A controllable preparation method of high aspect ratio molybdenum disulfide nanobelt or microbelt

Abstract

The application relates to a controllable preparation method of high-length-width-ratio molybdenum disulfide nanobelt or microbelt, and belongs to the field of low-dimensional material preparation. A molybdate solution is used as a molybdenum source, a sodium hydroxide solution is used as a catalyst, and sulfur powder is used as a sulfur source, and the molybdenum disulfide nanobelt or microbelt is obtained through a chemical vapor deposition method; by adjusting the different proportions of the mixed solution of sodium molybdate and sodium hydroxide, the size and orientation of the nanobelt / microbelt can be controlled and adjusted; by adjusting the growth time, the layer number of the nanobelt / microbelt can be adjusted; finally, the molybdenum disulfide nanobelt / microbelt with a length-width ratio greater than 100, different sizes, orientations and layer numbers can be controllably obtained on a substrate. The preparation process is simple, the production cost is low, the size, orientation and layer number are controllable, and the method is suitable for batch production.

Description

Technical Field

[0001] This invention belongs to the field of low-dimensional material preparation, and more specifically, relates to a controllable preparation method of molybdenum disulfide nanoribbons or microribbons with high aspect ratio. Background Technology

[0002] Molybdenum disulfide (MoS2) possesses excellent mechanical, electrical, and optoelectronic properties, showing great potential for applications in ultrathin electronic, optoelectronic, sensing, and storage devices. Especially when its morphology is altered or further reduced to quasi-one-dimensional (nano / microbands), it exhibits novel properties such as metallic edge states, one-dimensional confined electrical and magnetic properties, and superior optoelectronic performance. Currently, research on low-dimensional MoS2 is primarily based on theoretical calculations, and the experimental fabrication of high aspect ratio nano / microbands remains challenging. The few existing methods for fabricating low-dimensional MoS2 nano / microbands mainly involve top-down etching using micro / nano fabrication techniques. However, this method is cumbersome and inevitably introduces impurities and defects, affecting the crystal quality of the obtained material. Compared to these top-down methods, chemical vapor deposition (CVD) is relatively simpler and less expensive; however, obtaining uniformly distributed MoS2 nano / microbands with controllable orientation, size, and number of layers using CVD remains a significant challenge. Summary of the Invention

[0003] This invention provides a controllable preparation method for molybdenum disulfide nano / microribbons with high aspect ratios. The method uses molybdate solution as the molybdenum source, sodium hydroxide solution as the catalyst, and sulfur powder as the sulfur source, obtained via tube furnace chemical vapor deposition. By adjusting the concentration of sodium hydroxide, the size and orientation of the nano / microribbons can be controlled. By adjusting the growth time, the number of nano / microribbon layers can be adjusted. Ultimately, high aspect ratio molybdenum disulfide nano / microribbons of different sizes, orientations, and number of layers can be controllably obtained on a substrate. This addresses the technical problem in existing nano / microribbon preparation techniques where impurities and defects are inevitably introduced, affecting the crystal quality of the obtained material.

[0004] According to a first aspect of the present invention, a controllable preparation method for molybdenum disulfide nanoribbons or microribbons is provided, comprising the following steps:

[0005] (1) A mixed solution of molybdenum source and sodium hydroxide as catalyst is spin-coated onto a substrate to obtain a substrate with molybdenum source and catalyst uniformly distributed, wherein the molybdenum source is sodium molybdate or ammonium molybdate.

[0006] (2) The substrate obtained in step (1) is placed in the third temperature zone of the three-temperature zone chemical vapor deposition apparatus, and the sulfur powder is placed in the first temperature zone. The third temperature zone and the first temperature zone are separated by the second temperature zone. The three-temperature zone chemical vapor deposition apparatus is evacuated and then cleaned, so that the gas flow is blown from the direction of the first temperature zone to the direction of the third temperature zone. Then, it is heated so that the sulfur powder in the first temperature zone sublimates into a gaseous state, and the spin-coated material on the substrate in the third temperature zone generates a sodium molybdenum oxide intermediate. The gaseous sulfur reacts with the sodium molybdenum oxide intermediate to obtain molybdenum disulfide nanoribbons or molybdenum disulfide microribbons.

