Ultra-narrow band chiral composite nanostructure with strong CD signal and capable of being dynamically regulated and controlled

Abstract

The invention relates to the field of chiral devices, in particular to an ultra-narrow-band chiral composite nanostructure which is strong in CD signal and can be dynamically regulated and controlled, the ultra-narrow-band chiral composite nanostructure comprises a substrate layer and a magneto-optical layer which are sequentially arranged from bottom to top, and chiral through holes which are periodically arranged are formed in the magneto-optical layer. The chirality of the composite nanostructure is regulated and controlled by applying a magnetic field, and the regulation and control cost is low; the CD signal peak bandwidth is wide, and application of chiral sensing is facilitated; in addition, the invention belongs to a three-dimensional nanostructure, has strong structure CD signal, and is beneficial to the generation of chiral signals and the application of chiral sensing. The invention has a micro-nano size, and accords with the trend of device miniaturization. In combination with the effects, the method has a good application prospect in the fields of chiral component development, chiral sensing and the like.

Description

Technical Field

[0001] The present application relates to the field of chiral devices, and in particular to an ultra-narrow-band chiral composite nanostructure with a strong CD signal and dynamic controllability. Background Art

[0002] Chirality refers to the property that a structure cannot be superimposed on its mirror image structure by translation or rotation. In nature, chiral structures are ubiquitous, such as DNA double helix, snail shells and spiral nebulae. Left-handed or right-handed enantiomers show significant differences in physical, chemical and biological properties. When left-handed circularly polarized (LCP) light and right-handed circularly polarized (RCP) light excite different enantiomers respectively, different absorption rates will be generated, and the difference is called circular dichroism (CD). CD refers to the difference in transmittance between left-handed circularly polarized light and right-handed circularly polarized light of a chiral structure. The generation of CD is due to the near-field coupling of electric dipoles and magnetic dipoles. The CD property can be used to design negative refractive materials, wide chiral molecular sensing and polarization-resolved imaging, etc., which are widely used in analytical chemistry, biosensing and other fields.

[0003] Recently, in order to explore the mechanism of the CD effect and obtain a stronger CD signal, researchers have proposed various chiral nanostructures to enhance the local electromagnetic field and achieve the effect of enhancing CD. It has been proven that single-layer chiral nanostructures are simple and only require one etching, so they have attracted widespread attention from researchers. For example, the CD intensity of a single-layer chiral nanostructure is 0.42 and the peak bandwidth is 0.1THz [Qureshi UUR, Hu B, Khan MI, et al. Multifunctional activeterahertz metasurface with electromagnetically induced transparency, perfectabsorption, and circular dichroism [J]. Optics Communications, 2024, 550.]; double-layer chiral nanostructures can generate CD signals through interlayer coupling. For example, the CD intensity of the double-layer chiral nanostructure is 0.7 and the peak bandwidth is 10nm [Tanaka K, Arslan D, Fasold S, et al. Chiral Bilayer All-Dielectric Metasurfaces [J]. ACS Nano, 2020, 14(11):15926-15935.]; the three-dimensional chiral nanostructure provides more degrees of freedom for controlling light waves. By adjusting the relative distance and shape between different chiral cell layers, richer chiral optical properties can be produced. For example, the CD intensity of the three-layer chiral nanostructure is 0.8 and the peak bandwidth is 30nm [Liu X, Liang Q, Zhang X, et al. Nano-kirigami enabled chiral nano-ciliawith enhanced circular dichroism at visible wavelengths [J]. Nanophotonics,2023, 12(8):1459-1468.]. In the above chiral nanostructures, the peak bandwidth of the CD signal is relatively wide, which has great limitations on the accuracy of chiral sensing. It is also difficult to achieve dynamic regulation of CD response, which is achieved by changing the structural dimensions, so the regulation cost is high and the applicability is poor. Moreover, the CD signal is weak, which makes the sensitivity of chiral sensing low. Summary of the invention

[0004] The purpose of the present invention is to provide an ultra-narrowband chiral composite nanostructure with a strong and dynamically adjustable CD signal in response to the above-mentioned deficiencies in the prior art, so as to solve the problems in the prior art of poor sensitivity of chiral devices caused by a wide CD signal bandwidth and a weak CD signal, and difficulty in dynamically controlling the CD signal, resulting in poor applicability of the chiral device.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows: The present application provides an ultra-narrowband chiral composite nanostructure with a strong CD signal and dynamic controllability, comprising a substrate layer and a magneto-optical layer arranged sequentially from bottom to top, wherein the interior of the magneto-optical layer is provided with periodically arranged chiral through holes.

