A method for growing multilayer and single layer tungsten ditelluride thin films by atmospheric pressure chemical vapor deposition

Abstract

The application discloses a method for growing multilayer and single layer tungsten ditelluride films by normal pressure chemical vapor deposition. The method uses tellurium powder and tungsten trioxide as precursors, and adds potassium bromide as an auxiliary growth agent, so that the tungsten trioxide generates a precursor with stronger volatility under the action of the potassium bromide, and the problem of high required temperature of the tungsten trioxide is solved; and the double-temperature-zone tube furnace is used to control the growth temperature and time of the tellurium source and the tungsten source respectively, the Si / SiO2 substrate and the hydrogen-argon mixed gas are used as the carrier gas, and by adjusting the distance between the precursors, the growth temperature and the precursor ratio, the controllable preparation of the tungsten ditelluride film thickness and shape is realized. The tungsten ditelluride film grown by the application has excellent uniformity and a larger size, and the maximum size of the single layer can reach 0.01 cm 2 , which has an important positive effect on subsequent basic physical property research and preparation of high-performance electronic devices.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor preparation. It relates to a method for growing multilayer and monolayer tungsten ditelluride films by atmospheric pressure chemical vapor deposition. BACKGROUND

[0002] Transition metal dichalcogenides (TMDCs) are a new type of two-dimensional layered material, whose atoms within the layer are combined by strong covalent bonds, while the layers are connected by weak van der Waals forces. This makes them exhibit a variety of crystal structures and unique physical properties. As an important member of TMDCs materials, tungsten ditelluride (WTe2) has high electron mobility and a wide range of light response characteristics. At the same time, tungsten ditelluride is also predicted and confirmed as a second class of Weyl semimetal, which has many novel physical properties, such as large and non-saturated magnetoresistance (MR) at low temperature, ferroelectricity, superconductivity under certain pressure, quantum spin Hall effect, and high electron mobility, etc. Therefore, tungsten ditelluride is considered to have broad application prospects in high-efficiency memory, spintronics, optical devices, transistors, etc.

[0003] The preparation methods of tungsten ditelluride include "top-down" mechanical exfoliation method and "bottom-up" synthetic preparation method. Compared with the traditional mechanical exfoliation method, chemical vapor deposition (CVD) has the characteristics of simple operation, high efficiency, uniform product, controllable thickness, and larger size, etc., and is considered as one of the best methods for preparing large-area, high-quality tungsten ditelluride. However, due to the influence of reaction kinetics and thermodynamics, as well as the complexity of the growth environment inside the tube furnace, the controllable synthesis of large-area monolayer tungsten ditelluride is still a challenge, which needs to be further optimized.

[0004] Currently, there are studies that use sodium chloride to assist in the growth of large-area tungsten ditelluride films by double-tube chemical vapor deposition method, but the thickness of the single film is uncontrollable, and the tungsten ditelluride film with a specific shape has not been synthesized. (Growth of few-layer WTe2 by a salt-assisted double-tube chemical vapor deposition method with high infrared photosensitivity. doi: 10.1039 / d3nr00849e.). Another skilled person proposes a two-step ALD-CVD method for growing tungsten ditelluride film (Patent No. CN116262970A). This method first deposits a layer of tungsten film on the substrate by atomic layer deposition, and then uses chemical vapor deposition (CVD) technology to tellurize the tungsten film, thereby realizing the preparation of tungsten ditelluride film with controllable thickness. However, the operation process is relatively complex, and the reaction time is relatively long, usually 80 to 120 minutes. SUMMARY

[0005] The present application aims to overcome the shortcomings of existing production technology, and realizes the one-step controllable growth of multi-layer and single-layer tungsten ditelluride film by a normal pressure chemical vapor deposition method, thereby solving the problems of uncontrollable thickness and uniformity during growth, and long reaction time. The method uses tellurium powder and tungsten trioxide as precursors, and adds potassium bromide as an auxiliary growth agent. Tungsten trioxide generates a more volatile precursor under the action of potassium bromide, solving the problem of high temperature required by tungsten trioxide. The growth temperature and time of the tellurium source and tungsten source are controlled by a double-temperature-zone tube furnace, and Si / SiO2 substrate and hydrogen-argon mixed gas are used as the carrier gas. By adjusting the distance between the precursors, the growth temperature and the precursor ratio, the controllable preparation of tungsten ditelluride film thickness and shape is realized. The tungsten ditelluride film grown by the present application has excellent uniformity and large size, and the maximum size of the single layer can reach 0.01 cm 2 , which has important positive effects on subsequent basic physical property research and preparation of high-performance electronic devices.

