WO2024066206A1 - Preparation method for and use of two-dimensional double-layer tungsten sulfide homojunction - Google Patents

Abstract

The present invention belongs to the technical field of homojunction two-dimensional materials, and specifically relates to a preparation method for and use of a two-dimensional double-layer tungsten sulfide homojunction. A chemical vapor deposition method is employed for the two-dimensional tungsten sulfide homojunction, and the growth of nucleation is controlled by adjusting the heating rate and flow rate, thus achieving the formation of a two-dimensional tungsten sulfide homogeneous junction having different twist angles. The Raman peak position of the obtained homogeneous junction experiences an obvious shift. The surface of said junction is clean, undamaged, large in size and high in quality. Moreover, the preparation method of the present invention is simple, features one-step synthesis, and is easy to operate. The present invention provides a material basis for studying fields such as the properties of twisted two-dimensional materials and uses thereof in optoelectronic devices.

Description

Preparation method and application of a two-dimensional double-layer tungsten sulfide homojunction Technical Field

The present invention belongs to the technical field of homojunction two-dimensional materials, and more specifically, relates to a preparation method and application of a two-dimensional double-layer tungsten sulfide homojunction.

Background technique

In 2018, Cao Yuan's team at MIT discovered strong electron correlation and unconventional superconductivity in corner-stacked double-layer graphene. This groundbreaking work set off a research boom in "twist electronics" and aroused widespread interest in twisted two-dimensional materials among researchers. At present, the preparation method of corner-stacked two-dimensional homojunctions is mainly mechanical exfoliation combined with dry transfer, that is, first prepare the two-dimensional material by mechanical exfoliation, and then use high molecular organic matter such as methyl methacrylate (PMMA) or polydimethylsiloxane (PDMS) to achieve the transfer of two-dimensional materials and stacking at different angles. However, atomic-layer two-dimensional materials are highly sensitive to the external environment. The transfer and stacking involved in this type of method can easily lead to damage, wrinkles or residual groups on the surface of the material, destroying the high quality of the material, thereby affecting the optical and electrical properties of the material. At the same time, the high molecular organic matter used will remain in the product as impurities. Chinese patent application CN112079387A discloses that tungsten disulfide powder is first placed in the middle of a tube furnace by physical vapor deposition, a silicon wafer with silicon dioxide on the surface is placed downstream of the tube furnace, and the temperature is raised to 1100-1150°C and kept warm in a nitrogen atmosphere. Reverse ventilation is performed before reaching the holding temperature to obtain a silicon wafer with two-dimensional tungsten disulfide, and then it is subjected to photoresist spin coating, heating, and photolithography. By controlling the channel width of the photoresist, the two-dimensional tungsten sulfide can be folded, and after development, electrodes can be successfully built at both ends of the homojunction to obtain a two-dimensional tungsten disulfide self-constructed homojunction, which has good prospects for light detection applications. However, this method involves multiple steps, resulting in complex material preparation, and the photoresist spin coating and other operations involved in the later stage of the method are prone to damage to the finished product, thereby affecting the optical and electrical properties of the material. More importantly, this preparation method can only obtain a two-dimensional single-layer tungsten sulfide homojunction, but fails to achieve the preparation of homojunctions with different twisted configurations, making it difficult to apply to the field of twist electronics.

Summary of the invention

The technical problem to be solved by the present invention is to overcome the defects and shortcomings of the existing homojunction preparation that easily lead to the introduction of impurities and damage of the finished product during the transfer process. A chemical vapor deposition method is used to synthesize two-dimensional double-layer tungsten sulfide homojunctions with different torsional configurations in one step, thereby avoiding the introduction of impurities and damage of the finished product during the transfer process of the existing technology, and providing a clean, lossless, large-size, high-crystallinity preparation method of two-dimensional double-layer tungsten sulfide homojunctions with different torsional configurations.

Another object of the present invention is to provide an application of a method for preparing a two-dimensional double-layer tungsten sulfide homojunction.

