Influence of growth conditions on the structural properties of CdSxSe1-x (x=0.4 and x=1) nanocrystals

The structural properties of CdSxSe1-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, CdS0.4Se0.6 nanocrystals are grown in glass matrix and show a size distribution characterized by a standard deviation sigma nearly proportional to the nanocrystals mean diameter d, the value sigma/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 sigma/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.