A method for growing molybdenum telluride based on molecular beam epitaxy

Abstract

This invention discloses a method for growing molybdenum telluride based on molecular beam epitaxy. A molybdenum source and a tellurium source are placed in separate evaporation sources. The evaporated tellurium and molybdenum atoms are deposited on the surface of a surface-treated Au(111) substrate in an ultra-high vacuum environment. The deposition rate of molybdenum atoms is 0.015~0.03 mL / min, and the deposition rate ratio of tellurium atoms to molybdenum atoms is 18~25:1. The surface temperature of the Au(111) substrate is 265~285℃. This method is based on the synergistic control of each process. By controlling the deposition rate of the raw materials and the surface temperature of the substrate, monolayer 1T′ phase molybdenum telluride single crystals can be synthesized controllably. The monolayer 1T′ phase molybdenum telluride single crystals obtained based on the technical solution provided by this invention can reach the micrometer scale, and the obtained crystals have few defects, high crystal quality, and no mixing of impurity phases such as 1H, which can meet the performance requirements of high-energy, low-power electronic device fabrication.

Description

Technical Field

[0001] This invention relates to a method for producing a single-layer 1T′ phase molybdenum telluride single crystal, specifically a method based on molecular beam epitaxy of a single-layer 1T′ phase molybdenum telluride single crystal, belonging to the field of functional materials preparation. Background Technology

[0002] Molecular beam epitaxy (MBE) has been widely applied to prepare various high-purity multi-component or single-unit thin films, becoming one of the important methods for preparing high-quality single-crystal thin films and nanostructures at the atomic scale. The basic process involves depositing high-purity molecular or atomic beams onto the surface of an atomically flat single-crystal substrate in an ultra-high vacuum environment. After adsorption, migration, and surface reactions at a suitable substrate temperature, a crystalline thin film is formed based on the atomic arrangement on the substrate surface. Using MBE, many high-quality two-dimensional transition metal chalcogenide (TMC) thin films have been successfully prepared, such as MoS₂, WS₂, MoTe₂, and WSe₂. Although these TMCs have different phases, such as the 2H phase and the 1T′ phase, they typically exist stably in the 2H phase. Furthermore, 2H-phase monolayer TMCs are direct bandgap semiconductors, with significant applications in two-dimensional optoelectronic devices, thus attracting widespread attention. Compared to 2H-phase two-dimensional transition metal chalcogenides (TMCs), research on 1T′-phase TMCs is relatively limited, primarily due to two reasons: First, synthesizing 1T′-phase TMCs remains a challenge. This is because the 2H phase often appears alongside the 1T′-phase during growth, making it difficult for the 1T′-phase TMCs to exist independently, let alone synthesize on a large scale. Currently, the single crystals of TMCs used for experimental research are only a few tens of nanometers in size. Second, 1T′-phase TMCs are not stable enough and require more stringent growth environments; otherwise, they are easily affected by environmental factors and undergo phase transitions.

[0003] As our understanding of two-dimensional transition metal chalcogenides (TMCs) deepens, theoretical predictions suggest that T1′-phase TMCs are a class of topological insulators. Unlike conventional insulators, topological insulators possess unique physical properties. In a two-dimensional topological insulator, the interior is insulating, while the boundary is a spin-momentum locked metallic state, where electrons with opposite spins move in opposite directions. Protected by time-reversal symmetry, scattering between electrons with opposite spins is strictly prohibited. Therefore, two-dimensional topological insulators are ideal material systems for realizing spin transport and can be used in novel low-energy-consumption, high-performance spintronic devices. Combining topological insulators with superconducting materials to form topological superconductors could potentially enable topological quantum computing. Meanwhile, experiments have experimentally confirmed the topological properties of monolayer T1′-WS2 and T1′-WSe2 TMCs. Based on these new discoveries, T1′-phase TMCs have rapidly attracted the interest of researchers. The synthesis of two-dimensional transition metal chalcogenides (TMCs) with the 1T′ phase is still in its early stages. No reports have been found of synthesizing high-quality, micron-sized TMC single crystals using molecular beam epitaxy (MBE). Therefore, the synthesis of large-size, high-quality TMCs using MBE remains a pressing problem. Among the many TMCs, the synthesis of 1T′-MoTe2 is particularly challenging. Because the energy difference between the 1T′-MoTe2 and 1H-MoTe2 phases is extremely small, only about 0.05 eV, they tend to coexist during growth, which is difficult to avoid and significantly limits the synthesis of large-size, high-quality monolayer 1T′-MoTe2 single crystals. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a method for molybdenum telluride growth based on molecular beam epitaxy. This invention achieves the controllable synthesis of micron-scale monolayer 1T′-MoTe2 single crystals on an Au(111) atomic-level planar platform. The resulting monolayer 1T′-MoTe2 single crystals have clean surfaces, high crystal quality, and are free of impurity phase mixing, meeting the performance requirements for high-energy, low-power electronic device fabrication. This method is based on the synergistic control of various processes, controlling the deposition rate of raw materials and the surface temperature of the substrate to controllably synthesize 1T′-MoTe2 single crystals. The preparation method provided by this invention has the advantages of simple process, high yield, and high crystal quality, making it suitable for large-scale industrial production.