The above-mentioned purpose of the present invention is achieved through the following technical solutions:

A method for preparing a two-dimensional double-layer tungsten sulfide homojunction comprises the following steps:

S1. Place a sulfur source, a tungsten source and a pretreated substrate in order from upwind to downwind. Under an inert gas atmosphere, maintain the flow rate of the inert gas at 60 to 120 sccm, set the heating rate at 20 to 25°C/min, and heat to 600 to 650°C.

S2. Set the heating rate to 5-15°C/min, raise the temperature to 800-1100°C, keep the temperature for 5-20 minutes, and cool to obtain a two-dimensional double-layer tungsten sulfide homojunction on the substrate.

The tungsten source is located at the center of the heating zone in the reaction equipment, and the sulfur source is not directly heated. The heat from the heating zone diffuses and the temperature is increased to turn it into gas to participate in the reaction.

Preferably, in step S1, the distance between the sulfur source and the tungsten source is 10 to 25 cm.

Preferably, in step S1, the substrate and the tungsten source are placed at a distance of 15 to 35 cm.

Preferably, in step S1, the molar ratio of the sulfur source to the tungsten source is 40:1 to 200:1.

Preferably, the sulfur source is sulfur powder or disodium sulfide trioxide.

Preferably, the tungsten source is one of tungsten trioxide, tungsten oxide and tungsten hexacarbonyl.

Preferably, the substrate is any one of SiO ₂ /Si, Cu, Ni, Pt, and Au.

Furthermore, in step S1, the pretreatment method is: washing the substrate with an organic solvent and water, and drying it for standby use.

Furthermore, in step S1, the pretreatment method is: soak the _SiO2 /Si substrate in acetone solution for 10-20 minutes, then ultrasonically clean it in isopropanol solution for 10-20 minutes, then repeat ultrasonic cleaning with deionized water for 3-5 times, and finally blow dry with high-purity nitrogen for standby use.

Preferably, in step S3, the torsion angle range of the two-dimensional double-layer tungsten sulfide homojunction is 0° and/or 60°.

Preferably, in step S2, the size of the two-dimensional double-layer tungsten sulfide homojunction is 20-70 um.

Preferably, in step S2, the thickness of the two-dimensional double-layer tungsten sulfide homojunction is 2 layers.

The invention also provides application of the preparation method in the fields of transistors, photodetectors and torsional electronics.

The present invention has the following beneficial effects:

The preparation method of the present invention realizes the preparation of two-dimensional double-layer tungsten sulfide homojunctions with different torsional configurations through a one-step synthesis method. The obtained homojunction has a clean, lossless surface, large size and high quality. Compared with the commonly used mechanical stripping combined with dry transfer method, the preparation method is simple and convenient and reduces the surface contamination of the sample by the outside world, which is beneficial to the application of two-dimensional double-layer homojunctions with different torsional configurations in the fields of transistors, photodetectors and torsional electronics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the preparation method using chemical vapor deposition.

Figure 2 shows optical microscope images of two-dimensional bilayer _WS2 homojunctions with different twisted configurations.

Figure 3 shows the Raman spectra of two-dimensional bilayer _WS2 homojunctions with different twisted configurations.

Figure 4 is an optical microscope image of a two-dimensional single-layer _WS2 homojunction.

Figure 5 is the Raman spectrum of a two-dimensional single-layer WS ₂ homojunction.

Detailed ways

The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

Example 1 A method for preparing a two-dimensional double-layer tungsten sulfide homojunction with different twisted configurations

A method for preparing a two-dimensional double-layer tungsten sulfide homojunction with different twisted configurations comprises the following steps:

S1. Soak the SiO ₂ /Si substrate in acetone solution for 20 minutes, then ultrasonically clean it in isopropanol solution for 20 minutes, then repeat ultrasonic cleaning with deionized water for 3 times, and finally blow dry with high-purity nitrogen gas for standby use;

S2. Place 0.6g S powder, 0.1g WO ₃ powder and pre-treated SiO ₂ /Si substrate in a corundum container from upwind to downwind, with the distance between S powder and WO ₃ being 20cm, and the distance between SiO ₂ /Si substrate and WO ₃ being 25cm, as shown in FIG1 ;

S3. Turn on the vacuum pump and pump the air pressure in the tube to below 2.0×10 ^-2 Torr. Then, introduce inert gas to make the air pressure in the tube 10 Torr higher than the atmospheric pressure and then pump the air again. Repeat this step 2 to 3 times to exhaust all the air.

