A method for preparing a large-area continuous 2H phase molybdenum telluride film

Abstract

The application discloses a preparation method of a large-area continuous 2H phase molybdenum telluride film, which comprises the following steps: (1) mixing molybdenum trioxide and sodium chloride as a metal precursor; placing the metal precursor, a c-surface sapphire substrate treated by super-clean, and tellurium powder in a tube furnace through a quartz sleeve; (2) during the heating process, continuously feeding a mixed gas of argon and hydrogen into the oxygen-removed reaction cavity; when the reaction temperature is reached, adjusting the flow ratio of argon and hydrogen in the mixed gas; and after sufficient reaction, obtaining a large-area continuous 2H phase molybdenum telluride film. The NaCl molten salt is in-situ reacted with molybdenum trioxide at high temperature to convert the molybdenum trioxide into an easily volatile metal oxychloride intermediate with high saturated vapor pressure, the kinetic bottleneck of traditional solid-gas direct sublimation mass transfer is broken, and the growth of a large-area continuous high-quality 2H phase molybdenum telluride film is realized.

Description

Technical Field

[0001] This invention relates to a method for preparing large-area continuous 2H phase molybdenum telluride thin films on c-plane sapphire substrates by NaCl-assisted chemical vapor deposition. Background Technology

[0002] MoTe2 has various crystal structures. Among them, the 2H phase MoTe2 is a semiconductor phase with a near-infrared bandgap, a bulk bandgap of about 1.0 eV, and a monolayer bandgap of about 1.1 eV. It also has high room-temperature carrier mobility and good switching characteristics, and can be used to construct field-effect transistors and low-power logic devices.

[0003] However, the formation energies of the 2H and 1T' phases of MoTe2 are relatively similar, leading to phase competition during conventional chemical vapor deposition (CVD) growth, making the controllable preparation of the 2H phase MoTe2 quite difficult. In existing technologies, when growing MoTe2 on conventional substrates such as sapphire using conventional CVD, the solid molybdenum trioxide precursor exhibits high melting points and extremely low vapor pressures, resulting in insufficient sublimation capacity at high temperatures. This leads to extremely low gas-phase mass transfer efficiency within the reaction chamber and an inability to maintain local supersaturation. This easily causes uneven distribution of precursor materials on the substrate surface, resulting in scattered nucleation sites, slow lateral expansion rates, and the formation of a 1T' / 2H mixed phase. Furthermore, the resulting films suffer from poor continuity, small size, and defects such as obvious pores, breaks, and grain boundary gaps on the surface. In addition, the lattice mismatch between the substrate and the epitaxial material, as well as the difficulty in effectively adjusting the surface nucleation barrier, further limit the preparation of high-purity, large-area, continuous 2H phase MoTe2 films. Therefore, the MoTe2 thin films prepared by existing technologies are difficult to meet the requirements of wafer-level device arrays and integrated circuits for high-quality semiconductor phase thin films. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to address the shortcomings of existing technologies, such as low precursor mass transfer efficiency, difficulty in precise phase control, and discontinuous films, by providing a method for preparing high-quality pure 2H phase MoTe2 films with large-area continuous growth.

[0005] Technical solution: The preparation method of the 2H phase molybdenum telluride thin film of the present invention includes the following steps:

[0006] (1) Preparation of metal precursor and system construction: Molybdenum trioxide and sodium chloride were mixed as metal precursor; the metal precursor, c-plane sapphire substrate and tellurium powder were placed in a tube furnace through a quartz sleeve;

[0007] (2) Lateral epitaxial growth by vapor deposition: During the heating process, a mixture of argon and hydrogen is introduced into the deoxygenated reaction chamber. When the reaction temperature is reached, the volume ratio of argon and hydrogen in the mixture is adjusted so that the active gaseous precursor generated by the molten salt-assisted in-situ reaction flows through the substrate surface and undergoes sufficient kinetic nucleation and seamless splicing growth. After sufficient reaction, a large-area continuously grown 2H phase molybdenum telluride film is obtained.

