal oxide nanowires are tungsten oxide nanowires and / or molybdenum oxide nanowires.

[0035] In some embodiments of the present invention, the transition metal oxide nanowires are arranged in a triple-symmetric preferred orientation array on the surface of the transition metal chalcogenide layer.

[0036] In another aspect, the present invention proposes applications of the above-described method and / or the above-described low-dimensional hybrid heterojunction in the fields of surface-enhanced Raman scattering detection, DNA sequencing, lasers, semiconductor devices, clean energy, and energy storage devices. This application possesses all the technical features and effects of the above-described method for preparing low-dimensional hybrid heterojunctions and / or the above-described low-dimensional hybrid heterojunctions, which will not be elaborated further here. In summary, the method and / or the low-dimensional hybrid heterojunction can significantly reduce the detection concentration limit of surface-enhanced Raman scattering substrates, improve the detection sensitivity of surface-enhanced Raman scattering, and exhibit good environmental stability, thus showing promising practical application prospects in the aforementioned fields.

[0037] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0038] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0039] Figure 1 This is a flowchart of a method for preparing a low-dimensional mixed-dimensional heterostructure according to an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of an apparatus for preparing transition metal chalcogenides according to an embodiment of the present invention;

[0041] Figure 3 This is a schematic diagram illustrating the oxygen plasma processing principle for preparing low-dimensional mixed-dimensional heterojunctions according to an embodiment of the present invention.

[0042] Figure 4 This is an optical microscope image of the tungsten diselenide layer formed according to Comparative Example 1 of the present invention;

[0043] Figure 5 This is an optical microscope image of the tungsten diselenide layer formed according to Comparative Example 2 of the present invention;

[0044] Figure 6 These are high-angle annular dark-field scanning transmission electron microscope images of one-dimensional transition metal oxide (tungsten oxide) nanowires prepared according to Example 1 of the present invention, wherein... Figure 6 a, b, and c in the image are high-angle annular dark-field scanning transmission electron microscope images of a one-dimensional nanowire at different magnifications.

[0045] Figure 7 These are high-angle annular dark-field scanning transmission electron microscope images of one-dimensional transition metal oxide (tungsten oxide) nanowires prepared according to Example 2 of the present invention, wherein... Figure 7a, b, and c are high-angle annular dark-field scanning transmission electron microscope images of a one-dimensional nanowire at different magnifications;

[0046] Figure 8 This is a scanning electron microscope image of the final product obtained according to Example 1 of the present invention;

[0047] Figure 9 This is a scanning electron microscope image of the final product obtained according to Comparative Example 3 of the present invention.

[0048] Figure 10 This is a geometric phase analysis diagram of the one-dimensional tungsten oxide nanowires prepared according to Example 1 of the present invention;

[0049] Figure 11 This is an electron diffraction image of the final product obtained according to Example 1 of the present invention;

[0050] Figure 12 This is a comparison of the Raman detection spectrum curves of the final products obtained according to Examples 2 and 5 and Comparative Examples 2 and 4 of the present invention at the same detection concentration.

[0051] Figure 13 This is a comparison of the Raman spectra of the final product obtained in Example 2 of the present invention when detecting different concentrations of methylene blue molecules.

[0052] Figure 14 This is a comparison of the Raman spectra of the final product prepared according to Comparative Example 2 of the present invention when detecting different concentrations of methylene blue molecules.

[0053] Figure 15 This is a comparison of the Raman spectra of the final product prepared according to Example 1 of the present invention when detecting different concentrations of methylene blue molecules;

[0054] Figure 16 This is a comparison of the Raman spectra of methylene blue molecules obtained by excitation on the surface of the final product prepared in Example 1 of the present invention after being placed in air for different times;

[0055] Figure 17 This is a comparison of the Raman spectra of the final product prepared according to Example 6 of the present invention and the final product prepared in Comparative Example 5 without oxygen plasma treatment. Detailed Implementation

[0056] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0057] In one aspect of the invention, a method for preparing low-dimensional mixed-dimensional heterojunctions is provided. According to an embodiment of the invention, the method includes:

[0058] S100: A precursor solution is obtained by mixing a transition metal oxide with an alkaline solution.

