The thermal conductivity of a pair of boron nanoribbons can be enhanced by up to 45 percent — a discovery that could give rise to a new tool for managing thermal effects in smartphones, computers, lasers and other devices. Although the engineers conducted the research with boron nanoribbons, the team believes the results are generally applicable to thin-film materials. “This points at an entirely new way to control thermal effects that is likely to have a significant impact in microelectronics on the design of smartphones and computers, in optoelectronics on the design of lasers and LEDs, and in a number of other fields,” said Greg Walker, an associate professor of mechanical engineering at Vanderbilt University and an expert in thermal transport who was not directly involved in the research. Mechanical engineer Deyu Li in the lab. (Image: Daniel Dubois/Vanderbilt University) Deyu Li, project collaborator and an associate professor of mechanical engineering at Vanderbilt, said the power that holds the two nanoribbons together is a weak electrostatic attraction called the van der Waals force (the same force that allows the gecko to walk up walls). “Traditionally, it is widely believed that the phonons that carry heat are scattered at van der Waals interfaces, which makes the ribbon bundles’ thermal conductivity the same as that of each ribbon,” Li said. “What we discovered is in sharp contrast to this classical view. We show that phonons can cross these interfaces without being scattered, which significantly enhances the thermal conductivity.” A pair of boron nanoribbons stuck together on a microdevice used to measure thermal conductivity. (Image: Courtesy of the Li Lab) In addition, the researchers found that they could control the thermal conductivity between a high and a low value by treating the interface of the nanoribbon pairs with different solutions. One of the first areas where this new knowledge is likely to be applied is in thermal management of microelectronic devices such as computer chips. “A better understanding of thermal transport across interfaces is the key to achieving better thermal management of microelectronic devices,” Li said. Another area where the finding will be important is in the design of nanocomposites (materials made by embedding nanostructure additives such as carbon nanotubes to a host material such as various polymers) that are being developed for flexible electronic devices, structural materials for aerospace vehicles and a variety of other applications. The research was published online Dec. 11 in Nature Nanotechnology. For more information, visit: www.vanderbilt.edu