A method for preparing a double-layer transition metal chalcogenide heterojunction single-crystal thin film

Abstract

The application relates to a method for preparing a double-layer transition metal chalcogenide heterojunction monocrystalline thin film, which adopts a chemical vapor deposition method, uses steps on a substrate surface to induce growth of a single-layer molybdenum disulfide thin film on the substrate, and then uses the steps on the substrate surface to continue inducing growth of a tungsten disulfide thin film which is consistent in orientation with the molybdenum disulfide on the molybdenum disulfide thin film, so as to obtain the double-layer transition metal chalcogenide heterojunction monocrystalline thin film. The method is simple in operation, the double-layer heterojunction monocrystalline thin film prepared has excellent photoelectric properties such as electron mobility, and can be applied to preparation of high-quality devices.

Description

Technical Field

[0001] The invention belongs to the technical field of material preparation, and in particular relates to a method for preparing a double-layer transition metal chalcogenide heterojunction single crystal thin film. Background Art

[0002] Two-dimensional heterojunctions have unique electrical, optical, mechanical, and magnetic physical properties. They are the basic units of semiconductor devices and are particularly suitable for applications in the fields of photonics and optoelectronics. They have unique advantages in the preparation of logic, storage, radio frequency, and optoelectronic devices.

[0003] Because two-dimensional materials exhibit central inversion symmetry, the energies of AA and AB stacking are similar, resulting in energy degeneracy. Therefore, double-layer heterojunctions produced using conventional vapor deposition processes often exhibit both AA and AB stacking patterns, preventing seamless splicing. When spliced ​​into thin films, grain boundaries form, resulting in polycrystalline films with inferior performance compared to single-crystal films. However, double-layer heterojunction single-crystal films exhibit only one AA stacking pattern and no grain boundaries. Consequently, their electron mobility and other optoelectronic properties are superior, resulting in higher-quality devices. Therefore, it is currently necessary to develop a method for preparing double-layer heterojunction single-crystal films. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a method for preparing a double-layer transition metal dichalcogenide heterojunction single crystal thin film. The method is simple to operate, and the obtained double-layer heterojunction single crystal thin film has excellent optoelectronic properties such as electron mobility, and can be used to prepare high-quality devices.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for preparing a double-layer transition metal chalcogenide heterojunction single crystal thin film is disclosed. The method adopts a chemical vapor deposition method to firstly grow a single-layer molybdenum disulfide thin film on a substrate by utilizing steps on the substrate surface to induce growth. Then, a tungsten disulfide thin film having the same orientation as the molybdenum disulfide is further grown on the molybdenum disulfide thin film by utilizing steps on the substrate surface to induce growth, thereby obtaining a double-layer transition metal chalcogenide heterojunction single crystal thin film.

[0007] More preferably, the method comprises the following steps:

[0008] S1. Deposition of a monolayer MoS2 film on a sapphire substrate with atomic steps distributed on the surface.

[0009] S2. placing sulfur powder in a first temperature zone of a CVD reactor, placing a mixture of tungsten trioxide and sodium chloride in a second temperature zone of the CVD reactor, and placing the sapphire substrate having a molybdenum disulfide film on its surface obtained in step S1 in a third temperature zone of the CVD reactor;

[0010] S3. After the CVD reactor is evacuated and heated, the heating temperature is set to:

[0011] Starting from 0 min, heating the third temperature zone, heating the third temperature zone to 970° C. from 0 min to 55 min, and then keeping the temperature; starting from 20 min, heating the first temperature zone and the second temperature zone, heating the first temperature zone to 120° C. from 20 min to 30 min, and then keeping the temperature; heating the second temperature zone to 640° C. from 20 min to 45 min, and then keeping the temperature;

[0012] When the temperature in the third temperature zone reaches 860° C., argon gas is continuously introduced into the CVD reactor as a carrier gas to start a growth process to grow a tungsten disulfide film on the molybdenum disulfide film;

[0013] S4. After the growth is completed, the heating power of the CVD reactor is turned off, and the sapphire substrate is allowed to cool naturally to room temperature along with the furnace, thereby obtaining a double-layer transition metal dichalcogenide heterojunction single crystal thin film prepared on the sapphire substrate.

