| Abstract
| - This paper describes the fabrication and characterization of colloidal crystals constructed from spheroidalbuilding blocks with well-controlled major-to-minor ratios. Such a crystalline lattice was fabricated byinfiltrating an opaline lattice of monodispersed polystyrene spheres with an elastomer precursor such aspoly(dimethylsiloxane) (or PDMS), followed by thermal curing and stretching of the composite film at atemperature higher than the glass transition temperature of polystyrene. In this process, the polystyrenespheres were transformed into spheroids through viscoelastic deformation, while the long-range order ofthis three-dimensional lattice was essentially preserved. Because of the low contrast in the refractiveindex, the colloidal crystal fabricated in the present work exhibited a stop band (rather than a completeband gap) in the optical regime. The position of this stop band was determined by the diameter of thepolystyrene spheres and the elongation ratio of the elastomeric composite. When the crystalline latticewas made of 240-nm polystyrene spheres, the stop band shifted from 594 to 522 nm, as the PDMS filmwas stretched by an elongation of 130%, and further down to 470 nm, as the incident angle was changedfrom 0 to 45°. These spectroscopic measurements were in good agreement with the partial band structurescalculated using the plane-wave-expansion-method (PWEM). In addition to their use as a model systemto investigate the dependence of photonic band structures on the shape (or symmetry) of lattice points,the nonspherical system described here also provides a potentially useful approach to fine-tuning theoptical properties of colloidal crystals.
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