[0059] According to embodiments of the present invention, by mixing transition metal oxides and alkaline solutions, a well-dispersed and uniform precursor solution can be obtained, providing a basis for the subsequent acquisition of transition metal chalcogenides. It should be noted that the present invention does not impose any particular limitation on the specific type of transition metal oxides, and those skilled in the art can flexibly select them according to the actual situation. For example, transition metal oxides may include tungsten trioxide and / or molybdenum trioxide, both of which can dissolve in alkaline solutions to generate transition metal salts, which is beneficial to promoting the reaction between the precursor and the chalcogenide elements in subsequent steps. Furthermore, the present invention does not impose any particular limitation on the specific type of alkaline solution, and those skilled in the art can flexibly select it according to the actual situation, such as an ammonia solution.

[0060] According to embodiments of the present invention, transition metal oxides, alkaline solutions, and alkali metal salts can be mixed to obtain a precursor solution. Introducing alkali metal salts allows them to combine with transition metal oxides to form intermediate products with lower melting points, which is beneficial for promoting the growth of transition metal chalcogenides in subsequent processing. Furthermore, the present invention does not impose any particular limitation on the specific type of alkali metal salt; those skilled in the art can choose flexibly according to actual conditions. For example, it can include at least one of sodium chloride, sodium iodide, and potassium iodide, preferably sodium chloride, which is not only widely available and low in cost but also more conducive to promoting the growth of transition metal chalcogenides. Additionally, according to embodiments of the present invention, the mass ratio of transition metal oxides to metal salts can be 8:(1-5), for example, 8:2, 8:3, or 8:4. The inventors have found that if the mass ratio of transition metal oxides to metal salts is too large, the size of the formed transition metal chalcogenides is too small; if the mass ratio is too small, the thickness of the formed transition metal chalcogenides is too large. Both excessively small and excessively thick transition metal chalcogenide layers will affect the sensitivity of molecular detection, limiting its performance and application prospects. By controlling the mass ratio of transition metal oxides and metal salts within the above-mentioned range, this invention facilitates the obtaining of a transition metal chalcogenide layer with moderate and uniform thickness, which in turn facilitates the obtaining of a stable low-dimensional mixed-dimensional heterojunction.

[0061] According to an embodiment of the present invention, the mixing temperature can be 60-80°C and the time can be 30-90 min. This not only promotes the dissolution of transition metal oxides and metal salts in alkaline solution, but also avoids energy waste caused by excessively high mixing temperature or excessively long mixing time.

[0062] According to embodiments of the present invention, the concentration of the transition metal oxide in the precursor solution can be (1-20) mg / mL, for example, 5 mg / mL, 10 mg / mL, 15 mg / mL, or 18 mg / mL. The inventors have found that if the concentration of the transition metal oxide is too low, the resulting transition metal chalcogenide layer is small; if the concentration is too high, it easily leads to an excessive number and thickness of transition metal chalcogenide layers, affecting their performance. The present invention, by controlling the concentration of the transition metal oxide in the precursor solution within the above-mentioned range, is more conducive to obtaining single-layer or few-layer transition metal chalcogenides, providing a foundation for subsequent low-dimensional mixed-dimensional heterojunctions.

[0063] S200: A precursor solution is coated onto the substrate surface, and the resulting substrate and chalcogenide are subjected to heat treatment under a protective reducing atmosphere to form a transition metal chalcogenide layer on the substrate surface.

[0064] According to an embodiment of the present invention, a substrate coated with a precursor is heated and reacted with a chalcogenide in a protective reducing atmosphere to obtain a transition metal chalcogenide layer grown on the substrate surface. The obtained transition metal chalcogenide can be a single crystal structure. There are no special requirements for the coating method of the precursor solution on the substrate surface. Those skilled in the art can flexibly choose according to the actual situation, such as spin coating.

[0065] According to embodiments of the present invention, the specific material of the substrate is not particularly limited, and those skilled in the art can flexibly select it according to actual conditions. For example, the substrate material may include at least one of silicon wafers, Al2O3, and silicates. Specifically, the substrate material may be SiO2 / Si, mica, sapphire, water glass, etc. Furthermore, the specific type of chalcogenide in the present invention is not particularly limited, and those skilled in the art can flexibly select it according to actual conditions. For example, the chalcogenide may be selected from selenium powder and / or sulfur powder, etc. In addition, the transition metal chalcogenide compound obtained by the preparation process of the present invention also has a layered structure. This layered structure is preferably a single-layer or few-layer structure, wherein the few layers may be no more than three layers. Specifically, it can be flexibly controlled by controlling the process parameters, which is more conducive to providing a foundation for subsequently obtaining low-dimensional mixed-dimensional heterojunctions.

