Method for preparing substrate doped low-dimensional transition metal chalcogenide thin film by utilizing ultrahigh vacuum

Abstract

The invention belongs to the technical field of low-dimensional material growth, and particularly discloses a method for preparing a substrate doped low-dimensional transition metal chalcogenide film by utilizing ultrahigh vacuum. HOPG or 4H-SiC / BLG is taken as a substrate, and a high-purity Te source and a high-purity Hf source are jointly deposited on the substrate to grow the 1T-HfTe2 thin film by adopting a molecular beam epitaxial growth method, so that synthesis of the low-dimensional 1T-HfTe2 thin film is realized, electron doping of the grown thin film sample is also realized, and the performance of the thin film is improved. And the conductivity of the 4H-SiC / BLG substrate can be adjusted by controlling the cycle index and the temperature of the 4H-SiC / BLG substrate in the cycle annealing process, so that films with different electron doping levels are obtained, and the problems that a high-quality large-area low-dimensional 1T-HfTe2 film is difficult to obtain and the physical property is difficult to regulate and control at the present stage are solved.

Description

Technical Field

[0001] The invention relates to the technical field of low-dimensional material growth, and in particular to a method for preparing a substrate-doped low-dimensional transition metal chalcogenide film by utilizing ultra-high vacuum. Background Art

[0002] Transition Metal Dichalcogenides (TMD's) have a general chemical formula of MX 2 (M is a transition metal element; X = S, Se, Te), with a typical layered structure. By replacing the type of transition metal M in the compound and combining it with different chalcogen elements X, TMD's materials can exhibit a variety of properties such as semiconductors, semimetals and metals.

[0003] Low-dimensional TMD's thin films have different physical properties from TMD's bulk; for example, a single layer of WTe 2 The film is a quantum spin Hall insulator with an energy gap of about 45meV, while the bulk does not have this property; it can be seen that the dimensional effect significantly affects the physical properties of the material.

[0004] To obtain low-dimensional TMD's thin films, chemical vapor deposition, mechanical exfoliation and molecular beam epitaxy are usually used. Chemical vapor deposition cannot accurately control the thickness of the obtained film, and usually introduces impurities that affect the intrinsic properties of the low-dimensional TMD's thin film; mechanical exfoliation makes it difficult to obtain high-quality and large-area low-dimensional TMD's thin films, and the types of low-dimensional TMD's thin films that can be prepared are limited. Using molecular beam epitaxy in an ultra-high vacuum environment is an ideal method to obtain large-area, high-quality low-dimensional TMD's thin films. Its basic atoms are high-purity molecules or atomic beams, which are deposited on the substrate in appropriate proportions, like building blocks according to the chemical formula MX 2 Build low-dimensional TMD's thin films. Compared with low-dimensional TMD's thin films grown by chemical vapor deposition, molecular beam epitaxy grows TMD's thin films in an ultra-high vacuum environment, which can not only minimize the influence of external impurities and obtain an atomically clean sample surface, but also monitor the growth state in real time during the growth process to obtain low-dimensional TMD's thin films with controllable thickness. Compared with low-dimensional TMD's thin films obtained by mechanical exfoliation, TMD's thin films grown by molecular beam epitaxy have a high yield, can be prepared on a large scale, and can produce a wide variety of thin films. Using molecular beam epitaxy, many low-dimensional TMD's thin films have been prepared, such as a single layer of MoS 2 , TiSe 2 and WSe 2 wait.