[0006] When used, the ultra-narrowband chiral composite nanostructure with strong and dynamically adjustable CD signal also includes a light source, a magnetic field control device, and a light detector. The magnetic field control device is arranged outside the magneto-optical layer of the device of the present invention, and is used to change the external magnetic field of the magneto-optical layer. The light detector is used to detect the transmitted light of the present invention. When performing chiral molecular chirality detection, the chiral molecule solution to be detected and the chiral molecule gas are filled in the through-hole structure of the device of the present invention.

[0007] Furthermore, the material of the magneto-optical layer is Ce:YIG, and the material of the substrate layer is silicon dioxide or ITO.

[0008] Furthermore, the shape of the chiral through-chiral hole is a regular hexagon, and a small hole is concave in each side, and the small holes are arranged in a chiral manner.

[0009] Furthermore, the shape of the concave hole is semicircular or square.

[0010] Furthermore, by enlarging or shrinking one of the concave holes, the rotational symmetry of the structure is broken, and the symmetry-protected BICs are converted into Q-BICs.

[0011] Furthermore, a phase change material layer is provided between the magneto-optical layer and the substrate layer.

[0012] Furthermore, the phase change material is vanadium dioxide or germanium antimony telluride.

[0013] Furthermore, when applied, the magnitude of the applied magnetic field is 0 mT – 200 mT.

[0014] Furthermore, it also includes a semiconductor layer, which is disposed on the magneto-optical layer.

[0015] Furthermore, the material of the semiconductor layer is graphene.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses a magnetic field to control the chirality of the composite nanostructure, and the control cost is low; (2) The CD signal peak bandwidth of the present invention is narrow, and the peak intensity is strong, which is beneficial to the application of chiral sensing; (3) The present invention belongs to a three-dimensional nanostructure with a strong structural CD signal, which is conducive to the generation of chiral signals and the application of chiral sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of an ultra-narrow-band chiral composite nanostructure with a strong CD signal and dynamic controllability provided in Example 1 of the present invention; Figure 2 A schematic diagram of an ultra-narrow-band chiral composite nanostructure with a strong CD signal and dynamic controllability provided in Example 2 of the present invention; Figure 3 Comparison results of CD spectra of an ultra-narrow-band chiral composite nanostructure with a strong and dynamically controllable CD signal provided in Example 2 of the present invention with and without an external magnetic field; Figure 4 The CD spectrum result of the magnetic field dynamic control of the ultra-narrow-band chiral composite nanostructure with strong and dynamically controllable CD signal provided in Example 2 of the present invention; Figure 5 A schematic diagram of an ultra-narrow-band chiral composite nanostructure with a strong CD signal and dynamic controllability provided in Example 3 of the present invention; Figure 6 A schematic diagram of an ultra-narrow-band chiral composite nanostructure with a strong CD signal and dynamic controllability provided in Example 5 of the present invention; Icons: 10 - substrate layer; 20 - magneto-optical layer; 21 - pinhole; 22 - enlarged pinhole; 30 - phase change material layer; 40 - semiconductor layer. DETAILED DESCRIPTION

[0018] In order to make the implementation process of the present invention clearer, it will be described in detail below with reference to the accompanying drawings.