[0066] According to embodiments of the present invention, the protective reducing atmosphere may include a protective gas and a reducing gas, wherein there are no particular limitations on the specific types of the protective gas and the reducing gas, and those skilled in the art can flexibly select them according to the actual situation. For example, the protective gas may include nitrogen and / or an inert gas, and the reducing gas may include hydrogen. In addition, the heating treatment may include a heating stage and a holding stage, wherein the heating stage can be carried out under a protective gas atmosphere to avoid introducing impurities that may affect the purity of the product, and the holding stage can be carried out under a protective reducing atmosphere to enhance the reducing properties of the reaction atmosphere and promote the reduction reaction.

[0067] According to embodiments of the present invention, during the heating and heat preservation processes, the flow rate of the protective gas can be 80–240 sccm, for example, 100 sccm, 150 sccm, 180 sccm, 200 sccm, or 230 sccm, etc., and the volumetric flow rate of the reducing gas can be 4–30 sccm, for example, 5 sccm, 8 sccm, 10 sccm, 15 sccm, 20 sccm, 25 sccm, etc. The inventors have found that if the volumetric flow rate of the reducing gas is too small, there will be insufficient reducing gas in the reaction environment, which may lead to incomplete reduction of the transition metal oxides; if the volumetric flow rate of the reducing gas is too large, ... A high concentration of reducing gas may cause excessive etching on the surface of the transition metal chalcogenide (TMC) or result in an excessively thick TMC layer. Conversely, if the volumetric flow rate of the protective gas is too low, fewer chalcogenides will be introduced, leading to a low concentration of chalcogenides reacting with the precursor on the substrate, resulting in insufficient reduction of the transition metal oxide. Conversely, if the volumetric flow rate of the protective gas is too high, more chalcogenides will be introduced. Excessive chalcogenides may react with unevaporated precursors, forming non-volatile substances that coat the precursor surface and hinder the reaction. Alternatively, excessive chalcogenide deposition on the precursor surface may also impede the formation of a uniform TMC layer. This invention, by controlling the volumetric flow rates of the protective and reducing gases within the aforementioned ranges, is more conducive to controlling the stable and uniform growth of the TMC. Furthermore, during the heat preservation stage, the ratio of the volumetric flow rate of the protective gas to the volumetric flow rate of the reducing gas can be (10-20):1, for example, 12:1, 14:1, 16:1 or 18:1, which is more conducive to controlling the appropriate concentration of reducing gas and chalcogens, while avoiding or reducing the risk of introducing impurities.

[0068] According to embodiments of the present invention, the heat treatment can be carried out in a tube furnace. The present invention does not impose any particular restrictions on the specific type of tube furnace or the heating method; those skilled in the art can flexibly select according to actual circumstances. For example, according to some specific examples of the present invention, combined with… Figure 2It is understood that a multi-temperature zone tubular furnace can be used. This allows for zoned heating of the furnace, resulting in a higher temperature in the center and lower temperatures at both ends. There are no particular limitations on the heating rate of the tubular furnace; those skilled in the art can choose flexibly according to the actual situation, for example, 5–20 °C / min. After reaching the target temperature, the temperature inside the tubular furnace is kept constant. The substrate coated with the precursor is placed in the center of the furnace, while the chalcogenide is placed above the substrate in the gas flow path. This ensures that the heating temperature of the chalcogenide is lower than the heating temperature of the substrate, allowing the chalcogenide to volatilize at a lower temperature and react with the precursor in gaseous form at a higher temperature. Specifically, the holding temperature of the substrate can be 750–850°C, for example, 780°C, 800°C, 820°C, or 840°C, and the holding time can be 3–10 minutes, for example, 5 minutes, 7 minutes, or 9 minutes. The inventors have found that if the holding temperature of the substrate is too low during the holding stage, it is easy to cause insufficient reaction and result in a small size of the obtained transition metal chalcogenide; if the holding temperature of the substrate is too high, it is easy to cause the transition metal chalcogenide layer to be too thick, affecting its practicality; if the holding time is too short, it is easy to cause a small amount of chalcogenide to be introduced, resulting in some precursors not reacting, and also reducing the degree of reaction; if the holding time is too long, it is easy to cause an excess of chalcogenide, resulting in an excessively thick transition metal chalcogenide layer. In this invention, controlling the temperature during the heat preservation stage within the aforementioned range is more conducive to obtaining a moderately thick and uniform transition metal chalcogenide layer, which in turn facilitates the formation of a stable low-dimensional mixed-dimensional heterojunction structure. Simultaneously, when selenium powder is used as the chalcogenide element, the heating temperature of the selenium powder can be 340–450°C, for example, 350°C, 380°C, 400°C, or 430°C. The inventors have found that if the heating temperature of the selenium powder is too low, it is difficult to achieve effective volatilization, easily leading to insufficient selenium powder concentration in the gas-phase reaction. If the heating temperature of the selenium powder is too high, the gas-phase concentration of the selenium powder is easily too high, resulting in an excessively thick transition metal chalcogenide layer. This invention, by controlling the heating temperature of the selenium powder within the aforementioned range, can effectively control the volatilization rate of the selenium powder, thereby controlling the selenium powder concentration in the gas-phase reaction within a suitable range, which is more conducive to promoting the formation of a uniform and stable transition metal chalcogenide layer.

