| The production of monodispersed non-spherical particles is necessary to fully explore the promise of colloidal systems for optical pigments, diffractive elements in smart sensors, and for photonic crystal applications. In the case of photonic crystals, the addition of asymmetry in the lattice enables photonic band gap realization at refractive index values insufficient for assemblies of monodispersed spheres. Additionally, complex building blocks lower the filling fraction of high index material due to geometric packing restrictions so that inverting the structures may not be required.; In this work, a route to the production of non-spherical zinc sulfide particles was developed and evaluated for photonic crystal applications. Monodispersed ZnS clusters of close-packed shapes including dimers, trimers, tetramers and tetrahedra were synthesized by two-stage chemical precipitation, starting from homogeneous solutions of metal salt and thioacetamide sulfide ion precursor. The non-spherical particles are hierarchically structured, composed of 500nm–3μm coagulated monodispersed spheres, which are themselves aggregates of 5–10nm single crystal spheroids. Though the particles were porous, the index of refraction was high, n ∼ 2.2, as compared with silica and polystyere, n ∼ 1.5. The mixtures of morphological types synthesized were quantitatively analyzed by image analysis and stereology as well as flow cytometry. The estimated yield of dimers was 23vol%, having average size 1.29 microns and polydispersity 5.67%, well within the requirements for self-assembly. The dimers were obtained in large quantities, ∼1012, for harvesting and use in photonic crystal applications. Techniques such as flow cytometry were explored and may be promising for the separation and collection of the particle populations.; Though the production of monodispersed ZnS spheres by the decomposition of thioacetamide has been utilized by other groups, this is the first report of their controlled coagulation leading to separable quantities of well-defined non-spherical ZnS colloids. These high refractive index particles expand the menu of complex colloid bases available for photonic crystal structures and can be used in studies considering the effect of building block orientation on photonic band structures. Additionally, small percentages of cluster particles can be added as dopants to sphere lattices to promote localized modes within the photonic band gap and engineer optical microcavity effects. |
