Optical Responses of Localized and Extended Modes in a Mesoporous Layer on Plasmonic Array to Isopropanol Vapor

Abstract

Mesoporous silica features open and accessible pores that can intake substances from the outside. The combination of mesoporous silica with plasmonic nanostructures represents an interesting platform for an optical sensor based on the dependence of plasmonic modes on the refractive index of the medium in which metallic nanoparticles are embedded. However, so far only a limited number of plasmonic nanostructures are combined with mesoporous silica, including random dispersion of metallic nanoparticles and flat metallic thin films. In this study, we make a mesoporous silica layer on an aluminum nanocylinder array. Such plasmonic arrangements support both localized surface plasmon resonances (LSPRs) and extended modes which are the result of the hybridization of LSPRs and photonic modes extending into the mesoporous layer. We investigate in situ optical reflectance of this system under controlled pressure of isopropanol vapor. Upon exposure, the capillary condensation in the mesopores results in a gradual spectral shift of the reflectance. Our analysis demonstrates that such shifts depend largely on the nature of the modes; that is, the extended modes show larger shifts compared to localized ones. Our materials represent a useful platform for the field of environmental sensing.

Multipolar Lattice Resonances in Plasmonic Finite-Size Metasurfaces

“…After closer inspection of the role of each particle of the array on its total electromagnetic response, it was shown that phase distribution for the EQ mode has significant inhomogeneities, while for the MD and ED modes it is relatively uniform for large arrays, which explains observed spectral behavior for finite and infinite arrays. We believe that our results are important for experimental setups where the uniform electromagnetic response across nanoparticles in the array is essential, for example in surface-enhanced Raman scattering [63], sensing [64] and other applications. Moreover, we anticipate that similar research would be of great interest for arrays with more complex unit cells [65][66][67].…”

Engineering Plasmonic Hybridization toward Advanced Optical Sensors

“…[ 303 ] Figure 7C‐i,ii describes a mesoporous silica layer with an embedded Al cylinder lattice for sensing studies with localized and extended modes. [ 304 ] The extended modes are generated due to hybridization between the LSPR resonances and the photonic quasi‐guided modes. Such a system is studied under controlled pressure of isopropanol vapor (IPA) where reflectance spectra (Figure 7C‐iii) show larger shifts for the quasi‐guided modes than LSPR ones.…”

“…C‐i–iii) Reproduced under the terms of the ACS AuthorChoice License. [ 304 ] Copyright 2020, the authors, published by ACS. D) 2D‐mPhCs composed of Pt nanodisc array and TiO 2 waveguide.…”

“…(iii) Transmittance spectra for mode identification with sensing study, carried under reflectance measurements. C-i-iii) Reproduced under the terms of the ACS AuthorChoice License [304]. Copyright 2020, the authors, published by ACS.…”