Method for growing large-area single-layer transition metal chalcogenide single-crystal film

Abstract

The invention discloses a method for growing a large-area single-layer transition metal chalcogenide single-crystal thin film. Firstly, transition metal is uniformly deposited on a single crystal gold substrate through magnetron sputtering to serve as a precursor; secondly, surface alloy is formed by the transition metal and the gold through high-temperature annealing; and finally, preparing a single-oriented single-layer transition metal chalcogenide single-crystal domain on the single-crystal gold substrate through a chemical vapor deposition process, and preparing the inch-level single-layer transition metal chalcogenide single-crystal thin film by regulating and controlling the deposition amount of the transition metal.

Description

Technical Field

[0001] The present invention belongs to the field of materials. Specifically, the present invention relates to a method of using magnetron sputtering and chemical vapor deposition to prepare a single-oriented single-layer transition metal sulfide, molybdenum diselenide, or other transition metal sulfide compound or alloy using a transition metal film / single-crystal gold foil as a substrate, thereby obtaining a single-layer single-crystal film of the transition metal sulfide compound or alloy. Background Art

[0002] Two-dimensional transition metal dichalcogenides (TMDCs) are a class of compounds composed of a Group IVB–VIII transition metal (M) and a chalcogen (X), with the general formula MX2. Combining different transition metal M and chalcogen X yields approximately 40 stable TMDCs. Two-dimensional TMDCs possess atomically flat surfaces, suitable direct band gaps, and excellent optical and electrical properties, demonstrating great potential for next-generation high-performance, low-power electronic / optoelectronic devices. Chemical vapor deposition (CVD) is a commonly used thin-film deposition method in semiconductor manufacturing. Its primary process involves chemical reactions between gaseous precursor species in the gas phase or at a gas-solid interface, ultimately forming a solid film on the substrate surface. This method offers advantages such as a wide range of controllable variables and the ability to precisely regulate the material growth process, making it widely used for the high-quality preparation of two-dimensional TMDCs.

[0003] However, under the traditional upstream and downstream vapor transport method of the precursor, the concentration distribution of the sulfide source on the substrate surface remains almost unchanged, while the concentration of the metal source decreases significantly along the gas flow direction (there is a large concentration gradient), resulting in uneven number of layers and coverage of two-dimensional TMDCs. Therefore, the uneven distribution of metal precursors on the substrate surface is the core problem that hinders the large-scale uniform growth of single-layer TMDCs. Exploring a method for uniformly supplying metal precursors to the substrate is the key to preparing large-area single-layer TMDCs films. In addition, the grain boundaries in polycrystalline films will break the long-range order of the two-dimensional TMDCs lattice and significantly reduce the mobility of the material. In comparison, two-dimensional TMDCs single crystals have higher crystal quality, and the crystal quality is highly consistent at the wafer scale, which ensures the yield and reliability of integrated devices from the material level. Therefore, it is extremely important to develop a method for preparing large-area uniform, single-oriented single-layer transition metal sulfide compounds, and then realize the preparation of wafer-level single-layer transition metal sulfide compound single crystal films. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for uniformly supplying an ultra-thin metal source for preparing a single-oriented single-layer transition metal chalcogenide, thereby obtaining an inch-scale single-layer transition metal chalcogenide single crystal film.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for growing a large-area single-layer transition metal chalcogenide single crystal thin film, the method comprising the following steps:

[0007] 1) Cleaning the commercial gold foil; annealing the cleaned polycrystalline gold foil in air for the first time;

[0008] 2) applying single-point stress to the gold foil after the first annealing, and performing a second high-temperature, long-term annealing in an argon and hydrogen atmosphere to obtain a gold (111) single crystal;

[0009] 3) placing a gold (111) single crystal in a magnetron sputtering chamber, placing a barrier filter on top to control the deposition amount of the transition metal, setting the sputtering power, and depositing an ultra-thin transition metal film on the gold (111) surface;

[0010] 4) annealing the sputtered gold (111) in an argon and hydrogen atmosphere to form a surface alloy;

[0011] 5) using the annealed transition metal film / gold (111) as a growth substrate and placing a chalcogen element upstream of the gas flow relative to the substrate;

[0012] 6) Residual air in the reaction chamber is removed, and a certain amount of argon and hydrogen are introduced. After the airflow stabilizes, the substrate and the chalcogen are heated to different temperatures, and then the temperature is maintained constant. After tens of minutes, a single-oriented monolayer of transition metal chalcogenide is grown on the substrate;

[0013] 7) By regulating the deposition amount of transition metal, a continuous monolayer transition metal sulfide compound single crystal film can be prepared.

