The Press-Dispatch
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NEW 2018 BUICK ENCLAVE NEW 2018 GMC TERRAIN The New 2018 Buick Regal Sportback Luxury Sedan has arrived at Bob Luegers Buick GMC! JEFF TEDER, DAVE LUEGERS, MARK GUDORF, KYLE DAUBY, EDDIE LUEGERS, SAM BEACH, WOODY FISCHER, KEITH HELMING, VALERIE LANGE FACTORY WARRANTY 2017 Jeep Patriot Latitude Black, 5,189 Miles, Stock#P20103 $18,490 * GM CERTIFIED WARRANTY 2016 Buick LaCrosse CXL White, 11,694 Miles, Stock#19685A $23,488 * GM CERTIFIED WARRANTY 2015 Buick Encore FWD, Silver, 22,300 Miles, Stock#P19775 $18,995 * BUICK Secrets of 'fluid-like' heat flow revealed in solid semiconductor Findings important for design of new devices By Emil Venere Purdue News Service venere@purdue.edu Researchers are applying the same "hydrodynamic transport model" used to study flow in flu- ids to explain heat transport in a solid semiconductor, with po- tential implications for the de- sign of high-speed transistors and lasers. Thermal imaging of tiny na- noscale semiconductor heat sources revealed details about vortices of heat-carrying objects called phonons. The new findings have poten- tially important implications for "thermal crosstalk," in which multiple heat sources next to each other impact the over- all temperature of the system, hindering performance. The researchers used a technique called full-field thermoreflec- tance thermal imaging to direct- ly visualize temperature chang- es produced by ultra-small heat sources, gold strips formed on top of the semiconductor indium gallium arsenide. The research concerns the crucial role of phonons, quan- tum-mechanical objects, or "quasiparticles," that describe how vibrations travel through a material's crystal structure. The phonons are said to be "heat car- riers" in solid materials. "This is the first time such hydrodynamic effects are indi- rectly observed for heat propa- gation in a solid," said Ali Shak- ouri, Purdue University's Mary Jo and Robert L. Kirk Director of the Birck Nanotechnology Center and a professor of electri- cal and computer engineering. "While structures called vorti- ces are common in fluid flows such as water or air, this is the first time we've seen that they can be present inside solids for phonon flow in the typical semi- conductor indium gallium ar- senide, which is used in high- speed transistors and lasers." Findings are detailed in a re- search paper appearing on Jan. 17 in Nature Communications. "The observed thermal cross- talk reduction has important im- plications in the design of na- noscale electronic and opto- electronic devices," said Purdue postdoctoral research associate Amirkoushyar Ziabari, the pa- per's lead author. "As the size of electronic and optoelectron- ic devices are getting smaller, there are more and more devic- es being packed into a small- er area, so the thermal cross- talk between these devices be- comes important. Knowing the accurate thermal behavior in the neighborhood and a few mi- crons from heat sources would help design better state-of-the- art devices in terms of perfor- mance, speed, thermal reliabil- ity, and so on." The researchers found that the reduced thermal crosstalk is caused by vortices generated near the edge of the heat sourc- es. "This is similar to the vortices that are observed at the edge of an obstacle placed inside of a current of air or water, such as behind an airplane wing," Shak- ouri said. The governing law of heat con- duction, known as the Fourier Law or the heat-diffusion equa- tion, does not accurately predict thermal transport for devices on the nanoscale. Because the Fou- rier diffusion equation doesn't explain the heat transport at those scales, this transport re- gime is called non-diffusive. "As the size of electronic and optoelectronic devices are get- ting smaller, it is important to consider this non-diffusive be- havior for design and optimiza- tion of such small devices," Zi- abari said. "These new measure- ments show that at nanoscales, heat propagation has interesting 'fluid-like' behavior." Conventional methods do not account for vortices of heat transport found at the na- noscale. "Vorticity only becomes im- portant when the characteristic source dimension is compara- ble to the hydrodynamic length scale of about 150 nanometers," he said. The Fourier theory substan- tially overestimates the experi- mentally observed temperature a short distance away from the heater lines. "The surprising effect was that the temperature decays much faster than what Fou- rier theory predicted," Shak- ouri said. "Within a distance of 1 or 2 microns of a small heat source - a line about 100 nano- meters wide - temperature could be one-third to one-fourth what Fourier theory predicts." The thermoreflectance ther- mal imaging approach allows re- searchers to create maps of tem- perature rise at far higher reso- lution than otherwise possible using light in the visible range. The work was performed by researchers at the Birck Nan- otechnology Center in Pur- due's Discovery Park, Purdue's School of Electrical and Com- puter Engineering, Universitat Autónoma de Barcelona, Com- missariat à l'Énergie Atomique in Grenoble, France, and the De- partment of Mechanical and Ma- terials Engineering at the Uni- versity of Cincinnati. All co-au- thors are listed in the abstract. The research was partially funded by the European Com- mission and the Spanish Min- istry of Economy and Compet- itiveness. Shakouri heat flow Purdue University researchers have visualized temperature changes produced by ultra-small heat sourc- es, gold strips formed on top of the semiconductor indium gallium arsenide. The work has potential implications for the de- sign of high-speed transistors and lasers. This image (a) depicts the device structure and experimental setup, an optical im- age (b) of the fabricated device and (c) an experimental thermal image. Purdue University image