[0006] The technical solution of the present application is:

[0007] A method for growing multi-layer and single-layer tungsten ditelluride film by normal pressure chemical vapor deposition, comprising the following steps:

[0008] S1, the Si / SiO2 substrate is placed in acetone, isopropanol and deionized water for ultrasonic cleaning, and then dried with nitrogen;

[0009] S2, put tellurium powder into a first quartz boat; put mixed powder of tungsten trioxide and halide into the front end of a second quartz boat, and arrange n pieces of Si / SiO2 substrates in turn at 0.5-1 cm behind the mixed powder;

[0010] wherein the mass ratio of tellurium powder and tungsten trioxide is 2.6:1-1:1; the mass ratio of tungsten trioxide and halide is 10:1-1:1; the halide is potassium bromide; the distance between the substrates is 0.2-0.5 cm; n=1-3;

[0011] S3, put the first quartz boat and the second quartz boat into the first temperature zone and the second temperature zone of the chemical vapor deposition equipment respectively, and the second quartz boat is behind; and vacuumize to 8.0-8.5 E-1 Pa;

[0012] wherein the distance between the first quartz boat and the second quartz boat is 15-30 cm;

[0013] S4, introduce hydrogen and argon mixed gas into the system to purge the growth pipeline until the pressure rises to normal pressure, and open the atmospheric valve channel, and in 15-20 minutes, the temperature of the first temperature zone and the second temperature zone is increased from room temperature to 550℃ and 750-880℃ respectively;

[0014] wherein the volume concentration of hydrogen is 10%;

[0015] The volume flow rate of hydrogen is 11 sccm, and the volume flow rate of argon is 99 sccm; (i.e. the time for the carrier gas to reach the second quartz boat from the first quartz boat is 31.2 s-62.2 s);

[0016] S5, keep the growth time at the set temperature for 5-10 min;

[0017] S6, after the growth is completed, the system is naturally cooled to room temperature under the protection of hydrogen and argon mixed gas, so as to obtain a tungsten ditelluride film on the Si / SiO2 substrate.

[0018] The thickness of the film is 0.7-51 nm;

[0019] When the distance between the first quartz boat and the second quartz boat is 15-17 cm, the tungsten ditelluride film obtained is 14-73 layers; when the distance is 18 cm-20 cm, it is 2-10 layers of tungsten ditelluride film; and when the distance is 22 cm-30 cm, it is a single layer of tungsten ditelluride film;

[0020] When the distance is 22 cm-30 cm, in the single layer of tungsten ditelluride film obtained, when the distance is 25 cm, the shape is close to a triangle; when the distance is 27 cm, the shape is close to a rhombus; and when the distance is 30 cm, the shape is close to a regular hexagon;

[0021] Under the condition of 25 cm distance and 850℃ in the second temperature zone, when the mass ratio of tellurium powder and tungsten trioxide is 2:1, the obtained film is close to triangle; when the mass ratio of tellurium powder and tungsten trioxide is 1.6:1, the shape of the obtained film is a truncated triangle or a triangle with jagged edges.

[0022] The substantial features of the present application are:

[0023] The present application relates to a method for growing tungsten ditelluride film by atmospheric pressure chemical vapor deposition. In this process, by adjusting the distance between the two groups of precursors, the gas molecule density of tellurium source reaching tungsten source and participating in the reaction can be changed, so that tungsten ditelluride films with different morphologies and thicknesses can be effectively obtained. In addition, by adding an auxiliary growth agent (potassium bromide), which generates a more volatile precursor with tungsten trioxide under the catalysis of hydrogen, the problem of high melting point of tungsten trioxide and poor product quality is effectively solved. This method greatly shortens the overall reaction time of preparing tungsten ditelluride film to 5 minutes, has the characteristics of fast film forming speed and low growth temperature, and the short high-temperature duration further reduces the possibility of Si / SiO2 breakdown by high temperature, opening up a new way for subsequent microelectronic circuit integration applications.

