Asymmetric angular dependence for multicolor display based on plasmonic inclined-nanopillar array

Three-dimensional surface lattice plasmon resonance effect from plasmonic inclined nanostructures via one-step stencil lithography

Plasmonic nanostructures allow the manipulation and confinement of optical fields on the sub-wavelength scale. The local field enhancement and environmentally sensitive resonance characteristics provided by these nanostructures are of high importance for biological and chemical sensing. Recently, surface lattice plasmon resonance (SLR) research has attracted much interest because of its superior quality factor (Q-factor) compared to that of localized surface plasmon resonances (LSPR), which is facilitated by resonant plasmonic mode coupling between individual nanostructures over a large area. This advantage can be further enhanced by utilizing asymmetric 3D structures rather than low-height (typically height < ∼60 nm) structure arrays, which results in stronger coupling due to an increased mode volume. However, fabricating 3D, high-aspect ratio, symmetry-breaking structures is a complex and challenging process even with state-of-the-art fabrication technology. Here, we report a plasmonic metasurface of 3D inclined structures produced via commercial TEM grid-based stencil lithography with a Q-factor of 101.6, a refractive index sensitivity of 291 nm/RIU, and a figure of merit (FOM) of 44.7 in the visible wavelength range at a refractive index of 1.5 by utilizing the 3D SLR enhancement effect, which exceeds the performance of most LSPR systems (Q < ∼10). The symmetry-breaking 3D inclined structures that are fabricated by electron beam evaporation at an angle increase the polarizability of the metasurface and the directionality of the diffractively scattered radiative field responsible for SLR mode coupling. Additionally, we explore the role of spatial coherence in facilitating the SLR effect and thus a high-Q plasmonic response from the nanostructures. Our work demonstrates the feasibility of producing 3D inclined structure arrays with pronounced SLR enhancement for high biological sensitivity by utilizing the previously unexplored inclined stencil lithography, which opens the way to fabricate highly sensitive plasmonic metasurfaces with this novel simple technique.

Plasmonic Nanostructure Engineering with Shadow Growth

Physical shadow growth is a vacuum deposition technique that permits a wide variety of 3D-shaped nanoparticles and structures to be fabricated from a large library of materials. Recent advances in the control of the shadow effect at the nanoscale expand the scope of nanomaterials from spherical nanoparticles to complex 3D shaped hybrid nanoparticles and structures. In particular, plasmonically active nanomaterials can be engineered in their shape and material composition so that they exhibit unique physical and chemical properties. Here, the recent progress in the development of shadow growth techniques to realize hybrid plasmonic nanomaterials is discussed. The review describes how fabrication permits the material response to be engineered and highlights novel functions. Potential fields of application with a focus on photonic devices, biomedical, and chiral spectroscopic applications are discussed.

Phase-assisted angular-multiplexing nanoprinting based on the Jacobi-Anger expansion

Featuring with ultracompactness and subwavelength resolution, metasurface-assisted nanoprinting has been widely researched as an optical device for image display. It also provides a platform for information multiplexing, and a series of multiplexed works based on incident polarizations, operating wavelengths and observation angles have emerged. However, the angular-multiplexing nanoprinting is realized at the cost of image resolution reduction or the increase of fabrication difficulty, hindering its practical applications. Here, inspired by the Jacobi-Anger expansion, a phase-assisted design paradigm, called Bessel metasurface, was proposed for angular multiplexing nanoprinting. By elaborately designing the phase distribution of the Bessel metasurface, the target images can be encoded into the desired observation angles, reaching angular multiplexing. With the merits of ultracompactness and easy fabrication, we believe that our design strategy would be attractive in the real-world applications, including optical information storage, encryption/concealment, multifunctional switchable optical devices, and 3D stereoscopic displays, etc.

Wafer-Scale LSPR Substrate: Oblique Deposition of Gold on a Patterned Sapphire Substrate

Label-free detection of biomolecules using localized surface plasmon resonance (LSPR) substrates is a highly attractive method for point-of-care (POC) testing. One of the remaining challenges to developing LSPR-based POC devices is to fabricate the LSPR substrates with large-scale, reproducible, and high-throughput. Herein, a fabrication strategy for wafer-scale LSPR substrates is demonstrated using reproducible, high-throughput techniques, such as nanoimprint lithography, wet-etching, and thin film deposition. A transparent sapphire wafer, on which SiO₂-nanodot hard masks were formed via nanoimprint lithography, was anisotropically etched by a mixed solution of H₂SO₄ and H₃PO₄, resulting in a patterned sapphire substrate (PSS). An LSPR substrate was finally fabricated by oblique deposition of Au onto the PSS, which was then applied to label-free detection of the binding events of biomolecules. To the best of our knowledge, this paper is the first report on the application of the PSS used as an LSPR template by obliquely depositing a metal.

Angular Multiplexing Nanoprinting with Independent Amplitude Encryption Based on Visible-Frequency Metasurfaces

Two-dimensional (2D) metasurfaces hold great promise to enable multiplexing and multifunctional optical devices due to their artificial freedom in design, device miniaturization, etc. Various multiplexing and multifunctional metasurfaces have been extensively studied, including polarization multiplexing, wavelength multiplexing, and orbit angular momentum (OAM) multiplexing. However, due to the lack of angular encoding freedom, angular multiplexing switchable nanoprinting has rarely been studied or demonstrated yet to the best of our knowledge. Here, we realize angular multiplexing switchable nanoprinting functionality with independent amplitude encryption based on visible-frequency metasurfaces. By screening a large number of structural designs and breaking the angular correlation, we eventually obtain optimal metasurface designs to realize dual-channel arbitrary image encryption. Furthermore, we illustrate that the proposed scheme would serve as an optical information concealment/retrieval strategy by combining the structural color and amplitude modulation. Overall, we believe that angular multiplexing metasurfaces would easily find promising applications, including optical information encryption/concealment, multifunctional switchable devices, and advanced eyeglass-free three-dimensional (3D) stereoscopic displays.