Method for adjusting optical performance of two-dimensional material
By annealing the composite substrate, the Van der Waals gap between the two-dimensional material and the target substrate is adjusted, and the problems of material structure failure, difficulty in regulation and low stability in the prior art are solved, and the optical performance of two-dimensional materials is improved.
Patent Information
- Application Number
- CN202510191284.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-20
- Publication Date
- 2025-05-16
AI Technical Summary
The existing methods for adjusting the photoelectric characteristics of two-dimensional materials have problems such as structural damage, difficulty in precise regulation and low stability.
By annealing the composite substrate at 260°C to 320°C for at least 6 hours in an inert atmosphere, the van der Waals gap between the two-dimensional material and the target substrate is reduced, thereby regulating the electronic band gap and exciton binding energy of the two-dimensional material.
It realizes precise control of the optical properties of two-dimensional materials, improves the optical properties of the materials, and is easy to operate, has strong universality and has little damage to the materials.
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Figure CN120015611A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of two-dimensional materials, and in particular, to a method for adjusting the optical properties of two-dimensional materials. Background Art
[0002] Emerging two-dimensional (2D) materials have attracted much attention due to their unique electronic band structures and tunable optoelectronic properties. Excitons are bound states formed by the mutual attraction of an electron and a hole in a material by the electrostatic Coulomb interaction. Due to the direct band gap and efficient light-matter coupling of two-dimensional materials in the monolayer limit, as well as charge confinement and reduced dielectric screening, the optical properties of semiconductor two-dimensional materials are mainly affected by the exciton effect.
[0003] At present, the optoelectronic properties of two-dimensional materials are improved by adjusting the interlayer van der Waals (vdW) gap, which provides a unique and effective method for modulating the interlayer coupling strength, changing the electronic band structure, and creating new artificial materials. In existing technologies, the van der Waals gap is mainly adjusted through strategies such as interlayer chemical intercalation, high-pressure physical compression, and ultrasonic treatment. For example, inserting a layer of water molecules into a double-layer MoS2 can change its interlayer van der Waals gap, making the double-layer MoS2 an excellent gap-dependent diode. [1] Applying pressure to the WSe2 / MoSe2 heterojunction through a diamond anvil cell can change the interlayer coupling between the two materials, leading to changes in the electronic band gap, exciton energy and species. [2] . However, these technologies have some shortcomings. Chemical intercalation may cause irreversible damage to the material structure or introduce impurities, affecting the intrinsic properties of the material; high-pressure physical compression requires extreme conditions, which is difficult to achieve precise control and may cause phase change or mechanical damage to the material; although ultrasonic treatment is easy to operate, it can easily lead to uneven peeling between material layers or defects, reducing the stability of the material and device performance. Summary of the invention
[0004] The present application provides a method for adjusting the optical properties of two-dimensional materials. The method is not only simple to operate, has strong universality, and causes little damage to the two-dimensional materials, but can also change the van der Waals gap between the two-dimensional material and the target substrate to accurately control the electronic band gap and exciton binding energy of the two-dimensional material, thereby improving the optical properties of the two-dimensional material.
[0005] The embodiment of the present application is implemented as follows:
[0006] In a first aspect, the present application example provides a method for adjusting the optical properties of a two-dimensional material, comprising:
[0007] obtaining a composite substrate, the composite substrate comprising a target substrate and a two-dimensional transition metal chalcogenide thin film transferred to a surface of the target substrate;
[0008] The composite substrate was annealed at 260° C.-320° C. for at least 6 h in an inert atmosphere.
[0009] In the method for adjusting the optical properties of two-dimensional materials provided in the present application, the van der Waals gap between the target substrate and the two-dimensional transition metal chalcogenide film on its surface can be effectively reduced by annealing the composite substrate, thereby accurately regulating the electronic band gap and exciton binding energy of the two-dimensional material, thereby improving the optical properties of the two-dimensional material. At the same time, the annealing method is simple to operate, has strong universality, and causes little damage to the material.
[0010] In some optional embodiments, the annealing time is 6 hours to 24 hours.
[0011] In some optional embodiments, the thickness of the two-dimensional transition metal chalcogenide film is 1-10 layers.
[0012] In some optional embodiments, the thickness of the two-dimensional transition metal chalcogenide thin film is a monolayer.
[0013] In some optional embodiments, the two-dimensional transition metal chalcogenide film includes at least one of WS2, WSe2, WTe2, MoS2, MoSe2 and MoTe2.
