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Reproducing the hierarchy of disorder for Morpho -inspired, broad-angle color reflection

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ABSTRACT

The scales of Morpho butterflies are covered with intricate, hierarchical ridge structures that produce a bright, blue reflection that remains stable across wide viewing angles. This effect has been researched extensively, and much understanding has been achieved using modeling that has focused on the positional disorder among the identical, multilayered ridges as the critical factor for producing angular independent color. Realizing such positional disorder of identical nanostructures is difficult, which in turn has limited experimental verification of different physical mechanisms that have been proposed. In this paper, we suggest an alternative model of inter-structural disorder that can achieve the same broad-angle color reflection, and is applicable to wafer-scale fabrication using conventional thin film technologies. Fabrication of a thin film that produces pure, stable blue across a viewing angle of more than 120 ° is demonstrated, together with a robust, conformal color coating.

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Parylene-deposited film.(a) Cross-sectional SEM image of a parylene deposited ridge structure with irregular layers. (b) The parylene deposited film attached on a Korean coin. The film follows the complex contours of the coin conformably.
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f5: Parylene-deposited film.(a) Cross-sectional SEM image of a parylene deposited ridge structure with irregular layers. (b) The parylene deposited film attached on a Korean coin. The film follows the complex contours of the coin conformably.

Mentions: In the present case, the overall film remains planar, with a total thickness of less than 2 μm, with features that are fully controlled via lithography and etching techniques. This greatly facilitates developing applications, as we here demonstrate by developing a robust coating application using parylene, a conformal protective polymer coating that is already in wide commercial use37, as a protective layer. Figure 5a shows a cross-section SEM image of an irregular-layered structure after parylene deposition. Full conformal coating and uniform infiltration of the inter-ridge space can be observed. After the deposition, the mechanical strength of the parylene layer enables detachment of the entire reflecting layer from the Si substrate, with the silica balls acting as the sacrificial layer. Due to the flexibility and thinness of the entire reflecting layer, conformal coating of arbitrary, non-planar shapes is possible. As shown in Fig. 5b, the film conformably coats the complex, convex pattern of a coin. The film naturally shows some specular reflection on the boundary of air and parylene, but retains the optical property of broad-angle blue reflection. (See Supplementary Information, Fig. S8 for the analysis of parylene coating). In fact, the film is robust enough to be dunked and folded in liquid nitrogen without suffering visible damage (see Supplementary Video).


Reproducing the hierarchy of disorder for Morpho -inspired, broad-angle color reflection
Parylene-deposited film.(a) Cross-sectional SEM image of a parylene deposited ridge structure with irregular layers. (b) The parylene deposited film attached on a Korean coin. The film follows the complex contours of the coin conformably.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384085&req=5

f5: Parylene-deposited film.(a) Cross-sectional SEM image of a parylene deposited ridge structure with irregular layers. (b) The parylene deposited film attached on a Korean coin. The film follows the complex contours of the coin conformably.
Mentions: In the present case, the overall film remains planar, with a total thickness of less than 2 μm, with features that are fully controlled via lithography and etching techniques. This greatly facilitates developing applications, as we here demonstrate by developing a robust coating application using parylene, a conformal protective polymer coating that is already in wide commercial use37, as a protective layer. Figure 5a shows a cross-section SEM image of an irregular-layered structure after parylene deposition. Full conformal coating and uniform infiltration of the inter-ridge space can be observed. After the deposition, the mechanical strength of the parylene layer enables detachment of the entire reflecting layer from the Si substrate, with the silica balls acting as the sacrificial layer. Due to the flexibility and thinness of the entire reflecting layer, conformal coating of arbitrary, non-planar shapes is possible. As shown in Fig. 5b, the film conformably coats the complex, convex pattern of a coin. The film naturally shows some specular reflection on the boundary of air and parylene, but retains the optical property of broad-angle blue reflection. (See Supplementary Information, Fig. S8 for the analysis of parylene coating). In fact, the film is robust enough to be dunked and folded in liquid nitrogen without suffering visible damage (see Supplementary Video).

View Article: PubMed Central - PubMed

ABSTRACT

The scales of Morpho butterflies are covered with intricate, hierarchical ridge structures that produce a bright, blue reflection that remains stable across wide viewing angles. This effect has been researched extensively, and much understanding has been achieved using modeling that has focused on the positional disorder among the identical, multilayered ridges as the critical factor for producing angular independent color. Realizing such positional disorder of identical nanostructures is difficult, which in turn has limited experimental verification of different physical mechanisms that have been proposed. In this paper, we suggest an alternative model of inter-structural disorder that can achieve the same broad-angle color reflection, and is applicable to wafer-scale fabrication using conventional thin film technologies. Fabrication of a thin film that produces pure, stable blue across a viewing angle of more than 120 ° is demonstrated, together with a robust, conformal color coating.

No MeSH data available.