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Charge transfer plasmons (CTPs) in coupled plasmonic cavities have gained attention for their interesting resonance mechanisms and potential applications in sensing. The authors present the first investigation of the CTP mode in top‐down fabricated tall plasmonic nanostructures with deep nanogaps, whose excitation becomes possible by the interaction of transversal and longitudinal plasmonic modes. Hybridization of dipole and CTP modes at different parts of the plasmonic nanostructures, for both capacitively coupled dimer of sub‐5 nm gap and conductively coupled dimer with junction bridge is extensively studied. Importantly, the authors demonstrate the conditional emergence of a hybrid dimer‐CTP mode based on the cladding refractive index and analyte thickness, which can present an opportunity for highly specific surface sensing applications. The sensing performances of these modes are evaluated, showing a figure‐of‐merit of ≈18.4 and Q≈ 44 for the hybrid dimer‐CTP mode in the visible spectrum. Surface sensing based on alkanethiol adsorption shows surface sensitivity as high as ≈3.2 nm/carbon‐chain for this mode, which is higher than the typical values obtained by LSP structures. [ABSTRACT FROM AUTHOR]

Achieving high transmission of light through a highly conductive structure implemented on a semiconductor remains a challenge in optoelectronics as the transmission is inevitably deteriorated by absorption and Fresnel reflection. There have been numerous efforts to design structures with near-unity transmission, yet they are typically constrained by a trade-off between conductivity and optical transmission. To address this problem, we propose and demonstrate a transmission mechanism enabled by a monolithic GaSb subwavelength grating integrated with Au stripes (metalMHCG). Near-unity transmission of polarized light is achieved by inducing low-quality factor resonance in the air gaps between the semiconductor grating stripes, which eliminates light absorption and reflection by the metal. Our numerical simulation shows 97% transmission of transverse magnetic polarized light and sheet resistance of 2.2 ΩSq−1. The metalMHCG structure was realized via multiple nanopatterning and dry etching, with the largest transmission yet reported of ∼90% at a wavelength of 4.5 µm and above 75% transmission in the wavelength range from 4 to 10 µm and sheet resistance at the level of 26 ΩSq−1. High optical transmission is readily achievable using any high refractive index materials employed in optoelectronics. The design of the metalMHCG is applicable in a wide electromagnetic spectrum from near ultraviolet to infrared. [ABSTRACT FROM AUTHOR]