Preparation method of temperature-regulated two-dimensional heterojunction and alloy structure

Abstract

A method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures includes the following steps: placing a substrate, a molybdenum source, a tungsten source, and a selenium source in a chemical vapor deposition system; using an inert gas as a carrier gas, heating the system to a preset growth temperature, maintaining the temperature at a constant temperature by introducing a reducing gas for a set time, and finally cooling; wherein, by adjusting the growth temperature, the saturated vapor pressure and evaporation rate of the molybdenum and tungsten sources are controlled, thereby controlling their contact sequence with the selenium source, thus controllably preparing two-dimensional products with different interface structures on the substrate. This invention, by simply adjusting the growth temperature in the chemical vapor deposition system, can prepare smooth transition heterojunctions, atomically sharp interface heterojunctions, and homogeneous alloys on the same substrate, such as polycrystalline gold foil. The method of this invention does not require changing the type, ratio, or substrate of the raw materials, significantly simplifying the process flow and reducing the complexity and cost of multi-step synthesis.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional material preparation technology, specifically to a method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures. Background Technology

[0002] Two-dimensional transition metal dichalcogenides (TMDCs) are considered ideal materials for next-generation optoelectronic devices due to their tunable bandgap structure, strong photo-matter interaction, and high carrier separation efficiency. Among the various TMDC configurations, lateral heterojunctions—composed of different TMDCs linked in a plane by chemical bonds—have become a hot topic in early two-dimensional material fabrication research due to their unique physical and device advantages. Compared to mechanical transfer or vertical stacking methods, lateral heterojunctions can avoid interface contamination and lattice mismatch problems, and achieve precise band alignment at atomically clean interfaces, thereby promoting the efficient generation and directional transport of photogenerated carriers.

[0003] In 2014, Huang et al. successfully prepared [a specific product] using a one-step chemical vapor deposition (CVD) method. Lateral heterojunction. However, high-resolution scanning transmission electron microscopy and interfacial photoluminescence characterization show that the interfacial region is actually an alloy phase. Instead of an ideal atomically sharp interface, this result reveals a key challenge in the fabrication of lateral heterostructures: how to precisely control growth kinetics while achieving an atomically sharp interface.

[0004] Recently, Pan et al. discovered that, compared to two-dimensional heterostructures with atomically sharp interfaces, monolayer gradient alloys (such as...) The alloy can achieve a wide-range photosensitive response (1.2–2.0 eV) from visible light to near infrared within a single atomic layer. In addition, the gradient band of the alloy can generate a built-in electric field, which promotes rapid spatial separation of photogenerated electron-hole pairs. Combined with the selective trapping of carriers by defect states, this effectively extends the lifetime of photogenerated carriers and significantly improves the stability of the photocurrent memory effect.

[0005] Although the above studies have demonstrated the potential of lateral heterojunctions and gradient alloys of TMDCs in optoelectronic devices, the existing technologies still have the following shortcomings: Interface purity is difficult to control: Transverse heterojunctions prepared by conventional CVD methods tend to form alloy phases at the interface, making it difficult to obtain atomically sharp interfaces, which affects the accuracy of band alignment and the consistency of device performance.

[0006] Limited interface types: Existing methods can only achieve one fixed type of interface, such as a sharp interface or an alloy interface, and lack the ability to flexibly prepare different interface structures in the same material system by adjusting growth parameters.

[0007] Insufficient control of growth kinetics: There is a lack of systematic research on how kinetic parameters such as temperature and precursor concentration affect the degree of alloying and the interface gradient during interface formation, which limits the customized design of transverse heterojunction structures. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures, which can solve the existing problems.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows: This invention is achieved through the following technical solution: a method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures, comprising the following steps: The substrate, molybdenum source, tungsten source, and selenium source are placed in a chemical vapor deposition system; Using an inert gas as the carrier gas, the system temperature is raised to the preset growth temperature, and a reducing gas is introduced and kept at a constant temperature for a set time before finally cooling. In this process, by adjusting the growth temperature, the saturated vapor pressure and evaporation rate of the molybdenum and tungsten sources are controlled, thereby controlling their contact sequence with the selenium source. This allows for the controllable preparation of two-dimensional products with different interface structures on a substrate. These products can be used to prepare optoelectronic devices such as photodetectors, optical switches, and photovoltaic devices.

[0010] Furthermore, the substrate comprises polycrystalline gold foil, and the molybdenum source is... Powder, wherein the tungsten source is The powder, wherein the selenium source is Se powder.