[0024] The beneficial effects of the present application are:

[0025] 1. The tungsten ditelluride grown by this method has high quality, high growth efficiency, good uniformity and controllable morphology. It effectively improves the shortcomings of traditional mechanical peeling method, such as time-consuming, laborious, complicated operation, single size and uncontrollable morphology. The chemical vapor deposition method used allows flexible adjustment of reaction parameters, including the type and proportion of reaction precursors, auxiliary growth agent, growth temperature and time, hydrogen and argon gas concentration, and the distance between precursors, so as to realize the accurate preparation of tungsten ditelluride film material. In addition, the one-step growth of tungsten ditelluride is more simple and efficient, and the raw materials tellurium powder, tungsten trioxide and potassium bromide are all cheap drugs, which are convenient for industrial production and application.

[0026] 2. Rapid low-temperature growth of tungsten ditelluride while maintaining its uniformity and cleanliness: by adding a new type of auxiliary growth agent potassium bromide, the problem of high evaporation temperature (1473℃) of tungsten trioxide is solved. Compared with the traditional sodium chloride auxiliary agent ( Figure 12 ), the reaction involving potassium bromide is more moderate and has fewer impurities ( Figure 14 ), the migration rate and deposition rate of the co-product gas molecules of hydrogen and potassium bromide reach equilibrium, the product tungsten ditelluride is more easily uniformly diffused from the central nucleation point, greatly shortening the growth time to 5 minutes, effectively solving the shortcomings of high energy consumption and long time of the prior art.

[0027] 3. Controllable preparation of material layer number and shape: By adjusting the distance and proportion between the precursors, the controllability of the thickness and shape of the tungsten ditelluride film can be realized. Embodiments 5 to 13 are all single-layer thin films. Currently, there is no special patterned tungsten ditelluride thin film reported. By optical microscopy, long strip-shaped ( Figure 3 ), bat-shaped ( Figure 9 ), c), triangle-like ( Figure 9 d), sawtooth edge hexagonal ( Figure 9 f), truncated triangle ( Figure 14 e) and the like are observed. These patterned growths may stimulate different physical properties. In addition, the multi-layer tungsten ditelluride thin film realizes large-area continuous growth ( Figure 7 ), and the maximum growth size of a single uniform single-layer tungsten ditelluride thin film can reach 0.01 cm 2 ( Figure 9 c), which provides a better choice for subsequent property research and application. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a schematic diagram of a chemical vapor deposition system used in the embodiments of the present application;

[0029] Figure 2 is a growth time-temperature diagram of the tungsten ditelluride thin film of the embodiments of the present application;

[0030] Figure 3 is an optical microscope (OM) and scanning electron microscope (SEM) image of the multi-layer tungsten ditelluride thin film in embodiment 1; wherein, Figure 3 (a) is an optical microscope image; Figure 3 (b) is a scanning electron microscope (SEM) image;

[0031] Figure 4 is a Raman spectrum (Raman) characterization of the multi-layer tungsten ditelluride thin film in embodiment 1;

[0032] Figure 5 is an energy dispersive X-ray spectrometer (EDS) characterization of the multi-layer tungsten ditelluride thin film in embodiment 1;

[0033] Figure 6 is an atomic force microscope (AFM) image and its step thickness characterization of the multi-layer tungsten ditelluride thin film in embodiment 1;

[0034] Figure 7 is an optical microscope image of the large-area continuous multi-layer tungsten ditelluride thin film in embodiment 2;

[0035] Figure 8 is an X-ray diffraction (XRD) pattern of the large-area continuous multi-layer tungsten ditelluride thin film in embodiment 2;

[0036] Figure 9 Optical microscope images of few-layer and monolayer tungsten ditelluride films in Example 3 to Example 8;

[0037] Figure 10 Scanning electron microscope images of few-layer and monolayer tungsten ditelluride films;

[0038] Figure 11 Raman spectra of monolayer tungsten ditelluride film in Example 6 and few-layer tungsten ditelluride film in Example 4, respectively;

[0039] Figure 12 Optical microscope images of Example 9 sample;

