Homogeneous, Core−Shell, and Hollow-Shell ZnS Colloid-Based Photonic Crystals

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Abstract
Ordered ZnS-based colloidal crystals from homogeneous, core−shell, and hollow building blocks were prepared via electrosteric colloid stabilization combined with a convective assembly technique. The polyelectrolyte stabilized colloids assembled into face-centered cubic arrays with the (111) face perpendicular to the substrate. Structure−property correlations were made using scanning electron microscopy, scanning transmission electron microscopy, and UV/visible/near-IR spectroscopy. Multilayer film growth, with film thickness of several micrometers, was achieved. Optical spectra showed (111) stopgaps along with pronounced higher order peaks. The spectral position of the photonic stopgap can be predicted using a volume average refractive index and the Maxwell−Garnett formula for the homogeneous and core−shell particles, respectively. This work holds the promise of harnessing ZnS for optical property engineering and enhanced photonic band gap materials.