Engineered defects in three-dimensional colloidal crystals

Abstract

We have fabricated three-dimensional (3D) colloidal crystals containing a defect by the Langmuir-Blodgett (LB) technique. A controlled number (from one to four) of layers of colloidal silica particles were inserted between two opal films of silica spheres of different size. The presence of the extrinsic defect led to an impurity mode within the photonic stop band, which was observed as a pass band in the near-infrared (NIR) spectra. The position of this defect mode was found to vary periodically with the value of the ratio of the thickness of the defect to the diameter of the colloids of the upper and lower opals. We also show that the amplitude of the pass band in the band gap is maximum when the two opals confining a defect monolayer made of smaller colloids have the same number of layers.