Preparation method of molybdenum disulfide nano-island modified tungsten disulfide film, product and application thereof

Abstract

The application discloses a preparation method, product and application of a MoS2 nano-island modified WS2 film. The steps comprise: growing a WS2 film on a substrate and performing surface activation treatment; preparing a precursor solution, spin-coating the precursor solution on the surface of the WS2 film, and then drying; using a chemical vapor deposition process to perform high-temperature sulfuration treatment in a sulfur atmosphere, and in-situ generating MoS2 nano-islands; and finally, annealing, heat preservation and natural cooling in an inert atmosphere. The obtained film is composed of a continuous WS2 bottom layer and a discrete MoS2 nano-island upper layer, and the interface is stable and the crystallization quality is high. The material is suitable for a room-temperature resistance type or field effect transistor type gas sensor, and can detect NO2, NH3, H2S, SO2, CO, water vapor or mixed gas.

Description

Technical Field

[0001] This invention belongs to the field of nanocomposite material preparation and gas sensing technology, and in particular relates to a method for preparing MoS2 nanoisland modified WS2 thin films, and the application of the composite material obtained by this method in gas sensing. Background Technology

[0002] With the development of environmental monitoring, industrial safety, food inspection, human health monitoring, and smart wearable devices, higher demands are being placed on gas sensors. While traditional metal oxide gas sensing materials possess high sensitivity, they typically require high operating temperatures and suffer from problems such as high power consumption, difficulties in flexible integration, and insufficient selectivity. Therefore, developing highly sensitive gas sensing materials that can operate at room temperature or low temperatures is of great significance.

[0003] Two-dimensional transition metal dichalcogenide (TMD) materials possess atomic-level thickness, large specific surface area, tunable band structure, and abundant surface active sites, making them promising candidates for gas sensing. Among them, WS2 (tungsten disulfide), a typical two-dimensional semiconductor, exhibits excellent response to oxidizing gases such as NO2 (nitrogen dioxide). However, pure WS2 films suffer from insufficient active sites, slow response recovery, and limited sensitivity to low-concentration gases.

[0004] Constructing heterojunctions is an effective strategy to improve the gas-sensing performance of TMDs. MoS2 (molybdenum disulfide) and WS2, due to their similar lattice constants (mismatch of about 4%) and both being hexagonal crystal systems, readily form high-quality van der Waals heterojunctions. Existing MoS2 / WS2 heterojunctions are mostly continuous layered stacked structures. Although interfaces can be formed, the continuous surface contact mode limits the exposure of the heterojunction interface, making it difficult for gas molecules to fully contact the active interface region.

[0005] In summary, a novel method for preparing MoS2 / WS2 is urgently needed to solve the aforementioned technical problems. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing MoS2 nano-island modified WS2 thin films, products and applications. The method involves growing discretely distributed MoS2 nano-islands in situ on the surface of WS2 thin films to form a localized heterojunction array, thereby significantly improving gas sensing performance.

[0007] To achieve the objectives of this invention, on one hand, this invention provides a method for preparing MoS2 nano-island modified WS2 thin films, comprising the following steps:

[0008] Step 1: A continuous monolayer WS2 thin film is grown on the substrate surface by chemical vapor deposition to obtain a WS2 thin film substrate;

[0009] Step 2: Activate the surface of the WS2 thin film substrate to introduce uniform active nucleation sites on the WS2 surface;

[0010] Step 3: Dissolve sodium molybdate and thiourea in deionized water and stir until dissolved to obtain a precursor solution;

[0011] Step 4: Drop the precursor solution onto the surface of the activated WS2 thin film substrate and spin-coat it several times. Then place it in a dry oven for baking until the surface is dry to obtain the treated WS2 thin film substrate.

[0012] Step 5: The treated WS2 thin film substrate is subjected to high-temperature sulfurization treatment in a sulfur atmosphere carried by an inert gas using chemical vapor deposition process, so that the precursor reacts in situ on the WS2 surface to generate discretely distributed monolayer triangular MoS2 nano islands. The MoS2 nano islands form a vertical van der Waals heterostructure with the underlying WS2 thin film to obtain a substrate of WS2 thin film modified with MoS2 nano islands.

[0013] Step 6: Anneal the substrate of the MoS2 nanoisland modified WS2 film to complete the preparation.

