In this letter we describe a novel but effective wet-chemical route for the simple preparation of snowflake-like dendritic nanostructures of Ag, which are homogeneous in size, carried out by directly mixing AgNO3 and p-phenylenediamine (PPD) aqueous solutions at room temperature. It reveals that such dendrites are aggregates of nanoparticles and highly crystalline in nature. It is found that the molar ratio of [PPD]/[Ag+] influences the final morphologies of the structures formed and that excessive PPD (the molar ratio of [PPD]/[Ag+] is higher than 1:1) is crucial to achieving dendrites. The possible dendritic growth mechanism is also predicted. This method can also be extended to the preparation of Au dendrites.
We have fabricated all-dielectric high-Q optical pillar resonators with embedded colloidal CdSe/ZnS quantum dots or rods as light emitters by focused ion beam milling. Three-dimensional light confinement and distinct pillar microcavity modes are observed. Results from a waveguide model for the mode patterns and their spectral positions are in excellent agreement with the experimental data. Cavities with elliptical cross sections show higher quality factors in the short axis direction than do circular resonators of the same cross-sectional area.
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