Nanoscale heat flow plays a crucial role in many modern electronic and optoelectronic applications, like thermal management, photodetection, thermoelectrics and data communication. 2D layered materials are starting to confirm their groundbreaking role in many of these applications.
Schematic representation of the highly efficient out-of-plane heat transfer from graphene hot electrons (yellow glow), created by optical excitation (red beam), to hyperbolic phonon-polaritons in hBN (wave lines).Source: ICFO
Van der Waals heterostructures are even more promising. These structures consist of different layered 2D materials stacked one on top of the other. These stacks can consist of materials with dramatically different physical properties while interfaces between them are ultra clean and atomically sharp.
Scientists from the European Graphene Flagship, led by Institut de Ciències Fotòniques (ICFO) researchers, have recently succeeded in observing and following the way heat transport occurs in van der Waals stacks. These stacks consist of graphene encapsulated by the dielectric 2D material hexagonal BN (hBN).
ICFO researchers Klaas-Jan Tielrooij, Niels C. H. Hesp, Mark B. Lundeberg, Mathieu Massicotte, Peter Schmidt and Diana Davydovskaya, led by ICREA Professor at ICFO Frank Koppens, along with researchers from the Netherlands, Italy, Germany and the U.K., identified the highly surprising effect. Rather than staying in the graphene sheet, the heat actually flows to the surrounding hBN sheets. This out-of-plane heat transfer process occurs on an ultrafast timescale of picoseconds and is dominant over competing for heat transfer process.
The heat transfer process occurs through hot graphene electrons that couple to hyperbolic phonon-polaritons in the hBN sheets. These phonon-polaritons propagate within the hBN, as light does in an optical fiber, but in this case, for infrared wavelengths and at the nanometer scale. It turns out that these exotic hyperbolic modes are very efficient at carrying the heat away.
The results will have far-reaching implications for many applications based on hBN-encapsulated graphene, sometimes referred to as the next-generation graphene platform owing to its superior electrical properties. In particular, it will provide direction to optoelectronic device design, where these heat flow processes can be thoroughly exploited.
The study on this research was published in Nature Nanotechnology.
