HABIT AND STRUCTURE OF CD(S,SE) QUANTUM DOTS IN SILICATE-GLASSES - HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY

Cd(S, Se) nanocrystals were developed in silicate glass by heat treatments and were characterized by high-resolution transmission electron microscopy. They are crystallized in the hexagonal structure of wurtzite type. Their average size increases with increasing heat-treatment time from 5 to 13 nm at 700-degrees-C and from 5 to 10 nm at 675-degrees-C. The crystal morphology depends on the size. Below a critical size s(c), the shape is close to either a sphere or a hexagonal prism with nearly equivalent dimensions in every direction. Above s(c), the crystallites definitely adopt a prismatic habit, growing longer in the direction of the c axis. The critical size depends on the temperature of the heat treatment: at 700-degrees-C, s(c) is about 10 nm and, at 675-degrees-C, it is around 6-7 nm. The basal faces of the prism present an asymmetry, indicating different growth rates in opposite directions of the c axis, in relation to the polarity of the wurtzite structure.