[0014] Preferably, the polycrystalline gold foil is cleaned in the following manner: the polycrystalline gold foil is placed in dilute hydrochloric acid and acetone in sequence for ultrasonic cleaning, and then blown dry with nitrogen to complete the cleaning of the polycrystalline gold foil.

[0015] Preferably, the polycrystalline gold foil is annealed in air in the following manner: the cleaned polycrystalline gold foil is placed in a tube furnace, heated to 900-1000° C. in an atmospheric atmosphere, kept at this temperature for 5-8 hours, and then cooled naturally.

[0016] Preferably, the single-point stress loading method is one or more of compression, scratching and shearing, and the shearing method is further preferred, wherein the compressive stress required to generate the scratch is 100-200 mN, and the depth of the scratch is 2-15 μm.

[0017] Preferably, after applying single-point stress, the gold foil is annealed at high temperature for a long time as follows: the gold foil is placed in a tube furnace and heated to 1000-1045°C, more preferably 1035°C, under an argon and hydrogen atmosphere, and kept at this temperature for 8-12 hours, more preferably 8 hours, and then naturally cooled to room temperature. The argon and hydrogen atmosphere is 100-500 sccm argon and 50-200 sccm hydrogen, where sccm is a volume flow unit, which is standard cubic centimeters per minute.

[0018] Preferably, the barrier filter used for magnetron sputtering deposition of transition metals has a mesh size of 400-1000, and the height difference between the gold (111) and the barrier filter is 5-20 mm.

[0019] Preferably, the sputtering power of the magnetron sputtering deposition transition metal film is 5-15 W, more preferably 10 W, the sputtering time is 20 s-2 min, and the transition metal is molybdenum, tungsten, niobium or rhenium.

[0020] Preferably, the transition metal / gold (111) film is annealed as follows: heated to 900-1050°C, preferably 1000-1050°C, in an argon and hydrogen atmosphere, kept constant for 1-2.5 hours, preferably kept constant for 1-1.5 hours, and then naturally cooled to room temperature. The argon and hydrogen atmosphere is 100-500 sccm argon and 30-100 sccm hydrogen.

[0021] Preferably, the mass of the chalcogen element is 50-300 mg, and the chalcogen element includes sulfur and / or selenium.

[0022] Preferably, the flow rate of argon gas is 100-500 sccm, the flow rate of hydrogen gas is 1-100 sccm, the chalcogen and the substrate are heated to 100-400° C. and 700-800° C. respectively, and the constant temperature time is 20-50 minutes.

[0023] According to a preferred embodiment of the present invention, the present invention provides a method for preparing a single-layer transition metal sulfide single crystal thin film on a gold (111) single crystal substrate, comprising the following steps:

[0024] 1) Clean the commercial gold foil; anneal the cleaned gold foil in air;

[0025] 2) applying single-point stress to the gold foil after the first annealing, and performing a second high-temperature, long-term annealing in an argon and hydrogen atmosphere to obtain a gold (111) single crystal;

[0026] 3) placing a gold (111) single crystal in a magnetron sputtering chamber, placing a barrier filter on top to control the deposition amount of the transition metal, setting the sputtering power, and depositing an ultra-thin transition metal film on the gold (111) surface;

[0027] 4) annealing the sputtered gold (111) in an argon and hydrogen atmosphere to form a surface alloy;

[0028] 5) using the annealed transition metal film / gold (111) as a growth substrate and placing a chalcogen element upstream of the gas flow relative to the substrate;

[0029] 6) performing a sulfidation / selenization reaction in a mixture of argon and hydrogen, with an argon flow rate of 100-500 sccm and a hydrogen flow rate of 1-100 sccm, heating the chalcogen and substrate to 100-400° C. and 700-900° C., respectively, and maintaining the temperature for 20-50 minutes;

[0030] 7) After growth is complete, turn off the heating program and allow the reaction chamber to cool naturally. Once the temperature drops below 400°C, open the tube furnace lid and rapidly cool it down. Once the temperature drops to room temperature, turn off the gas. By controlling the amount of transition metal deposited, a continuous monolayer transition metal chalcogenide single crystal thin film can be produced.