[0011] Furthermore, the growth temperature includes 720℃±20℃, 820℃±20℃, or 920℃±20℃; wherein 720℃±20℃ corresponds to the growth range of a smooth transition heterojunction, 820℃±20℃ corresponds to the growth range of an atomically sharp interface heterojunction, and 920℃±20℃ corresponds to the growth range of a uniform alloy.

[0012] Furthermore, the growth temperature includes 720°C, 820°C, or 920°C; When the growth temperature is 720℃, a smooth transition heterojunction is prepared, the structure of which is as follows: ; When the growth temperature is 820℃, an atomically sharp interface heterostructure is prepared, the structure of which is: ; When the growth temperature is 920℃, a homogeneous alloy is prepared, the structure of which is .

[0013] Furthermore, the molybdenum source and the tungsten source are... The mixture is provided in powder form with a molar ratio of 1:9 and an amount of 2 mg; the amount of the Se powder is 120 mg.

[0014] Furthermore, the aforementioned The mixed powder is placed at a high temperature of 1 cm around a polycrystalline gold foil substrate, while the Se powder is placed in the upstream low-temperature region. The 1 cm area around the substrate is... The axial distance between the mixed powder and the polycrystalline gold foil substrate.

[0015] Furthermore, the chemical vapor deposition system is a tube furnace, the operating pressure is atmospheric pressure, the carrier gas is Ar, the flow rate is 80 sccm, the heating rate is 20 °C / min, the reducing gas H2 is introduced into the constant temperature for heat preservation at a flow rate of 4 sccm for 2 min, and the cooling method is natural cooling.

[0016] Furthermore, the substrate undergoes a cleaning process before use, which includes ultrasonic cleaning with acetone, isopropanol, and water for 15 minutes in sequence, followed by drying with nitrogen gas.

[0017] Compared with the prior art, the beneficial effects of the present invention include: This invention enables the fabrication of smooth transition heterojunctions, atomically sharp interface heterojunctions, and uniform alloys on the same substrate, such as polycrystalline gold foil, simply by adjusting the growth temperature in the chemical vapor deposition system. The method of this invention does not require changes to the type, ratio, or substrate of the raw materials, significantly simplifying the process and reducing the complexity and cost of multi-step synthesis.

[0018] The method of this invention reveals the mechanism by which temperature regulates the precursor evaporation rate and contact sequence, providing clear theoretical guidance for the controllable growth of two-dimensional heterojunctions and alloy structures. Furthermore, this invention employs a conventional chemical vapor deposition system and a commercially available polycrystalline gold foil substrate, with common oxide powders as the raw material. The process involves selenium powder, with inert gas Ar and a small amount of H2 as the carrier gas. The entire process requires only one heating, isothermal, and cooling cycle, without the need for complex equipment or intermediate transfer steps, demonstrating good repeatability and prospects for large-scale application.

[0019] The products prepared by this invention have high crystal quality and clear interface transitions. Raman spectroscopy characterization confirms that the smooth transition heterojunction exhibits continuous peak position shifts, the sharp interface heterojunction shows abrupt peak position changes at the interface, and the homogeneous alloy exhibits a single characteristic peak, which can meet the diverse needs of different optoelectronic devices for band arrangement. Attached Figure Description

[0020] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts. Wherein: Figure 1 This is a schematic diagram of the CVD tube furnace apparatus of the present invention, wherein 1-tube furnace, 2-selenium source placement area, 3-carrier gas and reducing gas inlet, and 4-substrate placement area. Mixed powder placement area.

[0021] Figure 2 The results of this invention were obtained at a growth temperature of 720℃. (a) is an optical microscope image, and (b) is a Raman scan of the area within the red box in (a). Figure (c) shows the Raman spectrum of the selected point shown in (b).

[0022] Figure 3 This invention uses 820℃ as an example. Heterojunction growth program diagram.

[0023] Figure 4 The results show the preparation of this invention at a growth temperature of 820℃. (a) is an optical microscope image, and (b) is a Raman scan of the area within the red box in (a). Figure (c) shows the Raman spectrum of the selected point shown in (b).

[0024] Figure 5 The results of this invention were obtained at a growth temperature of 920℃. (a) is an optical microscope image, and (b) is a Raman scan of the area within the red box in (a). Figure (c) shows the Raman spectrum of the selected point shown in (b).

