Metallic materials made to order

A new process for creating specifically patterned microstructures could lead to new catalysts and optoelectronic devices.

To make the materials, Rolf Hempelmann of Saarland University in Saarbrücken, Germany, and his colleagues prepared tiny latex spheres made of the polymer polybutylacrylate, each with a diameter of about 200 nanometers and a negatively charged surface.

When the scientists placed enough of the mutually repelling spheres in water, they settled into a uniform, three-dimensional lattice. This pattern was easily disrupted, so the team added the chemical acrylamide and applied ultraviolet light. This turned the liquid into a gel, locking the lattice in place.

The researchers then used the lattice as a template for organizing metal atoms into a regular pattern. They achieved this by putting their lattice-containing gel on an electrode, immersing it in a silver nitrate solution, and then applying current. Silver filled the vacancies between the latex spheres.

The researchers describe the method in the Jan. 4 issue of Angewandte Chemie International Edition.

Hempelmann and his colleagues are now exploring applications. In one effort, they’re trying to fill the vacancies with semiconducting materials instead of silver. Because the distance between the spheres is on the order of the wavelengths of visible light, Hempelmann says, the resulting structures could behave like photonic crystals, which can steer light–even around corners.

The material might also serve as a catalyst if the latex spheres were burned away, leaving behind a metallic structure with a high surface area on which chemical reactions could occur, says Hempelmann.