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New metamaterial boosts invisibility briefs Engineers at Stanford University, Calif., took another step toward designing a meta- material that works across the entire visible spectrum. The new material exhibits a refrac- Staples Inc., Framingham, Mass., tive index well below anything found in nature, such as air, whose refractive index hovers is the first major U.S. retailer to just above 1. Interesting physical phenomena can occur if this index is near-zero or nega- sell 3-D printers. The Cube from 3D Systems Inc., Rock Hill, S.C., tive. Researchers designed a single metamaterial atom with characteristics that would allow is available on Staples.com for it to efficiently interact with both the electric and magnetic components of light. The team $1299.99 and will be sold in a few began with a 2-D planar structure then folded it into a 3-D nanoscale object, preserving the stores by late June. It includes Wi- original properties. The metamaterial consists of nanocrescent-shaped atoms arranged in Fi, Mac or Windows compatibility, a periodic array and it exhibits a negative refractive index over a wavelength range of and 25 3-D templates. It can print roughly 250 nm in multiple regions of the visible and near- spectrum. A few tweaks items up to 5.5 × 5.5 × 5.5 in. could make it useful across the entire visible spectrum. For more information: Ashwin Atre, using material cartridges in 16 different colors. Users can print [email protected], www.stanford.edu. from a template or create a design using Cubify Invent software, sold Stainless steel fuel cell charges phones separately. www.staples.com, Point Source Power Inc., Alameda, Calif., www.3DSystems.com. used technology developed at Lawrence Technologies, Novato, Berkeley National Laboratory (Calif.) to create Calif., was issued U.S. Patent an inexpensive way to recharge cell phones in Number 8,420,042 for a process the developing world. The new device is based for atom-by-atom synthesis of on a solid oxide fuel cell powered by burning graphene by the exothermic charcoal, wood, or cow dung. The fuel cell sits chemical reduction of CO2. in the fire and is attached to circuitry in a han- According to company sources, the process represents a dramatic dle that is charged as the cell heats to 800°C. departure from current methods of The handle contains an LED bulb, which can producing graphene, such as be detached and used for lighting or to charge chemical vapor deposition. By a phone. The fuel cell tolerates contaminants combusting magnesium in the like sulfur and carbon, which would kill simi- Craig Jacobson, in the test labs of Point presence of CO2, bulk volumes of lar devices, says CEO Craig Jacobson, who co- Source Power. Courtesy of Julie pristine, few-layer graphene invented the device called VOTO while platelets are produced from Chao/Berkeley Lab. commonly available feedstock. working as a materials scientist at Berkeley Lab. Replacing most of the ceramics in the fuel cell with stainless steel allows it to withstand CO2 is used to oxidize magnesium at temperatures up to 7000°F, welding and thermal shock and is less expensive to manufacture. VOTO will debut in Kenya forming nanoscale magnesium later this year. www.lbl.gov, www.pointsourcepower.com. oxide and carbon. www.graphenetechnologies.com. Nanowires grown on graphene have surprising structure When engineers at University of Illinois, Urbana-Champaign, set out to grow compound nanowires on top of a sheet of graphene, they did not expect to discover a new paradigm of epitaxy. The self-assembled wires have a core of one composition and an outer layer of another, highly desirable for advanced applications. Led by professor Xi- uling Li, the research team used a method called van der Waals epitaxy to first grow nanowires on a flat substrate of semiconductor materials, such as silicon. The group has since grown nanowires made of indium arsenide (InGaAs) on a sheet of graphene, which is more flexible than silicon. It also conducts like a metal, allowing for direct electrical contact to the nanowire. Researchers pump gases containing gallium, indium, and arsenic into a chamber with a graphene sheet and the nanowires self-assemble into a dense carpet. By using three elements, the group made a unique finding: The InGaAs wires grown on graphene spontaneously segregate into an (InAs) core with an InGaAs shell around the out- side. By tuning the ratio of gallium to indium in the semiconductor mix, researchers can tune the wires’ optical and conductive properties. For more information: Xiuling Li, 217/265-6354, [email protected], www.illinois.edu.

A dense array of InGaAs nanowires grown on graphene. Courtesy of Parsian Mohseni.