Abstract
Metallic woodpile photonic crystals and metamaterials operating across the visible spectrum are extremely difficult to construct over large areas, because of the intricate three-dimensional nanostructures and sub-50 nm features demanded. Previous routes use electron-beam lithography or direct laser writing but widespread application is restricted by their expense and low throughput. Scalable approaches including soft lithography, colloidal self-assembly, and interference holography, produce structures limited in feature size, material durability, or geometry. By multiply stacking gold nanowire flexible gratings, we demonstrate a scalable high-fidelity approach for fabricating flexible metallic woodpile photonic crystals, with features down to 10 nm produced in bulk and at low cost. Control of stacking sequence, asymmetry, and orientation elicits great control, with visible-wavelength band-gap reflections exceeding 60%, and with strong induced chirality. Such flexible and stretchable architectures can produce metamaterials with refractive index near zero, and are easily tuned across the IR and visible ranges.
Highlights
Metallic woodpile photonic crystals and metamaterials operating across the visible spectrum are extremely difficult to construct over large areas, because of the intricate three-dimensional nanostructures and sub-50 nm features demanded
Scalable approaches including soft lithography, colloidal self-assembly, and interference holography, produce structures limited in feature size, material durability, or geometry
By multiply stacking gold nanowire flexible gratings, we demonstrate a scalable high-fidelity approach for fabricating flexible metallic woodpile photonic crystals, with features down to 10 nm produced in bulk and at low cost
Summary
Polarized light interacts very differently with successive layers possessing perpendicular wire orientations (Supplementary Fig. S3) This effect disappears for gratings with absent or continuous gold coatings, removing the polarization anisotropy, and halving the vertical periodicity of the stacks. The measured band gap (Fig. 2a) is found to be 60% broader than from planar stacks, showing the benefit of coupling to plasmonic effects in full 3D rather than just 1D planar periodicity These metamaterials have refractive index near zero (Supplementary Fig. S5), that is highly promising to enhance nonlinear optical switching which dominates wherever the linear index is negligible. The artificially obtained and tunable low refractive indices in the metamaterials regime give great promise for diverse 3D nonlinear optical devices
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