Chiral metamaterial sensor based on vanadium dioxide

Abstract

The invention discloses a vanadium dioxide-based chiral metamaterial sensor, which comprises a periodically arranged nanostructure array, each nanostructure comprises a U-shaped structure, a |-shaped structure and an L-shaped structure which are sequentially connected, the U-shaped structure and the L-shaped structure are made of metal, and the |-shaped structure is made of vanadium dioxide. On the basis of active regulation and control of a vanadium dioxide temperature control material, wide-range refractive index change and design of a chiral structure pattern with a simple structure, metal with a U-shaped structure and metal with an L-shaped structure are adopted, vanadium dioxide with a |-shaped structure is embedded between the metal and the metal, a metal-medium-metal MIM structure is achieved, and compared with a conventional MIM structure, the light contact area is increased; in the visible light wave band, the phase change material vanadium dioxide is utilized to realize active regulation and control, the multifunctional integration effect and the active regulation and control capability are improved for chiral sensing, and meanwhile, the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and particularly to a chiral metamaterial sensor based on vanadium dioxide. Background Art

[0002] Chiral metamaterials have received extensive attention in the field of optical sensing due to their unique optical properties and enhanced chiral response. Compared with natural chiral materials, chiral metamaterials exhibit stronger optical activity and customizability, making them have great application potential in fields such as biosensing and chemical sensing.

[0003] The sensing design of chiral metamaterials is gradually innovating, including the optimization of two-dimensional and three-dimensional chiral structures, the combination of all-metal structures to metal and dielectric materials, the development of all-dielectric materials, and the addition of ceramic materials and hybrid nanomaterials, the development of dynamic regulation capabilities, multifunctional integration, and a wide frequency response range, high sensitivity to the environment, high quality factor, etc., which continuously enhances the requirements for chiral metamaterial sensors.

[0004] Currently, there is a core pursuit for high quality factor, high Q value and high chiral response of sensors. In addition, for realizing multifunctional integrated devices, higher requirements are put forward for the flexibility of sensors, reducing the complexity and cost of equipment.

[0005] Existing chiral metamaterial absorbers are generally designed as switchable switches in the terahertz band, dynamic tunable absorbers, lacking sensing performance and chiral discrimination functions, and having difficult material regulation and high costs, which limit the application of chiral metamaterial sensors. Summary of the Invention

[0006] Aiming at the deficiencies in the prior art, the present invention provides a chiral metamaterial sensor based on vanadium dioxide, which is provided with U-shaped and L-shaped metal structures, and vanadium dioxide (VO 2 ) is embedded between the two. In the visible light band, active regulation is realized by using the phase change material vanadium dioxide, and double absorption peak sensitivities of 897.85 nm / RIU and 117.85 nm / RIU are achieved in a wide range of n = 1.0 - 1.4, with quality factors of FOM = 33.5 and FOM = 3.5 respectively, which improves the multifunctional integration effect and active regulation ability for chiral sensing, and reduces costs at the same time.

[0007] To solve the above technical problems, the present invention provides a chiral metamaterial sensor based on vanadium dioxide, including a periodically arranged nanostructure array, and each nanostructure includes a U-shaped structure, a ┃-shaped structure and an L-shaped structure connected in sequence, the materials of the U-shaped structure and the L-shaped structure are metals, and the material of the ┃-shaped structure is vanadium dioxide.

[0008] Based on the active regulation of vanadium dioxide temperature control materials and the wide-range refractive index change, a chiral structure pattern with a simple structure is designed. Metals with U-shaped and L-shaped structures are used, and a ┃-shaped vanadium dioxide is embedded between them, realizing a metal-insulator-metal (MIM) structure. Compared with the conventional MIM structure, the light contact area is increased; in the visible light band, the phase change material vanadium dioxide is used to achieve active regulation, and double absorption peak sensitivities of 897.85 nm / RIU and 117.85 nm / RIU are achieved in a wide range of n = 1.0 - 1.4, with figure of merit (FOM) values of 33.5 and 3.5 respectively. This improves the multi-functional integration and active regulation capabilities for chiral sensing, while reducing costs.