[0014] Furthermore, in step 3, the molar ratio of sodium molybdate to thiourea is 1:3 to 1:8, the concentration of sodium molybdate is 0.005 to 0.09 mol / L, the amount of deionized water is 10 ml, and the stirring time is 10 to 30 minutes.

[0015] Furthermore, the spin coating in step 4 is performed using a spin coater, with 1 to 4 spin coats, each spin coat at a speed of 1000 to 4000 rpm and a spin coat time of 30 to 60 seconds; the baking temperature is 60 to 90°C and the baking time is 5 minutes.

[0016] Furthermore, the chemical vapor deposition process in step 5 is as follows: the treated WS2 thin film substrate is placed in the center of the quartz tube of the chemical vapor deposition equipment, 0.5-4g of sulfur powder is placed at a position of 23-25cm at the front end of the substrate, and an inert gas is introduced into the reaction environment. The ambient temperature is raised to 650-720℃ at a rate of 5℃ / min, and then kept at this temperature for 5 minutes before naturally cooling to room temperature to obtain a substrate of MoS2 nano-island modified WS2 thin film.

[0017] Furthermore, the annealing process in step 6 specifically involves heating the substrate of the MoS2 nanoisland modified WS2 film to 300~450°C under an inert atmosphere and holding it at that temperature for 30~120 minutes, followed by natural cooling to room temperature.

[0018] On the other hand, the present invention also provides a MoS2 nano-island modified WS2 film, which is prepared by the above preparation method. The film consists of a bottom continuous monolayer WS2 film and an upper discretely distributed monolayer triangular MoS2 nano-islands. The MoS2 nano-islands and the WS2 film form a vertical van der Waals heterostructure.

[0019] The film consists of a bottom continuous WS2 film and an upper discretely distributed MoS2 nanoislands. The lateral dimensions of the MoS2 nanoislands are 50~500 nm, the height is 10~80 nm, and the coverage is 5%~50%.

[0020] Finally, the present invention also provides an application of the above-mentioned MoS2 nanoisland modified WS2 thin film, wherein the thin film is used in the preparation of a resistive or field-effect transistor gas sensor for detecting ppb-level concentrations of gas at room temperature.

[0021] The gas sensor is one of a resistive or field-effect transistor type gas sensor, used to detect NO2, NH3, H2S, SO2, CO, water vapor, or mixed gases at room temperature.

[0022] The significant advancement of this invention compared to existing technologies lies in:

[0023] (1) Structural innovation: This invention constructs discretely distributed MoS2 nano-islands on the surface of WS2 thin film to form a localized heterojunction array; compared with continuous stacked heterojunctions, the discrete nano-island structure has a large number of exposed edge sites, which greatly improves the utilization rate of the heterojunction interface and the adsorption activity of gas molecules.

[0024] (2) Improved sensing performance of low concentration NO2 at room temperature: The MoS2 and WS2 interface of the present invention forms a built-in electric field, which promotes charge separation and transfer in the gas-sensitive reaction; at the same time, due to the discrete distribution of nano-islands, each nano-island works independently, avoiding the carrier short-circuit effect that may occur in continuous thin films, thus achieving high sensitivity detection of ppb level NO2 at room temperature, with fast response speed and good recovery.

[0025] (3) Simple and controllable process: The present invention adopts a solution spin-coating precursor combined with a short-time chemical vapor phase sulfidation process, which does not require complex photolithography steps; by adjusting the precursor concentration, spin-coating times and sulfidation temperature, the size, density and coverage of MoS2 nano islands can be precisely controlled. The process is simple, low-cost and suitable for large-scale preparation.

[0026] (4) High interface quality: By controlling the sulfidation temperature and time (holding for only 5 minutes at 650~720℃), the present invention effectively suppressed the excessive growth and aggregation of MoS2, and obtained a nano-island structure with high lattice quality and good bonding with WS2 substrate; the subsequent annealing treatment further improved the interface stability.

[0027] (5) Good application effect: The gas-sensing performance of the MoS2 nano-island modified WS2 composite film of the present invention has excellent detection effect on a variety of gases.

