A method for preparing wafer-level tungsten disulfide or tungsten diselenide two-dimensional nanofilm

Abstract

The present invention discloses a method for preparing a wafer-level two-dimensional nanofilm of tungsten disulfide or tungsten diselenide. By subjecting sapphire wafers to high-temperature annealing treatment, the treated sapphire is more conducive to the growth of high-quality, large-area, and highly uniform tungsten disulfide and tungsten diselenide films. By adopting a chemical vapor deposition method, the preparation of tungsten disulfide and tungsten diselenide nanofilms with different layer thicknesses (single layer, double layer, or triple layer) can be achieved through the regulation of gas flow, the design of a precursor metal tungsten source, and the adjustment of the confinement height. The method includes: 1. The hydrogen flow rate is regulated to achieve the preparation of single-layer and double-layer tungsten disulfide nanofilms. The present invention does not need to introduce catalysts such as chlorides or hydroxides during the growth process, so that the growth of wafer-level films is more efficient and convenient, and no impurity elements are introduced.

Description

Technical Field

[0001] The invention relates to the preparation of transition metal dihalogenated compounds, and in particular to a method for preparing a wafer-level tungsten disulfide or tungsten diselenide two-dimensional nanofilm. Background Art

[0002] Among many two-dimensional materials, semiconductor transition metal dihalides are considered to be the most promising materials due to their excellent electrical and optoelectronic properties. Tungsten disulfide and tungsten diselenide, as a type of transition metal dihalides, have suitable band gap size, high carrier mobility, strong light-matter interaction and very large spin splitting. Its crystal structure is layered, and each layer consists of three atomic planes. The monolayer structure is a W atom that forms a covalent bond with the surrounding 6 X (S / Se) atoms, and an X (S / Se) atom combines with 3 W atoms to form an 'XW-X' sandwich structure. The layers are bound together by van der Waals interactions. Monolayer tungsten disulfide and tungsten diselenide are direct band gap semiconductors. The band gap of tungsten disulfide is 2.01eV, and the band gap of tungsten diselenide is 1.6eV. The size of the band gap will decrease with the increase of the number of layers. When the thickness of tungsten disulfide and tungsten diselenide is more than two layers, it will change from a direct band gap to an indirect band gap. Theoretically, the room temperature mobility of a monolayer of tungsten disulfide is 1103 cm 2 V -1 s -1 The room temperature mobility of a monolayer of tungsten diselenide is 705 cm 2 V -1 s -1 , are all regarded as highly promising channel materials for high-performance field-effect transistors.

[0003] However, a daunting challenge facing the application of van der Waals layered materials in high-end electronics and optoelectronics is the growth from the micrometer scale to the wafer level, which is very necessary to expand the application of two-dimensional materials and meet the needs of today's semiconductor processes. Summary of the invention

[0004] In view of the technical problem that the nanoscale and macroscale of transition metal dihalide compounds are not uniform enough in high-end applications such as light-emitting devices and memristors, the present invention provides a method for preparing wafer-level tungsten disulfide and tungsten diselenide two-dimensional nanofilms. Through chemical vapor deposition, based on strategies such as precursor design and substrate engineering, the preparation of high-quality wafer-level tungsten disulfide and tungsten diselenide two-dimensional nanofilms with controllable layer thickness is successfully achieved. The method is simple to operate, highly repeatable, and low in cost, and the process can be easily extended to other transition metal dihalide compounds. The wafer-scale film further provides the possibility of application in large-scale integrated devices and the semiconductor industry.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing a wafer-level tungsten disulfide and tungsten diselenide two-dimensional nanofilm comprises the following steps:

[0007] (1) placing the C-surface polished sapphire in the center of the heating zone of a tube furnace and annealing at a high temperature of 800-1200° C. in an argon-oxygen mixed gas environment to obtain a sapphire substrate;

[0008] (2) Place the metal tungsten foil in the center of the heating zone of the tube furnace, heat it up and oxidize it in the air to obtain tungsten trioxide foil;

[0009] (3) According to the order of airflow from upstream to downstream, the alumina boat containing sulfur powder or selenium powder is first pushed to the center of the first heating zone, and then the tungsten trioxide foil is covered on the sapphire substrate and pushed to the center of the second heating zone;

