Printing scheme could yield 3-D photonic crystals

Photonic crystals are latticelike structures that can manipulate the flow of light. Materials scientists have now devised a way of making such crystals with complex three-dimensional structures that could serve as the basic elements of optical computers.

The new technique prints 3-D patterns on a surface layer by layer using a specially designed ink. “This allows us to directly write the structures we want,” says lead investigator Jennifer Lewis of the University of Illinois at Urbana-Champaign. She and her colleagues describe the process in an upcoming Advanced Materials.

The ink consists of an organic chemical containing titanium mixed with a polymer. A 1-micrometer wide nozzle dispenses filaments of ink as it travels over a silicon wafer. The ink dries rapidly, causing the filaments to solidify. Heating at 600° C burns away the polymer and organic material, leaving behind a structure composed almost entirely of polycrystalline titanium dioxide.

The research team used its new technique to make woodpile structures in which layers of 520-nanometer-wide rods are stacked on top of one another, with rods in each layer perpendicular to those immediately beneath. The researchers are also experimenting with transparent and electrically conducting inks that might be useful for printing components in displays and solar cells.