Ultra-narrow-band chiral composite nanostructure with strong CD signal and dynamic regulation

Abstract

The application relates to the field of chiral devices, in particular to an ultra-narrow-band chiral composite nanostructure with strong CD signal and dynamic regulation, which comprises a substrate layer and a magneto-optical layer arranged in sequence from bottom to top, and a periodically arranged chiral through-hole is arranged in the interior of the magneto-optical layer. The chiral of the composite nanostructure is regulated by a magnetic field, and the regulation cost is low; the CD signal peak bandwidth of the application is wide, which is beneficial to the application of chiral sensing; in addition, the application belongs to a three-dimensional nanostructure, the structural CD signal is strong, which is beneficial to the generation of chiral signals and the application of chiral sensing. The application is of micro-nano size, and conforms to the trend of device miniaturization. In combination with the above effects, the application has good application prospect in the fields of chiral component development and chiral sensing.

Description

TECHNICAL FIELD

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

[0002] Chirality refers to a structure that cannot be superimposed on its mirror image by translation or rotation. In nature, chiral structures are ubiquitous, such as DNA double helix, snail shell and spiral nebula. 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, different absorption rates are produced, and the difference is called circular dichroism (CD). CD refers to the difference in transmittance of 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 coupling dipoles. Using CD characteristics, negative refractive materials, wide chiral molecule sensing and polarization resolution imaging can be designed, and widely used in analytical chemistry, biosensing and other fields.

[0003] Recently, in order to explore the mechanism of CD effect and obtain 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 proved that single-layer chiral nanostructure is simple and only needs one etching, so it has attracted much attention of researchers. For example, the CD intensity of single-layer chiral nanostructure is 0.42, and the peak bandwidth is 0.1THz [Qureshi U U R, Hu B, Khan M I, et al. Multifunctional active terahertz metasurface with electromagnetically induced transparency, perfect absorption, and circular dichroism [J]. Optics Communications, 2024, 550.]; the CD intensity of 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.]; three-dimensional chiral nanostructure provides more degrees of freedom for controlling light waves, and by adjusting the relative distance and shape between different chiral cell layers, more abundant chiral optical properties can be generated. For example, the CD intensity of 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-cilia with 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 wide, which has great limitations on the accuracy of chiral sensing. And it is difficult to realize the dynamic regulation of CD response, which is realized by changing the structure size, 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

[0004] The CD signal of the super-narrow-band chiral composite nanostructure is strong and dynamically adjustable, and the chiral device sensitivity is improved.

[0005] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0006] The present application provides a kind of CD signal strong and dynamically adjustable super-narrow-band chiral composite nanostructure, including substrate layer and magneto-optical layer arranged from bottom to top, and the inside of magneto-optical layer is provided with periodic arrangement chiral through hole.

[0007] When applied, the CD signal strong and dynamically adjustable super-narrow-band chiral composite nanostructure further includes light source, magnetic field control device, light detector.The magnetic field control device is arranged outside the magneto-optical layer of the device of the present application, for changing the applied magnetic field of magneto-optical layer.Light detector is used for detecting the transmitted light of the present application.Chiral molecule chiral detection is carried out, and the chiral molecule solution and chiral molecule gas to be detected are filled in the through hole structure of the device of the present application.

[0008] Further, the material of magneto-optical layer is Ce:YIG, and the material of substrate layer is silicon dioxide or ITO.

[0009] Further, the shape of chiral through hole is regular hexagon, and a small hole is recessed in each side, and the small holes are arranged in chiral.

[0010] Further, the shape of recessed small hole is semicircle or square.

[0011] Further, in the recessed small hole, one of the recessed small holes is enlarged or reduced, the rotational symmetry of the structure is broken, and the symmetric protection type BICs is converted into Q-BICs.

[0012] Further, a phase change material layer is arranged between magneto-optical layer and substrate layer.

[0013] Further, the phase change material is vanadium dioxide or germanium antimony tellurium.

[0014] Further, when applied, the size of applied magnetic field is 0 mT-200 mT.

[0015] Further, it further includes semiconductor layer, and the semiconductor layer is arranged on magneto-optical layer.

[0016] Further, the material of semiconductor layer is graphene.

