A nano-circle structure based metasurface perfect cut-off absorber

Abstract

The application discloses a kind of perfect cutoff absorber of metasurface based on nano round structure, adopt nanometer cylinder and ring array grown on silicon dioxide, two groups of ring structure are respectively selected using dielectric material gallium arsenide and silicon.Optimizing structure parameter, wavelength from ultraviolet to mid-infrared, 0.913 average absorption is realized in absorption band 100-710nm, and average absorption is only 0.02 in non-absorption band 1260nm-20μm wave band.ER is 9.6dB, ED is 0.81, and CS is 0.0015nm ‑1 The perfect cutoff absorber provided by the application has exactly this spectral selectivity, which provides an effective method for designing ideal solar heat absorber, which has important application in the field of renewable energy, such as solar thermal photovoltaic and solar thermal energy application.

Description

Technical Field

[0001] This invention relates to an optical device, and more specifically to a metamaterial absorber. Background Technology

[0002] Metamaterials are man-made materials designed to exhibit extraordinary electromagnetic properties not found in nature. Their potential applications are diverse, including antenna systems, electromagnetic stealth, optical imaging, and high-sensitivity sensing. In most applications, the absorption loss of metamaterials typically degrades performance; however, for artificial light absorbers, absorption loss becomes useful, and metamaterial absorbers can be designed by adjusting the geometry and shape of the metamaterial structure. Perfect absorption of electromagnetic waves in specific frequency bands has already been achieved. A perfect absorber is an optical device that eliminates both transmission and reflection and absorbs all incident light.

[0003] In recent years, metasurface nanostructures have attracted widespread attention due to their optical manipulation capabilities and multifunctionality in ultrathin optical applications. They have been widely used in many fields, such as structural colors, photodetectors, and sensors, and broadband perfect absorbers based on nanostructures have also been extensively studied and published.

[0004] In many applications, a clear absorption cutoff is required between the absorption band and the non-absorption band. The cutoff absorption efficiency can be expressed as the extinction ratio ER = 10 * log(A). a / A n )dB, where A a For the minimum absorption within the absorption band, A n The maximum absorption is within the non-absorption band; extinction difference ED = A a -A n Cutoff slope CS = (A a -A n ) / (λ a -λ n ), where λ a λ represents the maximum / minimum wavelength within the absorption band. n The minimum / maximum wavelengths are within the non-absorption band. Hossain et al. proposed a highly efficient radiation-cooled metamaterial emitter with absorbers exhibiting ER, ED, and CS values ​​of 6.40 dB, ~0.64 nm, and ~0.00013 nm, respectively. -1 [1]. Zou et al. proposed an absorber based on the principle of extended bandwidth by superimposing multiple absorption peaks, which showed an absorptivity of over 0.8 in a bandwidth of about 1.2 THz at the center frequency of 4.98 THz, and the absorption outside this range decreased to 0.1 and 0.2, respectively [2]. Ideally, ER, ED and CS should be as large as possible. These works have made great progress in the field of broadband absorbers, but they have not considered the cutoff efficiency, which is important in applications.

[0005] [1]Md,Muntasir,Hossain,et al.A Metamaterial Emitter for HighlyEfficient Radiative Cooling[J].Advanced Optical Materials,2015,3(8):1047-1051.

[0006] [2]Zou TB, Hu FR, Jing X, et al. Design of a polarization-insensitive and broadband terahertz absorber using metamaterials[J]. Acta Physica Sinica, 63(17). Summary of the Invention

[0007] Purpose of the invention: In view of the above-mentioned prior art, a metasurface perfect cutoff absorber based on a nanocircular structure is proposed, which has high absorption in the range from ultraviolet to mid-infrared, while the absorption rate is close to zero in any wavelength range longer than the cutoff wavelength.

[0008] Technical solution: A metasurface perfect cutoff absorber based on a nanocircular structure includes a substrate on which an array of nanocylinders is disposed. Each nanocylinder has a coaxial inner ring and an outer ring at its top. The inner ring and the outer ring are made of different dielectric materials. The height of the outer ring is less than the height of the inner ring, and the outer diameter of the inner ring is equal to the inner diameter of the outer ring.

[0009] Furthermore, the diameter of the nanocylinder is consistent with the array period.

[0010] Furthermore, the inner ring is made of gallium arsenide, and the outer ring is made of silicon.

[0011] Furthermore, the nanocylinders are made of aluminum, and the substrate is made of silicon dioxide.

[0012] Furthermore, the inner ring has an inner diameter r1 = 68 nm and a height h2 = 120 nm; the outer ring has an outer diameter r3 = 130 nm and a height h3 = 50 nm; the nanocylinder has a height h1 = 146 nm, and the nanocylinder array has a period P = 292 nm.