[0019] Example 1 The present invention provides an ultra-narrowband chiral composite nanostructure with strong and dynamically adjustable CD signal. The schematic diagram of the structure is shown in FIG. Figure 1As shown, the structure includes a substrate layer 10 and a magneto-optical layer 20 from bottom to top. The material of the magneto-optical layer 20 is a magneto-optical material. Specifically, the material of the substrate layer 10 can be glass, and its refractive index is 1.44. The thickness of the substrate layer 10 is 150nm-250nm. The material of the magneto-optical layer 20 can be cerium-doped yttrium iron garnet (Ce:YIG). The thickness of the magneto-optical layer 20 is 450nm-550nm. There are chiral through holes inside the magneto-optical layer 20, and the chiral through holes are periodically arranged in the magneto-optical layer 20. The chiral through holes are periodically arranged in a square with a side length of 400nm. Since the through holes have rotational symmetry as a whole, the structure is a symmetric protection type BIC, and the BIC mode in the device does not couple with other radiation modes, resulting in light being localized inside the structure at a specific wavelength, and not lost in the form of radiation. At this time, the Q factor of the device tends to infinity. When a disturbance is introduced to destroy the rotational symmetry of the structure, the symmetric protection type BIC is transformed into a quasi-BIC. The BIC mode that was originally completely confined begins to couple with the outside world to form an extremely narrow radiation mode. Since the through-hole is chiral, when the CPL passes through the chiral hole and interacts with each other. The chiral structure exhibits different phase and absorption characteristics for LCP and RCP light, resulting in differences in the absorption or transmission spectrum, forming a CD signal. Due to the BIC mode, the CD signal at this time also maintains the characteristics of the BIC mode with extremely high Q factor and extremely narrow bandwidth. After the external magnetic field is added, the electronic magnetic moment in the magneto-optical layer interacts with the external magnetic field, causing the excited state energy level to split into more energy levels under the Zeeman effect, increasing the transition path. The absorption difference between the magneto-optical layer and LCP and RCP is enlarged, thereby enhancing the CD signal. On the other hand, the degree of energy level splitting will increase with the increase of the external magnetic field strength. Therefore, by changing the size of the external magnetic field, the CD signal can be actively adjusted to achieve a dynamically adjustable effect.

[0020] Example 2 Based on Example 1, the chiral through holes are periodically arranged on the magneto-optical layer 20. The schematic diagram of the device is as follows: Figure 2As shown, the chiral through-hole includes a regular hexagon with a side length of 300nm and a plurality of small holes 21 that are concave on each side. These small holes 21 are arranged in a chiral manner, and the edges of the small holes are the vertices of the regular hexagons and conform to the C3 rotational symmetry. The small holes 21 are semicircular in shape. The radius of the small semicircular hole 21 is 60nm. The rotational symmetry of the structure is destroyed by enlarging or reducing the size of one of the small holes 22, so that the symmetry-protected BICs are transformed into Q-BICs, generating a narrowband signal. Preferably, the size of the enlarged small hole 22 is 80nm. Since the narrow band of the device is mainly generated by the small hole destroying the rotational symmetry of the structure, when the magnetic field is added, the CD signal enhancement effect when the small hole 21 is concave is better than that when the small hole 21 is convex. After the external magnetic field is added, the electronic magnetic moment in the magneto-optical layer interacts with the external magnetic field, so that the excited state energy level is split into more energy levels under the Zeeman effect, increasing the transition path. The absorption difference between the magneto-optical layer and LCP and RCP is enlarged, thereby enhancing the CD signal. On the other hand, the degree of energy level splitting increases with the increase of the external magnetic field strength. Therefore, by changing the magnitude of the external magnetic field, the CD signal can be actively adjusted to achieve a dynamically adjustable effect.

