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Posted: September 5, 2007

Beautiful blooms from nano-weeds

(Nanowerk News) Chinese researchers have discovered a simple way to grow nanowire clusters and transform them into an array of tiny flower-like forms.
Nanowires hold great promise as key components in nanoscale electronic and optoelectronic devices and sensors. But any future application depends on being able to make the wires with precise control over morphology, shape and structure.
controlling the structure of nanoclusters
The structure of the nanocluster can be controlled (Copyright: Wiley)
Xiu-Ping Yan from Nankai University and co-workers have now discovered how to make highly regular nanoclusters of cysteine-lead wires, which initially resemble dandelions. The wires form spontaneously when a solution of lead acetate and cysteine is concentrated by steadily evaporating off the solvent - a simple process that works on large scale and at room temperature and pressure ("Facile Shape-Controlled Synthesis of Well-Aligned Nanowire Architectures in Binary Aqueous Solution").
A variety of other nanoflowers can be made from the dissolved nanodandelions (Copyright: Wiley)
Yan proposes that the flowers form by a crystal splitting mechanism. The crystals grow quickly, and successively split apart as they grow, until finally forming the spherical dandelion structure.
The team could control the cluster's structure by changing the reaction conditions. At higher initial concentration of solution gives a denser dandelion with more wire 'petals'. Yan also showed that adding more cysteine into the mixture gave less extensively split, more sheaf-like structures, while extra lead produced very high splitting.
A few drops of acid and the dandelions dissolved, but subsequent heating in an autoclave gave a variety of new four- or eight-petaled nanoflower structures. The blooms consist of lead sulfide, a semi-conducting material. Yan's team are now studying the exact mechanism by which these final structures form.
Source: Reprinted with permission from Chemistry World (James Mitchell Crow )
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