Method for growing multi-layer and single-layer tungsten telluride film by normal-pressure chemical vapor deposition method

Abstract

The invention relates to a method for growing multi-layer and single-layer tungsten telluride films by a normal-pressure chemical vapor deposition method. According to the method, tellurium powder and tungsten trioxide serve as precursors, potassium bromide is added to serve as an auxiliary growth agent, tungsten trioxide generates a precursor with higher volatility under the action of potassium bromide, and the problem that the temperature needed by tungsten trioxide is high is solved; the preparation method comprises the following steps: preparing a tellurium source and a tungsten source, respectively controlling the growth temperature and time of the tellurium source and the tungsten source through a double-temperature-zone tubular furnace, taking a Si / SiO2 substrate and hydrogen-argon mixed gas as carrier gas, and adjusting the distance between precursors, the growth temperature, the proportion of the precursors and the like to realize controllable preparation of the thickness and the shape of the tungsten ditelluride film. The tungsten telluride thin film grown by the method has excellent uniformity and larger size, the maximum size of a single layer can reach 0.01 cm < 2 >, and the method has an important positive effect on subsequent basic physical property research and preparation of high-performance electronic devices.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor preparation and relates to a method for growing multilayer and single-layer tungsten ditelluride films by atmospheric pressure chemical vapor deposition. Background Art

[0002] Transition Metal Dichalcogenides (TMDCs) are a new type of two-dimensional layered materials. The atoms in the layers are bound by strong covalent bonds, while the layers are connected to each other by weaker van der Waals forces. This makes them exhibit diverse crystal structures and unique physical properties. 2 ) As an important member of TMDCs materials, it has high electron mobility and a wide range of light response. At the same time, tungsten ditelluride has been predicted and confirmed to be a type-II Weyl semimetal, which has many novel physical properties, such as large and non-saturated magnetoresistance (MR) at low temperatures, ferroelectricity, superconductivity under a certain pressure, quantum spin Hall effect and high electron mobility. Therefore, tungsten ditelluride is considered to have broad application prospects in high-efficiency memory, spin electronics, optical devices, transistors, etc.

[0003] The preparation methods of tungsten ditelluride include "top-down" mechanical stripping method and "bottom-up" synthetic preparation method. Compared with the traditional mechanical stripping method, chemical vapor deposition (CVD) has the characteristics of simple operation, high efficiency, uniform product, controllable thickness and larger size. It is considered to be 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 single-layer tungsten ditelluride is still a challenge, which urgently needs further optimization.

[0004] At present, studies have used sodium chloride-assisted double-tube chemical vapor deposition to achieve the growth of large-area tungsten telluride thin films, but the thickness of a single film is uncontrollable, and tungsten telluride thin films with specific shapes have not been synthesized. (Growth of few-layer WTe2 by a salt-assisted double-tube chemical vapordeposition method with high infrared photosensitivity. doi: 10.1039 / d3nr00849e.). Other technicians have proposed a two-step ALD-CVD method for growing tungsten telluride thin films (patent number CN116262970A). This method first deposits a layer of tungsten film on a substrate by atomic layer deposition, and then uses chemical vapor deposition (CVD) technology to tellurize the tungsten film, thereby achieving the preparation of tungsten telluride thin films with controllable thickness. However, the operation process is relatively complicated and the reaction time is long, usually requiring 80 to 120 minutes. Summary of the invention

[0005] The present invention aims to achieve one-step controllable growth of multilayer and single-layer tungsten ditelluride thin films by a normal pressure chemical vapor deposition method in view of the shortcomings of existing production technologies, thereby solving the problems of uncontrollable thickness and uniformity and long reaction time during the growth process. 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 for tungsten trioxide; and the growth temperature and time of the tellurium source and tungsten source are controlled separately by a double-temperature zone tubular furnace, and Si / SiO 2 The substrate is a hydrogen-argon mixed gas as a carrier gas. By adjusting the distance between the precursors, the growth temperature and the precursor ratio, the thickness and shape of the tungsten ditelluride film can be controlled. The tungsten ditelluride film grown by the present invention has excellent uniformity and a large size, and the maximum size of a single layer can reach 0.01 cm 2 , which plays an important and positive role in the subsequent research on basic physical properties and the preparation of high-performance electronic devices.