[0014] In some optional embodiments, the two-dimensional transition metal chalcogenide thin film is a single layer WS2.
[0015] In some optional embodiments, annealing is performed under low pressure or normal pressure, and low pressure includes 100Pa-300Pa.
[0016] In some optional embodiments, the surface material of the target substrate in contact with the two-dimensional transition metal chalcogenide film is silicon dioxide, sapphire or boron nitride.
[0017] In some optional embodiments, the two-dimensional transition metal chalcogenide thin film is obtained by a mechanical exfoliation method.
[0018] In some optional embodiments, annealing is performed in a furnace chamber of a tube furnace, the furnace chamber includes a first temperature zone, a second temperature zone, and a third temperature zone sequentially arranged along a gas flow direction, and the composite substrate is placed in the second temperature zone;
[0019] The temperature difference between any two of the first temperature zone, the second temperature zone and the third temperature zone is 0-5°C. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.
[0021] Figure 1 is a schematic diagram of placing a composite substrate in a furnace chamber;
[0022] Figure 2 Schematic diagram of the change of the van der Waals gap between the single-layer WS2 and the SiO / Si target substrate in Example 1 and Comparative Example 1;
[0023] Figure 3 Photoluminescence spectra of the monolayer WS2 transferred to SiO / Si target substrate before and after annealing at room temperature;
[0024] Figure 4 Schematic diagram of the optical response and exciton Riboud state of two-dimensional materials;
[0025] Figure 5 Schematic diagram of the second derivative of the differential reflectance spectrum of a single layer of WS2 transferred to a SiO / Si target substrate before and after annealing. DETAILED DESCRIPTION
[0026] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.
[0027] At present, the optoelectronic properties of two-dimensional materials are mainly improved by adjusting the changes in the interlayer van der Waals (vdW) gap. That is, the main focus is on the regulation of the interlayer van der Waals gap between materials on the exciton behavior. The inventors found during the research process that for the two-dimensional material transferred to the target substrate, the exciton behavior of the two-dimensional material can also be regulated by adjusting the van der Waals gap between the two-dimensional material and the target substrate.
[0028] In view of this, this application is hereby filed.
[0029] The following is a specific description of a method for adjusting the optical properties of a two-dimensional material according to an embodiment of the present application:
[0030] The present application provides a method for adjusting the optical properties of a two-dimensional material, comprising:
[0031] obtaining a composite substrate, the composite substrate comprising a target substrate and a two-dimensional transition metal chalcogenide thin film transferred to a surface of the target substrate;
[0032] The composite substrate was annealed at 260° C.-320° C. for at least 6 h in an inert atmosphere.
[0033] It can be understood that the two-dimensional transition metal sulfide compound film transferred to the surface of the target substrate means that the two-dimensional transition metal sulfide compound film is not directly grown on the surface of the target substrate, but after the two-dimensional transition metal sulfide compound film is obtained, the two-dimensional transition metal sulfide compound film is transferred to the surface of the target substrate by transfer. The transfer method can be directly referred to the relevant technology and is not limited here.
[0034] The inert atmosphere includes but is not limited to at least one of argon and nitrogen. By annealing in an inert atmosphere, impurities are avoided during annealing.
[0035] If the annealing temperature is too low, the improvement effect is not obvious or there is basically no improvement. If the annealing temperature is too high, the two-dimensional transition metal chalcogenide film will decompose. Therefore, in this application, by annealing the composite substrate at 260℃-320℃ for at least 6h, the van der Waals gap between the target substrate and the two-dimensional transition metal chalcogenide film on its surface can be effectively reduced. The possible reason is that: during the transfer of the two-dimensional transition metal chalcogenide film, the surface of the film may adsorb impurities or wrinkles, causing stress or doping, thereby affecting the performance and stability. High-temperature annealing can effectively remove impurities and eliminate stress, so that the material reaches a more stable state, thereby improving the van der Waals gap between the target substrate and the two-dimensional transition metal chalcogenide film, while avoiding the complexity, equipment dependence and possible material damage of methods such as chemical doping, strain engineering and insertion layer.
[0036] Illustratively, the annealing temperature is any one of 260°C, 265°C, 270°C, 275°C, 280°C, 285°C, 290°C, 295°C, 300°C, 305°C, 310°C, 315°C, 320°C or between any two values.