[0009] Further, the U-shaped structure includes a first base structure, a first convex structure and a second convex structure respectively arranged at both ends of the first base structure, wherein the second convex structure is connected to the ┃-shaped structure;

[0010] The length L of the first base structure 1 is 160 - 200 nm;

[0011] The length w of the first convex structure 1 is 35 - 55 nm;

[0012] The length s of the second convex structure is 35 - 55 nm.

[0013] Further, the L-shaped structure includes a second base structure and a third convex structure arranged at one end of the second base structure;

[0014] The second base structure has the same length as the first base structure;

[0015] The sum of the lengths of the third convex structure and the ┃-shaped structure l 2 is 135 - 155 nm.

[0016] Further, the length g of the ┃-shaped structure is 80 - 100 nm.

[0017] Further, the ┃-shaped structure, the second convex structure and the third convex structure form a straight line.

[0018] Further, the height h of the nanostructure is 180 - 220 nm.

[0019] Further, the thicknesses of the U-shaped structure, the ┃-shaped structure and the L-shaped structure are the same, w = 40 - 50 nm.

[0020] Further, the period length P of the nanostructure array x and P y are both 445 - 455 nm.

[0021] Further, both the U-shaped structure and the L-shaped structure are integral structures.

[0022] Further, the materials of the U-shaped structure and the L-shaped structure are independently selected from Au or Ag.

[0023] Advantages of the present invention:

[0024] Based on the active regulation of vanadium dioxide temperature control material, with wide-range refractive index change, a chiral structure pattern with a simple design is developed. By using metals with U-shaped and L-shaped structures, and embedding vanadium dioxide in the shape of ┃ between them, a metal-insulator-metal (MIM) structure is achieved. Compared with the conventional MIM structure, the light contact area is increased.

[0025] In the visible light band, the present invention realizes active regulation by using the phase change material vanadium dioxide, and achieves double absorption peak sensitivities of 897.85 nm / RIU and 117.85 nm / RIU in a wide range of n = 1.0 - 1.4, with figure of merit (FOM) values of 33.5 and 3.5 respectively. It improves the multi-functional integration and active regulation capabilities for chiral sensing, and at the same time reduces the cost. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0027] Figure 1 is a three-dimensional view of the chiral metamaterial sensor based on vanadium dioxide of the present invention;

[0028] Figure 2 is a plan view of the chiral metamaterial sensor based on vanadium dioxide of the present invention;

[0029] Figure 3 Among them, a, b, and c are respectively the absorption spectrum diagram, circular dichroism spectrum, and tunability analysis of vanadium dioxide when circularly polarized light is perpendicularly incident under the sensor parameters of Example 1 of the present invention;

[0030] Figure 4 is the surface charge distribution diagram of the sensor of Example 1 of the present invention under different resonance modes, where a, c, e, and g are respectively the distribution diagrams of the left-handed wavelengths 740 nm, 818 nm, 882 nm, and 1170 nm, and b, d, f, and h are respectively the distribution diagrams of the right-handed wavelengths 740 nm, 818 nm, 882 nm, and 1170 nm;

[0031] Figure 5 In it, a, b, and c are respectively the relationship diagram of CD varying with different refractive indices, the relationship diagrams of refractive index and wavelength, and quality factor under the sensor parameters of Embodiment 1 of the present invention;

[0032] Explanation of reference numerals in the figure: 1. U-shaped structure, 11. First base structure, 12. First convex structure, 13. Second convex structure, 2. ┃-shaped structure, 3. L-shaped structure, 31. Second base structure, 32. Third convex structure. Detailed implementation manners

[0033] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0034] This embodiment provides a vanadium dioxide-based chiral metamaterial sensor, including a periodically arranged nanostructure array. Referring to Figure 1-2 as shown, each nanostructure includes a U-shaped structure 1, a ┃-shaped structure 2, and an L-shaped structure 3 that are sequentially connected in series. The materials of the U-shaped structure 1 and the L-shaped structure 3 are metals, and the material of the ┃-shaped structure 2 is vanadium dioxide.

