Metal spiral-thin film composite structure, wide-spectrum chiral absorber and preparation method

Abstract

The invention discloses a metal spiral-thin film composite structure with a wide-spectrum chiral absorption function. The metal spiral-thin film composite structure comprises a thin film I of a plane structure, a chiral spiral structure axially and vertically arranged on the thin film I and a thin film II covering the outer surface of the chiral spiral structure. Meanwhile, the invention further discloses a wide-spectrum chiral absorber based on the metal spiral-thin film composite structure and a preparation method of the wide-spectrum chiral absorber. The problem that high circular dichroism absorptivity and wide-spectrum modulation are difficult to realize at the same time in the existing chiral optical field is solved. The chiral absorption device with wide spectrum modulation and high circular dichroism has outstanding advantages and good application prospects in the fields of chiral sensing, chiral imaging and the like.

Description

Technical Field

[0001] The present invention belongs to the field of 3D chiral metamaterials, and in particular relates to a metal spiral-thin film composite structure, a wide-spectrum chiral absorber and a preparation method thereof. Background Art

[0002] Circular dichroism (CD) of micro-nanostructures is a dichroism that involves the interaction between circularly polarized light and structure, that is, the difference in reflectivity of the structure to left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP). Many chiral molecules in nature can produce circular dichroism in specific wavelengths, but the circular dichroism response of most of these natural materials is relatively weak and cannot meet the needs of chiral applications.

[0003] In recent years, researchers have proposed many chiral devices based on artificial metamaterials. Through structural design, they can achieve selective transmission and reflection of specific circularly polarized light in a wide spectral range. The wavelength of the device can be designed by adjusting the structural feature size. Among them, terahertz frequency band chiral metamaterials have been studied in depth due to their wide application prospects in communications, radar, electromagnetic shielding and other fields.

[0004] However, the existing technology can mainly regulate the transmission and reflection of light, but has little effect on absorption, which limits its application and development in the fields of terahertz chiral imaging, chiral sensing, photoelectric detectors, etc. Therefore, designing and processing a new type of chiral absorber with high CD response and wide spectrum modulation has become a research hotspot. Summary of the invention

[0005] The present invention proposes a novel metal spiral-thin film composite structure and a wide-spectrum chiral absorption device with a wide-spectrum chiral absorption function. The spiral-thin film composite structure can selectively absorb circularly polarized light in a wide band (such as a 3-7 micron wide band).

[0006] The present invention cooperates with the circular dichroism response of the chiral helix and utilizes the selective enhancement generated by the chiral light at the film to increase the absorption CD of the structure to 0.8. This solves the problems of small circular dichroism and narrow modulation range of the current terahertz chiral absorber.

[0007] In order to achieve the above object, the present invention selects the following technical solutions:

[0008] The present invention proposes a novel metal spiral-film composite structure. In order to make it have the advantages of strong circular dichroism absorption and wide modulation frequency band in the terahertz frequency band, the technical solution uses finite element simulation software to optimize the structure design.

[0009] A metal spiral-film composite structure with a wide-spectrum chiral absorption function comprises: a film I with a planar structure, and a chiral spiral structure axially and vertically arranged on the film I.

[0010] The chiral helical structure is an equal-radius helical structure similar to a spring structure, and is a micro-nano sized structure as a whole.

[0011] Preferably, the chiral helical structure consists of a chiral helical structure body and a film II covering the outer surface of the chiral helical structure body.

[0012] The chiral helical structure can localize chiral light of a specific wavelength and a specific direction on the film, thereby achieving enhanced absorption of specific chiral light by film I, and ultimately achieving selective enhanced absorption of a wide spectrum of chiral light by the combined action of the micro-nano chiral helical structure and the film.

[0013] The main material of the chiral helical structure is mainly determined by its processing technology, which serves as a template for the chiral helical structure and ultimately forms a metallic chiral helical structure with a metal shell.

[0014] Preferably, the number of turns of the chiral helical structure is 1 to 3, and the array period is 1 to 3 microns (more preferably 2 microns).

[0015] Preferably, the radius and height of the chiral helical structure are determined by the operating wavelength. That is, the present invention can select the characteristic parameters (height, radius, number of turns, spiral radius, etc.) of the chiral helical structure according to the operating wavelength. Preferably, the chiral helical structure is a chiral helical structure of micro-nano size. The present invention utilizes the combined effect of the micro-nano chiral helical structure and the film to achieve selective absorption of a wide spectrum of chiral light. Among them, the maximum characteristic parameter of the chiral helical structure is less than 10 microns, more preferably less than 8 microns, and further less than 5 microns.

