Method for improving secondary harmonic signal strength of single-layer WSe2
By introducing defects into monolayer WSe2 material through heavy ion irradiation and controlling the defect concentration, the problem of weak second harmonic signal was solved, achieving efficient and permanent signal enhancement, which is suitable for the preparation of large-area uniform samples.
Patent Information
- Application Number
- CN202511855333.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-10
- Publication Date
- 2026-03-17
AI Technical Summary
Existing technologies struggle to effectively enhance the intensity of second harmonic signals in two-dimensional materials, especially monolayer WSe2 materials. Furthermore, existing methods suffer from complex fabrication processes, low susceptibility to loss, and poor low-power consumption.
By subjecting monolayer WSe2 material to heavy-ion irradiation, defects such as vacancies and lattice distortions are introduced. The defect concentration is controlled to enhance the second harmonic signal. Irradiation is performed using keV-level low-energy ions and GeV-level high-energy ions. The nonlinear optical properties of the material are then controlled by defect engineering.
It achieves a significant increase in the intensity of the second harmonic signal, up to more than 10 times, and the enhancement effect is permanent, requiring no continuous energy consumption. It combines high precision and low power consumption, and is suitable for the preparation of large-area uniform samples.
Smart Images
Figure CN121679962A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for improving the intensity of the second harmonic signal of a single-layer WSe2, belonging to the field of semiconductor technology. Background Technology
[0002] Nonlinear optics, a modern branch of optics that studies the interaction between light and matter, exhibits response characteristics that are nonlinearly dependent on the intensity of the incident light field, and holds significant application potential in fields such as photoelectric detection and imaging, information storage and processing, and communication. Second harmonic generation (SHG), a key nonlinear optical process, has seen its research focus shift in recent years towards the integration and miniaturization of on-chip photonic and optoelectronic devices. Two-dimensional TMDC materials possess large second-order nonlinear polarizability, atomic-level thickness, and excellent phase-matching characteristics; however, due to their extremely thin layered structure, the interaction length between light and matter is limited, resulting in low second harmonic conversion efficiency. Improving the SHG signal intensity of TMDC materials is crucial for advancing next-generation technologies such as nanophotonics, quantum optics, and valleytronic devices.
[0003] Researchers have employed various strategies to enhance the light-mass conversion (SHG) performance of two-dimensional materials. These include coupling a time-to-displacement (TMDC) circuit with an optical microcavity to leverage the Purcell effect and enhance light-matter interaction, thereby improving nonlinear conversion efficiency. However, this method suffers from poor tunability and complex fabrication processes. Inducing out-of-plane nonlinear responses through external electric fields faces challenges such as integration difficulties and the rapid loss of enhancement effects after the external field is removed. Constructing symmetry-broken structures, such as 3R phase stacks and helical arrangements, can achieve SHG enhancements of two orders of magnitude or more in materials like WSe2. However, these methods require extremely precise material preparation, demanding accurate control of the number of layers and stacking method, making it difficult to obtain large-area uniform samples and limiting their practical applications. Therefore, developing SHG enhancement and control methods that combine non-volatility, low power consumption, and high stability remains a key challenge in this field. Summary of the Invention
[0004] To address the aforementioned problems, the purpose of this invention is to provide a method for improving the intensity of the second harmonic signal of a single-layer WSe2 material, which can uniformly improve the SHG signal of a two-dimensional material with high control precision and high efficiency.
[0005] To achieve the above objectives, the present invention proposes the following technical solution: a method for improving the second harmonic signal intensity of a monolayer WSe2 material, comprising the following steps: preparing a monolayer WSe2 material; subjecting the monolayer WSe2 material to heavy ion irradiation to generate defects in the monolayer WSe2 material; and controlling the defect concentration in the monolayer WSe2 material by controlling the energy of the heavy ion irradiation to improve the second harmonic signal intensity of the monolayer WSe2 material.
[0006] Furthermore, the monolayer WSe2 material is prepared by mechanical exfoliation and is located on a silicon oxide substrate.
[0007] Furthermore, the defects include vacancy defects and lattice distortions, which enhance the degree of spatial inversion symmetry breaking of the monolayer WSe2 material by generating defects.
[0008] Furthermore, the heavy ion radiation is applicable to both keV-level low-energy ions and GeV-level high-energy heavy ions.