[0007] Preferably, when the concentration of sodium hydroxide in the mixed solution is 1 mM, six-fold symmetrical orientation nanoribbons are obtained;

[0008] When the concentration of sodium hydroxide in the mixed solution is greater than 1 mM and less than 1.5 mM, nanoribbons grown with six-fold symmetry orientation and microribbons grown with two-fold symmetry orientation are obtained.

[0009] When the concentration of sodium hydroxide in the mixed solution is 1.5 mM, micron bands with a double symmetry orientation are obtained;

[0010] When the concentration of sodium hydroxide in the mixed solution is greater than 1.5 mM and less than 5 mM, micron bands with dual symmetry orientation and disordered growing network micron bands are obtained.

[0011] When the concentration of sodium hydroxide in the mixed solution is greater than or equal to 5 mM and less than or equal to 7 mM, disordered growing network micron bands are obtained.

[0012] Preferably, in step (2), when the growth time is less than or equal to 5 min, a single-layer molybdenum disulfide nanoribbon or molybdenum disulfide microribbon is obtained; when the growth time is greater than 5 min but less than 10 min, a molybdenum disulfide nanoribbon or microribbon containing both single and multiple layers is obtained; when the growth time is greater than or equal to 10 min, a multilayer molybdenum disulfide nanoribbon or microribbon is obtained.

[0013] Preferably, the reaction temperature in the first temperature zone is 150℃~250℃, the reaction temperature in the second temperature zone is 300℃~400℃, and the reaction temperature in the third temperature zone is 700℃~850℃.

[0014] Preferably, in step (2), the substrate is placed face down in the third temperature zone of the three-temperature zone chemical vapor deposition apparatus, which makes it more conducive to the flow of sodium molybdenum oxide intermediate on the substrate surface during the growth process.

[0015] Preferably, in step (1), the spin coating speed is 1000 rpm to 3000 rpm and the time is more than 60 s.

[0016] Preferably, the aspect ratio of the molybdenum disulfide nanoribbons or molybdenum disulfide microribbons is 100 or higher.

[0017] Preferably, the substrate is subjected to oxygen plasma treatment before spin coating.

[0018] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0019] (1) The molybdenum disulfide nano / microbands obtained by the present invention have excellent crystal quality and a high aspect ratio, which can be greater than 100. Compared with the molybdenum disulfide nano / microbands obtained by previous methods, they are all at a higher level.

[0020] (2) This method employs a pre-spin-coating of the reactant solution onto the substrate and effectively improves the wetting properties between the solution and the substrate through oxygen plasma treatment. Compared with the method using reactant powder, this is more conducive to obtaining molybdenum disulfide nano / microbands with better uniformity on the substrate.

[0021] (3) This method allows for the adjustment of the size and orientation of the grown molybdenum disulfide nano / microribbons by regulating the concentration of sodium hydroxide in the mixed solution of sodium molybdate and sodium hydroxide. Compared with previous growth methods, this method offers greater controllability over the size and orientation of the obtained material.

[0022] (4) This method can adjust the number of molybdenum disulfide nano / microbands obtained by simply adjusting the reaction time. Compared with the previous growth method, this method has higher controllability of the number of layers.

[0023] (5) The present invention uses a low-cost sapphire substrate, eliminating the need for a high-cost special substrate; and achieves direct chemical vapor deposition of molybdenum disulfide nano / micro strips, effectively avoiding contamination and defects introduced by etching through cumbersome and high-cost micro / nano processing technology. Attached Figure Description

[0024] Figure 1 and Figure 2 The characterization diagram of the obtained high aspect ratio molybdenum disulfide nano / microbands is shown, where: Figure 1 For scanning electron microscopy, Figure 2 This refers to X-ray photoelectron spectroscopy.

[0025] Figure 3 This is a schematic diagram of the preparation process, in which: Figure 3 (a) in the diagram is a schematic diagram of the dropwise addition and spin-coating of a mixed solution of sodium molybdate and sodium hydroxide. Figure 3 (b) in the diagram is a schematic diagram of a chemical vapor deposition system.

