Photonic crystals Fabrication of Tunable Spherical Colloidal Crystals Immobilized in Soft Hydrogels**
نویسندگان
چکیده
Spherical colloidal crystals are three-dimensional periodic arrays of monodisperse colloidal particles with a spherical geometry. The spatial periodicity of the refractive index of the colloidal crystalline arrays results in an optical stop band and, hence, they act as photonic crystals in the optical regime. In contrast to conventional film-type colloidal crystals where the crystals are aligned by the film, the optical stop band of spherical colloidal crystals is independent of the rotation under illumination of the surface at a fixed incident angle of the light. Therefore, spherical colloidal crystals are potentially useful not only for conventional photonic-crystal applications but also as a new type of spectrum-encoding carrier for biomolecular screening, non-bleachable color pigments, and refractive color displays. Spherical colloidal crystals can be fabricated using droplets as templates; droplets of aqueous colloidal suspension are dispensed on a hydrophobic surface or in oil and then dried. The evaporation of the liquid medium leads to the assembly of particles into close-packed structures witha spherical geometry. Sinceupondrying theparticles touch one another, the crystal lattice constant is uniquely determined by the diameter of the particles. Therefore, fabrication of colloidal crystals with different wavelengths for their optical stop band requires colloidal particles with different size or refractive index. It is difficult to tune the diffractionwavelength after the colloidal crystal spheres are formed; this lack of tunability limits theutility of these structures formanypractical applications.
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