Researchers from the University of Texas at Austin report in today's Journal of the American Chemical Society that silicon, in the form of nanoscale crystals, can be forced to emit light¿a trick that could lead to cheap silicon lasers and flat-panel displays in the future. "Bulk silicon does not emit visible light, but our structures do," principal investigator Brian Korgel says. "Our crystals have the added advantage of being tunable, meaning that we can create a specific color of light by adjusting the crystal's size. Smaller crystals give off blue light, larger ones green or even red."
Korgel and his colleague Keith Johnston created the tiny spherical silicon crystals through a process called arrested precipitation. First they heated a mix containing an organic solvent (hexane) and a chain hydrocarbon ligand (octanol) to about 500 degrees Celsius in a highly pressurized titanium chamber. Then they added pure silicon, which degraded into individual atoms. The octanol chains bound to the silicon atoms, preventing them from recombining into ordinary large crystals. When the solvent evaporated, only the small silicon crystals¿structures called nanocrystals or quantum dots¿remained. "You end up with these sort of fuzzy particles of silicon that don't stick to each other," Korgel says. "What controls their size is how many ligands you have. If you have a lot, the crystals will stay small. If you don't have very many, they'll continue to grow into very large crystals."
The researchers have managed to make the nanocrystals emit blue and green light so far, and say they are close to coaxing red emissions from their fabrications as well. Whereas other researchers have produced silicon emitters in the past, none have created crystals that emit light in the visible spectrum or that can be tuned to emit different colors. Korgel is optimistic about future applications: "Say you want a smaller and smaller computer. The challenge of shrinking the computer comes down to the technology to shrink the materials. That's what we do."