Biologically Inspired Biophotonic Surfaces with Self‐Antireflection

Abstract

with interstitial medium can be considered as single-layer ARS. Based on the Maxwell Garnett model, [ 5 ] the self-antirefl ection can be realized by using the spontaneous index modulation of ARS, i.e., medium-fi lled GNA with ∼0.5 FF, at both air-substrate ( n air and n sub ) and solution-substrate ( n sol and n sub ) interfaces, where a surrounding medium with an index ranging from 1.0 to 1.8 completely fi lls the interstitial gaps between the nanopillars. As a result, the effective index naturally meets an antirefl ection condition (Supporting Information Figure S2). The biophotonic surfaces exhibit diverse examples such as antirefl ective substrates with single-side GNA (SS-GNA) and double-side GNA (DS-GNA) or nanoplasmonic surfaces for highly sensitive fl uorescence sensing or surface enhanced Raman scattering (SERS) as well as high contrast imaging (Figure 1 c).A wafer-level nanofabrication of GNA with self-antirefl ection was done by using thin silver fi lm annealing and reactive ion etching (RIE) on a borosilicate glass substrate (n≈1.47). Thermal annealing transforms thin silver fi lm into size-controllable silver nanoislands, which serve as an etching mask for nanopillar formation during the RIE process. Note that the FF of GNA was precisely controlled with the density of Ag nanoislands depending on the initial thickness of thin silver fi lm. This method was applied on both sides of the glass wafer, where the top-side GNA can also be further functionalized as plasmonic nanostructures by evaporating thin silver or gold fi lm ( Figure 2 a). The GNA were etched down by a quarter-wavelength to suppress specular refl ection at air-substrate interface. The effective index for 0.5 ± 0.01 FF GNA with 130 nm in nanopillar height naturally varies from 1.22 to 1.64 for 1.0 to 1.8 in surrounding index, close to the geometric mean of substrate and surrounding indices, i.e., an ideal antirefl ection condition at the interface (Supporting Information Figure S2). In experiment, the maximum transmission through the SS-GNA is clearly shown at 130 nm in nanopillar height, which improves transmission by ∼3.8 percent at air-substrate interface, compared with the fl at surface (Figure 2 b). The DS-GNA remarkably double the transmission improvement, which shows transmittance over 99 percent. In particular, the size distribution of GNA offers broadband antirefl ection in a visible range from 485 nm to 655 nm. The optical images show specular refl ections from fl at surfaces, SS-GNA, and DS-GNA on 4-inch glass wafers, respectively (Figure 2 b). The DS-GNA provides a clear image of the letters whereas those behind the fl at surfaces are visually unreadable due to the substantial specular refl ection.

Merging Biology and Solid‐State Lighting: Recent Advances in Light‐Emitting Diodes Based on Biological Materials

“…In 2014, Jeong and co‐workers proposed the fabrication of biophotonic surfaces with antireflection features inspired by biological nanoarchitectures ( Figure ) . These antireflective structures were based on the corneal surface of moth eyes, which allows a successful modulation of the effective index via its fill factor (FF), i.e., control of the relative fraction of subwavelength nanostructures leads to the desired antireflective condition at the air–solid interface.…”

“…SEM pictures of biologically inspired surfaces with self‐antireflection for highly sensitive biophotonic sensing and imaging. Reproduced with permission . Copyright 2014, WILEY‐VCH Verlag GmbH & Co. KGaA.…”

Mining the Smartness of Insect Ultrastructures for Advanced Imaging and Illumination

“…Localized surface plasmon resonance observed in noble metal nanoparticles has received much attention for the enhancement of surface sensing and biophotonic imaging . Oh et al reported biologically inspired biophotonic surface with self‐antireflection together with the nanoplasmonic surface in Figure a . Unlike typical antireflective structures using the modulation of effective index by tailoring the fill factor, antireflection for diverse surrounding media in different indices can serve as a self‐antireflection.…”

“…Plasmonics and metamaterials with insect smartness for ultrathin, miniaturized nanoscale structures: a) Plasmonic self‐antireflection by employing glass nanopillars on dual sides of a substrate for biological sensing and imaging. Reproduced with permission . Copyright 2014, Wiley‐VCH.…”

Fabrication of biomimetic patterns for high transmission and antifogging property

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