[0021] When used, the above device also includes a light source, a magnetic field control device, and a light detector. The magnetic field control device is arranged outside the magneto-optical layer 20 in the device of the present invention, and is used to change the strength of the external magnetic field of the magneto-optical layer 20. The light detector is used to detect the light emitted by the device of the present invention, and a CD spectrum is obtained after data processing. The circularly polarized light is irradiated on the upper surface of the magneto-optical layer 20. Due to the existence of the chiral through-hole structure, the magneto-optical layer 20 has chirality, so that the magneto-optical layer 20 is coupled with the circularly polarized light. Due to the rotational symmetry of the structure and the existence of symmetric protection type BICs, all the energy is localized in the magneto-optical layer 20. When a tiny disturbance is introduced to break the original rotational symmetry of the structure, the symmetric protection type BICs are converted into Q-BICs. At this time, the energy localized in the magneto-optical layer is leaked out, passes through the substrate layer 10, and is emitted from the lower surface of the substrate layer 10 and enters the light detector. The entire device has chirality, and an ultra-high Q narrow-band CD signal is obtained. When CD is enhanced, an external magnetic field is applied to the magneto-optical layer 20 through a magnetic field control device, resulting in a change in the path of electron transitions in the magneto-optical layer 20, which increases the absorption difference between LCP and RCP of the magneto-optical layer, thereby enhancing the CD signal of the device. When regulating, the external magnetic field of the magneto-optical layer 20 is changed through a magnetic field control device, and the degree of energy level splitting increases with the increase of the external magnetic field strength, resulting in the absorption difference between LCP and RCP of the magneto-optical layer changing with the magnetic field, thereby changing the CD signal of the device. That is, the present application can achieve the enhancement and dynamic regulation of the CD signal by changing the external magnetic field strength.

[0022] In order to further illustrate the technical effect brought by the device, numerical simulation results are used for illustration. The single square period of the device is 850nm, wherein the refractive index of the magneto-optical layer 20 is 2.34 and the thickness is 475nm. The material of the substrate layer 10 is silicon dioxide, with a refractive index of 1.45 and a thickness of 200nm. When modeling, the regular hexagonal through-hole is located at the center of the xy plane of the magneto-optical layer, and the radius of the regular hexagonal through-hole is 300nm. The concave small semicircles are at the vertices of each edge, and the radius of the small semicircles is 60nm. One of the small semicircles is enlarged, and its radius is 80nm. Figure 3 The CD spectrum comparison results when no magnetic field is added and when a magnetic field is added are provided. The CD spectrum when no magnetic field is added shows that the device has two resonant CD signals at wavelengths of 1540.2 nm and 1551.2 nm, and the peak values ​​of the CD signals are -0.18 and 0.07, respectively; after the magnetic field is added, the CD signal amplitudes are enhanced to -0.96 and 0.56, respectively, and the half-peak widths of the CD signals are 0.015 nm and 0.019 nm, respectively. This shows that after introducing an external magnetic field into the device, the amplitude of the CD signal can be significantly enhanced, thereby improving the control sensitivity of the device of the present invention. And due to its ultra-narrow half-peak width, the device is also very accurate. Data Figure 4 It shows that when the external magnetic field is gradually increased, the CD signal of the device will also gradually increase and slightly red shift. This shows that the CD signal can be dynamically regulated by changing the magnitude of the external magnetic field.

[0023] Example 3 On the basis of Example 1 or 2, Figure 5 As shown, a phase change material layer 30 is added between the magneto-optical layer 20 and the dielectric layer 10, and the phase change material of the phase change material layer 30 can be selected as vanadium dioxide or germanium antimony telluride. The phase change material can adjust its conductivity by regulating the temperature, thereby changing the refractive index of the phase change material to achieve dynamic regulation of the CD signal. In addition, temperature regulation will also enhance the asymmetry of the chiral through-hole, making the CD signal regulation capability of the entire device stronger. On the other hand, the refractive index of the phase change material is higher than that of the magneto-optical material, and the localization effect of the light is better. Combining magneto-optical materials, phase change materials and BICs can make the energy of the light field better localized in the magneto-optical layer, making the bandwidth of the CD signal narrower.

[0024] Example 4 On the basis of Example 3, the penetration direction of the chiral through-hole structure is set to be non-parallel to the main z-axis in the design. This inclined through-hole design breaks the original symmetry, so that the directionality of the through-hole is no longer strictly extended along the main z-axis, but is distributed inside the magneto-optical layer at a certain inclination angle. This change brings about the following effects. First, since the through-hole is no longer perpendicular to the main z-axis, the position of the through-hole in the magneto-optical material will be offset. This relative dislocation between the layers further destroys the symmetry of the system in the z-direction, thereby significantly enhancing the asymmetry of the entire device. This makes the interaction between light and the chiral structure more complex when passing through the magneto-optical layer. Specifically, the inclined hole will change the propagation path and electromagnetic field distribution of the light field inside the structure, causing the system to have greater deviations in the scattering, transmission and absorption characteristics of circularly polarized light, and the selective response to left-handed and right-handed circularly polarized light is more significant, thereby significantly enhancing the intensity of the CD signal. Combining the magneto-optical effect and the geometric characteristics of the inclined through-hole, the design can greatly improve the optical activity of the system within a specific wavelength range and form a stronger CD response. In summary, by introducing the tilted chiral through-hole structure, the asymmetry of the device is further optimized, thus providing important structural support for enhancing the CD signal. This design also provides more adjustable parameters for dynamically controlling the circular dichroism signal, which has important practical application value.