[0040] Figure 13 Optical microscope images of Example 10 sample;

[0041] Figure 14 Optical microscope images of Example 11 to 13, wherein Figure 14 (a) corresponds to Example 11, Figure 14 (b) corresponds to Example 6 as a control group, Figure 14 (c) corresponds to Example 13, Figure 14 (d), Figure 14 (e) corresponds to Example 12;

[0042] Figure 15 Optical microscope images of monolayer tungsten ditelluride film at different temperatures, wherein Figure 15 (a) is the image of Example 14, Figure 15 (b) is the image of Example 15, Figure 15 (c) is the image of Example 16. DETAILED DESCRIPTION

[0043] The application will be described in more detail below with specific examples. The examples are only used to help understand the application and should not be regarded as specific limitations of the application.

[0044] Example 1:

[0045] This embodiment discloses a method for preparing a multilayer tungsten ditelluride film, specifically comprising the following steps:

[0046] S1, use 0.5*0.5 cm Si / SiO2 (the thickness of the oxide layer is 285 nm) as a growth substrate, immerse it in acetone, isopropanol and deionized water respectively for ultrasonic cleaning for 10 min to remove surface contaminants. Finally, dry it with a nitrogen gun for standby.

[0047] S2, 0.4 g of tellurium powder, 0.2 g of tungsten trioxide and 0.05 g of potassium bromide are weighed using an electronic balance. The weighed tellurium powder is placed in the quartz boat I; the mixed powder of tungsten trioxide and potassium bromide is placed in the front end of the quartz boat II; at the same time, the Si / SiO2 substrates treated in sequence are arranged at 1 cm behind the mixed powder on the quartz boat II, a total of three substrates are placed, and the spacing between the substrates is 0.5 cm.

[0048] S3, the quartz boat I and the quartz boat II are respectively placed in the first temperature zone and the second temperature zone of the chemical vapor deposition furnace; and vacuumized to 8.0~8.5 E-1 Pa (the definition of the temperature zone is that the first temperature zone is the first region passed according to the direction of the carrier gas flow, and then the second temperature zone; in the second temperature zone, the gas passes the tungsten source mixture and the substrate in sequence);

[0049] wherein the distance between the quartz boat I and the quartz boat II is adjusted to 15 cm;

[0050] The growth schematic diagram is shown in Figure 1 .

[0051] S4, a hydrogen-argon mixed gas (hydrogen concentration is 10%; hydrogen 11 sccm, argon 99 sccm) is introduced into the system to purge the growth pipeline until it rises to normal pressure, and the atmospheric valve door is opened, the temperature rising time is set to 20 minutes, and the temperature of the first temperature zone and the second temperature zone is respectively increased from room temperature to 550℃ and 850℃.

[0052] S5, the growth time is kept for 5 min;

[0053] S6, after the growth is completed, the system is naturally cooled to room temperature, and the sample is taken out.

[0054] Example 2:

[0055] The difference between this embodiment and example 1 is that the temperature of the second temperature zone in S4 is adjusted to 750℃, and the rest of the parameters remain unchanged, so as to obtain the sample to be detected.

[0056] Example 3:

[0057] The difference between this embodiment and example 1 is that the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 18 cm, and the rest of the parameters remain unchanged, so as to obtain the sample to be detected.

[0058] Example 4:

[0059] The difference between this embodiment and example 1 is that the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 20 cm, and the rest of the parameters remain unchanged, so as to obtain the sample to be detected.

[0060] Example 5:

[0061] The difference between this embodiment and embodiment 1 is that the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 22 cm, and the rest of the parameters remain unchanged, so as to obtain the sample to be detected.

[0062] Embodiment 6:

[0063] The difference between this embodiment and embodiment 1 is that the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 25 cm, and the rest of the parameters remain unchanged, so as to obtain the sample to be detected.

[0064] Embodiment 7:

[0065] The difference between this embodiment and embodiment 1 is that the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 27 cm, and the rest of the parameters remain unchanged, so as to obtain the sample to be detected.

[0066] Embodiment 8:

[0067] The difference between this embodiment and embodiment 1 is that the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 30 cm, and the rest of the parameters remain unchanged, so as to obtain the sample to be detected.

