A two-dimensional molybdenum telluride alloy and a method for preparing the two-dimensional molybdenum telluride alloy under ultra-high vacuum

Abstract

The present invention discloses a two-dimensional molybdenum tellurium alloy and a method for preparing the two-dimensional molybdenum tellurium alloy under ultra-high vacuum. The method includes: preparing a 2H-phase MoTe2 thin film by molecular beam epitaxy in an ultra-high vacuum environment; annealing the 2H-phase MoTe2 thin film at 400°C to 450°C in an ultra-high vacuum environment to enable chemical bonding between Mo and Te, thereby obtaining a two-dimensional molybdenum tellurium alloy. By annealing the 2H-phase MoTe2 thin film at 400°C to 450°C, the present invention obtains a two-dimensional molybdenum tellurium alloy with an ordered, mirror-symmetric twin boundary superlattice. The two-dimensional molybdenum tellurium alloy has high scientific research value and wide application potential, and the preparation method is simple, effective, and controllable.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and particularly to a two-dimensional molybdenum telluride alloy and a method for preparing the two-dimensional molybdenum telluride alloy under ultra-high vacuum. Background Art

[0002] Following the discovery of graphene, various novel two-dimensional materials have become a hot topic in the scientific research community recently due to their rich physical and chemical properties and huge potential application values, which also brings new opportunities for the development of novel electronic devices. Transition metal dichalcogenide (TMD) materials with a "sandwich" structure are predicted to have up to dozens of stable existences. They not only have multiple phase structures (such as 1T, 2H, 3R, etc.), but also cover a variety of electrical properties (from insulator to semiconductor, then to semimetal, and finally to metal). The metal elements Mo and Te can also be chemically bonded to form novel two-dimensional TMD materials, and MoTe2 is a typical one among them. MoTe2 has rich phases, such as 2H-MoTe2 with semiconductor properties and 1T'-MoTe2 with semimetal properties. The energy difference between the two phases is small (~0.03 eV), and it is relatively easy to achieve the conversion between the two phases. During the growth process, the metastable 1T'-MoTe2 thin film grows first. Under suitable external conditions, the 1T'-MoTe2 thin film gradually transforms from the 1T’ phase to the semiconductor 2H phase through a "solid-solid" phase transition. Inevitably, mirror-symmetric twin boundaries with disordered distributions and different sizes are formed during the formation of the 2H phase, which is one of the common defects in the growth of monolayer TMDs by methods such as chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). This kind of defect will strongly affect the electronic and optical properties of two-dimensional materials, making them exhibit rich electronic states. Summary of the Invention

[0003] In order to overcome the deficiencies in the growth of two-dimensional molybdenum telluride alloy by methods such as chemical vapor deposition and molecular beam epitaxy, the present invention provides a method for preparing a two-dimensional molybdenum telluride alloy under ultra-high vacuum. The two-dimensional molybdenum telluride alloy obtained by this method has a superlattice structure of mirror-symmetric twin boundaries with ordered distribution and uniform size.

[0004] The technical solutions adopted by the present invention to solve the above problems are as follows:

[0005] In a first aspect, the present invention provides a method for preparing a two-dimensional molybdenum telluride alloy under ultra-high vacuum, including:

[0006] Preparing a 2H-phase MoTe2 thin film by molecular beam epitaxy under ultra-high vacuum;

[0007] Annealing the 2H-phase MoTe2 thin film at 400°C to 450°C under ultra-high vacuum to enable chemical bonding between Mo and Te to obtain a two-dimensional molybdenum telluride alloy.

[0008] In some embodiments provided by the present invention, the annealing time is 1 to 3 hours.

[0009] In some embodiments provided by the present invention, the preparation of the 2H-phase MoTe2 thin film by molecular beam epitaxy includes:

[0010] According to the deposition rate ratio of Mo and Te being 1:25 to 35, Mo atoms and Te atoms are co-evaporated and deposited on a substrate at 250 ± 5 °C, and then heat preservation is carried out to obtain the 2H-phase MoTe2 thin film.

[0011] In some embodiments provided by the present invention, a bilayer graphene is provided on the substrate, and Mo and Te are deposited on the (0001) plane of the bilayer graphene.

[0012] In some embodiments provided by the present invention, the substrate is a 6H-SiC substrate, and the bilayer graphene provided thereon is generated by direct current heating of the 6H-SiC substrate.