[0014] More preferably, in step S3, the second temperature zone is heated to 570°C at 35 minutes, and the third temperature zone is heated to 860°C at 39 minutes.

[0015] More preferably, in step S3, the duration of the growth process is 30 minutes.

[0016] More preferably, in the mixture of step S2, the mass ratio of tungsten trioxide to sodium chloride is 10:1.

[0017] More preferably, in step S4, the CVD reactor is naturally cooled to room temperature in an atmosphere in which argon gas is continuously introduced.

[0018] More preferably, in step S3 and step S4, the flow rate of argon gas continuously introduced into the CVD reactor is 35 sccm.

[0019] The present invention also provides a double-layer transition metal sulfide heterojunction single crystal film prepared by the method.

[0020] Existing vapor deposition processes typically utilize layer-by-layer growth on sapphire substrates to produce tungsten disulfide / molybdenum disulfide heterojunction thin films. However, the interaction between molybdenum disulfide and tungsten disulfide results in the formation of two antiparallel tungsten disulfide crystal domains: AA stacking and AB stacking. This prevents the tungsten disulfide from maintaining a single orientation. When the thin films are spliced ​​together, grain boundaries form, resulting in a polycrystalline film.

[0021] Compared with the existing process, the method of the present invention uses a sapphire substrate with steps in combination with two chemical vapor depositions for preparation. In the first vapor deposition, the steps are used to induce the growth of a single-crystal single-layer molybdenum disulfide film. During the second vapor deposition, since the molybdenum disulfide film produced by the first vapor deposition is only a single atomic layer thick, the steps on the substrate still exist and can continue to play the same inductive role. The step edge of the sapphire interacts with the tungsten disulfide, guiding the grown tungsten disulfide crystal domains to have a consistent orientation, further preparing a continuous single-crystal tungsten disulfide film, forming only a single AA stacking mode, thereby preparing tungsten disulfide with a consistent orientation on the molybdenum disulfide film, and realizing the growth of a double-layer heterojunction single crystal film.

[0022] The method of the present invention uses the CVD method twice to directly prepare a double-layer heterojunction single crystal thin film on sapphire. The method is simple and easy to operate. The prepared double-layer heterojunction is larger in size and higher in quality. It has the opportunity to achieve large-scale quantitative production and can be expanded to the growth of other two-dimensional materials, which is of great significance.

[0023] The double-layer heterojunction single crystal thin film prepared by the present invention has excellent photoelectric properties such as electron mobility and can be used to prepare high-quality devices.

[0024] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figure is a schematic diagram of the process for preparing tungsten disulfide / molybdenum disulfide heterojunction single crystal thin films according to the method of the present invention.

[0026] Figure 2 Shown is the corresponding Figure 1 Optical images of the products obtained at each stage of the process.

[0027] Figure 3 FIG. 4 is a schematic diagram of a CVD reactor used in a vapor deposition process according to the method of the present invention.

[0028] Figure 4 The temperature adjustment curves and gas adjustment curves of the three temperature zones in the furnace during the vapor deposition process according to the method of the present invention are shown.

[0029] Figure 5 The figure is a Raman spectrum of a tungsten disulfide / molybdenum disulfide heterojunction single crystal thin film prepared according to the method of the present invention.

[0030] Figure 6 The optical image of the tungsten disulfide / molybdenum disulfide heterojunction single crystal film prepared according to the method of the present invention and the Raman spectra of 9 randomly selected points A to I therein are shown. DETAILED DESCRIPTION

[0031] The present invention provides a method for preparing a double-layer transition metal chalcogenide heterojunction single crystal thin film. The method comprises the following steps: first, a single-layer molybdenum disulfide thin film is grown on a substrate by inducing growth of the steps on the surface of the substrate; then, a tungsten disulfide thin film having the same orientation as the molybdenum disulfide is grown on the molybdenum disulfide thin film by inducing growth of the steps on the surface of the substrate; and finally, a double-layer transition metal chalcogenide heterojunction single crystal thin film is obtained.

