Biomimetic structural coloration with tunable degree of angle-independence generated by two-photon polymerization

Abstract

A successful realization of photonic systems with characteristics of the Morpho butterfly coloration is reported using two-photon polymerization. Submicron structure features have been fabricated through the interference of the incident beam and the reflected beam in a thin polymer film. Furthermore, the influence of the lateral microstructure organization on the color formation has been studied in detail. The design of the polymerized structures was validated by scanning electron microscopy. The optical properties were analyzed using an angleresolved spectrometer. Tunable angle-independence, based on reflection intensity modulation, has been investigated by using photonic structures with less degree of symmetry. Finally, these findings were used to demonstrate the high potential of two-photon polymerization in the field of biomimetic research and for technical application, e.g. for sensing and anti-counterfeiting.

Structural colors with angle-insensitive optical properties generated by Morpho-inspired 2PP structures

“…The color formation can be attributed to the multilayer system formed within the cross-sections of the individual lines (see SEM images in Fig. 2) since fully polymerized Femtobond 4B is generally transparent [30]. Furthermore, diffraction, as well-known from optical gratings, can be excluded as the origin of the colors, as proven by our previous work.…”

“…Only an explicit feature at approximately 440 nm is common for all of the graphs. This feature can be explained by Rayleigh scattering on the nanostructures in the cross-section of the polymer lines [29,30,48]. The angle-insensitivity of blue and green can be attributed to the disorder characteristics mentioned in Sec.…”

“…Furthermore, diffraction, as well-known from optical gratings, can be excluded as the origin of the colors, as proven by our previous work. In this work, we showed that varying the distance between individual polymer lines only affects the color intensity [30]. For color imaging, the structured areas were aligned planar on a sample holder below a light microscope (Eclipse LV 100 N, Nikon, Düsseldorf, Germany).…”

“…For the generation of an anti-counterfeiting feature with 2PP, the previous findings of our research were applied such that our structural colors only resulted from the interference system in the lines' cross-section [30] Therefore, various structure geometries with different symmetries (see Supplementary file) can be used to individually adjust the angleinsensitive optical properties in different tilting directions. For this purpose, structures referred to as arc structures were Here, the optical properties show characteristics of the conventional thin film-and multilayer interference.…”

“…Two-photon polymerization (2PP) provides this capability. Thus, structural colors inspired by nature could already be produced [27][28][29][30]. Arbitrary high resolution, 3D microstructures can be generated in a photosensitive material without specific exposure masks and vacuum [31,32].…”