[0008] Preferably, in step (1), the c-plane sapphire substrate is a (0001) crystal plane single-crystal sapphire substrate; the ultra-cleaning treatment involves sequentially placing the c-plane sapphire substrate into an ultrasonic cleaner containing acetone, anhydrous ethanol, and deionized water for ultrasonic cleaning for 15-20 minutes each, followed by drying with high-purity nitrogen. The mass ratio of molybdenum trioxide to sodium chloride is 27:5; under this specific ratio, NaCl acts as a molten salt aid, reacting with solid at high temperature. An in-situ chemical reaction occurs, and the reaction equation can be expressed as:

[0009]

[0010] The generated intermediate metal chloride oxide ( Compared to the original With an extremely low melting point and extremely high saturated vapor pressure, it can spontaneously and violently volatilize at relatively low temperatures. This in-situ chemical transformation completely breaks through the kinetic bottleneck of traditional solid-gas direct sublimation mass transfer, improving the gas phase partial pressure and lateral mass transfer efficiency of the molybdenum source by several orders of magnitude. As a result, a highly supersaturated, highly uniform material concentration, steady-state two-dimensional gas-phase boundary diffusion layer was successfully constructed above the c-plane sapphire substrate, laying the precursor material foundation for the formation of large-area, continuous 2H phase thin films.

[0011] In step (1), the tellurium powder and the metal precursor ( The overall mass ratio of the mixed powder (NaCl and NaCl) is 40:1 to ensure that the reaction system is in a highly tellurium-rich environment and to inhibit the formation of anion vacancy defects.

[0012] In step (2), the flow ratio of argon to hydrogen is 3:2 during the heating process; the flow ratio of argon to hydrogen is 4~5:1 during the reaction process; the heating time is 30 min; the isothermal reaction temperature is 680~700 ℃, and the holding time for growth is 35 min. Under this specific macroscopic thermodynamic temperature range and precise control of hydrogen reduction flow rate, the system spontaneously anchors within the thermodynamic stability window of the 2H semiconductor phase, fundamentally suppressing phase competition of the 1T' phase. At the same time, the high mass transfer efficiency makes the lateral expansion rate of the high-density 2H phase domains far exceed the vertical stacking rate. The high-density and highly consistent unidirectional domains can achieve ideal seamless splicing during the subsequent growth process, fundamentally suppressing the generation of lattice defects such as antiparallel domain boundaries, thereby forming a high-crystallinity pure 2H phase continuous single-layer or few-layer film that completely covers the entire single-crystal substrate.

[0013] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: Based on a c-plane (0001) sapphire substrate, the present invention ingeniously utilizes the in-situ molten salt chemical reaction of NaCl and molybdenum source at high temperature to transform a solid high-melting-point precursor into a highly volatile gaseous chlorine oxide intermediate, breaking the limitations of chemical vapor deposition growth. The technical bottleneck of limited mass transfer in molybdenum sources was overcome. By constructing a high local gas-phase supersaturation environment, extremely rapid lateral epitaxy of high-density isotropic 2H phase domains was induced on c-plane sapphire, achieving seamless splicing growth of highly crystalline pure 2H phase materials of 1.5 cm × 1.5 cm and above. The resulting films exhibited excellent phase purity (pure 2H phase) and surface smoothness (no obvious breaks, cracks, pores, or micro-gaps throughout the entire area). Two-dimensional field-effect transistor arrays fabricated based on this high-quality pure 2H phase continuous film showed excellent mechanical strength and micro / nano fabrication compatibility. Their macroscopic electrical transport characteristics exhibited high uniformity, p-type semiconductor characteristics dominated by positive gate voltage, and excellent conductivity with a high conductivity of 9.44. The room temperature carrier mobility meets the performance specifications of large-scale integrated micro / nano circuits. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating the preparation of 2H-phase molybdenum telluride thin films and the fabrication of field-effect transistor devices based on 2H-phase molybdenum telluride thin films according to the present invention.

[0015] Figure 2 A flowchart for constructing a field-effect transistor device;

[0016] Figure 3 An optical microscope image (50x magnification) of a large area of ​​MoTe2 two-dimensional material (prepared in Example 1) grown on a c-plane sapphire substrate.