[0025] Figure 6 This invention explores the effect of temperature on regulation. Mechanism diagram of heterojunction interface structure. Detailed Implementation

[0026] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0027] This invention discloses a method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures, comprising the following steps: The substrate, molybdenum source, tungsten source, and selenium source are placed in a chemical vapor deposition system; Using an inert gas as the carrier gas, the system temperature is raised to the preset growth temperature, and a reducing gas is introduced and kept at a constant temperature for a set time before finally cooling. By adjusting the growth temperature, the saturated vapor pressure and evaporation rate of the molybdenum and tungsten sources are controlled, thereby controlling their contact sequence with the selenium source, thus enabling the controllable preparation of two-dimensional products with different interface structures on the substrate.

[0028] This application uses polycrystalline gold foil (Au) as the substrate and molybdenum (Mo) source as... Powder, tungsten (W) source adopted The example of using Se powder as a selenium (Se) source is provided, but it is not limited to this.

[0029] The growth temperature includes 720℃±20℃, 820℃±20℃ or 920℃±20℃; 720℃±20℃ corresponds to the growth range of a smooth transition heterojunction, 820℃±20℃ corresponds to the growth range of an atomically sharp interface heterojunction, and 920℃±20℃ corresponds to the growth range of a uniform alloy.

[0030] Preferably, the growth temperature includes 720°C, 820°C, or 920°C.

[0031] In one implementation case, when the growth temperature is 720℃, a smooth transition heterojunction is prepared, the structure of which is... The specific operation is as follows: 1.1 The purchased commercial polycrystalline Au was ultrasonically cleaned for 15 minutes in sequence with acetone, isopropanol and water to remove surface stains and grease.

[0032] 1.2. Mix the cleaned Au, Mo, W, and Se sources according to... Figure 1 The image shows a quartz boat placed inside a CVD tube furnace. The mixed powder (1:9 molar ratio, 2 mg) was placed 1 cm around the Au substrate (high-temperature zone), and the Se powder (120 mg) was placed in the upstream low-temperature zone; the area 1 cm around the substrate was... The axial distance between the mixed powder and the polycrystalline gold foil substrate. Using 80 sccm Ar as the carrier gas, the temperature was increased from room temperature to 720°C at a heating rate of 20°C / min; during the isothermal stage, 4 sccm H2 was introduced, and after holding at this temperature for 2 min, the mixture was allowed to cool naturally. This yields... The interface smoothly transitions to the heterojunction.

[0033] Figure 2 (a) shows the product prepared using the above method. Optical microscope image of a heterojunction on an Au substrate. Figure 2 (b) for Figure 2 In (a) the Raman scan image of the area within the red box, it can be clearly seen that when the characteristic peak is selected as... At that time, the nucleation center was removed. Apart from being dark in color, most areas are light in color, proving that the heterostructure prepared at 720℃ should possess the following properties. Structure, i.e. The two materials can be interchanged or replaced, resulting in a smooth interface transition. Figure 2 (c) is for Figure 2 (b) In the Raman spectrum of the selected points, the peak positions from point 1 to point 6 can be clearly observed to change from... The gradual shift further proves that there is a relatively smooth interface transition between the two materials.

[0034] Implementation Case 2: When the growth temperature is 820℃, an atomically sharp interface heterojunction is prepared, the structure of which is as follows: Specifically: 2.1 The purchased commercial polycrystalline gold foil (Au) was ultrasonically cleaned for 15 minutes in sequence with acetone, isopropanol and water to remove surface stains and grease.

[0035] 2.2. Mix the cleaned Au with the Mo, W, and Se sources according to... Figure 1 The image shows a quartz boat placed inside a CVD tube furnace. The mixed powder (1:9 molar ratio, 2 mg) was placed 1 cm around the Au substrate (high-temperature zone), and the Se powder (120 mg) was placed in the upstream low-temperature zone; the area 1 cm around the substrate was... The axial distance between the mixed powder and the polycrystalline gold foil substrate. Using 80 sccm Ar as the carrier gas, the temperature was increased from room temperature to 820°C at a heating rate of 20°C / min; during the isothermal stage, 4 sccm H2 was introduced, and after holding at this temperature for 2 min, the mixture was allowed to cool naturally. This yields... The interface transitions sharply to heterojunctions; specific experimental parameters are as follows: Figure 3 As shown.

