November 22, 2006, Rochester, NY--Scientists at the University of Rochester claim to have found a way to change the properties of almost any metal, to render it, literally, black. The process, using a femtosecond laser pulse, appears to hold the promise of making everything from fuel cells to a space telescope's detectors more efficient.
"We've been surprised by the number of possible applications for this," says Chunlei Guo, assistant professor of optics . "We wanted to see what would happen to a metal's properties under different laser conditions and we stumbled on this way to completely alter the reflective properties of metals."
Intense femtosecond laser stimulus causes the surface of the metal to form nanostructures -- pits, globules, and strands that dramatically increase the area of the surface and also capture radiation. Guo's research team has tested the absorption capabilities for the blackened metal and confirmed that it can absorb virtually all the light that fall on it, making it pitch black.
Other similar attempts have turned silicon black, but those use a gas to produce chemically etched microstructures. Regular silicon already absorbs most of the visible light that falls on it, so the etching technique only offers about a 30 percent improvement, whereas regular metals absorb only a few percent of visible light before Guo hits them with the laser.
The huge increase in light absorption enabled by Guo's femtosecond laser processing means nearly any metal becomes extremely useful anytime radiation gathering is needed. For instance, detectors of all kinds, from space probes to light meters, could capture far more data than an ordinary metal-based detector could.
And turning a metal black without paint, scoring, or burning could easily lead to everyday uses such as replacing black paint on automobile trim, or presenting your spouse with a jet-black engagement ring.
Guo is also quick to point out that the nanostructures' remarkable increase in a metal's surface area is a perfect way to catalyze chemical reactions. Along with one of his research group members, postdoctoral student Anatoliy Vorobyev, he hopes to learn how the metal can help derive more energy from fuel cell reactions.
The new process has worked on every metal Guo has tried, and since it's a property of the metal itself, there's no worry of the black wearing off, he says.
Currently, the process is slow. To alter a strip of metal the size of your little finger easily takes 30 minutes or more, but Guo is looking at how different burst lengths, different wavelengths, and different intensities affect metal's properties. For more information, contact the University of Rochester.