[0017] Figure 4The image shows an optical microscope image (50x magnification) of the two-dimensional MoTe2 material grown on a c-plane sapphire substrate (prepared in Comparative Example 1).

[0018] Figure 5 The images show the continuous MoTe2 Raman surface scan pattern and Raman dot scan pattern grown on the c-plane sapphire substrate in Example 1.

[0019] Figure 6 Raman surface scan and point scan spectra of a single hexagonal domain of MoTe2 grown on a common sapphire substrate prepared in Comparative Example 1.

[0020] Figure 7 The XRD results (orange line) of the molybdenum ditelluride material prepared in Example 1 and the XRD results (purple line) of the molybdenum ditelluride material prepared in Comparative Example 1 are shown.

[0021] Figure 8 This is a SEM image of the hexagonal molybdenum ditelluride material on the sapphire substrate prepared in Example 1;

[0022] Figure 9 A schematic diagram and optical micrograph of a two-dimensional field-effect transistor device constructed from a 2H-phase molybdenum telluride thin film prepared according to the present invention;

[0023] Figure 10 (a) Electrical characteristic curves of a field-effect transistor device; (b) Electrical characteristic curves of a two-dimensional field-effect transistor device constructed based on the 2H phase molybdenum telluride thin film of Example 1; (c) Electrical characteristic curves of a two-dimensional field-effect transistor device constructed based on the 2H phase molybdenum telluride thin film of Comparative Example 1.

[0024] Figure 11 The optical microscope images show the effect of different carrier gas flow rates on the crystal domain growth state in Examples 2-4.

[0025] Figure 12 The optical microscope images show the effect of different reaction temperatures on the film growth quality in Examples 5-7.

[0026] Figure 13 The images show Raman mappings of 20 randomly selected regions of the molybdenum telluride thin film obtained in Example 1. Detailed Implementation

[0027] Example 1

[0028] The present invention discloses a method for preparing a large-area continuous 2H phase molybdenum telluride thin film, comprising the following steps:

[0029] (1) Substrate ultra-cleaning: The single crystal c-plane (0001) sapphire substrate (size 2 cm × 2 cm) was placed in an ultrasonic cleaner containing acetone, anhydrous ethanol and deionized water for 15 min respectively to thoroughly remove organic and micro dust contamination on the surface. Then, it was dried with high-purity nitrogen gas to obtain a c-plane sapphire substrate with a clean surface and atomically flat surface.

[0030] (2) Weigh 27 mg of molybdenum trioxide and 5 mg of sodium chloride, mix them to obtain metal precursor powder, grind it 3 times and take 20 mg for later use; weigh 800 mg of tellurium powder; spread the ground metal precursor powder on the crucible, place the c-side sapphire substrate on the crucible, and place the tellurium powder in the quartz boat; place the quartz boat and crucible (airflow direction from tellurium source to metal precursor / substrate) into the quartz sleeve, with the tellurium powder placed upstream of the tube furnace (to provide constant tellurium vapor) along the airflow direction, and the metal precursor (mixed powder of molybdenum trioxide and sodium chloride) placed in the high-temperature zone in the center of the tube furnace; the c-side sapphire substrate is inverted and placed directly above the metal precursor or immediately downstream to ensure that the volatilized metal chloride oxide intermediate can be deposited on the substrate surface in a high concentration and uniformly; after checking the gas valve in the furnace, turn on the argon gas to atmospheric pressure, place the quartz sleeve in the tube furnace, and evacuate to a furnace pressure of 1.0. After Pa, turn off the evacuation equipment; turn on argon gas to atmospheric pressure, adjust the argon flow rate to 300 sccm and purge for 10 minutes, set the temperature to 700 ℃ for 30 min, and adjust the argon flow rate to 15 sccm and the hydrogen flow rate to 10 sccm during the heating process; when the furnace temperature reaches 700 ℃, adjust the hydrogen flow rate to 10 sccm and the argon flow rate to 40 sccm, and hold for 35 min; when the holding time ends and the temperature cools to 475 ℃, turn off the hydrogen gas, adjust the argon flow rate to 200 sccm until the furnace temperature drops to room temperature, and remove the c-side sapphire substrate with the 2H molybdenum telluride thin film grown on it.