[0026] Figure 4The effect of sodium hydroxide concentration on the size and orientation of molybdenum disulfide nano / microbands is given by: Figure 4 (a) Figure 4 (b) Figure 4 (c) in the figure shows optical micrographs of molybdenum disulfide nano / microbands obtained with sodium hydroxide concentrations of 1 mM, 1.5 mM and 5 mM.

[0027] Figure 5 The effect of growth time on the number of layers in molybdenum disulfide nano / microbands is shown, where: Figure 5 (a) Figure 5 (b) shows optical micrographs of molybdenum disulfide nano / microbands obtained at growth times of 5 min and 10 min, respectively.

[0028] Figure 6 The electrical and photoelectric properties of the phototransistor fabricated based on this molybdenum disulfide nanoribbon / microribbon are shown, wherein: Figure 6 (a) in the figure is its transfer characteristic curve. Figure 6 (b) is a graph showing the relationship between responsivity and specific detectivity and incident light power. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] This invention proposes a high aspect ratio molybdenum disulfide nano / microribbons and a controllable preparation method thereof, enabling the controllable growth of molybdenum disulfide nano / microribbons of different sizes, orientations, and number of layers on sapphire substrates. In practical preparation, according to the requirements of the designed target material, the desired size, orientation, and thickness of the high aspect ratio molybdenum disulfide nano / microribbons can be obtained by adjusting the concentration of sodium hydroxide in the mixed solution and the growth time of chemical vapor deposition. Because this method is simple, controllable, and low-cost, and the obtained molybdenum disulfide nano / microribbons have excellent crystal quality and a high aspect ratio, it has great potential for practical applications.

[0031] This invention uses molybdate solution as the molybdenum source, sodium hydroxide solution as the catalyst, and sulfur powder as the sulfur source, and obtains them through tube furnace chemical vapor deposition. By adjusting different ratios of the sodium molybdate and sodium hydroxide mixed solution, the size and orientation of the nano / microbands can be controlled. By adjusting the growth time, the number of nano / microband layers can be adjusted. Finally, high aspect ratio molybdenum disulfide nano / microbands of different sizes, orientations, and number of layers can be controllably obtained on the substrate.

[0032] This invention discloses a controllable preparation method for high aspect ratio molybdenum disulfide nano / microbands, comprising:

[0033] (1) Prepare a mixed solution of sodium molybdate and sodium hydroxide in a specific ratio.

[0034] According to the different sizes and orientations of molybdenum disulfide nano / microbelts to be grown, different proportions of sodium molybdate and sodium hydroxide mixed solutions are prepared; wherein, the concentration of sodium molybdate is constant at 7.5 mM (mmol / L), and the concentration of sodium hydroxide is adjusted according to the growth requirements, as follows: (1) Sodium hydroxide concentration 1 mM: nanobelts with a sixfold symmetry orientation and a width of less than 1 μm; (2) Sodium hydroxide concentration 1.5 mM: microbelts with a double symmetry orientation and a width of 2 to 10 μm; (3) Sodium hydroxide concentration 5 mM: disordered network microbelts with a width of 2 to 10 μm;

[0035] That is, when the concentration of sodium hydroxide in the mixed solution is 1 mM, the obtained nanoribbons are grown with sixfold symmetry orientation.

[0036] When the concentration of sodium hydroxide in the mixed solution is greater than 1 mM and less than 1.5 mM, nanoribbons grown with six-fold symmetry orientation and microribbons grown with two-fold symmetry orientation are obtained.

[0037] When the concentration of sodium hydroxide in the mixed solution is 1.5 mM, micron bands with a double symmetry orientation are obtained;

[0038] When the concentration of sodium hydroxide in the mixed solution is greater than 1.5 mM and less than 5 mM, micron bands with dual symmetry orientation and disordered growing network micron bands are obtained.

[0039] When the concentration of sodium hydroxide in the mixed solution is greater than or equal to 5 mM and less than or equal to 7 mM, disordered growing network micron bands are obtained.