[0025] Example 5 On the basis of Example 1 or Example 2 or Example 3 or Example 4, Figure 6 As shown, a semiconductor layer 40 is laid flat on the upper layer of the magneto-optical layer 20. The material of the semiconductor layer 40 is a semiconductor material. Preferably, the material of the semiconductor layer 40 is a layered graphene with a thickness of about 0.5nm-1.0nm. Since the high electrical conductivity of graphene can efficiently conduct charges and interact with the incident light field, the localization effect of light in the magneto-optical layer can be better enhanced. The enhancement of this light field localization effect usually leads to the amplification of the chiral light response, making the circular dichroism effect more significant. And graphene can adjust its Fermi level through the electric field, thereby changing its photoelectric response characteristics. By regulating the Fermi level of graphene, it is possible to achieve precise control of the CD signal to achieve the dynamic regulation effect of the electric field on the device. In addition, the electronic structure of graphene is also very sensitive to the external magnetic field, and it can be used as a good magneto-optical material. Under the action of the external magnetic field, the high conductivity of graphene will couple with the magneto-optical effect, further enhancing the optical response of the system. The Faraday effect causes the rotation of circularly polarized light, and this rotation effect can be combined with the optical absorption mechanism in graphene to enhance the absorption of specific circularly polarized light, thereby enhancing the CD response of the device.

[0026] Example 6 In order to further enhance the CD response of the dynamically adjustable ultra-narrowband chiral composite nanodevice, on the basis of Example 5, the magneto-optical layer 20 is divided into a first magneto-optical layer and a second magneto-optical layer. The chiral through-hole structure in the entire magneto-optical layer remains unchanged, and the second magneto-optical layer is rotated clockwise by 90°; the first magneto-optical layer remains unchanged. The single-layer structure is changed to a double-layer, destroying the symmetry of the device in the z direction. In addition, the double-layer structure will cause the light field to interfere and couple with each other between layers. A locally enhanced electromagnetic field region can be formed through interlayer coupling, and the difference in response to left-handed and right-handed circularly polarized light will be further amplified, thereby significantly enhancing the CD response.

[0027] In addition, the chiral through-hole can also be other structures, for example, the chiral through-hole includes a square and a small hole, the small holes protruding along the two symmetrical sides of the square are arranged in a chiral manner, and the shape is a square hole. More preferably, the side length of the small square hole is 50nm, so that the whole device has chirality and can generate CD signals, and the through-hole structure has C2 rotational symmetry. By introducing a small perturbation to break the C2 rotational symmetry, the symmetry-protected BICs are converted into Q-BICs, generating ultra-high Q narrow-band CD signals. The small perturbation can be a small square protruding from the third side of the square periodic hole.