[0006] The technical solution of the present invention is: A method for growing multilayer and single-layer tungsten ditelluride thin films by atmospheric pressure chemical vapor deposition comprises the following steps: S1、Si / SiO 2 The substrate was ultrasonically cleaned in acetone, isopropanol and deionized water respectively, and then dried with nitrogen gas. S2, put tellurium powder into the first quartz boat; put the mixed powder of tungsten trioxide and halide into the front end of the second quartz boat, and arrange n pieces of Si / SiO in sequence 0.5~1 cm behind the mixed powder.2 substrate; Among them, 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; S3, placing 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, with the second quartz boat at the rear; and evacuating to 8.0~8.5 E-1 Pa; Among them, the distance between the first quartz boat and the second quartz boat is 15~30 cm; S4, introducing a hydrogen-argon mixed gas into the system to purge the growth pipeline until it reaches normal pressure, and opening the atmospheric valve channel, and within 15-20 minutes, raising the temperature of the first temperature zone and the second temperature zone from room temperature to 550°C and 750-880°C respectively; Among them, the volume concentration of hydrogen is 10%; 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 to 62.2 s); S5, maintain the growth time at the set temperature for 5-10 min; S6. After the growth is completed, the system is naturally cooled to room temperature under the protection of hydrogen and argon mixed gas, so that the Si / SiO 2 A tungsten ditelluride thin film is obtained on the substrate.

[0007] The film thickness is between 0.7 and 51 nm; When the distance between the first quartz boat and the second quartz boat is 15-17 cm, the obtained tungsten ditelluride film is 14-73 layers; when the distance is 18 cm-20 cm, the obtained tungsten ditelluride film is 2-10 layers; when the distance is 22 cm-30 cm, the obtained tungsten ditelluride film is a single layer; In the single-layer tungsten ditelluride film obtained when the spacing is 22 cm to 30 cm, when the spacing is 25 cm, the shape is close to a triangle; when the spacing is 27 cm, it is close to a rhombus; when the spacing is 30 cm, it is close to a regular hexagon; 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 shape of the obtained film is a truncated triangle or a triangle with jagged edges.

[0008] The essential features of the present invention are: The present invention relates to a normal pressure chemical vapor deposition method for growing tungsten ditelluride thin films. In this process, by adjusting the distance between two groups of precursors, the density of gas molecules that reach the tungsten source and participate in the reaction is changed, and tungsten ditelluride thin films with different morphologies and thicknesses can be effectively obtained. In addition, by adding an auxiliary growth agent (potassium bromide), under the catalysis of hydrogen, it reacts with tungsten trioxide to generate a more volatile precursor, which effectively solves the problem of high melting point of tungsten trioxide and poor product quality. This method greatly shortens the overall reaction time for preparing tungsten ditelluride thin films to 5 minutes, and has the characteristics of fast film formation speed and low growth temperature. The short duration of high temperature further reduces Si / SiO 2 The possibility of breakdown due to high temperature has opened up new paths for subsequent integrated applications of microelectronic circuits.

[0009] The beneficial effects of the present invention are: 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 the traditional mechanical stripping method, such as time-consuming and labor-intensive, cumbersome 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 agents, growth temperature and time, hydrogen and argon gas concentration, and the distance of precursors, so as to achieve precise preparation of tungsten ditelluride thin film materials. In addition, the one-step method for growing tungsten ditelluride is simpler and more efficient, and the raw materials used, tellurium powder, tungsten trioxide, and potassium bromide, are all cheap drugs, which are convenient for industrial production and application.

[0010] 2. Rapid low-temperature growth of tungsten ditelluride while maintaining its uniformity and cleanliness: By adding a new auxiliary growth agent, potassium bromide, the problem of high temperature (1473°C) required for tungsten trioxide evaporation is solved. Compared with the traditional sodium chloride auxiliary agent ( Fig.12 ) compared to potassium bromide, the reaction is milder and contains fewer impurities ( Fig.14 b) The migration rate of the co-product gas molecules with hydrogen reaches a balance with the deposition rate, and the product tungsten ditelluride is easier to diffuse evenly from the central nucleation point, greatly shortening the growth time to 5 minutes, effectively solving the shortcomings of the existing technology of high energy consumption and long time.