[0031] pass Figure 3 It can be seen that the MoTe2 thin film grown on the c-plane sapphire substrate achieves a large-scale surface coverage on a macroscopic scale. The film has a uniform color and no visible holes, cracks or grain boundary gaps, indicating that seamless splicing and continuous growth of large-area crystal domains was successfully achieved through molten salt-assisted epitaxial growth.

[0032] pass Figure 5 Raman characterization revealed that, regardless of whether it was a large-area scan or a single-domain scan, the 2H molybdenum telluride thin film prepared in Example 1 showed a 234 cm⁻¹ domain of 2H-MoTe₂. -1 Characteristic peak, and the film at 234 cm⁻¹ -1The high intensity, sharp shape, and lack of significant peak shift of the characteristic peaks indicate that the film has good crystallinity, is a pure 2H phase molybdenum telluride film, and is free of impurity doping and obvious lattice defects. That is, the MoTe2 film grown in Example 1... Characteristic peak (approximately 234 cm) -1 The Raman signal intensity distribution of the film is highly uniform, with no obvious dark areas or frequency shifts, which confirms that the film has a pure 2H phase structure with extremely high crystallinity, good spatial uniformity and no obvious defects.

[0033] pass Figure 7 It can be seen that Example 1 (orange line) only corresponds to phase 2H. The presence of sharp and highly diffractive characteristic peaks at specific crystal planes proves that it has a highly consistent c-axis orientation and excellent pure-phase single-crystal characteristics.

[0034] pass Figure 13 It can be seen that the thin film prepared in Example 1 basically covers the entire substrate. Through measurement, it was found that the film size reaches more than 1.5 cm × 1.5 cm and is macroscopically continuous. Therefore, the 2H phase molybdenum telluride thin film prepared in Example 1 has a large size, is continuous, and also has high flatness.

[0035] Example 2

[0036] pass Figures 1-2 It is understood that the method for constructing a field-effect transistor device based on the 2H molybdenum telluride thin film obtained in Example 1 includes the following steps:

[0037] Step 1, Thin film transfer: Prepare a NaOH solution of 16 g potassium hydroxide + 50 mL deionized water, spin-coat PMMA (polymethyl methacrylate) onto the c-side sapphire substrate on which a 2H molybdenum telluride thin film has been grown, and cure it at 150 °C; after curing, immerse it in the prepared NaOH solution to perform film peeling; after peeling, soak the film in deionized water.

[0038] Step 2: First, bombard the 300 nm silicon substrate (SiO2 / Si, i.e., the silicon substrate is a silicon substrate with a dielectric layer; the dielectric layer is silicon dioxide) with oxygen plasma. Then, transfer the peeled film onto the silicon substrate, heat to remove water, and then remove the adhesive with acetone to obtain a clean two-dimensional material. Specifically, heat the sample to 100 °C for 30 min, then place it in a petri dish and soak it in acetone overnight. After soaking for 12 h, take it out and rinse it with acetone, ethanol, and deionized water in sequence, and then blow it dry with gas.

[0039] Step 3, Semiconductor material patterning: The molybdenum telluride thin film is patterned using photolithography and Ar ion bombardment. The Ar ion bombardment energy is 290 eV, the beam current is 61 mA, and the time is 3 min.

[0040] Step 4, source and drain electrode patterning: spin-coat negative photoresist NR9-3000, pre-bake at 110 ℃ for 180 s on a heated stage; after exposure, post-bake at 100 ℃ for 60 s; develop in RD6 developer for 10 s to complete development;

[0041] Step 5, electrode deposition; electron beam deposition is used at a depth of less than 5 × 10⁻⁶. -4 Under a high vacuum environment of Pa, metal electrodes are vacuum-deposited to obtain an effect transistor device. The device structure is as follows: Figure 9 As shown, the electrical performance of the obtained field-effect transistor device was tested.