[0005] To achieve the above-mentioned technical objectives, this invention provides a method for growing molybdenum telluride based on molecular beam epitaxy. In this method, a Mo source and a Te source are placed in separate evaporation sources. The evaporated Te atoms and Mo atoms are deposited on the surface of a surface-treated Au(111) substrate in an ultra-high vacuum environment. The deposition rate of Mo atoms is 0.015~0.03 mL / min, and the deposition rate ratio of Te atoms to Mo atoms is 18~25:1. The surface temperature of the Au(111) substrate is 265~285 °C.

[0006] As a preferred embodiment, the Au(111) substrate is placed at the intersection of the Mo atomic beam and the Te atomic beam.

[0007] As a preferred embodiment, the surface treatment process of the Au(111) substrate is as follows: the Au(111) substrate is sputtered with argon ions at room temperature for 0.5~1h to remove impurities adsorbed on the substrate surface, and then annealed at 600~700℃ for 0.2~1h to reconstruct the surface.

[0008] As a preferred embodiment, the annealing time during the surface treatment of the Au(111) substrate is 0.2~0.5h, and the temperature is 600~680℃. More preferably, the annealing time is 20min, and the annealing temperature is 650℃.

[0009] As a preferred embodiment, the argon ion sputtering time during the surface treatment of the Au(111) substrate is 0.5~0.8h, and more preferably, the argon ion sputtering time is 40 min.

[0010] As a preferred embodiment, the processing of the Au(111) substrate is repeated 1 to 3 times. More preferably, the processing of the Au(111) substrate is repeated 2 times.

[0011] As a preferred embodiment, the parameters for argon ion sputtering are: emission current of 8~10mA, accelerating voltage of 1.6~2.2 kV, and argon concentration of 0.5~1.5×10⁻⁶. -5 Torr. Further preferably, the parameters for the argon ion sputtering are: emission current of 10 mA, accelerating voltage of 2 kV, and argon concentration of 1.1 × 10⁻⁶. -5 Torr.

[0012] As a preferred embodiment, the Mo source is a high-purity Mo rod or high-purity Mo powder, and the Te source is a high-purity Te powder.

[0013] As a preferred embodiment, the evaporation source is an electron beam evaporation source or a resistance evaporation source.

[0014] As a preferred embodiment, the evaporation source for the Mo rod is an electron beam evaporation source, and the evaporation source for the Te powder is a resistance evaporation source.

[0015] As a preferred embodiment, the atomic deposition process includes: the evaporation source baffle is in a closed state, the evaporation rates of the Mo source and the Te source are adjusted, the system is running stably, the evaporation source baffle is opened for epitaxial growth, the evaporation source baffle is closed at the end of the epitaxial growth, the evaporation source is then turned off, and after heat preservation, the desired result is obtained.

[0016] As a preferred embodiment, the epitaxial growth time is 8-15 minutes; the holding temperature is 265-285°C, and the holding time is 8-15 minutes. More preferably, the epitaxial growth time is 10 minutes; the holding temperature is 275°C, and the holding time is 10 minutes.

