Today’s designers are working toward production of components measured in nanometers, units approximately one four-thousandth the width of a human hair. "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," he explained.
Korgel and Johnston grew the minute and colorful spheres by a relatively simple, inexpensive process known as arrested precipitation. In a highly pressurized titanium chamber, they first heat a mixture of chain hydrocarbon "ligand" (octanol) and organic solvent (hexane), to a temperature of 500 degrees. Next, they add pure silicon reagent, causing it to degrade to silicon atoms. Ordinarily, the same atoms would soon recombine to form large crystals. But the octanol chains bind to the silicon surfaces inhibiting crystal growth, Korgel said.
"You end up with these sort of fuzzy particles of silicon that don’t stick to each other," he said. "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."
Once the chemical reaction is complete, the nanocrystals are harvested by evaporating the solvent, and can be assembled into devices. Typically, the nanocrystals contain between 100 and 2,000 atoms.
While other researchers in the United States and abroad have produced their own silicon emitters using different techniques, none have achieved Korgel and Johnston’s combination of high efficiency, emission of light in the visible spectrum and the ability to "tune" crystals to produce different colors. Korgel said the new materials "test our fundamental understanding of quantum mechanics. You can use them to do experiments and answer questions like: How do the properties of silicon change as it grows from an atom to a bulk solid?"
The work was funded in part by the Welch Foundation, the Petroleum Research Fund, and through Korgel’s National Science Foundation Faculty Early Career Development Award and a DuPont Young Professor Grant.
For more information contact Dr. Korgel at (512) 471-5633 or Becky Rische at (512) 471-7272. For images, see <www.utexas.edu/admin/opa/news/01newsreleases/nr_200104/korgel2.html>.