Physico-chemical investigation of ZnS thin-film deposited from ligand-free nanocrystals synthesized by non-hydrolytic thio-sol-gel

Ultra-small and monodispersed zinc sulfide nanocrystals (d≤3 nm) have been prepared without the use of any surfactants by a synthetic route using benzyl mercaptan as a source of sulfur. The prepared nanocrystals are dispersible in highly polar solvents and display the capability to closely pack-up in a bulky film. The nanocrystals were characterized by TEM, XRD and UV-Vis optical absorption as well as by steady-state and time-resolved photoluminescence spectroscopies. Uniform films of ZnS were spin-coated on glass and ITO-glass substrates using a nanocrystals dispersion in N,N-dimethylformamide. The nanocrystals and the resulting films were characterized by morphological and optoelectronic probing techniques such as AFM, SEM, diffuse reflectance, photoluminescence and photoelectron spectroscopy in air. These physical investigations confirmed that the chalcogenide nanocrystals grown by this method have the potential to be utilized directly as photocatalysts and are potentially useful building blocks/starting materials for the fabrication of semiconductor thin films for optoelectronic applications such as LED, luminescent screens, field effect transistor and solar cells. Insights on the chemistry involved in the nanocrystals growth have been provided revealing that their formation proceeds through a mechanism involving a thioether elimination reaction.