[0010] (4) Open the gas flow valve, introduce hydrogen and argon mixed gas into the tube furnace, and flush the reaction chamber for 30-60 minutes before heating;

[0011] (5) Setting a programmed temperature rise, under a hydrogen-argon mixed gas, raising the temperature of the first heating zone to 200°C-250°C, and raising the temperature of the second heating zone to 750°C-800°C, to grow and prepare a wafer-level tungsten disulfide nanofilm; or under a hydrogen-argon mixed gas, raising the temperature of the first heating zone to 350°C-400°C, and raising the temperature of the second heating zone to 780°C-820°C, to grow and prepare a wafer-level tungsten diselenide nanofilm;

[0012] (6) After the growth is completed, the tube furnace is cooled naturally to room temperature, and the hydrogen and argon gases are turned off to obtain a wafer-level tungsten disulfide or tungsten diselenide nanofilm.

[0013] Preferably, in step (1), the annealing time is 2-5 hours, and in the argon-oxygen mixed gas, the flow rate of oxygen is 80-150 sccm, and the flow rate of argon is 80-150 sccm.

[0014] Preferably, in step (2), the temperature of oxidation of the tungsten foil in air is 650-750° C., and the oxidation time is 40-70 minutes.

[0015] Preferably, in step (3), the confined space between the tungsten trioxide foil and the sapphire substrate is 0.2-2 mm.

[0016] Preferably, in step (4), the flow rate of argon in the hydrogen-argon mixed gas is 120-180 sccm, and the flow rate of hydrogen is 15-30 sccm.

[0017] Preferably, the growth time of the wafer-level tungsten disulfide nanofilm or the wafer-level tungsten diselenide nanofilm is 8-16 minutes.

[0018] Compared with the prior art, the present invention has the following significant advantages:

[0019] 1) Different from tungsten disulfide and tungsten diselenide nanosheets grown on substrates such as silicon, glass, and mica, the present invention uses high-temperature annealed C-plane sapphire as a substrate. By regulating the annealing time and annealing conditions, the growth and preparation of wafer-level tungsten disulfide and tungsten diselenide two-dimensional nanofilms can be achieved.

[0020] 2) Different from the hydrothermal method, liquid phase stripping and other methods, the present invention adopts the chemical vapor deposition method, which can accurately prepare two-dimensional nanofilms of tungsten disulfide and tungsten diselenide with different layer thicknesses by regulating the growth temperature, hydrogen flow rate and confined space.

[0021] 3) The tungsten source precursor is designed. Different from the conventional use of trioxide powder as the tungsten source, the present invention uses tungsten foil oxidized in the air as the tungsten source. Because it is flat and smooth, and the metal source and the substrate grow face to face, the uniformity of the tungsten source diffusion is improved during the growth process, which is more conducive to the preparation of highly uniform and high-quality films.

[0022] 4) Compared with other wafer-level growth methods, the present invention does not add catalysts such as hydroxides or chlorides, thus avoiding the introduction of impurity elements and achieving high-quality, high-uniformity, wafer-level two-dimensional nanofilm preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A digital picture of a wafer-level tungsten disulfide two-dimensional nanofilm prepared by the chemical vapor deposition method corresponding to Example 1;

[0024] Figure 2 The optical characterization results of the wafer-level tungsten disulfide two-dimensional nanofilm prepared by the chemical vapor deposition method corresponding to Example 1;

[0025] Figure 3 The Raman characterization results of the wafer-level tungsten disulfide two-dimensional nanofilm prepared by the chemical vapor deposition method corresponding to Example 1;

[0026] Figure 4 The Kelvin probe microscope characterization results of the wafer-level tungsten disulfide two-dimensional nanofilm prepared by the chemical vapor deposition method corresponding to Example 1;

[0027] Figure 5 The X-ray photoelectron spectroscopy characterization results of the wafer-level tungsten disulfide two-dimensional nanofilm prepared by the chemical vapor deposition method corresponding to Example 1;

