Microstructure characterization of mechanically synthesized ZnS quantum dots

ZnS quantum dots (QDs) with cubic phase have been prepared by mechanical alloying the stoichiometric mixture of Zn and S powders at room temperature in a planetary ball mill under Ar. Initially, an amorphouslike thin wurtzite (hexagonal) shell is formed on major zinc-blende (cubic) core after 3.5 h of milling and, in the course of milling up to 20 h, strain free single phase (cubic) QDs are formed with ∼4.5 nm in size. These ball-milled QDs contain different kinds of stacking faults and the Rietveld analysis of x-ray powder diffraction data reveals their concentration in milled samples. Though the high resolution transmission electron microscope (HRTEM) images could not detect the presence of the wurtzite phase but confirm the presence of cubic phase, core-shell structure, and different kinds of stacking faults in ball-milled samples. The particle size of QDs and their distributions obtained from Rietveld analysis agree well with the observations of HRTEM images.