A method for fabricating large-area Te-MX2 vertical heterojunctions with enhanced nonlinear optical properties

Abstract

The present invention discloses a method for preparing a large-area Te-MX2 vertical heterojunction nanostructure with enhanced nonlinear optical properties. A two-step growth method is adopted, and by adjusting the confinement height, growth time and MX2 treatment process, the size, orientation and density of one-dimensional tellurium nanowires grown on the two-dimensional MX2 surface can be effectively controlled. Tellurium powder is placed on an alumina boat and placed in a heating temperature zone. Then a glass substrate is used to cover the glass substrate with a single layer of MX2 to form a confined space, and the glass substrate is placed downstream of the heating temperature zone. One-dimensional Te nanowires are epitaxially grown on the surface of the single-layer two-dimensional MX2 using low-pressure vapor phase epitaxial growth technology to form a Te-MX2 vertical heterojunction. The Te-MX2 vertical heterojunction exhibits excellent nonlinear optical absorption characteristics, the saturation absorption characteristics are greatly increased, and the modulation depth is increased to 28.1%. It has broad application prospects in the fields of saturable absorbers and optical modulators.

Description

Technical Field

[0001] The present invention relates to materials and nonlinear optics, and in particular to a method for preparing a large-area Te-MX2 vertical heterojunction with enhanced nonlinear optical properties. Background Art

[0002] Tellurium is an element of Group VI A (oxygen family) in the fifth period. Among all non-metallic elements, it has the strongest metallic properties and has good electrical and thermal conductivity. Tellurium is a narrow-bandgap p-type semiconductor material with a bandgap of approximately 0.35 eV. Tellurium single crystal material has a unique one-dimensional van der Waals structure, and the molecular chains are connected by van der Waals forces. Previous theories and experiments have shown that it has excellent ferroelectric, piezoelectric, thermoelectric, photoelectric and other physical properties, and has shown great application potential in photodetectors, gas sensors, field-effect transistors, piezoelectric devices, optical modulators, etc. Studies have found that tellurium nanostructures have excellent nonlinear optical response characteristics, which makes it one of the excellent optical materials. Te has a high effective broadband saturation absorption rate, and Te can be used as a saturable absorber to manufacture photonic devices. Te has broad application prospects in the fields of passive Q-switches, mode lockers, optical switches or optical modulators. Therefore, it is particularly important to prepare high-quality tellurium nanomaterials with excellent saturation absorption characteristics.

[0003] To prepare high-quality tellurium nanomaterials with excellent saturable absorption properties, researchers have used liquid-phase exfoliation to produce a novel, few-layer, two-dimensional single-element material, tellurene, which exhibits excellent properties as a saturable absorber. However, this method has several drawbacks, including low tellurene concentrations and significant dispersity in size and number of layers. Te-MX2 heterojunction nanostructures hold promise for addressing these issues.

[0004] The construction of Te-MX2 heterojunction nanostructures is of great scientific significance, and the application of two-dimensional van der Waals heterojunctions in the construction of new devices has attracted great interest. Compared with traditional bonded heterostructures, the surface of two-dimensional layered materials lacks dangling bonds, allowing the growth of various materials to form van der Waals heterojunctions without the stringent requirements of lattice matching and processing compatibility. However, interface quality and production scalability remain major challenges. Summary of the Invention

[0005] To address the technical issues of insufficient interface quality and production scalability in existing Te-MX2 heterojunction nanostructures, the present invention provides a method for preparing large-area Te-MX2 vertical heterojunctions with enhanced nonlinear optical properties. The method, wherein M is Mo or W and X is S or Se, allows for controllable preparation of Te-MX2 heterojunction nanostructures via chemical / physical vapor deposition. This method for preparing van der Waals heterojunctions using vapor phase epitaxial growth exhibits strong interfacial coupling and relatively high controllability and flexibility. By adjusting growth parameters such as temperature, precursors, substrate, and carrier gas, high-quality van der Waals heterojunctions and wafer-scale samples thereof can be controllably grown. The prepared Te-MX2 heterojunction nanostructures significantly enhance the nonlinear saturation absorption performance of the samples, offer significant process flexibility, repeatability, and controllability, and are suitable for industrial production. The resulting Te-MX2 heterojunction nanostructures exhibit excellent performance in optoelectronics, nonlinear optics, and other fields. Furthermore, the Te-MX2 heterojunction nanostructures are stable in air, providing an ideal experimental platform for studying the optical and electrical properties of two-dimensional van der Waals heterojunction materials.