[0068] Embodiment 9:

[0069] The difference between this embodiment and embodiment 1 is that the auxiliary growth agent in S2 is adjusted from potassium bromide to sodium chloride, the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 25 cm, and the rest of the parameters remain unchanged, so as to obtain the sample to be detected.

[0070] Embodiment 10:

[0071] The difference between this embodiment and embodiment 1 is that the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 25 cm, and the growth time in S5 is adjusted to 10 min, and the rest of the parameters remain unchanged, so as to obtain the sample to be detected.

[0072] Embodiment 11:

[0073] The difference between this embodiment and embodiment 1 is that the precursor in S2 is adjusted to 0.4 g of tellurium powder, 0.15 g of tungsten trioxide and 0.0375 g of potassium bromide (Te:W≈2.6:1 mass ratio), the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 25 cm, and the rest of the parameters remain unchanged, so as to obtain the sample to be detected.

[0074] Embodiment 12:

[0075] The difference between this embodiment and embodiment 1 is that the precursor in S2 is adjusted to 0.4 g of tellurium powder, 0.25 g of tungsten trioxide and 0.0625 g of potassium bromide (Te:W ≈ 1.6:1 mass ratio), the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 25 cm, and the remaining parameters remain unchanged, thereby obtaining the sample to be detected.

[0076] Embodiment 13:

[0077] The difference between this embodiment and embodiment 1 is that the precursor in S2 is adjusted to 0.4 g of tellurium powder, 0.4 g of tungsten trioxide and 0.1 g of potassium bromide (Te:W = 1:1 mass ratio), the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 25 cm, and the remaining parameters remain unchanged, thereby obtaining the sample to be detected.

[0078] Embodiment 14:

[0079] The difference between this embodiment and embodiment 1 is that the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 25 cm, and the second temperature zone temperature in S4 is adjusted to 750°C, and the remaining parameters remain unchanged, thereby obtaining the sample to be detected.

[0080] Embodiment 15:

[0081] The difference between this embodiment and embodiment 1 is that the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 25 cm, and the second temperature zone temperature in S4 is adjusted to 800°C, and the remaining parameters remain unchanged, thereby obtaining the sample to be detected.

[0082] Embodiment 16:

[0083] The difference between this embodiment and embodiment 1 is that the distance between the quartz boat I and the quartz boat II in S3 is adjusted to 25 cm, and the second temperature zone temperature in S4 is adjusted to 880°C, and the remaining parameters remain unchanged, thereby obtaining the sample to be detected.

[0084] The surface morphology of the samples of the above 16 embodiments was preliminarily characterized by an optical microscope, and the micro-morphology was further observed by a scanning electron microscope, and the domain and thickness of the tungsten ditelluride film were measured by an atomic force microscope. In addition, we also used micro-Raman spectroscopy (532 nm excitation laser), energy dispersive X-ray spectroscopy and X-ray diffraction technology to characterize the chemical bond composition and crystal structure. Through the above methods, we evaluated the overall quality of the tungsten ditelluride film.

[0085] Figure 1 Growth schematic diagram of the double-temperature zone tube furnace used for the method; Figure 2 Time-temperature diagram of the growth process of the tungsten ditelluride film.

[0086] Figure 3 Characterization of the multilayer tungsten ditelluride thin film grown in Example 1. Figure 3 (a) is a macroscopic image observed under an optical microscope. Figure 3 (b) is a microscopic morphology image under a scanning electron microscope. By combining the macroscopic and microscopic characterization results, we can conclude that the tungsten ditelluride film grown in Example 1 exhibits a multilayer nanoribbon structure, with thinner edges that appear dark under an optical microscope, while the central part, being the nucleation point, is thicker and appears bright white.

[0087] Figure 4 This is the Raman spectrum of Example 1. As can be seen from the figure, the tungsten ditelluride thin film exhibits high Raman spectral density at 100 cm⁻¹. -1 Up to 250cm -1 There are five vibration modes in total, with a value of 108.8 cm. -1 place Peak, 116.1 cm -1 place Peak, 134.4cm -1 place Peak, 161.8 cm -1 place Peak and 211.6 cm -1 place The peaks are consistent with previous literature reports. Qualitative analysis of the tungsten ditelluride thin film samples was performed using energy-dispersive X-ray spectroscopy, such as... Figure 5 As shown, apart from the characteristic peaks of the Si / SiO2 substrate, all other elements belong to tungsten ditelluride, and the EDS results show that Te:W = 2.36:1. All of this evidence directly proves that we have successfully synthesized tungsten ditelluride thin films.