[0035] Based on the active regulation of the vanadium dioxide temperature control material in this embodiment, with a wide range of refractive index changes, a chiral structure pattern with a simple design is adopted. The metals of the U-shaped structure 1 and the L-shaped structure 3 are used, and the vanadium dioxide of the ┃-shaped structure 2 is embedded between them, realizing a metal-insulator-metal (MIM) structure. Compared with the conventional MIM structure, the light contact area is increased; in the visible light band, active regulation is realized by using the phase change material vanadium dioxide, having a multifunctional sensing function.

[0036] As a preferred implementation manner, the U-shaped structure 1 includes a first base structure 11, a first convex structure 12 and a second convex structure 13 respectively disposed at both ends of the first base structure 11. Among them, the second convex structure 13 is connected to the ┃-shaped structure 2; the length L 1 of the first base structure 11 is 160 - 200 nm, preferably 200 nm; the length w 1 of the first convex structure 12 is 35 - 55 nm, preferably 40 nm; the length s of the second convex structure 13 is 35 - 55 nm, preferably 45 nm.

[0037] As a preferred embodiment, the L-shaped structure 3 includes a second substrate structure 31 and a third protrusion structure 32 disposed at one end of the second substrate structure 31; the second substrate structure 31 has the same length as the first substrate structure 11; the sum of the lengths of the third protrusion structure 32 and the ┃-shaped structure 2, l 2 is 135 - 155 nm, preferably 145 nm.

[0038] As a preferred embodiment, the length g of the ┃-shaped structure 2 is 80 - 100 nm, preferably 100 nm.

[0039] As a preferred embodiment, the ┃-shaped structure 2, the second protrusion structure 13, and the third protrusion structure 32 form a straight line. The U-shaped structure 1 and the L-shaped structure 3 are both integral structures. The materials of the U-shaped structure 1 and the L-shaped structure 3 are independently selected from Au or Ag, preferably Au.

[0040] As a preferred embodiment, the height h of the nanostructure is 180 - 220 nm, preferably 190 nm; the thicknesses w of the U-shaped structure 1, the ┃-shaped structure 2, and the L-shaped structure 3 are the same, w = 40 - 50 nm, preferably 45 nm; the period length P of the nanostructure array x and P y are both 445 - 455 nm, preferably 450 nm.

[0041] Example 1

[0042] In this example, the specific parameters of the above-described example sensor are: L 1 = 200 nm, w 1 = 40 nm, s = 45 nm, g = 100 nm, l 2 = 145 nm, w = 45 nm, Px = Py = 450 nm, h = 190 nm; the materials of the U-shaped structure 1 and the L-shaped structure 3 are both gold.

[0043] Effect simulation

[0044] Taking the phase transition temperature as the boundary, vanadium dioxide has a metallic state and an insulating state. When the temperature rises, vanadium dioxide changes from the low-temperature insulating state to the high-temperature metallic state, and its electromagnetic characteristics will change greatly. The Drude model is used to represent the dielectric constant of vanadium dioxide material in the simulation modeling process:

[0045]

[0046] Among them, ε is the dielectric constant at high frequencies, ε ∞ = 12, γ is the collision frequency at high frequencies, γ = 5.75×10 13 rad / s, based on ω p(σ 0 ) = 1.40×10 15 rad / s σ 0 = 3×10 5 S / m

[0047] ,, ω p (σ 0 ) is the plasma frequency when the conductivity is 300000 S / m, where ω p is the plasma frequency. Generally speaking, ω p = (Ne 2 / mε 0 ) 1 / 2 , N is the number of electrons per unit volume of the medium, e is the electron charge, m is the effective mass of the free electrons in the medium, ε 0 is the vacuum permittivity. The effective mass m can be calculated through the band structure, and the free electron density n can be estimated in combination with the crystal structure. However, due to the influence of correlation effects and electron defects in the actual material, its value is not very accurate, and the results here are all proven correct formula and data results. ω is the angular frequency, ω = 2πf, c is the speed of light, λ is the wavelength, and ω changes according to the calculated band range.

