Researchers at the University of Colorado Boulder made a new discovery that explains why small heat sources cool down faster when placed close together.
The study’s findings will be published this week in the Proceedings of the National Academy of Sciences journal.
Professors Margaret Murnane and Henry Kapteyn led the research, which began in 2015. Their team was experimenting with laser-heated nanoscale lines — tiny metal lines thinner than human hair — patterned on silicon when they observed those heat sources cooled down faster when packed close together.
“Usually if you want to cool something down, you surround it with cold material,” Murnane said. “In a surprising experimental discovery, we found that for nanoscale hotspots, instead of spreading them out so they’re in contact with cold material, you pack them closer together to cool faster, which is very counterintuitive.”
Now, the researchers have discovered why this phenomenon happens.
Co-author Joshua Knobloch, a postdoctoral research assistant at JILA, a joint institute of CU Boulder and the National Institute of Standards and Technology, said the reason the nanolines cool faster in this way is because the vibrational energy of the atoms scatter off each other and cool down the hot bars faster when they are packed close together.
“It’s a very counterintuitive idea for us because it goes against typically the way that we think about thermal transport,” Knobloch said. “And I think that’s why it’s a really amazing discovery. It’s kind of revolutionary in that way. It goes against the common thinking.”
In this new study, researchers used computer-based simulations to model every atom in a system to track the dissipation of heat.
This study was a collaboration effort of two teams, one led by Murnane and another led by CU Boulder professor Mahmoud Hussein, a coauthor of the study. Murnane’s group used light beams of X-rays to observe the behavior of materials more precisely than can be seen using visible light. Hussein’s group studied theory and simulations at the atomic scale to understand material behavior related to heat and temperature.
Knobloch said this research can be applied to many technological applications, including manufacturing computer chips and cell phones that do not heat up as much.
The researchers said these findings could impact the future of electronics. They hope their study inspires further research and development of models and experimental investigations of thermal transport.
Hussein said these findings are important for two reasons: the continuous problem of high concentration of high-temperature zones in modern devices, and the ongoing quest in the high-tech industry to make electronics smaller and more efficient. These problems are at the core of what the researchers are addressing in their paper.
“I think it potentially could impact the future of electronic miniaturization,” Hussein said. “The industry is continuously seeking to make devices smaller and smaller. So with this discovery, there’ll be a better understanding of how to manage the heat in the ever-diminishing size of electronics.”
Other contributors for this study include postdoctoral researcher Hossein Honarvar, JILA graduate student Brendan McBennett and former JILA researchers Travis Frazer, Jorge Hernandez-Charpak and Begoña Abad.