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Number 366, April 9, 1998 by Phillip F. Schewe and Ben Stein
ANTI-HYDROGEN ATOMS AT FERMILAB. Producing elementary anti-particles such as antiprotons and positrons is relatively easy. Producing anti-atoms, which are composite things, is harder. Both CERN and Fermilab have made precious small amounts of anti- hydrogen atoms by shooting a gas through an antiproton beam. Physicists naturally want to make measurements, starting with the cross section (the likelihood) for making the anti-atoms in the first place. In this case the cross section (using a data sample of 70 anti-H's) is about 1 pico-barn (the barn is a unit equal to 10-24 cm2), about what theorists expected. Not much yet can be done to study individual anti-H atoms. In a proposed next-step experiment the anti-atoms (500-5000 will be needed) might be zapped with a laser as they escape. This would put the atoms into excited states. This would allow the first spectroscopic test of whether the rules of quantum mechanics apply equally to anti-atoms and conventional atoms. (G. Blanford et al., Physical Review Letters, 6 April 1998, contact David Christian at Fermilab, dcc@fnal.gov, 630-840-4001.)
THE SILICON-SILICON DIOXIDE INTERFACE in ultrasmall silicon-based transistors must be smooth on the atomic level or else their performance is degraded. If the boundary is too rough, electrons moving through the semiconducting silicon layer can scatter from the insulating SiO2 boundary, increasing electrical resistance to undesirable levels. Addressing this problem at the recent APS March Meeting in Los Angeles, Melissa Hines of Cornell (607-255-3040) showed that an ammonium fluoride solution could etch away surface roughness on Si(111) and produce surfaces of near-atomic smoothness over a large area. Hines hopes to find similar chemical methods for the Si(100) surfaces used in integrated circuits. Marcus Weldon of Lucent Technologies (908-582-5645) presented studies of how H2O reacts with silicon at elevated temperatures during the beginning stages of forming a silicon dioxide layer. Marrying infrared spectroscopy and quantum chemistry calculations, Weldon and colleagues discovered for the first time a silicon "epoxide," a triangular arrangement of silicon-oxygen-silicon that apparently dominates the surface at the intermediate stages of these reactions. Controlling the quality of SiO2 layers is increasingly important in state-of-the-art silicon devices; one recently fabricated SiO2 layer has a thickness of just three SiO2 molecular units in an ultrasmall silicon transistor announced by Lucent last year and envisioned for mass production by 2010. Built by Greg Timp and colleagues at Lucent, this 60-nm transistor is four times smaller, five times faster, and needs 60 to 160 times less power than present transistors.
IN SANDIA'S "Z" MACHINE millions of amps of current are passed through a tiny spool of tungsten wires, producing a flood of x rays. Essentially the most powerful terrestrial producer of x rays, the Z device recently achieved the following milestones during a test shot: temperatures of 1.8 million K, a power output of 290 terawatts, and an energy release of 2.0 megajoules. The researchers believe nuclear fusion could be attained inside the device (by bombarding a fuel pellet with x rays) if the conditions were pushed further, to temperatures of 3.5 million K and power levels of 1000 terawatts. Sandia officials have encapsulated these ideas in a proposal for a larger machine, to be called X-1. (Sandia press release, April 9.)
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