Preparation Method of Large-Area Molybdenum Diselenide Thin Film

Abstract

The present invention provides a method for preparing a large-area molybdenum diselenide thin film, which method comprises: first, ultrasonically cleaning the substrate and then drying the surface of the substrate; weighing a corresponding amount of (NH4)2MoO4, selenium powder and KCl on weighing paper respectively, fully mixing the weighed (NH4)2MoO4 and KCl and then putting them into a clean first corundum boat, and placing the weighed selenium powder in a second corundum boat; buckling the cleaned substrate right above the mixed drugs placed in the first corundum boat at a distance of 10-20 mm, placing the first corundum boat in the downstream temperature zone of a multi-temperature zone tube furnace, placing the other second corundum boat loaded with selenium powder in the upstream temperature zone, then introducing an argon-hydrogen mixed gas, performing three gas purges on the multi-temperature zone tube furnace, and then turning on the multi-temperature zone tube furnace. Selenization reaction is carried out by continuously introducing the argon-hydrogen mixed gas at 8×10 4 Pa - 9×10 4 Pa to obtain a two-dimensional molybdenum diselenide thin film. The MoSe2 thin film obtained by the present invention can reach the centimeter level and has the characteristics of good uniformity, strong controllability and good crystallinity.

Description

Technical Field

[0001] The present invention relates to the technical field of molybdenum diselenide thin film material preparation, and particularly relates to a method for preparing a large-area molybdenum diselenide thin film. Background Art

[0002] Two-dimensional materials are a class of sheet-like materials with single / multi-atomic thickness, having excellent physical, chemical, optical, electronic, mechanical and other properties, and having great application prospects in many fields such as field-effect transistors, photodetectors, biosensors, catalysts, batteries and many other aspects. Among them, graphene-like MX2 compounds (where M represents two transition metal elements Mo and W, and X represents three chalcogen elements S, Se, Te) have attracted extensive attention from researchers in many fields. The crystal structure of the MoSe2 we prepared is mainly that Mo atoms and Se atoms alternately appear at the vertex positions of a hexagon, forming a six-membered ring structure to form a 1H phase. Different stacking modes of the 1H phase respectively form two main phase structures, the 2H phase and the 3R phase. In the 2H phase, along the z-axis direction perpendicular to the two-dimensional plane, the atomic stacking order is Se-Mo-Se (ABA), having a hexagonal symmetry structure and a triangular prism coordination, belonging to the D point group. Each unit cell in the 2H structure has two 1H phase layers. Compared with the 2H phase between two layers, each unit cell in the 3R structure has three 1H phase layers, and the stacking order between each layer is different, and the Mo atoms have a triangular prism coordination. Therefore, the unit cell height of 3R is about 1.5 times that of the 2H unit cell. A single-layer 1T phase is equivalent to rotating the upper and lower two layers of X atoms in the 1H phase by 180° relative to each other. In the multi-layer phase, along the z-axis direction perpendicular to the two-dimensional plane, the atomic stacking order is Se-Mo-Se' (ABA'), having a square symmetry structure and an octahedral coordination, belonging to the C3v point group. Due to lattice distortion, the 1T phase can also be transformed into the 1T' phase, such as WTe2, MoTe2, which have an octahedral structure similar to the 1T phase, but each single layer has a superstructure. Different phases have different thermodynamic stabilities, and these phases can be transformed into each other. For example, the 2H phase of MoSe2 is the most stable in nature. The energy band gap of single-layer MoSe2 reaches 1.52 ev due to the quantum confinement effect, and the electron transition mode is a direct band gap. Therefore, the unique structure, excellent physical properties, adjustable band gap, and relatively high carrier mobility of the MoSe2 thin film make it have great potential in the optoelectronic field.