[0048] As can be seen from the formula, the conductivity related to temperature can be used to equivalently simulate dynamic IMT. Therefore, the change in conductivity is used to effectively replace the change in temperature to simulate and reflect the IMT of vanadium dioxide. The relative permittivity of vanadium dioxide in the insulating state is set to a constant 9, and the conductivity in the insulating state is less than 200 S / m, and the conductivity in the metallic state is as high as 10 5 S / m.

[0049] In this Example 1 sensor, vanadium dioxide is in the insulating phase at room temperature, and its initial conductivity value is set to 200 S / m and then changes. Left-handed (LCP) and right-handed (RCP) circularly polarized light are set to be perpendicularly incident (perpendicularly incident along the -z direction), and the spectral diagrams of the left-handed and right-handed absorption rates and circular dichroism in the visible light band are obtained. The absorbances of the LCP and RCP lights can be calculated by integrating the resistive losses of the entire metal domain, and are represented by A - and A + respectively. The difference in absorbance between LCP and RCP is characterized by circular dichroism (CD). Therefore, CD can be expressed by CD = A - - A + . Under the structural parameter settings of this Example 1 sensor, Figure 3 is obtained, where Figure 3 a is the absorption spectral diagram when left-handed (LCP) and right-handed (RCP) circularly polarized light are perpendicularly incident,Figure 3 b is the circular dichroism (CD) in the insulating phase state, Figure 3 c is the active regulation of CD under temperature change. Since the conductivity also changes drastically with temperature change, the temperature effect is indirectly replaced by the conductivity change here. Among them, Figure 3 a and Figure 3 σ in b VO2 is 200 S / m, Figure 3 σ in c VO2 is 200 S / m to 1e 5 S / m.

[0050] As can be seen from Figure 3 a, at σ VO2 = 200 S / m, at about wavelengths λ 1 = 740 nm, λ 2 = 818 nm, λ 3 = 882 nm, λ 4 = 1170 nm, 4 obvious absorption peaks are observed, which are respectively denoted as modes 1, 2, 3, 4. The difference between the left-handed and right-handed absorption values leads to the CD effect. Figure 3 a shows that the absorption coefficients of the LCP wave and the RCP wave are significantly different in modes 2 and 3, while the absorption is slightly different in modes 1 and 4. Therefore, as Figure 3 shown in b, an obvious CD valley is observed at modes 2 and 3, and its value is relatively large, being 0.35 and -0.31, which indicates that this structure has a strong chiral effect and simultaneously realizes double-peak positive and negative CD. And Figure 3 as can be seen from c, by simulating by changing the conductivity related to temperature, in this simulation, from 200 S / m (25 °C) to 10e 5 S / m (85 °C), other parameters remain unchanged. With the change of σ VO2 , the CD of modes 2 and 3 initially weakens slowly and then rapidly weakens. This phenomenon confirms that the CD effect of the structure can be regulated by changing the temperature, because the CD values of modes 1 and 4 are too small and are not discussed here.

[0051] As can be seen from the electric field diagram, under the incidence of left-handed and right-handed circularly polarized light, the surface charge distributions in different resonance modes are shown. As Figure 4 shown, red and blue respectively represent positive and negative charges. In mode 1, at a wavelength of 740 nm, under the irradiation of LCP, on one side of the vanadium dioxide gap, referring to Figure 4 a, there is an electric hexapole response mode; under the incidence of left-handed and right-handed circularly polarized light, their dominant multipole resonance modes in mode 1 are different, so the resulting absorption rates are slightly different. Refer to Figure 4b. In modes 2 and 3, i.e., at wavelengths of 818 nm and 882 nm, under LCP illumination, there are two opposite antipole signs on both sides of the vanadium dioxide gap, thus indicating a response mode dominated by an electric quadrupole. Reference Figure 4 c and Figure 4 e. In the case of RCP illumination, as Figure 4 d, Figure 4 f shows, relatively weak resonances can be observed. Therefore, there are significant differences in absorption under modes 2 and 3. Under mode 4, both LCP and RCP form electric dipole oscillations, and the oscillation intensities are slightly different, so the absorptions are relatively close. Reference Figure 4 g and Figure 4 h.