[0028] To more clearly illustrate the functional characteristics and structural parameters of the present invention, further explanation is provided below in conjunction with the accompanying drawings and specific embodiments. Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0030] Figure 1 This is a schematic diagram of the structure of the WS2 thin film modified with MoS2 nanoislands in this invention;

[0031] Figure 2 This is an optical mirror image of the WS2 thin film modified with MoS2 nanoislands in this invention;

[0032] Figure 3 The Raman spectrum in Embodiment 1 of this invention shows both MoS2 and WS2 characteristic peaks.

[0033] Figure 4 This is a schematic diagram of the interpolation electrode structure in Embodiment 1 of the present invention;

[0034] Figure 5 This is the dynamic response curve of the gas sensor in Embodiment 1 of the present invention to 50 ppb NO2 at room temperature;

[0035] Figure 6 This is a bar chart comparing the responses of Example 1 of the present invention and the comparative example (pure WS2 film) to 50 ppb NO2, 50 ppm NH3, 50 ppm H2S, 200 ppm CO, and 200 ppm H2. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The present invention discloses a method for preparing a MoS2 nano-island modified WS2 thin film, comprising the following steps:

[0038] Step 1: A continuous monolayer WS2 thin film is grown on the substrate surface by chemical vapor deposition to obtain a WS2 thin film substrate;

[0039] Step 2: Activate the surface of the WS2 thin film substrate to introduce uniform active nucleation sites on the WS2 surface;

[0040] Step 3: Dissolve sodium molybdate and thiourea in deionized water and stir until dissolved to obtain a precursor solution;

[0041] Step 4: Drop the precursor solution onto the surface of the activated WS2 thin film substrate and spin-coat it several times. Then place it in a dry oven for baking until the surface is dry to obtain the treated WS2 thin film substrate.

[0042] Step 5: The treated WS2 thin film substrate is subjected to high-temperature sulfurization treatment in a sulfur atmosphere carried by an inert gas using chemical vapor deposition process, so that the precursor reacts in situ on the WS2 surface to generate discretely distributed monolayer triangular MoS2 nano islands. The MoS2 nano islands form a vertical van der Waals heterostructure with the underlying WS2 thin film to obtain a substrate of WS2 thin film modified with MoS2 nano islands.

[0043] Step 6: Anneal the substrate of the MoS2 nanoisland modified WS2 film to complete the preparation.

[0044] Furthermore, the substrate on the substrate surface in step 1 is selected as a silicon substrate, a silicon substrate with an oxide layer, a sapphire substrate, or a quartz substrate.

[0045] Furthermore, the thickness of the WS2 film in step 1 is 1~10 nm.

[0046] Furthermore, the surface activation treatment in step 2 specifically includes: oxygen plasma treatment or ultraviolet light irradiation using a mask;

[0047] Furthermore, the oxygen plasma treatment time is 1-3 minutes;

[0048] Furthermore, the ultraviolet irradiation method using a mask: the mask is composed of uniform holes with a hole size of 100~500nm, a hole coverage rate of 50~70%, and an ultraviolet irradiation time of 3~8min.

[0049] Furthermore, in step 3, the molar ratio of sodium molybdate to thiourea is 1:3 to 1:8, the concentration of sodium molybdate is 0.005 to 0.09 mol / L, the amount of deionized water is 10 ml, and the stirring time is 10 to 30 minutes.

[0050] Furthermore, the spin coating in step 4 is performed using a spin coater, with 1 to 4 spin coats, each spin coat at a speed of 1000 to 4000 rpm and a spin coat time of 30 to 60 seconds; the baking temperature is 60 to 90°C and the baking time is 5 minutes.

[0051] Furthermore, the chemical vapor deposition process in step 5 is as follows: the treated WS2 thin film substrate is placed in the center of the quartz tube of the chemical vapor deposition equipment, 0.5-4g of sulfur powder is placed at a position of 23-25cm at the front end of the substrate, and nitrogen gas with an inert gas flow rate of 50-180sccm is continuously introduced into the reaction environment to protect the entire reaction environment. The ambient temperature is raised to 650-720℃ at a rate of 5℃ / min, and then held at that temperature for 5 minutes before naturally cooling to room temperature to obtain the substrate of the MoS2 nano-island modified WS2 thin film.

[0052] Furthermore, the annealing process in step 6 specifically involves heating the substrate of the MoS2 nanoisland modified WS2 film to 300~450°C under an inert atmosphere and holding it at that temperature for 30~120 minutes, followed by natural cooling to room temperature.