[0013] In some embodiments provided by the present invention, the co-evaporation and deposition of Mo atoms and Te atoms on a substrate at 250 °C includes: evaporating Te atoms through a molecular evaporation source and evaporating Mo atoms through a metal evaporation source.

[0014] In some embodiments provided by the present invention, the co-evaporation deposition time is 15 to 25 minutes.

[0015] In some embodiments provided by the present invention, the heat preservation time is not less than 10 minutes, and the Te atomic beam current is maintained constant during the heat preservation process.

[0016] In a second aspect, the present invention provides a two-dimensional molybdenum tellurium alloy prepared by the method for preparing a two-dimensional molybdenum tellurium alloy under the above-mentioned ultra-high vacuum.

[0017] In a third aspect, the present invention provides the application of the above two-dimensional molybdenum tellurium alloy in the semiconductor field.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0019] By annealing the 2H-phase MoTe2 thin film, the present invention obtains a two-dimensional molybdenum tellurium alloy with a mirror-symmetric twin boundary superlattice structure having an ordered distribution and uniform size. The mirror-symmetric twin boundary superlattice structure of this two-dimensional molybdenum tellurium alloy is dense and uniform, similar to graphene, and has some very advanced quantum properties, with very considerable physical research value. In addition, the preparation method of this two-dimensional molybdenum tellurium alloy is simple, effective, and controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Hereinafter, the technical solutions of the present invention will be described in detail with reference to the drawings, where:

[0021] Figure 1 Shows large - scale scanning tunneling microscopy images of molybdenum tellurium alloys with multiple phases implemented according to the present invention and corresponding experimental parameters; Figure 1 a to Figure 1 c are large - scale scanning tunneling microscopy images of molybdenum tellurium alloys obtained by heat preservation at 150 °C, 250 °C, and 500 °C respectively, Figure 1 d to Figure 1 g are large - scale scanning tunneling microscopy images of molybdenum tellurium alloys obtained after annealing at 280 °C, 350 °C, 400 °C, and 450 °C respectively.

[0022] Figure 2 Shows small - scale scanning tunneling microscopy images of 1T'-MoTe2, 2H - MoTe2, and Mo6Te6 nanowires implemented according to the present invention; among them, Figure 2 a to Figure 2 c are small - scale scanning tunneling microscopy images of molybdenum tellurium alloy samples obtained by heat preservation at 150 °C, 250 °C, and 500 °C respectively.

[0023] Figure 3 Shows different phase structures obtained after annealing of 2H - MoTe2; among them, Figure 3 a to Figure 3 c are small - scale and high - resolution scanning tunneling microscopy images of molybdenum tellurium alloys obtained after annealing at 350 °C, 400 °C, and 450 °C respectively.

[0024] Figure 4 Shows high - resolution scanning tunneling microscopy images of the "wheel - shaped" MTB superstructure under different bias voltages, among which, Figure 4 a has a bias voltage of 1.0 V, Figure 4 b has a bias voltage of 0.1 V, Figure 4 c has a bias voltage of - 0.1 V, Figure 4 c has a bias voltage of - 1.0 V. Detailed implementation manners

[0025] The following further describes the present invention in detail in combination with specific implementation manners. The examples given are only to clarify the present invention, rather than to limit the scope of the present invention.

[0026] The method for preparing two - dimensional molybdenum tellurium alloy under ultra - high vacuum of the present invention includes: preparing a 2H - phase MoTe2 thin film by molecular beam epitaxy in an ultra - high vacuum environment; annealing the 2H - phase MoTe2 thin film at 400 °C - 450 °C under ultra - high vacuum to enable chemical bonding between Mo and Te to obtain a two - dimensional molybdenum tellurium alloy. Preferably, the annealing time is 1 - 3 h.

[0027] After annealing the 2H-MoTe2 sample, it was found that with the change of the annealing temperature, molybdenum telluride alloy structures with different phases would also be obtained: when annealing the 2H-phase MoTe2 thin film at 400 °C to 450 °C, twin boundaries with the same size and morphology were obtained as a whole; when annealing the 2H-phase MoTe2 thin film at 325 °C to 340 °C, the overall size of the twin boundaries was not uniform; when annealing the 2H-phase MoTe2 thin film at 360 °C to 390 °C, twin boundaries with two different sizes were obtained; when annealing the 2H-phase MoTe2 thin film above 450 °C, a new structure Mo5Te8 was obtained; therefore, in order to obtain ordered and uniformly sized twin boundaries, the annealing temperature needs to be controlled between 400 °C and 450 °C.