S4, starting to heat the tube furnace, heating it to 650°C at 20°C/min, then heating it to 850°C at 8°C/min, then keeping it at that temperature for 15 minutes, and finally cooling it naturally to room temperature, to obtain a two-dimensional double-layer tungsten sulfide homojunction on the SiO ₂ /Si substrate;

The inert gas flow rate is maintained at 100 sccm throughout the entire process and the gas flow direction is from the sulfur source area to the deposition area via the tungsten source area.

The optical microscope image of the obtained sample is measured, and the result is shown in Figure 2. The torsion angles of the two-dimensional tungsten sulfide homojunction obtained by this method are 0° and 60°, and most of the sample sizes are concentrated at 20um. Among them, it can be seen from the figure that the prepared two-dimensional tungsten sulfide presents triangular flakes and the color of the flakes is uniform, indicating that a highly crystalline two-dimensional tungsten sulfide homojunction has been prepared. This is because during the growth process in the high temperature zone, the appropriate heating rate and gas flow rate are conducive to the growth of nucleation sites and the deposition growth of source materials.

The Raman spectra of the obtained samples were measured, and the results are shown in Figure 3. The two-dimensional tungsten sulfide homojunctions corresponding to the samples in Figures 2b and 2c obtained by this method have different Raman peak positions. It can be seen from Figure 3 that the two-dimensional tungsten sulfide homojunction has the characteristic Raman peaks E ¹ _2g and A _1g of tungsten sulfide. Compared with the 0° twisted two-dimensional sulfide homojunction, the 60° twisted two-dimensional homojunction shows an obvious peak position shift phenomenon, which indicates the successful preparation of two-dimensional tungsten sulfide homojunctions with different twist configurations. In addition, the Raman peak positions of the single-layer two-dimensional tungsten sulfide in the two-dimensional double-layer tungsten sulfide homojunctions with different twist angles are basically the same, E ¹ _2g and A _1g are located at 355.1cm ^-1 and 420.2cm ^-1 respectively, and the difference is 65.1cm ^-1 , which confirms that the prepared two-dimensional double-layer tungsten sulfide is composed of two layers of single-layer tungsten sulfide. In summary, it can be shown from the spectrum that this method obtains two-dimensional double-layer tungsten sulfide homojunctions with different twist configurations.

Example 2 Preparation method of a two-dimensional double-layer tungsten sulfide homojunction with different twisted configurations

A method for preparing a two-dimensional double-layer tungsten sulfide homojunction with different twisted configurations comprises the following steps:

S1. Soak the SiO ₂ /Si substrate in acetone solution for 20 minutes, then ultrasonically clean it in isopropanol solution for 20 minutes, then repeat ultrasonic cleaning with deionized water for 3 times, and finally blow dry with high-purity nitrogen gas for standby use;

S2. Place 0.6g S powder, 0.1g WO ₃ powder and pre-treated SiO ₂ /Si substrate in a corundum container from upwind to downwind, with the distance between S powder and WO ₃ being 20cm, and the distance between SiO ₂ /Si substrate and WO ₃ being 25cm, as shown in FIG1 ;

S3. Turn on the vacuum pump and pump the air pressure in the tube to below 2.0×10 ^-2 Torr. Then, introduce inert gas to make the air pressure in the tube 10 Torr higher than the atmospheric pressure and then pump the air again. Repeat this step 2 to 3 times to exhaust all the air.

S4, starting to heat the tube furnace to 600°C at 20°C/min, then heating to 910°C at 10°C/min, then keeping the temperature for 13 minutes, and finally cooling naturally to room temperature, to obtain a two-dimensional tungsten sulfide homojunction on the SiO ₂ /Si substrate;

The inert gas flow rate is maintained at 90 sccm throughout the entire process and the gas flow direction is from the sulfur source area to the deposition area via the tungsten source area.

The optical microscope images of the obtained samples were measured, and the results were basically consistent with the results of Example 1. The torsion angles of the two-dimensional double-layer tungsten sulfide homojunction obtained by this method were 0° and 60°, and most of the samples were concentrated in size of 40um with high crystallinity.