[0011] 3. Achieve controllable preparation of material layers and shapes: By adjusting the distance and ratio between the precursors, the thickness and shape of tungsten ditelluride can be controlled. Examples 5 to 13 are all single-layer films. Currently, no tungsten ditelluride films with special patterns have been reported. Through optical microscopy, it was observed that there were long strips ( Figure 3 ), Bat Shape ( Fig. 9 c), triangle-like ( Fig. 9 d), jagged hexagon ( Fig. 9 f), truncated triangle ( Fig.14 These patterned growths may stimulate different physical properties. In addition, multilayer tungsten ditelluride films can achieve large-area continuous growth ( Figure 7 ), the maximum growth size of a single uniform monolayer of tungsten ditelluride film can reach 0.01 cm 2 ( Fig. 9 c), providing a better choice for subsequent property research and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A schematic diagram of a chemical vapor deposition system used in an embodiment of the present invention; Figure 2 Schematic diagram of growth time-temperature of tungsten telluride thin film according to Example 2 of the present invention; Figure 3 The optical microscope (OM) and scanning electron microscope (SEM) images of the multilayer tungsten ditelluride film in Example 1 are shown; wherein, Figure 3 (a) is an optical microscope image; Figure 3 (b) is a scanning electron microscope (SEM) image; Figure 4 Raman spectroscopy characterization of the multilayer tungsten ditelluride film in Example 1; Figure 5 Energy dispersive X-ray spectroscopy (EDS) characterization of the multilayer tungsten ditelluride film in Example 1; Figure 6 The atomic force microscope (AFM) image of the multilayer tungsten ditelluride film in Example 1 and the characterization of its step thickness; Figure 7 This is an optical microscope image of a large-area continuous multilayer tungsten ditelluride film in Example 2; Figure 8 The X-ray diffraction (XRD) pattern of the large-area continuous multilayer tungsten ditelluride thin film in Example 2; Fig. 9 Optical microscope images of the few-layer and single-layer tungsten ditelluride films in Examples 3 to 8; Fig.10 Scanning electron microscope images of few-layer and single-layer tungsten ditelluride films; Fig.11 Raman spectra characterization of the single-layer tungsten ditelluride thin film in Example 6 and the few-layer tungsten ditelluride thin film in Example 4 respectively; Fig.12 is an optical microscope image of the sample of Example 9; Fig.13 is an optical microscope image of the sample of Example 10; Fig.14 is the optical microscope image of Examples 11 to 13, wherein Fig.14 (a) corresponds to Example 11, Fig.14 (b) as a control group corresponding to Example 6, Fig.14 (c) corresponds to Example 13, Fig.14 (d) Fig.14 (e) corresponding to Example 12; Fig.15 Optical microscope images of single-layer tungsten ditelluride films at different temperatures. Fig.15 (a) is an image of Example 14, Fig.15 (b) is an image of Example 15, Fig.15 (c) is the image of Example 16. DETAILED DESCRIPTION

[0013] The present invention is described in more detail below by means of specific examples. The examples are only used to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0014] Embodiment 1: This embodiment discloses a method for preparing a multilayer tungsten ditelluride thin film, which specifically includes the following steps: S1, using 0.5×0.5 cm Si / SiO 2 The substrate (the oxide layer thickness is 285 nm) was used as the growth substrate and was immersed in acetone, isopropanol and deionized water for ultrasonic cleaning for 10 min to remove surface pollutants. Finally, it was dried with a nitrogen gun for later use.

[0015] S2. Use an electronic balance to weigh 0.4 g of tellurium powder, 0.2 g of tungsten trioxide, and 0.05 g of potassium bromide. Place the weighed tellurium powder in quartz boat I; place the mixed powder of tungsten trioxide and potassium bromide at the front end of quartz boat II; at the same time, arrange the processed Si / SiO 2 Three substrates are placed, and the spacing between the substrates is 0.5 cm.

[0016] S3, placing quartz boat I and quartz boat II into the first temperature zone and the second temperature zone of the chemical vapor deposition furnace respectively; and evacuating to 8.0~8.5 E-1 Pa (the definition of the temperature zone is based on the direction of carrier gas flow, the first area passed is the first temperature zone, followed by the second temperature zone; in the second temperature zone, the gas passes through the tungsten source mixture and the substrate in sequence); Among them, the distance between quartz boat I and quartz boat II was adjusted to 15 cm; Growth diagram Figure 1 shown.

[0017] S4. Introduce a hydrogen-argon mixed gas (hydrogen concentration of 10%; hydrogen 11 sccm, argon 99 sccm) into the system to purge the growth pipeline until it reaches normal pressure, open the atmospheric valve channel, set the heating time to 20 minutes, and raise the temperature of the first temperature zone and the second temperature zone from room temperature to 550°C and 850°C, respectively.

