Fabrication of Micro- and Nanostructures with Monodispersed Colloidal Spheres as the Active Components
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Fabrication of Micro- and Nanostructures with Monodispersed Colloidal Spheres as the Active Components
Byron Gates, Brian Mayers, Zhi-Yuan Li, and Younan Xia* Department of Chemistry, University of Washington, Seattle, WA 98195-1700 [email protected] ABSTRACT Monodispersed colloidal spheres with dimensions in the range of 100 nm to 10 µm can be used as building blocks to fabricate highly ordered 3D micro- and nanostructures. For example, they can be self-assembled into closely packed lattices, which can be subsequently used as templates to generate 3D porous structures. Here we present the recent progress in our group regarding this approach. INTRODUCTION Crystalline arrays of monodispersed colloidal spheres have found a number of applications in the fabrication of micro- and nanostructured materials. For example, spherical colloids have been extensively exploited as the building blocks to fabricate long-range ordered, 3D structures through processes such as crystallization[1] or template-directed synthesis.[2] These periodic lattices have been pursued for the fabrication of photonic bandgap (PBG) crystals that are characterized by a spatially periodic variation of high and low dielectric regions.[3] Such a crystal is capable of manipulating photons in all three dimensions of space: for example, to block the propagation of photons or confine photons to a specific area at restricted frequencies. A number of approaches have been successfully demonstrated by various groups to fabricate these crystals for use in different spectral regions.[1,2,4] Spherical colloids have been used as building blocks to generate periodic lattices with well-defined and highly ordered structures. These crystalline arrays of colloids have been found to exhibit stop bands with the midgap position easily controlled by changing the size of the colloidal spheres. The optical properties of these lattices are dependent on the structure and long-range order of the crystalline array. Understanding the influence of bulk and point defects will be important to fabricating and controlling the optical properties of PBG crystals.[5] This paper presents our recent studies on the defects within crystalline lattices of colloidal particles with an analysis by transmission spectroscopy and scanning electron microscopy (SEM). Theoretical predictions are also presented along with a synthetic approach to fabricating PBG crystals with the appropriate structure to obtain a complete bandgap. EXPERIMENT Crystalline lattices with micro- and nanostructured periodicity were selfassembled from polystyrene (PS) colloids (Bangs Laboratories, Fishers, IN; Polysciences, Warrington, PA) using a procedure demonstrated by our group.[6] The crystalline arrays D9.15.1
obtained by this method usually have a cubic-close-packed (ccp) structure with the ABC stacking sequence perpendicular to the substrates between which the crystal is grown. Monodispersed colloidal suspensions of 230-nm PS colloids were used to form host lattices to study the influence of defects on the stru
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