[0028] Figure 6The Raman spectroscopy characterization results of different number of layers of wafer-level tungsten disulfide two-dimensional nanofilms prepared by the chemical vapor deposition method corresponding to Example 2;

[0029] Figure 7 The photoluminescence characterization results of different numbers of wafer-level tungsten disulfide two-dimensional nanofilm layers prepared by the chemical vapor deposition method corresponding to Example 2;

[0030] Figure 8 The atomic force microscope characterization results of different numbers of wafer-level tungsten disulfide two-dimensional nanofilms prepared by the chemical vapor deposition method corresponding to Example 2;

[0031] Fig. 9 A digital picture of a wafer-level tungsten diselenide two-dimensional nanofilm prepared by the chemical vapor deposition method corresponding to Example 3;

[0032] Fig.10 Optical characterization results of the wafer-level tungsten diselenide two-dimensional nanofilm prepared by the chemical vapor deposition method corresponding to Example 3;

[0033] Fig.11 The Raman characterization results of the wafer-level tungsten diselenide two-dimensional nanofilm prepared by the chemical vapor deposition method corresponding to Example 3;

[0034] Fig.12 The Kelvin probe microscope characterization results of the wafer-level tungsten diselenide two-dimensional nanofilm prepared by the chemical vapor deposition method corresponding to Example 3;

[0035] Fig.13 The X-ray photoelectron spectroscopy characterization results of the wafer-level tungsten diselenide two-dimensional nanofilm prepared by the chemical vapor deposition method corresponding to Example 3;

[0036] Fig.14 The Raman spectroscopy characterization results of different number of layers of wafer-level tungsten diselenide two-dimensional nanofilms prepared by the chemical vapor deposition method corresponding to Example 4;

[0037] Fig.15 The photoluminescence characterization results of different numbers of wafer-level tungsten diselenide two-dimensional nanofilm layers prepared by the chemical vapor deposition method corresponding to Example 4;

[0038] Fig.16 These are the atomic force microscopy characterization results of different numbers of wafer-level tungsten diselenide two-dimensional nanofilms prepared by the chemical vapor deposition method corresponding to Example 4. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

[0040] Example 1

[0041] Place the C-side sapphire wafer in a tube furnace for high-temperature annealing at a temperature of 1000°C for 3 hours. The gas atmosphere in the tube furnace is an oxygen-argon mixed gas with an oxygen flow rate of 100 sccm and an argon flow rate of 100 sccm. After cooling naturally to room temperature, take out the sapphire wafer as a growth substrate. Then place the tungsten foil in a tube furnace and heat it in an air atmosphere at a temperature of 700°C for 40 minutes to obtain an oxidized tungsten foil as a metal tungsten source. Take 250 mg of sulfur powder and put it into an alumina boat as a sulfur source. Then cover the oxidized tungsten foil face to face on the annealed sapphire wafer with a spatial confinement height of 1 mm. Then push the sapphire wafer into the center of the second heating temperature zone, and push the alumina boat filled with sulfur powder into the center of the first heating temperature zone. Next, introduce 250sccm argon gas into the tube furnace for 45 minutes to stabilize the gas environment in the reaction chamber, and then introduce a hydrogen-argon mixed gas with a hydrogen flow rate of 20sccm and an argon flow rate of 150sccm. Set the program temperature rise to make the center of the first heating temperature zone reach 250℃, the center of the second heating temperature zone reach 800℃, and the growth time is 12 minutes. After the growth is completed, cool naturally to room temperature, turn off the hydrogen and argon, and remove the sapphire substrate.

[0042] The wafer-level tungsten disulfide film grown is as follows Figure 1 The tungsten disulfide film was characterized by optical microscopy, Raman spectroscopy, atomic force microscopy, and Kelvin probe microscopy. The results are shown in Figures 2 to 5 As shown in the figure. From the optical microscope characterization results, it can be seen that the scratch is a sapphire substrate, the grown film is highly uniform, and the surface is smooth and flat. The Raman spectrum characterization results show that its two characteristic peaks E 2g and A 1g 354cm respectively -1 、419cm -1 The characteristic peaks are consistent with the reported data, and the grown film is a tungsten disulfide film. From the characterization results of atomic force microscopy and Kelvin probe microscopy, it can be seen that the surface of the film is flat and smooth, with low roughness, and the surface potential distribution is uniform. From the X-ray photoelectron energy spectrum, it can be seen that the tested W 4f and S 2p orbital fitting curves are consistent with their standard binding energy fitting curves.

