Scientists have created a sparkling form of carbon that can scatter light like opal. The relatively simple technique for making the carbon, described in tomorrow's Science , may provide an easier way to make structures that can process light signals. Scientists hope that carbon may make a more efficient band-gap material--a material that excludes light of certain wavelengths and is therefore the photonic counterpart of a semiconductor--in future optoelectronics applications.
To create a new carbon structure with this ability, an international team tried mimicking opal, which consists of tightly packed silica spheres. Because these spheres are the size of light waves, they diffract light in rainbow colors.
As a template, the team used artificial opals made of silica spheres ranging in diameter from 150 to 300 nanometers. They infiltrated the faux opal with a phenolic resin that filled the empty space between the spheres. Then they dissolved the silica spheres with hydrofluoric acid, leaving just the newly built phenol resin walls, which were transformed into a pure carbon structure by heating up to 1000oC. "We were very surprised that this process that we developed actually works to make beautifully opalescent materials," says team leader Ray Baughman of AlliedSignal Inc. in Morristown, New Jersey. Because the basic elements of this spongelike structure are cubic, they christened the material "cubic-graphite."
The scientists used "a very clever method" to create the new material, says Eli Yablonovitch of the University of California, Los Angeles. The method will really be fruitful if it can be used to make photonic structures out of other materials, such as metals, oxides, and ceramics that may have even better properties, such as not conducting electricity or absorbing light. The obtained structure is "a very promising system.... It is likely to be very successful" for applications in optoelectronics.