[0088] Figure 6 As shown in the AFM image and step thickness curve of Example 1, we can further observe that the height dimension from the edge to the center ranges from approximately 9.8 nm to 51 nm, corresponding to a thickness of 14 to 73 layers.

[0089] Figure 7 This is an optical microscope image of the large-area multilayer tungsten distelluride thin film grown in Example 2. Compared to Example 1, lowering the temperature in the second temperature zone to 750°C is more conducive to the formation of a large-area continuous thin film. This is because the evaporation rate of the tungsten source is reduced, and the residence time is longer, allowing the tellurium and tungsten sources to react more fully, resulting in a high-density distribution of nucleation sites on the substrate. As the growth process proceeds, the distance difference between adjacent nucleation sites decreases, and the crystal edges come into contact and merge. This merging process leads to a significant increase in the continuity and density of the thin film, forming a dense thin film. Figure 8For the XRD pattern of the sample of Example 2, by comparing with the standard card (PDF #24-1352), the diffraction peaks of the synthesized tungsten ditelluride sample match well with the standard card of (002), (004), (006), (008) crystal surface diffraction peaks, that is, the tungsten ditelluride film has better crystal preferred orientation along the c-axis (001) direction.

[0090] In order to better study the few-layer tungsten ditelluride film, we keep other parameters unchanged and try to adjust the concentration in the reaction system by adjusting the distance between the tellurium source and the tungsten source (Dss). As shown in Figure 9 , optical microscope images of tungsten ditelluride films grown under different conditions are shown, covering Example 3 to Example 8. Smaller Dss values (18 cm ~20 cm) always produce few-layer tungsten ditelluride films with larger domain sizes (a, b in Figure 9 , with about 2~10 layers; while larger Dss values (25 cm ~30 cm) tend to produce single-layer tungsten ditelluride films with smaller domain sizes (d, e, f in Figure 9 , with a thickness of about 0.7 nm; Figure 9 (c) in between, is a transitional state, a bat-shaped single-layer film with a large size, with an area reaching 0.01 cm 2 . In terms of shape, among the single-layer tungsten ditelluride films obtained at a distance of 22 cm~30 cm, when the distance is 25 cm, the shape is close to a triangle; when the distance is 27 cm, the shape is close to a rhombus; when the distance is 30 cm, the shape is close to a regular hexagon; this dependence on Dss shows that the synthesis of tungsten ditelluride domains is highly dependent on the density of the gaseous precursor. The results show that changing Dss can effectively control the thickness distribution, the size of the domain and the shape.

[0091] Figure 10 are several groups of representative SEM images, in which Figure 10 (a), (b) in correspond to Example 4 (b is a partial enlarged view of a), Figure 10 (c) in corresponds to Example 5, Figure 10 (d) in corresponds to Example 6, Figure 10 (e), (f) in correspond to Example 8 (f is a partial enlarged view of e). Further micrographs show that the growth of large-area tungsten ditelluride follows a typical surface-limited epitaxial growth mode, and the completely covered tungsten ditelluride film undergoes a process of regional nucleation, regional growth and regional splicing. Figure 10 The domain boundaries can be identified in (b), which is likely due to the gas adsorption of air in the environment on these domain walls. Small-area single-layer tungsten ditelluride films will each independently nucleate and grow, eventually forming a regular morphology with jagged edges. Figure 11For the Raman spectra of single-layer and few-layer tungsten ditelluride films, it can be observed from the figure that as the layer number decreases to a single layer, the peak at 116.1 cm -1 The peak intensity at 161.7 cm -1 is enhanced; The peak shifts from 211 cm -1 to 214.4 cm -1 , with a slight blue shift. According to this rule, we can determine the layer thickness of tungsten ditelluride. Next, we mainly discuss the sample when the distance between the tellurium tungsten source is 25 cm.