[0005] Recent studies have found that single-layer 1T-HfTe 2The film can change from metallic properties at room temperature to an insulator at low temperatures, and the formation of this insulating phase may be related to spontaneous exciton condensation. However, to confirm this hypothesis, angle-resolved photoelectron spectroscopy (ARPES) is needed to measure the band structure above the Fermi level. For the study of the conduction band part of the sample above the Fermi level, the method of doping alkali metal atoms on the surface of the film to change the chemical potential is usually adopted. However, in actual research, it is found that the doping amount of surface alkali metal doping is difficult to accurately control, and the alkali metal atoms cause defects on the surface of the film, which deteriorates the quality of the sample and may change the intrinsic band structure, leading to problems such as band bending effect. Another commonly used method is to introduce doping atoms during film preparation, but this method also has the problems of introducing different chemical phases, the doping amount is difficult to control, and it is easy to cause sample growth failure. The present invention finds that 1T-HfTe grown on substrates with different electrical conductivities 2 The film exhibits a band shift relative to the Fermi level, which indicates that 1T-HfTe 2 The interaction between the film and the substrate can also achieve electron doping. Compared with the surface alkali metal doping method, the electron doping of the substrate not only does not introduce other ions on the surface of the film, but also substrates with different conductive specifications are easier to prepare, making it possible to quantitatively control the 1T-HfTe 2 The surface electrical properties of the film become feasible.

[0006] As mentioned above, due to its rich and excellent physical properties, low-dimensional TMD's thin films have always been the research focus in the field of new semiconductor materials. However, given the rich chemical coordination forms of low-dimensional TMD's thin films and the complex and changeable growth conditions, it has always been an urgent problem to explore the conditions for preparing high-quality large-area low-dimensional T-phase TMD's thin films and to find a method that can quantitatively control doping. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing high-quality, large-area, low-dimensional 1T-HfTe based on a doped substrate. 2 Thin film method to solve the current high-quality large-area low-dimensional 1T-HfTe 2 The present invention uses HOPG or 4H-SiC / BLG as substrate and combines molecular beam epitaxial growth method to achieve low-dimensional 1T-HfTe 2 The synthesis of the thin film also realizes the electron doping of the grown thin film sample. Under the method conditions obtained by the present invention, the low-dimensional 1T-HfTe 2 The film is stably synthesized, the number of layers is controllable, and the yield is high; and the low-dimensional 1T-HfTe can be quantitatively controlled by changing the substrate conductivity specifications 2 Electrical properties of thin films.

[0008] In order to achieve the above object, the specific technical solution adopted by the present invention is as follows:

[0009] A method for preparing a substrate-doped low-dimensional transition metal chalcogenide film using ultra-high vacuum is to use a molecular beam epitaxial growth method to co-deposit a high-purity Te source and a Hf source on a HOPG substrate or a 4H-SiC / BLG substrate to epitaxially grow 1T-HfTe 2 The 4H-SiC / BLG substrate is obtained by subjecting a 4H-SiC substrate to cyclic annealing to form a double-layer graphene (BLG) on its surface.

[0010] Preferably, the high-purity Te source is Te powder with a purity of 99.99%, which is heated by a resistive evaporation source to form a molecular beam; the high-purity Hf source is an Hf rod with a purity of 99.99%, which is heated by an electron beam evaporation source to form a molecular beam.

[0011] Furthermore, the HOPG or 4H-SiC / BLG substrate is placed at the intersection center of the molecular beam of the Te source and the molecular beam of the Hf source for epitaxial growth.

[0012] Preferably, during the epitaxial growth process, the Hf source deposition rate is stably maintained at 0.022 ML / min, and the beam current ratio of the Te source to the Hf source is maintained at 20:1. The Hf source deposition rate and the beam current ratio of the Te source to the Hf source need to be strictly implemented as required, otherwise 1T-HfTe with a specific chemical ratio cannot be formed. 2 Thin films, such as when the beam ratio is changed to 30:1, it is possible to form HfTe 5 Thin film, this compound has no exciton insulator phase. Single layer 1T-HfTe 2 It has the property of forming an insulating phase at low temperature (i.e., an energy gap is opened near the Fermi surface), which directly reflects the electron doping effect of the substrate of the present invention; the substrates with different electrical conductivities below directly regulate the size of the energy gap (Gap), that is, regulate the surface electrical properties of the film.