[0003] Common preparation methods of MoSe2 include physical exfoliation, chemical exfoliation, molecular beam epitaxy, physical vapor deposition, etc. These methods all have certain problems, such as size limitations, difficulty in controlling thickness, low yield, poor repeatability, high equipment price, etc. Therefore, it is necessary to explore a new preparation method to obtain high-quality MoSe2 thin films with large area, good uniformity, strong controllability, good crystallinity, simple operation, short time consumption, and suitable for large-scale production and application. Summary of the Invention

[0004] Based on this, the object of the present invention is to propose a preparation method for large-area molybdenum diselenide thin films. Through chemical vapor deposition at near atmospheric pressure and relatively low temperature using metal oxides, the obtained MoSe2 thin films can reach the centimeter level, and have the characteristics of good uniformity, strong controllability, good crystallinity, etc. This method is simple to operate, time-consuming, and compared with the traditional chemical vapor deposition method for growing MoSe2 thin films, the required growth temperature is significantly reduced, the film quality is higher, and it is more suitable for large-scale industrial applications.

[0005] A preparation method for large-area molybdenum diselenide thin films according to the present invention, the preparation method adopts chemical vapor deposition, uses (NH4)2MoO4 and selenium powder as precursor sources, and KCl as a cosolvent to prepare large-area two-dimensional molybdenum diselenide thin films on a substrate.

[0006] Preferably, the preparation method includes:

[0007] (1) First, ultrasonically clean the substrate successively with acetone, isopropyl alcohol, and deionized water, and then dry the surface of the substrate with a nitrogen gun.

[0008] (2) Weigh a certain amount of corresponding (NH4)2MoO4, selenium powder, and KCl on weighing paper respectively. After fully mixing the weighed (NH4)2MoO4 and KCl, put them into a clean first corundum boat, and place the weighed selenium powder in the second corundum boat.

[0009] (3) Invert the cleaned substrate 10 - 20 mm directly above the mixed drugs placed in the first corundum boat. Place the first corundum boat in the downstream temperature zone of the multi-temperature zone tube furnace, and place the second corundum boat loaded with selenium powder in the upstream temperature zone. Then, introduce an argon-hydrogen mixed gas, wash the multi-temperature zone tube furnace three times, and then turn on the multi-temperature zone tube furnace. Continuously introduce the argon-hydrogen mixed gas at 8×10 4 Pa - 9×10 4 Pa for seleniumization reaction to obtain two-dimensional molybdenum diselenide thin films.

[0010] Preferably, the substrate in step (1) is any one of a silicon wafer substrate, a strontium titanate substrate, a sapphire substrate, and a quartz substrate.

[0011] Preferably, the mass ratio of (NH4)2MoO4 to KCl is 2.5:1 - 5:1, and the mass ratio of (NH4)2MoO4 to selenium powder is 1:3000 - 1:2000.

[0012] Preferably, in step (3), the temperature of the upstream temperature zone is 300°C - 350°C, and the temperature of the downstream temperature zone is 600°C - 700°C.

[0013] Preferably, the purity of the Se powder in step (2) > 99.99%.

[0014] Preferably, in step (3), the concentration of the mixed argon-hydrogen gas is 4% - 6% hydrogen, and the gas flow rate is 100 - 200 sccm.

[0015] Compared with the existing technology, the present invention has the following advantages:

[0016] 1. Using the preparation method proposed by the present invention, single-layer and few-layer molybdenum diselenide with uniform number of layers, high quality and large area can be prepared, and the area can reach the centimeter level;

[0017] 2. The operating temperature is generally low. In the downstream temperature zone, growth can be achieved at only 650°C, and in the upstream temperature zone, growth can be achieved at only about 300°C. Compared with the traditional preparation process using molybdenum trioxide and sodium chloride, the preparation cost is greatly reduced;

[0018] 3. The substrates used for preparing single-crystal thin films of high-quality single-layer and few-layer molybdenum diselenide with uniform number of layers and large area are any high-temperature chemically inert materials, including but not limited to SiO2 / Si wafers, strontium titanate (SrTiO3), sapphire (Al2O3), quartz, etc., and the applicability is very wide;

[0019] 4. High-quality MoSe2 thin films can be deposited and grown on different substrates, and the required growth temperatures for using different substrates are also different. When using substrates such as silicon wafers, the required growth temperature can be no more than 700°C. That is to say, the growth temperature conditions of the present invention are lower than those required by the general chemical vapor deposition method, and the repeatability is good.