[0013] Furthermore, the outer diameter of the inner ring is r2 = 100 nm.

[0014] Beneficial Effects: This invention, as a cutoff perfect absorber, employs an array of nanocylinders and rings grown on silicon dioxide. The cylindrical structure uses low-cost aluminum, while the two sets of ring structures are made of gallium arsenide and silicon, respectively, dielectric materials. After optimizing the structural parameters, an average absorptivity of 0.913 is achieved in the absorption band of 100-710 nm, from ultraviolet to mid-infrared (100 nm-20 μm). Furthermore, the absorption drops sharply from 0.911 at 710 nm to 0.1 at 1260 nm, and the average absorption in the non-absorption band of 1260 nm-20 μm is only 0.02. The extinction ratio is 9.6 dB, the extinction difference is 0.81, and the cutoff slope is 0.0015 nm. -1 .

[0015] To prevent the re-radiation of energy spontaneously absorbed by an object in the mid-infrared wavelength range, an ideal solar thermal absorber exhibits high absorption from the ultraviolet to the mid-infrared, while its absorptivity approaches zero in any wavelength range longer than the cutoff wavelength. The perfect cutoff absorber proposed in this invention possesses precisely this spectral selectivity, providing an effective method for designing ideal solar thermal absorbers, which has important applications in the field of renewable energy, such as solar thermal photovoltaic and solar thermal energy applications. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the metasurface perfect cutoff absorber of the present invention;

[0017] Figure 2 A schematic diagram of a cross-sectional structure cut along the diameter of a hole for one cycle;

[0018] Figure 3 The theoretical value curve of the absorption spectrum of the metasurface perfect cutoff absorber in the 100nm to 20μm band is shown in the example.

[0019] Figure 4 The simulation diagram shows the effect of parameter P on the overall absorption.

[0020] Figure 5 The simulation diagram shows the effect of parameter h1 on the overall absorption.

[0021] Figure 6 The simulation diagram shows the effect of parameter h2 on the overall absorption.

[0022] Figure 7 The simulation diagram shows the effect of parameter h3 on the overall absorption.

[0023] Figure 8 The simulation diagram shows the effect of parameter r1 on the overall absorption.

[0024] Figure 9 The simulation diagram shows the effect of parameter r3 on the overall absorption. Detailed Implementation

[0025] The invention will now be further explained with reference to the accompanying drawings.

[0026] like Figure 1 , Figure 2 As shown, a metasurface perfect cutoff absorber based on a nanocircular structure is constructed by uniformly epitaxially growing an array of aluminum nanopillars on a silicon dioxide (SiO2) substrate. The diameter of the nanopillars is consistent with the array period P, and the height is h1. Each nanopillar has a coaxial GaAs inner ring and a Si outer ring at its top. The inner ring has an inner diameter of r1, an outer diameter of r2, and a height of h2; the outer ring has an inner diameter of r2, an outer diameter of r3, and a height of h3.

[0027] The broadband absorption of the metasurface perfect cutoff absorber of this invention was calculated and optimized using the finite-difference time-domain (FDTD) method, and the optimized parameters were: r1 = 68 nm, r2 = 100 nm, r3 = 130 nm, h1 = 146 nm, h2 = 120 nm, h3 = 50 nm, and P = 292 nm. Figure 3 The theoretical values ​​of the absorption spectrum of the optimized structure are shown, with light incident along the -Z direction, i.e. Figure 1 As indicated by the arrows, the average absorption is 0.913 in the wavelength band (absorption band) between 100-710 nm, decreasing sharply from 0.911 at 710 nm to 0.1 at 1260 nm. In the non-absorption band (1260 nm-20 μm), the average absorption is only 0.02. The extinction ratio (ER) is 9.6 dB, the extinction difference (ED) is 0.81, and the cutoff slope (CS) is 0.0015 nm. -1 .

[0028] The physical mechanism of perfect cutoff absorption in the metasurface perfect cutoff absorber of this invention is studied using the finite-difference time-domain (FDTD) method. The allowable range of parameter error in actual manufacturing is explored. The influence of different geometric parameters on the working performance of the absorber is studied by changing each geometric parameter in turn using the controlled variable method.

[0029] With other simulation parameters remaining constant, the change in the absorption rate of the structure to incident light as the array period P changes is as follows: Figure 4 As shown. The simulation range was set from 272nm to 322nm, with a simulation step size of 10nm. Figure 4It can be seen that when P is small, the absorption in the absorption band is too low (the lowest average absorption is 0.890) to achieve an ideal absorber. When the period P = 292 nm, the absorption in the absorption band reaches its maximum, with an average absorption of 0.913. When the P value is further increased, although the cutoff region between the absorption band and the non-absorption band shortens from 710-1260 nm to 710-1200 nm, the cutoff performance increases, but the difference is not significant, and the absorption in the absorption band decreases to varying degrees. In order to maintain both high absorption and sharp cutoff in the absorption band, this invention sets P = 292 nm in the cutoff perfect absorber.