[0013] Preferably, during the epitaxial growth process, the HOPG substrate temperature is maintained at 300-500°C, and the epitaxial growth time is 45 minutes; the 4H-SiC / BLG substrate temperature is maintained at 450°C, and the epitaxial growth time is 45 minutes. 2 The appearance of the insulating phase plays a huge role in reflecting the electron doping effect of the substrate, and the appearance of the insulating phase and HfTe 2 The quality of the film is directly related to the high-quality atomic-level flatness. To meet this requirement, the temperature of the HOPG substrate and the 4H-SiC / BLG substrate must be strictly implemented as required. When the temperature is lower or higher than the specified range, island growth forms a multilayer film at the same time, and the insulating phase cannot be generated, and the standard high-quality 1T-HfTe cannot be obtained.2 film.

[0014] Furthermore, 1T-HfTe 2 After the film growth is completed, the Te source rate is maintained unchanged, the substrate temperature is increased to 500 °C, and annealing is performed for 20 min to further improve the single-layer 1T-HfTe 2 Film quality. Without this annealing step, the film quality is reduced and has more defects.

[0015] Preferably, the HOPG substrate uses a mechanical stripping method to obtain an atomically smooth surface, and is degassed at 650° C. in an ultra-high vacuum chamber to remove impurities adsorbed on the substrate surface before epitaxial growth.

[0016] Preferably, the 4H-SiC / BLG substrate is formed by cyclic annealing of industrial-grade nitrogen-doped conductive 4H-SiC, specifically, the 4H-SiC is degassed at 650°C in an ultra-high vacuum chamber, and then cyclically annealed between the (cyclic) maximum temperature and 650°C.

[0017] Furthermore, the present invention provides a 4H-SiC / BLG standard annealing cycle method: the number of 4H-SiC / BLG standard annealing cycles is 80 times, the standard maximum temperature is 1350°C, too many or too few cycles, too high or too low cycle maximum temperature, will affect the formation of the standard 4H-SiC / BLG substrate. Under this standard condition, the double-layer graphene formed by scanning tunneling microscopy has better quality and a larger single domain area. When deviating from the standard value, the domain area is reduced at the microscopic level, and the defects of the double-layer graphene are more, which is different in conductivity at the macroscopic level.

[0018] Furthermore, the time interval of the 4H-SiC / BLG standard annealing cycle is: heating from 650° C. to 1350° C. within 10 seconds, maintaining this temperature for 50 seconds; then decreasing from 1350° C. to 650° C. within 5 seconds, maintaining this temperature for 55 seconds.

[0019] Furthermore, the present invention provides an annealing cycle method for obtaining 4H-SiC / BLG substrates with different conductivity specifications, wherein the number of cycles is 60 to 100 and the maximum cycle temperature is within the range of 1300 to 1400°C, and the conductivity of the 4H-SiC / BLG substrate can be adjusted, thereby realizing a single-layer 1T-HfTe 2 Thin film property control, observation of 1T-HfTe using angle-resolved photoemission spectroscopy 2 The change in the film band structure can determine the amount of electron doping, and thus quantitatively calculate the electrical properties of the film surface. The specific method for regulating the conductivity of the 4H-SiC / BLG substrate is as follows:

[0020] In the high temperature annealing cycle of 4H-SiC / BLG substrate, when the number of cycles is 60 ≤ and the number of cycles is < 80, and the maximum cycle temperature is 1300°C ≤ and < 1350°C, it will be unfavorable for the formation of double-layer graphene, resulting in low surface conductivity of 4H-SiC / BLG substrate;

[0021] In the high temperature annealing cycle of the 4H-SiC / BLG substrate, when 80 times<cycle number≤100 times and 1350℃<cycle maximum temperature≤1400℃, it will be beneficial to the formation of double-layer graphene, making the surface conductivity of the 4H-SiC / BLG substrate higher.

