Sonochemically Produced ZnS-Coated Polystyrene Core−Shell Particles for Use in Photonic Crystals

Abstract

Zinc sulfide films were grown on carboxyl-modified polystyrene microspheres (PS-CO2) through sonochemical deposition in an aqueous bath containing zinc acetate and sulfide, released through the hydrolysis of thioacetamide. The resulting particles were “optically hollow”, due to a large refractive index contrast between the core and shell materials. Continuous, uniform films were obtained after 3−4 h and reached a maximum thickness of 70−80 nm after 13 h of growth, as characterized by transmission electron microscopy (TEM). Aggregation was minimized by subsequent modification of the core−shell particles with mercaptoacetic acid to increase their surface charge and produce good colloidal suspensions. Oscillations in the optical spectra of dilute suspensions of the particles were indicative of interference patterns as expected from Mie light scattering calculations. X-ray diffraction (XRD) patterns match the zinc blende structure of ZnS and indicate a compression in the crystal lattice (a = 5.305 ± 0.037 Å), as compared to the bulk material (a = 5.406 Å). Hollow ZnS shells were formed by annealing the core−shell particles in a thermal gravimetric analysis (TGA) oven, at 400 °C. A 34% weight loss was observed upon heating, a value approximately equal to that of the polystyrene core. The hollow shells remained intact and readily resuspended in water. Both core−shell and hollow ZnS particles self-assemble to form well-ordered, hexagonal close-packed layers.

Photonic crystals of core-shell colloidal particles

“…We study optical transmission at normal incidence on thin photonic crystals. In accordance with previous calculations, 5 we demonstrate that photonic crystals of high-index core and low-index shell particles posses a larger relative L-stopgap width in comparison to crystals of low-index core and high-index shell 17 or homogeneous particles.…”

“…These calculations demonstrate the effect of the morphology and optimization of the filling fraction of the high dielectric material, using core-shell particles, on the optical properties of photonic crystals. For the L-stopgap the high-index core low-index shell morphology is clearly better than the low-index-core high-index shell 17 for photonic applications. Figure 4 compares measured optical transmission spectra of thin photonic crystals from silica, ZnS-core-SiO 2 -shell, and homogeneous ZnS-SiO 2 composite particles of similar radii.…”

Laser assisted solid state reaction for the synthesis of ZnS and CdS nanoparticles from metal xanthate

“…The syntheses of the II -VI group of nanoparticles have been achieved using different techniques which include thermolysis of a single-source precursor [4,5], solventothermal [6], sonochemical [7], and colloidal precipitation [8]. However, most of these techniques are complex to perform with limited control over particle size [9].…”

Influence of Co-Dopant on Structural, Optical and Electrochemical Properties of Zinc Sulphide Quantum Dots

“…Among these, semiconductors are the most excellent material showing appreciable modification in the optical and electronic properties through the alteration in the energy band gap via doping with other foreign metals. Recently semiconducting nanocrystalline materials have immensely attracted the interest in electronics and photonics application [1] such as light emitting diodes [2], photonics [3], chemical, biological and UV sensors [4], phosphors in displays and also in biomedical applications for biological labelling [5], diagnostics [6].…”