Progress of novel fabrications for functional surfaces using various shapes and materials are introduced such as subwavelength optics, biomimetic, electric devices, related to capability of advanced nanoimprint technology
We have developed a method for controlling the creation of voids in polymer thin films by using non-uniform crosslinking followed by expansion of the films in a weak solvent. Due to the unique deformation mechanism, this method creates a new type of polymer photoresist that is neither positive type, nor negative type and can be applied to any cross-linkable polymers. By applying Lippmann-type interference to polymer thin films on a mirrored substrate, periodic voids can be created and vivid structural color can be printed.
The Morpho butterfly's blue is an exceptional and special structural color, which has both high brilliance and single color in wide angular range. Considering the high potential of this coloration for wide industrial applications, we have long advanced several applied researches in various directions. We have recently solved a remaining mystery about the optical role of nano-randomness on the butterfly's scale. This analysis based on the numerical simulation can reveal a new relationship between the optical properties of 2D and 3D nanostructures. Since 2D nanostructures are well compatible with nanoimprint lithography, our obtained results may give a clue not only for Morpho-color devices, but more generally for convenient manufacturing methods of optical devices.
Colloidal crystal films are fabricated self-assembly process. 3D closely packed colloidal particles form a face-centered cubic structure with (111) planes. Polystyrene (PS) colloidal crystal was infilled with silicone elastomer. The lattice distance of (111) planes, d111, selectively diffracts white light based on Bragg's equation with Snell laws. High-quality colloidal crystal films were coated on an A3 scale flat substrate and non-flat 3D surface. This coating process has a potential application for coloring surfaces without using dyes and pigments. In addition, PS colloidal crystal film embedded in poly dimethyl silicone PDMS elastomer with tunable d111 enables by swelling or deformation changes the structural color of colloidal crystal films. By measurement of the peak shift of Bragg's diffraction, the colloidal crystal films can be applied to liquid sensor or strain sensor.
Nanoimprint technology is a mold processing fabrication technology from single-digit nanometers consisting of mold imprinting and lithography processes, which attracts attention as industrially acceptable micro/nano-fabrication methods. A novel “print-and-imprint” method, named by us, is to add laser-drilled screen printing to the conventional ultraviolet (UV) nanoimprint lithography. We are under developing the fabrication processes to combine fluorescence imprint alignment. Polyimide masks with through holes made by laser drilling are used in laser-drilled screen printing, which enables the site-selective and quantitative placement of constant-volume droplets of wide-range high-viscosity UV-curable liquid on substrate surfaces and the formation of imprint resist patterns with a uniform residual layer thickness independently of variation of mold-recess surface densities. Fluorescence imprint alignment using UV-curable liquid with visible fluorescence has a characteristic of the availability of silica molds without any optically functional layer, which will lead the reduction of mold cost. We emphasized the importance of surface treatment at a molecular level in the nanoimprint technology.
Micro stereolithography techniques using single-photon and two-photon polymerization have widely been used for making three-dimensional (3D) micro/nano structures applicable in various application fields such as photonics, microfluidics, micromechanical systems, and medicine. In addition, 3D molding techniques using micro stereolithography have also been applied to create large-scale micropatterns useful for functional surfaces such as superhydrophobic surfaces and adhesive surfaces. In this paper, the overview of micro stereolithography and 3D molding techniques is described. The future prospects of these techniques are discussed.