[0018] S5, maintain the growth time for 5 minutes; S6. After the growth is completed, the system is naturally cooled to room temperature and the sample is taken out.

[0019] Embodiment 2: The difference between this embodiment and embodiment 1 is that the temperature of the second temperature zone in S4 is adjusted to 750° C., and the other parameters remain unchanged, thereby obtaining a sample to be tested.

[0020] Embodiment 3: The difference between this embodiment and embodiment 1 is that the distance between quartz boat I and quartz boat II in S3 is adjusted to 18 cm, and other parameters remain unchanged, thereby obtaining a sample to be tested.

[0021] Embodiment 4: The difference between this embodiment and embodiment 1 is that the distance between quartz boat I and quartz boat II in S3 is adjusted to 20 cm, and other parameters remain unchanged, thereby obtaining a sample to be tested.

[0022] Embodiment 5: The difference between this embodiment and embodiment 1 is that the distance between quartz boat I and quartz boat II in S3 is adjusted to 22 cm, and other parameters remain unchanged, thereby obtaining a sample to be tested.

[0023] Embodiment 6: The difference between this embodiment and embodiment 1 is that the distance between quartz boat I and quartz boat II in S3 is adjusted to 25 cm, and other parameters remain unchanged, thereby obtaining a sample to be tested.

[0024] Embodiment 7: The difference between this embodiment and embodiment 1 is that the distance between quartz boat I and quartz boat II in S3 is adjusted to 27 cm, and other parameters remain unchanged, thereby obtaining a sample to be tested.

[0025] Embodiment 8: The difference between this embodiment and embodiment 1 is that the distance between quartz boat I and quartz boat II in S3 is adjusted to 30 cm, and other parameters remain unchanged, thereby obtaining the sample to be tested.

[0026] Embodiment 9: 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 quartz boat I and quartz boat II in S3 is adjusted to 25 cm, and the other parameters remain unchanged, thereby obtaining the sample to be tested.

[0027] Embodiment 10: The difference between this embodiment and embodiment 1 is that the distance between quartz boat I and quartz boat II in S3 is adjusted to 25 cm, the growth time in S5 is adjusted to 10 min, and the other parameters remain unchanged, thereby obtaining the sample to be tested.

[0028] Embodiment 11: The difference between this embodiment and embodiment 1 is that the precursor in S2 is adjusted to 0.4 g tellurium powder, 0.15 g tungsten trioxide and 0.0375 g potassium bromide (Te:W≈2.6:1 mass ratio), the distance between quartz boat I and quartz boat II in S3 is adjusted to 25 cm, and the other parameters remain unchanged, thereby obtaining the sample to be tested.

[0029] Embodiment 12: The difference between this embodiment and embodiment 1 is that the precursor in S2 is adjusted to 0.4 g tellurium powder, 0.25 g tungsten trioxide and 0.0625 g potassium bromide (Te:W≈1.6:1 mass ratio), the distance between quartz boat I and quartz boat II in S3 is adjusted to 25 cm, and the other parameters remain unchanged, thereby obtaining the sample to be tested.

[0030] Embodiment 13: The difference between this embodiment and embodiment 1 is that the precursor in S2 is adjusted to 0.4 g tellurium powder, 0.4 g tungsten trioxide and 0.1 g potassium bromide (Te:W=1:1 mass ratio), the distance between quartz boat I and quartz boat II in S3 is adjusted to 25 cm, and the other parameters remain unchanged, thereby obtaining the sample to be tested.

[0031] Embodiment 14: The difference between this embodiment and embodiment 1 is that the distance between quartz boat I and quartz boat II in S3 is adjusted to 25 cm, the temperature of the second temperature zone in S4 is adjusted to 750° C., and the other parameters remain unchanged, thereby obtaining the sample to be tested.

[0032] Embodiment 15: The difference between this embodiment and embodiment 1 is that the distance between quartz boat I and quartz boat II in S3 is adjusted to 25 cm, the temperature of the second temperature zone in S4 is adjusted to 800° C., and the other parameters remain unchanged, thereby obtaining the sample to be tested.

