NEWS OF THE WEEK ON THE MOVE Exposing amorphous silicon (left) to hydrogen atoms causes structural rearrangements, indicated by arrows. The rearrangements reduce bond strain (red and blue lines) and lead to nanoscale crystallization (right).
IN BRIEFS BIGFLARE
MATERIALS
SCIENCE
NANOCRYSTALLINE SILICON Study elucidates mechanism for amorphous-to-crystalline transition
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ILICON W I T H NANOSCALE
crystalline grains outperforms amorphous silicon in a number of industrial applications. Procedures for converting the disordered form of silicon to nanocrystalline forms are known, however the techniques are not applicable to some technologies, and the mechanism governing the transition has remained the subject of debate for some 30 years. Now, researchers at the University of California, Santa Barbara, have figured out how hy-
drogen atoms generated in a plasma infiltrate a silicon matrix and stimulate bond rearrangement, leading to crystallization of amorphous silicon films [Nature, 418, 62(2002)}. Using infrared spectroscopy methods and molecular dynamics simulations, chemical engineering professors Eray S. Aydil and Dimitrios Maroudas and graduate students Saravanapriyan Sriraman and Sumit Agarwal determined that exposing hydrogenated amorphous silicon films to a plasma containing H atoms causes the atoms to be inserted into strained (stretched or compressed) Si—Si bonds as hydrogen diffuses through the films.
BUSINESS
NOVA REVAMPS STYRENICS Move reflects emphasis on cost-cutting and high-end styrene derivatives Thirty Earths, says NASA, could fit into the huge, curling, molten prominence (lower left) that erupted from the sun's surface on July 1. Prominences are massive clouds of relatively cool, dense plasma suspended in the sun's hot, tenuous corona that are eventually propelted by magnetic fields out beyond the sun's surface. 8
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CHEMICALS,
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world's fourth-largest styrene and polystyrene producer, is making a series of capacity expansions in specialty styrenics and shutdowns in commodity polystyrene that it says will reduce costs and allow it to focus on more value-added products. Nova will close suspension polystyrene resin capacity in Breda, the Netherlands, and Chesapeake, Va., on Sept. 1. In Chesapeake, it will close a 100 million-lb-per-year plant, leaving 14 workers without
jobs. In Breda, the closure of 75 million lb of capacity will mean the loss of 23 positions. Christopher Pappas, president of Nova's styrenics business, said at a press conference in N e w a r k City that Nova's goal is to increase the share of high-performance, high-growth products like its styrene copolymers and certain grades of polystyrene and expandable polystyrene (EPS) from 15% of its product slate today to 25% by 2004 and 30% by 2005. To this end, Nova says it will
Further diffusion breaks or perturbs the bonds, ultimately causing structural relaxation, which leads to crystallization on the nanometer scale. In a commentary in the same issue of Nature, University of Cambridge engineering professor John Robertson notes that the Santa Barbara study may lead to improved nanocrystalline Si solar cells, which currently are prepared using plasma-deposition methods. Thin-film transistors used in liquid-crystal displays also benefit from nanocrystalline Si, but for that application the material is prepared via laser methods. Based on the present study, Robertson comments, plasma deposition is a promising and less expensive avenue worth exploring. Methods for controlling grain size and orientation still need to be developed, he says, "but easy manufacture of stable transistors by plasma deposition would have a major impact on the displaytechnology industry."—MITCH JACOBY
double capacity for Arcel resin at its BeaverVdley, Pa, site in the first quarter of 2003. Arcel is a polystyrene/polyethylene interpolymer touted as being 10 times stronger than EPS. Arcel has a 100 million-lb market potential, Pappas said. Nova is also expanding capacity for its Dylark styrenemaleic anhydride copolymers— used for car dashboards—by 30% to 90 million lb by the first quarter of 2003. On the technology front, Nova has received three patents for volatile organic compound-free EPS that uses water instead of pentane as a blowing agent. It already has one product that uses 50% less pentane than normal grades on the market. Nova says market potential for these products is about 500 million lb. "By 2006,50% of US. EPS will be required to have 3% or less pentane in it," Pappas said.-ALEX TULL0 HTTP://PUBS.ACS.ORG/CEN