[0069] S300: Oxygen plasma treatment is applied to the transition metal chalcogenide layer to form transition metal oxide nanowires on the surface of the transition metal chalcogenide layer, resulting in a low-dimensional mixed-dimensional heterostructure.

[0070] According to an embodiment of the present invention, in combination Figure 3It is understood that, through oxygen plasma post-processing, the target region of two-dimensional transition metal sulfides can be selectively converted into one-dimensional transition metal oxide nanowires, resulting in a low-dimensional hybrid heterostructure with a transition metal oxide nanowire upper layer and a transition metal chalcogenide lower layer. This fabrication process is not only simple and efficient, enabling mass production, but also offers good controllability and high reproducibility of the heterostructure. Furthermore, the strain at the interface of the one-dimensional transition metal oxide nanowires and the strong interlayer coupling between the one-dimensional transition metal oxide and two-dimensional transition metal sulfides in the one-dimensional / two-dimensional heterostructure obtained by this method promote effective charge transport between the surface-enhanced Raman scattering substrate and the probe molecules, thus endowing it with highly sensitive molecular detection performance and good environmental stability. In addition, this low-dimensional hybrid heterostructure obtained by this method shows promising applications in DNA sequencing, lasers, semiconductor devices, clean energy, and energy storage devices.

[0071] According to an embodiment of the present invention, in oxygen plasma treatment, a substrate on which transition metal chalcogenides are grown can be placed in a plasma treatment chamber, and plasma glow discharge is turned on to treat it. Specifically, the frequency of oxygen plasma treatment can be 40 kHz, and the treatment time can be 2 to 75 s, for example, 20 s, 30 s, 50 s, 60 s, or 70 s. The inventors have found that during oxygen plasma treatment, vacancies are first formed on the surface of the transition metal chalcogenides through physical impact, and then oxygen atoms are replaced, thereby obtaining one-dimensional transition metal oxide nanowires. If the frequency of oxygen plasma treatment is too high or the treatment time is too long, the layered structure of the transition metal chalcogenides may be destroyed; if the frequency of oxygen plasma treatment is too low or the treatment time is too short, the transition metal oxide nanowires may be difficult to grow or the production may be insufficient. The present invention, by controlling the frequency and time of oxygen plasma treatment within the above range, is beneficial to obtaining one-dimensional transition metal oxide nanowires with triple symmetric preferred orientation. Furthermore, by controlling process parameters such as plasma treatment time, the length and diameter of the formed one-dimensional transition metal oxide nanowires can be flexibly controlled. For example, based on the above plasma treatment conditions, the length of the one-dimensional transition metal oxide nanowires in the prepared low-dimensional mixed-dimensional heterojunction can be 1-4 μm, such as 2 μm, 3 μm, or 3.5 μm, and the diameter of the one-dimensional transition metal oxide nanowires can be 0.01-0.3 μm, such as 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, or 0.25 μm. This can provide the heterojunction with richer electronic structure and physicochemical properties, improve its charge transport interaction with target molecules, and significantly improve detection sensitivity.