[0053] The present invention discloses a MoS2 nano-island modified WS2 film, which is prepared by the above preparation method. The film consists of a bottom continuous monolayer WS2 film and an upper discretely distributed monolayer triangular MoS2 nano-islands. The MoS2 nano-islands and the WS2 film form a vertical van der Waals heterostructure.

[0054] The film consists of a bottom continuous WS2 film and an upper discretely distributed MoS2 nanoislands. The lateral dimensions of the MoS2 nanoislands are 50~500 nm, the height is 10~80 nm, and the coverage is 5%~50%.

[0055] One application of the above-mentioned MoS2 nanoisland modified WS2 thin film of the present invention is the application of the thin film in the preparation of a resistive or field-effect transistor gas sensor for detecting gas concentrations at ppb level at room temperature.

[0056] The gas sensor is one of a resistive or field-effect transistor type gas sensor, used to detect NO2, NH3, H2S, SO2, CO, water vapor, or mixed gases at room temperature.

[0057] Example 1

[0058] This embodiment describes a method for preparing a MoS2 nano-island modified WS2 thin film, comprising the following steps:

[0059] (1) A continuous WS2 thin film was prepared on a SiO2 or Si (where the SiO2 thickness is 298nm) substrate by chemical deposition. Specifically, 0.005g of WO3 powder and 3g of sulfur powder were placed in the center and upstream of a tube furnace, respectively, with the sulfur powder 25cm upstream of the WO3. Nitrogen was used as the carrier gas, and the film was sulfurized at 760 °C for 10 minutes to obtain a continuous WS2 thin film with a thickness of about 3nm.

[0060] (2) The above WS2 thin film substrate was subjected to oxygen plasma treatment (power 50 W, time 2 minutes) to improve the surface hydrophilicity;

[0061] (3) Weigh 0.0242 g sodium molybdate (Na2MoO4·2H2O, 0.1 mmol) and 0.0228 g thiourea (0.3 mmol), dissolve them in 10 ml deionized water, stir for 15 minutes until completely dissolved, and obtain a clear solution;

[0062] (4) Use a dropper to draw up the above solution and drop it onto the surface of the WS2 film treated in step (2). Spin coat at 3000 rpm for 60 seconds and repeat the spin coating 5 times. After spin coating, place the substrate in an 80 ℃ oven and bake for 5 minutes.

[0063] (5) Place the dried substrate in the center of the quartz tube of the tubular furnace; place 0.3g of sulfur powder at a distance of 24 cm from the substrate; introduce argon gas with a flow rate of 170 sccm, heat to 680℃ at a rate of 5℃ / min, hold for 5 minutes and then cool naturally to room temperature to obtain the WS2 film modified with MoS2 nano islands.

[0064] (6) The MoS2 nanoisland-modified WS2 film was annealed at 380 °C for 1 hour under an argon atmosphere to finally obtain the MoS2 nanoisland-modified WS2 film, the structure of which is as follows: Figure 1 As shown, the optical mirror diagram of its 50μm magnification lens is as follows. Figure 2 As shown, its Raman characteristic peaks are Figure 3 As shown.

[0065] The comparative example is a pure WS2 film containing only step (1) above.

[0066] The gas-sensing performance of Example 1 and Comparative Example 1 was tested. Specifically, the thin films of Example 1 and Comparative Example 1 were fabricated into resistive sensors (Au / Ti interdigitated electrodes, interdigitation width 10 μm, spacing 50 μm), as follows: Figure 4 As shown; tested at 25℃ room temperature and 5% relative humidity;

[0067] Test results show that the sensor in Example 1 has a response value of 55.9% to 50 ppb NO2. ;in, The resistance in air. This represents the difference in resistance between the device and the target gas. (This is the response value). The device has a response time of 257 seconds and a recovery time of 94 seconds. Figure 5 As shown, the selectivity for NO2 is significantly better than that for 50 ppm NH3, 50 ppm H2S, 100 ppm CO, and 100 ppm H2. Figure 6 As shown; while the response value of the sensor in Comparative Example 1 to 50 ppb NO2 was 22.8%, indicating that the MoS2 nano-island modification of the present invention significantly improves the room temperature NO2 gas sensing performance of the WS2 film.

