Abstract
Localized surface plasmon resonances (LSPR) and plasmon couplings in Ag capped Si Nanopillar (Ag NP) structures are studied using 3D FEM simulations and dark-field scattering microscopy. Simulations show that a standalone Ag NP supports two LSPR modes, i.e. the particle mode and the cavity mode. The LSPR peak position of the particle mode can be tuned by changing the size of the Ag cap, and can be hybridized by leaning of pillars. The resonance position of the cavity resonance mode can be tuned primarily via the diameter of the Si pillar, and cannot be tuned via leaning of Ag NPs. The presence of a substrate dramatically changes the intensity of these two LSPR modes by introducing constructive and destructive interference patterns with incident and reflected fields. Experimental scattering spectra can be interpreted using theoretical simulations. The Ag NP substrate displays a broad plasmonic resonance band due to the contribution from both the hybridized particle LSPR and the cavity LSPR modes.
Highlights
Plasmonic nanostructures [1,2] are the key components for extensive applications such as surface-enhanced Raman Scattering (SERS) [3,4,5], refractive index sensing [6,7,8], surfaceenhanced infrared absorption (SEIRA) [9,10], plasmonic optical devices [11,12] and thermal sensing [13], due to their ability to controllably confine light energy at the nanoscale
Simulations show that a standalone Ag capped Si Nanopillar (Ag NP) supports two Localized surface plasmon resonances (LSPR) modes, i.e. the particle mode and the cavity mode
The LSPR peak position of the particle mode can be tuned by changing the size of the Ag cap, and can be hybridized by leaning of pillars
Summary
Plasmonic nanostructures [1,2] are the key components for extensive applications such as surface-enhanced Raman Scattering (SERS) [3,4,5], refractive index sensing [6,7,8], surfaceenhanced infrared absorption (SEIRA) [9,10], plasmonic optical devices [11,12] and thermal sensing [13], due to their ability to controllably confine light energy at the nanoscale. A new class of Si pillar based nanoplasmonic structures fabricated using maskless reactive ion etching has been developed [24, 25] In order to open new possibilities for optimizing the substrate towards a multifunctional plasmonic sensing platform that fulfills all the requirements of an ideal LSPR substrate, optical properties of isolated and interacting Au/Ag nanopillars need to be systematically investigated To carry out such a study, a major challenge is that the geometry of the fabricated nanopillars varies from pillar to pillar significantly. The cavity mode is the electron oscillations in the Ag cap coupled via the Si pillar It can be distinguished from the enhanced and highly localized fields near the neck of the Ag cap.
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