Structural transformations in II-VI semiconductor nanocrystals

Colloidal CdS and CdS/ZnS nanostructures were obtained by nucleation and growth in colloidal solution. Their mean sizes range between 3 and 10 nm. The structural properties were studied by the use of high-resolution transmission electron microscopy (HRTEM). Phase transition between the metastable cubic blende-type structure and the stable hexagonal wurtzite-type structure was evidenced to be a function of the size of the CdS clusters. The mechanism of the transition involving stacking faults was determined by the heating of CdS clusters at 200 °C for 30 h. Results concerning structural relations between CdS and ZnS that occur during the epitaxial growth of ZnS on the CdS nanocrystals showed the existence of the hexagonal structure of ZnS, which is the high-temperature phase of ZnS.