[0006] To achieve the above object, the present invention provides a method for preparing a large-area Te-MX2 vertical heterojunction with enhanced nonlinear optical properties, wherein M is Mo or W and X is S or Se, comprising the following steps:

[0007] (1) Prepare a glass substrate with MX2, place graphite spacers on both sides of the substrate, and place another clean glass sheet on the glass substrate with MX2 in a "face-to-face" manner to form a micro-reaction chamber. The spatial height of the reaction chamber is controlled by controlling the height of the graphite spacers. Then, the entire micro-reaction chamber is placed at the downstream end of the tube furnace 20-24 cm away from the central heating temperature zone;

[0008] (2) Place tellurium powder in an alumina boat and place it in the central heating zone;

[0009] (3) purging the reaction chamber of the tube furnace by introducing argon gas for 15-30 minutes;

[0010] (4) After cleaning, the vacuum pump is turned on, argon is introduced as a carrier gas, and the temperature of the tube furnace is increased to heat the temperature zone where the tellurium powder is located to 280-300°C. The growth time is set to 15-25 minutes to grow a large area of ​​Te-MX2 vertical heterojunction nanostructure;

[0011] (5) After the growth is completed, the temperature naturally drops to room temperature, and the vacuum pump and argon are turned off to obtain a large-area Te-MX2 heterojunction nanostructure. The area of ​​the obtained Te-MX2 heterojunction nanofilm can be as high as 4*4cm 2 .

[0012] Furthermore, in step (1), the graphite pad controls the distance between the clean glass sheet and the glass substrate with MX2 to be 1-3 mm; the graphite sheet is used as the substrate for placing the entire micro-reaction chamber to adjust the position of the micro-reaction chamber in the tube furnace.

[0013] Furthermore, the glass substrate with MX2 is a glass substrate with a single layer of large-area MX2, and the preparation method includes the following steps:

[0014] 1) Place the metal molybdenum foil in the center of the heating zone of a tube furnace, increase the temperature to 470-490°C, and oxidize it in an air atmosphere to obtain molybdenum oxide foil; or place the metal tungsten foil in the center of the heating zone of a tube furnace, increase the temperature to 580-620°C, and oxidize it in an air atmosphere to obtain tungsten oxide foil;

[0015] 2) Cover a glass substrate with molybdenum oxide foil or tungsten oxide foil and place it in the heating center of a high-temperature tube furnace. Place an alumina boat filled with sulfur powder or selenium powder and the growth substrate in the order of airflow from upstream to downstream. Purge the reaction chamber of the high-temperature tube furnace by introducing argon gas.

[0016] 3) Raise the temperature of the tube furnace to heat the sulfur powder to 300-320°C, the selenium powder to 360-400°C, the molybdenum oxide foil to 750°C, or the tungsten oxide foil to 780-800°C. The growth time is 10 minutes. After the growth is completed, the temperature naturally drops to room temperature and the argon gas is turned off to obtain a glass substrate with a single layer of large-area MX2.

[0017] Furthermore, in step (4), the carrier gas is argon gas at 30-50 sccm.

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

[0019] 1) The method of preparing van der Waals heterojunctions by vapor phase epitaxial growth shows strong interfacial coupling and has relatively high controllability and flexibility;

[0020] 2) The experiment does not require a catalyst, thus avoiding the introduction of impurity ions into the product. Furthermore, there are no impurity products on the growth substrate, which will not affect the subsequent device preparation process and performance.

[0021] 3) Using ordinary glass as the growth substrate offers significant advantages in terms of experimental cost. The use of chemical / physical vapor deposition methods enables the universal preparation of large-area Te-MX2 heterojunction nanostructures.