[0037] In the method for regulating the optical properties of two-dimensional materials provided in the present application, the van der Waals gap between the target substrate and the two-dimensional transition metal chalcogenide film on its surface is effectively reduced by annealing the composite substrate, thereby precisely regulating the electronic band gap and exciton binding energy of the two-dimensional material and improving the optical properties of the two-dimensional material. At the same time, the annealing method is simple to operate, has strong universality, and causes little damage to the material.
[0038] In some optional embodiments, the annealing time is 6h-24h.
[0039] Illustratively, the annealing time is any value among 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, or between any two values.
[0040] By controlling the annealing time within the above range, the van der Waals gap between the target substrate and the two-dimensional transition metal chalcogenide film on its surface can be effectively reduced, while reducing energy consumption.
[0041] In some optional embodiments, the thickness of the two-dimensional transition metal chalcogenide film is 1-10 layers.
[0042] Exemplarily, the thickness of the two-dimensional transition metal chalcogenide film is any value among 1 layer, 2 layers, 3 layers, 4 layers, 5 layers, 6 layers, 7 layers, 8 layers, 9 layers, and 10 layers.
[0043] In some optional embodiments, the thickness of the two-dimensional transition metal chalcogenide film is a monolayer.
[0044] That is, the thickness of the two-dimensional transition metal chalcogenide film is 1 layer.
[0045] In some optional embodiments, the two-dimensional transition metal chalcogenide film includes at least one of WS2, WSe2, WTe2, MoS2, MoSe2 and MoTe2.
[0046] Exemplarily, the two-dimensional transition metal chalcogenide film is WS2, WSe2, WTe2, MoS2, MoSe2 or MoTe2.
[0047] In some optional embodiments, the two-dimensional transition metal chalcogenide film is a single layer WS2.
[0048] After annealing treatment, the van der Waals gap between the monolayer tungsten disulfide and the target substrate can be effectively reduced, so that most of the exciton electric field is distributed to the target substrate area, enhancing the dielectric shielding and the two-dimensional material-target substrate coupling strength, reducing the Coulomb attraction between electrons and holes, preventing the conversion of excitons to charged excitons (trions), and then accurately and effectively suppressing the formation of charged excitons (trions), thereby improving the stability of excitons and significantly enhancing the optical properties of monolayer WS2.
[0049] In some optional embodiments, annealing is performed under low pressure or normal pressure, and the low pressure includes 100Pa-300Pa.
[0050] Exemplarily, the low pressure is any value of 100 Pa, 150 Pa, 200 Pa, 250 Pa, 300 Pa or between any two values.
[0051] In some optional embodiments, the surface material of the target substrate in contact with the two-dimensional transition metal chalcogenide film is silicon dioxide, sapphire or boron nitride.
[0052] It can be understood that the surface of the target substrate in contact with the two-dimensional transition metal chalcogenide film is used as the target surface, and the overall material of the target substrate can be the same as the material of the target surface, for example, the target substrate is made of sapphire as a whole, or, the target substrate is a target surface and the material is different from that of the rest, for example, a Si / SiO2 target substrate, wherein the SiO2 layer is formed on the Si surface, and the two-dimensional transition metal chalcogenide film is transferred to the surface of the SiO2 layer of the Si / SiO2 target substrate.
[0053] The target substrate has a flat surface, which is beneficial to reducing the amount of wrinkles generated in the two-dimensional transition metal sulfide compound film after transfer.
[0054] It is understandable that before obtaining the composite substrate, a two-dimensional transition metal sulfide compound film needs to be obtained, wherein the preparation method of the two-dimensional transition metal sulfide compound film includes but is not limited to chemical vapor deposition, chemical intercalation, mechanical exfoliation and ball milling, etc. Usually, in order to transfer to a new target substrate after preparation, a two-dimensional transition metal sulfide compound film prepared by chemical intercalation or mechanical exfoliation can be selected.
[0055] In some optional embodiments, the two-dimensional transition metal chalcogenide thin film is obtained by a mechanical exfoliation method.
[0056] In some optional embodiments, annealing is performed in a furnace chamber of a tube furnace, the furnace chamber includes a first temperature zone, a second temperature zone, and a third temperature zone sequentially arranged along a gas flow direction, and the composite substrate is placed in the second temperature zone;
[0057] The temperature difference between any two of the first temperature zone, the second temperature zone and the third temperature zone is 0-5°C.
[0058] By controlling the temperature difference between any two temperature zones within the range of 0-5°C, the life of the tube furnace can be extended while achieving annealing.