[0017] As a preferred embodiment, the deposition rate of molybdenum atoms is 0.015~0.025 mL / min, and the deposition rate ratio of Mo atoms to Te atoms is 20~25:1. More preferably, the deposition rate of Mo atoms is 0.02 mL / min, and the deposition rate ratio of Mo atoms to Te atoms is 20:1.

[0018] The deposition rates of Mo and Te atoms are crucial for the synthesis of 1T′-MoTe2 single crystals. During deposition, due to the high deposition rate ratio of Te to Mo atoms and the strong bonding ability of Te atoms with the Au(111) substrate, Te atoms readily adsorb onto the Au(111) substrate surface, rapidly forming an ordered Te structure. This Te structure exhibits selective growth on the Au(111) substrate, displaying a consistent orientation on a single mesa. Furthermore, as growth progresses, Te and Mo atoms combine with the Te structure on the substrate surface, thus forming 1T′-MoTe2 single crystals. Additionally, during the formation of 1T′-MoTe2 single crystals, Te atoms readily desorb, while Mo atoms are less prone to desorption, which explains the high deposition rate ratio of Te to Mo atoms. Therefore, the deposition rates of Mo and Te atoms must strictly adhere to the aforementioned requirements during the deposition process.

[0019] As a preferred embodiment, the surface temperature of the Au(111) substrate is 270~280℃. More preferably, the surface temperature of the Au(111) substrate is 275℃.

[0020] The surface temperature of the Au(111) substrate must be strictly controlled according to the above requirements. When the Au(111) substrate temperature is 300~320℃, the obtained sample is Mo6Te6 nanowire, which grows along the steps of the single crystal gold substrate. The length of the nanowire can reach 200 nm~300 nm. Within this temperature range, the higher the temperature, the more obvious the nanowire features and the clearer the boundary. When the Au(111) substrate temperature is 265~285℃, the sample is mainly composed of 1T′-MoTe2, with a size of 500~1500 nm. As the temperature increases, the size of the sample first increases and then decreases. The sample size reaches its maximum at 275℃. When the Au(111) substrate temperature is below 260℃, the sample is mainly composed of Te structure formed by Te atoms. Therefore, the controllable synthesis of the sample can only be achieved under the conditions required by this invention.

[0021] As a preferred embodiment, the molybdenum telluride is a single-atom-layer 1T′ phase molybdenum telluride single crystal with a side length of 0.6~1.2μm and a size of 0.6~1.2μm. 2 The space group is P21 / m.

[0022] This invention also provides a detailed method for preparing a two-dimensional large-size single-atom layer 1T′-MoTe2 single crystal, including the following steps: Step 1: Treatment of the Au (111) substrate surface. Adjust the sample stage position so that 5 5 A 0.5 mm Au(111) substrate is positioned directly opposite the argon ion gun. The argon gas micro-leak valve is opened to release argon gas, and the argon concentration is adjusted to 1.1. 10 -5 Torr. Accelerating voltage was adjusted to 2 kV, and emission current was 10 mA. Argon ion sputtering was initiated and lasted for 40 min.

[0023] Step 2: After the argon ion sputtering treatment is completed, Au (111) is annealed at 650 °C for 20 min.

[0024] Step 3: Repeat steps 1 and 2 twice to completely remove impurities from the Au (111) surface, making its surface atomically smooth and obtaining a single Au (111) mesa with a length of more than 1 micrometer.

[0025] Step 4: Confirm that the baffle of the resistive evaporation source is in the closed state, adjust the input power of the resistive evaporation source, and control the deposition rate of the evaporated Te atoms to 0.4 mL / min.

[0026] Step 5: Confirm that the baffle of the electron beam evaporation source is in the closed state; adjust the input power of the electron beam evaporation source to control the deposition rate of the evaporated Mo atoms to 0.02 mL / min.

[0027] Step 6: The Au (111) substrate is heated during Step 4 to a temperature of 275°C. After everything is ready and the system has stabilized for 5 minutes, the baffles of the electron beam evaporation source and the resistive evaporation source are opened simultaneously, and epitaxial growth begins. The growth time is 10 minutes.

[0028] Step 7: After sample growth is complete, simultaneously close the baffles of both the electron beam evaporation source and the resistance evaporation source, then turn off the evaporation source. Incubate the sample at 275 °C for 10 min. After incubation, slowly cool the sample to room temperature; epitaxial growth is now complete.