[0072] In summary, the method for preparing low-dimensional hybrid heterojunctions according to the above embodiments of the present invention, through an oxygen plasma post-processing technique, can selectively convert the target region of two-dimensional transition metal sulfides into one-dimensional transition metal oxide nanowires, resulting in a low-dimensional hybrid heterojunction structure. This method is not only simple and efficient, enabling mass production, but also offers good controllability and high reproducibility in heterojunction preparation. Furthermore, the strain at the interface of the one-dimensional transition metal oxide nanowires and the strong interlayer coupling between the one-dimensional transition metal oxide and the two-dimensional transition metal sulfide in the one-dimensional / two-dimensional heterojunction obtained by this method promote effective charge transfer between the surface-enhanced Raman scattering substrate and the detector molecules, thereby endowing it with highly sensitive molecular detection performance and good environmental stability. Moreover, the low-dimensional hybrid heterojunction obtained by this method shows promising application prospects in fields such as DNA sequencing, lasers, semiconductor devices, clean energy, and energy storage devices.

[0073] In another method of the present invention, a low-dimensional hybrid heterojunction prepared by the above method is proposed. According to an embodiment of the present invention, the heterojunction comprises: a substrate, a transition metal chalcogenide layer, and transition metal oxide nanowires, wherein the transition metal chalcogenide layer is located on the surface of the substrate, and the transition metal oxide nanowires are located on the surface of the transition metal chalcogenide layer away from the substrate. Compared with the prior art, this low-dimensional hybrid heterojunction not only has a simple and efficient preparation process, but also possesses better molecular detection performance and better environmental stability, significantly improving the detection sensitivity of surface-enhanced Raman scattering. Furthermore, this low-dimensional hybrid heterojunction also shows promising application prospects in fields such as DNA sequencing, lasers, semiconductor devices, clean energy, and energy storage devices.

[0074] According to embodiments of the present invention, the transition metal chalcogenide layer can be tungsten diselenide and / or molybdenum diselenide layer, and the transition metal oxide nanowires can be tungsten oxide nanowires and / or molybdenum oxide nanowires; further, the length of the transition metal oxide nanowires can be 1–4 μm and the diameter can be 0.01–0.3 μm. This further ensures that the low-dimensional hybrid heterojunction possesses good molecular detection performance and good environmental stability, which is beneficial for improving the detection sensitivity of surface-enhanced Raman scattering.

[0075] According to embodiments of the present invention, based on the three-dimensional symmetrical structure of transition metal chalcogenides such as tungsten diselenide and molybdenum diselenide, transition metal oxide nanowires can also form an array structure with triple symmetrical preferred orientation on the surface of the transition metal chalcogenide layer.

[0076] In another aspect of this invention, the invention proposes applications of the above-described method and / or the aforementioned low-dimensional hybrid heterojunction in the fields of surface-enhanced Raman scattering (SERS) detection, DNA sequencing, lasers, semiconductor devices, clean energy, and energy storage devices. This application possesses all the technical features and effects of the above-described method for preparing low-dimensional hybrid heterojunctions and / or the aforementioned low-dimensional hybrid heterojunctions, which will not be elaborated further here. In summary, the method and / or the low-dimensional hybrid heterojunction can significantly reduce the detection concentration limit of SERS substrates, improve the detection sensitivity of SERS, and exhibit good environmental stability, thus showing promising practical application prospects in the aforementioned fields.

[0077] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0078] Example 1

[0079] (1) Add 200 mg of tungsten trioxide and 75 mg of sodium chloride to 10 mL of ammonia solution, and heat and stir in an 80 °C water bath for 60 min to obtain a precursor solution;

[0080] (2) Spin-coat 5 μL of the above precursor solution onto the surface of a silicon wafer. Introduce argon gas into a tube furnace at a flow rate of 80 sccm. Heat the wafer to 850°C at a rate of 20°C / min in the argon atmosphere. Place the silicon wafer with the spin-coated precursor in the center of the tube furnace, and place 800 mg of selenium powder at the upward flow point of the silicon wafer within the tube furnace. Figure 2 As shown, the temperature of the selenium powder was controlled at 360℃, and 6 sccm of hydrogen gas was introduced at the same time during the heat preservation process. The heat preservation was continued for 6 minutes. After that, the silicon wafer was pulled out of the furnace and quickly cooled to room temperature to obtain a few-layer tungsten diselenide single crystal sample.

[0081] (3) Place the tungsten diselenide single crystal in a plasma cleaner, turn on the plasma glow discharge treatment for 60s, and control the frequency at 40kHz to obtain a one-dimensional / two-dimensional tungsten oxide / tungsten diselenide heterojunction.

[0082] Example 2

[0083] The difference from Example 1 is as follows: in step (1), 200 mg of tungsten trioxide and 25 mg of sodium chloride are added to 10 mL of ammonia solution; in step (2), a single-layer tungsten diselenide single crystal sample is obtained; and in step (3), one-dimensional tungsten oxide nanowires are obtained.