[0022] 4) The Te-MX2 heterojunction nanostructure samples prepared on transparent glass substrates can be directly characterized by atomic force microscopy and scanning electron microscopy, thereby enabling the exploration of their micromorphology and electronic structure;

[0023] 5) Large-area Te-MX2 heterojunction nanostructured devices can be directly integrated on glass substrates for systematic exploration of nonlinear optics and photodetectors, avoiding the introduction of impurity residues due to sample transfer.

[0024] In summary, the present invention utilizes low-pressure vapor phase epitaxial growth technology to epitaxially grow one-dimensional Te nanowires on a single-layer two-dimensional MX2 surface, forming a Te-MX2 vertical heterojunction. This Te-MX2 vertical heterojunction exhibits excellent nonlinear optical absorption properties, significantly enhancing saturation absorption characteristics and increasing the modulation depth to over 28.1%. This has broad application prospects in the fields of saturable absorbers and optical modulators, and is amenable to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Optical microscope characterization results of MoS2 nanosheets prepared by the chemical vapor deposition method corresponding to Example 1;

[0026] Figure 2 Raman characterization results of MoS2 nanosheets prepared by the chemical vapor deposition method corresponding to Example 1;

[0027] Figure 3 These are the atomic force microscopy characterization results of MoS2 nanosheets prepared by the chemical vapor deposition method corresponding to Example 1.

[0028] Figure 4 Optical microscopy characterization results of the Te-MoS2 heterojunction nanostructure prepared by the low-pressure physical vapor deposition method corresponding to Example 2;

[0029] Figure 5 The Raman characterization results of the Te-MoS2 heterojunction nanostructure prepared by the low-pressure physical vapor deposition method corresponding to Example 2;

[0030] Figure 6 These are the atomic force microscopy characterization results of the Te-MoS2 heterojunction nanostructure prepared by the low-pressure physical vapor deposition method corresponding to Example 2.

[0031] Figure 7 Optical microscopy characterization results of large-area Te-MoS2 heterojunction nanostructures prepared by low-pressure physical vapor deposition method corresponding to Example 2;

[0032] Figure 8 Optical microscopy characterization results of large-area Te-MoS2 heterojunction nanostructures prepared by the chemical vapor deposition method corresponding to Example 2;

[0033] Figure 9The results of the open hole z-scan test on MoS2, Te, and Te-MoS2 heterojunction nanostructure samples corresponding to Example 2;

[0034] Figure 10 These are the results of the z-scan test of the MoS2-Te heterojunction nanostructure sample at different laser powers corresponding to Example 2.

[0035] Figure 11 Optical microscopy characterization results of the Te-WS2 heterojunction nanostructure prepared by low-pressure physical vapor deposition method corresponding to Example 3;

[0036] Figure 12 These are the Raman characterization results of the Te-WS2 heterojunction nanostructure prepared by the low-pressure physical vapor deposition method corresponding to Example 3.

[0037] Figure 13 Optical microscopy characterization results of the Te-MoSe2 heterojunction nanostructure prepared by low-pressure physical vapor deposition method corresponding to Example 4;

[0038] Figure 14 These are the Raman characterization results of the Te-MoSe2 heterojunction nanostructure prepared by the low-pressure physical vapor deposition method corresponding to Example 4.

[0039] Figure 15 Optical microscopy characterization results of the Te-WSe2 heterojunction nanostructure prepared by low-pressure physical vapor deposition method corresponding to Example 5;

[0040] Figure 16 These are the Raman characterization results of the Te-WSe2 heterojunction nanostructure prepared by the low-pressure physical vapor deposition method corresponding to Example 5.

[0041] Figure 17 The results of the open hole z-scan test on the WS2, Te, and Te-WS2 heterojunction nanostructure samples corresponding to Example 2;

[0042] Figure 18 The results of the open hole z-scan test on MoSe2, Te, and Te-MoSe2 heterojunction nanostructure samples corresponding to Example 2;

[0043] Figure 19 These are the results of the open hole z-scan test on the MoSe2, Te, and Te-MoSe2 heterojunction nanostructure samples corresponding to Example 2. DETAILED DESCRIPTION

[0044] Unless otherwise stated, any feature disclosed in this specification may be replaced by an equivalent or similar alternative feature. Unless otherwise stated, each feature is merely an example of a set of equivalent or similar features. The description is intended solely to facilitate understanding of the present invention and should not be construed as a limitation of the present invention.

