CommunicationsMonodisperse magnetic iron oxide nanoparticles with a continuous size spectrum of 6-13 nm were produced by controlled growth on previously synthetisized monodisperse nanoparticle seeds. The detailed synthetic procedure and characterization is described in the communication by T. Hyeon et al. on the following pages.

No abstract

No abstract

Quantum-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 x 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 degrees C, followed by aging at 300 degrees C. Subsequent secondary aging of the nanocrystals in oleylamine at 60 degrees 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 degrees C, followed by aging at 300 degrees 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.