[0042] pass Figure 9 As can be seen from the optical micrographs The channel region remained intact, without any issues such as film tearing or wrinkling. The source and drain electrode patterns were clear and regular, demonstrating that this large-area 2H phase film possesses excellent mechanical strength and micro / nano fabrication compatibility, making it suitable for constructing large-scale field-effect transistor arrays.

[0043] This invention also achieves lossless transfer of large-area thin films to silicon substrates and the fabrication of highly uniform p-type field-effect transistor devices. At the electrical transport level, in the large-area molybdenum ditelluride lattice fabricated by this invention, trace amounts of intrinsic tellurium vacancies tend to introduce shallow donor levels near the conduction band bottom. Therefore, the fabricated p-type field-effect transistor devices exhibit superior electrical performance in electrical testing (I... d -V d with I d -V g In macroscopic terms, it will inevitably exhibit the superior p-type semiconductor characteristics dominated by the positive gate voltage.

[0044] Electrical performance test results: The thin film prepared in Example 1 exhibits excellent conductivity and high carrier mobility, indicating a regular internal lattice structure, smooth charge transport paths, and good charge transport efficiency. Therefore, the thin film prepared in Example 1 possesses excellent electrical properties and can meet the performance requirements for the fabrication of related devices. Figure 10 It can be seen that the MoTe2 transistor prepared in Example 2 has a mobility of 9.44 cm⁻¹. 2 / Vs.

[0045] Comparative Example 1

[0046] The preparation method of Comparative Example 1 is the same as that of Example 1, except that sodium chloride (NaCl) was not added to the metal precursor powder in step (2). Specifically, 27 mg of molybdenum trioxide was weighed, ground 3 times, and 20 mg was taken for later use; 800 mg of tellurium powder was weighed; the ground molybdenum trioxide powder was spread evenly on the crucible, the c-side sapphire substrate was also placed on the crucible, and the tellurium powder was placed in the quartz boat; the quartz boat and crucible (the airflow direction is from the tellurium source to the molybdenum trioxide / substrate) were placed in the quartz sleeve, and the tellurium powder was placed upstream of the tube furnace (to provide constant tellurium vapor) along the airflow direction in the quartz sleeve, and the molybdenum trioxide powder was placed in the high-temperature zone in the center of the tube furnace; the c-side sapphire substrate was placed upside down directly above or immediately downstream of the molybdenum trioxide powder; after checking the gas valve in the furnace, argon gas was turned to atmospheric pressure, the quartz sleeve was placed in the tube furnace, and the furnace pressure was evacuated to 1.0. After Pa, turn off the evacuation equipment; turn on argon gas to atmospheric pressure, adjust the argon flow rate to 300 sccm and purge for 10 minutes, set the temperature to 700 ℃ for 30 min, and adjust the argon flow rate to 15 sccm and the hydrogen flow rate to 10 sccm during the heating process; when the furnace temperature reaches 700 ℃, adjust the hydrogen flow rate to 10 sccm and the argon flow rate to 40 sccm, and hold for 35 min; when the holding temperature ends and the temperature cools to 475 ℃, turn off the hydrogen gas, adjust the argon flow rate to 200 sccm until the furnace temperature drops to room temperature, and remove the c-side sapphire substrate with the molybdenum telluride thin film grown on it.

[0047] In NaCl-free systems lacking molten salt assistance, the volatilization of molybdenum trioxide is severely constrained, resulting in excessively low concentrations of Mo precursors in the gas phase and consequently, low mass transfer efficiency. For example... Figure 4 As shown, only sporadic clusters or extremely small isolated crystal domains can form on the substrate surface, making it impossible to spread into a continuous thin film. However, after adding NaCl in Example 1, low-melting-point intermediate metal chloride oxides were generated in situ at high temperature, and the local gas phase supersaturation was greatly improved, directly promoting the efficient growth of a large-area, continuous 2H phase lattice.

