Nano Focus: Individual quantum dots immobilized and positioned at the nanoscale
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In a cell with ionic liquid electrolyte, the researchers applied a negative potential to a SnO2 nanowire with respect to a LiCoO2 counter electrode. This y ear ago at Sandia National spurred lithium ions to react with the Laboratories, a nanowire wrigtin oxide nanowire, producing a reacgled and twisted like a snake hatchtion front that propagated longitudinally ing from an egg. Researchers watched through the single crystal. In the front’s in real time as a SnO2 nanowire elecwake, an amorphous-reacted phase actrode charged with lithium inside a tively started to bend and coil while tiny electrochemical device. In the lengthening and swelling. After fully December 10, 2010 issue of Science charging, the nanowire was composed (DOI: 10.1126/science; p. 1515), of amorphous Li2O and nanoparticles of LixSn and Sn, as determined by elecJ.Y. Huang, L. Zhong, C.M. Wang, and tron diffraction and electron energy-loss colleagues across five institutions have spectroscopy, and had a total volume reported on the design of the device inchange of over 200%. side a high-resolution transmission elecSnO2 has promising electrochemical tron microscope and have analyzed the storage capacity, but in bulk, the material phase and morphological changes that is brittle. The researchers reported, howoccurred in the electrode. Nanowire ever, that the tested nanowires showed electrodes recently have shown the pohigh plasticity during phase transformatential for longer life and improved pertion and no signs of fracture after lithiformance over other material structures ation. During charging, they witnessed for electrochemical energy storage. a high density of dislocations continuously nucleate Dislocation Cloud Amorphous Single Crystal SnO at the amorphouscrystalline inter+ Li face and subsequently consumed by the advancing reaction front A dislocation cloud forms at the reaction front where the single crystal (see figure). The SnO2 nanowire charges with lithium ions. The reaction front propagates to the left, leaving behind a plastically-deformed, amorphous phase of researchers said Li2O with nanoparticles of LixSn and Sn. Reproduced with permission that the very high from Science 330 (2010) DOI: 10.1126/science; p. 1515. © 2010 AAAS. stresses resulting from the differSnO2 nanowire lithiation in a TEM viewed in real time
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Nano Focus Individual quantum dots immobilized and positioned at the nanoscale
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echniques for precisely arranging nanoscopic objects are essential to fully realizing their potential in emerging technologies. Controlled placement of quantum dots (QDs) on a surface could be key to engineering photonic or plasmonic structures on the nanoscale. C. Ropp and a multidisciplinary team from the University of Maryland have recently devel-
oped a microfluidic technique for moving quantum dots with nanometer precision before individually immobilizing them within a polymer shell. Published in the November 10, 2010 issue of Nano Letters (DOI: 10.1021/ nl1029557; p. 4673), their work makes use of the electroosmotic control of CdSe/Z
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