Plasmonic nano structures fabricated using inexpensive and abundant aluminum metal shows intense narrow reflection
peaks with strong response to the external stimuli, provides a simple yet powerful detection mechanism that is well
suited for the development of low cost and low power sensors, such as colorimetric sensors, which transduces external
stimuli or environmental changes in to visible colour changes. Such low cost and disposable sensors have huge demands
in the point-of-care and home health care diagnostic applications. We present the design of a colorimetric sensing
platform based on reflection mode plasmonic colour filters on both silicon and glass substrate, which demonstrate a
sharp colour change for varying ambient refractive index. The sensor is essentially a plasmonic metamaterial in which
the aluminum square plate hovering on a PMMA nano pillar in the background of a perforated aluminum reflector forms
the unit cell which is arranged periodically in a 2D square lattice. The meta-surface has two distinct absorption peaks in
the visible region leaving a strong reflection band, which strongly responds to the ambient refractive index change,
provides a means for the realization of low cost colorimetric sensing platform.
We present the design of a perfect light absorber using 3D metamaterial for operation in the mid IR region. The 3D
metamaterial is a metal half ring projecting normal to the substrate plane, which ensures wide-angle operation for the
direct magnetic coupling. The absorber is essentially a 3-layer architecture having the 3D metamaterial on top acting as
impedance matching layer to the surrounding medium, which ensures near zero reflection. A ground metal plane of
120nm thickness at the bottom layer cancels any transmission through the structure for incident electromagnetic field. A
dielectric spacer layer of thickness 100nm separates the top and bottom layers. The metal parts of the absorber are
realized using gold and the dielectric spacer layer is defined by SiN thin film deposited using PECVD. The 3D half rings
are formed from the lithographically defined 2D template by releasing residual stress in the thermally evaporated gold
thin film using ICP RIE of SiN sacrificial layer. We report an absorbance of more than 90% at a peak wavelength of
12.5μm with a FWHM of 2μm.
Plasmonics have been actively explored for the structural colour printing applications owing to their preferential photon absorption and scattering. To date, many schemes have been demonstrated for the realization of full colour pixels employing various plasmonic geometries. However the quest for a perfect plasmonic geometry that offers pure colour pixels with distinct reflective peaks and high colour saturation combined with low cost and high throughput scalable fabrication is not yet fulfilled. We propose a scheme for generating all colours from violet to red in the visible spectrum with high colour purity and saturation by a clever engineering of concomitant multiple plasmonic resonances in 2D arrays of aluminum based nano antennas.
In order to realize vivid full colour pixels, we fabricated 2D arrays of aluminum nano squares raised on top of PMMA nano posts in the back ground of a perforated back reflector by systematically varying the square size (D) and periodicity (P). In the single layer fabrication process the PMMA nano posts were defined by electron beam lithography and subsequently aluminum thin film was deposited by thermal evaporation to form both the nano squares and the fishnet like back reflector. The colour formation is based on the excitation of plasmonic light absorption at two distinct wavelengths leaving a central reflective peak that is coherently scattered by coupling to a strongly radiating dipole resonance. Pure colours both in the RGB and CMY colour schemes with extreme reflective peaks of high quality factor (FWHM of 100nm) across the visible spectrum are demonstrated.
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