[0092] Figure 12 For the optical microscope image of Example 9 sample, after replacing the auxiliary growth agent with sodium chloride, although a large area of single-layer film can also be generated, the uniformity and cleanliness are still not as good as the product assisted by potassium bromide, because the catalytic effect of sodium chloride is more intense, which is easy to nucleate and diffuse around impurity points.

[0093] Figure 13 For the optical microscope image of Example 10 sample, it can be observed from the figure that tungsten ditelluride mainly presents as irregular elongated strips, which may be because the tungsten ditelluride at the edge is not firmly combined with the substrate and reacts with hydrogen gas and then evaporates, and the molecules lose a certain degree of regularity in direction.

[0094] According to the above data, the growth process of tungsten ditelluride can be summarized as follows. Since the reactivity of tellurium and tungsten is low, and the melting point of tungsten precursor is high, the addition of hydrogen can play a role in two aspects: on the one hand, it can promote the reduction of tellurium powder and tungsten trioxide to generate more reactive hydrogen telluride and halogen tungsten oxide; on the other hand, as the reaction proceeds, the source concentration gradually decreases, and excess hydrogen will react with the generated tungsten ditelluride, thereby playing an etching effect. The relevant reaction equations are as follows:

[0095] (1)

[0096] (2)

[0097] (3)

[0098] (4)

[0099] The halide reacts with tungsten trioxide to generate halogen tungsten oxide with a lower melting point, which helps to reduce the required temperature, significantly increases the concentration of the precursor, and promotes the progress of the reaction.

[0100] Figure 14 ​​The images shown are optical microscope images of Examples 11-13, with Example 6 used as a control. Figure 14 (b) This study mainly explores the effect of changing the mass ratio of the tellurium to tungsten sources on the products while keeping other parameters constant, with a distance of 25 cm between the tellurium and tungsten sources. As can be seen from the figure, Te:W ≈ 2.6:1 ( Figure 14 In step a), the tellurium source is excessive. After the tungsten source reacts completely, tellurium or its derivatives dominate and evaporate and deposit on the substrate surface, forming impurities that affect performance. When the tungsten source is increased to Te:W = 2:1, the reaction reaches equilibrium, and tungsten ditelluride exhibits good morphology and quality. Increasing the tungsten source to Te:W ≈ 1.6:1 causes the triangular-like structure of the product to disappear. This may be due to insufficient tellurium source, causing the deposited tungsten ditelluride to be etched by hydrogen at the edges or vertices, forming serrated triangles. Figure 14 d) and truncated triangle ( Figure 14 (e). Under the above conditions, the tungsten ditelluride thin film size is approximately 30–50 μm. Further increasing the tungsten source to Te:W = 1:1 (… Figure 14 In step c), hydrogen etching plays a dominant role in the growth process, resulting in small, elongated shapes. Therefore, controlling the mass ratio of tellurium source to tungsten source to be 2:1 is more conducive to growing high-quality tungsten distelluride films with a specific shape.

[0101] Previous studies have shown that growth temperature has a significant effect on multilayer tungsten ditelluride films. To further investigate the effect of temperature on monolayer tungsten ditelluride films, we designed three sets of experiments for comparison. Figure 15 (a) Figure 15 (b) Figure 15 (c) Optical microscope images of Examples 14, 15, and 16 are shown. As can be seen from the figures, the growth results of tungsten ditelluride differ significantly under different tungsten source temperatures. At 750°C, the molecular mobility of tellurium and tungsten is low, making it difficult to diffuse uniformly to the edges, leading to a tendency for the film to stack and grow, resulting in small and thick tungsten ditelluride films. When the temperature rises to 800°C, although the film size increases, the balance between tungsten trioxide volatilization and crystal growth is not achieved, resulting in poor uniformity within the film. In contrast, at 850°C (… Figure 14 In step b), the reactant atoms have sufficient kinetic energy, increased mobility, and enhanced diffusivity. At this point, the volatilization of the tellurium-tungsten source and the film growth reach an optimal balance, resulting in a film with good uniformity. However, when the temperature is further increased to 880℃, the rate at which the tellurium source is reduced by hydrogen cannot keep up with the rate of the tungsten source reaction. This leads to a large amount of tellurium source being carried away by the carrier gas without participating in the reaction, making it difficult to control the crystal quality. The final product is mostly an irregular shape with a size of about 10 μm.

