1 research outputs found
Twinning and Phase Control in Template-Directed ZnS and (Cd,Zn)ÂS Nanocrystals
We report on the nucleation and growth
of ZnS and (Cd<sub><i>x</i></sub>ÂZn<sub>1–<i>x</i></sub>)ÂS
nanocrystals on polydiacetylene Langmuir films. It was found that
the 3–5 nm nanocrystals form ordered linear arrays aligned
at a constant 27° angle with respect to the conjugated direction
of the polydiacetylene film, as derived from the optimal alignment
between the two phases. ZnS nanocrystals were found to nucleate specifically
from the zinc blende (001) face. Because of closely matched interfacial
relations, twinning defects were induced on the {111} planes. These
nanometer-sized twin crystals exhibit extra {111} electron diffraction
reflections due to elongation of reciprocal space spots, despite their
off axis orientation. The composition of solid solution (Cd,Zn)ÂS
nanocrystals depends on the Zn<sup>2+</sup>\Cd<sup>2+</sup> ratio
in the aqueous subphase. Their structure is affected by the template
mismatch both by twinning, as is the case for ZnS, for which continuous
compositional shift is observed, and by phase shift to hexagonal wurtzite,
with a pure CdS composition. The nanocrystals exhibited a continuous
energy-gap shift, reflecting the Zn/Cd ratio in the solid solution.
We demonstrate control over the nanocrystals’ crystal structure,
defect structure, orientation, and composition, providing a potentially
effective tool for band-gap engineering in organic–inorganic
hybrid assemblies