[0009] Furthermore, for keV-level low-energy ions, the ion fluence of heavy ion radiation is 5 × 10⁻⁶. 10 ions / cm 2 .
[0010] Furthermore, for GeV-level high-energy heavy ions, the ion fluence of heavy ion radiation is 1×10⁻⁶. 9 ions / cm 2 .
[0011] Furthermore, the low-energy ions are Xe ions, and the high-energy ions are Ta ions; both the low-energy ions and the high-energy ions are perpendicularly radiated onto the surface of the monolayer WSe2 material.
[0012] Furthermore, both the low-energy ions and high-energy ions need to pass through a scanning magnet to uniformly enhance the second harmonic signal intensity of the monolayer WSe2 material.
[0013] The technical solution of the present invention has at least the following technical effects or advantages: This invention overcomes the difficulties in material preparation using existing methods by introducing vacancy defects and micro-disordered regions into the material, while preserving the intrinsic photoelectric properties of the monolayer material, thus achieving intrinsic enhancement. Compared to external field manipulation methods, the defects caused by ion irradiation are permanent structural changes. Once formed, their enhancement effect persists without requiring continuous energy consumption, thus meeting the key requirements of non-volatility and low power consumption.
[0014] This invention possesses the potential for high-precision spatial selectivity control, enabling selective enhancement of SHG in specific regions on a chip through methods such as photomasks. It is compatible with existing microelectronics technologies and exhibits scalability and feasibility for high-volume, wafer-level sample production. Attached Figure Description
[0015] Figure 1 This is a TEM image of lattice distortion in WSe2 after low-energy Xe ion irradiation in one embodiment of the present invention; Figure 2 This is a TEM (a) and IFFT (b) image of WSe2 vacancy clusters after low-energy Xe ion irradiation in one embodiment of the present invention. Figure 3 This is the SHG single-point polarization response of WSe2 before and after irradiation with different fluences of 700 keVXe ions in one embodiment of the present invention; Figure 4 This is an embodiment of the present invention showing the SHG single-point polarization response of WSe2 before and after Ta ion irradiation with different fluences of 2.1 GeV; Figure 5 This is the maximum SHG polarization intensity change of WSe2 before and after Ta ion irradiation with different fluences of 2.1 GeV in one embodiment of the present invention; Figure 6 These are SHG surface scan signals of a monolayer WSe2 material before (a) and after (b) irradiation with 700 keV Xe ions in one embodiment of the present invention, with an irradiation flux of 5 × 10⁻⁶. 10 ions / cm 2 ; Figure 7 In one embodiment of the present invention, 1×10 9 ions / cm 2 SHG surface scan signals of monolayer WSe2 materials before (a) and after (b) irradiation of Ta ions; Figure 8 This is a Raman diagram of WSe2 before and after irradiation with different fluences of Ta ions (a) and Xe ions (b) in one embodiment of the present invention. Detailed Implementation
[0016] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention is described in detail through specific embodiments. However, it should be understood that the specific embodiments are provided only for a better understanding of the present invention and should not be construed as limiting the present invention. In the description of the present invention, it should be understood that the terminology used is for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0017] To address the issues of weak second harmonic generation (SHG) signals in existing technologies, the need for precise control of the number and stacking of WSe2 material layers in current signal enhancement methods, and the difficulty in obtaining large-area uniform samples, this invention proposes a method to improve the second harmonic signal intensity of monolayer WSe2. The method includes the following steps: preparing a monolayer WSe2 material; subjecting the monolayer WSe2 material to heavy ion irradiation to induce defects; and controlling the defect concentration in the monolayer WSe2 material by controlling the energy of the heavy ion irradiation to improve the second harmonic signal intensity. This method introduces vacancy defects and micro-disordered regions into the material while preserving the intrinsic photoelectric properties of the monolayer material, achieving intrinsic enhancement. Compared to external field manipulation methods, the defects caused by ion irradiation are permanent structural changes. Once formed, the enhancement effect persists without requiring continuous energy consumption, thus meeting the key requirements of non-volatility and low power consumption.
