Reflectance spectroscopy of single photonic crystal island fabricated by ink-jet printing
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Reflectance spectroscopy of single photonic crystal island fabricated by ink-jet printing Dake Wang and Minseo Park1 Laboratory for Nanophotonics, Department of Physics Auburn University, Auburn, AL 36849, U. S. A. Jungho Park and Jooho Moon School of Advanced Materials Engineering, Yonsei University 134 Shinchon-dong, Seodaemun-gu, Seoul 129-749, Korea. 1
Corresponding Author: electronic mail ([email protected])
ABSTRACT A micro-reflectance spectroscopy was performed on a single island of photonic crystal array. An array of islands of photonic crystal with colloidal polystyrene beads was assembled on Si using ink-jet printing. The polystyrene colloids with three different sizes (190 nm, 210 nm, and 270 nm in diameter) were used and the polystyrene colloidal particles were self-assembled to form fcc lattices with three different lattice spacing. It was observed from the reflectance spectra that the position of the optical stop band shifts as the size of the colloidal particle changes. Effective medium approximations were used to model the dielectric properties of the colloid/air composite. The theoretically expected reflectance peak position agrees well with those of the experimentally observed peaks. The effect of finite size of the photonic crystal island on its reflectance spectroscopy was investigated by comparing the reflectance spectra collected from four different photonic crystal islands assembled from the same polystyrene colloidal particles, but with different lateral size for each island. It was found that the primary reflection peak was broadened and its intensity was reduced when the lateral size of the island was decreased.
INTRODUCTION Photonic crystal (PC) that possesses a 3D periodic structure was first realized by Yablonovitch et al.[ 1 ]. In their experiment, a PC working in microwave regime was mechanically drilled out of a dielectric block. Soon after their pioneer work, this top-down technique was scaled down to optical regime by utilizing the existing lithography and etching techniques used in microelectronic fabrication or optical technique like multiple laser beam interference [2, 3, 4, 5, 6]. As the monodisperse colloidal particle becomes readily available, the self-assembly of colloidal suspension provides a bottom-up way to synthesize 3D crystals without the need of elaborate micro-fabrication techniques. Several different techniques such as the gravitational sedimentation [7], controlled shear stress [8] and the convective self-assembly [9, 10, 11, 12], were employed during the crystal growth of the self-assembly of colloidal suspension to facilitate and improve the crystallization process. In order to fabricate PC based functional device, it is necessary to develop techniques that can produce desired patterns out of the bulk PC. Traditionally, to make the patterned colloidal
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PC structure the substrate needs to be patterned first or a template has to be used to control the self-assembly of the colloidal suspension [13,14,15,16].
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