Nano Focus: Self-cooling observed in graphene electronics
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Nano Focus Self-cooling observed in graphene electronics
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ooling electronic devices such as computers consumes a great deal of energy, typically in the form of air or water cooling. But what if the materials used in making the electronics cooled themselves during operation? Recent findings by William King and Eric Pop of the University of Illinois, UrbanaChampaign, published April 3rd in the online journal Nature Nanotechnology (DOI: 10.1038/nnano.2011.39), suggest that graphene components may be able to do just that. Using a method they developed to measure the nanoscale temperature distribution with atomic force microscopy (AFM) tips, they were able to determine the temperature distribution in a working graphene field-effect transistor (FET) with a spatial resolution of about 10 nm and a thermal resolution of about 0.25°C. They used this data to construct tempera-
Computational method used to construct database of new zeolite-like materials
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ndustrial applications for zeolites include catalysis, ion exchange, and separations. The scope of applicability would increase with the discovery of new zeolites (currently fewer than 200 zeolites are known), which can be stimulated with computational predictions of stable, zeolite-like structures. Recently, R.S. Pophale and M.W. Deem of Rice University, in collaboration with
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VOLUME 36 • MAY 2011
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which results in polydisperse seeds for nanofiber growth. Coalescence occurs only prior to nanofiber growth: Once growth is initiated, no further coalescence can occur, and the fibers grow separately. The researchers have also demonstrated the formation of graphitic shells
around the ligand-capped particles during the pre-growth heating. The shells are made of the carbon atoms from the ligand molecules. They protect the particles from agglomeration and also serve as a carbon source for the initial stage of carbon nanofiber growth. Elsa Couderc
ture maps of the FET. “The first thing that was remarkable to me,” King said, “was that we could actually measure the temperature of a working FET where the device layer was just 1 atom thick.” By feeding temperature data from these maps into a simulation program developed by Pop, they discovered that the temperature rise at a graphene/metal junction in the circuit differed depending on the direction of current flow through the device. In fact, they found a thermoelectric “nanoscale cooling” effect that accounted for about one-third of the temperature difference; the rest was due to resistive heating. Additional simulations that looked at possible future improvements in graphene materials and metal contacts showed further promise for self-cooling electronics. “If graphene improves in the way that everyone thinks it will, the thermoelectric effect will grow in importance, and the resistive heating will shrink,” King said. “Projecting forward to carbon electronics of the future, the
thermoelectric cooling effect will govern everything about the contacts.” Tim Palucka
P.A. Cheeseman of Purdue University, refin
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