[0018] Example 1 Faced with the dual challenges of miniaturization and performance improvement, nonlinear optics is the core physical foundation of optoelectronic devices. The generation of second harmonics (SHG) is a particularly valuable benchmark for material symmetry and a key mechanism for applications such as compact lasers, frequency doublers, and on-chip quantum light sources. Two-dimensional transition metal chalcogenides (TMDCs) possess advantages such as high nonlinear polarizability and tunable bandgap, showing broad application prospects in integrated nonlinear optical devices. However, limited by the extremely thin thickness of a single atomic layer, the nonlinear conversion efficiency is low, hindering device development. This embodiment discloses a method for improving the second harmonic signal intensity of a single-layer WSe2, including the following steps: S1 is used to prepare monolayer WSe2 materials.
[0019] The monolayer WSe2 material was prepared by mechanical exfoliation and was located on a silicon oxide substrate.
[0020] S2 irradiates monolayer WSe2 material with heavy ions to create defects in the monolayer WSe2 material while maintaining the properties of the monolayer WSe2 material.
[0021] Heavy ion irradiation technology can introduce various types of defects into materials, such as vacancies, clusters, dislocations, and even disorder. By controlling the heavy ion irradiation flux, the defect concentration in the material can be effectively controlled, and defect engineering can be used to effectively regulate the optoelectronic properties of the material. Heavy ion irradiation is performed on a single-layer WSe2 material in a vacuum at room temperature.
[0022] Defects include vacancy site defects and lattice distortions, which enhance the degree of spatial inversion symmetry breaking in monolayer WSe2 materials by generating defects.
[0023] S3 controls the defect concentration in monolayer WSe2 material by controlling the energy of heavy ion radiation, thereby increasing the intensity of the second harmonic signal in monolayer WSe2 material.
[0024] Heavy ion radiation is suitable for keV-level low-energy ions and GeV-level high-energy heavy ions. For eV-level low-energy ions, the ion fluence of heavy ion radiation is 5 × 10⁻⁶. 10 ions / cm 2 For GeV-level high-energy heavy ions, the ion fluence from heavy ion radiation is 1 × 10⁻⁶. 9 ions / cm 2 .
[0025] The low-energy ions are Xe ions, and the high-energy ions are Ta ions; both low-energy and high-energy ions are perpendicularly irradiated onto the surface of the monolayer WSe2 material. In this embodiment, the low-energy ions are 700 keV Xe ions provided by a 320 kV low-energy heavy ion accelerator, and the high-energy heavy ions are 2.1 GeV Ta ions provided by the Lanzhou Heavy Ion Accelerator.
[0026] Both low-energy and high-energy ions need to pass through a scanning magnet to uniformly enhance the second harmonic signal intensity of the monolayer WSe2 material.
[0027] The method in this embodiment can uniformly improve the SHG signal of two-dimensional materials, with high control precision and efficiency. It increases the SHG signal intensity of the material by more than 10 times, achieving a uniformity of 90%.
[0028] The reason why high and low energy heavy ions increase the SHG signal intensity of materials is that heavy ion irradiation introduces vacancy defects, lattice distortion, and micro-disordering into the material, causing the regular lattice period to be distributed in an island-like localized pattern, changing the spatial symmetry of the material, modulating the electronic structure of the material, and thus altering the nonlinear optical effects. To observe the defect structure in the material, a single-layer WSe2 transmission sample was prepared. The single-layer continuous thin film WSe2 prepared by chemical vapor deposition was immersed in ethanol and separated from the Al2O3 substrate. Then, it was retrieved using a copper mesh microgrid without carbon film support, thus preparing a copper mesh sample carrying the WSe2 single-layer thin film. The prepared WSe2 copper mesh sample was exposed to a heavy ion beam for irradiation, such as... Figure 1 and Figure 2The image shows the microstructure of the material after 700 keV Xe ion irradiation. Low-energy ions introduce a large number of lattice distortions and vacancy clusters into the material. Previous literature indicates that high-energy heavy-ion irradiation, in addition to introducing latent track defects, also introduces associated vacancy defects and lattice distortions. Monolayer WSe2 itself possesses D3h symmetry, and its SHG polarization pattern exhibits a six-lobed structure. Heavy-ion irradiation introduces an appropriate concentration of ordered defects such as vacancies, reducing the symmetry to C3v while maintaining triple rotational symmetry, thus activating the previously forbidden nonlinear optical tensor components. The defect-induced response and the intrinsic lattice response undergo vector superposition, causing the six-lobed pattern to rotate overall. When rotated by a certain angle, the two response directions are closest and the constructive interference is most significant, thereby enhancing the SHG signal.