[0031] The present invention prepares a single-layer transition metal sulfide compound single crystal thin film on a gold (111) single crystal substrate by magnetron sputtering and chemical vapor deposition, which can achieve single-orientation growth of the single-layer transition metal sulfide compound domain area. The preparation of the single-layer transition metal sulfide compound single crystal thin film can be achieved by regulating the amount of transition metal deposition.

[0032] Compared with the wafer-level transition metal chalcogenide growth method in the prior art, the present invention redesigns the supply method of the metal precursor and uses sputtering to directly deposit the transition metal on a gold single crystal substrate. This method has more advantages in terms of sample size enlargement and is compatible with the growth of doped materials, and has the advantage of scalable preparation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The single crystal Au(111) substrate is prepared;

[0034] Figure 2 The mesh size of the barrier filter is 400, the sputtering time is 20s, and the scanning electron microscope image of the single-layer single-oriented MoS2 obtained after sulfurization;

[0035] Figure 3 The mesh size of the barrier filter is 400, the sputtering time is 40s, and the scanning electron microscope image of the single-layer single-oriented MoS2 obtained after sulfurization;

[0036] Figure 4 This is a scanning electron microscope image of a single-layer single-oriented MoS2 obtained after sulfurization with a sputtering time of 20 seconds without using a barrier filter;

[0037] Figure 5Raman spectrum of single-layer MoS2 grown on Au;

[0038] Figure 6 The mesh size of the barrier filter is 400, the sputtering time is 20s, and the scanning electron microscopy image of the single-layer single-oriented MoSe2 obtained after selenization;

[0039] Figure 7 This is the Raman spectrum of a single-oriented monolayer MoSe2 grown on Au. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Example 1

[0042] The purchased polycrystalline gold foil (30 μm thick) was placed in dilute hydrochloric acid and acetone for ultrasonic cleaning in turn, and then dried with nitrogen to complete the cleaning of the gold foil. The cleaned gold foil was placed in a tube furnace, heated to 950 ° C in an atmospheric atmosphere, kept at a constant temperature for 5 hours, and then naturally cooled to complete the first annealing. The gold foil after the first annealing was locally sheared and placed in a tube furnace again, annealed at 1035 ° C for 8 hours in an atmosphere of 200 sccm argon and 100 sccm hydrogen to obtain a gold (111) single crystal (such as Figure 1 ). A gold (111) single crystal was placed in a magnetron sputtering chamber, a 400 mesh barrier filter was placed 1 cm above it, the transition metal target was set to molybdenum, the sputtering power was 10W, the sputtering time was 20s, and an ultra-thin molybdenum layer was sputtered. The sputtered gold (111) was placed in a tube furnace and annealed for 1 hour at 1035°C, 200sccm argon and 50sccm hydrogen atmosphere to form a gold-molybdenum surface alloy, which was used as a metal precursor. 80 mg of elemental sulfur powder was placed upstream of the gas flow relative to the substrate in the tube furnace, and the final temperatures of the sulfur powder and the substrate were set to 130°C and 700°C, respectively. Growth was carried out at a constant temperature for 40 minutes in an atmosphere of 200sccm argon and 50sccm hydrogen. After the growth of molybdenum disulfide is completed, the heating program is turned off and the reaction chamber is allowed to cool naturally. When the temperature drops below 400°C, the tube furnace cover is opened for rapid cooling. When the temperature drops to room temperature, the gas is turned off to obtain a single-oriented single-layer molybdenum disulfide single crystal sample ( Figure 2 ).