[0029] Compared with the prior art, the beneficial technical effects of the present invention are as follows: 1) The present invention provides a method for growing molybdenum telluride based on molecular beam epitaxy. Based on an ultra-high vacuum platform, a molecular beam epitaxy system is built, which can control the growth conditions very precisely and realize the controllable growth of two-dimensional materials. That is, by utilizing the characteristic that Te forms an ordered Te structure on Au (111), the micron-scale high-quality monolayer 1T′-MoTe2 single crystal is grown on Au (111) substrate.

[0030] 2) In the technical solution provided by the present invention, the controllable synthesis of micron-level monolayer 1T′-MoTe2 single crystals is realized on the Au(111) atomic-level planar platform. The obtained monolayer 1T′-MoTe2 single crystals have clean surfaces, high crystal quality, and no impurity phase mixing, which can meet the performance requirements for the fabrication of high-energy and low-power electronic devices. Attached Figure Description

[0031] Figure 1 These are scanning tunneling microscope images, electron microscope images, and Raman images of the sample prepared in Example 1; in, Figure 1 (a) is a scanning tunneling microscope image of a 1T′-MoTe2 single crystal; Figure 1 (b) is an atomically resolved scanning tunneling microscope image of a 1T′-MoTe2 single crystal; Figure 1 (c) is an electron microscope image of a 1T′-MoTe2 single crystal; Figure 1 (d) is the Raman characteristic diagram of 1T′-MoTe2 single crystal; Figure 2 This is a scanning tunneling microscope image of the sample prepared in Example 2; Figure 3 This is a scanning tunneling microscope image of the sample prepared in Comparative Example 1; Figure 4 This is a scanning tunneling microscope image of the sample prepared in Comparative Example 2; Figure 5 This is a scanning tunneling microscope image of the sample prepared in Comparative Example 3; Figure 6 This is a scanning tunneling microscope image of the sample prepared in Comparative Example 4; Figure 7 This is a schematic diagram of the preparation process of the present invention. Detailed Implementation

[0032] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0034] To ensure the controllable deposition of molybdenum and tellurium atoms on a single-crystal gold substrate, the Mo and Te atomic beams were calibrated on Au (111) substrates in the following examples and comparative examples. The specific process was as follows: Te and Mo films were grown on surface-treated Au (111) substrates at room temperature for 3 minutes. After growth, the coverage of the two films on the Au (111) substrates was observed using a scanning tunneling microscope. Based on the coverage and growth time, the deposition rates of the two materials on the Au (111) substrates were calculated. This process was repeated multiple times under different beam conditions to accurately determine the deposition rates corresponding to the Mo and Te atomic beams. After determining the deposition rates of the Mo and Te atomic beams, growth optimization was performed to determine multiple sets of Mo and Te atomic beam deposition rate ratios. Then, sample growth was carried out according to the deposition rate ratio parameters of each set. Example 1

[0035] After the Au(111) substrate is transferred onto the sample stage, the mechanical displacement stage is moved up and down to bring the Au(111) substrate and the argon ion gun to the same horizontal position. Then, the mechanical displacement stage is rotated so that the Au(111) substrate faces the argon ion gun directly. The micro-leak valve of the argon ion gun is adjusted to release argon gas. At this time, the argon gas concentration is maintained at 1.1 × 10⁻⁶. -5Torr; The argon ion sputtering parameters were adjusted by the argon ion gun control system, with an emission current of 10 mA, an acceleration voltage of 2 kV, and a sputtering time of 20 min; After argon ion sputtering, the Au (111) substrate was annealed for surface reconstruction at a temperature of 650 °C for 40 min. After the initial treatment, the impurities on the Au(111) substrate surface were mostly removed, but a small amount remained. Furthermore, the Au(111) surface was not yet sufficiently smooth, necessitating a second surface treatment. The parameters for the second treatment were the same as the first, with the primary goal of making the Au(111) substrate surface smoother and the individual mesa larger. A third treatment was then performed, with the same parameters as the first. After this third treatment, the individual mesa of the Au(111) substrate became even larger, reaching a size of 1 μm. 2 .