[0016] The wide-spectrum action band of the micro-nano chiral helical structure is terahertz (3-7 μm). Taking the working wavelength terahertz (3-7 μm) as an example, the height of the chiral helical structure is 2 to 10 μm, the radius of the chiral helical structure is 0.1 to 1 μm, the number of turns is 1 to 3 turns, and the maximum size of the helical cross section is 0.5 to 2 microns.

[0017] Preferably, the height of the chiral helical structure is 10 to 20 times the radius.

[0018] The chiral absorption medium used in the present invention is a metal film, that is, the film I is a metal film. The metal types include but are not limited to gold, silver, platinum, etc. Preferably, the metal film is gold.

[0019] Preferably, the materials of the thin film I and the thin film II may be the same or different, and are independently selected from gold, silver, platinum and copper.

[0020] Preferably, the film I and the film II are made of the same material and have a thickness of less than 100 nm. Preferably, the thickness of the metal film is 10 to 30 nanometers; more preferably, the thickness of the metal film is 20 nm.

[0021] The metal spiral-film composite structure has a large difference in absorptivity for left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP), and has a polarization selective absorption effect. The chiral absorption CD of the metal spiral-film composite structure can reach up to 0.8.

[0022] A wide-spectrum chiral absorber based on a metal spiral-thin film composite structure comprises a substrate and a composite structure arranged on the substrate, wherein the composite structure is the metal spiral-thin film composite structure described in any one of the above technical solutions.

[0023] A method for preparing the wide-spectrum chiral absorber based on the metal spiral-thin film composite structure comprises: processing the chiral spiral structure body on a substrate, and precipitating thin film I and thin film II.

[0024] Preferably, the main part of the chiral helical structure is processed by two-photon polymerization or focused ion beam induced deposition; and thin films I and II are prepared by magnetron sputtering, thermal evaporation, electron beam evaporation, chemical plating deposition, etc.

[0025] The chiral absorption used in the present invention can be designed to be compatible with different wavebands, including but not limited to terahertz, near infrared, visible light, etc.

[0026] Preferably, the wave band is the terahertz wave band.

[0027] The present invention provides a novel wide-spectrum chiral absorption device based on a metal chiral spiral-thin film composite structure. The circular dichroism response of the metal spiral can produce chirality enhancement of the light field at the metal film, so that the device produces a large circular dichroism absorption (maximum CD is 0.8) in the red infrared (3-7μm), which solves the problem that high circular dichroism absorption and wide spectrum modulation are difficult to achieve simultaneously in the current field of chiral optics. Experimentally, we used two-photon polymerization 3D printing and magnetron sputtering coating to process the device, and proved the optical performance of the device from both finite element simulation and experimental characterization. This type of chiral absorption device with wide spectrum modulation and high circular dichroism has outstanding advantages and good application prospects in the fields of chiral sensing and chiral imaging.

[0028] In summary, the present invention solves the problem that high chiral circular dichroism and wide spectrum modulation are difficult to achieve simultaneously in the current field of chiral optics by designing a new type of metal spiral-thin film composite chiral absorption structure, and realizes high absorption CD optical response in the 3-7μm band. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the design of metal chiral helix-film composite structure.

[0030] Among them, (a) is a metal chiral helix (left-handed), (b) is a metal film, and (c) is a metal chiral helix-film composite structure.

[0031] Figure 2 The presence or absence of an absorption film affects the absorption performance of the device.

[0032] Among them, (a) is the absorption spectrum of the metal chiral helix, and (b) is the absorption spectrum of the metal chiral helix-thin film composite structure.

[0033] Figure 3 This is the SEM image of the metal chiral helix-thin film composite structure.

[0034] Among them, (a) is a side view, and (b) is a top view.

[0035] Figure 4 FDTD simulation chiral absorption spectrum and experimental characterization spectrum for the structure.

[0036] Among them, (a) is the simulated spectrum, and (b) is the experimental characterization spectrum.

[0037] Figure 5 This is the FDTD simulation chiral absorption spectrum and experimental characterization spectrum of the metal chiral spiral-thin film composite structure after being magnified 1.5 times. DETAILED DESCRIPTION

[0038] For ease of understanding, the present invention is further described below in conjunction with the accompanying drawings. The present invention designs a novel metal chiral spiral-film composite structure chiral absorber, comprising a film I and a chiral spiral structure axially arranged vertically on the film, wherein the chiral spiral structure is composed of a chiral spiral body and a film II laid on the chiral spiral structure body. The chiral spiral structure is as follows Figure 1 As shown in (a) (structural parameters are as follows: height: 5 μm, radius: 0.4 μm, number of turns: 2 turns, spiral cross section is similar to an ellipse, and the major axis size is about 1 micron), the material used for film I and film II is gold. In order to produce better circular dichroism, the period of the array structure (x, y direction) is designed to be 2 microns. Note that the above parameters are only preferred embodiments of the present invention to help understand the present invention, and therefore should not be considered to limit the scope of the present invention. Figure 1 As shown in (b), a metal film absorption layer (film II) is designed between the spiral and the substrate, and a metal film II is deposited on the outer wall of the chiral spiral structure to form Figure 1 (c) shows the metal chiral spiral-film composite structure, wherein the thickness of metal film I and metal film II is 20 nm.

