Micro-nano chiral spiral array structure with core-shell structure and application

Abstract

The application discloses a micro-nano chiral spiral array structure with a core-shell structure, comprising a substrate and a micro-nano chiral spiral array arranged on the substrate, and characterized in that each spiral is a core-shell structure, wherein the core layer material is a material capable of being processed by two-photon polymerization 3D printing, and the cladding layer material is metal. The application solves the problem that high circular dichroism and wide spectrum modulation cannot be simultaneously realized in the current chiral optics field by designing a novel core-shell structure chiral spiral array structure, and realizes high CD optical response in the 3-7 mu m wave band.

Description

Technical Field

[0001] This invention belongs to the field of 3D chiral metamaterials, specifically relating to a core-shell micro / nano chiral helical array structure fabricated by two-photon polymerization 3D printing and metal coating. Background Technology

[0002] Circular dichroism (CD) of micro / nano structures involves the interaction between circularly polarized light and the structure; specifically, it is the difference in reflectance of the structure for left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) light. Many chiral molecules in nature can exhibit circular dichroism in specific wavelength ranges, but the circular dichroism responses of most such natural materials are relatively weak and cannot meet the requirements of chiral applications.

[0003] In recent years, researchers have proposed many chiral absorbers based on artificial metamaterials. Through structural design, selective transmission and reflection of specific circularly polarized light can be achieved, and the effective wavelength of the device can be designed by adjusting the structural feature dimensions. Among them, terahertz chiral metamaterials have been a focus of research due to their broad application prospects in communication, radar, electromagnetic shielding, and other fields.

[0004] Currently, most existing terahertz chiral absorbers are based on planar metasurfaces or multilayer planar structures, which suffer from low CD values ​​and narrow modulation ranges, limiting their application and development in terahertz chiral imaging, chiral sensing, and photodetectors. Therefore, designing and fabricating a novel chiral metamaterial with high CD response and a wide-spectrum modulation capability has become a research hotspot. Summary of the Invention

[0005] This invention proposes a novel micro / nano chiral helical array structure with a broadband terahertz circular dichroism response. This micro / nano chiral helical structure can selectively reflect circularly polarized light over a wide wavelength range of 3-7 micrometers, with a g-factor of [missing information]. It has reached a value close to the theoretical limit of 2. This solves the problems of small circular dichroism and narrow modulation range in current terahertz chiral absorbers.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A terahertz broadband circular dichroic response micro / nano chiral helical array structure includes a substrate and a micro / nano chiral helical array disposed on the substrate. Each helical array is a core-shell structure, wherein the core material is a material that can be processed by two-photon polymerization 3D printing, and the cladding material is a metal.

[0008] Preferably, the cladding material includes one or more of gold, silver, platinum, and copper; the core material is a photosensitive resin.

[0009] Preferably, the thickness of the cladding material is 10–100 nm. More preferably, it is 10–50 nm. Even more preferably, it is 20 nm.

[0010] The spiral described in this invention is a helical structure with equal radii, that is, when projected from the spiral axis onto a certain plane, all the spiral structures overlap on the same ring (see...). Figure 1 In the two-photon polymerization 3D printing process, the laser spot prints layer by layer along a predetermined spiral line, forming a spiral structure with an elliptical or approximately elliptical cross-section (i.e., the plane containing the spiral axis). The shape of the cross-section corresponds to the shape of the laser spot. In this invention, the laser spot used is a Gaussian spot, with a circular or approximately circular xy-section and elliptical or approximately elliptical xz and yz-sections (major axis of 1–1.5 micrometers, minor axis of 200–400 nanometers).

[0011] Preferably, the minimum geometric dimension of each spiral is less than 1 micrometer, and the array period is 1 to 5 micrometers; more preferably, it is 1 to 3 micrometers.

[0012] Preferably, each spiral has 1 to 3 turns (more preferably 1 to 2 turns, even more preferably 1.5 to 2.5 turns; specifically preferably 2 turns); a height of 2 to 8 micrometers (more preferably 3 to 7 micrometers, even more preferably 4 to 6 micrometers); a horizontal projection radius of 0.2 to 0.6 micrometers (more preferably 0.4 to 0.6 micrometers); and a spiral cross-section of an elliptical structure with a major axis of 1 to 1.5 micrometers and a minor axis of 200 to 400 nanometers.