[0036] After the Au (111) substrate is processed, turn on the water chiller to ensure that the electron beam evaporation source is within a safe operating temperature range; confirm that the baffle of the electron beam evaporation source is in the closed state; adjust the filament current of the electron beam evaporation source to 4.1 A, and then adjust the voltage of the electron beam evaporation source to 1500 V. After adjustment, the electron beam evaporation source begins to evaporate Mo atoms; adjust the linear thruster of the electron beam evaporation source to control the size of the Mo atom beam current. The Mo atom beam current is about 3500 pA. At this time, the emission power of the electron beam evaporation source is 32W; after the electron beam evaporation source is adjusted, preheat for 10 minutes to ensure that the Mo atom beam current of the electron beam evaporation source remains stable; under these conditions, the deposition rate of Mo atoms is about 0.02 ML / min. Meanwhile, it was confirmed that the baffle of the resistive evaporation source was in a closed state; the input power of the resistive evaporation source was adjusted so that the Te powder inside the resistive evaporation source was slowly heated; finally, by controlling the input power of the resistive evaporation source, the temperature of the Te powder was maintained at about 230°C; after the resistive evaporation source was properly adjusted, it was preheated for 10 minutes to ensure that the Te atom beam of the resistive evaporation source remained stable; under these conditions, the deposition rate of Te atoms was about 0.4 ML / min; The surface-treated Au(111) substrate is heated to 275 °C, and the whole process takes about 10 minutes. At this time, the deposition rate of the electron beam evaporation source and the resistive evaporation source has been maintained at the set value, and the temperature of the Au(111) substrate is also stable near the set value. At the same time, the baffles of the electron beam evaporation source and the resistive evaporation source are opened, and epitaxial growth begins. The growth time is 10 minutes. After sample growth was completed, the baffles of both the electron beam evaporation source and the resistive evaporation source were closed simultaneously, and the control systems of both sources were shut down. The sample was held at 275 °C for 10 min. After the sample was held at 275 °C, the control system of the Au(111) substrate heating device was turned off, allowing the sample to cool slowly to room temperature, thus ending the epitaxial growth. A micron-sized, high-quality monolayer 1T′-MoTe2 single crystal was obtained. Raman spectroscopy of the obtained sample is as follows. Figure 1 As shown in (d), at 125 cm -1 It has a characteristic peak of 1T′-MoTe2. Example 2

[0037] The preparation process in this embodiment is completely consistent with that in Example 1, except that the deposition rate of Te atoms is 0.6 ML / min. The sample obtained by growth is basically the same as that in Example 1.

[0038] Comparative Example 1 The preparation process of this comparative example is completely consistent with that of Example 1, except that the temperature of the Au (111) substrate is 255 °C. The grown sample is mainly composed of a structure formed by Te atoms.

[0039] Comparative Example 2 The preparation process of this comparative example is completely consistent with that of Example 1, except that the temperature of the Au (111) substrate is 305 ℃. The grown sample is mainly composed of Mo6Te6 nanowires, which are grown along the steps of the Au (111) substrate and can reach a length of about 100 nm.

[0040] Comparative Example 3 The preparation process of this comparative example is completely consistent with that of Example 1, except that the deposition rate of Mo atoms is approximately 0.01 ML / min. The grown sample is mainly composed of 1T′-MoTe2 and Te atomic structures, and the sample does not completely cover the surface of the Au (111) substrate.

[0041] Comparative Example 4 The preparation process of this comparative example is completely consistent with that of Example 1, except that the deposition rate of Te atoms is approximately 0.1 ML / min. The grown sample mainly consists of clusters of Mo and Te atoms, and 1T′-MoTe2 single crystals were not obtained.

[0042] As can be seen from Examples 1 and 2 and Comparative Examples 3 and 4, due to the strong bonding ability between Te and Au(111), in the early stage of epitaxial growth, Te atoms form an oriented Te structure on the substrate surface. Mo atoms further synthesize with Te on the Te structure to generate a single-layer 1T′-MoTe2 single crystal. Since the Mo-Au binding energy > Te-Au binding energy > Te-Te binding energy, it is necessary to ensure that there is sufficient Te in the synthesis process to uniformly cover the Au(111) substrate surface. However, it should be noted that the deposition rate of Te and Mo should not be too high or too low. If the deposition rate of Mo atoms is too low, the size of 1T′-MoTe2 crystal will be too small, and it will be impossible to form a large-sized 1T′-MoTe2 single crystal. If the deposition rate of Te atoms is too low, the growth will fail and Te and Mo clusters will be formed.