[0017] Compared with the prior art, the present application has the following advantages:

[0018] (1) The application applies a magnetic field to control the chirality of the composite nanostructure, and the cost is low;

[0019] (2) The CD signal peak bandwidth of the application is relatively narrow, and the peak strength is relatively strong, which is beneficial to the application of chiral sensing;

[0020] (3) The application belongs to a three-dimensional nanostructure, and the structure CD signal is strong, which is beneficial to the generation of chiral signals and the application of chiral sensing. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A CD signal strong and dynamically controllable ultra-narrow band chiral composite nanostructure provided for embodiment 1 of the application is shown in the schematic diagram;

[0022] Figure 2 A CD signal strong and dynamically controllable ultra-narrow band chiral composite nanostructure provided for embodiment 2 of the application is shown in the schematic diagram;

[0023] Figure 3 The CD spectrum comparison results of the CD signal strong and dynamically controllable ultra-narrow band chiral composite nanostructure provided for embodiment 2 of the application with and without an external magnetic field are shown in the schematic diagram;

[0024] Figure 4 The CD spectrum results of the CD signal strong and dynamically controllable ultra-narrow band chiral composite nanostructure provided for embodiment 2 of the application with magnetic field dynamic regulation are shown in the schematic diagram;

[0025] Figure 5 A CD signal strong and dynamically controllable ultra-narrow band chiral composite nanostructure provided for embodiment 3 of the application is shown in the schematic diagram;

[0026] Figure 6 A CD signal strong and dynamically controllable ultra-narrow band chiral composite nanostructure provided for embodiment 5 of the application is shown in the schematic diagram;

[0027] Figure: 10 - substrate layer; 20 - magneto-optical layer; 21 - small hole; 22 - enlarged small hole; 30 - phase change material layer; 40 - semiconductor layer. DETAILED DESCRIPTION

[0028] In order to make the implementation process of the application more clear, the following will be described in detail in combination with the drawings.

[0029] Embodiment 1

[0030] The application provides a CD signal strong and dynamically adjustable ultra-narrow band chiral composite nanostructure, and the schematic diagram of the structure is as follows Figure 1As shown, the structure sequentially comprises 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 the refractive index thereof is 1.44. The thickness of the substrate layer 10 is 150-250 nm. 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 450-550 nm. There are chiral through holes in 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 400 nm. Since the through holes as a whole have rotational symmetry, the structure is a symmetrically protected BIC, and the BIC mode in the device does not couple with other radiation modes, resulting in that the light is localized in the structure at a specific wavelength without being lost in the form of radiation, and at this time, the Q factor of the device tends to infinity. When a perturbation is introduced to destroy the rotational symmetry of the structure, the symmetrically protected BIC is converted into a quasi-BIC. The originally completely trapped BIC mode begins to couple with the outside, forming an extremely narrow radiation mode. Since the through holes are chiral, when the CPLs pass through the chiral holes and interact. The chiral structure exhibits different phase and absorption characteristics for LCP and RCP light, thereby producing differences in the absorption or transmission spectrum, forming a CD signal. And due to the BIC mode, the CD signal at this time also maintains the characteristics of the BIC mode Q factor being extremely high and the bandwidth being extremely narrow. After an external magnetic field is added, the electron magnetic moment in the magneto-optical layer interacts with the external magnetic field, so that the excited state level is split into more levels under the Zeeman effect, increasing the path of transition. The absorption difference of the magneto-optical layer to LCP and RCP is expanded, thereby enhancing the CD signal. On the other hand, the degree of energy level splitting will increase with the increase of the strength of the external magnetic field. Therefore, by changing the size of the external magnetic field, active adjustment of the CD signal can be realized, and a dynamically adjustable effect is realized.

