New method speeds material discovery.

An artist searching for the perfect tint blends daubs of color together on a palette, varying the mix to get the desired hue. Now, scientists are adopting the same technique in their search for new materials, using palettes that are disks of silicon only 3 inches in diameter.

By mixing together tiny amounts of chemical ingredients in varying proportions on these silicon wafers, researchers at Symyx Technologies in Santa Clara, Calif., can synthesize and screen up to 25,000 different compounds at one time. "It makes the discovery process much shorter and cheaper," says Xin Di Wu, director of electronics materials at Symyx. Pharmaceutical companies already use a similar approach, known as combinatorial chemistry, to find candidate drugs.

The group chose to demonstrate the technique by creating phosphors, glowing substances used in color display screens. First, the team deposited one phosphor component on the silicon in columns, then crisscrossed it with rows of another component. The group layered on additional ingredients in thinner stripes, masking areas of the chip to control the composition of the materials. The resulting grid contained squares of many different mixes, which could then be assessed for the color and intensity of their emitted light.

"It's easy to demonstrate whether phosphors are working," says Wu. "When you shine [ultraviolet] light on them, they give visible emissions." He and his colleagues describe their method in the Oct. 30 Nature.

Their test turned up one promising substance that glowed red. When the scientists mixed up this material as a bulk powder, it proved better than the standard commercial red phosphor, which gives off a more orange-colored light. Testing the phosphor in bulk form was important, he adds, because the powder would ultimately be used to coat the back of a computer screen. Materials can exhibit very different properties as thin films on a chip.

In 1995, a group including Symyx cofounder Peter G. Schultz of Lawrence Berkeley (Calif.) Laboratory applied the combinatorial method on a smaller scale to superconductors. Symyx scientists plan to use the technique to look for new compounds with catalytic, magnetic, or thermoelectric properties.