[0048] pass Figure 4 It can be seen that in Comparative Example 1, due to the lack of molten salt reaction, the gas-phase mass transfer of the precursor (molybdenum trioxide) is hindered, and only sparsely scattered, randomly nucleated, completely isolated, and small-sized isolated hexagonal crystal domains are present on the substrate surface, resulting in a large area of ​​uncovered bare substrate, making continuous film formation impossible. Figure 6 It can be seen that the Raman surface scan spectrum of the crystal domains grown in Comparative Example 1 shows an uneven distribution of signal intensity, with local dark areas inside.

[0049] Based on the molybdenum telluride thin film obtained in Comparative Example 1, a field-effect transistor device was constructed using the method described in Example 2, and the electrical performance of the constructed field-effect transistor device was tested.

[0050] Electrical performance test results: The conductivity of the thin film prepared in Comparative Example 1 decreased significantly, and the carrier mobility decreased. The core reason is the decrease in film crystallinity and the increase in lattice defects, which hindered the effective transport of charge, resulting in its electrical performance being inferior to that of Example 1. Figure 10 It can be seen that the MoTe2 transistor prepared in Comparative Example 1 has a mobility of 3.72 cm⁻¹. 2 / Vs.

[0051] Comparative Example 2

[0052] The preparation method of Comparative Example 2 is the same as that of Example 1, except that in step (2), the flow rate of the carrier gas (argon) during the heat preservation reaction is 10 sccm. Specifically, after checking the gas valve in the furnace, the argon gas is turned on to atmospheric pressure, the quartz sleeve is placed in the tube furnace, the vacuum is drawn until the pressure in the furnace is 1.0 Pa, and then the pumping equipment is turned off; the argon gas is turned on to atmospheric pressure, the argon gas flow rate is adjusted to 300 sccm and the gas is purged for 10 minutes, and the temperature is set to rise to 700 ℃ for 30 minutes. During the temperature rise, the argon gas flow rate is adjusted to 15 sccm and the hydrogen gas flow rate is adjusted to 10 sccm; when the temperature in the furnace rises to 700 ℃, the hydrogen gas flow rate is adjusted to 10 sccm and the argon gas flow rate is adjusted to 10 sccm, and the heat preservation growth is carried out for 35 minutes; when the heat preservation ends and the temperature is cooled to 475 ℃, the hydrogen gas is turned off, and the argon gas flow rate is adjusted to 200 sccm until the temperature in the furnace drops to room temperature, and the molybdenum telluride film is obtained.

[0053] Comparative Example 3

[0054] The preparation method of Comparative Example 3 is the same as that of Example 1, except that in step (2), the flow rate of the carrier gas (argon) during the heat preservation reaction is 50 sccm. Specifically, after checking the gas valve in the furnace, the argon gas is turned on to atmospheric pressure, the quartz sleeve is placed in the tube furnace, the vacuum is drawn until the pressure in the furnace is 1.0 Pa, and then the pumping equipment is turned off; the argon gas is turned on to atmospheric pressure, the argon gas flow rate is adjusted to 300 sccm and the gas is purged for 10 minutes, and the temperature is set to rise to 700 ℃ for 30 minutes. During the temperature rise, the argon gas flow rate is adjusted to 15 sccm and the hydrogen gas flow rate is adjusted to 10 sccm; when the temperature in the furnace rises to 700 ℃, the hydrogen gas flow rate is adjusted to 10 sccm and the argon gas flow rate is adjusted to 50 sccm, and the heat preservation growth is carried out for 35 minutes; when the heat preservation ends and the temperature is cooled to 475 ℃, the hydrogen gas is turned off, and the argon gas flow rate is adjusted to 200 sccm until the temperature in the furnace drops to room temperature, and the molybdenum telluride film is obtained.

