A near-infrared metasurface perfect absorber

Abstract

This invention discloses a near-infrared metasurface perfect absorber for thermionic photoelectric conversion. The absorber includes a silicon dioxide substrate, on which a rectangular array of chromium material is arranged. Four layers of cylinders are stacked on each rectangular unit. The four cylinders all have a radius R and a height H1. The materials of the four cylinders, from bottom to top, are silicon, magnesium fluoride, chromium, and gallium arsenide, respectively. The period P of the rectangular array is consistent with the side length of the rectangular unit. After parameter optimization, an average absorption of 0.923 is achieved in the wavelength range of 800nm ​​to 1800nm, and a maximum absorption of 0.991 is achieved at a wavelength of 1100nm.

Description

Technical Field

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

[0002] Perfect absorbers operating in the near-infrared (NIR) band are widely used in optical communications, broadband thin-film thermal emitters, thermophotovoltaic cells, and photovoltaic cells. Classical light absorbers utilize the natural absorption properties of materials, as well as their recombination and multilayer arrangement, to effectively improve the light absorption rate. However, they typically suffer from narrow operating bandwidth and low efficiency. Therefore, it is necessary to improve the absorption characteristics of absorbers using special materials.

[0003] High-efficiency absorption films play a crucial role in the application of some devices, such as thermal detectors and solar cells. The absorption spectra of these devices can cover all regions from infrared to visible light. Previous researchers have proposed some absorber structures, such as bare metal gratings[1], which can completely absorb electromagnetic waves of a specific band. However, since the absorption of the grating depends on nonlocal surface effects, the incident angle has a large influence on the absorption, which limits the application of the absorber. Another widely used method is the microwave absorber layer[2] and the resonant electromagnetic wave absorbing screen[3] formed based on the metal-dielectric interface. They can selectively absorb electromagnetic waves of a specific frequency, but the minimum thickness of these structures must be greater than a quarter wavelength, which greatly limits their application in miniaturized devices.

[0004] In the electromagnetic spectrum, the region with wavelengths between 0.76 and 1000 μm is generally referred to as the infrared spectrum, which can be further divided into near-infrared (0.76-2.5 μm), mid-infrared (2.5-25 μm), and far-infrared (25-1000 μm). The mid-infrared, also known as thermal infrared or emitted infrared, can be used for nighttime infrared scanning imaging. Furthermore, the fundamental absorption bands of most organic and inorganic substances appear in the mid-infrared region. Therefore, researching a metamaterial perfect absorber in the mid-infrared band has significant practical application value in the detection of hazardous substances.

[0005] To improve absorption, metamaterials are a better choice. Metamaterials are artificial composite materials with subwavelength structures, and subwavelength metal nanophotonic structures have become a research hotspot. Metal-dielectric-metal three-layer metal cavity structure, the upper metal structure of the cavity has a periodic distribution, with subwavelength slits, while the metal film of the substrate is thick enough to prevent wave transmission [4]. Studies have found that such microcavities have absorption characteristics in the optical and microwave bands. Such microstructures have application value in the integration of photonic devices. Metamaterials have many exotic properties that cannot be obtained from naturally occurring materials. They can produce the required dielectric constant or permeability by adjusting the size and geometry of the structure. These structures have a variety of applications in the field of light trapping and manipulation. The electromagnetic properties of metamaterials are described according to effective parameters. This property makes metamaterials have great potential in various applications, including optical manipulation, imaging, sensing, superlenses and other processes. Among them, field metamaterial perfect absorbers (MPAs) have been a considerable research topic in recent years.

[0006] In addition, selective optical perfect absorbers also have significant applications. A selective optical perfect absorber is an optical device capable of achieving near 100% absorption of incident light within a specific wavelength or band. Based on the relationship between absorptivity A, reflectivity R, and transmittance T: A = 1 - RT, to achieve perfect absorption, suitable materials and structural parameters need to be selected to match the free-space impedance in the desired wavelength band. The overall impedance is calculated and designed to reduce reflectivity R, and a thicker metal layer is used to bring the transmittance close to zero.

[0007] In addition to the methods mentioned above, the experimental fabrication of various periodic micro / nano structures has become possible in the last decade or so with the development of nanofabrication technology. Currently, most absorber structures are centrosymmetric, achieving perfect absorption when electromagnetic waves are incident perpendicularly, and the absorption effect is affected by the angle and polarization of the incident electromagnetic wave.

[0008] [1]Collin S, Pardo F, Teissier R, Pelouard J. Efficient light absorption in metal–semiconductor–metal nanostructures. Appliedphysics letters 2004,85:194.

[0009] [2]Reinert J,Psilopoulos J,Grubert J,Jacob A.On the potentialofgraded-chiral Dallenbach absorbers.Microwave and Optical Technology Letters2001,30:254.

