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 < similar to 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 < similar to 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.