[0031] Embodiment 2

[0032] On the basis of embodiment 1, the chiral through holes are periodically arranged on the magneto-optical layer 20, and the schematic diagram of the device is as shown in Figure 2As shown, the chiral through-hole includes a regular hexagon with a side length of 300 nm and a plurality of small holes 21 recessed on each side, the small holes 21 are arranged in a chiral manner, the edges of the small holes are the vertices of the regular hexagon, and conform to C3 rotational symmetry. The small holes 21 are semicircular in shape. The radius of the semicircular hole 21 is 60 nm. By expanding or reducing the size of one of the small holes 22 to destroy the rotational symmetry of the structure, the symmetrically protected BICs are converted into Q-BICs, and a narrowband signal is generated. Preferably, the size of the expanded small hole 22 is 80 nm. Since the narrowband 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 of the small hole 21 recessed is better than that of the small hole 21 protruding. After the external magnetic field is added, the electron magnetic moment in the magneto-optical layer interacts with the external magnetic field, so that the excited state level is split into more levels under the Zeeman effect, increasing the transition path. The absorption difference of the magneto-optical layer to LCP and RCP is expanded, 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, active adjustment of the CD signal can be realized, and a dynamically adjustable effect is realized.

[0033] In application, the above device further 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 application, and is used to change the external magnetic field strength of the magneto-optical layer 20. The light detector is used to detect the light emitted by the device of the application, and the CD spectrum is obtained after data processing. The circularly polarized light is irradiated on the upper surface of the magneto-optical layer 20, and the magneto-optical layer 20 has chirality due to the existence of the chiral through-hole structure, so that the magneto-optical layer 20 is coupled with the circularly polarized light. Due to the rotational symmetry of the structure, the symmetrically protected BICs exist, and the energy is all localized in the magneto-optical layer 20. When a small perturbation is introduced to break the original rotational symmetry of the structure, the symmetrically protected 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 whole device has chirality, and an ultra-high Q narrowband CD signal is obtained. When the CD is enhanced, the magnetic field control device is used to apply an external magnetic field to the magneto-optical layer 20, which causes the path of electron transition in the magneto-optical layer 20 to change, and the absorption difference of the magneto-optical layer to LCP and RCP is expanded, thereby enhancing the CD signal of the device. When the CD is adjusted, the magnetic field control device is used to change the external magnetic field of the magneto-optical layer 20, and the degree of energy level splitting will increase with the increase of the external magnetic field strength, which causes the absorption difference of the magneto-optical layer to LCP and RCP to change with the magnetic field, thereby changing the CD signal of the device. That is, the application can realize the enhancement and dynamic adjustment of the CD signal by changing the external magnetic field strength.

[0034] To further illustrate the technical effects of this device, numerical simulation results are used. The period of a single square in the device is 850 nm. The magneto-optical layer 20 has a refractive index of 2.34 and a thickness of 475 nm. The substrate layer 10 is made of silicon dioxide with a refractive index of 1.45 and a thickness of 200 nm. In the modeling, the hexagonal through-hole is located at the center of the xy plane of the magneto-optical layer, and the radius of the hexagonal through-hole is 300 nm. The concave semicircles are located at the vertices of each side, and the radius of the semicircles is 60 nm. One of the semicircles is enlarged to have a radius of 80 nm. Figure 3 A comparison of CD spectra with and without a magnetic field is provided. The CD spectrum without a magnetic field shows two resonant CD signals at wavelengths of 1540.2 nm and 1551.2 nm, with peak values ​​of -0.18 and 0.07, respectively. After applying a magnetic field, the CD signal amplitudes increased to -0.96 and 0.56, respectively, with full width at half maximum (FWHM) values ​​of 0.015 nm and 0.019 nm. This indicates that introducing an external magnetic field significantly enhances the CD signal amplitude, improving the control sensitivity of the device. Furthermore, due to its ultra-narrow FWHM, the device also exhibits high accuracy. Figure 4 The results show that as the applied magnetic field is gradually increased, the CD signal of the device also gradually increases, and a slight redshift occurs. This indicates that the CD signal can be effectively dynamically controlled by changing the magnitude of the applied magnetic field.

[0035] Example 3

[0036] Based on Example 1 or 2, such as Figure 5 As shown, a phase change material layer 30 is added between the magneto-optical layer 20 and the dielectric layer 10. The phase change material of the phase change material layer 30 can be vanadium dioxide or germanium-antimony-tellurium. The conductivity of the phase change material can be adjusted by regulating the temperature, thereby changing the refractive index of the phase change material and realizing dynamic control of the CD signal. Furthermore, temperature control also enhances the asymmetry of the chiral through-hole, making the CD signal adjustment 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, resulting in better localization of light. Combining the magneto-optical material, the phase change material, and BICs can better localize the energy of the light field in the magneto-optical layer, making the bandwidth of the CD signal narrower.