[0010] [3]EnghetaN.Thin absorbing screens using metamaterialsurfaces.Antennas and Propagation Society International Symposium 2002,2:392.

[0011] [4]Hibbins A,Murray W,Tyler J,Wedge S,Barnes W,Sambles P.Resonantabsorption of electromagnetic fileds by surface plasmons buried in amultilayeredplasmonic nano-structure.Physical Review B 2006,74:073408. Summary of the Invention

[0012] Purpose of the invention: In view of the above-mentioned prior art, a near-infrared metasurface perfect absorber is proposed for thermionic photoelectric conversion, achieving an average absorption rate of up to 0.923 in the wavelength range of 800nm ​​to 1800nm.

[0013] Technical solution: A near-infrared metasurface perfect absorber includes a silicon dioxide substrate, on which a rectangular array of chromium material is disposed, and four layers of cylinders are superimposed on each rectangular unit; the radius of the four cylinders is R and the height is H1, and the materials of the four cylinders from bottom to top are silicon, magnesium fluoride, chromium and gallium arsenide; the period P of the rectangular array is the same as the side length of the rectangular unit.

[0014] Furthermore, the value of H1 ranges from 0.21 μm to 0.22 μm, the value of R ranges from 0.14 μm to 0.15 μm, and the value of P ranges from 0.46 μm to 0.50 μm.

[0015] Furthermore, H1 = 0.22 μm, R = 0.14 μm, and P = 0.50 μm.

[0016] Furthermore, the thickness of the transparent substrate is H = 10 μm, and the height of the rectangular unit is H2 = 0.44 μm.

[0017] Beneficial Effects: This invention designs a near-infrared metasurface perfect absorber for thermionic photoelectric conversion. This absorber consists of a single rectangular layer and four cylindrical layers. Silicon dioxide (SiO2) serves as the substrate, with a rectangular array of chromium (Cr) material at the bottom. Four cylindrical layers are stacked on top, consisting of a silicon (Si) layer, a magnesium fluoride (MgF2) layer, a chromium (Cr) layer, and a gallium arsenide (GaAs) layer, respectively, from bottom to top. Each layer has the same thickness, and the layers are stacked without gaps. After parameter optimization, an average absorption of 0.923 is achieved in the 800nm ​​to 1800nm ​​wavelength range, with a peak absorption of 0.991 at 1100nm. This device provides a foundation for the design and fabrication of near-infrared perfect absorbers. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the near-infrared metasurface perfect absorber of the present invention;

[0019] Figure 2 A cross-sectional view of the structure cut along the diameter of the hole for one period;

[0020] Figure 3 This represents the theoretical value of the absorption spectrum of the absorber in the wavelength range of 800 nm to 1800 nm.

[0021] Figure 4 The absorption spectra of the structure and the comparative structure are shown below. (a) is the absorption spectrum of the cylinder without the materials GaAs, Cr, Si and MgF2, (b) is the absorption spectrum of the cylinder without GaAs, Cr and MgF2, (c) is the absorption spectrum of the cylinder without GaAs and Cr, (d) is the absorption spectrum of the cylinder without GaAs, and (e) is the absorption spectrum of the entire structure.

[0022] Figure 5 The effect of parameter P on the overall absorption rate;

[0023] Figure 6 The effect of parameter H1 on the overall absorption rate;

[0024] Figure 7 Let R be the effect of the parameter on the overall absorption rate. Detailed Implementation

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

[0026] like Figure 1 , Figure 2As shown, a near-infrared metasurface perfect absorber includes a silicon dioxide substrate with height H. A rectangular array of chromium material is disposed on the substrate. The height of the rectangular array is H2, and the period of the rectangular array is P, which is consistent with the side length of the rectangular unit. Four cylindrical layers are sequentially deposited on each rectangular unit. The radius of each of the four cylinders is R, and the height of each cylinder is H1. The materials of the four cylinders, from bottom to top, are silicon, magnesium fluoride, chromium, and gallium arsenide, respectively. The values ​​of H1 range from 0.21 μm to 0.22 μm, R ranges from 0.14 μm to 0.15 μm, and P ranges from 0.46 μm to 0.50 μm.

[0027] A perfect absorber was fabricated using two-beam interference lithography and sputtering deposition, with optimized parameters: H1 = 0.22 μm, R = 0.14 μm, P = 0.50 μm, H2 = 0.44 μm, and H = 10 μm. Figure 1 As shown by the arrow, light is incident along the Z direction, that is, perpendicularly incident from the bottom of the transparent substrate. Figure 3 The theoretical absorption spectra of the optimized structure are shown. It can be seen that an average absorption of 0.923 is achieved in the 800 nm to 1800 nm wavelength range, with a peak absorption of 0.991 at 1100 nm. Because this near-infrared perfect absorber is symmetrical along the X and Y directions, the high broadband absorption is independent of polarization.