[0028] In some embodiments provided by the present invention, the preparation of the 2H-phase MoTe2 thin film by molecular beam epitaxy includes: co-evaporating and depositing Mo atoms and Te atoms onto a substrate at 250 ± 5 °C according to a deposition rate ratio of Mo and Te of 1:25 to 35, and then holding the temperature to obtain the 2H-phase MoTe2 thin film. Preferably, the deposition rate ratio of Mo and Te is 1:30; the deposition time is 15 to 25 minutes, and preferably, the deposition time is 20 minutes. Preferably, the holding time is not less than 10 minutes, and the Te atomic beam current is maintained constant during the holding process. Through experiments, the present invention found that when the temperature of the substrate is ~150 °C, ~250 °C, and ~500 °C respectively, the obtained are 1T'-phase MoTe2, 2H-phase MoTe2, and Mo6Te6 thin films. Therefore, 250 ± 5 °C is selected as the substrate temperature for the co-evaporation deposition of Mo atoms and Te atoms.

[0029] In some embodiments provided by the present invention, there is bilayer graphene on the substrate, and Mo and Te are deposited on the (0001) plane of the bilayer graphene. At present, the present invention has only prepared a disordered mirror-symmetric twin boundary superlattice structure on other substrates, and has not obtained such a mirror-symmetric twin boundary superlattice structure with uniform size on other substrates. The applicant believes that the reason for the generation of this mirror-symmetric twin boundary superlattice structure with ordered distribution and uniform size is that tellurium atoms are desorbed during the annealing process, and graphene has no surface dangling bonds and is stable in nature, which is suitable for the desorption of tellurium atoms. For this kind of transition metal chalcogenide material, their combination and desorption are not greatly affected by the substrate. Therefore, the substrate with bilayer graphene is one of the keys for the 2H-phase MoTe2 thin film to form a mirror-symmetric twin boundary superlattice structure with ordered distribution and uniform size.

[0030] In some embodiments provided by the present invention, the substrate is a 6H-SiC substrate, and the double-layer graphene disposed thereon is generated by direct-current heating of the 6H-SiC substrate. Specifically, it is first heated to 1350 °C by direct current and held for 1 minute, then slowly cooled to 650 °C and held for 2 minutes, and then heated to 1350 °C by direct current and held for 1 minute, and this cycle is repeated forty times.

[0031] In some embodiments provided by the present invention, co-evaporating Mo atoms and Te atoms onto a substrate at 250 °C includes: evaporating Te atoms through a molecular evaporation source and evaporating Mo atoms through a metal evaporation source. Specifically, evaporating Te atoms through a molecular evaporation source includes: placing Te powder in the molecular evaporation source, with an evaporation temperature of 140 °C and a time of 20 minutes; evaporating Mo atoms through a metal evaporation source includes: placing a Mo rod in the metal evaporation source, with an evaporation power of 63 W and a time of 20 minutes.

[0032] Unless otherwise specified, the "ultra-high vacuum" referred to in the present invention means a vacuum environment with a pressure in the range of 10 -6 ~10 -8 Pa.

[0033] Test instruments and equipment:

[0034] E-Beam metal evaporation source: Zhongke AikeMi (Beijing) Technology Co., Ltd.

[0035] Film thickness monitor: Inficon SQM 160.

[0036] Raw materials:

[0037] Te powder: Purchased from Shanghai Pumi Precision Instrument Technology Co., Ltd., with a purity of 99.999%.

[0038] Mo rod: Purchased from Shanghai Pumi Precision Instrument Technology Co., Ltd., with a purity of 99.95%.

[0039] 6H-SiC substrate (0001): Purchased from Shanghai Pumi Precision Instrument Technology Co., Ltd.

[0040] Examples

[0041] 1. Preparation of double-layer graphene / silicon carbide substrate:

[0042] Fix a 6H-SiC substrate (size: 2 mm × 10 mm) on a DC heating sample stage. The resistance between the electrodes on both sides of the 6H-SiC substrate and the DC heating sample stage is about 3 kΩ. Place the 6H-SiC substrate in the rapid injection chamber of a low-temperature scanning tunneling microscope and evacuate it. After about 1 h, transfer the 6H-SiC substrate to the sample preparation chamber and perform heating degassing. After the degassing is completed, gradually heat the 6H-SiC substrate to 1350 °C, hold for 1 minute, then quickly cool it to 650 °C, hold for 2 minutes, and repeat the operation 40 times to obtain a bilayer graphene / silicon carbide substrate.

