A team of physicists from the University of Colorado has solved the mystery behind a well-known phenomenon in the nanoscale: why extremely tiny heating sources cool faster if they are packed more tightly

[Translation by Dr. Moshe Nachmani]

The findings, which have long been published in the prestigious scientific journalProceedings of the National Academy of Sciences (PNAS), will be able to help the hi-tech industry in the future for the development of faster electronic devices that will heat up much less.  

"In most cases, heating is a challenging consideration in the development of electronic components. The device narrows and only at the end do they find out that it heats up faster than necessary," said one of the researchers. "Our goal is to understand the physical foundations underlying this mechanism in order to develop future devices that can dissipate the heat generated in them more efficiently."

The research began with an unexplained observation - in 2015 a research group (Margaret Murnane and Henry Kapteyn at JILA) performed experiments with metal wires that were thinner than the thickness of a human hair placed on a silicon substrate. When they heated these wires with a laser something strange happened - the more tightly packed the nanostructures were, the faster they cooled. Only now do researchers understand why this happened.

In the new study, the scientists used computer simulations to track the flow of heat inside these nanometer wires. They discovered that when the structures are placed close to each other, the energy vibrations of these heat sources begin to "jump" from one to the other, while dispersing the heat and actually causing the wires to cool. The findings of the research group highlight a significant challenge in the field of development of the next generation of tiny devices, such as microprocessors or quantum computer chips: when the device is further and further miniaturized, the heat flow will not necessarily behave as we expect.

The way heat is transferred in the devices is very important, the researchers add. Even tiny defects in the structure of electronic components such as a computer chip may allow the local temperature to rise and thereby increase the wear and tear of the device. As high-tech companies strive to produce smaller and smaller electronic components, they will need to pay more attention than ever to phonons (from Wikipedia) - Vibrations of atoms that transfer heat in solid materials. "Heat flow involves very complex processes that are difficult to control," explains the researcher. "However, if we can understand how phonons behave on a small scale, then we can build more efficient devices in terms of heat transfer. At the atomic level, the true nature of the heat transfer mechanism is revealed in a new light," said the researcher.

Practically speaking, the researchers repeated the same experiments they had previously performed, however, this time only with the help of a computer. They performed simulations of silicon surfaces placed side by side, like the plates of a railroad track, and then heated them. The simulations were so detailed that the researchers were able to track each and every atom in the model - millions of them in total - from the first moment to the end of the simulation.

The method has been proven to be successful. The researchers found, for example, that when the surfaces are separated from each other by a sufficient distance, the heat tends to be emitted from the surfaces in the expected mechanism already known to scientists - the energy is transferred from the surfaces into the materials below them in all directions. When the surfaces are brought closer and closer, on the other hand, another phenomenon occurs - the heat is dispersed in one main direction, the mechanism of which the researchers called 'directional thermal channeling'. "This phenomenon increases the passage of heat down, towards the surface, and away from the heat sources", concludes the lead researcher. In light of these findings, the researchers predict that in the future engineers will be able to take advantage of this phenomenon and develop tiny electronic components while routing the heat emitted from them along a desired path, instead of everywhere.

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