New Article in Langmuir

posted Feb 12, 2014, 4:34 PM by Shin-Hyun Kim
Joon-Seok Lee, Che Ho Lim, Seung-Man Yang, and Shin-Hyun Kim"Monolithic Photonic Crystals Created by Partial Coalescence of Core-Shell Particles," Langmuiraccepted for publication (2014). (Corresponding author) [pdf

Colloidal crystals and their derivatives have been intensively studied and developed during last two decades due to their unique photonic bandgap properties. However, complex fabrication procedures and low mechanical stability severely limit their practical uses. Here, we report stable photonic structures created by using colloidal building blocks composed of inorganic core and organic shell. The core-shell particles are convectively assembled into opal structure, which is then subjected to thermal annealing. During the heat treatment, the inorganic cores which are insensitive to the heat retain regular arrangement in face-centered cubic (fcc) lattice, while the organic shells are partially fused with their neighbors; this forms monolithic structure with high mechanical stability. The interparticle distance and therefore stop band position are precisely controlled by annealing time; the distance decreases and the stop band blue-shifts during the annealing. The composite films can be further treated to make high contrast in refractive index. The inorganic cores are selectively removed from the composite by wet etching, thereby providing organic film containing regular arrays of air cavities. High refractive index contrast of the porous structure gives rise to pronounced structural colors and high reflectivity at stop band position.