[0037] Example 4

[0038] Building upon Example 3, the design sets the penetration direction of the chiral through-hole structure to be non-parallel to the principal z-axis. This tilted through-hole design breaks the original symmetry, causing the directionality of the through-hole to no longer strictly extend along the principal z-axis, but rather to be distributed at a certain angle within the magneto-optical layer. This change brings several effects. First, since the through-hole is no longer perpendicular to the principal z-axis, its position within the magneto-optical material shifts. This interlayer misalignment further disrupts the system's symmetry in the z-direction, significantly enhancing the overall asymmetry of the device. This makes the interaction between light and the chiral structure more complex when passing through the magneto-optical layer. Specifically, the tilted hole alters the propagation path of the light field and the electromagnetic field distribution within the structure, causing greater deviations in the system's scattering, transmission, and absorption characteristics of circularly polarized light. The selective response to left-handed and right-handed circularly polarized light becomes more pronounced, thus significantly enhancing the intensity of the CD signal. Combining the magneto-optical effect and the geometric characteristics of the tilted through-hole, this design can significantly improve the optical activity of the system within a specific wavelength range, resulting in a stronger CD response. In summary, by introducing an inclined 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, and has significant practical application value.

[0039] Example 5

[0040] Based on Example 1, Example 2, Example 3, or Example 4, such as Figure 6 As shown, a semiconductor layer 40 is also laid flat on top of the magneto-optical layer 20. The semiconductor layer 40 is made of semiconductor material, preferably layered graphene with a thickness of approximately 0.5 nm to 1.0 nm. Due to the high electrical conductivity of graphene, it can efficiently conduct charge and interact with the incident light field, thus enhancing the localization effect of light in the magneto-optical layer. This enhanced localization effect typically leads to an amplification of chiral light response, making the circular dichroism effect more pronounced. Furthermore, graphene's Fermi level can be tuned by an electric field, thereby altering its photoelectric response characteristics. By controlling the Fermi level of graphene, precise control of the CD signal can be achieved, enabling dynamic control of the device by the electric field. In addition, graphene's electronic structure is highly sensitive to external magnetic fields, making it an excellent magneto-optical material. Under the influence of an external magnetic field, graphene's high conductivity couples with the magneto-optical effect, further enhancing the system's optical response. The Faraday effect causes circularly polarized light to rotate, and this rotation effect can combine with the optical absorption mechanism in graphene to enhance the absorption of specific circularly polarized light, thereby enhancing the CD response of the device.

[0041] Example 6

[0042] To further enhance the CD response of the dynamically adjustable ultra-narrow-band chiral composite nano device, on the basis of Embodiment 5, the magneto-optic layer 20 is divided into a first magneto-optic layer and a second magneto-optic layer. The chiral through-hole structure in the entire magneto-optic layer remains unchanged, the second magneto-optic layer is rotated clockwise by 90°, and the first magneto-optic layer remains unchanged. The single-layer structure is changed to a double-layer structure, which destroys the z-direction symmetry of the device. And the double-layer structure will cause the light field to interfere and couple between the layers. Through the interlayer coupling, a locally enhanced electromagnetic field region can be formed, and the response difference of left-handed and right-handed circularly polarized light will be further amplified, thereby significantly enhancing the CD response.

[0043] In addition, the chiral through-hole can also be other structures, for example, the chiral through-hole includes a square and a small hole, and the small hole is chiral arranged along the two symmetric sides of the square and protrudes outward, and the shape is a square hole, and more preferably, the side length of the small square hole is 50 nm, so that the entire device has chirality and can generate a CD signal, and the through-hole structure has C2 rotational symmetry. By introducing a small perturbation to break the C2 rotational symmetry, the symmetrically protected BICs are converted into Q-BICs, generating an ultra-high Q narrow-band CD signal. The small perturbation can be a small square protruding outward on the third side of the square periodic hole.

