University of California, Davis, researchers have synthesized ultra-fine, light-emitting silicon clusters in bulk glass for the first time, reported Subhash H. Risbud in a paper at the spring meeting of the Materials Research Society (MRS) in San Franscisco today. Theoretically, ultra-fine silicon structures (smaller than one-millionth of a millimeter) might someday have applications in light-emitting devices, optical switches and other components for telecommunications and computers. The phenomenon of light-emitting porous silicon was first reported 18 months ago as an effect possibly arising from silicon structures that had been etched down to a thin skeleton of quantum wires. However, it is still not clear whether the luminescence came from a "quantum confinement" effect in the silicon or from surface chemicals formed during the etching process. Quantum confinement is an effect unique to ultra-fine semiconductors when they become so small they lose their bulk properties, which leads to changes in the wavelength of light they absorb. "Our samples are likely to be closer to showing true, three-dimensional quantum dot effects," said Risbud, a professor of materials science and engineering at UC Davis. When excited by light from a laser during experiments at UC Davis (which were substantiated at UC Berkeley), the extremely small silicon dots (about 1.5 nanometers) emitted a greenish-yellow glow that slowly faded after the light source was turned off, said Risbud, director of the Materials Research Center at UC Davis. Risbud and graduate student Li-chi Liu made their dots by mixing pure silicon and glass powders together and cooking the concoction in ceramic crucibles in an oven heated to 1,400 degrees Centigrade. The dots can be tuned to different wavelengths by adjusting the size of the silicon particles; the longer the samples cook, the smaller the silicon dots become, until they achieve quantum confinement size. -more- 2-2-2 Luminescent Silicon "I believe this new process for making quantum dots is especially versatile for any semiconductor by the appropriate choice of glass and heat treatment," Risbud said. Risbud will present his paper at the symposium titled "Chemical Processes in Inorganic Materials: Metal and Semiconductor Clusters," which begins at 2 p.m. in the San Francisco Marriott Hotel.