[0013] This invention utilizes a core-shell structure fabricated by two-photon polymerization 3D printing micro-nano processing and metal coating.

[0014] The micro / nano chiral helical structure obtained by this invention exhibits a significant difference in reflectivity for left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP), thus achieving polarization-selective reflection. The micro / nano chiral helical structure operates in the terahertz (3-7 μm) band.

[0015] A method for fabricating a micro / nano chiral helical array structure as described in any one of the above claims includes: firstly, fabricating a core structure on a substrate using a two-photon polymerization 3D printing method and a core material; and then, depositing a metal shell structure on the surface of the core structure using a coating process and a cladding material to obtain the core-shell structure micro / nano chiral helical array structure.

[0016] Furthermore, the fabrication method of the micro / nano chiral helical array structure includes coating, two-photon exposure, development and cleaning, and film deposition.

[0017] This invention utilizes two-photon polymerization 3D printing technology to fabricate the micro / nano structures. This technology achieves a processing precision as low as 200 nm, and when combined with high-performance photoresist, it can produce high-quality helical array structures. The specific fabrication steps include: photoresist dispensing, two-photon laser exposure, development, and cleaning.

[0018] In this invention, the photoresist used is a conventional photoresist, including but not limited to one or more of IP-Dip, IP-S, and IP-L. That is, the core layer material is a material formed by curing one or more of the photoresist IP-Dip, IP-S, and IP-L.

[0019] Preferably, the photoresist is an IP-Dip.

[0020] Preferably, the coating process includes one or more of magnetron sputtering, thermal evaporation, electron beam evaporation, and electroless plating.

[0021] Preferably, the two-photon laser parameters in the two-photon polymerization 3D printing process are: wavelength of 700-1000nm; laser power of 10-30mW; and laser scanning speed of 100-500μm / s.

[0022] As a preferred option, the two-photon laser parameters used are: wavelength of 800 nm; laser power of 27.5 mW; and laser scanning speed of 200 μm / s.

[0023] In this invention, the developing agent used is propylene glycol methyl ether acetate (PGMEA); the cleaning solution used is isopropanol (IPA).

[0024] As a further preferred embodiment, the present invention employs magnetron sputtering for metal coating, and the metal types include, but are not limited to, gold, silver, platinum, copper, etc.

[0025] Preferably, the metal film is made of platinum.

[0026] A chiral reflective device having a micro / nano chiral spiral array structure as described in any one of the above claims, which selectively modulates broadband chiral light using the micro / nano chiral spiral array.

[0027] As a preliminary selection, the wavelength of the chiral light is 3-7 μm.

[0028] This invention proposes a novel core-shell type micro / nano chiral helical array structure. To enable it to possess the advantages of good circular dichroism and a wide modulation band in the terahertz frequency range, the structure was optimized using finite element simulation software in the technical solution.

[0029] This invention proposes a method for structural optimization based on different application scenarios. By designing the geometric dimensions of the structure (period P, radius R), the circular dichroism frequency band of the chiral spiral array can be adjusted. This method broadens the application scenarios and design flexibility of the structure.

[0030] This invention discloses a novel broadband chiral absorption device based on a core-shell helical array structure. Through geometric design optimization, the device can generate high circular dichroism in the red-infrared (3-7 μm) range, solving the current problem of simultaneously achieving high circular dichroism and broadband modulation in chiral optics. Experimentally, we fabricated the device using two-photon polymerization 3D printing and magnetron sputtering coating, and demonstrated its optical performance through both finite element simulation and experimental characterization. This type of broadband modulation, high circular dichroism chiral device has significant advantages and promising application prospects in chiral sensing, chiral imaging, and other fields.

[0031] In summary, this invention solves the problem of simultaneously achieving high circular dichroism and broadband modulation in the current field of chiral optics by designing a novel core-shell chiral helical array structure, and realizes high CD optical response in the 3-7μm band. Attached Figure Description

[0032] Figure 1 The diagram shows a chiral helical array structure unit. The left image is a top view, and the right image is an oblique view (axonometric view).