[0022] The present invention has the following beneficial effects:

[0023] 1. The present invention proposes the use of molecular beam epitaxy to grow high-quality large-area 1T-HfTe 2 Using HOPG or 4H-SiC / BLG as substrate, combined with molecular beam epitaxy, by strictly controlling the substrate temperature, Hf source deposition rate, Te source, Hf source beam ratio and other conditions during the molecular beam epitaxy growth process, standard high quality (RHEED stripes are clear and the brightness is uniform, and the band structure is clear) 1T-HfTe 2 Thin films not only realize low-dimensional 1T-HfTe 2 The synthesis of the thin film also realizes the electron doping of the grown thin film sample.

[0024] 2. This application also proposes to regulate the single-layer 1T-HfTe 2 Specifically, in the cyclic annealing process during the preparation of the 4H-SiC / BLG substrate, 4H-SiC / BLG substrates with different conductivity are obtained by controlling the number of cycles and temperature, thereby achieving the 1T-HfTe 2 Quantitative control of thin film surface electrical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention realizes electron doping of 1T-HfTe by 4H-SiC / BLG substrate 2 Schematic diagram of the film.

[0026] Figure 2 Schematic diagram of the molecular beam epitaxial growth device, temperature detection and reflection high energy electron diffraction device (RHEED) used in the present invention.

[0027] Figure 3 In Example 1, the RHEED pattern of the 4H-SiC / BLG substrate is formed after the 4H-SiC substrate is degassed at 650° C. in an ultra-high vacuum chamber and annealed for 80 cycles.

[0028] Figure 4 In Example 1, a single layer of 1T-HfTe is grown on a 4H-SiC / BLG substrate. 2 RHEED patterns of the film over time.

[0029] Figure 5 The 4H-SiC / BLG substrate with different conductive specifications is used in Example 2 to electron-dope the single layer 1T-HfTe 2 ARPES spectra after film deposition. In the figure, (a)-(e) are room temperature spectra, and (f)-(k) are low temperature spectra.

[0030] Figure 6 In Example 3, a single layer of 1T-HfTe is grown on a HOPG substrate. 2 RHEED patterns of the film over time.

[0031] Figure 7 In Comparative Example 1, a single layer of 1T-HfTe grown on a standard 4H-SiC / BLG substrate 2 RHEED results of the film after growth for 45 minutes at a substrate temperature of 300℃.

[0032] Figure 8 In Comparative Example 2, a single layer of 1T-HfTe grown on a standard 4H-SiC / BLG substrate 2 RHEED results of the film after growth for 45 minutes at a substrate temperature of 600℃.

[0033] Fig. 9 In Comparative Example 3, a single layer of 1T-HfTe grown on a standard 4H-SiC / BLG substrate 2 Photoelectron spectrum of thin film after surface alkali metal doping. In the figure, the upper one is the room temperature spectrum, and the lower one is the low temperature spectrum. DETAILED DESCRIPTION

[0034] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific implementation cases. Unless otherwise defined, the abbreviations of scientific and technical terms used in this article have the same meanings as the commonly used terms in the technical field to which the present invention belongs; in addition, the relevant testing techniques and methods appearing in this article, their testing principles and the physical meanings represented by the test data are generally known to those skilled in the art and will not be described one by one here. In this article, "room temperature" means a thermodynamic temperature of 250K; "low temperature" means a thermodynamic temperature of 10K; "ultra-high vacuum" means that the ambient pressure is always better than 2.0×10 -10 torr.

[0035] Example 1: 1T-HfTe with 4H-SiC / BLG as substrate 2 Film preparation

[0036] In this example, 1T-HfTe is grown on a 4H-SiC / BLG substrate. 2 Thin film, substrate-thin film structure diagram Figure 1 The schematic diagram of the molecular beam epitaxial growth device, temperature detection and reflection high energy electron diffraction device (RHEED) used is shown in FIG. Figure 2 As shown, the specific preparation process is as follows:

[0037] The 4H-SiC substrate is fixed on a Ta metal tray with a hole at the bottom, and transferred to an ultra-high vacuum chamber (pressure less than 2.0×10-10torr), and the substrate is heated to 650°C for high-temperature degassing for 1 hour. After 1 hour, the chamber pressure should be restored to about 2.0×10-10torr under the degassing state of the 4H-SiC substrate; a pressure higher than this indicates that the degassing is incomplete, and the degassing should be continued for 1 hour. After the 4H-SiC is degassed, its substrate surface is detected by RHEED; its clean 4H-SiC surface will form a clear and symmetrical diffraction spot, such as Figure 3 (a).