[0033] Embodiment 16: The difference between this embodiment and embodiment 1 is that the distance between quartz boat I and quartz boat II in S3 is adjusted to 25 cm, the temperature of the second temperature zone in S4 is adjusted to 880° C., and the other parameters remain unchanged, thereby obtaining the sample to be tested.

[0034] The surface morphology of the 16 samples of the above examples was preliminarily characterized by optical microscopy, the microscopic morphology was further observed by scanning electron microscopy, and the structural domain and thickness of the tungsten ditelluride film were measured by atomic force microscopy. In addition, we also used micro-Raman spectroscopy (532 nm excitation laser), energy dispersive X-ray spectrometer and X-ray diffraction technology to characterize its chemical bond composition and crystal structure. Through the above methods, we evaluated the overall quality of the tungsten ditelluride film.

[0035] Figure 1 This is a schematic diagram of the growth of the dual-temperature zone tube furnace used in this method; Figure 2 Time-temperature diagram of the tungsten ditelluride film growth process.

[0036] Figure 3 The following are the relevant characterizations of the multilayer tungsten ditelluride thin film grown in Example 1. Figure 3 (a) is the 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 presents a multilayer nanobelt structure, with thinner edges and darker colors under an optical microscope, while the center part is thicker and heavier because it is a nucleation point, and visually presents a whitish bright color.

[0037] Figure 4 is the Raman spectrum of Example 1. It can be seen from the figure that the tungsten ditelluride film has a Raman spectrum of 100 cm -1 Up to 250cm -1 There are five vibration modes, 108.8 cm -1 Where Peak, 116.1 cm -1 Where Peak, 134.4 cm -1 Where Peak, 161.8 cm -1 Where Peak and 211.6 cm -1 Where The peak is consistent with that reported in previous literature. The qualitative analysis of tungsten ditelluride thin film samples was carried out by energy dispersive X-ray spectroscopy, such as Figure 5 As shown, in addition to Si / SiO 2Except for the characteristic peak of the substrate, all other elements belong to tungsten ditelluride, and the EDS results show that Te:W=2.36:1. The above evidence directly proves that we have synthesized tungsten ditelluride thin films.

[0038] Figure 6 From the AFM image and step thickness curve of Example 1, we can further observe that the height size ranges from the edge to the center is about 9.8 nm to 51 nm, and the corresponding thickness is 14 to 73 layers.

[0039] Figure 7 This is an optical microscope image of a large-area multilayer tungsten ditelluride film grown in Example 2. Compared with Example 1, the temperature in the second temperature zone is reduced to 750°C, which is more conducive to the formation of a large-area continuous film. This is because the evaporation rate of the tungsten source is reduced and the residence time is longer, so that the tellurium source and the tungsten source can react more fully, and the nucleation points on the substrate are distributed in a high density. As the growth process proceeds, the distance difference between adjacent nucleation points decreases, and the edges of the crystals contact and merge with each other. This merging process leads to a significant improvement in the continuity and density of the film, forming a dense film. Figure 8 This is the XRD spectrum of the sample in Example 2. By comparing with the standard card (PDF#24-1352), the diffraction peaks of the tungsten ditelluride sample synthesized by us match well with the (002), (004), (006), and (008) crystal plane diffraction peaks of the standard card, that is, the tungsten ditelluride film has a better crystal preferential orientation along the c-axis (001) direction.

[0040] In order to better study the few-layer tungsten ditelluride film, we kept other parameters unchanged and tried to adjust the concentration in the reaction system by adjusting the distance between the tellurium source and the tungsten source (Dss). Fig. 9 As shown, optical microscope images of tungsten ditelluride films grown under different conditions are shown, covering Examples 3 to 8. Smaller Dss values ​​(18 cm~20 cm) always produce few-layer tungsten ditelluride films with larger domain sizes ( Fig. 9 a, b), the number of layers is about 2~10; while larger Dss values ​​(25 cm~30 cm) tend to produce single-layer tungsten ditelluride films with smaller domain sizes ( Fig. 9 d, e, and f), with a thickness of about 0.7 nm; Fig. 9 (c) is in the transition state and is a bat-shaped monolayer film with a larger size, with an area of ​​0.01 cm 2. In terms of shape, in the single-layer tungsten ditelluride film obtained with a spacing of 22 cm to 30 cm, when the spacing is 25 cm, the shape is close to a triangle; when the spacing is 27 cm, it is close to a rhombus; when the spacing is 30 cm, it is close to a regular hexagon; this dependence on Dss is reflected in the fact that the synthesis of the tungsten ditelluride domain is highly dependent on the density of the vaporized precursor. The results show that changing Dss can effectively control the thickness distribution, domain size and shape.