[0032] The method specifically prepares tungsten disulfide / molybdenum disulfide (WS2 / MoS2) heterojunction single crystal thin films. Figure 1 and Figure 2 , Figure 1 The process and principle of preparing tungsten disulfide / molybdenum disulfide heterojunction single crystal thin films are shown. Figure 2 Shown is the corresponding Figure 1 Optical images of the products obtained at each stage of the process.

[0033] The method uses a sapphire substrate with steps and prepares a double-layer film by two chemical vapor deposition processes. During the first vapor deposition, the steps are used to induce the nucleation of uniformly oriented molybdenum disulfide. The interaction between the sapphire step edge and the molybdenum disulfide breaks the symmetry of the antiparallel direction, making the energy of growth down the step lower, thereby guiding the growing molybdenum disulfide crystal domains to have a uniform orientation, and further preparing a continuous single-crystal monolayer molybdenum disulfide film. During the second vapor deposition, because the molybdenum disulfide film prepared by the first vapor deposition is only a single atomic layer thick, the steps on the substrate still exist and can continue to exert the same inductive effect. The interaction between the sapphire step edge and the tungsten disulfide guides the growing tungsten disulfide crystal domains to have a uniform orientation, further preparing a continuous single-crystal tungsten disulfide film, forming only a single AA stacking mode, thereby preparing tungsten disulfide with a uniform orientation on the molybdenum disulfide film, and achieving the growth of a double-layer heterojunction single crystal film.

[0034] The CVD system used in the method includes Figure 3 The three-temperature-zone CVD tubular reactor (hereinafter referred to as the CVD reactor) shown in FIG. has a first temperature zone, a second temperature zone, and a second temperature zone arranged therein in sequence.

[0035] The method specifically takes the following steps:

[0036] S1. In a CVD reactor, a single-layer MoS2 thin film is deposited on a sapphire substrate with atomic steps distributed on the surface using chemical vapor deposition.

[0037] The sapphire substrate is annealed and other treatments are performed to produce steps on its surface, and a single-layer molybdenum disulfide film is grown on its surface under appropriate vapor deposition conditions. The specific process of step S1 belongs to the existing technology and will not be described in detail.

[0038] S2.See Figure 3 , place the porcelain boat filled with sulfur powder in the first temperature zone, place the crucible filled with the mixed powder of tungsten trioxide and sodium chloride in the second temperature zone, place the sapphire substrate with the molybdenum disulfide film on the surface obtained in step S1 on the quartz plate, and then place them together in the third temperature zone in the CVD reactor.

[0039] In the mixed powder, the mass ratio of tungsten trioxide to sodium chloride is preferably 10:1.

[0040] S3. Use a vacuum pump to evacuate the CVD reactor and then heat it, as shown in the following example. Figure 4 As shown, the heating temperature settings are as follows:

[0041] The third temperature zone is heated starting from 0 min, and is heated to 970°C from 0 min to 55 min, and then kept warm; the first temperature zone and the second temperature zone are heated starting from 20 min, and the first temperature zone is heated to 120°C from 20 min to 30 min, and then kept warm; the second temperature zone is heated to 640°C from 20 min to 45 min, and then kept warm.

[0042] More specifically, the first temperature zone is heated to 120°C at the 30th minute, the second temperature zone is heated to 570°C at the 35th minute, and the third temperature zone is heated to 830°C at the same time, the third temperature zone is heated to 860°C at the 39th minute, the second temperature zone is heated to 640°C at the 45th minute, and the third temperature zone is heated to 970°C at the 55th minute.

[0043] Among them, when the third temperature zone reaches 860°C, argon gas with a flow rate of 35sccm is continuously introduced into the CVD reactor as a carrier gas to start the growth process, and a tungsten disulfide film is grown on the molybdenum disulfide film. The duration of the growth process is preferably 30 minutes.

