Science News Online Week of July 30, 2005; Vol. 168, No. 5 In search of the imperfect nanocrystal Peter Weiss The unsung heroes of the microelectronics revolution are impurities intentionally added to semiconducting materials. A sprinkling of such atoms as boron or phosphorus, for example, is pivotal to much of the electronic and optical performance that makes microchips useful. Nevertheless, attempts to include such impurities in tiny clumps of atoms known as semiconductor nanocrystals have often failed. A study in the July 7 Nature offers an explanation for this roadblock---and a way around it. Experiments on the nanocrystals, also called quantum dots, find them promising as fluorescent tracers for monitoring biomolecules (SN: 8/7/04, p. 94: Available to subscribers at http://www.sciencenews.org/articles/20040807/note15.asp) and as additives to such technologies as light-emitting diodes (SN: 7/16/05, p. 43: Available to subscribers at http://www.sciencenews.org/articles/20050716/bob10.asp). Still more could be done with impurity-containing nanocrystals, but researchers have struggled to achieve even small concentrations of impurities. Many researchers explained this difficulty by hypothesizing that the minuscule clumps are self-purifying. A different picture emerges from calculations by physicist Steven C. Erwin and his colleagues at the Naval Research Laboratory in Washington, D.C., and from experiments by a materials science group led by David J. Norris of the University of Minnesota, Twin Cities. The new findings indicate that when certain impurities integrate into a growing nanocrystal, some of its facets have atomic arrangements that strongly adhere to those foreign atoms. The scientists predicted and confirmed that zinc-selenide nanocrystals with certain shapes were particularly prone to incorporate manganese atoms. The researchers then went a step farther and induced nanocrystals of cadmium-selenide, which are known to shun manganese atoms, to accept those impurities. The scientists grew the nanocrystals on a template that formed manganese-accepting facets that are ordinarily absent on cadmium-selenide crystals. If you have a comment on this article that you would like considered for publication in Science News, send it to editors@sciencenews.org. Please include your name and location. References: Erwin, S.C.... and D.J. Norris. 2005. Doping semiconductor nanocrystals. Nature 436(July 7):91-94. Abstract available at http://dx.doi.org/10.1038/nature03832. Galli, G. 2005. Solid-state physics: Doping the undopable. Nature 436(July 7):32-33. Further Readings: Goho, A. 2005. Bright future. Science News 168(July 16):43-44. Available to subscribers at http://www.sciencenews.org/articles/20050716/bob10.asp. ______. 2005. Infrared vision: New material may enhance plastic solar cells. Science News 167(Jan. 22):53. Available to subscribers at http://www.sciencenews.org/articles/20050122/fob5.asp. ______. 2004. Quantum dots light up cancer cells in mice. Science News 166(Aug. 7):94. Available to subscribers at http://www.sciencenews.org/articles/20040807/note15.asp. Gorman, J. 2003. Layered approach. Science News 164(Aug. 9):91-92. Available at http://www.sciencenews.org/articles/20030809/bob9.asp. ______. 2003. Nanolights! Camera! Action! Science News 163(Feb. 15):107-109. Available at http://www.sciencenews.org/articles/20030215/bob10.asp. ______. 2002. Taming high-tech particles. Science News 161(March 30):200-201. Available at http://www.sciencenews.org/articles/20020330/bob8.asp. Klarreich, E. 2004. Quantum sentinels. Science News 165(March 6):157. Available to subscribers at http://www.sciencenews.org/articles/20040306/note13.asp. Weiss, P. 2004. Photon double whammy: Careening electrons may rev up solar cells. Science News 165(April 24):259. Available at http://www.sciencenews.org/articles/20040424/fob2.asp. ______. 2001. From silicon seeds, laser might sprout. Science News 159(Jan. 6):14. Available to subscribers at http://www.sciencenews.org/articles/20010106/note11.asp. Sources: Steven C. Erwin Naval Research Laboratory Washington, DC 20375 Giulia Galli Lawrence Livermore National Laboratory P.O. Box 808 Livermore, CA 94551 David J. Norris Department of Chemical Engineering and Materials Science University of Minnesota Minneapolis, MN 55455 http://www.sciencenews.org/articles/20050730/note15.asp From Science News, Vol. 168, No. 5, July 30, 2005, p. 77. Copyright (c) 2005 Science Service. All rights reserved. --------------------------------- Interested in new developments in science and technology? Consider subscribing to Science News. Visit Science News Online at http://www.sciencenews.org/ for access to additional news articles and subscription information.