[0033] Figure 2 This is a schematic diagram of the device manufacturing process;

[0034] Figure 3 For structural SEM images;

[0035] Figure 4 FDTD simulation of the reflection spectrum of the structure;

[0036] Figure 5 The experimentally measured reflection spectrum of the structure;

[0037] Figure 6 The experimentally measured g-factor of the structure picture;

[0038] Figure 7 and Figure 8 The graph shows the variation of the reflection spectrum with the geometric dimensions (P,R) of the structure in the FDTD simulation.

[0039] Among them, (a) is the reflection spectrum with the structural period (P) changed, (b) is the g-factor diagram with the structural period (P) changed, (c) is the reflection spectrum with the structural radius (R) changed, and (d) is the g-factor diagram with the structural radius (R) changed. Detailed Implementation

[0040] For ease of understanding, the invention will be further described below with reference to the accompanying drawings. The invention designs a novel core-shell chiral reflector, with a helical monolithic structure as follows: Figure 1 As shown (structural parameters are as follows: helix height H: 5 μm, helix radius R: 0.4 μm). To produce better circular dichroism, the period P of the array structure (the period is the same in both the x and y directions) is designed to be 2 micrometers. Note that the above parameters are only preferred embodiments of the present invention to aid in understanding the invention, and therefore should not be considered as limiting the scope of the invention.

[0041] The two-photon micro / nano 3D printing parameters used in this embodiment are: wavelength 800nm; laser power 27.5mW; laser scanning speed 200μm / s; effective spot distribution area with a major axis of 1–1.5 μm and a minor axis of 200–400nm. The scanning path is a point-by-point scan along a spiral. The spiral has two turns, and the processed structure is a 50*50 spiral array with a period of 2μm.

[0042] The spiral structure consists of a core layer and a cladding layer, where the core layer is made of photosensitive resin and the cladding layer is made of metal. The processing flow is as follows: Figure 2 As shown, the core layer is first fabricated using two-photon micro / nano 3D printing, and then a cladding layer is created by metal coating of the 3D structure using magnetron sputtering. Specifically, this includes:

[0043] (1) Dip-coating photoresist (the photoresist used in this embodiment is IP-Dip);

[0044] (2) The spiral core structure was printed using the two-photon micro-nano 3D printing process.

[0045] (3) Develop the structure using a developer (the developer used in this embodiment is propylene glycol methyl ether acetate (PGMEA)) and wash with isopropanol to obtain a complete spiral core structure;

[0046] (4) The spiral core structure is coated using magnetron sputtering. In this embodiment, the magnetron sputtering conditions are: DC sputtering; the metal to be coated is platinum, and the cladding thickness is 20 nm.

[0047] The final SEM image of the chiral helical array is as follows: Figure 3 As shown.

[0048] This invention analyzes and explains the circular dichroism of the obtained chiral helical array structure from both finite element simulation and experimental characterization. The simulated reflection spectrum is as follows: Figure 4 As shown (where LCP represents left-handed circularly polarized light; RCP represents right-handed circularly polarized light), the experimentally measured reflection spectrum is as follows. Figure 5As shown in the figure. The results show that the chiral helical structure exhibits excellent circular dichroism in the 3-7 μm wavelength range. Furthermore, while the structure shows a high reflectivity of 75% for LCP, its reflectivity for RCP approaches zero, demonstrating its selective reflection of circularly polarized light. The experimentally measured g-factor calculation results for this chiral helical array structure are presented below. like Figure 6 As shown, the g factor approaches the theoretical value of 2 in the 3-7 μm wide spectrum range.

