Evaporation-induced self-assembly of capillary cylindrical colloidal crystal in a face-centered cubic structure with con
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Ming Wanga) School of Physical Science and Technology, Nanjing Normal University, Jiangsu Key Lab on Opto-Electronic Technology, Nanjing 210097, China
Wei Xia School of Physical Science and Technology, Nanjing Normal University, Jiangsu Key Lab on Opto-Electronic Technology, Nanjing 210097, China
Lihua Dai School of Physical Science and Technology, Nanjing Normal University, Jiangsu Key Lab on Opto-Electronic Technology, Nanjing 210097, China (Received 30 December 2011; accepted 17 April 2012)
The fabrication of capillary cylindrical crystals from colloidal suspension with controllable thickness by evaporation-induced self-assembly method has been investigated. The thickness of the hollow cylinders can be precisely controlled ranging from monolayer to tens of layers by varying the suspension concentration. With the increase of suspension concentration, the particles fill completely inside capillaries to form solid bulk crystals and the critical values are found in capillaries with various diameters. Scanning electron microscope images confirm the facecentered-cubic structure in both crystals, but with two different [111] crystalline directions. The experiment parameters, such as the solvent, concentration of the suspension and inner diameter of capillary are studied for the quality and the number of film layers control. Qualitative analysis has been performed to probe into the solvent evaporation modes and the mechanism of particle arrangement inside the capillary.
I. INTRODUCTION
In the last few years, the self-assembly of monodispersed spheres into ordered three-dimensional (3D) structures, which we call colloidal crystals (CCs), has attracted great attention. CCs have unique properties in terms of light propagation and are expected to have applications in optical devices such as photonic crystals.1–3 CCs can be easily fabricated through self-assembly techniques from microspheres made of silica or polymers. The routes for creating colloidal crystals can be roughly divided into two types: gravity sedimentation of colloids from dispersions4 and solvent evaporation method.5 Also, template-directed crystalline,6 patterned or nonplanar substrates,7 and physical confinement8 have been used to direct the photonic crystal growth. Yang et al.9 have buried synthetic opal crystals inside parallel arrays of rectangular-shaped microchannels for potential applications in microphotonic crystal devices and a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.128 J. Mater. Res., Vol. 27, No. 13, Jul 14, 2012
chips. Ye et al.10 have successfully introduced air-core line defects into inverse 3D CCs by simply growing them on top of lithographically patterned substrates. Besides, the patterned substrates such as a grating with a periodic onedimensional profile,11 an optical rib waveguide,12 and a silicon wafer with V-shaped groove13 have been selected for the arrangement of colloidal particles and the formation of functional materials with 3D complete photonic band gaps. Some groups have
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