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Posted: Jun 6th, 2012 Shaped gold catalysts spark longer, faster-growing, rule-breakingnanowires ( Nanowerk News ) A research team at Case Western Reserve University has found thatgold catalysts shaped in the form of a cube, triangle, or otherhigher order structures grow nanowires about twice as fast andtwice as long compared to wires grown with the more typicalspherically-shaped catalysts. This finding could prove useful to other scientists who are growingnanowires to build sensors fast enough to detect changes in red andwhite blood cells. These sensors in turn could help identifyvarious forms of cancer in the body. The wires are so small assmall as one-5,000th the width of a human hair - they could also beused to build the next generation of "invisible" computer chips. Xuan Gao, assistant professor of physics, and R. Mohan Sankaran,associate professor of chemical engineering, describe their work inthe paper, "Shape-Controlled Au Particles for InAs Nanowire Growth" , published in the journal Nano Letters . Their research team included Case Western Reserve graduate studentsPin Ann Lin and Dong Liang and Hathaway Brown Upper School studentSamantha Reeves. The researchers tested growth using both the preferentially-shapedand spherical catalysts under identical conditions to rule outerror in the comparisons. They suggest that the long accepted model of vapor-liquid-solid, orVLS, growth is incomplete, and that more tests are needed in orderto fully understand the process. Here's why: the researchers found that that the nanowires grownwith the triangular catalyst have a much thicker layer of the metalIndium than the VLS nanowire growth model predicts. The finding suggests a correlation between Indium concentration andgrowth enhancement. The team made the discovery when they beamedelectrons at the nanowires to release high energy x-rays, a processcalled energy-dispersive X-ray spectroscopy. The magnitude of theseenergy bursts were used to determine chemical properties of thenanowires. To grow nanowires, the researchers combined elements such as indiumand arsenic, from rows 4 and 5 of the periodic table of elements.Elements from these rows bond to the gold particle to create asemiconductor that neither allows great flow of electric currentnor greatly prevents its flow. This is called the "bottom-upmethod" which Gao describes as truly like "growing a plant from aseed." Nanowires can also be made "top-down" with precise cuts on a largepiece of semiconducting material, reducing it to a tiny structureof wires. The disadvantage to this, Sankaran explains, is that cutting wiressmaller than around 45 nm, which is the current standard incomputer chips, "is impossible if we are using a machine. But if wewere to grow the wires from chemical compounds we could make themas small as 10 nm, meaning we could fit more wires in a smallerspace for greater speed." However the bottom-up method only produces wires in bunches asopposed to the large interwoven structures made from the top-downmethod of cutting. The challenge is combining chemically-grownwires in ways that they work in complex electronics such ascomputer chips or highly-sensitive sensors. Both Gao and Sankaran describe their research efforts as trulycollaborative. Sankaran makes catalysts of different shapes to growthe nanowires, and Gao tests the properties of these wires andconnects them to possible uses in the field. This duo plans to continue exploring the correlation betweencatalyst shape and other structural characteristics of the wires inorder to further develop the VLS model, and move closer toimplementing nanowires in new technology. We are high quality suppliers, our products such as China Cold Rolled Steel Strips , China Stainless Steel Protective Film for oversee buyer. To know more, please visits Cold Rolled Steel Strips.
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