[0084] Example 3

[0085] The difference from Example 1 is that in step (3), the plasma glow treatment time is 2s.

[0086] Example 4

[0087] The difference from Example 1 is that in step (3), the plasma glow treatment time is 30s.

[0088] Example 5

[0089] The difference from Example 2 is that in step (3), the plasma glow treatment time is 30s.

[0090] Example 6

[0091] (1) Add 200 mg of molybdenum trioxide to 10 mL of ammonia solution and heat and stir in an 80 °C water bath for 60 min to obtain a precursor solution;

[0092] (2) Spin-coat 5 μL of the above precursor solution onto the surface of a silicon wafer. Introduce argon gas into a tube furnace at a flow rate of 80 sccm. Heat the wafer to 850°C at a rate of 20°C / min in the argon atmosphere. Place the silicon wafer with the spin-coated precursor in the center of the tube furnace, and place 800 mg of selenium powder at the upward flow point of the silicon wafer within the tube furnace. Figure 2 As shown, the temperature of the selenium powder was controlled at 360℃, and 6 sccm of hydrogen gas was introduced at the same time during the heat preservation process. The heat preservation was continued for 10 minutes. After that, the silicon wafer was pulled out of the furnace and quickly cooled to room temperature to obtain a few-layer molybdenum diselenide single crystal sample.

[0093] (3) Place the molybdenum diselenide single crystal in a plasma cleaner, turn on the plasma glow discharge treatment for 60s, and control the frequency at 40kHz to obtain a one-dimensional / two-dimensional molybdenum oxide / molybdenum diselenide heterojunction.

[0094] Comparative Example 1

[0095] The difference from Example 1 is that only a few-layer tungsten diselenide single crystal sample was prepared, and it was not subjected to oxygen plasma treatment.

[0096] Comparative Example 2

[0097] The difference from Example 2 is that only a single-layer tungsten diselenide single crystal sample was prepared, and it was not subjected to oxygen plasma treatment.

[0098] Comparative Example 3

[0099] The difference from Example 1 is that in step (3), the oxygen plasma treatment frequency is 13.56MHz.

[0100] Comparative Example 4

[0101] The difference from Example 2 is that in step (3), the plasma glow treatment time is 90s.

[0102] Comparative Example 5

[0103] The difference from Example 6 is that the few-layer molybdenum diselenide single crystal sample prepared is not subjected to oxygen plasma treatment.

[0104] Results and characterization:

[0105] (1) The morphology of tungsten diselenide prepared in Comparative Example 1 and Comparative Example 2 was observed under an optical microscope, as shown in the figures below. Figure 4 , Figure 5 As shown, both are triangular in shape, with dimensions of approximately 10 μm and 25 μm, respectively. Furthermore, the difference in brightness between the images indicates that the tungsten diselenide obtained in Comparative Example 1 has increased optical contrast compared to Comparative Example 2. This is mainly because the tungsten diselenide layer obtained in Comparative Example 1 is relatively thick, consisting of a few layers, while the tungsten diselenide layer obtained in Comparative Example 2 is thinner, consisting mainly of a single layer.

[0106] (2) The final products obtained in Examples 1 and 2 were tested by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and the results are as follows: Figure 6 and Figure 7 As shown, through Figure 6 As can be seen, the one-dimensional tungsten oxide nanowires obtained in Example 1 exhibit a three-dimensional symmetrical and ordered arrangement on the two-dimensional tungsten diselenide surface. Figure 7 As can be seen, the tungsten oxide obtained in Example 2 has a one-dimensional nanowire morphology and a four-fold symmetrical atomic structure.

[0107] (3) The final products obtained in Example 1 and Comparative Example 3 were subjected to scanning electron microscopy (SEM) testing, and the results are as follows: Figure 8 and Figure 9 As shown, the one-dimensional tungsten oxide nanowires obtained in Example 1 are arranged in a three-dimensional symmetrical and ordered manner on the two-dimensional tungsten diselenide surface, while no one-dimensional nanowire structure was obtained in Comparative Example 3. This indicates that it is difficult to obtain a one-dimensional nanowire structure when the oxygen plasma treatment frequency is 13.56MHz.