[0038] The 4H-SiC substrate is cyclically annealed between 650℃-1350℃, and the time interval of the annealing cycle is: heating from 650℃ to 1350℃ within 10s, maintaining this temperature for 50s; then reducing from 1350℃ to 650℃ within 5s, and maintaining this temperature for 55s. During the cyclic annealing, an infrared thermometer is used to ensure the accuracy of the annealing cycle temperature. During the cyclic annealing process, the Si atoms on the Si surface of the 4H-SiC substrate will gradually evaporate to form double-layer graphene. After 80 cycles of annealing, a standard 4H-SiC / BLG substrate will be formed; clear and symmetrical diffraction spots can be seen on the surface of the substrate through RHEED detection, such as Figure 3 (b).

[0039] Using 99.99% pure Te powder as Te source, the Te source was heated to 195°C and maintained at this temperature for half an hour to ensure the stability of the beam velocity during the growth process. Using 99.99% pure Hf rod as Hf source, the Hf source was heated to 31W through an electron beam evaporation source and preheated for half an hour in this state to ensure the stability of the beam velocity during the growth process. During the preheating process, the molecular beam baffle of the evaporation source was kept in the closed state.

[0040] The 4H-SiC / BLG substrate is placed at the intersection of the molecular beam of the Te source and the molecular beam of the Hf source. The 4H-SiC / BLG substrate is heated to 400°C and the temperature is kept stable. At the same time, the Te source and Hf source molecular beam baffles are opened, and epitaxial growth begins. During the epitaxial growth process, the Hf source deposition rate is stably maintained at 0.022ML / min, and the beam ratio of the Te source and the Hf source is maintained at 20:1. The growth time is 45min. During the epitaxial growth process, the RHEED pattern will gradually change from the diffraction spot formed by the 4H-SiC / BLG substrate to a single layer of 1T-HfTe 2 The diffraction fringes formed by the thin film, such as Figure 4 After the growth is completed, the single layer 1T-HfTe 2 The RHEED stripes formed by the film are clear and have uniform brightness, indicating that the film has good quality.

[0041] After the sample growth is completed, the shutter and heating system of the electron beam evaporation source are turned off, but the state of the Te source remains unchanged. The substrate temperature is raised to 500℃ to anneal 1T-HfTe 2 After the sample is annealed, turn off the substrate heating device and allow the film sample to cool naturally to room temperature.

[0042] The samples were characterized by angle-resolved photoelectron spectroscopy at room temperature and low temperature, such as Figure 5 (c) and (h); the characterization results show that the sample has a clear band structure, reflecting the good quality of the film sample.

[0043] Example 2: 1T-HfTe with different electrical properties based on 4H-SiC / BLG substrate 2 Film preparation

[0044] The 4H-SiC substrates were annealed at 1300°C for 60 cycles, 1300°C for 80 cycles, 1350°C for 80 cycles (standard cycle), 1400°C for 80 cycles, and 1400°C for 100 cycles to form 4H-SiC / BLG substrates with different surface conductivities. Subsequently, single-layer 1T-HfTe was prepared on all substrates under the same conditions. 2 The preparation process and characterization methods of the film are exactly the same as those in Example 1. Due to the different conductivity of 4H-SiC / BLG substrates, the monolayer 1T-HfTe 2 The electron doping degree of the film is different. ARPES spectrum shows that the single layer 1T-HfTe 2 The films exhibit different surface electrical properties, such as Figure 5 As shown, the conductivity of the 4H-SiC / BLG substrate increases from left to right, and the Gap becomes larger and larger. 2The electron doping of the film is becoming more and more obvious. The band structures of the five experimental groups are clear and consistent, and the only difference is the size of the energy gap formed between the valence band top and the Fermi level. The size of the gap formed near the Fermi level and the band structure of the valence band top will significantly affect the conductivity of the film, thus determining whether it is a semiconductor or an insulator.

