A newly-proposed technology could effectively control heat flow in electronic devices.
The method employs "tiny triangular structures" to control "quantum-mechanical phenomena [called phonons] that describe how vibrations travel through a material's crystal structure," a Purdue University news release reported.
These triangular structures are capable of "thermal rectification," which allows heat to flow in one direction but restricts it from flowing in another.
These devices could be used in "transistors, diodes and memory circuits" and would use phonons instead of electrical currents.
"In most systems, heat flow is equal in both directions, so there are no thermal devices like electrical diodes. However, if we are able to control heat flow like we control electricity using diodes then we can enable a lot of new and exciting thermal devices including thermal switches, thermal transistors, logic gates and memory," Xiulin Ruan, an associate professor in Purdue University's School of Mechanical Engineering and Birck Nanotechnology Center, said in the news release. "People are just starting to understand how it works, and it is quite far from being used in applications."
The research team used a simulation method called molecular dynamics to look at thermal rectification in "asymmetric graphene nanoribbons."
The simulations showed thermal rectification could be successful when using pyramidal, trapezoidal or T-shaped designs as well.
Past studies have looked at graphene nanoribbons as a thermal rectifier but this is the first time researchers have gained insight into the mechanism behind rectification. The team found thermal rectification works by restricting vibrations that "travel through the small lateral direction of an asymmetrical structure."
"We demonstrate that other asymmetric materials, such as asymmetric nanowires, thin films, and quantum dots of a single material can also be high-performance thermal rectifiers, as long as you have lateral confinement," Ruan said. "This really broadens the potential of this rectification to a much wider spectrum of applications."
In order for thermal rectification to occur the triangle-like structures must be very small, anything larger would lack lateral confinement.
Lateral confinement requires that the cross section of the structure is smaller than the average distance a phonon can travel before colliding with another, or "mean free path."
The small structures could be linked in a series to produce an overall larger structure that is even better at performing thermal rectification. This could also allow for "thermal management" applications in devices such as computers and even clothing.
"For example, on a winter night you don't want a building to lose heat quickly to the outside, while during the day you want the building to be warmed up by the sun, so it would be good to have building materials that permit the flow of heat in one direction, but not the other," Ruan said.