[0108] (4) Geometric phase analysis was performed on the interface of the one-dimensional tungsten oxide nanowires in the final product obtained in Example 1. The results are as follows: Figure 10As shown, the strain-free region of nanowire II is used as the reference lattice, with the axial and radial directions of nanowire II being x and y, respectively. It can be seen that a normal strain exists in the x-direction at the interface between nanowires II and III, while both normal and shear strains exist in the y-direction at the interfaces between nanowires I and II, and between nanowires II and III. The presence of this localized strain can alter the electronic structure of the material, thereby increasing the probability of charge transport between it and molecules.

[0109] (5) Electron diffraction experiments were performed on the final product obtained in Example 1, and the results are as follows: Figure 11 As shown, this indicates that the heterojunction has two sets of diffraction spots: one set is a large diffraction spot marked by a dashed line, and the other set is a number of small diffraction spots marked by dashed lines surrounding the large diffraction spot. The large diffraction spot (large dashed circle) corresponds to the (200) crystal plane of tungsten oxide, and the number of small diffraction spots (small dashed circles) surrounding the large diffraction spot corresponds to the (100) crystal plane of tungsten diselenide.

[0110] (6) Using methylene blue (MB) as the target molecule, the molecule was adsorbed onto the surface of the products prepared in the examples by immersion, and then Raman spectroscopy was performed based on the enhanced Raman scattering effect. First, 5×10 -5 An ethanol solution of methylene blue molecules with a molar concentration of M was prepared and then diluted tenfold to obtain molecular solutions of different concentrations. The substrate was then immersed in the methylene blue molecular solutions of different concentrations for a period of time, removed and dried for later use to detect its Raman spectrum. The characteristic Raman peaks of the molecules were marked with the symbol "#".

[0111] Figure 12 The curves in the middle represent the effect of the final products on the Raman detection spectra in Examples 2 and 5 and Comparative Examples 2 and 4. They can reflect the effect of oxygen plasma treatment time on the molecular detection performance of the sample. It can be seen that when the plasma treatment time is 60s (Example 2), a strong Raman signal of methylene blue molecules can be excited on its surface.

[0112] Figure 13 Raman spectra of different concentrations of methylene blue molecules were detected for the final product in Example 2. Figure 14 To detect the Raman spectra of methylene blue molecules at different concentrations in the final product of Comparative Example 2, it was found that the lowest detection concentration of methylene blue molecules by the tungsten diselenide prepared in Comparative Example 2 was only 5 × 10⁻⁶. -8 M; and for the product obtained in Example 2, when the concentration of methylene blue molecules decreased to 5 × 10 -13 At M, the characteristic Raman peaks of the molecules were barely detectable on the surface of tungsten oxide, indicating that the detection concentration limit of tungsten oxide for methylene blue molecules is 5 × 10⁻⁶. -13M, therefore, shows that compared to tungsten diselenide, oxygen plasma treatment can greatly improve its detection sensitivity; furthermore... Figure 15 Raman spectra of different concentrations of methylene blue molecules were detected for the final product of Example 1. It can be seen that when the concentration of methylene blue molecules is reduced to 5 × 10⁻⁶, the concentration of methylene blue molecules decreases. -18 M, whose characteristic Raman peaks can still be detected on its surface, indicates that the detection concentration limit for methylene blue molecules in the one-dimensional / two-dimensional tungsten oxide / tungsten diselenide heterojunction is 5 × 10⁻⁶. -18 M is reduced by 6 orders of magnitude compared to Example 2, resulting in higher detection accuracy; Figure 16 The Raman spectra of methylene blue molecules excited on the surface of the final product prepared in Example 1 after being placed in air for different times are shown. Compared with the Raman intensity of methylene blue molecules excited on the surface of the initial sample, the Raman intensity of the molecules on the sample surface after being placed in air for 4 weeks showed almost no decay, indicating that the sample has good air stability.

[0113] Figure 17 This is a comparison chart of the molecular detection performance of the final product prepared in Example 6 and the final product prepared in Comparative Example 5 without oxygen plasma treatment. It can be seen that, compared to Comparative Example 5, the molecular detection performance of Example 6 is significantly enhanced after plasma treatment.

[0114] In summary, the method for preparing low-dimensional mixed-dimensional heterojunctions in this invention exhibits both good molecular detection sensitivity and good environmental stability.