[0049] This invention can also be structurally optimized according to different usage scenarios. For example... Figure 7 and Figure 8 As shown, the same preparation method can be used to design the geometric dimensions of the structure (P: 1.8-2.6 μm, R: 0.43-0.55 μm), where in (a) R is 0.4 μm, and from top to bottom are LCP-P1.8 μm (representing the reflectivity of LCP when P is 1.8 μm, the same below), LCP-P2.0 μm, LCP-P2.2 μm, LCP-P2.4 μm, LCP-P2.6 μm, RCP-P1.8 μm (representing the reflectivity of RCP when P is 1.8 μm, the same below), RCP-P2.0 μm, RCP-P2.2 μm, RCP-P2.4 μm, RCP-P2.6 μm); (b) is the g-factor result corresponding to (a); Figure 8 In (c), P is 2 micrometers, and the ratios from top to bottom are LCP-R0.55 micrometers (meaning: the reflectivity of LCP when R is 0.55 micrometers, the same below) micrometers, LCP-R0.52 micrometers, LCP-R0.49 micrometers, LCP-R0.46 micrometers, LCP-R0.43 micrometers, RCP-R0.55 micrometers (meaning: the reflectivity of RCP when R is 0.55 micrometers, the same below) micrometers, RCP-R0.52 micrometers, RCP-R0.49 micrometers, RCP-R0.46 micrometers, and RCP-R0.43 micrometers; in (d), the ratios from top to bottom are R0.43 micrometers, R0.46 micrometers, R0.49 micrometers, R0.52 micrometers, and R0.55 micrometers.

[0050] Depend on Figure 7 and Figure 8 It is evident that the circular dichroism operating frequency band of the chiral spiral array can be adjusted while maintaining excellent circular dichroism. This method broadens the application scenarios and design flexibility of the structure.

Claims

1. A micro / nano chiral helical array structure with a core-shell structure, comprising a substrate and a micro / nano chiral helical array disposed on the substrate, characterized in that, Each spiral has a core-shell structure, with the core material being a material that can be processed by two-photon polymerization 3D printing, and the cladding material being a metal. Each spiral has 1 to 3 turns; a height of 2 to 8 micrometers; a horizontal projection radius of 0.2 to 0.6 micrometers; a spiral cross-section of an elliptical structure with a major axis of 1 to 1.5 micrometers and a minor axis of 200 to 400 nanometers; and an array period of 1 to 5 micrometers. The wavelength range of the micro-nano chiral helical array structure is 3-7 μm. The micro / nano chiral spiral array structure can achieve selective reflection of circularly polarized light; Each spiral is projected from its axis onto a plane, and all the spiral structures overlap.

2. The micro / nano chiral helical array structure with a core-shell structure according to claim 1, characterized in that, The cladding material is one or a mixture of gold, silver, platinum, and copper; the core material is photosensitive resin.

3. The micro / nano chiral helical array structure with a core-shell structure according to claim 1, characterized in that, The thickness of the cladding material is 10~100nm.

4. The micro / nano chiral helical array structure with a core-shell structure according to claim 1, characterized in that, The minimum geometric dimension of each spiral is less than 1 micrometer, and the array period is 1 to 3 micrometers.

5. The micro / nano chiral helical array structure with a core-shell structure according to claim 1, characterized in that, Each spiral has 1 to 2 turns; a height of 3 to 7 micrometers; and a horizontal projection radius of 0.4 to 0.6 micrometers.

6. A method for fabricating a micro / nano chiral helical array structure with a core-shell structure as described in any one of claims 1 to 5, characterized in that, include: First, a core structure is fabricated on a substrate using a two-photon polymerization 3D printing method and a core material. Then, a metal shell structure is deposited on the surface of the core structure using a coating process and a cladding material, thus obtaining the fabrication method with a core-shell structure.

7. The fabrication method of the micro / nano chiral helical array structure with a core-shell structure according to claim 6, characterized in that, The coating process includes one or more of magnetron sputtering, thermal evaporation, electron beam evaporation, and electroless plating.

8. The fabrication method of the micro / nano chiral helical array structure with a core-shell structure according to claim 6, characterized in that, The two-photon polymerization 3D printing processing method uses the following two-photon laser parameters: wavelength 700~1000nm; laser power 10~30mW; and laser scanning speed 100~500μm / s.

9. A chiral reflective device, characterized in that, A micro / nano chiral helical array structure with a core-shell structure as described in any one of claims 1 to 5 is used to selectively modulate broadband chiral light using a micro / nano chiral helical array; the wavelength of the chiral light is 3-7 μm.

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