Using light to focus chilled chromium atoms.To fabricate microscopic circuits on silicon chips, semiconductor manufacturers typically shine light through a mask onto a photosensitive A material that changes when exposed to light. See photoelectric. surface to create the necessary patterns. But the width of the mask's lines limits the fineness of features that can be etched etch v. etched, etch·ing, etch·es v.tr. 1. a. To cut into the surface of (glass, for example) by the action of acid. b. on a chip. To create much liner features, some researchers have been exploring the possibility of using light itself as a lens to guide atoms to particular positions on a surface. Last year, Gregory L. Timp of AT&T Bell Laboratories in Holmdel, N.J., and his collaborators demonstrated the effect with sodium atoms (SN: 3/14/92, p. 166). Now, Robert J. Celotta and his colleagues at the National Institute of Standards and Technology National Institute of Standards and Technology, governmental agency within the U.S. Dept. of Commerce with the mission of "working with industry to develop and apply technology, measurements, and standards" in the national interest. (NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. ) in Gaithersburg, Md., have shown that light can also be used to position chromium atoms. "The work that Celotta has done is really a big step forward," Timp says. "He has moved atomic physics atomic physics Scientific study of the structure of the atom, its energy states, and its interaction with other particles and fields. The modern understanding of the atom is that it consists of a heavy nucleus of positive charge surrounded by a cloud of light, negatively to the center of the periodic table. He has proved... that you can, in principle, use any element that you want." In separate reports, Timp and Celotta described their findings at last week's American Physical Society The American Physical Society was founded in 1899 and is the world's second largest organization of physicists. The Society publishes more than a dozen science journals, including the world renowned Physical Review and Physical Review Letters, and organizes more than twenty science meeting, held in Seattle. To deposit parallel lines of sodium atoms on a silicon surface, Timp and his co-workers first cool a beam of sodium atoms to temperatures of less than 1 millikelvin. The cooled beam then passes through a standing wave of laser light, which nudges the atoms into certain paths in the same way that a pattern of ripples on the surface of a pond focuses sunlight into a comparable pattern of bright and dark areas on the pond's bottom. The researchers have obtained indirect evidence that their technique deposits evenly spaced lines of sodium atoms about 300 nanometers apart and probably less than 100 nanometers wide. But because sodium reacts readily with stray atoms and molecules still roaming the ultrahigh ul·tra·high adj. Exceedingly high: an ultrahigh vacuum. vacuum in which the experiment is done, the pattern deteriorates too quickly to be imaged. Chromium reacts far less readily than sodium, but it takes a much higher temperature to create a beam of chromium atoms. The NIST team had to go to great lengths to produce the beam and then cool the atoms to temperatures low enough for a standing light wave to focus the beam into narrow lines. "We were pleased just before the meeting ... to come up with images of the chromium lines:' Celotta says. "They look to be quite high resolution." |
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