Greener semiconductor crystals

Dimethylcadmium is a toxic reagent used for forming cadmium chalcogenides nanocrystals that are found in semiconductors, energy storage applications, optoelectronics, and medical tools. The substance is unstable at room temperature and even explosive at higher temperatures, so it's no wonder that researchers are looking for an alternative. Professor Xiaoganag Peng and others from the University of Arkansas are studying the growth mechanism of nanocrystals. Peng says that replacing dimethylcadmium with cadmium oxide is not only safer, it's less expensive too. "The existing scheme using dimethylcadmium as the precursor was invented about ten years ago and does generate high-quality cadmium selenide nanocrystals," says Peng. "Although the method has some serious limitations, most people are pretty much satisfied with the quality," he says. Peng also says that the situation has changed in recent years for several reasons. "One, nanomaterials and nanotechnologies have become the center stage of the R&D programs in many countries. Two, semiconductor nanocrystals are being developed for industrial products, namely bio-medical labeling reagents. Most groups that want to start the research cannot afford the existing dimethylcadmium method," he says. In addition, the existing method is not suitable for industrial production, he points out. "We believe that the solution must come from an understanding of the growth mechanisms of the nanocrystals and the role of dimethylcadmium in the existing method," he explains. The cadmium oxide that Peng is using as a replacement to dimethylcadmium is less toxic. He believes that, starting with cadmium oxide, researchers at the University of Arkansas can make uniformly sized nanocrystals from several different substances, which is another advantage over dimethylcadmium. The properties of nanocrystals vary greatly depending upon their size. The crystals are suitable for use in solar cells, biomedical labels, and in light-emitting diodes used in computer displays. "We are interested in commercializing the invention," he says. For more information, contact Peng at the University of Arkansas, Department of Chemistry and Biochemistry, Fayetteville, AR 72701; Tel: (501) 575-4612; FAX: (501) 575 4049; e-mail [email protected].