[0043] Example 2

[0044] By changing the mesh size of the barrier filter and the sputtering time in magnetron sputtering, the amount of molybdenum deposited can be controlled, which ultimately affects the coverage of the prepared MoS2 sample. For example, when the mesh size of the barrier filter is 1000, the transition metal is completely blocked, and the coverage of MoS2 is zero. When the mesh size of the barrier filter is 400 and the sputtering time is 40s, the obtained single-oriented monolayer MoS2 sample is as follows: Figure 3When the barrier net is not added and the sputtering time is 20s, a single-layer MoS2 single crystal film is obtained ( Figure 4 By changing the barrier filter mesh size and sputtering time in magnetron sputtering, the amount of molybdenum deposition can be controlled, and a single-layer MoS2 single crystal film can be obtained. The thickness of the film can be preliminarily determined by Raman spectroscopy ( Figure 5 ).

[0045] Example 3

[0046] The obtained gold-molybdenum surface alloy is used for subsequent growth of a single layer of molybdenum diselenide. In a tubular furnace, 200 mg of elemental selenium powder is placed 30 cm upstream of the airflow relative to the substrate, and 100 sccm of argon and 2 sccm of hydrogen are introduced. After the airflow stabilizes, the temperature rise program is started to heat the reaction chamber. The final temperatures of the selenium powder and the substrate are 350°C and 750°C, respectively. The heating time is 35 minutes, and then the temperature is kept constant for 40 minutes for growth. After the growth of molybdenum diselenide is completed, the heating program is turned off and the reaction chamber is allowed to cool down naturally. After the temperature drops below 400°C, the tubular furnace cover is opened for rapid cooling. After the temperature drops to room temperature, the gas is turned off to obtain a single-layer molybdenum diselenide single crystal sample. From the morphology of the sample ( Figure 6 ) and Raman spectroscopy ( Figure 7 ) It can be seen that the MoSe single crystal film sample has consistent orientation and a single layer.

[0047] Example 4

[0048] During the magnetron sputtering process, one or more transition metals can be deposited on a gold single crystal substrate to ultimately produce a doped transition metal sulfide single crystal (the amount of two metals deposited is quite different, one is dominant and the other is used as a dopant), a transition metal sulfide alloy (a sulfur source and a selenium source are introduced simultaneously during the chemical deposition process), or a heterojunction (the amount of two transition metals deposited is equivalent and phase separation occurs during the chemical vapor deposition process). Taking the preparation of niobium-doped molybdenum disulfide as an example, the specific parameters are as follows: a gold (111) single crystal is placed in a magnetron sputtering chamber, a 400 mesh barrier filter is placed 1 cm above it, and the transition metal target is set to a mixed target of metal molybdenum and metal niobium (niobium accounts for 1%). The sputtering power is set to 10W and the sputtering time is 20s. An ultra-thin molybdenum layer (containing a small amount of niobium) is sputtered. The sputtered gold (111) was placed in a tube furnace and annealed for 1 hour at 1035°C in an atmosphere of 200 sccm argon and 50 sccm hydrogen to form a gold-molybdenum-niobium surface alloy. Nb-doped molybdenum disulfide was then prepared through a sulfurization process. After the growth was completed, the heating program was turned off and the reaction chamber was allowed to cool naturally. After the temperature dropped below 400°C, the tube furnace lid was opened and the temperature was rapidly cooled. After the temperature dropped to room temperature, the gas was turned off to obtain a single-oriented niobium-doped monolayer molybdenum disulfide single crystal sample.

[0049] The process parameters (such as temperature, time, etc.) of the present invention can realize the method by taking upper and lower limits and interval values, and the embodiments are not listed here one by one.

[0050] Any content not described in detail in the present invention can be based on conventional technical knowledge in the art.

[0051] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and are intended to be encompassed by the claims of the present invention.