[0043] 2. Determination of the deposition rates of Mo and Te:

[0044] Before depositing Mo atoms and Te atoms, it is necessary to degas and remove impurities from the two metal sources respectively.

[0045] Place Te powder in the crucible of the K-Cell molecular evaporation source and gradually heat it. After the temperature stabilizes, open the baffle of the K-Cell molecular evaporation source, close the baffle after 10 minutes, and record the deposition thickness at this time with a film thickness monitor. After 10 minutes, repeat the above experimental operations several times and record the corresponding film thickness values. If the obtained values are inconsistent, increase the temperature of the K-Cell molecular evaporation source by 10 °C and repeat the above operation; if the obtained values are basically consistent, lower the temperature of the K-Cell molecular evaporation source by 5 °C and hold for impurity removal.

[0046] Place a metal Mo rod in the E-Beam metal evaporation source. First, degas the filament of the E-Beam metal evaporation source, slowly increase the output current of the filament to 4.3 A, and turn off the output of the filament after the vacuum degree stabilizes. Apply a high voltage of 1800 V to the E-Beam metal evaporation source and gradually increase the output power of the filament of the E-Beam metal evaporation source. After the output power stabilizes and is maintained for a period of time (such as 5 minutes), open the baffle of the E-Beam metal evaporation source, close the baffle after 10 minutes, and record the deposition thickness at this time with a film thickness monitor. After 10 minutes, repeat the above experimental operations several times and record the corresponding film thickness values. If the obtained values are inconsistent, increase the power of the E-Beam metal evaporation source by 0.5 W and repeat the above operation; if the obtained values are basically consistent, lower the power of the E-Beam metal evaporation source by 0.5 W and hold for impurity removal.

[0047] After the impurity removal is completed, use a film thickness monitor to record the deposition thicknesses of the Mo source and the Te source in the same time respectively. By adjusting the output power and temperature of the two respectively, make the deposition rate ratio between Mo and Te 1:30.

[0048] 3. Regulating the substrate temperature to obtain molybdenum telluride alloys with different phases and their structural characterization

[0049] After obtaining the bilayer graphene / silicon carbide substrate, multiple bilayer graphene / silicon carbide substrates were taken and kept at 150 °C, 250 °C, and 500 °C respectively. Then, Mo and Te were co-deposited onto the bilayer graphene / silicon carbide substrates kept at each temperature at a deposition rate ratio of Mo:Te of 1:30, and the deposition time was 20 minutes. After deposition, the E-Beam metal evaporation source and the K-Cell molecular evaporation source were turned off, and the sample was kept warm for 10 minutes. Figure 1 a to Figure 1 c are respectively large-scale scanning tunneling microscope images of the molybdenum telluride alloy obtained by keeping at 150 °C, 250 °C, and 500 °C. Among them, the molybdenum telluride alloy obtained by keeping at 150 °C and 250 °C is two-dimensional sheet / island-shaped, while the molybdenum telluride alloy obtained by keeping at 500 °C is one-dimensional chain-shaped. In addition, when the holding temperature increases, the coverage of the sample decreases significantly, indicating that the bonding ability of Mo and Te in the molybdenum telluride alloy is weak. Figure 2 a to Figure 2 c are respectively small-scale scanning tunneling microscope images of the molybdenum telluride alloy samples obtained by keeping at 150 °C, 250 °C, and 500 °C. Combining the large-scale, small-scale, and high-resolution scanning tunneling microscope images indicates that although the molybdenum telluride alloys obtained at 150 °C and 250 °C are both sheet-shaped or island-shaped, the high-resolution images show that their structures are striped patterns (150 °C) and a large number of triangular patterns with different sizes (250 °C) respectively, and the bright spots between the stripes are staggered. Combining the literature, these two structures are 1T'-phase MoTe2 (hereinafter referred to as 1T'-MoTe2) and 2H-phase MoTe2 (hereinafter referred to as 2H-MoTe2) respectively. For the one-dimensional nanochain structure obtained at 500 °C, its high-resolution image shows that the atomically resolved morphology shows a chain-like structure with two columns distributed side by side, and combining the literature shows that it is the Mo6Te6 structure. These experimental results show that by controlling the temperature of the substrate during deposition, molybdenum telluride alloys with different phases are achieved.

