V. Platschek et al., QUANTIZED AGGREGATION PHENOMENA IN II-VI-SEMICONDUCTOR COLLOIDS, Berichte der Bunsengesellschaft fur Physikalische Chemie, 102(1), 1998, pp. 85-95
Citations number
35
Categorie Soggetti
Chemistry Physical
Journal title
Berichte der Bunsengesellschaft fur Physikalische Chemie
Highly concentrated 0.5 M IT-VI semiconductor quantum dot solutions fo
r coating applications can be synthesized employing chalcogenolysis an
d condensation of functionalized cluster-like cadmium and zinc ethoxya
cetates. Furthermore, in nucleation studies on CdSe solutions, new mag
ic clusters between 0.42 and 1.7 nm in size were found exhibiting shar
p HOMO-LUMO resonances (lowest absorption features) in the optical abs
orption spectra. High resolution small angle X-ray scattering (SAXS) m
easurements performed on 1.7 and 3.4 nm CdSe clusters corroborate the
size. Information on the intra-cluster structure was hard to derive wi
th respect to the small cluster size. These species could be Koch pyra
mids with a fractal dimension D-f=2 as well as non-fractal zincblende
pyramids (additionally checked by XRD and HRTEM). In any case rather c
hain-like (D-f=1) aggregates are formed. It further will be shown that
in alcoholic CdSe sols the initially nucleated ''seeds'' are highly r
eactive. Their sharp HOMO-LUMO transitions are found to be strongly mo
dified by externally induced chemical reactions. For example, aminosil
ane capped 1.7 nm clusters decompose rapidly upon exposure to phosphin
es. After a period of few hours, they begin to re-grow to their origin
al size or they reorganize to give smaller 0.85 nm subunits depending
on the P/N ratio. In contrast, 0.85 nm phosphine-capped clusters doubl
e their size if exposed to amines. The last process liberates cadmium
ions into the solution as found in complementary polarographic measure
ments.