Highly strung nanocrystal comes down to earth

A University of Arkansas research team has created semiconductor nanocrystals made from materials that are said to be inexpensive and non-volatile. Such nanocrystals could be used in semiconductor, energy storage, optoelectonics and medical industries.

Researchers hope to develop these nanocrystals into biological labelling reagents much like those used for medical applications.

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.

For the past ten years, scientists have formed cadmium chalcogenides nanocrystals using the hazardous material dimethylcadmium, a toxic reagent that is said to be costly, unstable at room temperature and explosive at higher temperatures.

The Arkansas research team decided to seek a greener way to approach the synthesis by studying the growth mechanism of the nanocrystals. When group looked at the process used to make these nanocrystals, they realised that dimethylcadmium could be replaced.

Peng replaced the dimethlylcadmium with a less expensive and more stable reagent, cadmium oxide, which is easy to acquire, store and is much less toxic.

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,’ said Peng.

Because of the expense and danger of using dimethylcadmium, only a few groups have actually attempted cadmium nanocrystal synthesis, but 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 synthesised nanocrystals in size ranges four times greater than before, and is using different solvent systems and precursors to create nanocrystals with different properties.