[0045] Example 3: 1T-HfTe with HOPG as substrate 2 Film preparation

[0046] The HOPG substrate was mechanically stripped to obtain an atomically smooth surface. The smooth HOPG substrate was transferred to an ultra-high vacuum chamber (pressure less than 2.0×10 -10 torr), heat the substrate to 650°C for high-temperature degassing for 1 hour. After 1 hour, the chamber pressure should be restored to 2.0×10 -10 torr; if the pressure is higher than this, it means that the degassing is incomplete and the degassing should be continued for 1 hour. After the HOPG substrate is degassed, the substrate surface is detected by RHEED; the clean HOPG substrate surface will form a clear and symmetrical diffraction spot.

[0047] The HOPG substrate was then heated to 450 °C to grow 1T-HfTe 2 The growth process and characterization process of the film are exactly the same as those in Example 1. Figure 6 As shown; the difference is that 1T-HfTe is grown on HOPG substrate 2 Thin films, due to the higher surface conductivity of HOPG substrate, characterization results show that 1T-HfTe 2 The film is doped with more electrons.

[0048] Comparative Example 1

[0049] Growth of monolayer 1T-HfTe on 4H-SiC / BLG substrate with standard annealing cycle 2 The preparation process and characterization methods of the film are exactly the same as those of Example 1, except that the 4H-SiC / BLG substrate temperature is 300°C during growth. Figure 7 As shown in the figure, the RHEED image is dim, which is mostly caused by the disorder of crystal domains and crystal orientations. The grown sample is no longer uniform and high-quality 1T-HfTe 2 film.

[0050] Comparative Example 2

[0051] Growth of monolayer 1T-HfTe on 4H-SiC / BLG substrate with standard annealing cycle 2The preparation process and characterization methods of the film are exactly the same as those of Example 1, except that the 4H-SiC / BLG substrate temperature is 600°C during growth. Figure 8 As shown in the figure, the brightness of the RHEED image stripes is uneven. The reason is that the island growth forms many layers of small islands at one time, and the number of such layers is uncontrollable. The sample obtained by growth is no longer uniform and high-quality 1T-HfTe 2 film.

[0052] Comparative Example 3

[0053] Growth of monolayer 1T-HfTe on 4H-SiC / BLG substrate with standard annealing cycle 2 The preparation process and characterization methods of the film are exactly the same as those in Example 1. The difference is that for the single-layer 1T-HfTe 2 The film is doped with alkali metals on the surface. Fig. 9 As shown. Figure 5 and Fig. 9 The purpose of doping is to make the gap at the top of the valence band larger. Fig. 9 In the process of achieving this goal, the energy band is deformed; although the result is a larger gap, it brings more background noise and severely deformed energy bands, which is not worth the loss. Therefore, the results obtained by alkali metal doping are more significant than those of substrate doping, but at the same time, more background signals are introduced, making it difficult to study the electronic energy band structure.

[0054] In summary, only in the technical solution provided by the present invention can high-quality, large-area, low-dimensional 1T-HfTe be achieved. 2 Preparation of thin films; and if the substrate processing parameters proposed in the present invention are followed, the preparation of 4H-SiC / BLG substrates with different conductivity can be achieved, thereby achieving the single-layer 1T-HfTe 2 Regulation of surface electrical properties of thin films.

[0055] This specific implementation is only an explanation of the present invention, not a limitation of the present invention. Any changes made by those skilled in the art after reading the specification of the present invention will be protected by the patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing a substrate-doped low-dimensional transition metal chalcogenide thin film using ultra-high vacuum, characterized in that: The method adopts a molecular beam epitaxial growth method to co-deposit a high-purity Te source and a Hf source on a HOPG substrate or a 4H-SiC / BLG substrate to epitaxially grow a 1T-HfTe2 film; the 4H-SiC / BLG substrate is obtained by subjecting a 4H-SiC substrate to cyclic annealing to form a double-layer graphene on its surface.

