Abstract
We report an effective antireflective surface structure fabricated by a sequential process comprising colloidal lithography, maskless plasma etching, and inverted nanoimprinting replication. The hierarchical inverse micro–nano structure is composed of randomly positioned microholes of 3–5 μm in diameter and numerous nanoprotrusions of 60–80 nm diameter located at the bottom surface of the microholes. The inverse micro–nano structure behaves as a high-performance light absorber, exhibiting outstanding optical performances of 0.78% for hemispherical reflectance, and 0.011% for specular reflectance at the incident angle 5° off normal, both on average in the visible range (380–780 nm). Additionally, the optical behavior of the inverse micro–nano structure is numerically investigated with the electric field strength in both frequency and time domains by the finite-element method for Maxwell's equation. As the inverse micro–nano structure exhibits significantly low reflectance and black appearance, it can be applied to antiglare/antireflective surfaces, suitable for the reduction of stray light existing inside of a housing of optical instruments.
Highlights
IntroductionAntireflective (AR) surface structures have been attracting a lot of interest since they were found in insect eyes.[1,2] Many efforts were concentrated on the fabrication of artificial AR structures by physical or chemical lithographic methods, aiming for the enhancement of photoelectric conversion efficiency in inorganic solar cells,[3,4] organic solar cells,[5,6] and improvement of light extraction efficiency in light-emitting diodes,[7] organic light-emitting diodes,[8] and reduction of lens reflection.[9,10]
We report an effective antireflective surface structure fabricated by a sequential process comprising colloidal lithography, maskless plasma etching, and inverted nanoimprinting replication
The hierarchical inverse micro–nano structure is composed of randomly positioned microholes of 3–5 μm in diameter and numerous nanoprotrusions of 60–80 nm diameter located at the bottom surface of the microholes
Summary
Antireflective (AR) surface structures have been attracting a lot of interest since they were found in insect eyes.[1,2] Many efforts were concentrated on the fabrication of artificial AR structures by physical or chemical lithographic methods, aiming for the enhancement of photoelectric conversion efficiency in inorganic solar cells,[3,4] organic solar cells,[5,6] and improvement of light extraction efficiency in light-emitting diodes,[7] organic light-emitting diodes,[8] and reduction of lens reflection.[9,10] Even though these so-called motheye structures exhibit very low reflectivity,[11,12] it is difficult to eliminate the specular reflectance perfectly. Even in the case of stepped paraboloidal AR structure we have previously reported,[13] which gives one of the lowest specular reflectance (0.077% on average in the visible range) compared with any other existing replicable motheye tapers, it is inevitable to show slight sensible reflection.
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