[0030] With other simulation parameters remaining constant, the change in the structure's absorptivity to incident light as the height h1 changes is as follows: Figure 5 As shown. The simulation range is set from 110nm to 182nm, with a simulation step size of 12nm. Figure 5 It can be seen that h1 has little relation to the cutoff value. When h1 is too small, the average absorption in the short-wavelength band decreases to 0.906, and when h1 exceeds 146 nm, it has almost no impact on device performance. This invention sets h1 = 146 nm to reduce the size of the structure, which is an advantage in manufacturing.

[0031] With other simulation parameters remaining constant, the change in the structure's absorptivity to incident light as the height h2 changes is as follows: Figure 6 As shown. The simulation range is set from 84nm to 156nm, with a simulation step size of 12nm. Figure 6 It can be seen that as the h2 value shifts by 120 nm, the absorption in the absorption band decreases to varying degrees, with the average absorption decreasing from 0.913 to 0.890. Regarding cutoff performance, as the h2 value increases, the cutoff region gradually lengthens from 710-1180 nm to 660-1360 nm, resulting in a slight decrease in cutoff performance. Similarly, to simultaneously maintain high absorption and sharp cutoff in the absorption band, this invention sets h2 = 120 nm in the cutoff perfect absorber. Figure 7 The absorption spectra of different h3 values ​​are shown, which are consistent with... Figure 6 Similar changes will not be elaborated here. For similar reasons, this invention sets h3 = 50nm.

[0032] With other simulation parameters remaining constant, the change in the absorption rate of the structure to incident light as the inner diameter r1 of the GaAs ring changes is as follows: Figure 8 As shown. The simulation range is set from 44nm to 92nm, with a simulation step size of 8nm. (From...) Figure 8It can be seen that when r1 deviates from 68 nm, the absorbance values ​​in the absorption band decrease to varying degrees (the lowest average absorbance is 0.878). As r1 increases from 44 nm to 84 nm (i.e., the ring width of the GaAS ring gradually narrows), the cutoff region gradually shortens from 720-1400 nm to 640-1140 nm, and the cutoff performance improves. When r1 further increases to 92 nm, a fluctuation appears in the cutoff region, and the cutoff performance decreases. Similarly, in order to maintain both high absorption and sharp cutoff in the absorption band, this invention sets r1 = 68 nm in the cutoff perfect absorber.

[0033] With other simulation parameters remaining constant, the change in the absorption rate of the structure to incident light as the outer diameter r3 of the Si ring changes is as follows: Figure 9 As shown. The simulation range was set from 106nm to 142nm, with a simulation step size of 6nm. Figure 9 It can be seen that when r3 deviates from 130 nm, the absorption value in the absorption band decreases to varying degrees, especially when r3 = 142 nm, the lowest average absorption drops to 0.878. As r3 increases from 106 nm to 136 nm (i.e., the ring width of the Si ring gradually widens), the cutoff region gradually stretches from 720-1180 nm to 720-1280 nm, and the cutoff performance decreases slightly. When r3 further increases to 142 nm, a dip appears in the cutoff, and the cutoff performance decreases. Similarly, in order to maintain both high absorption and sharp cutoff in the absorption band, this invention sets r3 = 130 nm in the cutoff perfect absorber.

[0034] r2 is not discussed here because it only serves to locate the connection point of the two rings. In this invention, r2 is set to 100nm, meaning that this invention only optimizes the width of the two rings, i.e., optimizing r1 and r3 is sufficient.

[0035] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A metasurface perfect cutoff absorber based on a nanocircle structure, characterized in that, The device includes a substrate on which an array of nanocylinders is disposed. Each nanocylinder has a coaxial inner ring and an outer ring at its top. The inner ring and the outer ring are made of different dielectric materials. The height of the outer ring is less than the height of the inner ring, and the outer diameter of the inner ring is equal to the inner diameter of the outer ring. The inner ring is made of gallium arsenide, and the outer ring is made of silicon. The inner ring has an inner diameter r1 = 68 nm, an outer diameter r2 = 100 nm, and a height h2 = 120 nm; the outer ring has an outer diameter r3 = 130 nm and a height h3 = 50 nm; the nanocylinder has a height h1 = 146 nm, and the nanocylinder array has a period P = 292 nm.

2. The metasurface perfect cutoff absorber based on a nanocircle structure according to claim 1, characterized in that, The diameter of the nanocylinder is consistent with the array period.

3. The metasurface perfect cutoff absorber based on a nanocircle structure according to claim 1, characterized in that, The nanocylinders are made of aluminum, and the substrate is made of silicon dioxide.

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