Nanoclusters of Metallic Gold Display Optical Chiral Properties
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bination of tin-plate scrap, aluminum scrap, and domestic incinerator scrap may serve to produce a “master alloy” or stepping stone to produce a higher quality material compared with remelted steel scrap. This would be particularly advantageous to countries that currently have no indigenous steel industry, he said. Initial studies show that the presence of aluminum causes an increase in the hardness of the steel, implying an increase in mechanical strength. These encouraging findings are being evaluated, and once this has been completed, the team intends to replicate the process at pilot-plant scale.
Si Nanowires Produced with Aid of Gold Quantum Dots Brian Korgel and Keith Johnston, professors in the Department of Chemical Engineering at the University of Texas—Austin, have produced silicon nanowires by using particles of gold suspended under pressure in a compressed fluid at a high temperature. As reported in Science, they heated silicon atoms connected to organic molecules until the Si atoms loosened and formed free Si atoms. Done in the presence of gold quantum dots (QD) or nanocrystals, the free Si atoms then dissolve in the QDs. When the silicon concentration inside the gold becomes great enough, the gold ejects the silicon in the form of a wire. Molecular capping ligands can be attached chemically to the gold QDs during their formation to keep them uniform in size. The researchers’ method involves the use of supercritical fluids, in this case, 5000 lbs/in2 at 500°C. Johnston said, “We have used supercritical fluids to control chemical reactions . . . but never for the nanoscale materials.” Korgel said, “At that temperature, we would expect the molecules to form a gas, but the pressure squeezes the molecules back into a fluid. Although this fluid is not a liquid in the sense that we think of liquids, it is, in fact, a supercritical fluid. These supercritical fluids have a variety of very interesting properties in their own right, and we are starting to exploit this unique medium to make new materials that cannot be made any other way.” Korgel said that at the nanoscale, silicon behaves differently than usual. For example, only at the nanoscale does silicon emit light. The researchers want to control the size of the quantum wire to engineer materials with specific properties. Changing the supercritical fluid’s pressure affects how the layers of Si in the nanowires are arranged, dramatically changing their optical properties. The researchers want to explore this behavior in order to channel electrons in one direction.
Nanoclusters of Metallic Gold Display Optical Chiral Properties Robert L. Whetten’s research group at the Georgia Institute of Technology has presented experimental evidence that nanoclusters of metallic gold—assemblies containing between 20 and 40 gold atoms encapsulated by a common biomolecule—can display distinctly chiral properties. The chiral nature of the clusters, which means they exist in distinct right-handed and left-handed variations, affects the way in which they absorb polarized lig
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