[0040] (2) Substrate pretreatment and source solution spin coating

[0041] The cut sapphire substrate was ultrasonically cleaned in acetone, isopropanol and deionized water for 15 minutes in sequence, and then dried with nitrogen. It was then treated with oxygen plasma for 5 minutes. The prepared mixed solution was dropped onto the substrate and spin-coated at 2000 rpm for 90 seconds, and then air-dried naturally.

[0042] (3) Growth by chemical vapor deposition method

[0043] The spin-coated substrate was placed face down in a quartz boat and placed in the third temperature zone of a 3-inch three-zone tube furnace. At the same time, a ceramic boat containing 400 mg of sulfur powder was placed in the first temperature zone upstream, with a distance of 50 cm between the two. After evacuation and gas purging, the flow rate of the carrier gas (nitrogen) was controlled at 250 sccm, and the gas pressure was maintained at atmospheric pressure. The three temperature zones were heated from room temperature to 200℃, 350℃, and 850℃ respectively. Depending on the number of molybdenum disulfide nano / microbelts to be obtained, a certain growth time was maintained. Maintaining the growth time for 5 minutes mainly yielded monolayer molybdenum disulfide nano / microbelts, while maintaining the growth time for 10 minutes or more mainly yielded multilayer molybdenum disulfide nano / microbelts.

[0044] In some embodiments, the concentration of sodium molybdate in the mixed solution is constant. By adjusting the concentration of sodium hydroxide in the mixed solution, the size and orientation of molybdenum disulfide nano / microribbons can be varied, from nanoribbons grown with six-fold symmetric orientation to microribbons grown with double symmetric orientation, and then to disordered network microribbons.

[0045] In some embodiments, the number of molybdenum disulfide nano / microribbons can be varied by adjusting the growth time during the chemical vapor deposition process: monolayer molybdenum disulfide nanoribbons or microribbons grown at 5 min or less, molybdenum disulfide nanoribbons or microribbons containing both monolayers and multilayers obtained between 5 and 10 min, and multilayer molybdenum disulfide nano / microribbons mainly grown at 10 min or more.

[0046] In some embodiments, the spin coating process is set with a rotation speed of 1000 rpm to 3000 rpm and a spin coating time of 60 seconds or more.

[0047] In some embodiments, in the chemical vapor deposition process, the reaction temperature of the first temperature zone is set to 150°C to 250°C, the reaction temperature of the second temperature zone is set to 300°C to 400°C, and the reaction temperature of the third temperature zone is set to 700°C to 850°C.

[0048] The molybdenum disulfide nano / microribbons obtained by this invention are grown on the surface of a substrate (preferably sapphire). The nanoribbons have a width of 200 nm to 1000 nm and a length of 20 to 60 μm; the microribbons have a width of 2 to 10 μm and a maximum length of 700 μm. The aspect ratio of the nano / microribbons can both reach over 100.

[0049] The following are specific embodiments.

[0050] Example 1

[0051] Combination Figure 1 and Figure 2 As shown, the molybdenum disulfide nano / microribbons demonstrated in this invention possess a high aspect ratio and good crystal quality. For example... Figure 1 As shown in the scanning electron microscope image, the narrowest width of the molybdenum disulfide nano / microband is only 200 nm, and the length can reach more than 50 μm, indicating that its aspect ratio can exceed 100, which is greater than most molybdenum disulfide nano / microbands obtained by current technical solutions. Figure 2 The X-ray photoelectron spectroscopy shown confirms that the obtained material is indeed molybdenum disulfide, and the ratio of molybdenum atoms to sulfur atoms is 1:1.95, indicating that the molybdenum disulfide nano / microbands have fewer sulfur vacancies, proving its good crystal quality.

[0052] In this embodiment, a mixed solution of sodium molybdate with a concentration of 7.5 mM (mmol / L) and sodium hydroxide with a concentration of 1 mM was spin-coated on a sapphire substrate that had been cleaned and treated with oxygen plasma at a speed of 2000 rpm for 90 s; then placed in a chemical vapor deposition system, the reaction temperatures of the three temperature zones were set to 200℃, 350℃ and 850℃, respectively, and the growth time was 5 min.