[0028] In summary, in the present invention, circularly polarized light is irradiated on the surface of the magneto-optical layer, and the chiral through-hole structure in the magneto-optical layer makes the magneto-optical layer chiral, so that the magneto-optical layer is efficiently coupled with the circularly polarized light, and then the circularly polarized light is coupled into the entire device; and by introducing a small disturbance to break the original rotational symmetry of the structure, the symmetric protection type BICs are converted into Q-BICs, and an ultra-high Q narrow-band CD signal is generated. At this time, the strong electric field of the device in the xy section is mainly concentrated in the central area of ​​the four edges in the magneto-optical layer, and the current flows from the center of the left and right boundaries of the magneto-optical layer to the center of the upper and lower boundaries, respectively, indicating that the surface current of the device at this time has components in both the x and y directions, and the components in the two directions are almost equal. The strong electric field in the yz section is mainly concentrated at the left and right boundaries, and a small part is concentrated at the junction of SiO2 and the magneto-optical layer. Its current flows from top to bottom along the z axis, indicating that the surface current of the device at this time also has a component in the z direction. After the external magnetic field is added, the electronic magnetic moment in the magneto-optical layer interacts with the external magnetic field, so that the excited state energy level is split into more energy levels under the Zeeman effect, increasing the transition path. From the electric field and current intensity diagram, it can be seen that the electric field and current distribution of the device remain basically unchanged, but when LCP is irradiated, its electron transition path is shortened and the electric field intensity is weakened; when RCP is irradiated, its electron transition path is extended and the electric field intensity is enhanced. This enlarges the absorption difference between the magneto-optical layer and LCP, thereby enhancing the CD signal. Therefore, the peak value of the CD peak of the magneto-optical layer can be enhanced from -0.18 to -0.96. In addition, the degree of energy level splitting will increase with the increase of the external magnetic field intensity. Therefore, by changing the size of the external magnetic field, the active adjustment of the CD signal can be achieved, and the dynamic adjustable effect can be achieved. The half-peak width of the CD signal obtained by the device of the present invention is about 0.015nm, which is much narrower than the half-peak width value published in the prior art. Therefore, the accuracy of the device of the present invention is high. In addition, the sensitivity of the device of the present invention is also high.

[0029] In addition, the device of the present invention can add different types of chiral molecular gases or chiral molecular solutions in the through-hole structure, which can enhance the coupling between the chiral molecules and the materials of each layer of the device, thereby improving the sensitivity of the device of the present invention in detecting chirality. In addition, the device of the present invention is a simple planar chiral structure, and the shape of each layer of the structure is the same, which is conducive to preparation, and the size of the entire device is micro-nanoscale, which is conducive to making optical integrated chips, which is in line with the trend of device miniaturization.

[0030] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An ultra-narrowband chiral composite nanostructure with strong CD signal and dynamic controllability, characterized in that: The invention comprises a substrate layer and a magneto-optical layer which are arranged in sequence from bottom to top, wherein the interior of the magneto-optical layer is provided with periodically arranged chiral through holes.

2. The ultra-narrowband chiral composite nanostructure with strong CD signal and dynamic controllability according to claim 1, characterized in that: The material of the magneto-optical layer is Ce:YIG, and the material of the substrate layer is silicon dioxide or ITO.

3. The ultra-narrowband chiral composite nanostructure with strong CD signal and dynamic controllability according to claim 1, characterized in that: The chiral through-chiral hole is in the shape of a regular hexagon, and each side has a small hole concave therein, and the small holes are arranged in a chiral manner.

4. The ultra-narrowband chiral composite nanostructure with strong and dynamically controllable CD signal according to claim 3, characterized in that: The shape of the concave small hole is semicircular or square.

5. The ultra-narrowband chiral composite nanostructure with strong CD signal and dynamic controllability according to claim 4, characterized in that: Among the concave holes, one of the concave holes is enlarged or reduced to break the rotational symmetry of the structure and transform the symmetry-protected continuous domain bound state into a quasi-bound state.

6. The ultra-narrowband chiral composite nanostructure with strong CD signal and dynamic controllability according to claim 5, characterized in that: A phase change material layer is arranged between the magneto-optical layer and the substrate layer.

7. The ultra-narrowband chiral composite nanostructure with strong CD signal and dynamic controllability according to claim 6, characterized in that: The phase change material is vanadium dioxide or germanium antimony telluride.

8. The ultra-narrowband chiral composite nanostructure with strong CD signal and dynamic controllability according to any one of claims 1 to 7, characterized in that: When applied, the magnitude of the applied magnetic field is 0 mT – 200 mT.

9. The ultra-narrowband chiral composite nanostructure with strong CD signal and dynamic controllability according to claim 8, characterized in that: Also included is a semiconductor layer, which is disposed on the magneto-optical layer.

10. The ultra-narrowband chiral composite nanostructure with strong CD signal and dynamic controllability according to claim 9, characterized in that: The material of the semiconductor layer is graphene.

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