A Large‐Area, Mushroom‐Capped Plasmonic Perfect Absorber: Refractive Index Sensing and Fabry–Perot Cavity Mechanism

In most plasmon resonance based sensor to date, only the surface of the sensor is accessible to the gas or liquid as the sensing target. In this work, an interferometric, lithographically fabricated, large‐area, mushroom‐capped plasmonic perfect absorber whose dielectric spacer is partially removed...

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Bibliographic Details
Published in:Advanced optical materials 2015-12, Vol.3 (12), p.1779-1786
Main Authors: Bhattarai, Khagendra, Ku, Zahyun, Silva, Sinhara, Jeon, Jiyeon, Kim, Jun Oh, Lee, Sang Jun, Urbas, Augustine, Zhou, Jiangfeng
Format: Article
Language:English
Subjects:
Detection
Fabry-Perot
metamaterials
Optics
perfect absorption
plasmon
Plasmonics
Refractive index
refractive index sensors
Refractivity
Resonators
Semiconductors
Sensors
Spacers
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Summary:In most plasmon resonance based sensor to date, only the surface of the sensor is accessible to the gas or liquid as the sensing target. In this work, an interferometric, lithographically fabricated, large‐area, mushroom‐capped plasmonic perfect absorber whose dielectric spacer is partially removed by a reactive‐ion‐etch process, thereby enabling the liquid to permeate into the sensitive region to a refractive index change, is demonstrated. Findings of this paper demonstrate experimentally and numerically that etching the spacer below the metamaterial resonator increases the spectral shift of the resonance wavelengths as the surrounding refractive index changes. The sensitivity and the figure of merit, as the measure of the sensor performance, are significantly improved. In this paper, it is shown that the plasmonic perfect absorber can be understood as a Fabry–Perot cavity bounded by a “resonator” mirror and metallic film, where the former exhibits a “quasi‐open” boundary condition and leads to the characteristic feature of subwavelength thickness. An interferometric, lithographically fabricated, large‐area, mushroom‐capped plasmonic perfect absorber with partially dry‐etched dielectric spacers enables the sensing target to enter the sensitive region responding to a refractive index change of the surrounding medium, thereby significantly improving the sensing performance. Additionally, a Fabry–Perot cavity model explains the perfect absorption and the characteristic feature of subwavelength thickness.
ISSN:2195-1071
2195-1071
DOI:10.1002/adom.201500231