NANOSCIENCE – A new way to create large amounts of materials with artificial structures could open the door to new materials for imaging molecules, sensors, and making objects difficult to detect visually. Xiang Zhang, a member of UC Berkeley’s Kavli Energy NanoScience Institute, led the research. Zhang is interested in making metamaterials, which have structures that do not exist in nature. These materials are often asymmetrical, and that gives them unusual properties. The problem is that the rules of thermodynamics do not want us to make asymmetrical materials. In fact, most scientists believed the type of nanostructures that Zhang’s group created were impossible to assemble. Zhang’s goal was to create optical metamaterials made from gold nanorods in liquid. To achieve the right properties, Zhang needed to bond pairs of nanorods to one another along their length and slightly offset. Unfortunately, the reaction produces lots of different bonds. Some are just right. Others are offset too much or symmetrical. Zhang used a trick that only works on the nanoscale to overcome the problem. He used a laser to excite the plasmonic resonance of particles produced in the reaction that he did not want. (The correctly offset particles did not resonate.) This generated enough heat to break apart the pairs. These free nanorods then rebounded, forming a variety of bonds. He then repeated the laser process. With each repetition, the percentage of perfectly bonded nanorods rose. “This is a brand new self-assembly fabrication method that people can commonly employ: we use the material’s own properties to drive nanostructure formation in solution,” Zhang said. The technique could be used to make many other metamaterials, and virtually any self-assembled structure. The work appeared in Nature Nanotechnology. You can learn more at bit.ly/1w7SEYj.
Posted on: Thu, 13 Nov 2014 18:47:34 +0000
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