[0041] Fig.10 Several representative SEM images are shown in Figure 2. Fig.10 (a) and (b) correspond to Example 4 (b is a partial enlarged view of a), Fig.10 (c) in the embodiment 5 corresponds to Fig.10 (d) in corresponds to Example 6, Fig.10 (e) and (f) in the figure correspond to Example 8 (f is a local magnified image of e). Further microscopic images show that the large-area tungsten ditelluride growth follows a typical surface-restricted epitaxial growth mode, and the fully covered tungsten ditelluride film undergoes regional nucleation, regional growth, and regional splicing processes. Fig.10 In (b), domain boundaries can be identified, which is likely due to gas adsorption of ambient air onto these domain walls. Small areas of monolayer tungsten ditelluride films nucleate and grow independently, eventually forming a regular morphology with jagged edges. Fig.11 The Raman spectra of single-layer tungsten ditelluride film and few-layer tungsten ditelluride film are shown in the figure. It can be observed that as the number of layers decreases to a single layer, the Raman peak at 116.1 cm -1 Where Peak, 161.7 cm -1 Where Peak intensity enhancement; Peak from 211cm -1 Offset to 214.4 cm -1 , a slight blue shift occurs. Based on this rule, we can determine the thickness of the tungsten ditelluride layer. Next, we will mainly discuss the sample when the tungsten telluride source is 25 cm away.

[0042] Fig.12 This is an optical microscope image of the sample in Example 9. After the auxiliary growth agent is replaced with sodium chloride, although a large-area single-layer film can also be generated, the uniformity and cleanliness are still somewhat different from those of the product assisted by potassium bromide. This is because the catalytic effect of sodium chloride is more intense and it is easy to nucleate and diffuse near the impurity points.

[0043] Fig.13This is an optical microscope picture of the sample of Example 10. It can be observed from the picture that tungsten ditelluride mainly appears in irregular elongated strips. This may be because the tungsten ditelluride that is not firmly bonded to the substrate at the edge reacts with hydrogen and then evaporates, and the molecules lose regularity in a certain direction.

[0044] Based on the above data, the growth process of tungsten ditelluride is summarized as follows. Since tellurium and tungsten have low reactivity 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 tungsten oxyhalide; on the other hand, as the reaction proceeds, the source concentration gradually decreases, and excess hydrogen will react with the generated tungsten telluride, thereby achieving an etching effect. The relevant reaction equation is: (1) (2) (3) (4) The tungsten oxyhalide generated by the reaction of halide and tungsten trioxide has a lower melting point, which helps to reduce the temperature required for the reaction, significantly increases the concentration of the precursor, and promotes the reaction.

[0045] Fig.14 are optical microscope images of Examples 11 to 13, and Example 6 is used as a control ( Fig.14 b). This paper mainly discusses the influence of changing the mass ratio of tellurium to tungsten source on the product when the distance between tellurium source and tungsten source is 25 cm and other parameters remain unchanged. As can be seen from the figure, Te:W≈2.6:1 ( Fig.14 When the tungsten source is in a), the tellurium source is in excess. After the tungsten source reacts, tellurium or tellurium derivatives play a dominant role and evaporate and deposit on the substrate surface, forming impurity points that affect performance. When the tungsten source is increased to Te:W=2:1, the reaction reaches equilibrium and tungsten ditelluride presents good morphology and quality. When the tungsten source is increased to Te:W≈1.6:1, the triangular structure of the product disappears. This may be due to insufficient tellurium source, which causes the deposited tungsten ditelluride to be etched by hydrogen at the edge or vertex, forming a jagged triangle ( Fig.14 d) and the truncated triangle ( Fig.14 e in the figure). The size of the tungsten ditelluride film under the above conditions is about 30~50 μm. Further increasing the tungsten source to Te:W=1:1 ( Fig.14 In c), hydrogen etching plays a dominant role in the growth process, resulting in a long strip of small size. Therefore, controlling the mass ratio of tellurium source to tungsten source to 2:1 is more conducive to the growth of high-quality and certain-shaped tungsten ditelluride films.