[0029] The key parameter in the invention is the heavy ion irradiation flux. The SHG signal enhancement does not exhibit a monotonically increasing trend with increasing irradiation flux. Figure 3 As shown in the SHG single-point polarized signal, the irradiation flux has an optimal window; at higher fluxes, the SHG signal intensity decreases. The optimal flux for low-energy Xe ion irradiation is 5 × 10⁻⁶. 10 ions / cm 2 At this injection level, the SHG signal intensity increased from 3000 in the original sample to 12500, such as Figure 3 As shown; GeV-level Ta ions, the optimal flux is 1×10⁻⁶. 9 ions / cm 2 At this injection level, the SHG signal strength increases to over 41,000, an increase of at least tenfold. Figure 4 single-point polarization response and Figure 5 The maximum polarization intensity of the SHG signal is shown. The SHG test conditions were: light source wavelength 1064 nm, objective lens 100x, and light intensity 5 mW. First, single-point polarization was tested with an angle spacing of 5°. Then, the angle of the petal with the strongest SHG signal was used as the parallel angle for surface scanning. The acquisition time was 0.04 s, and the point spacing was 1 micrometer. Figure 6 (a) and (b) show 5×10 10 ions / cm 2 SHG surface scan signals of WSe2 materials before and after Xe ion irradiation Figure 7 (a) and (b) show 1×10 9 ions / cm 2 The SHG surface scan signal of the material after Ta ion irradiation shows that the uniformly distributed heavy ions, after magnetic scanning, significantly enhanced the SHG signal of the monolayer WSe2. For example... Figure 8 (a) shows the Raman spectrum of WSe2 material after Ta ion irradiation. Figure 8(b) The Raman spectrum of WSe2 material after Xe ion irradiation is shown. The spectral results show that heavy ion irradiation did not change the monolayer properties of the material.
[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific embodiments of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention. The above content is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.
Claims
1. A method for improving the second harmonic signal intensity of monolayer WSe 2, characterized in that, The method comprises the following steps: preparing a single-layer WSe2 material; subjecting the single-layer WSe2 material to heavy ion irradiation to generate defects in the single-layer WSe2 material; controlling the defect concentration in the single-layer WSe2 material by controlling the energy of the heavy ion irradiation to improve the second harmonic signal intensity of the single-layer WSe2 material.
2. The method of claim 1, wherein the monolayer WSe2 is grown on a substrate. The single-layer WSe2 material is prepared by a mechanical exfoliation method, and the single-layer WSe2 material is located on a silicon oxide substrate.
3. The method of claim 1, wherein the monolayer WSe2 is grown on a substrate. The defects include vacancy point defects and lattice distortions, and the spatial inversion symmetry breaking degree of the single-layer WSe2 material is enhanced by generating defects.
4. The method of claim 1, wherein the monolayer WSe2 is grown on a substrate. The heavy ion irradiation is suitable for low-energy ions at the keV level and high-energy heavy ions at the GeV level.
5. The method for increasing the intensity of a single-layer WSe2 second harmonic signal as described in claim 4, characterized in that, For keV low-energy ions, the ion fluence of heavy ion radiation was 5 x 10 10 ions / cm 2 .
6. The method for increasing the intensity of a single-layer WSe2 second harmonic signal as described in claim 4, characterized in that, For GeV-level high-energy heavy ions, the ion fluence of heavy ion radiation is 1 x 10 9 ions / cm 2 .
7. The method for increasing the intensity of a single-layer WSe2 second harmonic signal as described in claim 4, characterized in that, The low-energy ions are Xe ions, and the high-energy ions are Ta ions; the low-energy ions and the high-energy ions are both vertically irradiated on the surface of the single-layer WSe2 material.
8. The method for increasing the intensity of a single-layer WSe2 second harmonic signal as described in claim 4, characterized in that, Both the low-energy ions and the high-energy ions need to pass through a scanning magnet to uniformly improve the second harmonic signal intensity of the single-layer WSe2 material.