[0068] Example 2

[0069] The difference between this embodiment and Example 1 is that in step (3), the amount of sodium molybdate is 0.0484 g (0.2 mmol) and the amount of thiourea is 0.0456 g (0.6 mmol); the number of spin coatings is 2; the resulting MoS2 nanoislands are smaller (about 80 nm) and have a lower coverage (about 15%); the gas-sensitive test shows that it still has a distinguishable response to low concentrations of NO2 (100 ppb).

[0070] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0071] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing MoS2 nano-island modified WS2 thin films, characterized in that, Includes the following steps: Step 1: A continuous monolayer WS2 thin film is grown on the substrate surface by chemical vapor deposition to obtain a WS2 thin film substrate; Step 2: Activate the surface of the WS2 thin film substrate to introduce uniform active nucleation sites on the WS2 surface; Step 3: Dissolve sodium molybdate and thiourea in deionized water and stir until dissolved to obtain a precursor solution; Step 4: Drop the precursor solution onto the surface of the activated WS2 thin film substrate and spin-coat it several times. Then place it in a dry oven for baking until the surface is dry to obtain the treated WS2 thin film substrate. Step 5: The treated WS2 thin film substrate is subjected to high-temperature sulfurization treatment in a sulfur atmosphere carried by an inert gas using chemical vapor deposition process, so that the precursor reacts in situ on the WS2 surface to generate discretely distributed monolayer triangular MoS2 nano islands. The MoS2 nano islands form a vertical van der Waals heterostructure with the underlying WS2 thin film to obtain a substrate of WS2 thin film modified with MoS2 nano islands. Step 6: Anneal the substrate of the MoS2 nanoisland modified WS2 film to complete the preparation.

2. The method for preparing a MoS2 nano-island modified WS2 thin film according to claim 1, characterized in that, In step 3, the molar ratio of sodium molybdate to thiourea is 1:3 to 1:8, the concentration of sodium molybdate is 0.005 to 0.09 mol / L, the amount of deionized water is 10 ml, and the stirring time is 10 to 30 minutes.

3. The method for preparing a MoS2 nano-island modified WS2 thin film according to claim 1, characterized in that, The spin coating in step 4 is performed using a spin coater, with 1 to 4 spin coats, each spin coat at a speed of 1000 to 4000 rpm and a spin coat time of 30 to 60 seconds; the baking temperature is 60 to 90°C and the baking time is 5 minutes.

4. The method for preparing a MoS2 nano-island modified WS2 thin film according to claim 1, characterized in that, The chemical vapor deposition process in step 5 is as follows: the treated WS2 thin film substrate is placed in the center of the quartz tube of the chemical vapor deposition equipment, 0.5-4g of sulfur powder is placed at a position of 23-25cm at the front end of the substrate, and an inert gas is introduced into the reaction environment. The ambient temperature is raised to 650-720℃ at a rate of 5℃ / min, and then kept at this temperature for 5 minutes before naturally cooling to room temperature to obtain a substrate of MoS2 nano-island modified WS2 thin film.

5. The method for preparing a MoS2 nano-island modified WS2 thin film according to claim 1, characterized in that, The annealing process in step 6 is as follows: under an inert atmosphere, the substrate of the MoS2 nano-island modified WS2 film is heated to 300~450℃ and held for 30~120 minutes, and then naturally cooled to room temperature.

6. A MoS2 nanoisland modified WS2 thin film, characterized in that, The film is prepared by any one of the preparation methods described in claims 1-5. The film consists of a bottom continuous monolayer WS2 film and an upper discretely distributed monolayer triangular MoS2 nanoislands. The MoS2 nanoislands and the WS2 film form a vertical van der Waals heterostructure.

7. The MoS2 nano-island modified WS2 thin film according to claim 6, characterized in that, The film consists of a bottom continuous WS2 film and an upper discretely distributed MoS2 nanoislands. The lateral dimensions of the MoS2 nanoislands are 50~500 nm, the height is 10~80 nm, and the coverage is 5%~50%.

8. The use of the MoS2 nanoisland modified WS2 thin film according to claim 7, characterized in that, The thin film is used in the fabrication of resistive or field-effect transistor gas sensors for detecting ppb-level gas concentrations at room temperature.

9. The use according to claim 8, characterized in that, The gas sensor is one of a resistive or field-effect transistor type gas sensor, used to detect NO2, NH3, H2S, SO2, CO, water vapor, or mixed gases at room temperature.

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