[0053] Example 2

[0054] Combination Figure 3 As shown, the technical solution for the controllable preparation of molybdenum disulfide nano / microbands proposed in this invention mainly includes the following steps:

[0055] (1) Step 1: Preparation of a mixed solution of sodium molybdate and sodium hydroxide

[0056] First, a measured amount of sodium molybdate powder was dissolved in deionized water to obtain a sodium molybdate solution with a constant ratio. Then, a certain mass of sodium hydroxide granules was added to obtain a mixed solution of sodium molybdate and sodium hydroxide of the desired concentration. In these mixed solutions, the concentration of sodium molybdate was kept constant at 7.5 mM (mmol / L), and the concentration of sodium hydroxide ranged from 1 mM to 7 mM. Three concentrations—1 mM, 1.5 mM, and 5 mM—were selected to demonstrate significant differences in effect.

[0057] (2) Step 2: Substrate pretreatment and source solution spin coating

[0058] This method uses a sapphire substrate. First, the substrate is ultrasonically cleaned sequentially in acetone, isopropanol, and deionized water, and then dried with a nitrogen gun. Next, it is treated with an oxygen plasma treatment machine for 5 minutes to enhance the wettability of the substrate. Then, a prepared mixed solution is dropped onto the substrate, and it is spin-coated at 2000 rpm for 90 seconds, followed by natural air drying to obtain a substrate with a uniform distribution of molybdenum source and catalyst.

[0059] The concentration of the mixed solution added is selected according to the growth requirements, as follows: (1) Sodium hydroxide concentration 1mM: nanoribbons with a width of less than 1μm along the sixfold symmetry orientation; (2) Sodium hydroxide concentration 1.5mM: microribbons with a width of 2 to 10μm along the double symmetry orientation; (3) Sodium hydroxide concentration 5mM: disordered network microribbons with a width of 2 to 10μm.

[0060] (3) Step 3: Growth of molybdenum disulfide nano / microbands by chemical vapor deposition

[0061] This method utilizes a three-zone chemical vapor deposition system with a three-inch diameter tube. First, the spin-coated substrate is placed face down in a quartz boat and positioned in the center of the third zone. Then, 400 mg of sulfur powder is weighed, placed in a ceramic boat, and positioned in the upstream first zone, 50 cm away from the substrate. Next, the chemical vapor deposition system is turned on, evacuated, and purged. The carrier gas (nitrogen) flow rate is controlled at 250 sccm, and the pressure is maintained at atmospheric pressure. The three zones are heated from room temperature at a rate of 30 °C / min to 200 °C, 350 °C, and 850 °C, respectively, and maintained for specific growth times. After the reaction is complete and the system is allowed to cool naturally to room temperature, the sample is removed, thus obtaining molybdenum disulfide nano / microbelts of the desired size, orientation, and number of layers.

[0062] The growth time needs to be adjusted according to the number of molybdenum disulfide nano / microbands to be obtained, as follows: (1) If a single layer of molybdenum disulfide nano / microband is to be obtained, the growth time is set to 5 min; (2) If a multilayer of molybdenum disulfide nano / microband is to be obtained, the growth time is set to 10 min or more.

[0063] Example 3

[0064] In this embodiment, the focus is on the controllable adjustment and growth of molybdenum disulfide nano / microribbons. For example... Figure 4 As shown, Figure 4Image (ac) shows an optical micrograph of molybdenum disulfide nano / microribbons obtained by spin-coating a mixed solution of sodium molybdate (7.5 mM) and sodium hydroxide (1 mM, 1.5 mM, and 5 mM) and growing it by chemical vapor deposition at 200℃ / 350℃ / 850℃ for 5 min. The specific growth steps are as described above. When the sodium hydroxide concentration is 1 mM, nanoribbons grown along a sixfold symmetry orientation are mainly obtained, with a width less than 1 μm; when the sodium hydroxide concentration is 1.5 mM, microribbons grown along a double symmetry orientation are mainly obtained, with a width of 2–10 μm; and when the sodium hydroxide concentration is 5 mM, disordered network microribbons are obtained, with a width of 2–10 μm.

