UNIVERSITY OF ARKANSAS RESEARCHERS CREATE GREENER, CHEAPER SEMICONDUCTOR NANOCRYSTALS

Researchers hope to develop these nanocrystals into biological labeling reagents much like those used for medical applications. The simpler, cheaper synthesis developed at the U of A will go a long way towards helping scientists achieve that goal.

Xiaogang Peng, assistant professor of chemistry and biochemistry, and research associate Z. Adam Peng, reported their findings in the Journal of the American Chemical Society.

"We can use common, safe reagents to make these nanocrystals," Peng said.

For the past ten years, scientists have formed cadmium chalcogenides nanocrystals using the hazardous material dimethylcadmium, a toxic reagent that is costly, unstable at room temperature and explosive at higher temperatures. Peng decided to seek a greener way to approach the synthesis by studying the growth mechanism of the nanocrystals. When his research group looked at the process used to make these nanocrystals, they realized that dimethylcadmium could be replaced.

Peng replaced the dimethlylcadmium with a less expensive and more stable reagent, cadmium oxide. This reagent is easy to acquire and store and is much less toxic. Using this compound leads to a more straightforward, "one pot" synthesis that was previously not possible, Peng said.

The researchers discovered that starting with cadmium oxide, they could make uniformly sized nanocrystals using several different substances -- another advantage over the dimethylcadmium method, which produced uniform crystals of only one kind.

Nanocrystals vary greatly in their properties depending upon their size. The crystals have different optical properties, some of which can be used in solar cells and in light-emitting diodes used in computer displays. Nanocrystals may also be used as biomedical labels to detect disease.

"They are better than conventional labels in many ways," Peng said.

Because of the expense and danger of using dimethylcadmium, only a few groups have actually attempted cadmium nanocrystal synthesis. Peng expects that to change.

"This new method is very affordable. Many groups will now jump into this field, and many applications will come out," he said.

Using this new method, Peng's group has synthesized nanocrystals in size ranges four times greater than before, and is using different solvent systems and precursors to create nanocrystals with different properties.