研究目的
To demonstrate an approach for spin-selective transmission using chiral folded metasurfaces in the infrared region, overcoming limitations of conventional bulky chiral materials.
研究成果
The folded metasurface enables strong intrinsic chirality and spin-selective transmission with high circular dichroism (up to 0.7) and transmittance (>90%), controllable via folding angle. It offers a simpler fabrication method compared to conventional 3D chiral metamaterials and has potential applications in polarization manipulation, chiral sensing, and optical devices.
研究不足
The folding angle is limited to 60 degrees in experiments to avoid damage to metal patterns; fabrication imperfections and material losses may cause slight differences in resonant strength; the technique may be complex for mass production without alternative lithography methods.
1：Experimental Design and Method Selection:
The study involves designing and fabricating 3D folded metasurfaces composed of anti-symmetric split ring resonators (SRRs) to break mirror symmetry and induce intrinsic chirality. Numerical simulations using CST Microwave Studio based on finite element method were performed to validate and optimize the design.
2：Sample Selection and Data Sources:
Samples were fabricated on 100-nm-thick low-stress SiNx windows, with metasurface patterns defined by electron-beam lithography and gold deposition.
3：List of Experimental Equipment and Materials:
Equipment includes electron-beam lithography system, focused-ion-beam system (Helios 600i, FEI), Fourier-transform infrared spectrometer (Vertex 80, Bruker), confocal microscope (Hyperion 2000 IR), ZnSe polarizer, achromatic quarter wave plate (B. Halle Nachfl. GmbH), and materials include PMMA resist, gold film, aluminum conductive layer, SiNx substrate.
4：Experimental Procedures and Operational Workflow:
Fabrication involved spin-coating PMMA, e-beam lithography, gold evaporation, lift-off, aluminum deposition, FIB cutting and folding of SiNx sheets, and wet etching. Optical characterization measured transmission spectra for circularly polarized light using FTIR with polarizer and quarter wave plate.
5：Data Analysis Methods:
Transmission spectra were normalized to air, and circular dichroism was calculated as CD = T_RCP - T_LCP. Multipole analysis was conducted using induced currents from simulations.
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Focused-Ion-Beam System
Helios 600i
FEI
Used for cutting and folding the SiNx film to create 3D metasurface structures.
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Fourier-Transform Infrared Spectrometer
Vertex 80
Bruker
Used to measure transmission spectra of the metasurface samples.
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Confocal Microscope
Hyperion 2000 IR
Bruker
Coupled with the FTIR for optical characterization, equipped with objective lens and MCT detector.
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Achromatic Quarter Wave Plate
λ/4 retardation
B. Halle Nachfl. GmbH
Inserted into the beam path to generate circularly polarized light for transmission measurements.
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ZnSe Polarizer
Used to polarize the incident electromagnetic field in the optical characterization setup.
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Electron-Beam Lithography System
Used to define metasurface patterns on the resist layer during fabrication.
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Thermal Evaporation System
Used for depositing gold and aluminum films onto the samples.
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CST Microwave Studio
Commercial software used for numerical simulations based on finite element method.
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