[0044] S4. After the growth is completed, argon gas is continuously supplied to the CVD reactor at a flow rate of 35 sccm. At the 70th minute, the heating power of the CVD reactor is turned off, and the sapphire substrate is allowed to naturally cool to room temperature with the furnace, thereby obtaining a WS2 / MoS2 heterojunction single crystal thin film prepared on the sapphire substrate.

[0045] See also Figure 5and Figure 6 , Figure 5 The Raman spectrum of the prepared WS2 / MoS2 heterojunction single crystal film is shown. Figure 6 The optical image of the prepared WS2 / MoS2 heterojunction single crystal film (left) and the Raman spectra of 9 randomly selected points A~I (right) are shown. Figure 5 and Figure 6 It can be seen that the WS2 / MoS2 heterojunction single crystal thin film prepared according to the method of the present invention is of high quality.

[0046] The present invention uses the CVD method twice to directly prepare a double-layer heterojunction single crystal film on sapphire. The method is simple and easy to operate. The prepared double-layer heterojunction is larger in size and higher in quality. It has the opportunity to achieve large-scale quantitative production and can be expanded to the growth of other two-dimensional materials, which is of great significance.

[0047] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A method for preparing a double-layer transition metal chalcogenide heterojunction single crystal thin film, characterized in that: A single-layer molybdenum disulfide thin film is first grown on a substrate using steps on the substrate surface to induce growth, and then a tungsten disulfide thin film having the same orientation as the molybdenum disulfide is grown on the molybdenum disulfide thin film using steps on the substrate surface to induce growth, thereby obtaining a double-layer transition metal disulfide heterojunction single crystal thin film; The method for preparing a double-layer transition metal chalcogenide heterojunction single crystal thin film comprises the following steps: S1. Deposition of a monolayer MoS2 film on a sapphire substrate with atomic steps distributed on the surface. S2. placing sulfur powder in a first temperature zone of a CVD reactor, placing a mixture of tungsten trioxide and sodium chloride in a second temperature zone of the CVD reactor, and placing the sapphire substrate having a molybdenum disulfide film on its surface obtained in step S1 in a third temperature zone of the CVD reactor; S3. After the CVD reactor is evacuated and heated, the heating temperature is set to: Heating the third temperature zone from 0 min to 55 min, heating the third temperature zone to 970° C., and then keeping the temperature; Starting from the 20th minute, heating the first temperature zone and the second temperature zone, heating the first temperature zone to 120° C. from the 20th minute to the 30th minute, and then keeping the temperature; heating the second temperature zone to 640° C. from the 20th minute to the 45th minute, and then keeping the temperature; When the temperature in the third temperature zone reaches 860° C., argon gas is continuously introduced into the CVD reactor as a carrier gas to start a growth process to grow a tungsten disulfide film on the molybdenum disulfide film; S4. After the growth is completed, the heating power of the CVD reactor is turned off, and the sapphire substrate is allowed to cool naturally to room temperature along with the furnace, thereby obtaining a double-layer transition metal dichalcogenide heterojunction single crystal thin film prepared on the sapphire substrate.

2. The method according to claim 1, characterized in that In step S3, the second temperature zone is heated to 570°C at 35 minutes, and the third temperature zone is heated to 860°C at 39 minutes.

3. The method according to claim 2, characterized in that In step S3, the duration of the growth process is 30 minutes.

4. The method according to claim 1, wherein In the mixture of step S2, the mass ratio of tungsten trioxide to sodium chloride is 10:

1.

5. The method according to claim 1, wherein In step S4, the CVD reactor is naturally cooled to room temperature in an atmosphere in which argon gas is continuously introduced.

6. The method according to claim 4, characterized in that In step S3 and step S4, the flow rate of argon gas continuously introduced into the CVD reactor is 35 sccm.

7. A double-layer transition metal chalcogenide heterojunction single crystal thin film prepared by the method according to any one of claims 1 to 6.

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