Chemists at the National Institute of Standards and Technology (NIST) have been the first to measure significant amounts of copper incorporated into zinc oxide (ZnO) nanowires during fabrication. The issue is important because copper plays a significantbut not well-understoodrole in important optical and electrical properties of the nanowires. Previous experiments found only trace amounts of copper.
Although zinc oxide is best known as a strong sunblock, cold remedy, itch reliever and paint pigment, nanotech engineers like it for its photoluminescence (the ability to emit light after absorbing electromagnetic radiation), field emission (the basis for advanced, high-definition flat-panel displays) and piezoelectric properties (stressing or changing shape when electricity is applied and producing electricity when stressed). ZnO nanomaterials may one day be used to improve solar cells, lasers, sensors, ultraviolet light sources, field emission sources and piezoelectric devices.
Copper enters the ZnO nanowires during fabrication. The nanowiresabout 50 to 150 nanometers wide and up to 40 micrometers longare grown on a copper substrate using a chemical vapor deposition process. The copper substrate forms droplets that absorb the zinc and oxygen vapors and deposits the ZnO on the substrate. As the nanowire grows, the zinc pushes the droplets up from the surface, but some copper remains inside the nanowires crystal lattice.
In a new paper,* NIST chemists report using a variety of measurement techniques to learn that the ZnO wires contain a surprising amount of copperbetween 5 and 15 percent. High-resolution imaging studies of ZnO nanowires reveal that the copper manages to fit into zinc oxides regular crystalline structure without disrupting it. It is in there somewhere, explains chemist Susie Eustis. Because the copper can be easily detected when you know what to look for, she says, researchers plan to use it to better unde
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National Institute of Standards and Technology (NIST)