[0059] Exemplarily, the temperature difference between any two of the first temperature zone, the second temperature zone and the third temperature zone is 0, that is, the temperatures of the first temperature zone, the second temperature zone and the third temperature zone remain the same.
[0060] It is understood that after the annealing is completed, the furnace is cooled while maintaining an inert atmosphere in the furnace chamber.
[0061] Optionally, the flow rate of the inert atmosphere can be set according to actual needs. For example, the flow rate of the inert gas is 200 sccm-500 sccm.
[0062] The following is a further detailed description of a method for adjusting the optical properties of a two-dimensional material in the present application in conjunction with embodiments.
[0063] Example 1
[0064] A method for adjusting the optical properties of a two-dimensional material comprises: transferring a single layer of WS2 obtained by a mechanical exfoliation method to a SiO / Si target substrate, wherein the single layer of WS2 contacts the SiO surface of the SiO / Si target substrate to obtain a composite substrate.
[0065] like Figure 1 As shown, the furnace chamber of the tubular furnace includes a first temperature zone, a second temperature zone and a third temperature zone which are sequentially arranged along the gas flow direction. The composite substrate is placed in the second temperature zone, 300 sccm argon gas is introduced, the pressure in the furnace chamber is controlled to be a low-pressure environment of about 200 Pa, and the temperatures in the first temperature zone, the second temperature zone and the third temperature zone are all controlled to be 290°C. Annealing is performed for 8 hours, and then the heating is stopped, the low-pressure argon atmosphere in the furnace chamber is maintained, and the sample is obtained while the furnace is cooled.
[0066] Comparative Example 1
[0067] The composite substrate obtained before annealing in Example 1 is used as Comparative Example 1.
[0068] Figure 2 Schematic diagram of the change of the van der Waals gap between the single-layer WS2 and the SiO / Si target substrate in Example 1 and Comparative Example 1. Figure 2 In parts a and b, the exciton electric field lines are represented by curves, and the balls with symbols represent holes and electrons, respectively. Figure 2 Parts a and b are schematic diagrams at different angles. Figure 2 It can be seen that after annealing, the van der Waals gap between the single-layer WS2 and its SiO / Si target substrate is reduced from an average height of ~6nm before annealing to ~3nm, which reduces the van der Waals gap between the single-layer WS2 and its SiO / Si target substrate. Figure 2 It can also be seen that before annealing, the material surface may adsorb impurities or wrinkles may appear, causing stress or doping, which in turn affects performance and stability. High-temperature annealing can effectively remove impurities, eliminate stress, and make the material reach a more stable state.
[0069] Figure 3 Photoluminescence spectra of a single layer of WS2 transferred to a SiO / Si target substrate before and after annealing at room temperature (25°C). Since the electric field lines of excitons in two-dimensional materials can extend outside the material and even into the target substrate, the size of this gap directly affects the local dielectric environment distribution in the nanoscale region around the material. Figure 3It can be seen that under low incident light power (200 μW at room temperature), the monolayer WS2 transferred to the SiO / Si target substrate can observe clear neutral exciton peaks (about 1.992 eV) and charged exciton (trion) peaks (about 1.956 eV) before annealing. After annealing, the photoluminescence (PL) peak of the charged exciton (trion) of the monolayer WS2 transferred to the SiO / Si target substrate was significantly suppressed, and under the same experimental conditions, the PL peak of the neutral exciton was blue-shifted by about 18 meV.
[0070] Similar to the hydrogen atom model, the electrons and holes in the excitons will produce a series of discrete exciton states (i.e., exciton Libode states) below the electron quasiparticle band gap (Eg) due to the Coulomb interaction. These quantized energy levels can be characterized by the principal quantum number n = 1, 2, 3, ..., such as Figure 4 shown.
[0071] Figure 4 Schematic diagram of the optical response and exciton Ribaud state of two-dimensional materials. B It can be defined as E g The energy difference between the first exciton level E1 and the B =E g In addition, the energy separation ΔE between the exciton ground state (n=1) and the first (n=2) and second (n=3) excited states is 12 , ΔE 13 With E B The following approximate relationship is also formed:
[0072] The differential reflectance spectra of the single-layer WS2 transferred to the SiO / Si target substrate before and after annealing were measured in a low temperature environment (83K), and the second-order derivative processing was performed to improve the characteristic peak resolution. Figure 5 , Figure 5 Schematic diagram of the second derivative of the differential reflectance spectrum of a single layer of WS2 transferred to a SiO / Si target substrate before and after annealing. Figure 5 A systematic change in the energy level spacing of n = 1 to 4 excitons can be observed: ΔE 12 From ~165meV to ~170meV, ΔE 34 From ~215meV to ~214meV.