Claims

1. A method for growing a large-area single-layer transition metal chalcogenide single crystal thin film, the method comprising the following steps: 1) After cleaning the polycrystalline gold foil, annealing in air to remove residual stress, applying single-point stress, and then annealing at high temperature for a long time in an argon and hydrogen atmosphere to obtain a gold (111) single crystal; 2) placing a gold (111) single crystal in a magnetron sputtering chamber, placing a barrier filter directly above the single crystal in parallel to control the deposition amount of the transition metal, connecting the transition metal target to a DC power supply, setting the sputtering power, and allowing the transition metal to be deposited on the gold (111) surface to obtain a transition metal / gold (111) thin film; 3) annealing the transition metal / gold (111) film obtained in step 2) in an argon and hydrogen atmosphere to obtain a gold-transition metal surface alloy, which is used as a transition metal source and a growth substrate; 4) placing a sulphur element upstream of the gas flow relative to the substrate; 5) Argon and hydrogen are introduced, and after the gas flow is stable, the substrate and the chalcogenide are heated to different temperatures respectively, and then the temperature is kept constant. After tens of minutes, an inch-scale single-layer transition metal chalcogenide single crystal thin film is grown on the substrate.

2. The method for growing a large-area single-layer transition metal chalcogenide single crystal thin film according to claim 1, characterized in that: The polycrystalline gold foil is cleaned in the following manner: the polycrystalline gold foil is placed in 20% dilute hydrochloric acid and acetone in sequence for ultrasonic cleaning, and then blown dry with nitrogen to complete the cleaning of the gold foil.

3. The method for growing a large-area single-layer transition metal chalcogenide single crystal thin film according to claim 1, characterized in that: The polycrystalline gold foil is annealed in air in the following manner: the cleaned polycrystalline gold foil is placed in a tube furnace, heated to 900-1000° C. in an atmospheric atmosphere, kept at a constant temperature for 5-8 hours, and cooled naturally.

4. The method for growing a large-area single-layer transition metal chalcogenide single crystal thin film according to claim 1, characterized in that: The single-point stress loading method includes one or more of compression, scratching and shearing, wherein the compressive stress required to generate scratches is 100-200 mN, and the depth of the scratches is 2-15 μm.

5. The method for growing a large-area single-layer transition metal chalcogenide single crystal thin film according to claim 1, characterized in that: After applying single-point stress, the gold foil is annealed at high temperature for a long time as follows: the gold foil is placed in a tubular furnace, heated to 1000-1045°C in an argon and hydrogen atmosphere, kept at a constant temperature for 8-12 hours, and then naturally cooled to room temperature. The argon and hydrogen atmosphere is 100-500 sccm argon and 50-200 sccm hydrogen, where sccm is a volume flow unit, which is standard cubic centimeters per minute.

6. The method for growing a large-area single-layer transition metal chalcogenide single crystal thin film according to claim 1, characterized in that: The mesh number of the barrier filter used for magnetron sputtering deposition of transition metals is 400-1000 meshes, and the height difference between gold (111) and the barrier filter is 5-20 mm.

7. The method for growing a large-area single-layer transition metal chalcogenide single crystal thin film according to claim 1, characterized in that: The sputtering power of the magnetron sputtering deposition transition metal film is 5-15W, the sputtering time is 20s-2min, and the transition metal is molybdenum, tungsten, niobium or rhenium.

8. The method for growing a large-area single-layer transition metal chalcogenide single crystal thin film according to claim 1, characterized in that: The transition metal / gold (111) film is annealed as follows: heated to 900-1050° C. in an argon and hydrogen atmosphere, kept constant for 1-2.5 hours, and then naturally cooled to room temperature. The argon and hydrogen atmosphere is 100-500 sccm argon and 30-100 sccm hydrogen.

9. The method for growing a large-area single-layer transition metal chalcogenide single crystal thin film according to claim 1, characterized in that: The mass of the chalcogen element is 50-300 mg, and the chalcogen element includes sulfur and / or selenium.

10. The method for growing a large-area single-layer transition metal chalcogenide single crystal thin film according to claim 1, characterized in that: In step 5), the argon gas flow rate is 100-500 sccm and the hydrogen gas flow rate is 1-100 sccm, and the sulfide and the substrate are heated to 100-400° C. and 700-900° C. respectively, and the constant temperature time is 20-50 minutes.

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