Influence of growth conditions on the structural properties of CdS_xSe_1-x (x = 0.4 and x = 1) nanocrystals

The structural properties of CdS_xSe_1-x nanocrystals elaborated by two different methods have been studied by means of high resolution transmission electron microscopy and optical absorption. In the first method, CdS_0.4Se_0.6 nanocrystals are grown in glass matrix and show a size distribution characterized by a standard deviation σ nearly proportional to the nanocrystals mean diameter d, the value σ/d being about 0.25. They are crystallized in the stable structure of wurtzite-type from the beginning of growth. Their morphology depends on the size: it changes from sphere to hexagonal prism as the size increases. In the second method CdS nanocrystals are grown in solution and show narrower size distribution; the ratio σ/d is about 0.15. The structure depends on the nanocrystal size: the blende-type structure is dominant at small diameter (d = 3 nm) and the wurtzite-type structure is more important at larger diameter (d > 5 nm). Their morphology also changes from quasi-sphere at small size (< 4 nm) to polyhedron-like at larger size.