Researchers create gold aluminum, black platinum, blue silver

Researchers create gold aluminum, black platinum, blue silver
Gold platinum, blue titanium, and gold aluminum. Credit: Richard Baker, University of Rochester

Using a tabletop laser, a University of Rochester optical scientist has turned pure aluminum, gold. And blue. And gray. And many other colors. And it works for every metal tested, including platinum, titanium, tungsten, silver, and gold.

Chunlei Guo, the researcher who a year ago used intense laser light to alter the properties of a variety of metals to render them pitch black, has pushed the same process further in a paper in today’s Applied Physics Letters. He now believes it’s possible to alter the properties of any metal to turn it any color—even multi-colored iridescence like a butterfly’s wings.

Since the process changes the intrinsic surface properties of the metal itself and is not just a coating, the color won’t fade or peel, says Guo, associate professor of optics at the Institute of Optics at the University of Rochester. He suggests the possibilities are endless—a cycle factory using a single laser to produce bicycles of different colors; etching a full-color photograph of a family into the refrigerator door; or proposing with a gold engagement ring that matches your fiancée’s blue eyes.

“Since the discovery of the black metal we’ve been determined to get full control on getting metals to reflect only a certain color and absorb the rest, and now we finally can make a metal reflect almost any color we wish,” says Guo. “When we first found the process that produced a gold color, we couldn’t believe it. We worked in the lab until midnight trying to figure out what other colors we could make.”

Guo and his assistant, Anatoliy Vorobeyv, use an incredibly brief but incredibly intense laser burst that changes the surface of a metal, forming nanoscale and microscale structures that selectively reflect a certain color to give the appearance of a specific color or combinations of colors.

The metal-coloring research follows up on Guo’s breakthrough “black metal” discovery in late 2006, when his research team was able to create nanostructures on metal surfaces that absorbed virtually all light, making something as simple as regular aluminum into one of the darkest materials ever created.

Guo’s black metal, with its very high absorption properties, is ideal for any application where capturing light is desirable. The potential applications range from making better solar energy collectors, to more advanced stealth technology, he says.

The ultra-brief/ultra-intense light Guo uses is produced by a femtosecond laser, which produces pulses lasting only a few quadrillionths of a second. A femtosecond is to a second what a second is to about 32 million years. During its brief burst, Guo’s laser unleashes as much power as the entire electric grid of North America does, all focused onto a spot the size of a needlepoint.

The intense blast forces the surface of the metal to form nanostructures—pits, globules, and strands that response incoming light in different ways depending on the way the laser pulse sculpted the structures. Since the structures are smaller than the wavelength of light, the way they reflect light is highly dependent upon their specific size and shape, says Guo. Varying the laser intensity, pulse length, and number of pulses, allows Guo to control the configuration of the nanostructures, and hence control what color the metal reflects.

Guo and Vorobyev also achieve the iridescent coloring by creating microscale lines covered with nanostructures. The lines, arranged in regular rows, cause reflected light of different wavelengths to interfere differently in different directions. The result is a piece of metal that can appear solid purple from one direction, and gray from another, or multiple colors all at once.

To alter an area of metal the size of a dime currently takes 30 minutes or more, but the researchers are working on refining the technique. Fortunately, despite the incredible intensity involved, the femtosecond laser can be powered by a simple wall outlet, meaning that when the process is refined, implementing it should be relatively simple.

The new process has worked on every metal Guo has tried, and the results are so consistent that he believes it will work for every metal known. His team is currently working to find the right tuning to create the rest of the rainbow for the solid-colored metal, including red and green.

Source: University of Rochester

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User comments

Feb 01, 2008
How about I bring out my DeLorean and have it colored?

Feb 01, 2008
Interesting question zevkirsh. I think it would just appear "black" however. See the article about the blackest material made to date.

Feb 01, 2008
Yeah, I'd be interested in hearing if this can be expanded to other wavelengths. I doubt it would work in a wide range of wavelengths simultaneously though.

Feb 01, 2008
Possible applications: 1) solar heating panels need to absorb light... surfaces often painted black, but would probably work better if etched this way instead of painted; 2) also, radiative cooling surfaces should work best if blacken this way; 3) similarly, if can make "white", surfaces should be cooler... i.e. cool roofing material, etc.

Feb 03, 2008
what is the durability of these surfaces? Could they be used to any advantage to replace ruled gratings? It seems that touching them would destroy the effect...but it's great work nevertheless

Feb 03, 2008
its proabably just cosmetic and aesthetic aplications, which is also cool. I've been wating for them to do something like this for a long time.

I was wondering where the wierd rainbow pattern come from when you weld to pieces of metal and can this be controlled too, it looks really cool.

Feb 03, 2008
deatopmg, I guess most of them won't be so easily destroyed by touching, since they are of metal. One need to at least scratch it. Maybe gold would be too soft but aluminum should be able to withstand touching.

Feb 03, 2008
I can't wait to see a pink jon boat...

Apr 21, 2008
Once all the colours are available it should be possible to burn a photographic image into the metal surface. Those rainbow colours after welding will be due to varying thickness of oxide layers. already with oxides it is possible to get some nice colour effects.

Dec 22, 2008
i was wondering if this technology can be applied to wedding rings to make a platinum band look like the blue metal in this link; http://img.photob...617.jpg.

Dec 22, 2008 /albums /v349 /Baranor /Guildwars /gw617.jpg

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