[0050] 4. Regulating the annealing temperature of 2H-MoTe2 to obtain molybdenum telluride alloys with different phases and their structural characterization

[0051] After obtaining 2H-MoTe2, the sample was annealed at 280 °C, 350 °C, 400 °C, and 450 °C respectively, and the annealing time was 1 - 3 h. Figure 1 d to Figure 1 g are respectively large-scale scanning tunneling microscope images of the molybdenum telluride alloy obtained after annealing at 280 °C, 350 °C, 400 °C, and 450 °C. The samples at the four annealing temperatures are all in the morphology of molecular sheets / islands. Figure 3 a to Figure 3Figures c are small-size, high-resolution scanning tunneling microscope images of molybdenum telluride alloys obtained after annealing at 350 °C, 400 °C, and 450 °C, respectively. Among them, Figure 3 a shows that there are some triangular regions with a wagon-wheel shape evenly distributed within an island, indicating that the disordered and differently sized mirror-symmetric twin boundaries (280 °C) begin to gradually transform into ordered mirror-symmetric twin boundaries. Figure 3 b shows that after annealing at 400 °C, the atomically resolved structure is a superstructure composed of a large number of dense "wagon-wheel" shapes, and the images of the left and right regions of this superstructure are mirror-symmetric, indicating its characteristics of mirror twin boundaries. To further describe this newly discovered "wagon-wheel" MTB superstructure, Figure 4 Figure is the high-resolution scanning tunneling microscope image obtained for this sample at different bias voltages, and the morphologies obtained at different scanning bias voltages are different, indicating that there are certain differences in the spatial distribution of the electronic states of this structure at different energies. After further annealing (450 °C, Figure 3 c), hexagonal Moiré superstructures ( Figure 1 the regions marked by circles in f) begin to appear in this "wagon-wheel" superstructure with a mirror distribution, indicating that with the increase of the annealing temperature, a new molybdenum telluride alloy phase (Mo5Te8) appears.

[0052] Table 1 Two-dimensional molybdenum telluride alloys prepared from 2H-MoTe2 thin films at different annealing temperatures

[0053]

[0054] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing two-dimensional molybdenum tellurium alloy under ultra-high vacuum, characterized in that, Including: Under ultra-high vacuum, a 2H-phase MoTe2 thin film is prepared by molecular beam epitaxy; The preparation of the 2H-phase MoTe2 thin film by molecular beam epitaxy includes: co-evaporating and depositing Mo atoms and Te atoms onto a substrate at 250 ± 5 °C according to a deposition rate ratio of Mo to Te of 1:25 to 35, and then keeping the temperature to obtain the 2H-phase MoTe2 thin film; a bilayer graphene is provided on the substrate; the ultra-high vacuum is a vacuum environment with a pressure in the range of 10 -6 ~10 -8 Pa. The 2H-phase MoTe2 thin film is annealed at 400°C to 450°C under ultra-high vacuum to bond Mo and Te chemically, obtaining a two-dimensional molybdenum tellurium alloy with a mirror-symmetric twin boundary superlattice structure having an ordered distribution and uniform size.

2. The method for preparing two-dimensional molybdenum telluride alloy under ultra-high vacuum according to claim 1, characterized in that: The annealing time is 1 to 3 hours.

3. The method for preparing a two-dimensional molybdenum tellurium alloy under ultra-high vacuum according to claim 1, wherein: Mo and Te are deposited on the (0001) plane of bilayer graphene.

4. The method for preparing two-dimensional molybdenum tellurium alloy under ultra-high vacuum according to claim 3, characterized in that: The substrate is a 6H-SiC substrate, and the bilayer graphene disposed thereon is generated by direct current heating of the 6H-SiC substrate.

5. The method for preparing a two-dimensional molybdenum tellurium alloy under ultra-high vacuum according to claim 1, characterized in that: The co-evaporation deposition of Mo atoms and Te atoms onto the substrate at 250 ± 5°C includes: evaporating Te atoms through a molecular evaporation source and evaporating Mo atoms through a metal evaporation source.

6. The method for preparing two-dimensional molybdenum tellurium alloy under ultra-high vacuum according to claim 1, characterized in that: The co-evaporation deposition time is 15 to 25 minutes.

7. The method for preparing a two-dimensional molybdenum tellurium alloy under ultra-high vacuum according to claim 1, characterized in that: The heat preservation time is not less than 10 minutes, and the Te atomic beam current is maintained constant during the heat preservation process.

8. A two-dimensional molybdenum tellurium alloy, characterized in that: Prepared by the method for preparing a two-dimensional molybdenum tellurium alloy under ultra-high vacuum according to any one of claims 1 to 7.

9. Application of the two-dimensional molybdenum tellurium alloy according to claim 8 in the semiconductor field.

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