[0046] Previous studies have shown that the growth temperature has a significant effect on multilayer tungsten ditelluride films. In order to further explore the effect of temperature on single-layer tungsten ditelluride, we designed three sets of experiments for comparison. Fig.15 (a) Fig.15 (b) Fig.15 (c) shows the optical microscope images of Examples 14, 15, and 16. It can be seen from the figure that under different tungsten source temperature conditions, there are obvious differences in the growth results of tungsten ditelluride. When the temperature is 750°C, the molecular mobility of tellurium and tungsten is low, and it is difficult to diffuse evenly to the edge, causing the film to tend to grow in a stacked manner, thus forming a small and thick tungsten ditelluride film. When the temperature rises to 800°C, although the film size increases, the volatilization of tungsten trioxide and crystal growth cannot reach a balance, resulting in poor uniformity inside the film. Relatively speaking, at 850°C ( Fig.14 b), the reactant atoms have sufficient power, increased mobility, and enhanced diffusivity. At this time, the volatilization of the tellurium tungsten source and the film growth reach the best balance, thus generating a film with good uniformity. However, when the temperature is further increased to 880°C, as the temperature rises, the speed at which the tellurium source is reduced by hydrogen cannot keep up with the speed of the tungsten source reaction, resulting in a large amount of tellurium source being carried away by the carrier gas without participating in the reaction. The crystal quality is difficult to control, and the final product is mostly irregular in shape with a size of about 10 μm.

[0047] Through the above embodiments, the present invention synthesizes a tungsten ditelluride thin 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 tellurium-tungsten source ratio and the selection of the auxiliary growth agent. It is expected to be implemented in industrial applications and has a certain positive effect on the subsequent basic physical property research and the preparation of high-performance electronic devices.

[0048] The applicant declares that the present invention illustrates its process through the above-mentioned embodiments, but is not limited to these specific steps. This does not mean that the implementation of the present invention must rely on the above-mentioned process steps. Professionals in the relevant technical field should be aware that any improvement of the present invention, equivalent replacement of the selected raw materials, addition of auxiliary components, and selection of specific implementation methods, etc., all fall within the scope of protection and disclosure of the present invention.

[0049] Matters not covered by the present invention are known technologies.

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. Place the Si / SiO2 substrate in acetone, isopropanol and deionized water for ultrasonic cleaning respectively; then blow dry with nitrogen; S2, put tellurium powder into the first quartz boat; put the mixed powder of tungsten trioxide and halide into the front end of the second quartz boat, and arrange n Si / SiO2 substrates in sequence 0.5~1 cm behind the mixed powder; in, The mass ratio of tellurium powder to tungsten trioxide is 2.6:1~1:1; the mass ratio of tungsten trioxide to 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; S3, placing 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 evacuating to 8.0~8.5 E-1 Pa; Among them, the distance between the first quartz boat and the second quartz boat is 15~30 cm; S4, introducing a hydrogen-argon mixed gas into the system to purge the growth pipeline until it reaches normal pressure, and opening the atmospheric valve channel, and within 15-20 minutes, raising the temperature of the first temperature zone and the second temperature zone from room temperature to 550°C and 750-880°C respectively; Among them, the volume concentration of hydrogen is 10%; S5, maintain the growth time at the set temperature for 5-10 min; S6. After the growth is completed, the system is naturally cooled to room temperature under the protection of a hydrogen-argon mixed gas, thereby obtaining a tungsten ditelluride thin film on the Si / SiO2 substrate.

2. The method for growing multilayer and single-layer tungsten ditelluride thin films by atmospheric pressure chemical vapor deposition as claimed in claim 1, characterized in that In step S4, the time for the carrier gas to reach the second quartz boat from the first 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 claimed in claim 1, wherein the thickness of the thin films is between 0.7 and 51 nm.

4. The method for growing multi-layer and single-layer tungsten ditelluride thin films by atmospheric pressure chemical vapor deposition as claimed in claim 1, characterized in that when the spacing between the first quartz boat and the second quartz boat is 15 to 17 cm, the obtained tungsten ditelluride thin film is 14 to 73 layers; when the spacing is 18 cm to 20 cm, the obtained tungsten ditelluride thin film is 2 to 10 layers; when the spacing is 22 cm to 30 cm, the obtained tungsten ditelluride thin film is a single layer.

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

6. The method for growing multilayer and single-layer tungsten telluride films by atmospheric pressure chemical vapor deposition as described in claim 4, 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 shape of the obtained film presents a truncated triangle or a triangle with jagged edges.

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