[0036] Figure 4 (a) shows the product prepared using the above method. Optical microscope image of a heterojunction on an Au substrate. Figure 4 (b) for Figure 4 (a) The Raman scan image of the area within the red box clearly shows that when the selected... Characteristic peaks At that time, only the internal region was bright, proving that the heterojunction prepared at 820 ℃ had a bright internal region. The outside is Furthermore, the interface between the two areas is clear and the transition is sharp. Figure 4 (c) is for Figure 4 (b) Raman spectra of selected points, points 1 and 2 only have Peak, corresponding Area; Points 5 and 6 only Peaks appear, corresponding to the WSe2 region; points 3 and 4 are in as well as Both have Raman peaks, which are used to cope with Figure 4 (b) At the interface, and the Raman spectrum shows that the peak position changes abruptly along the interface, which further proves that there is a sharp atomic-level interface transition between the two materials.

[0037] Implementation Case 3: When the growth temperature is 920℃, a uniform alloy is prepared, the structure of which is Specifically: 3.1 The purchased commercial polycrystalline Au was ultrasonically cleaned for 15 minutes in sequence with acetone, isopropanol and water to remove surface stains and grease.

[0038] 3.2. Mix the cleaned Au with the Mo, W, and Se sources according to... Figure 1 The image shows a quartz boat placed inside a CVD tube furnace. The mixed powder (1:9 molar ratio, 2 mg) was placed 1 cm around the Au substrate (high-temperature zone), and the Se powder (120 mg) was placed in the upstream low-temperature zone; the area 1 cm around the substrate was... The axial distance between the mixed powder and the polycrystalline gold foil substrate. Using 80 sccm Ar as the carrier gas, the temperature was increased from room temperature to 920 °C at a heating rate of 20 °C / min; during the isothermal stage, 4 sccm of H2 was introduced, and after holding at this temperature for 2 min, the mixture was allowed to cool naturally. This yields... Homogeneous alloy.

[0039] Figure 5 (a) shows the product prepared using the above method. Optical microscope image of a homogeneous alloy on an Au substrate. Figure 5 (b) for Figure 5 (a) In the Raman scan image of the area within the red box, it can be clearly seen that when the characteristic peak is selected at 245 cm⁻¹... -1 At that time, the entire area was bright, proving that it was prepared at 920 ℃. Alloyed structure. Figure 5 (c) is for Figure 5 (b) The Raman spectra of the selected points, the peak positions of points 1 to 6 are all This further proves The presence of an alloy structure.

[0040] To delve deeper into the temperature regulation mechanism in the final structure, this invention discusses the temperature regulation mechanism on the interface and the final structure from the perspective of the influence of temperature on the precursor evaporation rate, such as... Figure 6As shown. When the growth temperature is 920℃, after the system enters the 2-minute holding stage, because the center temperature is much higher than the melting point of MoO3 powder (795℃), the Mo and W sources are almost simultaneously evaporated in large quantities and come into contact with the Se source that diffuses from the upstream to the center temperature zone, thus leading to... Growth of the alloy structure. At a growth temperature of 820 ℃, after a 2-minute holding period, the Mo source continued to evaporate relatively quickly and first contacted the Se source to form... Deposited on an Au substrate, the Mo source evaporates and is consumed rapidly. By the time the W source reaches its saturation vapor pressure and evaporates in large quantities, the Mo source has been completely depleted, leading to... growth stages and The growth stages do not overlap, corresponding to the formation of sharp interface heterojunctions at 820 ℃; when the growth temperature is 720 ℃, after the system enters the 2-minute holding stage, the growth temperature is lower than... The melting point of the powder causes a delay in the evaporation time of the Mo source. The latter part of the growth period overlaps with the evaporation period of the W source, thus leading to... The formation of the structure corresponds to the generation of a smooth interface heterojunction at 720 °C.

[0041] The preparation method of the present invention has good repeatability. After no less than 5 repeated experiments, the same interface structure and Raman characteristics can be obtained, indicating that the method has good repeatability.

[0042] This invention discloses a controllable fabrication method for multiple interface structures using a single temperature parameter: This invention allows for the fabrication of smooth transition heterojunctions on the same substrate (such as polycrystalline gold foil) simply by adjusting the growth temperature (720℃~920℃) in the chemical vapor deposition system. Atomic-level sharp interface heterostructure ( ) and homogeneous alloys ( This method requires no change in the type, ratio, or substrate of raw materials, significantly simplifying the process and reducing the complexity and cost of multi-step synthesis.