[0065] Example 4

[0066] In this embodiment, the focus is on the controllable adjustment and growth of the number of molybdenum disulfide nano / microbands. For example... Figure 5 As shown, Figure 5 (a) and Figure 5 Image (b) shows optical micrographs of molybdenum disulfide nano / microribbons obtained by spin-coating with a mixed solution of 7.5 mM sodium molybdate and 1.5 mM sodium hydroxide in chemical vapor deposition systems with growth temperatures set to 200℃ / 350℃ / 850℃ for 5 min and 10 min, respectively. The specific growth steps are as described above. When the growth time is controlled at 5 min, monolayer molybdenum disulfide nano / microribbons are mainly obtained; while when the growth time is controlled at 10 min, multilayer molybdenum disulfide nano / microribbons are mainly obtained.

[0067] Example 5

[0068] In this embodiment, a phototransistor was fabricated primarily based on the grown molybdenum disulfide nano / microribbons. Its electrical and photoelectric properties were tested to highlight the beneficial effects of the invention. Molybdenum disulfide nano / microribbons were obtained by spin-coating with a mixed solution of 7.5 mM sodium molybdate and 1 mM sodium hydroxide in a chemical vapor deposition system with growth temperatures set to 200℃ / 350℃ / 850℃ for 5 min. These nanoribbons were then fabricated into a phototransistor device using micro / nano fabrication techniques. Figure 6 As shown, Figure 6 (a) and Figure 6 (b) shows the electrical and photoelectric performance of the phototransistor, indicating that the device has a very high current on / off ratio (9 × 10⁻⁶). 5 Excellent responsivity (8.6 A / W) and specific detectivity (9.8 × 10⁻⁶). 12 Jones).

[0069] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing molybdenum disulfide nanoribbons with high aspect ratio, characterized in that, Includes the following steps: (1) A mixed solution of molybdenum source and sodium hydroxide as catalyst is spin-coated onto a sapphire substrate to obtain a substrate with molybdenum source and catalyst uniformly distributed, wherein the molybdenum source is sodium molybdate; (2) The substrate obtained in step (1) is placed face down in the third temperature zone of the three-temperature zone chemical vapor deposition apparatus, which makes it more conducive to the flow of sodium molybdenum oxide intermediate on the substrate surface during the growth process. The sulfur powder is placed in the first temperature zone. The third temperature zone and the first temperature zone are separated by the second temperature zone. The three-temperature zone chemical vapor deposition apparatus is evacuated and then washed with gas, so that the gas flow is blown from the direction of the first temperature zone to the direction of the third temperature zone. Then it is heated so that the sulfur powder in the first temperature zone sublimates into gaseous state, and the spin-coated material on the substrate in the third temperature zone generates sodium molybdenum oxide intermediate. The gaseous sulfur reacts with the sodium molybdenum oxide intermediate to obtain molybdenum disulfide nanoribbons or molybdenum disulfide microribbons. The reaction temperature of the first temperature zone is 150℃~250℃, the reaction temperature of the second temperature zone is 300℃~400℃, and the reaction temperature of the third temperature zone is 700℃~850℃. When the growth time is greater than 5 min; when the growth time is greater than 5 min but less than 10 min, molybdenum disulfide nanoribbons containing both single and multilayers are obtained; when the growth time is greater than or equal to 10 min, multilayer molybdenum disulfide nanoribbons are obtained. The molybdenum disulfide nanoribbons have a width of 200 nm to 1000 nm, a length of 20 to 60 μm, and an aspect ratio of 100 or higher. The concentration of sodium hydroxide in the mixed solution is greater than or equal to 1 mM and less than 1.5 mM. When the concentration of sodium hydroxide in the mixed solution is 1 mM, six-fold symmetric orientation nanoribbons are obtained. When the concentration of sodium hydroxide in the mixed solution is greater than 1 mM and less than 1.5 mM, nanoribbons grown with six-fold symmetry orientation and microribbons grown with two-fold symmetry orientation are obtained.

2. The method for preparing high aspect ratio molybdenum disulfide nanoribbons as described in claim 1, characterized in that, In step (1), the spin coating speed is 1000 rpm to 3000 rpm and the time is more than 60 s.

3. The method for preparing high aspect ratio molybdenum disulfide nanoribbons as described in claim 1, characterized in that, Prior to spin coating, the substrate is subjected to oxygen plasma treatment.

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