[0055] Comparative Example 4

[0056] The preparation method of Comparative Example 4 is the same as that of Example 1, except that in step (2), the flow rate of the carrier gas (argon) during the heat preservation reaction is 100 sccm. Specifically, after checking the gas valve in the furnace, the argon gas is turned on to atmospheric pressure, the quartz sleeve is placed in the tube furnace, the vacuum is drawn until the pressure in the furnace is 1.0 Pa, and then the pumping equipment is turned off; the argon gas is turned on to atmospheric pressure, the argon gas flow rate is adjusted to 300 sccm and the gas is purged for 10 minutes, and the temperature is set to rise to 700 ℃ for 30 minutes. During the temperature rise, the argon gas flow rate is adjusted to 15 sccm and the hydrogen gas flow rate is adjusted to 10 sccm; when the temperature in the furnace rises to 700 ℃, the hydrogen gas flow rate is adjusted to 10 sccm and the argon gas flow rate is adjusted to 100 sccm, and the heat preservation growth is carried out for 35 minutes; when the heat preservation ends and the temperature is cooled to 475 ℃, the hydrogen gas is turned off, and the argon gas flow rate is adjusted to 200 sccm until the temperature in the furnace drops to room temperature, and the molybdenum telluride film is obtained.

[0057] like Figure 11 As shown, when the carrier gas flow rate is too low (10 sccm), the precursor stays in the upstream region of the substrate for too long, and the local concentration overload causes severe secondary nucleation, resulting in a large number of bright small particles or multilayer small crystal domains of varying depths. When the flow rate is a suitable 50 sccm, the mass transport and epitaxial diffusion rates are matched, and the film exhibits a single, uniform light-colored monolayer or a few-layer contrast, with no excess bright particles or overlapping domain boundaries on the surface. When the flow rate is too high (100 sccm), the strong gas flow changes the local partial pressure and deposition mode of the reaction region, causing the growth to enter the stable range of the 1T' phase, and the film completely loses the characteristics of the 2H phase.

[0058] Comparative Example 5

[0059] The preparation method of Comparative Example 5 is the same as that of Example 1, except that in step (2), the reaction temperature is 550 ℃. Specifically, after checking the gas valve in the furnace, the argon gas is turned on to atmospheric pressure, the quartz sleeve is placed in the tube furnace, the vacuum is drawn until the pressure in the furnace is 1.0 Pa, and then the pumping equipment is turned off; the argon gas is turned on to atmospheric pressure, the argon gas flow rate is adjusted to 300 sccm and the gas is purged for 10 minutes, and the temperature is raised to 550 ℃ in 30 minutes. During the heating process, the argon gas flow rate is adjusted to 15 sccm and the hydrogen gas flow rate is adjusted to 10 sccm; when the temperature in the furnace rises to 550 ℃, the hydrogen gas flow rate is adjusted to 10 sccm and the argon gas flow rate is adjusted to 40 sccm, and the growth is carried out for 35 minutes; molybdenum telluride film is obtained.

[0060] Comparative Example 6

[0061] The preparation method of Comparative Example 6 is the same as that of Example 1, except that in step (2), the reaction temperature is 680 ℃. Specifically, after checking the gas valve in the furnace, argon gas is turned on to atmospheric pressure, the quartz sleeve is placed in the tube furnace, and the vacuum is drawn until the pressure in the furnace is 1.0 Pa and then the pumping equipment is turned off. Argon gas is turned on to atmospheric pressure, the argon gas flow rate is adjusted to 300 sccm and the gas is washed for 10 minutes. The temperature is set to rise to 680 ℃ in 30 minutes. During the temperature rise, the argon gas flow rate is adjusted to 15 sccm and the hydrogen gas flow rate is adjusted to 10 sccm. When the temperature in the furnace rises to 680 ℃, the hydrogen gas flow rate is adjusted to 10 sccm and the argon gas flow rate is adjusted to 40 sccm. The temperature is maintained for 35 minutes to grow. A molybdenum telluride film is obtained.

[0062] Comparative Example 7

[0063] The preparation method of Comparative Example 7 is the same as that of Example 1, except that in step (2), the reaction temperature is kept at 750 ℃. Specifically, after checking the gas valve in the furnace, argon gas is turned on to atmospheric pressure, the quartz sleeve is placed in the tube furnace, and the vacuum is drawn until the pressure in the furnace is 1.0 Pa before the pumping equipment is turned off. Argon gas is turned on to atmospheric pressure, the argon gas flow rate is adjusted to 300 sccm and the gas is purged for 10 minutes. The temperature is set to rise to 750 ℃ ​​in 30 minutes. During the temperature rise, the argon gas flow rate is adjusted to 15 sccm and the hydrogen gas flow rate is adjusted to 10 sccm. When the temperature in the furnace rises to 750 ℃, the hydrogen gas flow rate is adjusted to 10 sccm and the argon gas flow rate is adjusted to 40 sccm. The temperature is kept at 750 ℃ ​​for 35 minutes to grow. Molybdenum telluride film is obtained.