[0052] The sensitivity is calculated under the sensor parameter settings of Example 1. Figure 5 a shows the relationship between CD and different refractive indices, Figure 5 b shows the relationship between refractive index and wavelength. It can be seen that as the refractive index changes from 1.0 to 1.40, within this range, the CD peaks in the short wavelength band continuously decrease and slightly redshift, and the CD peaks in the long wavelength band are relatively stable and continuously redshift, indicating that this structure is sensitive to external changes and at the same time maintains the stability of the CD of this structure. And Figure 5 b clearly shows the relationship between refractive index and wavelength. The ratio S = df / dn, that is, the sensitivity. Here, the sensitivities corresponding to the two CD peaks are calculated to be 897.85 nm / RIU and 117.85 nm / RIU, indicating sensitivity to external environmental changes. At the same time, it can maintain the structural stability and have high sensitivity within the wide range of 1.0 - 1.4. The quality factors corresponding to the two CD peaks are 33.5 and 3.5 respectively, as Figure 5 c shows.

[0053] In summary, the present invention is based on the active regulation of vanadium dioxide temperature control materials, wide-range refractive index changes, designs a chiral structure pattern with a simple structure, uses metals with U-shaped and L-shaped structures, and embeds vanadium dioxide with a ┃-shaped structure between them, realizing a metal - dielectric - metal MIM structure. Compared with the conventional MIM structure, the light contact area is increased; in the visible light band, the phase change material vanadium dioxide is used to achieve active regulation, improving the multifunctional integration effect and active regulation ability for chiral sensing, while reducing costs.

[0054] The present invention has been described in detail above in combination with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent replacements, modifications or improvements can be made to the technical solutions and implementation manners of the present invention, and these all fall within the scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A chiral metamaterial sensor based on vanadium dioxide, characterized in that: It comprises a periodically arranged nanostructure array, each nanostructure comprises a U-shaped structure, a ┃-shaped structure and an L-shaped structure connected in sequence, the U-shaped structure and the L-shaped structure are made of metal, and the ┃-shaped structure is made of vanadium dioxide.

2. The chiral metamaterial sensor based on vanadium dioxide according to claim 1, characterized in that: The U-shaped structure includes a first base structure, a first protruding structure and a second protruding structure respectively arranged at two ends of the first base structure, wherein the second protruding structure is connected to the ┃-shaped structure; The length L1 of the first substrate structure is 160-200 nm; The length w1 of the first protrusion structure is 35-55 nm; The length s of the second protrusion structure is 35-55 nm.

3. The chiral metamaterial sensor based on vanadium dioxide according to claim 2, characterized in that: The L-shaped structure includes a second base structure and a third protruding structure arranged at one end of the second base structure; The second base structure has the same length as the first base structure; The sum of the lengths of the third protruding structure and the ┃-shaped structure, l2, is 135-155 nm.

4. The chiral metamaterial sensor based on vanadium dioxide according to claim 1, characterized in that: The length g of the ┃-shaped structure is 80-100 nm.

5. The chiral metamaterial sensor based on vanadium dioxide according to claim 3, characterized in that: The ┃-shaped structure, the second protruding structure and the third protruding structure form a straight line.

6. The chiral metamaterial sensor based on vanadium dioxide according to claim 1, characterized in that: The height h of the nanostructure is 180-220 nm.

7. The chiral metamaterial sensor based on vanadium dioxide according to claim 1, characterized in that: The thickness w of the U-shaped structure, the ┃-shaped structure and the L-shaped structure is the same, w=40-50nm.

8. The chiral metamaterial sensor based on vanadium dioxide according to claim 1, characterized in that: The period length P of the nanostructure array x and P y Independent is 445-455nm.

9. The chiral metamaterial sensor based on vanadium dioxide according to claim 1, characterized in that: The U-shaped structure and the L-shaped structure are both integral structures.

10. The chiral metamaterial sensor based on vanadium dioxide according to claim 1, characterized in that: The materials of the U-shaped structure and the L-shaped structure are independently selected from Au or Ag.

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