[0043] Example 2

[0044] The growth process of Example 1 is maintained, and the hydrogen flow rate is reduced to 15 sccm. Other experimental conditions remain unchanged, so that a single-layer tungsten disulfide film can be prepared. Figure 6 For Raman spectroscopy characterization, the peak frequency difference between the two characteristic peaks of the monolayer tungsten disulfide is 62cm -1, which is consistent with the reported data of monolayer tungsten disulfide. Monolayer tungsten diselenide exhibits a direct band gap and has a strong response to photoluminescence. Figure 7 For photoluminescence characterization, tungsten disulfide showed strong luminescence efficiency. Figure 8 The atomic force microscopy characterization results show that the thickness of the tungsten disulfide film is 0.82nm. The above characterization results can prove that a single-layer tungsten disulfide film has been successfully prepared. Maintaining the growth process and experimental conditions of Example 1, the preparation of a double-layer tungsten disulfide film can be achieved. The double-layer tungsten disulfide exhibits an indirect band gap and has a weak response to photoluminescence. The peak frequency difference between the two characteristic peaks of the Raman spectrum of the double-layer tungsten disulfide is 64cm -1 . Figure 6 , 7 This was demonstrated by both photoluminescence and Raman spectroscopy characterization. Figure 8 Atomic force microscopy shows that the thickness of the double-layer tungsten disulfide film is 1.7nm. Maintaining the growth process and experimental conditions of Example 1, the preparation of a three-layer tungsten disulfide film can be achieved by changing the oxidation conditions of the tungsten foil to 700°C for 60 minutes. Continuing to maintain the growth process and experimental conditions of Example 1, the preparation of a bulk tungsten disulfide film can be achieved by reducing the height of the confined space to 0.2mm. The three-layer and bulk tungsten disulfide also show an indirect band gap, which is basically unresponsive to photoluminescence, and the Raman spectrum characteristic peak of tungsten disulfide shows E 2g Redshift, A 1g Blue shift. Figure 6 , 7 These characteristics were confirmed. Figure 8 For AFM characterization, the thickness of the tri-layer and bulk tungsten disulfide films were 2.2 nm and 7.2 nm.

[0045] Example 3

[0046] The high temperature annealing of the sapphire wafer, oxidation of the metal tungsten foil and the experimental operation process are consistent with Example 1. Take 200 mg of selenium powder and put it into the alumina boat as the selenium source. The spatial confinement height between the tungsten foil and the sapphire wafer is 1 mm. A hydrogen-argon mixed gas is introduced, and the hydrogen flow rate is 12 sccm and the argon flow rate is 100 sccm. Set the program temperature rise so that the center of the first heating temperature zone reaches 400°C, the center of the second heating temperature zone reaches 800°C, and the growth time is 14 minutes.

[0047] The wafer-level tungsten diselenide film grown is as follows Fig. 9 The tungsten diselenide film was characterized by optical microscopy, Raman spectroscopy, atomic force microscopy, and Kelvin probe microscopy. The results are shown in Figures 10 to 13 As shown in the figure, the optical microscope characterization results show that the grown tungsten diselenide film has high uniformity, a smooth surface and no impurities. From the Raman spectrum characterization, it can be seen that its characteristic peak E 2g / A1g Divided into 254cm -1 The characteristic peaks are consistent with the data reported in the literature, confirming that the grown film is a tungsten diselenide film. The atomic force microscope and Kelvin probe microscope characterization results show that the film surface is uniform and flat, with low roughness, and the surface potential distribution is uniform. The X-ray photoelectron spectroscopy characterization shows that the tested W 4f and Se 3d orbital fitting curves are consistent with their standard binding energy fitting curves.