[0115] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0116] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing low-dimensional mixed-dimensional heterostructures, characterized in that, include: (1) The transition metal oxide and alkaline solution are mixed to obtain a precursor solution; (2) The precursor solution is coated on the substrate surface, and the obtained substrate and chalcogenide are supplied to a protective reducing atmosphere for heating treatment so as to form a transition metal chalcogenide layer on the substrate surface. (3) The transition metal chalcogenide layer is subjected to oxygen plasma treatment to form transition metal oxide nanowires on the surface of the transition metal chalcogenide layer, thereby obtaining a low-dimensional mixed-dimensional heterojunction. The transition metal of the transition metal oxide nanowire is the same as the transition metal of the transition metal chalcogenide layer.

2. The method according to claim 1, characterized in that, Step (1) satisfies at least one of the following conditions: The transition metal oxide, the alkaline solution, and the alkali metal salt are subjected to the aforementioned mixing treatment; The transition metal oxides include tungsten trioxide and / or molybdenum trioxide; The alkaline solution is an ammonia solution; The mixing process is carried out at a temperature of 60-80°C for 30-90 minutes.

3. The method according to claim 2, characterized in that, In step (1), at least one of the following conditions must be met: In the precursor solution, the concentration of the transition metal oxide is (1~20) mg / mL; The mass ratio of the transition metal oxide to the alkali metal salt is 8:(1~5). The alkali metal salt includes at least one of sodium chloride, sodium iodide, and potassium iodide.

4. The method according to any one of claims 1 to 3, characterized in that, In step (2), at least one of the following conditions must be met: The transition metal chalcogenide layer is a single layer and / or has few layers; The heat treatment is carried out in a tube furnace, with the chalcogenide placed at the upper gas flow point of the substrate, and the heating temperature of the chalcogenide controlled to be lower than the heating temperature of the substrate. The substrate is made of at least one of silicon wafers, Al2O3, and silicates; The chalcogenides are selected from selenium powder and / or sulfur powder; The protective reducing atmosphere includes a protective gas and a reducing gas, wherein the protective gas includes nitrogen and / or an inert gas, and the reducing gas includes hydrogen.

5. The method according to claim 4, characterized in that, The heating treatment includes a heating stage and a holding stage. The heating stage is carried out in the protective gas atmosphere, and the holding stage is carried out in the protective reducing atmosphere.

6. The method according to claim 4, characterized in that, In the heat treatment, the volumetric flow rate of the protective gas is 80~240 sccm.

7. The method according to claim 4, characterized in that, The volumetric flow rate of the reducing gas is 4~30 sccm.

8. The method according to claim 5, characterized in that, During the heat preservation stage, the ratio of the volumetric flow rate of the protective gas to the volumetric flow rate of the reducing gas is (10~20):

1.

9. The method according to claim 4, characterized in that, In step (2), the chalcogenide is selenium powder and meets at least one of the following conditions: The heating temperature of the selenium powder is 340~450℃; The heat treatment of the substrate is carried out at a temperature of 750~850℃ for 3~10 minutes.

10. The method according to claim 1 or 9, characterized in that, In step (3), the oxygen plasma treatment is performed at a frequency of 40 kHz for a duration of 2–75 s; and / or, The transition metal oxide nanowires have a length of 1~4μm and a diameter of 0.01~0.3μm.

11. A low-dimensional hybrid heterojunction prepared by the method according to any one of claims 1 to 10, characterized in that, include: Base; A transition metal chalcogenide layer is located on the surface of the substrate; Transition metal oxide nanowires, wherein the transition metal oxide nanowires are located on the surface of the transition metal chalcogenide layer on the side away from the substrate.

12. The low-dimensional hybrid heterojunction according to claim 11, characterized in that, The transition metal oxide nanowires have a length of 1~4μm and a diameter of 0.01~0.3μm.

13. The low-dimensional hybrid heterojunction according to claim 11, characterized in that, The transition metal chalcogenide layer is a tungsten diselenide and / or a molybdenum diselenide layer, and the transition metal oxide nanowires are tungsten oxide nanowires and / or molybdenum oxide nanowires.

14. The low-dimensional hybrid heterojunction according to claim 11, characterized in that, The transition metal oxide nanowires are arranged in a triple-symmetric preferred orientation array on the surface of the transition metal chalcogenide layer.

15. The use of the method according to any one of claims 1 to 10 and / or the low-dimensional hybrid heterojunction according to any one of claims 11 to 14 in the fields of surface-enhanced Raman scattering detection, DNA sequencing, lasers, semiconductor devices, clean energy, and energy storage devices.

Images