[0064] like Figure 12 As shown, when the reaction temperature is too low at 550 ℃, the sublimation driving force of the molybdenum precursor is insufficient, and the surface migration kinetic energy of the adsorbed atoms reaching the substrate is extremely low. In the image, there is basically no complete two-dimensional film, only a few blurry and dark small areas dotting the substrate with very few nucleation points. When the molybdenum source temperature is the optimal 680 ℃, the reaction activity is moderate, and the atoms tend to expand laterally along the edge of the substrate step. The image shows a smooth, continuous, and uniform two-dimensional film with a completely consistent thickness. When the molybdenum source temperature is too high, reaching 750 ℃, the excessively high reaction rate and thermodynamic conditions break the stable growth window of the 2H phase, causing it to enter the stable range of the 1T' phase and triggering obvious vertical growth. In the image, the film becomes significantly thicker and the contrast is greatly increased. It completely loses the typical characteristics of the 2H phase and instead presents a micromorphology composed of a large area of ​​thick crystal domains. This indicates that the system underwent a thermodynamic phase transition under this high temperature condition, spontaneously transforming into the growth of a thick 1T' phase film.

Claims

1. A method for preparing a large-area continuous 2H phase molybdenum telluride thin film, characterized in that, Includes the following steps: (1) Molybdenum trioxide and sodium chloride are mixed as a metal precursor; the metal precursor, ultra-cleaned c-plane sapphire substrate and tellurium powder are placed in a tube furnace through a quartz sleeve. (2) During the heating process, a mixture of argon and hydrogen is continuously introduced into the deoxygenated reaction chamber. When the reaction temperature is reached, the flow ratio of argon and hydrogen in the introduced mixture is adjusted. After the reaction is complete, a large-area continuously grown 2H phase molybdenum telluride film is obtained.

2. The method for preparing a large-area continuous 2H phase molybdenum telluride thin film according to claim 1, characterized in that: In step (1), the c-plane sapphire substrate is a (0001) crystal plane single crystal sapphire substrate.

3. The method for preparing a large-area continuous 2H phase molybdenum telluride thin film according to claim 2, characterized in that: The ultra-cleaning process involves sequentially placing the c-side sapphire substrate into an ultrasonic cleaner containing acetone, anhydrous ethanol, and deionized water for ultrasonic cleaning for 15-20 minutes each, followed by drying with high-purity nitrogen.

4. The method for preparing a large-area continuous 2H phase molybdenum telluride thin film according to claim 1, characterized in that: In step (1), the mass ratio of molybdenum trioxide to sodium chloride is 27:5~10.

5. The method for preparing a large-area continuous 2H phase molybdenum telluride thin film according to claim 1, characterized in that: In step (1), the mass ratio of tellurium powder to metal precursor is 40:1~5.

6. The method for preparing a large-area continuous 2H phase molybdenum telluride thin film according to claim 1, characterized in that: In step (2), during the heating process, the flow rate ratio of argon to hydrogen is 3~4:2; the heating time is not less than 30 min.

7. The method for preparing a large-area continuous 2H phase molybdenum telluride thin film according to claim 1, characterized in that: In step (2), the flow rate ratio of argon to hydrogen is 4~5:1 during the reaction.

8. The method for preparing a large-area continuous 2H phase molybdenum telluride thin film according to claim 1, characterized in that: In step (2), the reaction temperature is 680~700 ℃ and the reaction time is 35~40 min.

9. The method for preparing a large-area continuous 2H phase molybdenum telluride thin film according to claim 1, characterized in that: In step (2), the size of the 2H phase molybdenum telluride film is 1.5 cm × 1.5 cm or larger.

Images