[0044] To sum up, in the application, 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 coupled with the circularly polarized light efficiently, and then the circularly polarized light is coupled into the whole device; and the original rotational symmetry of the structure is broken by introducing a small perturbation, so that the symmetrically protected BICs are converted into Q-BICs, and an ultra-high Q narrowband CD signal is generated. At this time, the strong electric field in the x-y cross section of the device is mainly concentrated in the central region of the four edges in the magneto-optical layer, and the current flows from the left and right boundary centers of the magneto-optical layer to the upper and lower boundary centers, indicating that the surface current of the device at this time has components in the x and y directions, and the components in the two directions are approximately equal. While in the y-z cross section, the strong electric field is mainly concentrated in the left and right boundaries, and a small part is concentrated in the junction of SiO2 and the magneto-optical layer, and the current flows along the z axis from top to bottom, 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 electron magnetic moment in the magneto-optical layer interacts with the external magnetic field, so that the excited state level is split into more levels under the Zeeman effect, increasing the path of transition. From the electric field and current intensity diagram, it can be seen that the electric field and current distribution of the device is basically unchanged, but when LCP is irradiated, the electron transition path is shortened, and the electric field strength is weakened; when RCP is irradiated, the electron transition path is lengthened, and the electric field strength is enhanced. Thus, the absorption difference of the magneto-optical layer to LCP and RCP is enlarged, thereby enhancing the CD signal. Therefore, the peak value of the CD peak of the magneto-optical layer can be increased from -0.18 to -0.96. In addition, the degree of energy level splitting will increase with the increase of the strength of the external magnetic field. Therefore, by changing the size of the external magnetic field, the CD signal can be actively adjusted, and the effect of dynamic adjustment can be realized. The half-peak width of the CD signal obtained by the device is about 0.015 nm, which is much narrower than the half-peak width value disclosed in the prior art. Therefore, the accuracy of the device of the application is higher. In addition, the sensitivity of the device of the application is also higher.

[0045] In addition, different kinds of chiral molecule gas or chiral molecule solution can be added to the through-hole structure of the device, 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 to detect chirality. In addition, the device of the application is a simple planar chiral structure, and the shape of each layer of the structure is the same, which is beneficial to preparation, and the size of the whole device is in the order of micro-nanometers, which is beneficial to the preparation of optical integrated chips and conforms to the trend of device miniaturization.

[0046] The above is only a preferred embodiment of the application and is not used to limit the application. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A CD signal strong and dynamically regulated ultra-narrow band chiral composite nanostructure, characterized in that, The application relates to a magnetic-optical layer and a substrate layer arranged in sequence from bottom to top, wherein the magnetic-optical layer is internally provided with periodically arranged chiral through holes; the chiral through holes are in the shape of regular hexagons, each side of which is concave with a small hole, and the small holes are arranged in a chiral manner; one of the concave small holes is enlarged or reduced to break the rotational symmetry of the structure, thereby converting a symmetrically protected continuous domain bound state into a quasi-bound state.

2. The CD signal strong and dynamically controllable ultranarrow chiral composite nanostructure according to claim 1, characterized in that, The material of the magnetic-optical layer is Ce:YIG, and the material of the substrate layer is silicon dioxide or ITO.

3. The CD signal strong and dynamically tunable ultra-narrow chiral plasmonic nanostructure according to claim 2, characterized in that, The shape of the concave small hole is semicircular or square.

4. The CD signal strong and dynamically controllable ultranarrow chiral composite nanostructure according to claim 3, characterized in that, A phase change material layer is arranged between the magnetic-optical layer and the substrate layer.

5. The CD signal strong and dynamically controllable ultranarrow chiral composite nanostructure according to claim 4, characterized in that, The phase change material is vanadium dioxide or germanium antimony tellurium.

6. The CD signal strong and dynamically tunable ultranarrow chiral plasmonic nanostructure according to any one of claims 1-5, characterized in that, In application, the size of an applied magnetic field is 0 mT-200 mT.

7. The CD signal strong and dynamically controllable ultranarrow chiral composite nanostructure according to claim 6, characterized in that, A semiconductor layer is further arranged on the magnetic-optical layer.

8. The CD signal strong and dynamically controllable ultranarrow chiral composite nanostructure according to claim 7, characterized in that, The material of the semiconductor layer is graphene.

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