Colloidal Crystal Wires from Directed Assembly
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J20.3.1
Colloidal Crystal Wires from Directed Assembly Feng Li,1 Xavier Badel,2 Jan Linnros,2 and John B. Wiley1,* 1 Department of Chemistry and the Advanced Materials Research Institute, University of New Orleans, New Orleans, LA 70148-2820 U.S.A. 2 Department of Microelectronics and Information Technology, KTH Royal Institute of Technology, SE-164 40 Kista, Sweden ABSTRACT Colloidal crystal wires with tubular-like packings are prepared by the directed assembly of spheres into cylindrical one-dimensional channels. Silica spheres are infiltrated into porous silicon membranes, treated with silane, and annealed. Single annealing cycles are found to result in colloidal crystal wires with varied packing geometries, while repeated annealing produces a thin translucent silica sheath around the wires. Packing in the wires varies with the relative channel diameter of the silicon membrane where typical wires contain 4 to 7 helical strands. Both chiral and achiral packing geometries are observed. The fabrication of these wires is discussed and the relationship between channel size and packing structure detailed. INTRODUCTION The study of the ordering of spheres in different packing geometries has been motivated by a variety of interests. Recently, there has been much attention on the formation of colloidal crystals for applications in photonics, for use as catalytic supports or as possible lightweight building materials [1-3]. Also, the importance of such structures to biological systems has been explored including biomaterials (e.g., viral capsids) and the study of geometric features in plants (phyllotaxis) [4,5] In terms of the packing of spheres in colloidal crystals, researchers have mostly examined the fabrication of bulk and thin film materials [6]. More recently researchers have looked at the packing of spheres in confined geometries; Xia and coworkers for example have looked at the formation of clusters containing various sphere sizes in shallow circular wells [7] as well as the formation of helical wires in V-shaped grooves [8]. Other researchers have formed sphere microfibers in rectangular grooves and microcapillaries [9,10]. We have reported the use of alumina and polymer templates to prepare inverse porous metal wire structures [11]. In these studies, where the diameter of the spheres (ds) is slightly smaller than that of the cylindrical channel (dc), unusual packing geometries were observed. Erickson and Pickett et al. have reported theoretical studies on some of the packings that are possible within confined cylindrical geometries [5,12]. Herein we describe the formation of tubular-like colloidal crystal wires that exhibit similar geometries. While the initial production of these materials has been described elsewhere [13], herein we highlight these efforts with a focus on synthesis and the varied sphere packing geometries accessible in the directed assembly with channels.
J20.3.2
EXPERIMENTAL Directed assembly of the silica spheres is carried out within porous silicon membranes. The silicon membranes are p
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