Self-assembling could lead to improved optical materials

Washington, April 23 : Chemical engineers have developed a "self-assembling" method that could lead to an inexpensive way of making diamond-like crystals to improve optical communications and other technologies.

The method, developed at Purdue University, works by positioning tiny particles onto a silicon template containing precisely spaced holes that are about one-hundredth the width of a human hair.

The template is immersed in water on top of which particles are floating, and the particles automatically fill in the holes as the template is lifted.

The researchers have used the technique to create a "nearly perfect two-dimensional colloidal crystal," or a precisely ordered layer of particles.

"This is a critical step toward growing three-dimensional crystals for use in optical technologies," said You-Yeon Won, an assistant professor of chemical engineering.

"Making the first layer is very difficult, so we have taken an important step in the right direction," he said. "Creating three-dimensional structures poses a big challenge, but I think it's feasible," he added.

The single-layer structures might be used to form "micro lenses" to improve the performance of optical equipment, such as cameras and scientific instruments, and to control the color and other optical properties of materials for consumer products.

More importantly, the technique represents one of several possible approaches to create "omni-directional photonic band gap materials."

Unlike conventional mirrored materials, which reflect light hitting the mirror at certain angles, the omni-directional materials would be "perfect mirrors," reflecting certain wavelengths of light coming from all directions.

The materials would dramatically improve the performance of optical fibers, which contain a mirrored coating to keep light from escaping.

Omni-directional coatings would increase how much light is transmitted by fiber-optics and could possibly be used in future sensor technology and "optical computers" and circuits that use light instead of electronic signals to process information.

It might be even possible to use Won's method to create special crystals with particles arranged in the same pattern as carbon atoms in diamonds.

"There is no conventional technology that allows you to easily fabricate the diamond-crystal structure, so our method could open the door to doing so," said Won.

Self-assembly is potentially promising for future manufacturing because devices could be made less expensively than using conventional processes, which require complex etching and other techniques common in the semiconductor industry.

"We envision that this self-assembly method will open a new possibility for mass fabricating complicated 3-D colloid crystal structures for various applications," said Won.

ANI