[0028] Next, we will analyze the physical mechanism of the perfect absorption by this near-infrared absorber. For light with wavelengths greater than 800 nm, the materials used, such as TiO2, SiO2, and MgF2, are all non-reflective. Figure 4 Figure (a) shows the absorption spectrum without the GaAs, Cr, Si, and MgF2 layers, indicating that the absorption is not high. However, when a Si layer is added, the absorption is significantly enhanced, as shown in Figure (a). Figure 4 As shown in (b). Figure 4 As shown in (c), adding a MgF2 layer can further reduce reflection and increase absorption, but the absorption is still not high near 1800 nm. Figure 4 (d) shows the absorption spectrum with an additional Cr layer. Figure 4 (e) is the absorption spectrum after adding a GaAs layer, with an average absorptivity of 0.923. MgF2 was also used as another AR layer to achieve high absorption. By repeatedly adjusting the parameters of each layer, perfect near-infrared absorption based on this material structure was achieved.

[0029] To further reveal the working principle of this metasurface three-dimensional structure and explore the allowable range of parameter errors that are unavoidable in actual manufacturing, this invention attempts to find the influence of different parameter values ​​on the absorption performance of the absorber by changing its various parameters using the controlled variable method, thus providing some guidance for actual production.

[0030] With other simulation parameters remaining constant—base layer thickness H = 10 μm, cylinder height H1 = 0.22 μm, rectangular unit height H2 = 0.44 μm, and cylinder radius R = 0.14 μm—changing the array period P, the change in the structure's transmittance to incident light is as follows: Figure 5 As shown, when parameter P changes from 460nm to 550nm in 10nm increments, the overall transmittance changes significantly. Figure 5 It can be seen that in the wavelength range of 1600nm-1800nm, the absorption rate increases from 80% to over 90% as the P value increases. It can be observed that the absorption rate reaches its optimal state when P = 0.50μm.

[0031] After determining the array period P = 0.50 μm, while keeping the substrate thickness H = 10 μm, the rectangular unit height H2 = 0.44 μm, the cylinder radius R = 0.14 μm, and the array period P = 0.50 μm constant, the height H1 of the cylinder was changed, and its effect on the overall performance was observed. The process of absorptivity change is as follows: Figure 6 As shown, when H1 = 0.22 μm, the absorption rate is most stable and averages over 90% across the entire near-infrared band of 800 nm to 1800 nm.

[0032] After determining the array period P = 0.50 μm and the cylinder thickness H1 = 0.22 μm, the effect of changing the cylinder radius R on the absorptivity was determined. Keeping other data constant, only the cylinder radius R was changed. The absorptivity change process is as follows: Figure 7 As shown, the overall absorption rate of the metasurface is not ideal when the radius R is small or large. Only when R = 0.14 μm is the absorption rate relatively ideal in the entire near-infrared band of 800 nm-1800 nm, with an average absorption rate of nearly 90% or more.

[0033] Analysis of the above geometric parameters reveals that the array period P, cylinder radius R, and cylinder height H1 significantly influence the absorptivity of the metasurface three-dimensional structure. Overall, the size of the absorber structure, the cylinder diameter, and the height greatly affect the absorptivity of the incident light, directly impacting the absorber's performance. Therefore, extensive simulations are needed to continuously optimize parameters P, R, and H1 to find the optimal balance. Chromium (Cr) and silicon dioxide (SiO2) are chosen as substrates for the perfect absorber due to their thermal stability at high temperatures, while the thickness H of the SiO2 substrate layer has little impact on the overall structure.

[0034] 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 near-infrared metasurface perfect absorber, characterized in that, The device includes a silicon dioxide substrate, on which a rectangular unit array made of chromium is disposed, and four layers of cylinders are superimposed on each rectangular unit; the radius of the four cylinders is R and the height is H1, and the materials of the four cylinders from bottom to top are silicon, magnesium fluoride, chromium and gallium arsenide, respectively; the period P of the rectangular unit array is the same as the side length of the rectangular unit; the value of H1 ranges from 0.21μm to 0.22μm, the value of R ranges from 0.14μm to 0.15μm, and the value of P ranges from 0.46μm to 0.50μm.

2. The near-infrared metasurface perfect absorber according to claim 1, characterized in that, H1=0.22μm, R=0.14μm, P=0.50μm.

3. The near-infrared metasurface perfect absorber according to claim 1 or 2, characterized in that, The thickness of the silicon dioxide substrate is H=10μm, and the height of the rectangular unit is H2=0.44μm.

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