2. The method for preparing a substrate-doped low-dimensional transition metal chalcogenide thin film using ultra-high vacuum according to claim 1, characterized in that: The high-purity Te source is Te powder with a purity of 99.99%, which is heated by a resistive evaporation source to form a molecular beam; the high-purity Hf source is an Hf rod with a purity of 99.99%, which is heated by an electron beam evaporation source to form a molecular beam.

3. The method for preparing a substrate-doped low-dimensional transition metal chalcogenide thin film using ultra-high vacuum according to claim 2, characterized in that: The HOPG or 4H-SiC / BLG substrate is placed at the intersection center of the molecular beam of the Te source and the molecular beam of the Hf source for epitaxial growth.

4. The method for preparing a substrate-doped low-dimensional transition metal chalcogenide thin film using ultra-high vacuum according to claim 1, characterized in that: During the epitaxial growth process, the Hf source deposition rate was stably maintained at 0.022 ML / min, and the beam current ratio of the Te source to the Hf source was maintained at 20:

1.

5. The method for preparing a substrate-doped low-dimensional transition metal chalcogenide thin film using ultra-high vacuum according to claim 1, characterized in that: During the epitaxial growth process, the temperature of the HOPG substrate is maintained at 300-500° C., and the epitaxial growth time is 45 minutes; the temperature of the 4H-SiC / BLG substrate is maintained at 450° C., and the epitaxial growth time is 45 minutes.

6. The method for preparing a substrate-doped low-dimensional transition metal chalcogenide thin film using ultra-high vacuum according to claim 5, characterized in that: After the growth of 1T-HfTe2 film was completed, the Te source rate was maintained unchanged, the substrate temperature was increased to 500℃, and annealing was performed for 20 minutes.

7. The method for preparing a substrate-doped low-dimensional transition metal chalcogenide thin film using ultra-high vacuum according to claim 1, characterized in that: The HOPG substrate uses a mechanical stripping method to obtain an atomically smooth surface, and is degassed at 650° C. in an ultra-high vacuum chamber to remove impurities adsorbed on the substrate surface before epitaxial growth.

8. The method for preparing a substrate-doped low-dimensional transition metal chalcogenide thin film using ultra-high vacuum according to claim 1, characterized in that: The 4H-SiC / BLG substrate is formed by cyclic annealing of industrial-grade nitrogen-doped conductive 4H-SiC, specifically, the 4H-SiC is degassed at 650° C. in an ultra-high vacuum chamber, and then cyclically annealed between the highest temperature and 650° C.

9. The method for preparing a substrate-doped low-dimensional transition metal chalcogenide thin film using ultra-high vacuum according to claim 8, characterized in that: The number of standard annealing cycles of 4H-SiC / BLG is 80 times, the standard maximum temperature is 1350°C, and the time interval of the standard annealing cycle is: heating from 650°C to 1350°C within 10s, maintaining this temperature for 50s; then reducing from 1350°C to 650°C within 5s, and maintaining this temperature for 55s.

10. The method for preparing a substrate-doped low-dimensional transition metal chalcogenide thin film using ultra-high vacuum according to claim 8, characterized in that: In the high temperature annealing cycle of 4H-SiC / BLG substrate, when the number of cycles is 60 ≤ and the number of cycles is < 80, and the maximum cycle temperature is 1300°C ≤ and < 1350°C, it will be unfavorable for the formation of double-layer graphene, resulting in low surface conductivity of 4H-SiC / BLG substrate; In the high temperature annealing cycle of the 4H-SiC / BLG substrate, when 80 times<cycle number≤100 times and 1350℃<cycle maximum temperature≤1400℃, it will be beneficial to the formation of double-layer graphene, making the surface conductivity of the 4H-SiC / BLG substrate higher.

Images