[0043] As shown in Example 1, Comparative Example 1, and Comparative Example 2, the temperature of the Au(111) substrate has a significant impact on the synthesis of the samples. If the temperature is too high, the samples will exhibit a nanowire morphology and will not be able to form 1T′-MoTe2 single crystals. If the temperature is too low, Te and Mo will be difficult to synthesize, and the samples will mainly exhibit a Te atomic structure.

[0044] Therefore, it can be seen that the sample can only be successfully prepared by following the technical solution provided by this invention. If the process requirements of this invention are not followed, the various properties and morphology of the final product will be adversely affected to a certain extent.

Claims

1. A method for growing molybdenum telluride based on molecular beam epitaxy, characterized in that: The Mo source and the Te source are placed in different evaporation sources. The evaporated Te and Mo atoms are deposited on the surface of the surface-treated Au(111) substrate in an ultra-high vacuum environment. The deposition rate of the Mo atoms is 0.015~0.03ML / min. The deposition rate ratio of the Te atoms to the Mo atoms is 18~25:

1. The surface temperature of the Au(111) substrate is 265~285℃.

2. The method for growing molybdenum telluride based on molecular beam epitaxy according to claim 1, characterized in that: The surface treatment process of the Au(111) substrate is as follows: the Au(111) substrate is cleaned by argon ion sputtering, and then annealed at 600~700℃ for 0.2~0.8h for surface reconstruction.

3. The method for growing molybdenum telluride based on molecular beam epitaxy according to claim 2, characterized in that: The Au(111) substrate is placed at the intersection of the Mo atomic beam and the Te atomic beam; the surface treatment process is repeated 1 to 3 times.

4. A method for growing molybdenum telluride based on molecular beam epitaxy according to claim 2, characterized in that: The parameters for argon ion sputtering are as follows: emission current 8~10mA, accelerating voltage 1.6~2.2 kV, sputtering time 0.3~0.5h, and argon concentration 0.5~1.5×10⁻⁶. -5 Torr.

5. The method for growing molybdenum telluride based on molecular beam epitaxy according to claim 1, characterized in that: The Mo source is a high-purity Mo rod or high-purity Mo powder, and the Te source is a high-purity Te rod or high-purity Te powder; the evaporation source is an electron beam evaporation source or a resistance evaporation source.

6. The method for growing molybdenum telluride based on molecular beam epitaxy according to claim 5, characterized in that: The evaporation source for the Mo rod is an electron beam evaporation source, and the evaporation source for the Te powder is a resistance evaporation source.

7. The method for growing molybdenum telluride based on molecular beam epitaxy according to claim 1, characterized in that: The atomic deposition process includes: with the evaporation source baffle in a closed state, adjusting the evaporation rates of the Mo and Te sources, opening the evaporation source baffle for epitaxial growth after the system is running stably, closing the evaporation source baffle at the end of the epitaxial growth, then turning off the evaporation source, and then heat preservation to obtain the final product.

8. The method for growing molybdenum telluride based on molecular beam epitaxy according to claim 7, characterized in that: The epitaxial growth time is 8-15 minutes; the heat preservation temperature is 265-285℃, and the heat preservation time is 8-15 minutes.

9. The method for growing molybdenum telluride based on molecular beam epitaxy according to claim 1, characterized in that: The deposition rate of Mo atoms is 0.015~0.025ML / min, and the deposition rate ratio of Te atoms to Mo atoms is 20~22:1; the surface temperature of the Au(111) substrate is 270~280℃.

10. A method for growing molybdenum telluride based on molecular beam epitaxy according to any one of claims 1 to 9, characterized in that: The molybdenum telluride is a single-atom-layer 1T′ phase molybdenum telluride single crystal with a side length of 0.6~1.2μm and a size of 0.6~1.2μm. 2 The space group is P21 / m.

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