Technology transfer from laboratory into practical application needs to meet the demands of economic viability and operational simplicity. This paper reports a simple and convenient strategy to fabricate large-scale and ultrasensitive surface-enhanced Raman scattering (SERS) substrates. In this strategy, no toxic chemicals or sophisticated instruments are required to fabricate the SERS substrates. On one hand, Ag nanoparticles (NPs) with relatively uniform size were synthesized using the modified Tollens method, which employs an ultra-low concentration of Ag+ and excessive amounts of glucose as a reducing agent. On the other hand, when a drop of the colloidal Ag NPs dries on a horizontal solid surface, the droplet becomes ropy, turns into a layered structure under gravity, and hardens. During evaporation, capillary flow was burdened by viscidity resistance from the ropy glucose solution. Thus, the coffee-ring effect is eliminated, leading to a uniform deposition of Ag NPs. With this method, flat Ag NPs-based SERS active films were formed in array-well plates defined by hole-shaped polydimethylsiloxane (PDMS) structures bonded on glass substrates, which were made for convenient detection. The strong SERS activity of these substrates allowed us to reach detection limits down to 10−14 M of Rhodamine 6 G and 10−10 M of thiram (pesticide).
We propose a polarization-controlled bifunctional metasurface composed of arrayed trapezoidal nanoantennas. Under orthogonal-polarized incidence, different types of gap-surface plasmons are generated, regulating the intensity and phase, respectively. Thus, structural color printing and beam deflection functions are achieved on a miniaturized chip. The color printing function works from 400 to 800 nm, exhibiting a subwavelength-scale chromatic image with a broad gamut. The beam deflection function works from 360 to 540 nm, mapping light to the first diffraction order with the anomalous angle from 40.4° to 76.6°. The proposed bifunctional metasurface could serve as a key component in integrated optics systems and will find many other wide-ranging applications in optical and biological areas.
Metasurfaces have attracted extensive attention in the
micro/nano-optics
field depending on their significant ability to modulate optical parameters.
However, the current numerical simulation technology cannot meet the
demand of the design and analysis of metasurfaces efficiently due
to consuming substantial calculating time and memory. Besides, they
cannot illustrate the physical mechanism straightforwardly behind
the optical responses. Herein, we propose and demonstrate two equivalent
circuit models systematically for a bifunctional metasurface with
metal–dielectric–metal structural meta-atoms based on
polarization multiplexing in the visible band. In the y-polarization state, the equivalent circuit model is established
to interpret the phase shift exactly with a high goodness of fit of
0.931, resulting in the beam splitting function from the anomalous
reflection phenomenon. The polychromatic light splits from 34 to 69°
to produce the grating-type high-saturation structural colors with
a large gamut of about 170.07% of the DCI-P3 standard. In the x-polarization state, the metasurface produces the surface
lattice resonance that is suitable for the refractive index sensing
function due to the high sensitivity to environmental changes. The
second equivalent circuit model simulates the linewidth narrowing
and red-shift phenomenon with a sensitivity relative error of 7.00%.
We introduce a branch with a narrow-band-pass filter and a capacitor
in series into the model to mimic the characteristic of Rayleigh anomalies.
Both models extend the application of equivalent circuit theory in
optics further and provide a crucial approach to enhance the insights
into the mechanism of metasurfaces.
Optical metasurfaces provide a significant approach for the production of structural colors due to their excellent optical control abilities. Herein, we propose trapezoidal structural metasurfaces for achieving multiplex grating-type structural colors with high comprehensive performance originating from the anomalous reflection dispersion in the visible band. Single trapezoidal metasurfaces with different x-direction periods can tune the angular dispersion regularly from 0.036 rad/nm to 0.224 rad/nm to generate various structural colors, and composite trapezoidal metasurfaces with three kinds of combinations can achieve multiplex sets of structural colors. The brightness can be controlled by adjusting the distance between the trapezoids in a pair accurately. The designed structural colors have higher saturation than traditional pigmentary colors, whose excitation purity can reach 1.00. The gamut is about 158.1% of the Adobe RGB standard. This research has application potential in ultrafine displays, information encryption, optical storage, and anti-counterfeit tagging.
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