[0020] 5. The controllability is relatively good. The present invention uses KCl as a cosolvent, and the ratio of (NH4)2MoO4 to KCl and the total amount of the precursors added during growth can be adjusted to control the thickness of the single-crystal thin film that can be grown during growth. When the content of KCl added is relatively high, the number of layers of the grown thin film is often more. On the uniformly thin MoSe2 thin film prepared, by controlling the content of KCl, the number of layers of the MoSe2 thin film can be further controlled;

[0021] 6. Simple operation, short total time consumption, and low cost. The most important aspect of the present invention is to control the content of the precursor and the temperature and pressure required for growth to control the growth of the thin film. The total time consumed in the growth process is often only about one hour, enabling the rapid growth and preparation of large-area MoSe2 thin films;

[0022] 7. The materials of the present invention are safe, environmentally friendly, and do not produce substances harmful to the environment.

[0023] Additional aspects and advantages of the present invention will be given in part in the following description, will become apparent in part from the following description, or will be understood through the embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flowchart of a method for preparing a large-area molybdenum diselenide thin film proposed in an embodiment of the present invention;

[0025] Figure 2 It is a schematic diagram of a device for preparing a large-area molybdenum diselenide thin film proposed in an embodiment of the present invention.

[0026] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. SPECIFIC EMBODIMENTS

[0027] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0029] Please refer to Figure 1 , which shows a flowchart of a method for preparing a large-area molybdenum diselenide thin film in an embodiment of the present invention. The method includes steps S01 to S05, where:

[0030] Step S01: First, the substrate is ultrasonically cleaned successively with acetone, isopropyl alcohol, and deionized water, and then the surface of the substrate is dried with a nitrogen gun;

[0031] It should be noted that in some alternative embodiments of the present invention, the preparation method uses chemical vapor deposition. Please refer to Figure 2, using (NH4)2MoO4 and selenium powder in a specific ratio as precursor sources and KCl as a co-solvent, a large-area two-dimensional molybdenum diselenide film is prepared on a substrate. In the process of preparing MoSe2 film by heating reaction of (NH4)2MoO4 and KCl using chemical deposition method, (NH4)2MoO4 has a low melting point and can decompose and provide Mo source at a lower temperature. Using alkali metal KCl as a promoter can first generate gaseous reaction intermediates in the reaction, which helps to increase the Mo source in the reaction system and accelerate the reaction film formation process.

[0032] The principle of chemical vapor deposition is to heat the reactants to make them gaseous, and through chemical reactions between atoms and molecules, the gases react with each other, and then deposit on the substrate to form a thin film. It is a typical "bottom-up" method for preparing two-dimensional materials. The main method of chemical vapor deposition is that the metal oxide reacts with the precursor of sulfur and selenium. This method generally heats the metal oxide and sulfur and selenium powder simultaneously or separately, and controls the program temperature so that they can reach the evaporation temperature at the same time to become gas. For the selenization reaction, a specific reducing gas hydrogen must be used in this process, but the content cannot be too high, and most of it is a mixed gas of inert gas as a carrier, so that the two materials that have been heated to become gaseous are reacted and deposited on the corresponding substrate. This is the most common and practical method. However, when this method is directly applied to the process of preparing MoSe2 thin film, the obtained MoSe2 thin film is not of large area size, and the uniformity is poor, and it is difficult to achieve stable large-area growth. Based on this, this embodiment proposes an improved vapor deposition method suitable for preparing MoSe2 thin film to achieve high-quality growth of large-area MoSe2 thin film, which is of great significance to its final industrialization.

[0033] Specifically, the substrate is firstly cleaned with acetone, isopropanol and deionized water ultrasonically in sequence to remove surface impurities, and then the surface is blown dry with a nitrogen gun.

[0034] Furthermore, the substrate may be any one of a silicon wafer substrate, a strontium titanate substrate, a sapphire substrate and a quartz substrate. That is to say, the solution in this embodiment is applicable to thin film growth on a variety of substrates.

