HOUSTON, Dec. 2 (Xinhua) -- Humble aluminum's plasmonic properties may make it far more valuable than gold and silver for certain applications, reckons a new research done by scientists with Rice University of the United States.
Because aluminum, as nanoparticles or nanostructures, displays optical resonances across a much broader region of the spectrum than either gold or silver, it may be a good candidate for harvesting solar energy and for other large-area optical devices and materials that would be too expensive to produce with coinage metals, said the university based in Houston, a city in the U.S. state of Texas, in a press release to announce the latest research result Monday.
Until recently, aluminum had not yet been seen as useful for plasmonic applications for several reasons: It naturally oxidizes, and some studies have shown dramatic discrepancies between the resonant color of fabricated nanostructured aluminum and theoretical predictions.
The combined work of two Rice labs has addressed each of those hurdles in their new publications.
The research by Rice scientists Naomi Halas and Peter Nordlander demonstrates that the color of aluminum nanoparticles depends not only on the size and shape, but also critically on the oxide content. They have shown that the color of an aluminum nanoparticle provides direct evidence of the amount of oxidation of the aluminum material itself.
The labs also characterized the weakening effect of naturally occurring but self-passivating oxidation on aluminum surfaces. " For iron, rust goes right through," Nordlander said. "But for pure aluminum, the oxide is so hard and impermeable that once you form a three-nanometer sheet of oxide, the process stops." To prove it, the researchers left their disks exposed to the open air for three weeks before testing again and found their response unchanged.
"The reason we use gold and silver in nanoscience is that they don't oxidize. But finally, with aluminum, nature has given us something we can exploit," Nordlander said. "In addition to being a cheap and tunable material, aluminum exhibits quantum mechanical effects at larger, more accessible and more precise ranges than gold or silver."
The new findings appeared in the American Chemical Society (ACS) journal ACS Nano.