Sha Liu, Hongwang Zhang, and Mark T. Swihart. Chemical and Biological Engineering, The University at Buffalo (SUNY), 303 Furnas Hall, Buffalo, NY 14260-4200
Zinc sulfide (ZnS) is a II-VI semiconductor with a large direct band gap in the near-UV region. It has potential applications in areas such as solar cells, lasers, sensors and displays. ZnS nanoparticles (or quantum dots) exhibit size-dependent optical and electronic properties. We have prepared ZnS nanoparticles through spray pyrolysis of two different sets of precursors, and both approaches will be described in this presentation. The single source precursor zinc diethyldithiocarbamate has been used alone, with no need to match flow rates of separate zinc and sulfur precursors to produce stoichiometric particles. In this approach, the precursor evaporation and decomposition and the nucleation of particles occur sequentially in the furnace. X-ray diffraction shows that cubic ZnS crystals are produced in this approach. Transmission electron microscopy shows that the average particle size is below 20 nm. They exhibit blue photoluminescence under UV excitation. We have also prepared ZnS nanocrystals using zinc acetate and thiourea as separate Zn and S sources. With a precursor molar ratio of 1:2, ZnS can be produced using the same reactor system that was used for producing ZnS particles from a single source precursor, by premixing these two precursors in one gas assisted atomizer. This produces larger, spherical particles characteristic of incomplete precursor evaporation. In addition, two ultrasonic atomizers have been used to separately atomize the two precursors and separately evaporate them in the furnace, then finally mix them to nucleate particles from the vapor phase.