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.

A systematic investigation of the mechanism of cadmium sulfide solution growth using atomic force and scanning electron microscopy was performed. The process that was studied involved the slow generation of sulfide ions via the controlled hydrolysis of thiourea in the presence of cadmium nitrate and triethanolamine, a chelating ligand. The formation of two types of films was observed, a mirrorlike primary film and a secondary layer of larger particles that was loosely attached to the first film. The substrates used for the deposition were either bare mica or mica with a partial self-assembled monolayer of octadecylphosphonic acid, CH 3 (CH 2 ) 17 PO 3 H, which served as an internal height standard due to the formation of submonolayer islands 18 ( 2 Å tall. Islands of CdS were observed to nucleate on the remaining bare patches of mica suggesting a potential route to lateral surface patterning. The CdS grew to a height of 22-23 nm, leveled off by 6.5 h, and then proceeded to grow in scattered domains 60-70 nm tall with a few spots as high as 80-100 nm after 10 h. The mechanism of growth has been attributed to either involve attachment of colloidal particles to the surface or an ion-by-ion deposition process. Atomic force microscopy has provided compelling evidence that the latter mechanism is the correct one.

Unusual metal carboxylates that are liquids at room temperature have been synthesized and applied to the preparation of nickel ferrite. These salts Ni(MEEA)2·0.5H2O and Fe3O(MEEA)7·5.5(H2O) bear the polyether carboxylate anion 2-[2-(2-methoxyethoxy)ethoxy]acetate (MEEA = CH3OCH2CH2OCH2CH2OCH2CO2 -). They may be utilized for the low-temperature preparation of nickel ferrite by using Ni(MEEA)2·0.5H2O to coat Fe2O3 powders with a continuous film of NiO. Upon heating this material to 800 °C, a remarkable solid-state reaction occurs to puff the precursor particles into broccoli floret-like collections of very small particles. A homogeneous precursor solution for nickel ferrite may be prepared via dissolution of Ni(NO3)2 in Fe3O(MEEA)7·5.5(H2O). This precursor solution yields a metastable amorphous NiFe2O4 phase at 300 °C which undergoes an exothermic crystallization at 374 °C with an energy change of −126.1 kJ/mol.