The Raman spectrum of the obtained sample was measured, and the result was basically consistent with the result of Example 1.

Example 3 Preparation method of two-dimensional tungsten sulfide homojunction with different twisted configurations

A method for preparing a two-dimensional double-layer tungsten sulfide homojunction with different twisted configurations comprises the following steps:

S1. Soak the SiO ₂ /Si substrate in acetone solution for 20 minutes, then ultrasonically clean it in isopropanol solution for 20 minutes, then repeat ultrasonic cleaning with deionized water for 3 times, and finally blow dry with high-purity nitrogen gas for standby use;

S2. Place 1g S powder, 0.05g WO ₃ powder and pre-treated SiO ₂ /Si substrate in a corundum container from upwind to downwind, with the distance between S powder and WO ₃ being 20cm, and the distance between SiO ₂ /Si substrate and WO ₃ being 25cm, as shown in FIG1 ;

S3. Turn on the vacuum pump and pump the air pressure in the tube to below 2.0×10 ^-2 Torr. Then, introduce inert gas to make the air pressure in the tube 10 Torr higher than the atmospheric pressure and then pump the air again. Repeat this step 2 to 3 times to exhaust all the air.

S4, starting to heat the tube furnace, heating it to 650°C at 20°C/min, then heating it to 1100°C at 15°C/min, then keeping it at that temperature for 10 minutes, and finally cooling it naturally to room temperature, to obtain a two-dimensional tungsten sulfide homojunction on the SiO ₂ /Si substrate;

The inert gas flow rate was maintained at 110 sccm throughout the entire process and the gas flow direction was from the sulfur source area to the deposition area via the tungsten source area.

Optical microscope images of the obtained samples were measured, and the twist angle of the two-dimensional double-layer tungsten sulfide homojunction obtained by this method was 60°. Most of the samples were concentrated in size of 50um and had high crystallinity.

The Raman spectrum of the obtained sample was measured, and the result was basically consistent with the result of Example 1 when the twist angle was 60°.

Example 4 Preparation method of a two-dimensional double-layer tungsten sulfide homojunction with different twisted configurations

A method for preparing a two-dimensional double-layer tungsten sulfide homojunction with different twisted configurations comprises the following steps:

S1. Soak the SiO ₂ /Si substrate in acetone solution for 20 minutes, then ultrasonically clean it in isopropanol solution for 20 minutes, then repeat ultrasonic cleaning with deionized water for 3 times, and finally blow dry with high-purity nitrogen gas for standby use;

S2. Place 1.5g S powder, 0.06g WO ₃ powder and pre-treated SiO ₂ /Si substrate in a corundum container from upwind to downwind. The distance between S powder and WO ₃ is 20cm, and the distance between SiO ₂ /Si substrate and WO ₃ is 25cm, as shown in FIG1 ;

S3. Turn on the vacuum pump and pump the air pressure in the tube to below 2.0×10 ^-2 Torr. Then, introduce inert gas to make the air pressure in the tube 10 Torr higher than the atmospheric pressure and then pump the air again. Repeat this step 2 to 3 times to exhaust all the air.

S4, starting to heat the tube furnace, heating it to 650°C at 20°C/min, then heating it to 850°C at 8°C/min, then keeping it at that temperature for 10 minutes, and finally cooling it naturally to room temperature, to obtain a two-dimensional tungsten sulfide homojunction on the SiO ₂ /Si substrate;

The inert gas flow rate was maintained at 110 sccm throughout the entire process and the gas flow direction was from the sulfur source area to the deposition area via the tungsten source area.

The optical microscope image of the obtained sample was measured, and the result was basically consistent with the result of Example 1.

The Raman spectrum of the obtained sample was measured, and the result was basically consistent with the result of Example 1.

