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'White graphene' structures can take the heat

Scientists find 3-D boron nitride structures will excel at thermal management for electronics

Date:
July 15, 2015
Source:
Rice University
Summary:
Three-dimensional structures of boron nitride sheets and nanotubes may offer a way to keep small electronic devices cool, according to scientists.
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A 3-D structure of hexagonal boron nitride sheets and boron nitride nanotubes could be a tunable material to control heat in electronics, according to researchers at Rice University.
Credit: Shahsavari Group/Rice University

Three-dimensional structures of boron nitride might be the right stuff to keep small electronics cool, according to scientists at Rice University.

Rice researchers Rouzbeh Shahsavari and Navid Sakhavand have completed the first theoretical analysis of how 3-D boron nitride might be used as a tunable material to control heat flow in such devices.

Their work appears this month in the American Chemical Society journal Applied Materials and Interfaces.

In its two-dimensional form, hexagonal boron nitride (h-BN), aka white graphene, looks just like the atom-thick form of carbon known as graphene. One well-studied difference is that h-BN is a natural insulator, where perfect graphene presents no barrier to electricity.

But like graphene, h-BN is a good conductor of heat, which can be quantified in the form of phonons. (Technically, a phonon is one part -- a "quasiparticle" -- in a collective excitation of atoms.) Using boron nitride to control heat flow seemed worthy of a closer look, Shahsavari said.

"Typically in all electronics, it is highly desired to get heat out of the system as quickly and efficiently as possible," he said. "One of the drawbacks in electronics, especially when you have layered materials on a substrate, is that heat moves very quickly in one direction, along a conductive plane, but not so good from layer to layer. Multiple stacked graphene layers is a good example of this."

Heat moves ballistically across flat planes of boron nitride, too, but the Rice simulations showed that 3-D structures of h-BN planes connected by boron nitride nanotubes would be able to move phonons in all directions, whether in-plane or across planes, Shahsavari said.

The researchers calculated how phonons would flow across four such structures with nanotubes of various lengths and densities. They found the junctions of pillars and planes acted like yellow traffic lights, not stopping but significantly slowing the flow of phonons from layer to layer, Shahsavari said. Both the length and density of the pillars had an effect on the heat flow: more and/or shorter pillars slowed conduction, while longer pillars presented fewer barriers and thus sped things along.

While researchers have already made graphene/carbon nanotube junctions, Shahsavari believed such junctions for boron nitride materials could be just as promising. "Given the insulating properties of boron nitride, they can enable and complement the creation of 3-D, graphene-based nanoelectronics.

"This type of 3-D thermal-management system can open up opportunities for thermal switches, or thermal rectifiers, where the heat flowing in one direction can be different than the reverse direction," Shahsavari said. "This can be done by changing the shape of the material, or changing its mass -- say one side is heavier than the other -- to create a switch. The heat would always prefer to go one way, but in the reverse direction it would be slower."

Shahsavari is an assistant professor of civil and environmental engineering and of materials science and nanoengineering. Sakhavand is a former graduate student at Rice.

The National Science Foundation and the Rice Department of Civil and Environmental Engineering supported the research. The researchers used the National Science Foundation-supported DAVinCI supercomputer administered by Rice's Ken Kennedy Institute for Information Technology. They also used computing resources supported by the National Institutes of Health, IBM, CISCO, Qlogic and Adaptive Computing.


Story Source:

Materials provided by Rice University. Original written by Mike Williams. Note: Content may be edited for style and length.


Journal Reference:

  1. Rouzbeh Shahsavari, Navid Sakhavand. Dimensional Crossover of Thermal Transport in Hybrid Boron Nitride Nanostructures. ACS Applied Materials & Interfaces, 2015; 150709153013004 DOI: 10.1021/acsami.5b03967

Cite This Page:

Rice University. "'White graphene' structures can take the heat: Scientists find 3-D boron nitride structures will excel at thermal management for electronics." ScienceDaily. ScienceDaily, 15 July 2015. <www.sciencedaily.com/releases/2015/07/150715122401.htm>.
Rice University. (2015, July 15). 'White graphene' structures can take the heat: Scientists find 3-D boron nitride structures will excel at thermal management for electronics. ScienceDaily. Retrieved May 23, 2017 from www.sciencedaily.com/releases/2015/07/150715122401.htm
Rice University. "'White graphene' structures can take the heat: Scientists find 3-D boron nitride structures will excel at thermal management for electronics." ScienceDaily. www.sciencedaily.com/releases/2015/07/150715122401.htm (accessed May 23, 2017).

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