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ABSTRACT: We report an improved convective self-assembly method for the fabrication of highly ordered, crack-free binary colloidal crystals (BCCs) and the associated inverse structures in large domains at length scales of several centimeters. With this method, BCCs can be fabricated in a non-close packed pattern and binary inverse opal films can be obtained over a centimeter scale. The presence of tetraethyl orthosilicate (TEOS) sol in the self-assembly system was found to play a significant role in the resultant structures. The pseudostop band positions are adjustable via varying the number ratio of small to large polystyrene (PS) spheres. At a given TEOS-to-PS ratio, the binary inverse opal film thickness was controllable by varying the colloidal volume fraction with an upper thickness threshold (>16 layers).
Journal of Colloid and Interface Science 05/2012; 380(1):42-50. · 3.07 Impact Factor
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ABSTRACT: Silicon-based photonic crystal is a promising material for terahertz (THz) waveguide due to its high refractive index contrast.
In this work, we introduce eye-shaped pillars as the feature building blocks for two-dimensional (2D) photonic crystals. The
simulation study shows that larger TE mode band gaps (PBGs) can be created by the arrangement of dielectric eye-shaped pillars
in air. The reflective spectra demonstrate that there are complex PBGs, where the peak position and intensity can be changed
by varying the parametere. Moreover, the peak of reflective spectra exhibits an obvious blue shift with the increase of incidence angle of light. When
the vacant space in the structure is filled by polystyrene (PS) microspheres of 2μm in diameter, the peak intensity of reflective
spectra reduces significantly compared with that without PS microspheres, which suggests that this design can act as a sensor
in the fields of biology, agriculture or medicine.
Applied Physics A 04/2012; 102(2):373-377. · 1.63 Impact Factor
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ABSTRACT: TiO(2) nanoparticles have been widely explored as photocatalysts in the degradation of organic matters present in water. However, spontaneous agglomeration of TiO(2) nanoparticles in a suspension is a crucial issue that must be addressed before the photocatalyst can be used for water treatment. In the present work, the nature of the agglomeration of TiO(2) nanoparticles in aqueous suspension was investigated. Two approaches to minimize the agglomeration of colloidal TiO(2) particles were investigated. A careful control over the pH of the system was found to be an effective method for stabilizing colloidal TiO(2) particles and to significantly enhance the adsorption of orange II. As a result, the overall photocatalytic degradation rate was greatly accelerated. In addition to pH control, modification of TiO(2) particles using polyelectrolyte poly allylamine hydrochloride (PAH) was observed to be an effective approach for preventing colloidal TiO(2) particles from agglomeration.
Journal of Colloid and Interface Science 08/2010; 348(2):342-7. · 3.07 Impact Factor
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ABSTRACT: We describe the use of a horizontal deposition method to prepare large-area binary colloidal crystals (bCCs). Two different sets of binary polystyrene spheres were employed to demonstrate the validity of this method. By varying the number ratios of small spheres with respect to large spheres, the stoichiometric configuration of the bCCs can be altered. Stable corresponding replica structures of the bCCs were also prepared, and the cross-sectional images of the binary inverse opals were obtained. Optical characterization demonstrated the presence of pseudostop bands, which were in agreement with the compositions of the material. The formation of the bCC by such a simple self-assembly method was attributed to the cooperative effect of interparticle electrostatic interactions and geometrical constrictions. This facile fabrication method further enhances the application potential of the bCCs and their inverse porous replicas with a binary pore system in the fields of photonics, solar cells, separations, catalysis, and biosensing.
Langmuir 07/2009; 25(12):6753-9. · 4.19 Impact Factor