Example 5 Preparation method of a two-dimensional double-layer tungsten sulfide homojunction with different twisted configurations

A method for preparing a two-dimensional double-layer tungsten sulfide homojunction with different twisted configurations comprises the following steps:

S1. Soak the SiO ₂ /Si substrate in acetone solution for 20 minutes, then ultrasonically clean it in isopropanol solution for 20 minutes, then repeat ultrasonic cleaning with deionized water for 3 times, and finally blow dry with high-purity nitrogen gas for standby use;

S2. Place 0.8g S powder, 0.06g WO ₃ powder and pre-treated SiO ₂ /Si substrate in a corundum container from upwind to downwind, with the distance between S powder and WO ₃ being 20cm, and the distance between SiO ₂ /Si substrate and WO ₃ being 25cm, as shown in FIG1 ;

S3. Turn on the vacuum pump and pump the air pressure in the tube to below 2.0×10 ^-2 Torr. Then, introduce inert gas to make the air pressure in the tube 10 Torr higher than the atmospheric pressure and then pump the air again. Repeat this step 2 to 3 times to exhaust all the air.

S4, starting to heat the tube furnace, heating it to 650°C at 20°C/min, then heating it to 910°C at 10°C/min, then keeping it at that temperature for 15 minutes, and finally cooling it naturally to room temperature, to obtain a two-dimensional double-layer tungsten sulfide homojunction on the SiO ₂ /Si substrate;

The inert gas flow rate is maintained at 100 sccm throughout the entire process and the gas flow direction is from the sulfur source area to the deposition area via the tungsten source area.

The optical microscope image of the obtained sample was measured, and the result was basically consistent with the result of Example 1.

The Raman spectrum of the obtained sample was measured, and the result was basically consistent with the result of Example 1.

Comparative Example 1: Preparation method of a two-dimensional single-layer tungsten sulfide homojunction

A method for preparing a two-dimensional single-layer tungsten sulfide homojunction comprises the following steps:

S1. Soak the SiO ₂ /Si substrate in acetone solution for 20 minutes, then ultrasonically clean it in isopropanol solution for 20 minutes, then repeat ultrasonic cleaning with deionized water for 3 times, and finally blow dry with high-purity nitrogen gas for standby use;

S2. Place 0.6g S powder, 0.1g WO ₃ powder and pre-treated SiO ₂ /Si substrate in a corundum container from upwind to downwind, with the distance between S powder and WO ₃ being 20cm, and the distance between SiO ₂ /Si substrate and WO ₃ being 25cm, as shown in FIG1 ;

S3. Turn on the vacuum pump and pump the air pressure in the tube to below 2.0×10 ^-2 Torr. Then, introduce inert gas to make the air pressure in the tube 10 Torr higher than the atmospheric pressure and then pump the air again. Repeat this step 2 to 3 times to exhaust all the air.

S4, starting to heat the tube furnace to 650°C at 20°C/min, then heating to 910°C at 20°C/min, then keeping the temperature for 13 minutes, and finally cooling naturally to room temperature, to obtain a two-dimensional tungsten sulfide homojunction on the SiO ₂ /Si substrate;

The inert gas flow rate is maintained at 90 sccm throughout the entire process and the gas flow direction is from the sulfur source area to the deposition area via the tungsten source area.

The difference between Comparative Example 1 and Example 2 is that the temperature is raised to 910° C. at 20° C./min, and the other raw materials and steps are the same as those in Example 2.

The optical microscope image of the obtained sample is measured, and the result is shown in Figure 4. The product obtained by this method is a two-dimensional monolayer tungsten sulfide. It can be seen from the figure that the prepared two-dimensional tungsten sulfide presents triangular flakes and the color of the flakes is uniform, indicating that a highly crystalline two-dimensional tungsten sulfide has been prepared. Due to the rapid temperature increase in the high-temperature reaction stage, the nucleation sites cannot be fully grown, which affects the deposition growth of the source material, so a two-dimensional monolayer tungsten sulfide is prepared.

The Raman spectrum of the obtained sample was measured, and the result is shown in FIG5 . The Raman peaks of the two-dimensional tungsten sulfide E ¹ _2g and A _1g obtained by this method are located at 355.2 cm ^-1 and 421.2 cm ^-1 , respectively, and the difference is 65.0 cm ^-1 , which proves that the prepared two-dimensional tungsten sulfide is a two-dimensional monolayer tungsten sulfide.