[0048] Example 4

[0049] The growth process of Example 3 is maintained, and the growth temperature is lowered to 780° C., while other experimental conditions remain unchanged, to achieve the preparation of a single-layer tungsten diselenide film. Fig.14 For Raman spectroscopy characterization, the peak frequency of the characteristic peak of monolayer tungsten diselenide is 252 cm -1 , which is consistent with the reported data of monolayer tungsten diselenide. Monolayer tungsten diselenide exhibits a direct band gap and has a strong response to photoluminescence. Fig.15 For photoluminescence characterization, tungsten diselenide showed strong luminescence efficiency. Fig.16 The atomic force microscopy characterization results show that the thickness of the tungsten diselenide film is 0.87nm. The above characterization results can prove that a single-layer tungsten diselenide film has been successfully prepared. Maintaining the growth process and experimental conditions of Example 3, the preparation of a double-layer tungsten diselenide film can be achieved. Continuing to maintain the growth process and experimental conditions of Example 3, by reducing the height of the confined space to 0.6mm and 0.2mm, the preparation of three-layer and multi-layer tungsten diselenide films can be achieved. Double-layer, three-layer and bulk tungsten diselenide exhibit indirect band gaps, weak response to photoluminescence, and the Raman spectrum characteristic peaks of tungsten diselenide show E 2g / A 1g Blue shift. Fig.14 , 15 These characteristics were also confirmed. Figure 8 For AFM characterization, the thicknesses of bilayer, trilayer and bulk tungsten disulfide films were 1.54 mm, 2.4 nm and 3.3 nm.

Claims

1. A method for preparing a wafer-level tungsten disulfide or tungsten diselenide two-dimensional nanofilm, characterized in that: The steps include: (1) Place the C-surface polished sapphire in the center of the heating zone of a tube furnace and anneal it at a high temperature of 800-1200°C in an argon-oxygen mixed gas environment to obtain a sapphire substrate; (2) Place the metal tungsten foil in the center of the heating zone of the tube furnace, heat it up and oxidize it in the air to obtain tungsten trioxide foil; (3) According to the order of airflow from upstream to downstream, the alumina boat filled with sulfur powder or selenium powder is first pushed to the center of the first heating zone, and then the tungsten trioxide foil is covered on the sapphire substrate and pushed to the center of the second heating zone. The height of the confined space between the tungsten trioxide foil and the sapphire substrate is 0.2-2 mm; (4) Open the gas flow valve, introduce hydrogen-argon mixed gas into the tube furnace, and flush the reaction chamber for 30-60 minutes before heating; (5) Setting a programmed temperature rise, under a hydrogen-argon mixed gas, raising the temperature of the first heating zone to 200°C-250°C, and raising the temperature of the second heating zone to 750°C-800°C, to grow and prepare a wafer-level tungsten disulfide film; or under a hydrogen-argon mixed gas, raising the temperature of the first heating zone to 350°C-400°C, and raising the temperature of the second heating zone to 780°C-820°C, to grow and prepare a wafer-level tungsten diselenide film; (6) After the growth is completed, the tube furnace is cooled naturally to room temperature, and the hydrogen and argon gases are turned off to obtain a wafer-level tungsten disulfide or tungsten diselenide two-dimensional nanofilm.

2. The method for preparing a wafer-level tungsten disulfide or tungsten diselenide two-dimensional nanofilm according to claim 1, characterized in that: In step (1), the annealing time is 2-5 hours, the flow rate of oxygen is 80-150 sccm, and the flow rate of argon is 80-150 sccm.

3. The method for preparing a wafer-level tungsten disulfide or tungsten diselenide two-dimensional nanofilm according to claim 1, characterized in that: In step (2), the temperature of tungsten foil oxidation in air is 650-750° C., and the oxidation time is 40-70 minutes.

4. The method for preparing a wafer-level tungsten disulfide or tungsten diselenide two-dimensional nanofilm according to claim 1, characterized in that: In step (4), the hydrogen-argon mixed gas has an argon flow rate of 120-180 sccm and a hydrogen flow rate of 15-30 sccm.

5. The method for preparing a wafer-level tungsten disulfide or tungsten diselenide two-dimensional nanofilm according to claim 1, characterized in that: The growth time of the wafer-level tungsten disulfide nanofilm or the wafer-level tungsten diselenide nanofilm is 8-16 minutes.

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