[0102] Through the above examples, the application synthesizes the tungsten ditelluride film with controllable thickness, good uniformity, high quality, large size and certain morphology by adjusting the distance between the tellurium source and the tungsten source, the reaction temperature, the reaction time, the ratio of the tellurium tungsten source and the selection of the auxiliary growth agent, which is expected to be implemented in industrial application, and has a certain positive effect on the subsequent basic physical property research and the preparation of high-performance electronic devices.

[0103] The applicant declares that the application illustrates its process method through the above examples, but is not limited to these specific steps. This does not mean that the implementation of the application must depend on the above process steps. The person skilled in the relevant technical field should know that any improvement on the application, equivalent replacement of the selected raw materials, addition of auxiliary ingredients and selection of specific implementation methods, etc. all belong to the protection and disclosure range of the application.

[0104] The unfinished matters of the application are the known technology.

Claims

1. A method for growing multilayer and single-layer tungsten ditelluride thin films by atmospheric pressure chemical vapor deposition, characterized by comprising the following steps: S1. The Si / SiO2 substrate was ultrasonically cleaned in acetone, isopropanol and deionized water respectively; then dried with nitrogen gas. S2. Place tellurium powder into the first quartz boat; place the mixed powder of tungsten trioxide and halide into the front end of the second quartz boat, and arrange n Si / SiO2 substrates sequentially at a distance of 0.5~1 cm after mixing the powder; in, The mass ratio of tellurium powder to tungsten trioxide is 2.6:1 to 1:1; the mass ratio of tungsten trioxide to halide is 10:1 to 1:1; the halide is potassium bromide; the distance between substrates is 0.2 to 0.5 cm; n = 1 to 3; S3. Place the first quartz boat and the second quartz boat into the first and second temperature zones of the chemical vapor deposition equipment, respectively; and evacuate to 8.0~8.5 E-1 Pa; The distance between the first quartz boat and the second quartz boat is 15-30 cm; S4. Purge the growth pipeline with a hydrogen-argon mixture until it reaches atmospheric pressure, and open the atmospheric valve passage. Within 15-20 minutes, raise the temperature of the first temperature zone to 550℃ and 750-880℃ respectively. The hydrogen volume concentration is 10%. S5. Maintain the growth time at the set temperature for 5-10 minutes; S6. After growth is complete, the system is naturally cooled to room temperature under the protection of a hydrogen-argon mixture, thereby obtaining a tungsten ditelluride thin film on the Si / SiO2 substrate. When the distance between the first quartz boat and the second quartz boat is 15-17 cm, the resulting tungsten ditelluride film has 14-73 layers; when the distance is 18-20 cm, it has 2-10 layers of tungsten ditelluride film; and when the distance is 22-30 cm, it has a single layer of tungsten ditelluride film.

2. The method for growing multilayer and single-layer tungsten ditelluride thin films by atmospheric pressure chemical vapor deposition as described in claim 1, characterized in that: In step S4, the time for the carrier gas to travel from the first quartz boat to the second quartz boat is 31.2s to 62.2s.

3. The method for growing multilayer and single-layer tungsten ditelluride thin films by atmospheric pressure chemical vapor deposition as described in claim 1, characterized in that the film thickness is 0.7~51 nm.

4. The method for growing multilayer and single-layer tungsten ditelluride thin films by atmospheric pressure chemical vapor deposition as described in claim 1, characterized in that, in the single-layer tungsten ditelluride thin film obtained with a spacing of 22 cm to 30 cm, the shape is close to a triangle when the spacing is 25 cm; close to a rhombus when the spacing is 27 cm; and close to a regular hexagon when the spacing is 30 cm.

5. The method for growing multilayer and single-layer tungsten ditelluride thin films by atmospheric pressure chemical vapor deposition as described in claim 1, characterized in that, under the conditions of a spacing of 25 cm and a growth temperature of 850°C in the second temperature zone, when the mass ratio of tellurium powder to tungsten trioxide is 2:1, the obtained film is close to a triangular shape; when the mass ratio of tellurium powder to tungsten trioxide is 1.6:1, the obtained film has a truncated triangle shape or a triangular shape with serrated edges.

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