Comparative Example 2: Preparation method of a two-dimensional single-layer tungsten sulfide homojunction

A method for preparing a two-dimensional single-layer tungsten sulfide homojunction comprises the following steps:

S1. Soak the SiO ₂ /Si substrate in acetone solution for 20 minutes, then ultrasonically clean it in isopropanol solution for 20 minutes, then repeat ultrasonic cleaning with deionized water for 3 times, and finally blow dry with high-purity nitrogen gas for standby use;

S2. Place 0.6g S powder, 0.1g WO ₃ powder and pre-treated SiO ₂ /Si substrate in a corundum container from upwind to downwind, with the distance between S powder and WO ₃ being 20cm, and the distance between SiO ₂ /Si substrate and WO ₃ being 25cm, as shown in FIG1 ;

S3. Turn on the vacuum pump and pump the air pressure in the tube to below 2.0×10 ^-2 Torr. Then, introduce inert gas to make the air pressure in the tube 10 Torr higher than the atmospheric pressure and then pump the air again. Repeat this step 2 to 3 times to exhaust all the air.

S4, starting to heat the tube furnace, heating it to 650°C at 20°C/min, then heating it to 910°C at 10°C/min, then keeping it at that temperature for 13 minutes, and finally cooling it naturally to room temperature, to obtain a two-dimensional tungsten sulfide homojunction on the SiO ₂ /Si substrate;

The inert gas flow rate is maintained at 150 sccm throughout the entire process and the gas flow direction is from the sulfur source area to the deposition area via the tungsten source area.

The difference between Comparative Example 2 and Example 2 is that the inert gas flow rate is maintained at 150 sccm throughout the process, and other raw materials and steps are the same as those in Example 2.

The optical microscope image of the obtained sample was measured, and the result was basically consistent with the result of Comparative Example 1. The method obtained a two-dimensional tungsten sulfide with high crystallinity. Since the inert gas flow rate was too fast in the high-temperature reaction stage, it affected the deposition growth of the source material and was not conducive to the growth of a double-layer homojunction, so a two-dimensional single-layer tungsten sulfide was prepared.

The Raman spectrum of the obtained sample was measured, and the result was basically consistent with the result of comparative example 1, proving that this method can prepare a two-dimensional single-layer tungsten sulfide.

The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims (10)

1. A method for preparing a two-dimensional double-layer tungsten sulfide homojunction, characterized in that it comprises the following steps:

   S1. Place a sulfur source, a tungsten source and a pretreated substrate in order from upwind to downwind. Under an inert gas atmosphere, maintain the flow rate of the inert gas at 60 to 120 sccm, set the heating rate at 20 to 25°C/min, and heat to 600 to 650°C.

   S2. Set the heating rate to 5-15°C/min, raise the temperature to 800°C-1100°C, keep the temperature for 5-20 minutes, and cool to obtain a two-dimensional tungsten sulfide homojunction on the substrate.
2. The preparation method according to claim 1 is characterized in that, in step S1, the placement distance between the sulfur source and the tungsten source is 10 to 25 cm.
3. The preparation method according to claim 1 is characterized in that, in step S1, the placement distance between the substrate and the tungsten source is 15 to 35 cm.
4. The preparation method according to claim 1 is characterized in that, in step S1, the molar ratio of the sulfur source to the tungsten source is 40:1 to 200:1.
5. The preparation method according to claim 1, characterized in that the sulfur source is sulfur powder or disodium trioxysulfide.
6. The preparation method according to claim 1 is characterized in that the tungsten source is one of tungsten trioxide, tungsten oxide, and tungsten hexacarbonyl.
7. The preparation method according to claim 1 is characterized in that in step S1, the pretreatment method is: washing the substrate with an organic solvent and deionized water, and drying it for standby use.
8. The preparation method according to claim 1, characterized in that the substrate is any one of SiO ₂ /Si, Cu, Pt, Ni, and Au.
9. The preparation method according to claim 1 is characterized in that, in step S2, the twist angle range of the homojunction is 0° and/or 60°.
10. Application of the preparation method according to any one of claims 1 to 9 in the fields of transistors, photodetectors and torsional electronics.