'Rainbow metal,' similar to opal, suggests light-steering computer parts and catalysts

October 06, 1999

Porous, rainbow-colored metal--inspired by opal--may suggest new materials to steer light inside superfast computers, or to more efficiently catalyze chemical reactions, University of Delaware researchers report Oct. 7 in Nature.

Because it's riddled with regularly spaced holes only slightly wider than the wavelength of light, the UD material acts like a prism, diffracting a spectrum of colors--from gold and blue to red, green and purple.

"It reflects different wavelengths of light, just like opal, only it's much sturdier," explains Research Assistant Prof. Orlin D. Velev, lead author of the Nature paper, with coauthors including graduate student Peter M. Tessier and Prof. Abraham M. Lenhoff.

In fact, tiny holes in the new material are 20,000 times smaller than the pores in an existing metal mesh that can be used to direct radar waves, reports coauthor Eric W. Kaler, the University's Elizabeth Inez Kelley Professor of Chemical Engineering and chairperson of his department.

Consequently, "It should help guide the much shorter light waves, perhaps in photooptic computer components," says Kaler. Such devices will be crucial in next-generation computers, he says, because "fiber optics can't turn sharp corners, and you don't have much room to maneuver in nanoscale devices."

A sister version of the rainbow metal features light-sized pores--20 times smaller than the smallest red blood cell--as well as even smaller pores, all of which are aligned in tightly packed, uniformly spaced rows. This versatile, "meso/macroporous" form of the material may also be photoactive, and could prove useful as a catalyst for, say, cracking hydrocarbon to produce gasoline, or as a filter for rapidly separating molecules of different sizes.

Dots of gold

Creating the material is a low-energy process involving latex beads, much smaller microspheres of gold and "very simple chemistry," Kaler says. The size of the resulting pores can be "tuned" or changed simply by selecting different sizes of latex and gold beads, he adds.

First, the UD researchers pour a watery solution containing the latex particles onto a polycarbonate membrane. Water slips right through the membrane's 50-nanometer pores. But, the 300-nanometer latex beads are trapped on top.

"It's a bit like dumping a bunch of marbles into a bathtub and then pulling the drain plug," Kaler explains. "After the water escapes, you're left with a densely packed layer of these spheres."

After many hundreds of layers of latex are deposited, bits of gold just one-tenth the size of the polymer beads can be slowly filtered onto them, to fill the gaps between neighboring spheres.

As a final step, the researchers either "bake" or "pickle" their sample to remove the latex.

A multicolored metal with pores about 600 nanometers wide--close to the wavelength of light--is created by heating the latex and fusing the gold for 30 minutes at 300 degrees Celsius (572 degrees Fahrenheit). For a sample with both large and small pores, the researchers instead chemically oxidize and dissolve the latex.

"Our system is a very powerful, versatile way to make porous nanostructures in a variety of materials," Kaler says.

In the past, Velev notes, researchers have used ion beams to drill individual holes into metals, one pore at a time. "Obviously," he says, "that's very time-consuming and expensive. We think we've found another way."

And, UD's material manufacturing technique could be applied to any type of material, Velev says, theoretically allowing polymers and carbon to "shine," or reflect light.

The UD research team, working from the University's Center for Molecular and Engineering Thermodynamics, has been at the forefront of the rapidly accelerating effort to develop porous nanostructures by using arrays of particles as templates, field launched by the same group just two years ago. Their earlier work with porous silica--supported by collaborator Raul Lobo, an Assistant Prof. with the UD Center for Catalytic Science and Technology--appeared in the Oct. 2, 1997 issue of Nature (Vol. 389, pp. 447-448). Similar efforts to develop porous metals are under way by teams at Rice University and the University of Minnesota.
-end-
Contacts:

John Brennan, 302-831-2072, jbrennan@udel.edu or
Laura Overturf, 302-831-1418, overturf@udel.edu

University of Delaware

Related Gold Articles from Brightsurf:

The "gold" in breast milk
Breast milk strengthens a child's immune system, supporting the intestinal flora.

From nanocellulose to gold
When nanocellulose is combined with various types of metal nanoparticles, materials are formed with many new and exciting properties.

Research brief: 'Fool's gold' may be valuable after all
In a breakthrough new study, scientists and engineers at the University of Minnesota have electrically transformed the abundant and low-cost non-magnetic material iron sulfide, also known as 'fool's gold' or pyrite, into a magnetic material.

Water molecules are gold for nanocatalysis
Nanocatalysts made of gold nanoparticles dispersed on metal oxides are very promising for the industrial, selective oxidation of compounds, including alcohols, into valuable chemicals.

As electronics shrink to nanoscale, will they still be good as gold?
As circuit interconnects shrink to nanoscale, will the pressure caused by thermal expansion when current flows through wires cause gold to behave more like a liquid than a solid -- making nanoelectronics unreliable?

Peppered with gold
Terahertz waves are becoming more important in science and technology.

No need to dig too deep to find gold!
Why are some porphyry deposits rich in copper while others contain gold?

An 18-carat gold nugget made of plastic
ETH researchers have created an incredibly lightweight 18-carat gold, using a matrix of plastic in place of metallic alloy elements.

What happens to gold nanoparticles in cells?
Gold nanoparticles, which are supposed to be stable in biological environments, can be degraded inside cells.

Turning 'junk' DNA into gold
Mining the rich uncharted territory of the genome or genetic material of a cancer cell has yielded gold for Princess Margaret scientists: new protein targets for drug development against prostate cancer.

Read More: Gold News and Gold Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.