[0043] The method of this invention reveals the mechanism by which temperature regulates the precursor evaporation rate and contact sequence: This invention systematically studies the effect of growth temperature on... Evaporation behavior and its effect on the sequence of contact with the Se source. Below At the melting point (795℃) (e.g., 720℃), the evaporation of the Mo source is delayed, partially overlapping with the evaporation period of the W source, forming a smooth interface. Above the melting point (e.g., 820℃), the Mo source evaporates rapidly and is preferentially consumed, followed by the independent growth of the W source, forming a sharp interface. At temperatures far above the melting point (e.g., 920℃), both evaporate in large quantities simultaneously, forming a homogeneous alloy. This mechanism provides clear theoretical guidance for the controllable growth of two-dimensional heterostructures and alloy structures.

[0044] The method of this invention produces high-quality products with excellent interface controllability: Raman spectroscopy (characteristic peaks 240~) Raman scans and other imaging confirm that the smooth interface heterojunction prepared by this invention exhibits continuous peak shifts, the sharp interface heterojunction shows abrupt peak changes at the interface, and the homogeneous alloy exhibits a single characteristic peak throughout the entire region (e.g., ...). This indicates that the obtained product has high crystallinity and a clear interface transition type, meeting the diverse requirements of different electronic devices for band arrangement.

[0045] The method of this invention has good process compatibility and is easy to promote: This invention uses a conventional chemical vapor deposition system and a commercial polycrystalline gold foil substrate, and the raw material is a common oxide powder ( ) and selenium powder, with an inert gas (Ar) and a small amount of The entire process requires only one heating, temperature control, and cooling cycle, without the need for complex equipment or intermediate transfer steps, and has good repeatability and prospects for large-scale application.

[0046] This document uses specific embodiments to illustrate the principles and implementation methods of this document. The descriptions of the embodiments above are only for the purpose of helping to understand the methods and core ideas of this document. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this document. Therefore, the content of this specification should not be construed as a limitation of this document.

Claims

1. A method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures, characterized in that: Includes the following steps: The substrate, molybdenum source, tungsten source, and selenium source are placed in a chemical vapor deposition system; Using an inert gas as the carrier gas, the system temperature is raised to the preset growth temperature, and a reducing gas is introduced and kept at a constant temperature for a set time before finally cooling. By adjusting the growth temperature, the saturated vapor pressure and evaporation rate of the molybdenum and tungsten sources are controlled, thereby controlling their contact sequence with the selenium source, thus enabling the controllable preparation of two-dimensional products with different interface structures on the substrate.

2. The method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures according to claim 1, characterized in that: The substrate includes polycrystalline gold foil, the molybdenum source is MoO3 powder, the tungsten source is WO3 powder, and the selenium source is Se powder.

3. The method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures according to claim 2, characterized in that: The growth temperature includes 720℃±20℃, 820℃±20℃ or 920℃±20℃; where 720℃±20℃ corresponds to the growth range of a smooth transition heterojunction, 820℃±20℃ corresponds to the growth range of an atomically sharp interface heterojunction, and 920℃±20℃ corresponds to the growth range of a uniform alloy.

4. The method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures according to claim 3, characterized in that: The growth temperature includes 720℃, 820℃ or 920℃; When the growth temperature is 720℃, a smooth transition heterojunction is prepared, the structure of which is as follows: ; When the growth temperature is 820℃, an atomically sharp interface heterostructure is prepared, the structure of which is: ; When the growth temperature is 920℃, a homogeneous alloy is prepared, the structure of which is .

5. The method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures according to claim 4, characterized in that: The molybdenum source and the tungsten source are The mixture is provided in powder form with a molar ratio of 1:9 and a dosage of 2 mg; the dosage of the Se powder is 120 mg.

6. The method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures according to claim 5, characterized in that: The The mixed powder is placed at a high temperature of 1 cm around a polycrystalline gold foil substrate, while the Se powder is placed in an upstream low-temperature region; the 1 cm region around the substrate is... The axial distance between the mixed powder and the polycrystalline gold foil substrate.

7. The method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures according to claim 1, characterized in that: The chemical vapor deposition system is a tube furnace, operating at atmospheric pressure, with Ar as the carrier gas and a flow rate of 80 sccm; the heating rate is 20 °C / min. Reducing gas is introduced into a constant temperature environment The heat preservation process was carried out at a flow rate of 4 sccm for 2 minutes; the cooling method was natural cooling.

8. The method for preparing temperature-controlled two-dimensional heterojunctions and alloy structures according to claim 1, characterized in that: The substrate undergoes a cleaning process before use, which includes ultrasonic cleaning with acetone, isopropanol, and water for 15 minutes in sequence, followed by drying with nitrogen.

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