[0073] The binding energy E of the neutral exciton can be calculated by the above formula: B From ~285meV to ~265meV, a decrease of ~20meV. Combined with E g =E B -E1, the electronic band gap E of the material can be further obtained gIt decreases from ~2.358 eV to ~2.344 eV (ΔEg≈-14 meV), which indicates that the reduction of vdW gap caused by annealing will promote band gap renormalization.
[0074] In summary, the van der Waals gap between the monolayer WS2 transferred to the SiO / Si target substrate is reduced from an average height of ~6nm to ~3nm before and after annealing, which reduces the van der Waals gap between the monolayer tungsten disulfide and the target substrate, so that most of the exciton electric field is distributed to the target substrate area, enhancing the dielectric shielding and the coupling strength between the two-dimensional material and the target substrate. After renormalization, the electronic band gap is red-shifted by ~14meV, and the exciton binding energy is reduced by ~20meV. The reduction in the exciton binding energy indicates that the Coulomb attraction between electrons and holes is weakened, which prevents the conversion of excitons to charged excitons (trions), and then accurately and effectively suppresses the formation of charged excitons (trions), thereby improving the stability of excitons and significantly enhancing the optical properties of the material.
[0075] This means that a simple and effective annealing method can significantly improve the optical properties of two-dimensional materials by suppressing the formation of charged excitons (trions) in a single-layer WS2, while avoiding the complexity, equipment dependence, and possible material damage of methods such as chemical doping, strain engineering, and insertion layers.
[0076] Example 2
[0077] The only difference between it and Example 1 is that the annealing temperature is 260° C. and the annealing time is 12 h.
[0078] After annealing, the van der Waals gap between the monolayer WS2 and its SiO / Si target substrate is reduced.
[0079] Example 3
[0080] The only difference between it and Example 1 is that the annealing temperature is 320° C. and the annealing time is 7 hours.
[0081] Example 4
[0082] The only difference between it and embodiment 1 is that WSe2 is used to replace WS.
[0083] After annealing, the van der Waals gap between the monolayer WSe2 and its SiO / Si target substrate is reduced.
[0084] In summary, the method for regulating the optical properties of two-dimensional materials provided in the present application is not only easy to operate, has strong universality, and causes little damage to the material, but can also change the van der Waals gap between the two-dimensional material and its target substrate to precisely regulate the electronic band gap and exciton binding energy of the two-dimensional material, thereby improving the optical properties of the two-dimensional material.
[0085] The above description is only a specific embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims
1. A method for adjusting the optical properties of a two-dimensional material, characterized in that: include: obtaining a composite substrate, the composite substrate comprising a target substrate and a two-dimensional transition metal chalcogenide thin film transferred to a surface of the target substrate; The composite substrate is annealed at 260° C.-320° C. for at least 6 hours in an inert atmosphere.
2. The method according to claim 1, characterized in that The annealing time is 6h-24h.
3. The method according to claim 1, characterized in that The thickness of the two-dimensional transition metal sulfide compound film is 1-10 layers.
4. The method according to claim 1, characterized in that The thickness of the two-dimensional transition metal sulfide compound film is a single layer.
5. The method according to claim 1, characterized in that The two-dimensional transition metal chalcogenide film includes at least one of WS2, WSe2, WTe2, MoS2, MoSe2 and MoTe2.
6. The method according to claim 1, characterized in that The two-dimensional transition metal chalcogenide film is a single layer WS2.
7. The method according to any one of claims 1 to 6, characterized in that: The annealing is performed under low pressure or normal pressure, wherein the low pressure includes 100Pa-300Pa.
8. The method according to any one of claims 1 to 6, characterized in that: The surface material of the target substrate in contact with the two-dimensional transition metal chalcogenide film is silicon dioxide, sapphire or boron nitride.
9. The method according to any one of claims 1 to 6, characterized in that: The two-dimensional transition metal sulfide compound film is obtained by a mechanical peeling method.
10. The method according to any one of claims 1 to 6, characterized in that: The annealing is performed in a furnace chamber of a tube furnace, the furnace chamber comprises a first temperature zone, a second temperature zone and a third temperature zone sequentially arranged along a gas flow direction, and the composite substrate is placed in the second temperature zone; The temperature difference between any two of the first temperature zone, the second temperature zone and the third temperature zone is 0-5°C.