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] Example 1

[0047] A method for preparing a large-area Te-MoS2 vertical heterojunction comprises the following steps:

[0048] 1) Place a clean glass substrate on the glass substrate with a large area of ​​MoS2, control the height between the two by placing a graphite spacer to form a confined space, and place it at the downstream end of the tube furnace 22 cm away from the central heating zone;

[0049] The preparation process of a glass substrate with a large area of ​​MoS2 is as follows: (1) placing a metal molybdenum foil in the center of the heating zone of a tube furnace, raising the temperature to 480°C, and oxidizing it in an air atmosphere to obtain a molybdenum trioxide foil; (2) covering the oxidized molybdenum foil on the glass substrate and placing it in the heating center of a high-temperature tube furnace, and placing an alumina boat filled with sulfur powder and a growth substrate in the order of air flow from upstream to downstream, and introducing argon gas into the reaction chamber of the high-temperature tube furnace for cleaning; (3) raising the temperature of the tube furnace to heat the temperature of the sulfur powder to 300°C and the temperature of the molybdenum oxide foil to 750°C, and growing the molybdenum disulfide nanostructure for 10 minutes. After the growth is completed, the temperature naturally drops to room temperature, and the argon gas is turned off to obtain a glass substrate with a large area of ​​single-layer molybdenum disulfide nanosheets;

[0050] 2) Place the tellurium powder in an alumina boat and place it in the central heating zone;

[0051] 3) Purge the reaction chamber of the tube furnace by introducing argon gas for 20 minutes;

[0052] 4) After cleaning, the vacuum pump was turned on, argon was introduced as a carrier gas, and the temperature of the tube furnace was increased to 300°C in the temperature zone where the tellurium powder was located. The growth time was set to 20 minutes to grow a large-area Te-MoS2 vertical heterojunction nanostructure.

[0053] 5) After the growth is completed, the temperature naturally drops to room temperature, and the vacuum pump and argon gas are turned off to obtain a large-area Te-MoS2 heterojunction nanostructure.

[0054] The MoS2 nanosheet samples were subjected to optical microscopy, Raman microscopy, and atomic force microscopy. Figures 1 to 3As shown. The optical microscope characterization data shows that the MoS2 nanosheets grow uniformly. The Raman characterization data shows that the sample has a uniform growth at 383 cm -1 and 404cm -1 There are obvious characteristic peaks, corresponding to molybdenum disulfide E 2g 1 and A 1g Two characteristic peaks. It can be seen from the atomic force microscopy data that the thickness of molybdenum disulfide is about 0.88nm. The obtained Te-MoS2 heterojunction nanostructure sample was subjected to optical microscopy, Raman and atomic force microscopy, and the results are as follows Figures 4-6 As shown in the Raman characterization data, the sample has a -1 、118cm -1 and 138cm -1 The obvious characteristic peaks near the 1 , A1 and E 2 Three characteristic peaks. Atomic force microscopy data shows that the thickness of tellurium is uniformly around 10nm.

[0055] Example 2

[0056] When preparing the Te-MoS2 heterojunction nanostructure in Example 1, the vacuum pump is turned on, and the vapor deposition method under low pressure environment can obtain dense and orderly growth of tellurium nanowires on molybdenum disulfide nanosheets, such as Figure 7 As shown; we can also prepare large-area Te-MoS2 heterojunction nanostructures, such as Figure 8 As shown, 4cm*4cm large area MoS2 film, large area Te-MoS2 heterojunction nanostructure Figure 9 We conducted open hole z-scan tests on MoS2, Te, and Te-MoS2 heterojunction nanostructure samples, as shown in Figure 2. Figure 10 As shown in the results, it can be seen that the constructed Te-MoS2 heterojunction nanostructure improves the saturation absorption characteristics of Te; Figure 11 As shown in Figure 3, the transmittance of the Te-MoS2 heterojunction nanostructure is improved as the laser power decreases.

