Engineered Three-dimensional Colloidal Crystals Containing a Planar Defect
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Engineered Three-dimensional Colloidal Crystals Containing a Planar Defect Pascal Massé1, Béatrice Agricole1, Elisabeth Sellier2, Serge Ravaine1 1 Centre de Recherche Paul Pascal – CNRS 115 avenue du Dr Schweitzer - 33600 Pessac, France 2 Centre de Ressources En Microscopie Electronique et Microanalyse 351 cours de la libération -33405 Talence ABSTRACT We have fabricated three-dimensional (3D) colloidal crystals containing a two-dimensional (2D) defect as the middle layer by the Langmuir-Blodgett (LB) technique. Either a homogeneous sheet made of hundreds layers of behenic acid or a single monolayer of silica colloidal particles of various sizes was inserted between two opal films of silica spheres. 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 layer to the diameter of the colloids of the upper and lower opals. INTRODUCTION In recent years, there has been tremendous activity in an attempt to fabricate and investigate the structure-property relationship of three-dimensional (3D) photonic crystals [1]. A key property of these materials is the presence of a photonic band gap, analogous to electronic band gap in a semiconductor, which arises from the inhibition of the electromagnetic waves propagation over a certain range of frequency. Thus photonic crystals are promising tools to manipulate, confine, and control light and they have been proposed for applications such as optical filters [2], switches [3], chemical and biological sensors [4,5] or waveguides for optoelectronic [6]. As they can be readily assembled into long-range ordered lattices, monodisperse colloidal particles are suitable building blocks for the elaboration of such materials. Several methods have been developed to organize colloids in such periodic arrays with well-defined crystal structures, sufficiently domain sizes and well-controlled thickness. Among those are sedimentation [7], electrophoretic deposition[8], physical confinement [9], multilayers deposition using the Langmuir-Blodgett technique [10,11] and vertical deposition [12,13]. Nevertheless, the formation of 3D lattices with arbitrary structures, which should exhibit interesting optical or nonlinear optical functionality, has met with limited success by using all of these procedures. As far as we know, the insertion of a monolayer of microspheres between two opal films containing spheres of different diameters has only been recently reported by Persoons and co-workers, through the association of convective self-assembly and the Langmuir-Blodgett (LB) technique [14]. The resulting sandwich structures present a donor mode in the photonic band gap, since the size of the defect layer was always larger than that of the spheres of the upper and lower stacks. In this paper we present the fabrication by the LB technique of 3D colloidal crys
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