[0035] Step S02: Weigh a certain amount of corresponding (NH4)2MoO4, selenium powder and KCl on weighing paper, mix the weighed (NH4)2MoO4 and KCl thoroughly and put them into a clean first corundum boat, and place the weighed selenium powder in a second corundum boat;

[0036] It should be noted that in this step, the mass ratio of (NH4)2MoO4 to KCl is 2.5:1 - 5:1, and the mass ratio of (NH4)2MoO4 to selenium powder is 1:3000 - 1:2000. Exemplarily, the mass ratio of (NH4)2MoO4 to KCl can be 2.5:1, 3.5:1, 5:1, etc., so that (NH4)2MoO4 can melt well and react fully, which is beneficial to the growth of monolayer or few-layer MoSe2 thin films. If the mass ratio of (NH4)2MoO4 to KCl is too high, only partial melting will occur, and the provided Mo source is limited, which is not conducive to the full reaction and deposition of the thin film. If the mass ratio of (NH4)2MoO4 to KCl is too low, (NH4)2MoO4 will melt prematurely, resulting in generally thicker thin films grown and poorer film formation quality. The mass ratio of (NH4)2MoO4 to selenium powder can be 1:2000, 1:2500, 1:3000 to ensure an excess of selenium powder. At the same time, the purity of Se powder should be greater than 99.99%.

[0037] Step S03: Invert the washed substrate 10 - 20 mm directly above the mixed drugs placed in the first corundum boat, place the first corundum boat in the downstream temperature zone of the multi-temperature zone tube furnace, place another second corundum boat loaded with selenium powder in the upstream temperature zone, then introduce an argon-hydrogen mixed gas, perform three gas purges on the multi-temperature zone tube furnace, and then turn on the multi-temperature zone tube furnace. At 8×10 4 Pa - 9×10 4 Pa, continuously introduce the argon-hydrogen mixed gas for selenization reaction to obtain a two-dimensional molybdenum diselenide thin film.

[0038] It should be pointed out that the washed substrate is inverted 10 - 20 mm directly above the mixed drugs placed in the first corundum boat, such as 10 mm, 15 mm, 20 mm, etc. If the distance is too high, during the reaction, most of the MoSe2 grown into the film is difficult to deposit on the substrate due to the large height, resulting in generally smaller areas of the finally grown thin films, or even no thin film deposition; if the distance is too low, during the reaction, due to being too close to the substrate, the reaction has not been fully reacted into the MoSe2 thin film before it is deposited on the substrate, resulting in generally poorer quality of the grown thin films, or even only intermediate reactants are deposited on the substrate.

[0039] It should be noted that the temperature of the upstream temperature zone is 300°C - 350°C, and the temperature of the downstream temperature zone is 600°C - 700°C. Exemplarily, the temperature of the upstream temperature zone can be 300°C, 325°C, 350°C, etc., and the temperature of the downstream temperature zone can be 600°C, 650°C, 700°C, etc.

[0040] Mix hydrogen gas with a mixed argon-hydrogen gas concentration of 4%-6%. Exemplarily, in some alternative embodiments of the present invention, the mixed argon-hydrogen gas concentration can be 4%, 5%, 6%, etc., and the gas flow rate is 100-200 sccm. Exemplarily, in some alternative embodiments of the present invention, the gas flow rate of the mixed argon-hydrogen gas can be 100 sccm, 150 sccm, 200 sccm.

[0041] Example 1

[0042] First, ultrasonically clean the silicon wafer substrate successively with acetone, isopropyl alcohol, and deionized water to remove surface impurities; then dry its surface with a nitrogen gun. Weigh 1.5 mg of (NH4)2MoO4 and 0.3 mg of KCl and mix them evenly, put them into a clean corundum boat, and then invert the cleaned silicon wafer substrate 10 mm directly above the mixed precursor. Subsequently, place the placed corundum boat in the downstream temperature zone of the high-temperature furnace. Weigh about 3.5 g of excessive selenium powder and put it into another corundum boat, and then place this corundum boat in the upstream temperature zone of the high-temperature furnace. Conduct a selenization reaction in an argon-hydrogen mixed gas atmosphere (5% hydrogen, flow rate 150 sccm) and near-atmospheric pressure conditions (8.5×10 4 Pa). Set the upstream temperature zone to 300 °C, the downstream temperature zone to 600 °C, and the growth time to 10 min. Then cool it naturally, and take out the silicon wafer substrate to obtain a large-area MoSe2 thin film.