[0057] Example 3

[0058] The sample with MoS2 nanosheets in Example 2 was replaced with a sample with WS2 nanosheets (the preparation method was the same as that in Example 1, except that the temperature of the sulfur powder was heated to 320°C and the temperature of the tungsten oxide foil was heated to 780°C, and other preparation conditions remained unchanged), and a Te-WS2 heterojunction nanostructure was obtained, such as Figure 12 shown.

[0059] Example 4

[0060] The sample with MoS2 nanosheets in Example 2 was replaced with a sample with MoSe2 nanosheets (the preparation method was the same as in Example 1, except that the temperature of the selenium powder was heated to 300°C and the temperature of the molybdenum oxide foil was heated to 750°C). Other preparation conditions remained unchanged, and a Te-MoSe2 heterojunction nanostructure was obtained, such as Figure 14 shown.

[0061] Example 5

[0062] The sample with MoS2 nanosheets in Example 3 was replaced with a sample with WSe2 nanosheets (the preparation method is the same as that in Example 1, except that the temperature of selenium powder is heated to 320°C and the temperature of tungsten oxide foil is heated to 800°C), and a Te-WSe2 heterojunction nanostructure can be obtained, such as Figure 16 shown.

[0063] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and are intended to be encompassed by the claims of the present invention.

Claims

1. A method for preparing a large-area Te-MX2 vertical heterojunction with enhanced nonlinear optical properties, wherein: M is Mo or W, X is S or Se, and the method comprises the following steps: (1) Prepare a glass substrate with MX2, place graphite pads on both sides of the substrate, and place another clean glass sheet on the glass substrate with MX2 in a "face-to-face" manner to form a micro-reaction chamber. The spatial height of the reaction chamber is controlled by controlling the height of the graphite pads. Then, place the entire micro-reaction chamber at the downstream end of the tube furnace 20-24 cm away from the central heating temperature zone; (2) Place tellurium powder in an alumina boat and place it in the central heating zone; (3) Introduce argon gas into the reaction chamber of the tube furnace for 15-30 minutes for cleaning; (4) After cleaning, turn on the vacuum pump, introduce argon as a carrier gas, increase the temperature of the tube furnace, heat the temperature of the tellurium powder temperature zone to 280-300 ° C, set the growth time to 15-25 minutes, and grow a large area of ​​Te-MX2 vertical heterojunction nanostructure; (5) After the growth is completed, the temperature naturally drops to room temperature, and the vacuum pump and argon gas are turned off to obtain a large-area Te-MX2 heterojunction nanostructure; In step (1), the graphite pad controls the distance between the clean glass sheet and the glass substrate with MX2 to be 1-3 mm; In step (1), a graphite sheet is used as a substrate for placing the entire micro-reaction chamber to adjust the position of the micro-reaction chamber in the tube furnace; The glass substrate with MX2 is a glass substrate with a single layer of large-area MX2, and the preparation method includes the following steps: 1) Place the molybdenum foil in the center of the heating zone of a tube furnace, increase the temperature to 470-490°C, and oxidize it in air to obtain molybdenum oxide foil; or place the tungsten foil in the center of the heating zone of a tube furnace, increase the temperature to 580-620°C, and oxidize it in air to obtain tungsten oxide foil; 2) Cover a glass substrate with molybdenum oxide foil or tungsten oxide foil and place it in the heating center of a high-temperature tube furnace. Place an alumina boat filled with sulfur powder or selenium powder and the growth substrate in the order of airflow from upstream to downstream. Purge the reaction chamber of the high-temperature tube furnace by introducing argon gas. 3) Raise the temperature of the tube furnace to heat the sulfur powder to 300-320°C, the selenium powder to 360-400°C, the molybdenum oxide foil to 750°C, or the tungsten oxide foil to 780-800°C. The growth time is 10 minutes. After the growth is completed, the temperature naturally drops to room temperature and the argon gas is turned off to obtain a glass substrate with a single layer of large-area MX2.

2. The method for preparing a large-area Te-MX2 vertical heterojunction with enhanced nonlinear optical properties according to claim 1, characterized in that: In step (4), the carrier gas is argon at 30-50 sccm.

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