[0039] However, if Figure 2 As shown in (a), the helical structure itself cannot produce selective chiral absorption response.

[0040] The chiral absorption spectrum of the composite structure obtained in this example is as follows: Figure 2 (b) as shown. Figure 2 In the figure, the dashed line represents right-handed circularly polarized light, and the solid line represents left-handed circularly polarized light. The chiral light response of the spiral can produce chirality enhancement at the film, which increases the film's absorptivity of right-handed circularly polarized light (RCP) by 0.4, while at the same time, does not change its absorption characteristics of left-handed circularly polarized light (LCP). Therefore, the addition of the metal film increases the chiral CD (circular dichroism factor) of the chiral system by 0.4.

[0041] In the experiment, two-photon micro-nano 3D printing was used to process the 3D spiral structure on the substrate, and then magnetron sputtering was used to coat the metal layer on the outer surface of the spiral structure and the substrate. Figure 3 shown.

[0042] The simulated absorption spectrum of the device is shown in Figure 4 (a) shows the experimentally measured reflectance spectrum. Figure 4 (b) The results show that the chiral helical structure has good absorption circular dichroism in the 3-7μm band. At the same time, the absorption rate of the structure to RCP is as high as nearly 100%, and the highest absorption CD of the device is about 0.8, which well reflects its selective absorption of circularly polarized light.

[0043] According to different actual application scenarios, the working wavelength range of the chiral device can be freely designed, and the characteristic size of the helical structure is positively correlated with the working wavelength. Figure 5 As shown in the figure, when the characteristic size of the chiral helical structure is enlarged by 1.5 times, the optical response wavelength of the chiral device is red-shifted to 5-9μm, which proves the designability of the device. In addition, when selecting thin film materials, the corresponding material with absorption performance for the specific light can be selected according to the size of the target working wavelength.

Claims

1. A metal spiral-thin film composite structure with broad-spectrum chiral absorption function, characterized in that: include: A film I with a planar structure and a chiral helical structure axially and vertically arranged on the film I.

2. The metal spiral-thin film composite structure with broad-spectrum chiral absorption function according to claim 1, characterized in that: The number of turns of the chiral helical structure is 1 to 3, and the array period is 1 to 3 microns.

3. The metal spiral-thin film composite structure with broad-spectrum chiral absorption function according to claim 1, characterized in that: The radius and height of the chiral helical structure are determined by the working wavelength, and the maximum characteristic parameter is less than 10 microns.

4. The metal spiral-thin film composite structure with broad-spectrum chiral absorption function according to claim 1, characterized in that: The height of the chiral helical structure is 10 to 20 times the radius.

5. The metal spiral-thin film composite structure with broad-spectrum chiral absorption function according to claim 1, characterized in that: The chiral helical structure consists of a chiral helical structure body and a thin film II covering the outer surface of the chiral helical structure body; the thin film I and thin film II can be the same or different, and are independently selected from gold, silver, platinum, and copper.

6. The metal spiral-thin film composite structure with broad-spectrum chiral absorption function according to claim 1, characterized in that: The film I and the film II are made of the same material and have a thickness of less than 100 nm.

7. The metal spiral-thin film composite structure with broad-spectrum chiral absorption function according to claim 1, characterized in that: The chiral helical structure has a wide spectrum effect in the terahertz band (3-7 μm); the number of turns of the chiral helical structure is 1 to 3, the array period is 1 to 3 microns, the height of the chiral helical structure is 2 to 10 μm, the radius of the chiral helical structure is 0.1 to 1 μm, the number of turns is 1 to 3 turns; the maximum size of the helical cross section is 0.5 to 2 microns.

8. A wide-spectrum chiral absorber based on a metal spiral-thin film composite structure, characterized in that: The invention comprises a substrate and a composite structure arranged on the substrate, wherein the composite structure is the metal spiral-film composite structure according to any one of claims 1 to 7.

9. A method for preparing a wide-spectrum chiral absorber based on a metal spiral-thin film composite structure as claimed in claim 8, characterized in that: include: The chiral helical structure body is processed on a substrate to deposit thin film I and thin film II.

10. The method for preparing a wide-spectrum chiral absorber based on a metal spiral-thin film composite structure according to claim 9, characterized in that: The chiral helical structure body is processed by two-photon polymerization method or focused ion beam induced deposition method; and thin film I and thin film II are precipitated by magnetron sputtering, thermal evaporation, electron beam evaporation and chemical plating.

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