[0043] Based on Example 1, use the method of controlling variables to separately and singly adjust one influencing factor among the distance from the substrate to directly above the precursor, the ratio of (NH4)2MoO4 to KCl, the upstream temperature zone temperature, the downstream temperature zone temperature, and the growth time to obtain the test data of the MoSe2 thin film. Refer to Table 1 below:

[0044] Table 1

[0045]

[0046]

[0047] As can be seen from the above table, large-area MoSe2 thin films can be prepared using (NH4)2MoO4 and KCl. Meanwhile, the growth temperature is relatively low (the upper temperature zone is 325 °C, and the lower temperature zone is around 625 °C), and the growth time is short (10 min), that is, the preparation conditions are simple and the repeatability is good. At the same time, the ratio of (NH4)2MoO4 to KCl, the temperatures of the upper and lower temperature zones, the distance from the substrate to directly above the precursor, and the reaction growth time will all affect the quality of the MoSe2 thin film. Also, when the ratio of (NH4)2MoO4 to KCl is 3:1, the upper temperature zone is 325 °C, the lower temperature zone is 650 °C, the distance from the substrate to directly above the precursor is 15 mm, and the growth time is 10 min, the obtained MoSe2 thin film has the best quality, mainly manifested as the largest size. At the same time, the color of the thin film is close to the color of the substrate, and the surface of the thin film is the smoothest and flattest.

[0048] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0049] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims

1. A method for preparing a large-area molybdenum diselenide thin film, characterized in that, The preparation method includes: (1) First, ultrasonically clean the substrate successively with acetone, isopropyl alcohol, and deionized water, and then dry the surface of the substrate with a nitrogen gun; (2) Weigh a certain amount of corresponding (NH4)2MoO4, selenium powder, and KCl on weighing paper respectively. After fully mixing the weighed (NH4)2MoO4 and KCl, put them into a clean first corundum boat, and place the weighed selenium powder in the second corundum boat; (3) Place the washed substrate upside down 10 - 20 mm directly above the mixed chemicals placed in the first corundum boat. Place the first corundum boat in the downstream temperature zone of the multi-temperature zone tube furnace, and place another second corundum boat loaded with selenium powder in the upstream temperature zone. Then, introduce an argon-hydrogen mixed gas, conduct gas washing on the multi-temperature zone tube furnace three times, and then turn on the multi-temperature zone tube furnace. Continuously introduce the argon-hydrogen mixed gas under 8×10 4 Pa - 9×10 4 Pa to carry out the selenization reaction to obtain a two-dimensional molybdenum diselenide film; Among them, (NH4)2MoO4 and KCl first generate a gaseous reaction intermediate during the reaction to provide a Mo source. The mass ratio of (NH4)2MoO4 to KCl is 2.5:1 - 5:1, and the mass ratio of (NH4)2MoO4 to selenium powder is 1:3000 - 1:2000; In step (3), the temperature of the upstream temperature zone is 300°C - 350°C, and the temperature of the downstream temperature zone is 600°C - 700°C; In step (3), the concentration of the mixed argon-hydrogen gas is 4% - 6% hydrogen, and the gas flow rate is 100 - 200 sccm.

2. The preparation method of the large-area molybdenum diselenide thin film according to claim 1, wherein, The substrate in step (1) is any one of a silicon wafer substrate, a strontium titanate substrate, a sapphire substrate, and a quartz substrate.

3. The method for preparing a large-area molybdenum diselenide thin film according to claim 1, characterized in that, The purity of the Se powder in step (2) > 99.99%.

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