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Synthesis of Quantum-Sized Cubic ZnS Nanorods by the Oriented Attachment Mechanism
journal contribution
posted on 2005-04-20, 00:00 authored by Jung Ho Yu, Jin Joo, Hyun Min Park, Sung-Il Baik, Young Woon Kim, Sung Chul Kim, Taeghwan HyeonQuantum-sized ZnS nanocrystals with quasi-spherical and rod shapes were synthesized by the
aging reaction mixtures containing diethylzinc, sulfur, and amine. Uniform-sized ZnS nanorods with the
average dimension of 5 nm × 21 nm, along with a small fraction of 5 nm-sized quasi-spherical nanocrystals,
were synthesized by adding diethylzinc to a solution containing sulfur and hexadecylamine at 125 °C,
followed by aging at 300 °C. Subsequent secondary aging of the nanocrystals in oleylamine at 60 °C for
24 h produced nearly pure nanorods. Structural characterizations showed that these nanorods had a cubic
zinc blende structure, whereas the fabrication of nanorods with this structure has been known to be difficult
to achieve via colloidal chemical synthetic routes. High-resolution TEM images and reaction studies
demonstrated that these nanorods are formed from the oriented attachment of quasi-spherical nanocrystals.
Monodisperse 5 nm-sized quasi-spherical ZnS nanocrystals were separately synthesized by adding
diethylzinc to sulfur dissolved in a mixture of hexadecylamine and 1-octadecene at 45 °C, followed by
aging at 300 °C. When oleic acid was substituted for hexadecylamine and all other procedures were
unchanged, we obtained 10 nm-sized quasi-spherical ZnS nanocrystals, but with broad particle size
distribution. These two different-sized quasi-spherical ZnS nanocrystals showed different proportions of
zinc blende and wurtzite crystal structures. The UV absorption spectra and photoluminescence excitation
spectra of the 5 nm ZnS quasi-spherical nanocrystals and of the nanorods showed a blue-shift from the
bulk band-gap, thus showing a quantum confinement effect. The photoluminescence spectra of the ZnS
nanorods and quasi-spherical nanocrystals showed a well-defined excitonic emission feature and size-
and shape-dependent quantum confinement effects.
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Keywords
zinc blendewurtzite crystal structureszinc blende structureUV absorption spectraexcitonic emission featureZnS nanorodsrod shapesphotoluminescence excitation spectraTEMnanocrystalphotoluminescence spectraparticle size distributionStructural characterizationsreaction mixturesreaction studies24 hquantum confinement effectoleic acid
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