The Morpho butterfly’s blue, which is a specific color produced by nanostructures, is expected to serve to various industrial applications such as posters, displays, cosmetics, etc. The natural Morpho blue has recently been emulated successfully by an artificial stepped nanostructure, but the fabrication of the nanostructure is too expensive using conventional lithography method. To solve the problem, nanocasting lithography (NCL) is newly applied using UV curable polymer to replicate the stepped nanostructure and improve heat resistance for the following deposition process. After fabrication of the stepped polymer structure by NCL, TiO2 and SiO2 layers are deposited using the vacuum electron beam deposition and the Morpho blue structure is efficiently reproduced at low cost. The reflective characteristic of the reproduced structure is almost same as the natural Morpho blue.

Strucural color of some blue Morpho butterflies has a physically mysterious feature, because it has both high reflectivity (>60%) and a single color in too wide angular range (> ± 40° from the normal), which are contradicting with each other from viewpoint of the interference phenomena. We have recently proven the principle of the mystery by extracting the physical essence, and emulating the nano-structures using nano-fabrication techniques. The key was exquisite combination of regular and random structures at nanometer scale. Such artificial structural color was found to concern wide applications, because the Morpho-color can produce a single color without pigment in wide angular range with high reflectivity. Also it makes colors impossible by pigment, and is resistant to fading due to chemical change over longtime. However, we must overcome several "death valleys" for wide industrial applications. A serious problem was low throughput in the fabrication process of nano-patterning by the conventional lithography, which was solved by use of nano-imprinting technique. Next research step is attempts at a precise control of the optical properties, in both terms of real space and wavelength, i.e. angular distribution and spectrum. We could successfully optimize the optical properties by controlling the parameters of nano-structures in the artificial film. In this process, optical simulations and micro-structural observations were taken in account. The optimization was achieved both theoretically and empirically by comparing a series of films fabricated with different nano-patterns. Also the relationship between the structural parameters and the optical properties was analyzed. The reflective characteristics of the optimized film were found to reproduce the optical properties closer to the natural Morpho-blue than the prototypes.

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The brilliant metallic blue in wings of Morpho butterflies has a mysterious feature. The blue luster is produced from the butterfly's scale, which does not contain a blue pigment at all. The origin of the coloration is then attributed to a microscopic structure that can also explain its high reflectivity. However, its optical characteristics on the scattered wavelength contradicts obviously the grating or multilayer, because it appears blue from wide angle. The mystery of the lack of multi-coloration has recently been explained using a model with a peculiar optical structure, and experimentally proven by fabricating the optical film by controlling the parameters in nanoscale. The reproduced Morpho-blue was found to be important from viewpoint of a wide variety of applications. However, the fabrication process of the nanostructure is too costly due to conventional lithography method. To solve the problem, nano-casting lithography (NCL) was newly applied using UV curable polymer to replicate the nanostructure and improve heat-resistance for the following process of deposition. After fabrication of the nano-patterned polymer structure by the NCL, TiO 2 and SiO 2 layers were deposited and the Morpho-blue structure was successfully replicated in low cost. The reflective characteristic of the replicated structure was found to reproduce the basic properties of the natural Morpho-blue, as well as the originally fabricated Morpho-blue.

218 1 大阪大学大学院工学研究科（〒565 0871 大阪府吹田市山田丘 2 1）  2 理化学研究所・播磨研究所/SPring 8（〒679 5148 兵庫県佐用郡佐用町光都 1 1 1）  3 JST さきがけ（〒102 0075 東京都千代田区三番町 5） Conspicuous metallic blue of Morpho butter‰ies is well known and attract interest because it is a brilliant luster of natural beings. The blue is produced by their proteins, which are almost transparent without pigment. The origin of the coloration with high re‰ectivi-ty (＞～60) is then attributed to an interference eŠect based on a periodic structure. However, the interference contradicts the blue that is maintained in too wide angular range (＞±40°from the normal). This mystery has recently been explained with a speciˆc multilayer, which is aˆne combination of regular and random structures at nanometer scale. We proved this hypothesis successfully by emulating the 3D structures by deposition of multilayerˆlm on a nano-patterned substrate. Such artiˆcial structural color can be applied to various industries, because it makes colors qualitatively impossible by pigment, and resistant to fading due to chemical change over longtime. Also we developed a high throughput nano-patterning process by use of nano-imprinting method, and succeeded in controlling the optical properties both in angular and wavelength distribution.