Stormy weather at crystal surfaces.Atoms on the surfaces of microscopic gold crystals appear to be in constant motion. Not only do they hop from site to site, but they also continually shuttle between a crystal's orderly columns and clouds of atoms hovering near certain surfaces. These recent observations result from the combination of a high-resolution electron microscope electron microscope: see microscope. and a video-recording system that magnifies gold crystals about 20 million times and, on an atomic scale, tracks their growth as it happens. "The motion of atomic columns and the existence of atom clouds revealed here may have important consequences for crystal growth, surface science and catalysis catalysis Modification (usually acceleration) of a chemical reaction rate by addition of a catalyst, which combines with the reactants but is ultimately regenerated so that its amount remains unchanged and the chemical equilibrium of the conditions of the reaction is not studies," say David J. Smith David J. Smith is a Regents' Professor of physics at Arizona State University. He is an Australian experimental physicist and his research is focussed on using electron microscope to study microstructure of different materials. of arizona State University Arizona State University, at Tempe; coeducational; opened 1886 as a normal school, became 1925 Tempe State Teachers College, renamed 1945 Arizona State College at Tempe. Its present name was adopted in 1958. in Tempe and his colleagues at the University of Lund in sweden. Their report appears in the Sept. 5 NATURE. The researchers use a powerfule electron beam A stream of electrons, or electricity, that is directed towards a receiving object. See electron beam imaging and electron beam lithography. to bombard bom·bard tr.v. bom·bard·ed, bom·bard·ing, bom·bards 1. To attack with bombs, shells, or missiles. 2. To assail persistently, as with requests. See Synonyms at attack, barrage2. 3. 55-atom clusters of gold scattered across a carbon film. These tiny crystals turn out to be unstable, and some crystals begin to grow at the expense of others. A TV monitor allows the scientists to watch the rapid changes in crystal shape and orientation. It's like watching living atoms, says Smith. "You can sit and look at one small particle for 10 minutes," he says. "You may get 29 different shapes in 30 seconds, and then it will sit still for a while, and then it goes on. We also see different effects according to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. how big the particles are." In addition, the ever-changing cloud shapes seem to show the pathways that atoms follow out of or into the lattice columns. In some instances, parts of a cloud look like miniature tornadoes directed toward particular crystal columns. "It may well be that column hopping and changes of cloud shape are an indication of how atoms locate the most favorable lattice position during crystal growth," the researchers say. Using the same equipment, it should also be possible to monitor the way in which a variety of atoms interact with a metal surface. This an important question in the study of how catalysts work. Once concern about the research is that the motion observed may be due to the effect of the electron beam rather than a characteristic of crystal behavior. "We're on a fact-finding mission," says Smith. "How general is the phenomenon that we have observed?" So far, the researchers have seen similar although not identical behavior at platinum crystal surfaces. |
|
||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion